JP7510296B2 - Inspection device and inspection method - Google Patents

Description

The present invention relates to an inspection device and an inspection method.

In order to cut a wafer having a semiconductor substrate and a functional element layer formed on one surface of the semiconductor substrate along each of a plurality of lines, an inspection device is known that irradiates the wafer from the other surface side of the semiconductor substrate with laser light to form a plurality of rows of modified regions inside the semiconductor substrate along each of the plurality of lines. The inspection device described in Patent Document 1 is equipped with an infrared camera, and is capable of observing the modified regions formed inside the semiconductor substrate and the processing damage formed in the functional element layer from the back side of the semiconductor substrate. In this inspection device, for example, based on such internal observation results, the crack state of the wafer after processing is estimated, and the success or failure of the processing (whether or not the desired processing is performed under the set processing conditions) is judged based on the estimated crack state result.

JP 2017-64746 A

The above-mentioned inspection device allows the crack state of the wafer to be estimated with high accuracy by observing the inside with an infrared camera. Here, in this technical field, there is a demand for estimating the crack state (processing state) of the wafer with high accuracy as well as estimating the crack state (processing state) more easily.

The present invention was made in consideration of the above-mentioned circumstances, and relates to an inspection device and an inspection method that can more easily estimate the processing state of a wafer.

The inventors focused on the fact that there is a correlation between the displacement (uneven shape) on the incident surface or the surface opposite the incident surface after laser processing and the processed state of the wafer, and came up with the idea of an inspection device that derives information related to the estimation of the processed state of the wafer based on such post-processing displacement of the wafer.

That is, an inspection device according to one aspect of the present invention includes a laser irradiation unit that irradiates a wafer with laser light, a measurement unit that measures the displacement of a measurement target surface, which is the incident surface of the laser light on the wafer or the surface opposite to the incident surface, and a control unit configured to execute the following: controlling the laser irradiation unit so that one or more modified regions are formed inside the wafer by irradiating the wafer with laser light; controlling the measurement unit so that a post-processing displacement, which is the displacement of the measurement target surface after the laser light is irradiated, is measured; and deriving information related to an estimation of the processing state of the wafer based on the post-processing displacement measured by the measurement unit.

In an inspection device according to one aspect of the present invention, the post-processing displacement of the measurement target surface, which is the incident surface or the surface opposite to the incident surface of the wafer irradiated with laser light, is measured, and information related to the estimation of the processing state of the wafer is derived based on the post-processing displacement. As described above, there is a correlation between the post-processing displacement (uneven shape) of the measurement target surface and the processing state of the wafer. Therefore, by deriving information related to the estimation of the processing state of the wafer based on the post-processing displacement, the processing state of the wafer can be appropriately estimated based on the information related to the estimation. Furthermore, the process of measuring the post-processing displacement of the measurement target surface is extremely easy compared to the process of identifying the processing state (crack state) of the wafer by observing the inside of the wafer with an infrared camera or the like. Therefore, the inspection device according to one aspect of the present invention makes it easier to estimate the processing state of the wafer.

The inspection device may further include a display unit, and the control unit may control the display unit so that the derived information relating to the estimation of the processing state of the wafer is displayed. By displaying the information relating to the estimation of the processing state of the wafer derived by the control unit on the display unit, for example, when information for estimating the processing state is displayed as the information relating to the estimation of the processing state, the user can easily estimate the processing state of the wafer based on the displayed content. In addition, when the estimation result of the processing state itself is displayed as the information relating to the estimation of the processing state, the user can confirm the validity of the estimation result of the processing state.

The measurement unit may have a measurement unit that irradiates the measurement surface with measurement light and receives and detects the reflected light of the measurement light from the measurement surface to measure the displacement on the measurement surface. With this configuration, the displacement on the measurement surface can be measured with high accuracy using a simple configuration and processing.

The measurement unit may be an autofocus unit that measures the displacement on the surface to be measured in order to adjust the focal point of the laser light irradiated onto the wafer by the laser irradiation unit. With this configuration, the displacement on the surface to be measured can be measured using an autofocus unit that is typically provided in an inspection device that irradiates a wafer with a laser. In other words, with this configuration, the autofocus unit can be used to measure the displacement (uneven shape) of the wafer surface, and the processed state of the wafer can be easily estimated based on the displacement.

The control unit may derive the difference between the post-processing displacement measured by the measurement unit and a reference displacement for each region of the surface to be measured, and derive information related to an estimation of the processed state of the wafer based on the difference. The difference between the post-processing displacement and the reference displacement more accurately indicates the amount of displacement caused by the effects of processing. Therefore, by deriving information related to an estimation of the processed state based on the difference, the processed state of the wafer can be more accurately estimated.

The control unit may control the measurement unit to further measure a pre-processing displacement, which is the displacement of the measurement target surface before the laser light is irradiated, and derive information related to the estimation of the processing state of the wafer using the pre-processing displacement as a reference displacement. In this way, the pre-processing displacement, which is the displacement of the measurement target surface before the laser light is irradiated, is actually measured and the pre-processing displacement is set as the reference displacement, so that the difference between the post-processing displacement and the reference displacement more accurately indicates the amount of displacement due to the influence of processing. Therefore, by deriving information related to the estimation of the processing state based on the difference, the processing state of the wafer can be more accurately estimated.

The control unit may estimate the state of a crack extending from a modified region formed inside the wafer by irradiating the laser light based on the difference. There is a correlation between the difference between the post-processing displacement and the reference displacement (the displacement on the measurement surface after laser processing) and the state of a crack extending from the modified region. Therefore, by estimating the state of the crack based on the difference, the state of the crack (i.e., the processed state of the wafer) can be estimated with high accuracy.

The control unit may estimate that, for a region where the absolute value of the difference is greater than a first threshold value, the crack has reached the incident surface but not reached the opposite surface, or has not reached the incident surface but reached the opposite surface, and may estimate that, for a region where the absolute value of the difference is equal to or less than the first threshold value, the crack has not reached either the incident surface or the opposite surface, or has reached both the incident surface and the opposite surface. The inventors have found that, for a region where the absolute value of the difference between the post-processing displacement and the reference displacement (the displacement on the measurement target surface after laser processing) is large, the crack has reached only one of the incident surface and the opposite surface (the so-called BHC or HC state), and, for a region where the difference is small, the crack has reached neither the incident surface nor the opposite surface (the so-called ST state) or has reached both the incident surface and the opposite surface (the so-called FC state). Based on this idea, the state of the crack is estimated depending on whether the difference is greater than a certain threshold value (first threshold value), so that the state of the crack (i.e., the processed state of the wafer) can be estimated with higher accuracy.

The control unit may estimate that, for an area where the difference in the absolute value of the difference with the surrounding area is greater than a second threshold value, the crack has reached the incident surface but not reached the opposite surface, or has not reached the incident surface but reached the opposite surface, and may estimate that, for an area where the difference in the absolute value of the difference is equal to or less than the second threshold value, the crack has not reached either the incident surface or the opposite surface, or has reached both the incident surface and the opposite surface. When estimating the state of the crack based on the difference, it may be easier and more accurate to judge from the difference between the absolute value of the difference with the surrounding area (to judge from the relative value) rather than judging from the absolute value of the difference. Based on this idea, the state of the crack is estimated depending on whether the difference in the difference with the surrounding area is greater than a certain threshold value (second threshold value), so that the state of the crack (i.e., the processed state of the wafer) can be estimated more accurately and easily.

The inspection device may further include an imaging unit that outputs light that is transparent to the wafer and detects the light propagated through the wafer, and the control unit may estimate the state of the crack by further considering the signal output from the imaging unit that detects the light. With this configuration, while the basic processing state of the wafer is estimated based on the displacement on the measurement target surface, it is possible to perform processing such as estimating only the crack state of a certain area (an area where the crack state, etc., is to be examined in more detail) based on the signal output from the imaging unit, thereby making it possible to estimate the crack state with higher accuracy. Even in this case, the processing state of the wafer can be estimated easily (with significantly shorter tact times) compared to estimating all crack states based only on the signal output from the imaging unit.

The control unit controls the measurement unit so that the measurement light is irradiated onto the measurement target surface along the first direction, and the reflected light of the measurement light on the measurement target surface is detected to measure the pre-processing displacement in each region along the first direction, controls the laser irradiation unit so that the wafer is irradiated with laser light for multiple lines along a second direction intersecting the first direction to form multiple processing lines, controls the measurement unit so that the measurement light is irradiated onto the measurement target surface along the first direction so as to straddle the multiple processing lines, and the reflected light of the measurement light on the measurement target surface is detected to measure the post-processing displacement in each region along the first direction, derives the difference between the post-processing displacement and the pre-processing displacement for each corresponding region, and derives information related to the estimation of the processing state for each region based on the difference. In this way, the post-processing displacement and the pre-processing displacement are measured for each region along the direction straddling the multiple processing lines (first direction), and the difference between the post-processing displacement and the pre-processing displacement is derived for each region, thereby identifying the degree of displacement after laser processing in each of the multiple processing lines, and appropriately estimating the processing state of each of the multiple processing lines. According to this configuration, for example, by setting different processing conditions for multiple processing lines and estimating the processing state under each processing condition, the suitability of the multiple processing conditions can be efficiently determined. Then, by identifying the degree of displacement of the multiple processing lines, the processing state of each of the multiple processing lines can be easily and accurately estimated based on not only the absolute amount of displacement but also the relative information of the amount of displacement compared to other processing lines by comparing the displacements of different processing lines.

The control unit controls the measurement unit so that the measurement light is irradiated onto the surface to be measured along a first direction and the reflected light of the measurement light on the surface to be measured is detected to measure the pre-processing displacement in each region along the first direction, controls the measurement unit so that the measurement light is irradiated onto the surface to be measured along a second direction intersecting the first direction and the reflected light of the measurement light on the surface to be measured is detected to measure the pre-processing displacement in each region along the second direction, controls the laser irradiation unit so that the laser light is irradiated onto the wafer for multiple lines along the second direction to form multiple processing lines, controls the laser irradiation unit so that the laser light is irradiated onto the wafer for multiple lines along the first direction to form multiple processing lines, and controls the measurement unit to measure along the first direction so as to straddle the multiple processing lines along the second direction. The measurement unit may be controlled so that the measurement light is irradiated onto the target surface and the reflected light of the measurement light on the target surface is detected to measure the post-processing displacement in each region along the first direction, the measurement light is irradiated onto the target surface along the second direction so as to straddle a plurality of processing lines along the first direction, and the reflected light of the measurement light on the target surface is detected to measure the post-processing displacement in each region along the second direction, the difference between the post-processing displacement and the pre-processing displacement is derived for each corresponding region along the first direction, and information related to the estimation of the processing state for each region may be derived based on the difference, and the difference between the post-processing displacement and the pre-processing displacement is derived for each corresponding region along the second direction, and information related to the estimation of the processing state for each region may be derived based on the difference.

According to this configuration, even when multiple processing lines are formed in each of the directions intersecting each other (when the processing lines are formed in a lattice pattern), information related to the estimation of the processing state is appropriately derived. That is, the post-processing displacement and the pre-processing displacement are measured for each region along the direction (second direction) that crosses the multiple processing lines formed along the first direction, and the difference between the post-processing displacement and the pre-processing displacement is derived for each region, so that the processing state of each of the multiple processing lines formed along the first direction can be appropriately estimated. In addition, the post-processing displacement and the pre-processing displacement are measured for each region along the direction (first direction) that crosses the multiple processing lines formed along the second direction, and the difference between the post-processing displacement and the pre-processing displacement is derived for each region, so that the processing state of each of the multiple processing lines formed along the second direction can be appropriately estimated. And, the formation of the multiple processing lines along the first direction and the measurement of the post-processing displacement in each region along the first direction (crossing the multiple processing lines along the second direction) are processes along the same direction and can be performed simultaneously, and by performing these processes together (simultaneously), the processing efficiency can be significantly improved.

The control unit may control the measurement unit and the laser irradiation unit so that the irradiation line of the measurement light irradiated along the first direction for measuring the post-processing displacement overlaps with any of the multiple processing lines along the first direction, and may control the measurement unit and the laser irradiation unit so that the irradiation line of the measurement light irradiated along the second direction for measuring the post-processing displacement does not overlap with the multiple processing lines along the second direction. Now, in order to measure the post-processing displacement with high accuracy, it is desired to eliminate the influence of the processing line whose processing direction is different from the processing line of the target for which the post-processing displacement is to be measured. That is, when measuring the post-processing displacement for multiple processing lines along a certain direction, it is desired to eliminate the influence of the processing line along a direction different from the certain direction. In this case, it is necessary that the irradiation line of the measurement light irradiated along a direction different from the certain direction so as to straddle the multiple processing lines along the certain direction does not overlap with the processing line along the direction different from the certain direction. In this regard, since the irradiation line of the measurement light along the second direction does not overlap with the multiple processing lines along the second direction, the post-processing displacement for the multiple processing lines along the first direction can be measured with high accuracy. Here, as described above, in this process, after the processing line along the second direction is formed, both the formation of the processing line along the first direction and the measurement of the post-processing displacement along the first direction are performed. In this way, when the formation of the processing line and the measurement of the post-processing displacement are both performed along the same direction, even if the processing line and the irradiation line of the measurement light for the displacement measurement overlap, the irradiation of the measurement light for the displacement measurement is performed prior to the formation of the processing line (while performing both, the irradiation of the measurement light is controlled so that it precedes the formation of the processing line), so that the post-processing displacement of the formed processing line can be measured without being influenced by the newly formed processing line. That is, in this process, since the formation of the processing line along the first direction and the measurement of the post-processing displacement along the first direction are both performed, even if any of the processing lines along the first direction and the irradiation line of the measurement light irradiated along the first direction overlap, the post-processing displacement of the multiple processing lines along the second direction can be estimated with high accuracy without being influenced by the formation of the processing line along the first direction. Furthermore, by overlapping any of the processing lines along the first direction with the irradiation line of the measurement light irradiated along the first direction, the processing lines can be formed and the processes related to the irradiation of the measurement light can be simplified (facilitated).

The control unit may control the measurement unit so that the measurement light is irradiated onto the measurement target surface along the first direction, and the reflected light of the measurement light on the measurement target surface is detected to measure the pre-processing displacement in each region along the first direction, control the laser irradiation unit so that the wafer is irradiated with laser light along the first direction to form a processing line, control the measurement unit so that the measurement light is irradiated onto the measurement target surface along the processing line, and the reflected light of the measurement light on the measurement target surface is detected to measure the post-processing displacement in each region along the processing line, derive the difference between the post-processing displacement and the pre-processing displacement for each corresponding region along the processing line, and derive information related to the estimation of the processing state for each region based on the difference. In this way, the irradiation direction of the measurement light for measuring the pre-processing displacement, the formation direction of the processing line, and the irradiation direction of the measurement light for measuring the post-processing displacement are common, making it unnecessary to rotate the wafer, and improving processing efficiency. In this embodiment, where the measurement light is irradiated along the processing line, unlike the case where the measurement light is irradiated across multiple processing lines, it is not possible to estimate the processing state based on relative information on the amount of displacement by comparing multiple processing lines, but it is possible to estimate the processing state of the processing line based on the absolute amount of displacement after processing.

The control unit performs processing control based on predetermined processing conditions, judges whether the processing is successful or not based on information related to the estimation of the processing state of the wafer, and may correct the processing conditions if the judgment result is failure. With such a configuration, the processing conditions can be changed taking into account the estimation result of the processing state of the wafer, and optimization of the processing conditions can be performed in a centralized and automatic manner.

An inspection method according to one aspect of the present invention includes a laser processing step of irradiating a wafer with laser light so as to form one or more modified regions inside the wafer, a post-processing measurement step of measuring a post-processing displacement, which is a displacement of the measurement target surface of the wafer after the laser processing, and an estimation step of estimating the processing state of the wafer based on the post-processing displacement.

The above inspection method may further include a pre-processing measurement process for measuring a pre-processing displacement, which is a displacement of the measurement target surface, before the laser processing process, and in the estimation process, a difference between the post-processing displacement and the pre-processing displacement is derived for each region of the measurement target surface, and the processing state of the wafer may be estimated based on the difference.

In the pre-processing measurement process, a measurement light is irradiated onto the measurement surface along a first direction, and the reflected light of the measurement light on the measurement surface is received and detected to measure the pre-processing displacement in each region along the first direction; in the laser processing process, a laser light is irradiated onto the wafer along a second direction intersecting the first direction to form multiple processing lines; in the post-processing measurement process, a measurement light is irradiated onto the measurement surface along the first direction so as to straddle the multiple processing lines, and the reflected light of the measurement light on the measurement surface is received and detected to measure the post-processing displacement in each region along the first direction.

The pre-processing measurement process includes a first pre-processing process of irradiating the measurement surface with measurement light along a first direction and measuring the pre-processing displacement in each region along the first direction by receiving and detecting the reflected light of the measurement light on the measurement surface, and a second pre-processing process of irradiating the measurement surface with measurement light along a second direction intersecting the first direction and measuring the pre-processing displacement in each region along the second direction by receiving and detecting the reflected light of the measurement light on the measurement surface, and the laser processing process includes a first processing process of irradiating the wafer with laser light for multiple lines along the second direction to form multiple processing lines, and a second pre-processing process of irradiating the wafer with laser light for multiple lines along the first direction to form multiple processing lines. and a second processing step of forming a plurality of processing lines, and the post-processing measurement step includes a first post-processing step of irradiating the measurement surface with measurement light along the first direction so as to straddle the plurality of processing lines along the second direction, and measuring the post-processing displacement in each region along the first direction by receiving and detecting the reflected light of the measurement light on the measurement surface, and a second post-processing step of irradiating the measurement surface with measurement light along the second direction so as to straddle the plurality of processing lines along the first direction, and measuring the pre-processing displacement in each region along the second direction by receiving and detecting the reflected light of the measurement light on the measurement surface, and the first post-processing step may be performed together with the second processing step.

In the pre-processing measurement process, a measurement light is irradiated onto the measurement surface along a first direction, and the reflected light of the measurement light on the measurement surface is received and detected to measure the pre-processing displacement in each region along the first direction; in the laser processing process, a laser light is irradiated onto the wafer along the first direction to form a processing line; in the post-processing measurement process, a measurement light is irradiated onto the measurement surface along the processing line, and the reflected light of the measurement light on the measurement surface is received and detected to measure the post-processing displacement in each region along the processing line.

The present invention makes it easier to estimate the processing state of a wafer.

FIG. 1 is a configuration diagram of an inspection device according to an embodiment. FIG. 2 is a plan view of a wafer according to an embodiment. 3 is a cross-sectional view of a portion of the wafer shown in FIG. 2. FIG. 2 is a configuration diagram of a laser irradiation unit shown in FIG. 1 . FIG. 2 is a configuration diagram of an inspection imaging unit shown in FIG. 1 . FIG. 2 is a configuration diagram of an alignment correction imaging unit shown in FIG. 1 . 1A to 1C are diagrams illustrating wafer cross sections for each state of cracks. FIG. 13 is an example of a display screen of an estimation result. 9 is a flowchart of the inspection process (inspection method) of FIG. 8 . 13 is a flowchart of an inspection method according to a modified example. 13 is an example of a display screen according to a modified example. 1A to 1C are diagrams illustrating wafer cross sections for each state of cracks. 13A to 13C are diagrams illustrating an inspection process according to a modified example. 15 is a flowchart of the inspection process (inspection method) of FIG. 14. 13A to 13C are diagrams illustrating an inspection process according to a modified example. 17 is a flowchart of the inspection process (inspection method) of FIG. 16. 13A to 13C are diagrams illustrating an inspection process according to a modified example. FIG. 13 is a diagram illustrating a schematic view of a part of the configuration of an inspection device according to a modified example. 13 is an example of a display screen according to a modified example. 13 is an example of a display screen according to a modified example. FIG. 13 is a diagram illustrating a schematic view of a part of the configuration of an inspection device according to a modified example. 13A to 13C are diagrams illustrating an inspection method according to a modified example.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted.
[Configuration of inspection device]

As shown in FIG. 1, the inspection device 1 includes a stage 2, a laser irradiation unit 3, multiple imaging units 4, 5, and 6, a drive unit 7, a control unit 8, and a display 150 (display unit). The inspection device 1 is a device that forms a modified region 12 in an object 11 by irradiating the object 11 with laser light L.

The stage 2 supports the object 11, for example, by adsorbing a film attached to the object 11. The stage 2 is movable along both the X direction and the Y direction, and is rotatable about an axis parallel to the Z direction. The X direction and the Y direction are a first horizontal direction and a second horizontal direction that are perpendicular to each other, and the Z direction is a vertical direction.

The laser irradiation unit 3 focuses laser light L, which is transparent to the object 11, and irradiates the object 11. When the laser light L is focused inside the object 11 supported by the stage 2, the laser light L is particularly absorbed in a portion corresponding to the focusing point C of the laser light L, and a modified region 12 is formed inside the object 11.

The modified region 12 is a region whose density, refractive index, mechanical strength, and other physical properties differ from those of the surrounding unmodified region. Examples of modified region 12 include a melting treatment region, a crack region, an insulation breakdown region, and a refractive index change region. The modified region 12 has the property that cracks tend to extend from the modified region 12 to the incident side of the laser light L and to the opposite side. These properties of the modified region 12 are utilized to cut the object 11.

As an example, when the stage 2 is moved along the X direction and the focal point C is moved along the X direction relative to the object 11, multiple modified spots 12s are formed in a row along the X direction. One modified spot 12s is formed by irradiating one pulse of laser light L. A row of modified regions 12 is a collection of multiple modified spots 12s lined up in a row. Adjacent modified spots 12s may be connected to each other or separated from each other depending on the relative moving speed of the focal point C with respect to the object 11 and the repetition frequency of the laser light L.

The imaging unit 4 is configured to be able to capture images of the modified area 12 formed in the target object 11 and the tip of the crack extending from the modified area 12. Although the imaging unit 4 is not an essential component, the present embodiment will be described assuming that the inspection device 1 has the imaging unit 4.

Under the control of the control unit 8, the imaging units 5 and 6 capture an image of the object 11 supported on the stage 2 using light transmitted through the object 11. The images captured by the imaging units 5 and 6 are used, for example, to align the irradiation position of the laser light L. Note that although the imaging units 5 and 6 are not essential components, the present embodiment will be described assuming that the inspection device 1 includes the imaging units 5 and 6.

The drive unit 7 supports the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6. The drive unit 7 moves the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6 along the Z direction.

The control unit 8 controls the operation of the stage 2, the laser irradiation unit 3, the multiple imaging units 4, 5, 6, and the drive unit 7. The control unit 8 is configured as a computer device including a processor, memory, storage, and a communication device. In the control unit 8, the processor executes software (programs) loaded into the memory, etc., and controls the reading and writing of data in the memory and storage, as well as communication by the communication device.

The display 150 functions as an input unit that accepts information input from the user, and as a display unit that displays information to the user.

[Configuration of the object]
The object 11 of this embodiment is a wafer 20, as shown in FIG. 2 and FIG. 3. The wafer 20 includes a semiconductor substrate 21 and a functional element layer 22. In this embodiment, the wafer 20 is described as having the functional element layer 22, but the wafer 20 may or may not have the functional element layer 22, and may be a bare wafer. The semiconductor substrate 21 has a front surface 21a and a back surface 21b. The semiconductor substrate 21 is, for example, a silicon substrate. The functional element layer 22 is formed on the front surface 21a of the semiconductor substrate 21. The functional element layer 22 includes a plurality of functional elements 22a arranged two-dimensionally along the front surface 21a. The functional elements 22a are, for example, light receiving elements such as photodiodes, light emitting elements such as laser diodes, circuit elements such as memories, etc. The functional elements 22a may be three-dimensionally configured by stacking a plurality of layers. The semiconductor substrate 21 is provided with a notch 21c indicating the crystal orientation, but an orientation flat may be provided instead of the notch 21c.

The wafer 20 is cut into functional elements 22a along each of the lines 15. When viewed from the thickness direction of the wafer 20, the lines 15 pass between each of the functional elements 22a. More specifically, the lines 15 pass through the center of the street region 23 (the center in the width direction) when viewed from the thickness direction of the wafer 20. The street region 23 extends in the functional element layer 22 so as to pass between adjacent functional elements 22a. In this embodiment, the functional elements 22a are arranged in a matrix along the surface 21a, and the lines 15 are set in a lattice pattern. Note that the lines 15 are virtual lines, but may be lines that are actually drawn.

[Configuration of laser irradiation unit]
As shown in Fig. 4, the laser irradiation unit 3 has a light source 31 (laser irradiation section), a spatial light modulator 32, and a condenser lens 33. The light source 31 outputs laser light L, for example, by a pulse oscillation method. The spatial light modulator 32 modulates the laser light L output from the light source 31. The spatial light modulator 32 is, for example, a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM: Spatial Light Modulator). The condenser lens 33 condenses the laser light L modulated by the spatial light modulator 32. The condenser lens 33 may be a correction ring lens.

In this embodiment, the laser irradiation unit 3 irradiates the wafer 20 with laser light L from the back surface 21b side of the semiconductor substrate 21 along each of the multiple lines 15, thereby forming two rows of modified regions 12a, 12b inside the semiconductor substrate 21 along each of the multiple lines 15. The modified region 12a is the modified region closest to the front surface 21a among the two rows of modified regions 12a, 12b. The modified region 12b is the modified region closest to the modified region 12a among the two rows of modified regions 12a, 12b, and is the modified region closest to the back surface 21b.

The two rows of modified regions 12a, 12b are adjacent to each other in the thickness direction (Z direction) of the wafer 20. The two rows of modified regions 12a, 12b are formed by moving the two focal points C1, C2 along the line 15 relative to the semiconductor substrate 21. The laser light L is modulated by the spatial light modulator 32, for example, so that the focal point C2 is located behind the focal point C1 in the traveling direction and on the incident side of the laser light L. The modified regions may be formed in a single focus or multiple focuses, and in one pass or multiple passes.

The laser irradiation unit 3 irradiates the wafer 20 with laser light L from the back surface 21b of the semiconductor substrate 21 along each of the multiple lines 15. As an example, for the semiconductor substrate 21, which is a single crystal silicon substrate having a thickness of 775 μm, two focusing points C1 and C2 are aligned at positions 54 μm and 128 μm from the front surface 21a, respectively, and the laser light L is irradiated from the back surface 21b of the semiconductor substrate 21 along each of the multiple lines 15 to the wafer 20. At this time, for example, when the condition is that the crack 14 across the two rows of modified regions 12a and 12b reaches the front surface 21a of the semiconductor substrate 21, the wavelength of the laser light L is 1099 nm, the pulse width is 700 ns, and the repetition frequency is 120 kHz. In addition, the output of the laser light L at the focal point C1 is 2.7 W, the output of the laser light L at the focal point C2 is 2.7 W, and the relative movement speed of the two focal points C1 and C2 with respect to the semiconductor substrate 21 is 800 mm/sec.

The formation of the two rows of modified regions 12a, 12b and the cracks 14 is carried out in the following case. That is, in a later process, for example, the back surface 21b of the semiconductor substrate 21 is ground to thin the semiconductor substrate 21 and expose the cracks 14 on the back surface 21b, and the wafer 20 is cut into a plurality of semiconductor devices along each of the plurality of lines 15.

As shown in FIG. 4, the laser irradiation unit 3 further includes an AF (autofocus) unit 71 (measurement section, measurement unit). The AF unit 71 is configured to precisely align the focal point of the laser light L at a position at a predetermined distance from the back surface 21b, which is the incident surface of the wafer 20, even when there is a displacement (waviness) in the thickness direction (Z direction) of the back surface 21b. The AF unit 71 measures the displacement on the back surface 21b (measurement target surface) in order to adjust the focal point of the laser light L irradiated to the wafer 20 by the light source 31. Specifically, the AF unit 71 irradiates the back surface 21b with AF laser light LA (measurement light) and receives and detects the reflected light of the AF laser light LA on the back surface 21b to obtain displacement data of the back surface 21b (measures the displacement).

The AF unit 71 has an AF light source 71a that outputs an AF laser light LA, and a displacement detection unit 71b that receives and detects the reflected light of the AF laser light LA. The AF laser light LA emitted from the AF light source 71a is reflected by the AF dichroic mirror 72 and irradiated onto the back surface 21b via the condenser lens 33. In this way, the AF laser light LA and the laser light L are irradiated onto the wafer 20 from the same condenser lens 33 (they are coaxial). Then, the reflected light of the AF laser light LA on the back surface 21b is reflected by the AF dichroic mirror 72 and detected by the displacement detection unit 71b. The displacement detection unit 71b is configured to include, for example, a four-segment photodiode. The four-segment photodiode is configured to divide and receive the condensed image of the reflected light of the AF laser light LA, and output a voltage value according to the respective light amounts. Because astigmatism is added to the reflected light of the AF laser light LA, the shape of the focused image (vertical, circular, horizontal) changes depending on the position of the back surface 21b of the wafer 20 relative to the focal point of the AF laser light LA. In other words, the focused image changes depending on the position of the back surface 21b of the wafer 20 relative to the focal point. Therefore, the voltage value output from the four-segment photodiode changes depending on the position of the back surface 21b of the wafer 20 relative to the focal point of the AF laser light LA.

The voltage value output from the four-segment photodiode of the displacement detection unit 71b is input to the control unit 8. Based on the voltage value output from the four-segment photodiode of the displacement detection unit 71b, the control unit 8 calculates a calculation value as position information regarding the position of the back surface 21b of the wafer 20 relative to the focal point of the AF laser light LA. Based on the calculation value, the control unit 8 controls the drive unit 7 (actuator) to finely adjust the position of the focusing lens 33 in the vertical direction so that the focal point of the laser light L irradiated from the light source 31 is at a certain depth from the back surface 21b. In this way, by performing control based on the distance measurement result by the AF unit 71 together with the laser processing using the laser light L (prior to the laser processing), the focal point of the laser light L can always be accurately aligned at a position at a predetermined distance from the back surface 21b, even if there is waviness on the back surface 21b, which is the incident surface.

In this embodiment, the AF unit 71 also functions as a measurement unit that measures the displacement of the back surface 21b (measurement target surface) used when estimating the processing state (crack state) of the wafer 20 (details will be described later).

[Configuration of inspection imaging unit]
As shown in Fig. 5, the imaging unit 4 (imaging section) has a light source 41, a mirror 42, an objective lens 43, and a light detection section 44. The imaging unit 4 captures an image of the wafer 20. The light source 41 outputs light I1 that is transparent to the semiconductor substrate 21. The light source 41 is composed of, for example, a halogen lamp and a filter, and outputs light I1 in the near-infrared region. The light I1 output from the light source 41 is reflected by the mirror 42, passes through the objective lens 43, and is irradiated onto the wafer 20 from the back surface 21b side of the semiconductor substrate 21. At this time, the stage 2 supports the wafer 20 on which the two rows of modified regions 12a and 12b are formed as described above.

The objective lens 43 passes the light I1 reflected by the surface 21a of the semiconductor substrate 21. In other words, the objective lens 43 passes the light I1 propagated through the semiconductor substrate 21. The numerical aperture (NA) of the objective lens 43 is, for example, 0.45 or more. The objective lens 43 has a correction ring 43a. The correction ring 43a corrects the aberration occurring in the light I1 in the semiconductor substrate 21 by, for example, adjusting the distance between the multiple lenses constituting the objective lens 43. Note that the means for correcting the aberration is not limited to the correction ring 43a, and may be other correction means such as a spatial light modulator. The light detection unit 44 detects the light I1 transmitted through the objective lens 43 and the mirror 42. The light detection unit 44 is, for example, composed of an InGaAs camera, and detects the light I1 in the near-infrared region. Note that the means for detecting (imaging) light I1 in the near-infrared region is not limited to an InGaAs camera, but may be any other imaging means that performs transmission imaging, such as a transmission confocal microscope.

The imaging unit 4 can capture images of each of the two rows of modified regions 12a, 12b, and the tips of each of the multiple cracks 14a, 14b, 14c, and 14d. Crack 14a is a crack that extends from modified region 12a to the front surface 21a. Crack 14b is a crack that extends from modified region 12a to the back surface 21b. Crack 14c is a crack that extends from modified region 12b to the front surface 21a. Crack 14d is a crack that extends from modified region 12b to the back surface 21b.

[Configuration of the imaging unit for alignment correction]
6, the imaging unit 5 has a light source 51, a mirror 52, a lens 53, and a light detection unit 54. The light source 51 outputs light I2 that is transparent to the semiconductor substrate 21. The light source 51 is composed of, for example, a halogen lamp and a filter, and outputs light I2 in the near-infrared region. The light source 51 may be shared with the light source 41 of the imaging unit 4. The light I2 output from the light source 51 is reflected by the mirror 52 and passes through the lens 53, and is irradiated onto the wafer 20 from the back surface 21b side of the semiconductor substrate 21.

The lens 53 passes the light I2 reflected by the surface 21a of the semiconductor substrate 21. In other words, the lens 53 passes the light I2 that has propagated through the semiconductor substrate 21. The numerical aperture of the lens 53 is 0.3 or less. In other words, the numerical aperture of the objective lens 43 of the imaging unit 4 is greater than the numerical aperture of the lens 53. The light detection unit 54 detects the light I2 that has passed through the lens 53 and the mirror 52. The light detection unit 55 is, for example, composed of an InGaAs camera, and detects the light I2 in the near-infrared region. The light detection unit 55 may be an SD camera, or may detect non-transparent light.

Under the control of the control unit 8, the imaging unit 5 irradiates the wafer 20 with light I2 from the back surface 21b side and detects the light I2 returning from the front surface 21a (functional element layer 22), thereby imaging the functional element layer 22. Similarly, under the control of the control unit 8, the imaging unit 5 irradiates the wafer 20 with light I2 from the back surface 21b side and detects the light I2 returning from the formation positions of the modified regions 12a and 12b in the semiconductor substrate 21, thereby acquiring an image of the region including the modified regions 12a and 12b. These images are used for alignment of the irradiation position of the laser light L. The imaging unit 6 has a similar configuration to the imaging unit 5, except that the lens 53 has a lower magnification (for example, 6x in the imaging unit 5 and 1.5x in the imaging unit 6), and is used for alignment in the same way as the imaging unit 5.

[Wafer Inspection by Inspection Device]
In the following, a process will be described in which, when performing a process of forming a modified region for the purpose of cutting the wafer 20, the processed state (crack state) of the wafer 20 is estimated when laser processing the wafer 20 under set processing conditions, and the appropriateness of the processing conditions (pass/fail of the inspection) is judged based on the estimation result. The inspection device 1 according to this embodiment measures the displacement of the back surface 21b (measurement target surface) of the wafer 20 irradiated with laser light using the AF unit 71, and estimates the processed state of the wafer 20 based on the measured displacement of the back surface 21b.

First, the principle of estimating the processing state (crack state) will be described with reference to FIG. 7. FIG. 7 is a diagram showing a schematic cross section (longitudinal cross section) of the wafer 20 for each crack state after laser processing. FIG. 7(a) shows a "BHC (Bottom side half-cut) state" in which the crack 14 does not reach the back surface 21b, which is the incident surface of the laser light L, but reaches the front surface 21a, which is the opposite surface. FIG. 7(b) shows a "ST (Stealth) state" in which the crack 14 does not reach either the back surface 21b or the front surface 21a. FIG. 7(c) shows a "FC (Full-cut) state" in which the crack 14 reaches both the back surface 21b and the front surface 21a. FIG. 7(d) shows a "HC (Half-cut) state" in which the crack 14 reaches the back surface 21b but does not reach the front surface 21a. Hereinafter, each state will be simply referred to as BHC, ST, FC, and HC.

Here, the crack state of the wafer 20 correlates with the displacement (uneven shape) on the incident surface (rear surface 21b) after laser processing. That is, in BHC, the rear surface 21b is concave (see FIG. 7(a)), in ST or FC, the rear surface 21b is flat (without unevenness) (see FIG. 7(b) and FIG. 7(c)), and in HC, the rear surface 21b is convex. Therefore, the inspection device 1 can estimate whether the measured location is BHC, ST (or FC), or HC by measuring the displacement of the rear surface 21b after laser processing with the AF unit 71. Note that ST and FC cannot be distinguished from only the displacement of the rear surface 21b after laser processing, but as described later, the inspection device 1 can distinguish ST and FC based on the imaging results of the rear surface 21b imaged by the imaging units 4, 5, and 6. As is clear from Figures 7(b) and 7(c), in order to distinguish between ST and FC, it is not necessary to capture the image of the inside of the wafer 20, but it is sufficient to capture the image of the back surface 21b of the wafer 20. Therefore, in order to distinguish between ST and FC, the light detection section of the imaging units 4, 5, and 6 may be an SD camera or the like instead of an InGaAs camera.

Figure 8 is a diagram showing a specific inspection process when estimating the processing state (crack state). As shown in Figure 8 (a), first, the displacement (pre-processing displacement) of each area before laser processing is measured along a direction (first direction) intersecting (for example, perpendicular) with the multiple processing lines PL formed by laser processing. Next, as shown in Figure 8 (b), the wafer 20 is rotated by 90 degrees, and the wafer 20 is irradiated with laser light L for multiple lines along a direction (second direction) intersecting the first direction to form multiple processing lines PL. In this case, the multiple processing lines PL are processed, for example, under processing conditions different from each other. Then, as shown in Figure 8 (c), the wafer 20 is rotated by 90 degrees again (oriented in the same direction as in Figure 8 (a)), and the displacement (post-processing displacement) of each area is measured along the first direction. After such measurements are performed, the inspection device 1 derives the difference between the post-processing displacement and the pre-processing displacement for each corresponding area. This derives the displacement (uneven shape of back surface 21b) caused by the laser processing for each processing line PL. The inspection device 1 estimates the processing state (crack state) of each processing line PL based on the displacement (uneven shape of back surface 21b) for each processing line PL, and judges the suitability of the processing conditions set for each processing line PL (pass/fail of the inspection) based on the estimation result. The processing of the inspection device 1 in this inspection process will be specifically described below.

The control unit 8 executes the following operations: controlling the light source 31 so that one or more modified regions are formed inside the wafer 20 by irradiating the wafer 20 with the laser light L; controlling the AF unit 71 so that a post-processing displacement, which is the displacement of the back surface 21b (measurement target surface) after irradiation with the laser light L, is measured; and deriving information related to an estimation of the processing state of the wafer 20 based on the post-processing displacement measured by the AF unit 71. The control unit 8 controls the display 150 so that the derived information related to the estimation of the processing state of the wafer 20 is displayed. FIG. 9 is an example of a display screen displayed on the display 150. The information related to the estimation of the processing state may be the estimation result of the processing state itself, or may be information for estimating the processing state. The estimation result of the processing state itself is, for example, information such as "BHC", "ST", and "HC" shown in FIG. 9. The information for estimating the processing state is, for example, information that enables a user to estimate the processing state (BHC, etc.) based on the information displayed on the display 150, and is, for example, information indicating the amount of displacement on the back surface 21b shown in FIG. 9. In this embodiment, the control unit 8 derives not only information for estimating the machining state, but also the estimation result of the machining state itself, and both pieces of information are displayed on the display 150. However, the control unit 8 may derive only information for estimating the machining state, and the display 150 may display only information for estimating the machining state.

In detail, the control unit 8 derives the difference between the post-processing displacement measured by the AF unit 71 and the reference displacement for each region of the back surface 21b, and estimates the processing state of the wafer 20 based on the difference. In this way, by deriving the difference between the post-processing displacement and the reference displacement, the displacement of the back surface 21b due to the influence of the laser processing (change in the unevenness state) is more accurately derived. For example, when the pre-processing displacement of each region of the back surface 21b is known in advance, the reference displacement may be the pre-processing displacement known in advance. In this embodiment, the control unit 8 sets the pre-processing displacement actually measured before the laser processing as the reference displacement. That is, the control unit 8 controls the AF unit 71 so that the pre-processing displacement, which is the displacement of the back surface 21b before the laser light is irradiated, is further measured (see FIG. 8(a)), and the processing state of the wafer 20 is estimated using the pre-processing displacement as the reference displacement. That is, the control unit 8 derives the difference between the post-processing displacement measured by the AF unit 71 (see FIG. 8(c)) and the pre-processing displacement measured by the AF unit 71 (see FIG. 8(b)), and estimates the processing state of the wafer 20 based on this difference.

The control unit 8 estimates the state of the crack 14 extending from the modified region formed inside the wafer 20 by irradiation with the laser light L for each region based on the difference between the post-processing displacement and the pre-processing displacement in each region of the measurement target surface. Each region here refers to each processing line PL shown in FIG. 8(b).

The control unit 8 may estimate that an area where the absolute value of the difference is greater than a certain threshold (first threshold) is BHC or HC, and that an area where the absolute value of the difference is equal to or less than the threshold (first threshold) is ST or FC. In this way, the control unit 8 may estimate the crack state of each area based on the absolute value of the difference. The control unit 8 may also estimate that an area where the difference in the absolute value of the difference with the surrounding areas is greater than a threshold (second threshold) is BHC or HC, and that an area where the difference in the absolute value of the difference with the surrounding areas is equal to or less than the threshold (second threshold) is ST or FC.

The control unit 8 controls each component so that inspection is performed in the inspection process shown in FIG. 8. The control unit 8 controls the AF unit 71 so that, as shown in FIG. 8(a), the rear surface 21b is irradiated with the AF laser light LA along the irradiation line AL1 in the first direction and the reflected light of the AF laser light LA on the rear surface 21b is detected, thereby measuring the pre-processing displacement in each area along the first direction. The AF unit 71 irradiates the rear surface 21b with the AF laser light LA and receives and detects the reflected light of the AF laser light LA on the rear surface 21b, thereby acquiring displacement data of the rear surface 21b in each area of the irradiation line AL1, and outputs the displacement data (voltage value) to the control unit 8. The AF unit 71 also outputs information (voltage value) indicating the total amount of light detected by receiving the reflected light of the AF laser light LA to the control unit 8.

Next, the control unit 8 controls the light source 31 so that the laser light L is irradiated to the wafer 20 along a second direction intersecting the first direction to form a plurality of processing lines PL, as shown in FIG. 8(b). Next, the control unit 8 controls the AF unit 71 so that the AF laser light LA is irradiated to the back surface 21b along the irradiation line AL2 in the first direction so as to straddle the plurality of processing lines PL, as shown in FIG. 8(c), and the reflected light of the AF laser light LA on the back surface 21b is detected, thereby measuring the post-processing displacement in each area along the first direction. The AF unit 71 acquires displacement data of the back surface 21b in each area of the irradiation line AL2, and outputs the displacement data (voltage value) to the control unit 8. The AF unit 71 also outputs information (voltage value) indicating the total amount of light detected by receiving the reflected light of the AF laser light LA to the control unit 8. In addition, the irradiation lines AL1 and AL2 do not necessarily have to have the same area as long as they have corresponding areas. That is, the irradiation line AL2 when measuring the post-processing displacement may completely overlap the irradiation line AL1 when measuring the pre-processing displacement, or may overlap partially, or may correspond to each other (are close to each other to a certain extent) but not overlap. Finally, the control unit 8 derives the difference between the post-processing displacement and the pre-processing displacement for each corresponding area of the irradiation lines AL1 and AL2, and estimates the crack state for each area based on the difference. Specifically, the control unit 8 estimates the crack state for each processing line PL.

To estimate the crack state for each processing line PL described above, the control unit 8 needs to identify which processing line PL the displacement data (signal indicating displacement) of the back surface 21b obtained by irradiating the AF laser light LA onto the irradiation lines AL1 and AL2 corresponds to. The control unit 8 performs a wafer edge identification process and a processing line identification process to link the displacement data with the processing line PL and realize an estimation of the crack state for each processing line PL. The wafer edge identification process and the processing line identification process will be described below with reference to FIG. 9.

9, the horizontal axis indicates time, the left vertical axis indicates the voltage value corresponding to the total amount of light detected by the AF unit 71, and the right vertical axis indicates the voltage value corresponding to the amount of displacement indicating the difference between the displacement data of the back surface 21b after laser processing and the displacement data of the back surface 21b before laser processing (more specifically, the 30-section moving average of the difference). In FIG. 9, the total amount of light is indicated by a solid line, and the amount of displacement is indicated by a dotted line. The control unit 8 first performs a wafer end identification process to identify the two change points of the total amount of light as both ends of the wafer 20. This is because the reflected light is not detected when the AF laser light LA is not irradiated to the wafer 20, whereas the reflected light is detected when the AF laser light LA is irradiated to the wafer 20, and therefore the wafer end can be identified from the detected total amount of light. The control unit 8 may identify the two points at which the amount of displacement is no longer a constant value as both ends of the wafer 20. Since the position of the edge of the wafer 20 is identified, the difference between the displacement data of the irradiation line AL1 (displacement data before laser processing) and the displacement data of the irradiation line AL2 (displacement data after laser processing) at the corresponding times is derived, and the displacement amount data showing the difference shown in FIG. 9 is obtained. Next, the control unit 8 performs a processing line identification process to identify the displacement data of the processing line PL from the processing index and the scanning speed of the AF unit 71. Now, for example, if the processing index is 5 mm and the scanning speed of the AF unit 71 is 5 mm/sec, the interval between the displacement data of each processing line PL is identified as 1 sec. In this case, as shown in FIG. 9, the displacement data of 1 sec, 2 sec, 3 sec, 4 sec, 5 sec, 6 sec... from the wafer edge is identified as the displacement data of each processing line PL. By the process up to this point, the difference (displacement amount) of the displacement data for each processing line PL is identified.

The control unit 8 may estimate that the processing line PL whose absolute value of the difference (displacement amount) of the displacement data is greater than a certain threshold value (first threshold value) is BHC or HC, and that the processing line PL whose absolute value of the displacement amount is equal to or less than the first threshold value is ST or FC. Now, for example, in the example shown in FIG. 9, the first threshold value is set to 0.04 V. Therefore, as shown in FIG. 9, the 1 sec processing line PL, the 2 sec processing line PL, and the 6 sec processing line PL whose absolute value of the difference (displacement amount) of the displacement data is greater than 0.04 V are estimated to be BHC or HC. Furthermore, in the case of BHC, the back surface 21b has a concave shape (see FIG. 7(a)), whereas in the case of HC, the back surface 21b has a convex shape, so that the positive and negative of the displacement amount are reversed. Now, it is assumed that the displacement amount is set to be negative in the case of BHC and positive in the case of HC. In this case, as shown in FIG. 9, the 1 sec processing line PL and the 2 sec processing line PL, in which the absolute value of the displacement is greater than 0.04 V and the displacement is a negative value, are estimated to be BHC. The 6 sec processing line PL, in which the absolute value of the displacement is greater than 0.04 V and the displacement is a positive value, is estimated to be HC. The 3 sec processing line PL, the 4 sec processing line PL, and the 5 sec processing line PL, in which the absolute value of the difference (displacement) of the displacement data is 0.04 V or less, are estimated to be ST or FC. Furthermore, the control unit 8 can distinguish ST and FC based on the imaging result of the back surface 21b imaged by any of the imaging units 4, 5, and 6. In the example shown in FIG. 9, the 3 sec processing line PL, the 4 sec processing line PL, and the 5 sec processing line are estimated to be ST.

The control unit 8 may also estimate that the processing line PL whose absolute difference in the displacement data (displacement amount) with the surrounding area is greater than a threshold (second threshold) is BHC or HC, and that the processing line PL whose absolute difference in the displacement data with the surrounding area is equal to or less than the second threshold is ST or FC. The displacement amount of the surrounding area here is, for example, the displacement amount of the area other than the processing line PL (between the processing lines PL). Since such areas are not laser processed, the difference in the displacement data (displacement amount) is small. Even with this processing, as shown in FIG. 9, the 1 sec processing line PL, the 2 sec processing line PL, and the 6 sec processing line PL whose absolute difference in the displacement data with the surrounding area is large are estimated to be BHC or HC, and the 3 sec processing line PL, the 4 sec processing line PL, and the 5 sec processing line PL whose absolute difference in the displacement data with the surrounding area is small are estimated to be ST or FC.

Through the above process, the control unit 8 estimates the processing state (crack state) for each processing line PL and displays the estimated result on the display 150. The control unit 8 then judges whether the processing is successful (suitableness of the processing conditions) based on the crack state of each processing line PL. If the crack state of each processing line PL is as expected (as per the inspection conditions), the processing conditions are deemed appropriate and the inspection is passed. On the other hand, if there is a processing line PL whose crack state is not as expected, the control unit 8 judges the inspection as unsuccessful, corrects the processing conditions, and performs the inspection again. Correcting the processing conditions includes, for example, correcting the output of the light source 31, correcting the laser parameters, correcting various aberrations, correcting the CP value, etc.

[Inspection method]
The inspection method of this embodiment will be described with reference to Fig. 10. Fig. 10 is a flow chart of the inspection process (inspection method) of Fig. 8.

As shown in FIG. 10, first, the display 150 accepts the selection input of the inspection conditions, and the inspection conditions are selected (step S1). As the inspection conditions, for example, the formation position of the modified area, the bottom end distance of the modified area, the crack state, etc. are set for each of the multiple processing lines PL. Then, the processing conditions are set so that the processing indicated by the inspection conditions is possible. The processing conditions are, for example, the output of the light source 31, laser parameters, correction of various aberrations, CP value, etc.

Next, the imaging units 5 and 6 are controlled to perform alignment processing for the irradiation position of the laser light L, and a height setting process is performed to set the Z height, which is the processing depth (height) when performing laser processing (step S2).

Next, as shown in FIG. 8(a), the AF laser light LA is irradiated onto the rear surface 21b and the reflected light of the AF laser light LA on the rear surface 21b is detected, and a pre-processing AF waveform, which is the displacement data of the rear surface 21b in each area of the irradiation line AL1 along the first direction, is obtained (step S3).

Next, as shown in FIG. 8(b), the stage 2 rotates to rotate the wafer 20 by 90° (step S4), and the laser light L is irradiated onto the wafer 20 in multiple lines along a direction (second direction) intersecting the first direction to form multiple processing lines PL (step S5).

Next, as shown in FIG. 8(c), the stage 2 rotates to rotate the wafer 20 by 90° to the same orientation as in FIG. 8(a) (step S6), the AF laser light LA is irradiated onto the rear surface 21b, and the reflected light of the AF laser light LA on the rear surface 21b is detected, and the post-processing AF waveform, which is the displacement data of the rear surface 21b in each region of the irradiation line AL2 along the first direction, is obtained (step S7).

Next, in the inspection device 1, various signal processes are performed to estimate the processing state of each processing line PL, and the estimation results are displayed on the display 150 (step S8). Specifically, after performing the wafer edge identification process and the processing line identification process, the inspection device 1 estimates the crack state for each processing line PL based on the difference (displacement amount) of the displacement data of the back surface 21b.

Then, based on the crack condition of each processing line PL, it is judged whether the inspection passes or fails (whether the processing conditions are appropriate or not) (step S9). If the inspection passes, the process ends. On the other hand, if there is a processing line PL where the crack condition is not as expected and the inspection fails, a correction process is performed to correct the processing conditions (step S10), and the process is performed again from step S1 under the new processing conditions.

[Action and Effect]
Next, the effects of the inspection device 1 according to this embodiment will be described.

The inspection device 1 includes a light source 31 that irradiates the wafer 20 with laser light, an AF unit 71 as a measurement unit that measures the displacement of the back surface 21b (surface to be measured) of the wafer 20, which is the incident surface of the laser light L, and a control unit 8 configured to perform the following: control the light source 31 so that one or more modified regions are formed inside the wafer 20 by irradiating the wafer 20 with the laser light L; control the AF unit 71 so that the post-processing displacement, which is the displacement of the back surface 21b after being irradiated with the laser light L, is measured; and derive information related to an estimation of the processing state of the wafer 20 based on the post-processing displacement measured by the AF unit 71.

In the inspection device 1 according to the present embodiment, the post-processing displacement of the back surface 21b (measurement surface) of the wafer 20 irradiated with the laser light L is measured, and information related to the estimation of the processing state of the wafer 20 is derived based on the post-processing displacement. As described above, there is a correlation between the post-processing displacement (uneven shape) of the back surface 21b and the processing state of the wafer 20. Therefore, by deriving information related to the estimation of the processing state of the wafer 20 based on the post-processing displacement, the processing state of the wafer 20 can be appropriately estimated based on the information related to the estimation. Furthermore, the process of measuring the post-processing displacement of the back surface 21b (measurement surface) is extremely easy compared to the process of identifying the processing state (crack state) of the wafer 20 by, for example, observing the inside of the wafer 20 with an infrared camera or the like. Therefore, according to the inspection device 1 according to the present embodiment, the processing state of the wafer 20 can be more easily estimated.

The inspection device 1 is equipped with a display 150, and the control unit 8 controls the display 150 so that the derived information relating to the estimation of the processing state of the wafer 20 is displayed. By displaying the information relating to the estimation of the processing state of the wafer derived by the control unit 8 on the display 150, for example, when information for estimating the processing state is displayed as information relating to the estimation of the processing state, the user can easily estimate the processing state of the wafer 20 based on the displayed content. In addition, when the estimation result of the processing state itself is displayed as information relating to the estimation of the processing state, the user can confirm the validity of the estimation result of the processing state.

The AF unit 71 irradiates the rear surface 21b with AF laser light LA and measures the displacement on the rear surface 21b by receiving and detecting the reflected light of the AF laser light LA on the rear surface 21b. With this configuration, the displacement on the rear surface 21b can be measured with high accuracy using simple configuration and processing.

In addition, in the inspection device 1, the measurement unit that measures the displacement on the back surface 21b is the AF unit 71 that measures the displacement on the back surface 21b in order to adjust the focal point of the laser light L irradiated onto the wafer 20 by the light source 31, so that the displacement on the back surface 21b can be measured using an autofocus unit that is typically provided in an inspection device that irradiates the wafer 20 with a laser. In other words, with this configuration, the autofocus unit is used to measure the displacement (uneven shape) of the back surface 21b, and the processed state of the wafer 20 can be easily estimated based on the displacement.

The control unit 8 derives the difference between the post-processing displacement measured by the AF unit 71 and the reference displacement for each region of the back surface 21b, and derives information related to the estimation of the processing state of the wafer 20 based on the difference. The difference between the post-processing displacement and the reference displacement more accurately indicates the amount of displacement caused by the effects of processing. Therefore, by deriving information related to the estimation of the processing state based on the difference, the processing state of the wafer 20 can be more accurately estimated.

The control unit 8 controls the AF unit 71 so that the pre-processing displacement, which is the displacement of the back surface 21b before the laser light L is irradiated, is further measured, and the pre-processing displacement is used as a reference displacement to derive information related to the estimation of the processing state of the wafer 20. In this way, the pre-processing displacement, which is the displacement of the back surface 21b before the laser light L is irradiated, is actually measured and the pre-processing displacement is used as the reference displacement, so that the difference between the post-processing displacement and the reference displacement more accurately indicates the amount of displacement due to the influence of processing. Therefore, by deriving information related to the estimation of the processing state based on the difference, the processing state of the wafer 20 can be more accurately estimated.

Based on the difference, the control unit 8 estimates the state of the crack 14 extending from the modified region formed inside the wafer 20 by irradiation with the laser light L. There is a correlation between the difference between the post-processing displacement and the reference displacement (displacement on the back surface 21b after laser processing) and the state of the crack extending from the modified region. Therefore, by estimating the state of the crack based on the difference, it is possible to estimate the state of the crack (i.e., the processed state of the wafer 20) with high accuracy.

The control unit 8 estimates that the region where the absolute value of the difference is greater than the first threshold is BHC or HC, and that the region where the absolute value of the difference is equal to or less than the first threshold is ST or FC. The inventors have found that the region where the absolute value of the difference between the post-processing displacement and the reference displacement (the displacement on the measurement target surface after laser processing) is large is in a state where the crack 14 reaches only one of the incident surface and the opposite surface (so-called BHC or HC state), and the region where the difference is small is in a state where the crack 14 does not reach either the incident surface or the opposite surface (so-called ST state) or the crack 14 reaches both the incident surface and the opposite surface (so-called FC state). Based on this idea, the state of the crack 14 is estimated depending on whether the difference is greater than a certain threshold (first threshold), so that the state of the crack 14 (i.e., the processing state of the wafer 20) can be estimated with higher accuracy.

The control unit 8 may estimate that an area where the difference in absolute value of the difference with the surrounding areas is greater than a second threshold value is BHC or HC, and may estimate that an area where the difference in absolute value of the difference is equal to or less than the second threshold value is ST or HC. When estimating the state of the crack 14 based on the difference, it may be easier and more accurate to judge from the difference in absolute value of the difference with the surrounding areas (judging from the relative value) rather than judging from the absolute value of the difference. Based on this idea, the state of the crack 14 is estimated depending on whether the difference in difference with the surrounding areas is greater than a certain threshold value (second threshold value), so that the state of the crack 14 (i.e., the processed state of the wafer 20) can be estimated more accurately and easily.

The control unit 8 controls the AF unit 71 so that the AF laser light LA is irradiated onto the back surface 21b along a first direction and the reflected light of the AF laser light LA on the back surface 21b is detected to measure the pre-processing displacement in each region along the first direction, controls the light source 31 so that the laser light is irradiated onto the wafer 20 for multiple lines along a second direction intersecting the first direction to form multiple processing lines PL, controls the AF unit 71 so that the AF laser light LA is irradiated onto the back surface 21b along the first direction so as to straddle the multiple processing lines PL and the reflected light of the AF laser light LA on the back surface 21b is detected to measure the post-processing displacement in each region along the first direction, derives the difference between the post-processing displacement and the pre-processing displacement for each corresponding region, and derives information related to an estimation of the processing state for each region based on the difference. In this way, the post-processing displacement and pre-processing displacement are measured for each region along the direction (first direction) spanning the multiple processing lines PL, and the difference between the post-processing displacement and the pre-processing displacement for each region is derived, thereby identifying the degree of displacement after laser processing in each of the multiple processing lines PL, and appropriately estimating the processing state of each of the multiple processing lines PL. According to this configuration, for example, by making the inspection conditions of the multiple processing lines PL different from each other and estimating the processing state under each inspection condition, it is possible to efficiently determine whether the processing conditions are appropriate. Then, by identifying the degree of displacement of the multiple processing lines PL, the processing state of each of the multiple processing lines PL can be easily and accurately estimated based on not only the absolute displacement amount but also the relative information on the displacement amount compared to other processing lines by comparing the displacements of different processing lines PL.

The control unit 8 performs processing control based on predetermined processing conditions, judges whether the processing is successful or not based on information related to the estimation of the processing state of the wafer 20, and may correct the processing conditions if the judgment result is failure. With this configuration, the processing conditions can be changed taking into account the estimation result of the processing state of the wafer 20, and the optimization of the processing conditions can be performed centrally and automatically.

[Modification]
Although the present embodiment has been described above, the present invention is not limited to the above embodiment. For example, the inspection device 1 may simply display the estimation result of the machining state on the display 150 without correcting the machining conditions, without deriving the information related to the estimation of the machining state. Also, the inspection device 1 may only perform processing up to deriving the information related to the estimation of the machining state, and may not display the estimation result, etc. on the display 150.

In addition, as described above, the inspection device 1 can estimate the processing state (crack state) from the displacement of the incident surface of the laser light on the wafer 20 without using a camera such as an InGaAs camera that detects light that is transparent to the wafer 20. However, by using the function of the imaging unit 4 that includes a camera that detects light that is transparent to the wafer 20, such as an InGaAs camera, the processing state of the wafer 20 can be estimated in more detail. That is, the inspection device 1 includes an imaging unit 4 that outputs light that is transparent to the wafer 20 and detects the light that has propagated through the wafer 20, and the control unit 8 may estimate the state of the crack 14 by further taking into account the signal output from the imaging unit 4 that detects the light. In this case, the inspection device 1 can estimate the processing state of the wafer 20 in more detail from the internal observation results of the wafer 20 using the imaging unit 4. For example, among multiple processing lines PL estimated to be BHC from the displacement of the incident surface, the inspection device 1 uses an InGaAs camera to measure the position of the modified area and the length of the crack 14 only for the processing line PL where the modified area is formed at the shallowest position under the inspection conditions (i.e., the processing line PL that is the boundary between the BHC and ST). This reduces the number of processing lines PL that are subject to internal observation, significantly shortening the tact time while ensuring the accuracy of the inspection.

Figure 11 is a flowchart of an inspection method when the results of internal observation by an InGaAs camera are also taken into consideration. Steps S101 to S108 shown in Figure 11 are the same as steps S1 to S8 in Figure 10 described above. Following step S108, the inspection device 1 performs internal observation by an InGaAs camera only on a specific processing line PL (for example, a processing line PL that has a BHC at the shallowest position) (step S109). Then, the inspection device 1 further takes into consideration the results of internal observation by the InGaAs camera and judges whether the inspection is successful (suitability of the processing conditions) based on the crack state of each processing line PL (step S110). The subsequent correction process (step S111) is the same as the process of step S10 in Figure 10.

In the above embodiment, the difference between the post-processing displacement and the pre-processing displacement is derived, and information related to the estimation of the processing state of the wafer 20 is derived based on the difference. However, the present invention is not limited to this. For example, information related to the estimation of the processing state of the wafer 20 (specifically, the crack state) may be derived only from the post-processing displacement. FIG. 12 is an example of a display screen displayed on the display 150 when the crack state of the wafer 20 is estimated only from the post-processing displacement. In the example of FIG. 9 described above, the difference between the post-processing displacement and the pre-processing displacement is shown as a displacement amount, whereas in the example of FIG. 12, the post-processing displacement is shown as a displacement amount. In this way, even if only the post-processing displacement is displayed as a displacement amount, for example, if it is possible to ensure that the wafer 20 before processing is relatively flat, the crack state of the wafer 20 can be estimated with high accuracy based on the displayed state. In the example shown in FIG. 9, the estimated result of the crack state itself (BHC, etc.) was displayed on the display 150, but as shown in FIG. 12, only information for the user to estimate the processing state (crack state) may be derived and displayed on the display 150.

In the above embodiment, the crack state of the wafer 20 is estimated by measuring the displacement of the back surface 21b after laser processing, assuming that there is a correlation between the crack state of the wafer 20 and the displacement (uneven shape) on the incident surface (back surface 21b) after laser processing (see FIG. 7). However, this is not limited to this, and for example, the crack state of the wafer 20 may be estimated by measuring the displacement of the surface (front surface 21a) opposite the incident surface after laser processing. That is, the inspection device 1 may measure the displacement of the surface 21a, which is the surface opposite the incident surface of the laser light L on the wafer 20, as the measurement target surface, measure the displacement of the surface 21a, and estimate the crack state of the wafer 20 based on the displacement. Figure 13 is a diagram showing a schematic cross section (longitudinal cross section) of the wafer 20 for each crack state after laser processing. Figure 13(a) shows the BHC state, Figure 13(b) shows the ST state, Figure 13(c) shows the FC state, and Figure 13(d) shows the HC state. As shown in FIG. 13(a), the surface 21a is convex in the case of BHC, as shown in FIG. 13(b) and FIG. 13(c) the surface 21a is flat (without unevenness) in the cases of ST and FC, and as shown in FIG. 13(d) the surface 21a is concave in the case of HC. In this way, there is a correlation between the crack state of the wafer 20 and the displacement (unevenness) of the surface 21a after laser processing. Therefore, the inspection device 1 can estimate whether the measured location is BHC, ST (or FC), or HC by measuring the displacement of the surface 21a after laser processing with the AF unit 71.

Also, as a specific inspection process for estimating the processing state (crack state), an example in which measurement of pre-processing displacement, 90° rotation of the wafer 20, laser processing, 90° rotation of the wafer 20, measurement of post-processing displacement, and estimation of the crack state are sequentially performed as shown in Figures 8 and 10 has been described, but the inspection process for estimating the crack state is not limited to this. Figure 14 is a diagram showing an inspection process according to a modified example. In the inspection method shown in Figure 14, first, the pre-laser processing displacement is measured along the irradiation line AL1 in the first direction (Figure 14(a)), then, multiple processing lines PL1 are formed in the second direction intersecting the first direction by laser processing (CH1), and multiple processing lines PL2 are formed in the first direction by laser processing (CH2) (Figure 14(b)), then, the post-laser processing displacement is measured along the irradiation line AL2 in the first direction (Figure 14(c)). The irradiation line AL1 and the irradiation line AL2 are, for example, lines that completely overlap each other and do not overlap the multiple processing lines PL2. After such measurements are performed, the inspection device 1 derives the difference between the post-processing displacement and the pre-processing displacement for each processing line PL1. As a result, the displacement (uneven shape of the back surface 21b) due to the influence of laser processing is derived for each processing line PL1. The inspection device 1 estimates the processing state (crack state) of each processing line PL1 based on the displacement (uneven shape of the back surface 21b) for each processing line PL1, and judges the suitability (pass/fail of the inspection) of the processing conditions set for each processing line PL1 based on the estimation result. In the example shown in FIG. 14, only the displacement along the irradiation lines AL1 and AL2 in the first direction is measured, so only the processing states of the multiple processing lines PL1 are estimated, but by measuring the displacement before and after processing of the irradiation line in the second direction, the processing states of the multiple processing lines PL2 can also be estimated.

Figure 15 is a flow chart of the inspection process (inspection method) of Figure 14. Steps S201 and S202 shown in Figure 15 are the same as steps S1 and S2 of Figure 10 described above. Following step S202, in the inspection device 1, as shown in Figure 14 (a), the AF laser light LA is irradiated onto the back surface 21b, and the reflected light of the AF laser light LA on the back surface 21b is detected, and a pre-processing AF waveform, which is the displacement data of the back surface 21b in each area of the irradiation line AL1 along the first direction, is acquired (step S203). Next, as shown in Figure 14 (b), the laser light L (CH1) is irradiated onto the wafer 20 along a direction (second direction) intersecting the first direction to form a plurality of processing lines PL1, and the laser light L (CH2) is irradiated onto the wafer 20 along a plurality of lines to form a plurality of processing lines PL2 (step S204). Next, as shown in FIG. 14(c), the AF laser light LA is irradiated onto the rear surface 21b, and the reflected light of the AF laser light LA on the rear surface 21b is detected, and the post-processing AF waveform, which is the displacement data of the rear surface 21b in each region of the irradiation line AL2 along the first direction, is obtained (step S205). The subsequent steps S206 to S208 are the same as steps S8 to S10 in FIG. 10 described above.

Figure 16 is a diagram showing an inspection process according to another modified example. In the inspection method shown in Figure 16, when a plurality of processing lines PL1, PL2 facing each other are formed, the displacement is derived for each of the plurality of processing lines PL1, PL2 facing each other, and the processing state (crack state) is estimated. In this inspection method, first, the pre-laser processing displacement is measured along the irradiation line AL11 in the first direction, and the pre-laser processing displacement is measured along the irradiation line AL21 in the second direction intersecting the first direction (Figure 16 (a)). Next, a plurality of processing lines PL1 are formed in the second direction by laser processing (CH1) (see Figure 16 (b)). Next, a plurality of processing lines PL2 are formed in the first direction by laser processing (CH2) (simultaneous with the formation of the processing line PL2), and the post-laser processing displacement is measured along the irradiation line AL12 in the first direction (Figure 16 (c)). Finally, the post-laser processing displacement is measured along the irradiation line AL22 in the second direction (see FIG. 16(d)). The irradiation line AL11 and the irradiation line AL12 are, for example, lines that completely overlap each other, and the irradiation line AL21 and the irradiation line AL22 are, for example, lines that completely overlap each other. In addition, the irradiation line AL11 and the irradiation line AL12 overlap with one of the multiple processing lines PL2, and the irradiation line AL21 and the irradiation line AL22 do not overlap with any of the multiple processing lines PL1. After such measurements are performed, the inspection device 1 derives the difference between the post-processing displacement and the pre-processing displacement for each of the processing lines PL1 and PL2. As a result, the displacement (uneven shape of the back surface 21b) due to the influence of laser processing is derived for each of the processing lines PL1 and PL2. The inspection device 1 estimates the processing state (crack state) of each processing line PL1, PL2 based on the displacement (uneven shape of the back surface 21b) for each processing line PL1, PL2, and judges the suitability of the processing conditions set for each processing line PL1, PL2 (pass or fail the inspection) based on the estimation result.

When the above-mentioned processing is performed, the control unit 8 controls the AF unit 71 so that the AF laser light LA is irradiated onto the back surface 21b along the irradiation line AL11 in the first direction, and the reflected light of the AF laser light LA on the back surface 21b is detected, thereby measuring the pre-processing displacement in each area along the irradiation line AL11, and the AF laser light LA is irradiated onto the back surface 21b along the irradiation line AL21 in the second direction intersecting the first direction, and the reflected light of the AF laser light LA on the back surface 21b is detected. The AF unit 71 is controlled so that a pre-processing displacement in each region along the irradiation line AL21 is measured by measuring the displacement before processing in each region along the irradiation line AL21, the light source 31 is controlled so that the laser light L (CH1) is irradiated onto the wafer 20 for a plurality of lines along the second direction to form a plurality of processing lines PL1, and the light source 31 is controlled so that the laser light (CH2) is irradiated onto the wafer 20 for a plurality of lines along the first direction to form a plurality of processing lines PL2, and The AF unit 71 is controlled so that the AF laser light LA is irradiated onto the back surface 21b along an irradiation line AL12 in the first direction, and the reflected light of the AF laser light LA on the back surface 21b is detected, thereby measuring the post-processing displacement in each region along the irradiation line AL12 in the first direction. The AF unit 71 is controlled so that the AF laser light LA is irradiated onto the back surface 21b along an irradiation line AL22 in the second direction so as to straddle a plurality of processing lines PL2 along the first direction, and the AF laser light LA on the back surface 21b is detected. The AF unit 71 is controlled so that the reflected light of the laser light LA is detected to measure the post-processing displacement in each area along the irradiation line AL22 in the second direction, the difference between the post-processing displacement and the pre-processing displacement is derived for each corresponding area along the first direction, and information related to the estimation of the processing state for each area is derived based on the difference, and the difference between the post-processing displacement and the pre-processing displacement is derived for each corresponding area along the second direction, and information related to the estimation of the processing state for each area is derived based on the difference.

According to this configuration, even when multiple processing lines PL1, PL2 are formed in each of the directions intersecting each other (when the processing lines are formed in a lattice), information related to the estimation of the processing state is appropriately derived. That is, the post-processing displacement and the pre-processing displacement are measured for each region along the direction (second direction) that straddles the multiple processing lines PL2 formed along the first direction, and the difference between the post-processing displacement and the pre-processing displacement for each region is derived, so that the processing state of each of the multiple processing lines PL2 formed along the first direction can be appropriately estimated. In addition, the post-processing displacement and the pre-processing displacement are measured for each region along the direction (first direction) that straddles the multiple processing lines PL1 formed along the second direction, and the difference between the post-processing displacement and the pre-processing displacement for each region is derived, so that the processing state of each of the multiple processing lines PL1 formed along the second direction can be appropriately estimated. Furthermore, the formation of multiple processing lines PL2 along the first direction and the measurement of post-processing displacement in each region along the first direction (spanning multiple processing lines along the second direction) are processes along the same direction and can be performed simultaneously (Figure 16 (c)). By performing these processes together (simultaneously), processing efficiency can be significantly improved.

In the above process, the control unit 8 may control the AF unit 71 and the light source 31 so that the irradiation line AL12 of the AF laser light LA irradiated along the first direction for measuring the post-processing displacement overlaps with any of the multiple processing lines PL2 along the first direction, and control the AF unit 71 and the light source 31 so that the irradiation line AL22 of the AF laser light LA irradiated along the second direction for measuring the post-processing displacement does not overlap with the multiple processing lines PL1 along the second direction. Now, in order to measure the post-processing displacement with high accuracy, it is desired to eliminate the influence of a processing line whose processing direction is different from that of the processing line of the target for which the post-processing displacement is to be measured. That is, when measuring the post-processing displacement for multiple processing lines along a certain direction, it is desired to eliminate the influence of a processing line along a direction different from the certain direction. In this case, it is necessary that the irradiation line of the AF laser light LA irradiated along a direction different from the certain direction so as to straddle the multiple processing lines along the certain direction does not overlap with the processing line along the direction different from the certain direction. In this regard, since the irradiation line AL22 of the AF laser light LA along the second direction and the multiple processing lines PL1 along the second direction do not overlap, the post-processing displacement of the multiple processing lines PL2 along the first direction can be measured with high accuracy. Here, as described above, in this process, after the processing line PL1 along the second direction is formed, the formation of the processing line PL2 along the first direction and the measurement of the post-processing displacement along the first direction are both performed (FIGS. 16(b) and 16(c)). In this way, when the formation of the processing line and the measurement of the post-processing displacement are both performed along the same direction, even if the processing line and the irradiation line of the AF laser light LA for displacement measurement overlap, the irradiation of the AF laser light LA for displacement measurement is performed prior to the formation of the processing line (while performing both, the irradiation of the AF laser light LA is controlled to precede the formation of the processing line), so that the post-processing displacement of the formed processing line can be measured without being affected by the newly formed processing line. That is, in this process, since both the formation of the processing line PL2 along the first direction and the measurement of the post-processing displacement along the irradiation line AL12 in the first direction are performed, even if any of the processing lines PL2 along the first direction overlaps with the irradiation line AL12 of the AF laser light LA irradiated along the first direction, the post-processing displacement for the multiple processing lines PL1 along the second direction can be estimated with high accuracy without being affected by the formation of the processing line PL2 along the first direction. And, since any of the processing lines PL2 along the first direction overlaps with the irradiation line AL12 of the AF laser light LA irradiated along the first direction, the formation of the processing line PL2 and the process related to the irradiation of the AF laser light LA can be simplified (facilitated).

Figure 17 is a flowchart of the inspection process (inspection method) of Figure 16. Steps S301 and S302 shown in Figure 17 are the same as steps S1 and S2 of Figure 10 described above. Following step S302, in the inspection device 1, as shown in Figure 16 (a), the AF laser light LA is irradiated onto the back surface 21b and the reflected light of the AF laser light LA on the back surface 21b is detected, thereby acquiring a pre-processing AF waveform which is the displacement data of the back surface 21b in each region of the irradiation line AL11 along the first direction, and acquiring a pre-processing AF waveform which is the displacement data of the back surface 21b in each region of the irradiation line AL21 along the second direction (step S303). Next, as shown in Figure 16 (b), the laser light L (CH1) is irradiated onto the wafer 20 for multiple lines along the second direction to form multiple processing lines PL1 (step S304). Next, as shown in FIG. 16(c), the wafer 20 is irradiated with the laser light L (CH2) along multiple lines in the first direction to form multiple processing lines PL2, and a post-processing AF waveform, which is the displacement data of the back surface 21b in each region of the irradiation line AL12 along the first direction, is obtained (step S305). Next, as shown in FIG. 16(d), a post-processing AF waveform, which is the displacement data of the back surface 21b in each region of the irradiation line AL22 along the second direction, is obtained (step S306). Subsequent steps S307 to S309 are similar to steps S8 to S10 in FIG. 10 described above.

In the above embodiment, the processing state of each processing line is estimated by irradiating the AF laser light LA across multiple processing lines and detecting the reflected light, but the present invention is not limited to this. The processing state of the processing line may be estimated by irradiating the AF laser light LA along the processing line and detecting the reflected light. FIG. 18 is a diagram showing an inspection process of estimating the processing state of the processing line by irradiating the AF laser light LA along the processing line. In the inspection process shown in FIG. 18, the control unit 8 first controls the AF unit 71 so that the AF laser light LA is irradiated to the back surface 21b along the irradiation line AL1 in the first direction, and the reflected light of the AF laser light LA on the back surface 21b is detected to measure the pre-processing displacement in each area along the irradiation line AL1 in the first direction (FIG. 18(a)). In this case, the control unit 8 may set all the processing planned lines as the irradiation line AL1, or may set only a part (for example, one) of the processing planned lines as the irradiation line AL1. Next, the control unit 8 controls the light source 31 so that the wafer 20 is irradiated with laser light along the first direction to form a plurality of processing lines PL (FIG. 18(b)). The control unit 8 may control the AF unit 71 and the light source 31 so that the measurement of the pre-processing displacement and the formation of a plurality of processing lines PL are performed simultaneously. Next, the control unit 8 detects the illumination line AL2 overlapping the processing line PL by irradiating the back surface 21b with the AF laser light LA along the irradiation line AL2 overlapping the processing line PL and detecting the reflected light of the AF laser light LA on the back surface 21b. The light source 31 is controlled so that the post-processing displacement in each region along the irradiation line AL2 is measured (FIG. 18(c)). The irradiation line AL1 and the irradiation line AL2 are, for example, lines that overlap each other. The control unit 8 may treat all the processing lines PL as the irradiation line AL2, or may treat only a portion (for example, one) of the processing lines PL as the irradiation line AL2. The control unit 8 then derives the difference between the post-processing displacement and the pre-processing displacement for each corresponding region along the irradiation line AL1 and the irradiation line AL2, and estimates the processing state (crack state) for each region based on the difference.

In this way, the irradiation direction of the AF laser light LA for measuring the pre-processing displacement, the formation direction of the processing line PL, and the irradiation direction of the AF laser light LA for measuring the post-processing displacement are common, so that the process of rotating the wafer 20 as described in the embodiment is not necessary, and processing efficiency can be improved. In this embodiment in which the AF laser light LA is irradiated along the processing line PL, unlike the case in which the AF laser light LA is irradiated across multiple processing lines PL, it is not possible to estimate the processing state based on relative information on the amount of displacement by comparing multiple processing lines PL, but it is possible to estimate the processing state of the processing line PL based on the absolute amount of displacement after processing.

18 described above, the inspection device 1 may be provided with a configuration for irradiating the AF laser light LA on a different axis from the irradiation of the laser light L (providing a separate axis AF on both sides), so that the irradiation of the AF laser light LA for measuring the pre-processing displacement, the formation of the processing line PL, and the irradiation of the AF laser light LA for measuring the post-processing displacement may be performed simultaneously. FIG. 19 is a diagram showing a schematic diagram of a part of the configuration of an inspection device having a separate axis AF unit on both sides. In the configuration shown in FIG. 19, AF units 571 and 671 are provided that irradiate the AF laser light LA on a different axis from the laser light L irradiated to the wafer 20 through the condenser lens 33. The AF unit 571 irradiates the AF laser light LA on the front side of the laser light L in the laser processing proceeding direction. The AF unit 571 irradiates the AF laser light LA on the rear side of the laser light L in the laser processing proceeding direction. When the laser processing direction is reversed on the outward and return paths, the roles of the AF units 571 and 671 are reversed. With this configuration of separate axes on both sides, in addition to the process of irradiating the AF laser light LA in the laser processing direction, it is possible to perform measurement of the pre-processing displacement by irradiating the AF laser light LA from the AF unit 571, and measurement of the post-processing displacement by irradiating the AF laser light LA from the AF unit 671. This allows for more efficient estimation of the processing state when performing the inspection process shown in FIG. 18.

Figure 20 shows an example of a display screen when estimating the machining state of the machining line PL with the above-mentioned double-axis AF configuration. Figure 20(b) shows the pre-machining displacement (pre-machining AF waveform) measured by AF unit 571, and Figure 20(c) shows the post-machining displacement (post-machining AF waveform) measured by AF unit 671. The difference between the pre-machining displacement (Figure 20(b)) and the post-machining displacement (Figure 20(c)) is derived, and the displacement amount, which is the difference between the displacement data shown in Figure 20(a), is displayed. Figure 20(a) shows the displacement amount when the crack state is HC.

As described above, when estimating the processing state of the processing line PL with the configuration of two-sided separate axes AF, since only the displacement in one processing line PL is measured, it is not possible to estimate the processing state based on relative information of the displacement amount by comparing multiple processing lines PL. However, as shown in FIG. 21, the absolute value and positive/negative of the displacement amount, which is the difference in the displacement data, differ depending on the crack state, so the processing state of the processing line PL can be appropriately estimated based on this information. For example, in the example shown in FIG. 21(a), the crack state can be estimated to be HC based on the average value of the absolute value of the displacement amount (value shown by the solid line) being relatively large and positive. Also, for example, in the example shown in FIG. 21(b), the crack state can be estimated to be ST or FC based on the average value of the absolute value of the displacement amount (value shown by the solid line) being relatively small, and further, by taking into account the imaging results of the imaging unit, the crack state can be estimated to be ST.

The configuration for simultaneously measuring the pre-processing displacement, forming the processing line PL, and measuring the post-processing displacement is not limited to the configuration of the two-sided separate axis AF in FIG. 19. For example, as shown in FIG. 22(a), the inspection device 1 may have a general distance measuring sensor 871 for measuring the unevenness of the back surface 21b as a configuration for measuring the post-processing displacement, instead of the AF unit 671 (FIG. 19) that irradiates the AF laser light LA rearward of the laser light L. Furthermore, as shown in FIG. 22(b), the inspection device 1 may have a general distance measuring sensor 771 for measuring the unevenness of the back surface 21b as a configuration for measuring the post-processing displacement, instead of the AF unit 571 (FIG. 19) that irradiates the AF laser light LA forward of the laser light L. In the configuration of FIG. 22(b), a separate axis AF configuration is not required, so a configuration (coaxial AF) can be adopted in which the laser light L and the AF laser light LA are irradiated from a single condenser lens 33, similar to the laser irradiation unit 3 in FIG. 4. Note that, for example, a two-dimensional laser displacement sensor can be used as the distance measurement sensors 771 and 871.

The inspection device 1 may also automatically set the pattern offset (LCOS pattern offset) of the spatial light modulator 32. It is known that the formation state of the modified region can be suitably controlled by offsetting the center of the modulation pattern of the spatial light modulator 32 by an appropriate amount relative to the center of the entrance pupil surface of the condenser lens 33. Automatic setting of the LCOS pattern offset is to automatically derive and set a suitable offset amount for the center of the modulation pattern. Now, for example, assume that the offset amount (pattern offset value) is changed in increments of 1.0 for five processing lines PL. That is, as shown in FIG. 23, the offset amount of the first line is set to center -2.0, the offset amount of the second line is set to center -1.0, the offset amount of the fourth line is set to center +1.0, and the offset amount of the fifth line is set to center +2.0, based on the third line (center) which is considered to be an appropriate offset amount. Then, suppose that the inspection device 1 estimates the crack state of each processing line PL under two patterns of inspection conditions, and as a result, the crack state becomes BHC only for the third line, as shown in FIG. 23. In this case, the inspection device 1 estimates that the offset amount of the third line, which became BHC under both inspection conditions, is the appropriate offset amount. The inspection device 1 determines that the offset amount assumed to be appropriate before inspection was actually appropriate, and sets the offset amount of the third line as the offset amount for inspection. On the other hand, if BHC occurs only on another line, the inspection device 1 sets the offset amount of the other line as the optimal value.

In the embodiment, the inspection device 1 is described as determining whether or not the predetermined processing conditions are appropriate, but the inspection device 1 may also be configured to newly derive processing conditions (set conditions) by estimating the crack state. Furthermore, the inspection device 1 may be used not only for stealth dicing devices, but also for automatic determination of crack states in slicing devices and trimming devices.

1... inspection device, 4... imaging unit (imaging section), 8... control section, 20... wafer, 21b... back surface (surface to be measured), 31... light source (laser irradiation section), 71... AF unit (measurement section, measurement unit), 150... display (display section).

Claims (18)

a laser irradiation unit that irradiates a wafer with laser light;
a measurement unit for measuring a displacement of a measurement target surface, which is an incident surface of the laser light on the wafer or a surface opposite to the incident surface;
a control unit configured to execute the following: controlling the laser irradiation unit so that one or more modified regions are formed inside the wafer by irradiating the wafer with the laser light; controlling the measurement unit so that a post-processing displacement, which is a displacement of the measurement target surface after the laser light is irradiated, is measured; and deriving information relating to an estimation of a processed state of the wafer based on the post-processing displacement measured by the measurement unit ;
the control unit derives a difference between the post-processing displacement measured by the measurement unit and a reference displacement for each region of the measurement target surface, and derives information related to an estimation of a processed state of the wafer based on the difference;
The control unit estimates a state of a crack extending from the modified region formed inside the wafer by irradiating the laser light based on the difference. Further comprising a display unit,
The inspection apparatus according to claim 1 , wherein the control unit controls the display unit so that the derived information relating to the estimation of the processed state of the wafer is displayed. The inspection device according to claim 1 or 2, wherein the measurement unit has a measurement unit that irradiates the measurement surface with measurement light and measures the displacement on the measurement surface by receiving and detecting the reflected light of the measurement light on the measurement surface. The inspection device according to claim 3, wherein the measurement unit is an autofocus unit that measures the displacement on the measurement target surface in order to adjust the focal point of the laser light irradiated onto the wafer by the laser irradiation unit. The control unit is
controlling the measurement unit so as to further measure a pre-processing displacement, which is a displacement of the measurement target surface before the laser light is irradiated;
5. The inspection apparatus according to claim 1, further comprising: a step of deriving information relating to an estimation of a processed state of the wafer by using the pre-processing displacement as the reference displacement. The control unit is
For a region in which the absolute value of the difference is greater than a first threshold value, it is estimated that the crack has reached the incident surface but has not reached the opposite surface, or has not reached the incident surface but has reached the opposite surface;
An inspection device as described in any one of claims 1 to 5, wherein, for an area where the absolute value of the difference is equal to or less than a first threshold value, it is estimated that the crack has not reached either the incident surface or the opposite side, or that it has reached both the incident surface and the opposite side. The control unit is
For a region where the difference between the absolute value of the difference and the surrounding region is greater than a second threshold value, it is estimated that the crack has reached the incident surface but not reached the opposite surface, or has not reached the incident surface but has reached the opposite surface;
An inspection device as described in any one of claims 1 to 6, wherein, for an area where the difference in absolute value of the difference is equal to or less than a second threshold value, it is estimated that the crack has not reached either the incident surface or the opposite side, or has reached both the incident surface and the opposite side. an imaging unit that outputs light that is transmissive to the wafer and detects the light that has propagated through the wafer;
8. The inspection device according to claim 1 , wherein the control unit estimates the state of the crack by further taking into consideration a signal output from the imaging unit that detects light. The control unit is
controlling the measurement unit so that a measurement light is irradiated onto the measurement target surface along a first direction, and a reflected light of the measurement light on the measurement target surface is detected to measure a pre-processing displacement, which is a displacement of the measurement target surface before the laser light is irradiated in each region along the first direction;
controlling the laser irradiation unit so that a plurality of lines are formed by irradiating the wafer with laser light along a second direction intersecting the first direction;
controlling the measurement unit so that the measurement light is irradiated onto the measurement target surface along the first direction so as to straddle the plurality of processing lines, and reflected light of the measurement light on the measurement target surface is detected to measure the post-processing displacement in each region along the first direction;
The inspection device according to any one of claims 1 to 8 , further comprising: a difference between the post-processing displacement and the pre-processing displacement for each corresponding region; and information relating to an estimation of the processing state for each region based on the difference. The control unit is
controlling the measurement unit so that a measurement light is irradiated onto the measurement target surface along a first direction, and a reflected light of the measurement light on the measurement target surface is detected to measure a pre-processing displacement, which is a displacement of the measurement target surface before the laser light is irradiated in each region along the first direction;
controlling the measurement unit so that the measurement light is irradiated onto the measurement target surface along a second direction intersecting the first direction, and reflected light of the measurement light on the measurement target surface is detected to measure the pre-processing displacement in each region along the second direction;
controlling the laser irradiation unit so that the laser light is irradiated onto the wafer in a plurality of lines along the second direction to form a plurality of processing lines;
controlling the laser irradiation unit so that the laser light is irradiated onto the wafer in a plurality of lines along the first direction to form a plurality of processing lines; and controlling the measurement unit so that the measurement light is irradiated onto the measurement target surface along the first direction so as to straddle the plurality of processing lines along the second direction, and reflected light of the measurement light on the measurement target surface is detected to measure the post-processing displacement in each region along the first direction;
controlling the measurement unit so that the measurement light is irradiated onto the measurement target surface along the second direction so as to straddle the plurality of processing lines along the first direction, and reflected light of the measurement light on the measurement target surface is detected to measure the post-processing displacement in each region along the second direction;
An inspection device according to any one of claims 1 to 8, which derives a difference between the post-processing displacement and the pre-processing displacement for each of corresponding regions along the first direction, derives information relating to an estimation of the processing state for each of the regions based on the difference, and derives a difference between the post-processing displacement and the pre-processing displacement for each of corresponding regions along the second direction, and derives information relating to an estimation of the processing state for each of the regions based on the difference. The control unit is
controlling the measurement unit and the laser irradiation unit so that an irradiation line of the measurement light irradiated along the first direction for measuring the post-processing displacement overlaps with any one of the plurality of processing lines along the first direction;
The inspection device according to claim 10, further comprising: a measuring unit that controls the laser irradiation unit so that an irradiation line of the measurement light irradiated along the second direction for measuring the post-processing displacement does not overlap with the multiple processing lines along the second direction. The control unit is
controlling the measurement unit so that a measurement light is irradiated onto the measurement target surface along a first direction, and a reflected light of the measurement light on the measurement target surface is detected to measure a pre-processing displacement, which is a displacement of the measurement target surface before the laser light is irradiated in each region along the first direction;
controlling the laser irradiation unit so that a processing line is formed by irradiating the wafer with laser light along the first direction;
controlling the measurement unit so that the measurement light is irradiated along the processing line onto the measurement target surface, and reflected light of the measurement light on the measurement target surface is detected to measure the post-processing displacement in each region along the processing line;
The inspection device according to any one of claims 1 to 8, further comprising: a difference between the post-processing displacement and the pre-processing displacement for each of the corresponding regions along the processing line; and information relating to an estimation of the processing state for each of the regions is derived based on the difference . The control unit performs processing control based on predetermined processing conditions, judges whether the processing is successful based on information related to an estimation of the processing state of the wafer, and corrects the processing conditions if the judgment result is failure. a laser processing step of irradiating the wafer with laser light so as to form one or more modified regions within the wafer;
a post-processing measurement step of measuring a post-processing displacement, which is a displacement of the measurement target surface of the wafer after the laser processing;
and estimating a processing state of the wafer based on the post-processing displacement ,
In the estimation step,
deriving a difference between the post-processing displacement measured in the post-processing measurement step and a reference displacement for each region of the measurement target surface, and deriving information related to an estimation of a processing state of the wafer based on the difference;
an inspection method for estimating a state of a crack extending from the modified region formed inside the wafer by irradiating the laser light based on the difference. The method further includes a pre-processing measurement step of measuring a pre-processing displacement, which is a displacement of the measurement target surface, before the laser processing step;
15. The inspection method according to claim 14 , wherein in the estimation step, a difference between the post-processing displacement and the pre-processing displacement is derived for each region of the measurement target surface, and the processed state of the wafer is estimated based on the difference. In the pre-processing measurement step, a measurement light is irradiated onto the measurement target surface along a first direction, and a reflected light of the measurement light is received and detected on the measurement target surface, thereby measuring the pre-processing displacement in each region along the first direction;
In the laser processing step, a laser beam is irradiated onto the wafer in a plurality of lines along a second direction intersecting the first direction to form a plurality of processing lines;
The inspection method described in claim 15, wherein in the post-processing measurement process, a measurement light is irradiated onto the measurement target surface along the first direction so as to straddle the multiple processing lines, and the reflected light of the measurement light on the measurement target surface is received and detected to measure the post-processing displacement in each region along the first direction. the pre-processing measurement step includes a first pre-processing step of irradiating the measurement surface with a measurement light along a first direction and receiving and detecting reflected light of the measurement light on the measurement surface to measure the pre-processing displacement in each region along the first direction, and a second pre-processing step of irradiating the measurement surface with a measurement light along a second direction intersecting the first direction and receiving and detecting reflected light of the measurement light on the measurement surface to measure the pre-processing displacement in each region along the second direction,
the laser processing step includes a first processing step of irradiating the wafer with laser light for a plurality of lines along the second direction to form a plurality of processing lines, and a second processing step of irradiating the wafer with laser light for a plurality of lines along the first direction to form a plurality of processing lines,
The post-processing measurement step includes a first post-processing step of irradiating the measurement object surface with a measurement light along the first direction so as to straddle the multiple processing lines along the second direction, and measuring the post-processing displacement in each region along the first direction by receiving and detecting the reflected light of the measurement light on the measurement object surface, and a second post-processing step of irradiating the measurement object surface with a measurement light along the second direction so as to straddle the multiple processing lines along the first direction, and measuring the pre-processing displacement in each region along the second direction by receiving and detecting the reflected light of the measurement light on the measurement object surface,
The inspection method according to claim 15 , wherein the first post-processing step is performed simultaneously with the second processing step. In the pre-processing measurement step, a measurement light is irradiated onto the measurement target surface along a first direction, and a reflected light of the measurement light is received and detected on the measurement target surface, thereby measuring the pre-processing displacement in each region along the first direction;
In the laser processing step, a laser beam is irradiated onto the wafer along the first direction to form a processing line;
The inspection method described in claim 15, wherein the post-processing measurement process includes irradiating a measurement light along the processing line to the measurement target surface, and receiving and detecting the reflected light of the measurement light on the measurement target surface, thereby measuring the post-processing displacement in each region along the processing line.

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