JP7625426B2 - Observation device and observation method - Google Patents

Description

One aspect of the present invention relates to an observation device and an observation method.

A laser processing device is known that cuts a wafer having a semiconductor substrate and a functional element layer formed on the semiconductor substrate along each of a plurality of lines by irradiating the wafer with laser light from one side of the semiconductor substrate to form a plurality of rows of modified regions inside the semiconductor substrate along each of the plurality of lines. The laser processing device described in Patent Document 1 is equipped with an imaging unit (e.g., an infrared camera), and makes it possible to observe the modified regions formed inside the semiconductor substrate and the processing damage formed in the functional element layer from one side of the semiconductor substrate.

JP 2017-64746 A

When observing information related to the modified region (for example, a crack extending from the modified region) in the laser processing device described above, for example, the tip of a crack extending from the modified region toward the other surface (the surface opposite to the surface irradiated with the laser light) cannot be detected by making the tip the focal point, but can be detected by making a point symmetrical to the tip on the other surface the focal point. In this way, when it is necessary to make a point symmetrical to the other surface the focal point, the imaging area becomes wide. Normally, the imaging unit is moved in the vertical direction (Z direction) by a control unit that moves the entire imaging unit, but if the imaging area is wide, the focal position cannot be moved at a sufficiently high speed. The time required to move the focal position becomes longer than the imaging rate, which causes a decrease in tact. In addition, even if the focal position can be moved at high speed, the vibrations are difficult to settle after the movement by moving the entire imaging unit at high speed, and imaging cannot be performed until the vibrations settle, which results in a decrease in tact.

One aspect of the present invention was made in consideration of the above situation, and relates to an observation device and an observation method that can improve takt time.

The observation device according to one aspect of the present invention is an observation device for observing a wafer having a first surface and a second surface, in which a modified region is formed by irradiating a laser beam from the first surface side, and is equipped with an imaging unit having a light source that outputs light that is transparent to the wafer, a focusing lens that focuses the light output from the light source at a focusing position on the wafer, and a light detection unit that detects the light propagated through the wafer, a drive unit that supports the imaging unit and moves the imaging unit in the Z direction, which is the vertical direction, an actuator provided on the focusing lens that moves the focusing lens in the Z direction, and a control unit, and the control unit is configured to execute a first control that controls the drive unit so that the imaging unit moves to a position where the second surface becomes the focusing position, and a second control that controls the actuator so that after the first control, the focusing lens moves to a position where at least a part of the first region, which is the region between the second surface and the first surface, becomes the focusing position, and so that the focusing lens moves to a position where at least a part of the second region, which is the region on the opposite side of the first surface with respect to the second surface, becomes the focusing position.

In the observation device according to one aspect of the present invention, in observing a wafer on which a modified region is formed, a drive unit that moves the imaging unit in the Z direction is controlled so that the imaging unit moves to a position where the second surface (rear surface) of the wafer becomes the focusing position, and then the focusing lens moves to a position where the first region, which is the region between the second surface and the first surface, becomes the focusing position, and an actuator that moves the focusing lens in the Z direction is controlled so that the focusing lens moves to a position where the second region, which is the region on the opposite side of the first surface with respect to the second surface, becomes the focusing position. In this way, by moving the focusing lens so that both the first region and the second region become focusing positions, it is possible to appropriately perform both direct observation of cracks, etc. from the modified region when the first region is the focusing position, and observation using the back surface (second surface) reflection of cracks, etc. when the second region is the focusing position. And, since the movement of the focusing lens to focus the first region and the second region is performed by an actuator that moves only the focusing lens of the imaging unit, the focusing position can be moved at a high speed compared to, for example, moving the entire imaging unit, and vibration after the movement can also be suppressed. Here, the observation device according to one aspect of the present invention has a drive unit that moves the entire imaging section in the Z direction, and an actuator that moves the condenser lens of the imaging section in the Z direction. By providing both the drive unit and the actuator in this way, for example, it is possible to perform rough alignment with the drive unit and detailed alignment with the actuator, and it is possible to perform alignment (such as condenser alignment in the imaging range) that requires precision with high accuracy while suppressing the device cost. In the observation device according to one aspect of the present invention, first, the imaging section is controlled by the drive unit so that the second surface, which is the boundary surface between the first area and the second area, becomes the condenser position, and then the condenser lens is controlled by the actuator so that the first area and the second area become the condenser positions. By aligning the condenser position with the second surface (the boundary surface between the first area and the second area) before the control by the actuator is started, it is possible to appropriately perform high-speed movement of the condenser lens with the first area and the second area as the condenser position by making the most of the movable range of the actuator. As described above, according to the observation device according to one aspect of the present invention, the condenser position can be moved at high speed to improve the tact time.

The control unit may further execute a pre-control before the first control, which controls the actuator so that the actuator is fixed at the center position of the actuator's movable range in the Z direction. This allows the second control to be executed in a state where the actuator can be fully movable in both directions (up and down) in the Z direction, and makes the most of the actuator's movable range to appropriately perform high-speed movement of the focusing lens with the first and second regions as focusing positions.

The control unit may be configured to execute a third control in which, in the second control, the actuator is controlled so that the position of the condenser lens moves in the Z direction in a state where the region near the second surface is the condensing position, the detailed position of the second surface is identified based on the light detection result by the light detection unit in this state, and the actuator is controlled so that the condenser lens moves to a reference position where the identified detailed position of the second surface is the condensing position, and a fourth control in which the actuator is controlled so that the condenser lens moves from the reference position to a position where at least a part of the first region is the condensing position, and the actuator is controlled so that the condenser lens moves from the reference position to a position where at least a part of the second region is the condensing position. Even with the first control, it is possible that the condensing position may deviate from the second surface, for example, if the actual wafer thickness is different from the expected one. In this case, there is a risk that imaging of the first and second regions cannot be achieved by making the most of the movable range of the actuator described above. In this regard, in the second control, the exact position of the second surface is identified based on the light detection results and is set as the reference position (third control), and the focusing lens is moved from the reference position to the imaging range of the first and second regions by the actuator (fourth control). Even if the focusing position deviates from the second surface in the first control, the reference position can be appropriately set to realize imaging of the first and second regions making maximum use of the actuator's movable range.

The control unit is configured to execute a third control in which, in the second control, the actuator is controlled so that the position of the condenser lens moves in the Z direction in a state where the area near the second surface becomes the condensing position, the detailed position of the second surface is identified based on the light detection result by the light detection unit in this state, and the actuator is controlled so that the condenser lens moves to a reference position where the condenser lens position where the identified detailed position of the second surface becomes the condensing position, and the control unit may further execute a fifth control in which the drive unit is controlled so that the imaging unit moves to a position where at least a part of an unimaged area, which is an area in the first area or the second area and is not set as the condensing position when the detailed position of the second surface is identified in the third control, becomes the condensing position, and a sixth control in which the actuator is controlled so that the condenser lens moves to a position where an area included in the unimaged area becomes the condensing position, with the position of the condenser lens of the imaging unit after the fifth control being set as a new reference position. According to the third control, imaging near the second surface can be performed in the process of identifying the detailed position of the second surface. Therefore, in this observation device, the drive unit is controlled so that the imaging section moves to a position where the unimaged region becomes the focusing position in the third control (fifth control), and the position of the focusing lens after the fifth control is set as a new reference position, and the actuator is controlled so that the focusing lens moves to a position where the unimaged region becomes the focusing position (sixth control). With this configuration, the unimaged region is controlled to become the focusing position in the third control, so that imaging can be performed more efficiently without performing unnecessary imaging. Also, with this configuration, even if the region to be imaged does not fit within the movable range of the actuator at the initial reference position, the region to be imaged can be reliably imaged by changing the reference position.

An observation method according to one aspect of the present invention is a method for observing a wafer having a first surface and a second surface, in which a modified region is formed by irradiating laser light from the first surface side, and includes a first step of moving the imaging unit to a position where the second surface is a focusing position by a drive unit that moves the imaging unit in the Z direction, which is the vertical direction, and a second step of moving the focusing lens included in the imaging unit to a position where at least a part of the first region, which is the region between the second surface and the first surface, is a focusing position by an actuator that moves the focusing lens in the Z direction, and moving the focusing lens to a position where at least a part of the second region, which is the region on the opposite side of the first surface with respect to the second surface, is a focusing position. According to the observation method according to one aspect of the present invention, the focusing position can be moved at high speed, thereby improving the takt time.

The observation method may further include a preliminary step of controlling the actuator before the first step so that the actuator is fixed at the center position of the actuator's movable range in the Z direction. With this configuration, the movable range of the actuator can be fully utilized to appropriately perform high-speed movement of the focusing lens with the first and second regions as focusing positions.

According to one aspect of the present invention, even when the imaging area is large, the focusing position can be moved quickly, improving the tact time.

FIG. 1 is a configuration diagram of a laser processing apparatus according to one embodiment. FIG. 2 is a plan view of a wafer of one 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 . 6A to 6C are cross-sectional views of a wafer for explaining the imaging principle by the inspection imaging unit shown in FIG. 5, and images at various locations by the inspection imaging unit. 6A to 6C are cross-sectional views of a wafer for explaining the imaging principle by the inspection imaging unit shown in FIG. 5, and images at various locations by the inspection imaging unit. 1 is a SEM image of modified regions and cracks formed within a semiconductor substrate. 1 is a SEM image of modified regions and cracks formed within a semiconductor substrate. 6 is a light path diagram for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and a schematic diagram showing an image at a focal point of the inspection imaging unit. FIG. 6 is a light path diagram for explaining the imaging principle of the inspection imaging unit shown in FIG. 5, and a schematic diagram showing an image at a focal point of the inspection imaging unit. FIG. FIG. 1 is a diagram illustrating the configuration of an objective lens equipped with an actuator. FIG. 1 is a diagram illustrating the configuration of an objective lens equipped with an actuator. 1A and 1B are diagrams for explaining an overview of movement of a focusing position using a drive unit and an actuator. 11A and 11B are diagrams for explaining details of movement of the focusing position using a drive unit and an actuator. 11 is a flowchart illustrating an example of an observation method. 11A and 11B are diagrams for explaining details of movement of the focusing position using a drive unit and an actuator.

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

As shown in FIG. 1, the laser processing 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. The laser processing 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 laser processing device 1 is also an observation device that observes the object 11 (a wafer 20 described later) in which the modified region 12 has been formed.

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 the 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 an imaging section that captures images of the modified area 12 formed in the object 11 and the tip of the crack extending from the modified area 12.

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 that passes 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.

The drive unit 7 supports the laser irradiation unit 3 and the multiple imaging units 4, 5, and 6. The drive unit 7 is a Z axis that 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 in this embodiment is a wafer 20, as shown in Figs. 2 and 3. The wafer 20 includes a semiconductor substrate 21 and a functional device layer 22. In this embodiment, the wafer 20 is described as having the functional device layer 22, but the wafer 20 may or may not have the functional device layer 22, and may be a bare wafer. The semiconductor substrate 21 has a back surface 21a (second surface) and a front surface 21b (first surface). The semiconductor substrate 21 is, for example, a silicon substrate. The functional device layer 22 is formed on the back surface 21a of the semiconductor substrate 21. The functional device layer 22 includes a plurality of functional devices 22a arranged two-dimensionally along the back surface 21a. The functional device 22a is, for example, a light receiving device such as a photodiode, a light emitting device such as a laser diode, a circuit device such as a memory, or the like. The functional device 22a may be configured three-dimensionally by stacking a plurality of layers. Although the semiconductor substrate 21 has a notch 21c indicating the crystal orientation, 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 back 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 includes a light source 31, a spatial light modulator 32, and a condenser lens 33. The light source 31 outputs the 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 front 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. Of the two rows of modified regions 12a, 12b, the modified region 12a is the closest to the back surface 21a. Of the two rows of modified regions 12a, 12b, the modified region 12b is the closest to the modified region 12a and is the closest to the front 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 surface 21b side 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 <100> substrate having a thickness of 400 μm, two focusing points C1 and C2 are aligned at positions 54 μm and 128 μm from the back surface 21a, respectively, and the laser light L is irradiated from the surface 21b side 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 back surface 21a of the semiconductor substrate 21, the wavelength of the laser light L is 1099 nm, the pulse width is 700 nsec, and the repetition frequency is 120 kHz. 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. For example, when the number of processing passes is 5, the processing positions for the above-mentioned wafer 20 may be, for example, ZH80 (position 328 μm from the back surface 21a), ZH69 (position 283 μm from the back surface 21a), ZH57 (position 234 μm from the back surface 21a), ZH26 (position 107 μm from the back surface 21a), and ZH12 (position 49.2 μm from the back surface 21a). In this case, for example, the wavelength of the laser light L may be 1080 nm, the pulse width may be 400 nsec, the repetition frequency may be 100 kHz, and the movement speed may be 490 mm/sec.

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

[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 (a condensing lens), and a light detection section 44. The imaging unit 4 captures an image of the wafer 20. Here, only an overview of the imaging unit 4 is described, and a more detailed configuration of the imaging unit 4 (specifically, the configuration of the objective lens 43 on which the actuator 70 (see FIG. 13) is mounted) will be described later. The light source 41 outputs light I1 that is transparent to the semiconductor substrate 21 of the wafer 20. 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 and passes through the objective lens 43, and is irradiated onto the wafer 20 from the surface 21b side of the semiconductor substrate 21. The objective lens 43 functions as a condensing lens that condenses the light I1 output from the light source 41 at a condensing position on the wafer 20. At this time, the stage 2 supports the wafer 20 on which the two rows of modified regions 12a, 12b have been formed as described above.

The objective lens 43 passes the light I1 reflected by the back surface 21a of the semiconductor substrate 21. That is, 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 that has passed through the objective lens 43 and the mirror 42 (i.e., the light that has propagated through the wafer 20). 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 (details will be described later). Crack 14a is a crack that extends from modified region 12a to the back surface 21a. Crack 14b is a crack that extends from modified region 12a to the front surface 21b. Crack 14c is a crack that extends from modified region 12b to the back surface 21a. Crack 14d is a crack that extends from modified region 12b to the front 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 of the wafer 20. 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 front surface 21b side of the semiconductor substrate 21.

The lens 53 passes the light I2 reflected by the rear 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 54 is, for example, composed of an InGaAs camera, and detects the light I2 in the near-infrared region.

Under the control of the control unit 8, the imaging unit 5 irradiates the wafer 20 with light I2 from the front surface 21b side and detects the light I2 returning from the rear 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 front 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.

[Principle of imaging by inspection imaging unit]
Using the imaging unit 4 shown in Fig. 5, the focal point F (the focal point of the objective lens 43) is moved from the front surface 21b side to the back surface 21a side with respect to the semiconductor substrate 21 in which the cracks 14 extending across the two rows of modified regions 12a, 12b reach the back surface 21a as shown in Fig. 7. In this case, when the focal point F is adjusted from the front surface 21b side to the tip 14e of the crack 14 extending from the modified region 12b to the front surface 21b side, the tip 14e can be confirmed (the image on the right side in Fig. 7). Hereinafter, the method of observing the tip 14e of the crack 14 by adjusting the focal point F to the tip 14e of the crack 14 in this manner may be referred to as direct observation. However, even if the focal point F is adjusted from the front surface 21b side to the tip 14e of the crack 14 itself and the tip 14e of the crack 14 reaching the back surface 21a, they cannot be confirmed (the image on the left side in Fig. 7). In addition, when the focal point F is adjusted from the front surface 21b side to the back surface 21a of the semiconductor substrate 21, the functional element layer 22 can be confirmed.

Using the imaging unit 4 shown in FIG. 5, the focal point F is moved from the front surface 21b side to the back surface 21a side for a semiconductor substrate 21 in which the cracks 14 that extend across the two rows of modified regions 12a and 12b have not yet reached the back surface 21a, as shown in FIG. 8. In this case, even if the focal point F is aligned from the front surface 21b side to the tip 14e of the crack 14 extending from the modified region 12a to the back surface 21a side, the tip 14e cannot be confirmed (the image on the left side in FIG. 8). However, if the focal point F is aligned from the front surface 21b side to the region on the opposite side of the back surface 21a from the front surface 21b (i.e., the region on the functional element layer 22 side of the back surface 21a) and a virtual focal point Fv that is symmetrical to the focal point F with respect to the back surface 21a is positioned at the tip 14e, the tip 14e can be confirmed by the reflected light from the back surface 21a (the image on the right side in FIG. 8). The virtual focal point Fv is a point that is symmetrical with the focal point F with respect to the back surface 21a, taking into account the refractive index of the semiconductor substrate 21. Hereinafter, this method of focusing F on the area on the opposite side of the back surface 21a from the front surface 21b and observing the tip 14e using back surface reflection may be referred to as back surface reflection observation.

As described above, the reason why the crack 14 itself cannot be confirmed is presumably because the width of the crack 14 is smaller than the wavelength of the light I1, which is the illumination light. Figures 9 and 10 are SEM (Scanning Electron Microscope) images of the modified region 12 and the crack 14 formed inside the semiconductor substrate 21, which is a silicon substrate. Figure 9(b) is an enlarged image of the region A1 shown in Figure 9(a), Figure 10(a) is an enlarged image of the region A2 shown in Figure 9(b), and Figure 10(b) is an enlarged image of the region A3 shown in Figure 10(a). Thus, the width of the crack 14 is about 120 nm, which is smaller than the wavelength of the light I1 in the near-infrared region (e.g., 1.1 to 1.2 μm).

The imaging principle assumed based on the above is as follows. As shown in FIG. 11(a), when the focus F is located in air, the light I1 does not return, and a dark image is obtained (the image on the right side of FIG. 11(a)). As shown in FIG. 11(b), when the focus F is located inside the semiconductor substrate 21, the light I1 reflected by the back surface 21a returns, and a whitish image is obtained (the image on the right side of FIG. 11(b)). As shown in FIG. 11(c), when the focus F is aligned with the modified region 12 from the front surface 21b side, the modified region 12 absorbs, scatters, etc., a portion of the light I1 reflected by the back surface 21a and returned, and an image is obtained in which the modified region 12 appears dark against a whitish background (the image on the right side of FIG. 11(c)).

As shown in (a) and (b) of FIG. 12, when the focal point F is focused on the tip 14e of the crack 14 from the surface 21b side, for example, due to optical singularities (stress concentration, distortion, discontinuity in atomic density, etc.) occurring near the tip 14e, and light confinement occurring near the tip 14e, a part of the light I1 reflected by the back surface 21a and returned is scattered, reflected, interfered, absorbed, etc., and an image is obtained in which the tip 14e appears dark on a whitish background (the right image in (a) and (b) of FIG. 12). As shown in (c) of FIG. 12, when the focal point F is focused on a part of the crack 14 other than the vicinity of the tip 14e from the surface 21b side, at least a part of the light I1 reflected by the back surface 21a is returned, and a whitish image is obtained (the right image in (c) of FIG. 12).

[Configuration of actuator-equipped objective lens]
The objective lens 43 equipped with an actuator, which is included in the imaging unit 4, will be described below with reference to Fig. 13 and Fig. 14. Fig. 13 is a configuration diagram of the objective lens 43 equipped with an actuator 70.

As shown in FIG. 13, the imaging unit 4 further includes an actuator 70 in addition to the components shown in FIG. 5. The actuator 70 is provided (attached) to the objective lens 43 and moves the objective lens 43 in the Z direction, which is the up-down direction. The actuator 70 is configured to be movable in the Z direction, and moves the objective lens 43 in the Z direction by moving in the Z direction. The movable range required for the actuator 70 is determined, for example, according to the size of the imaging area. The movable range of the actuator 70 is set, for example, so that the tip of the crack 14 extending from the modified area 12 is imaged when the imaging unit 4 is fixed in a predetermined position by the drive unit 7 (details will be described later).

Now, as shown in FIG. 13, two modified regions 12a, 12b are formed inside the wafer 20, and a crack 14 extends from the two modified regions 12a, 12b to the front surface 21b side and the back surface 21a side of the wafer 20. In the example shown in FIG. 13, the crack 14 does not reach the front surface 21b and the back surface 21a of the wafer 20. In such a case, in order to properly image the tip of the crack 14 extending from the modified region 12, it is required that the tip of the crack 14 on the front surface 21b side extending from the modified region 12b on the front surface 21b side can be directly observed (the tip of the crack 14 on the front surface 21b side can be the focusing position), and that the back surface reflection can be observed by focusing on a point on the opposite side of the tip of the crack 14 on the front surface 21b side with respect to the back surface 21a (the point on the opposite side can be the focusing position). In this case, the movable range required for the actuator 70 is the "ACT movable range" shown in FIG. 13.

In addition, in the case where the modified region 12 is formed so that the crack 14 reaches at least the front surface 21b, such as when the modified region 12 is formed so that the crack 14 in the wafer 20 is in a full cut state in which the crack 14 reaches the front surface 21b and the back surface 21a, as shown in FIG. 14, in order to properly image the tip of the crack 14 extending from the modified region 12, it is required that the tip of the crack 14 on the front surface 21b side extending from the modified region 12d closest to the front surface 21b among the modified regions 12a, 12b, 12c, and 12d can be directly observed (the front surface 21b can be used as the focusing position), and that the back surface reflection can be observed by focusing on a point on the opposite side of the front surface 21b with respect to the back surface 21a (the point on the opposite side can be used as the focusing position). In this case, the movable range required for the actuator 70 is the "ACT movable range" shown in FIG. 14. For example, if the thickness of the wafer 20 made of a silicon substrate is 400 μm and the wafer 20 is in a fully cut state, the imaging range in the silicon is 400 μm + 400 μm = 800 μm (including the area on the opposite side of the back surface 21a from the front surface 21b). In this case, taking into account the difference in refractive index, it is preferable that the movable range of the actuator 70 in air is about 100 μm + 100 μm = 200 μm.

[Image capture control using drive units and actuators]
In the following, with reference to Figs. 15 to 18, imaging control by the imaging unit 4 using the drive unit 7 (see Fig. 1) and the actuator 70 will be described. In the laser processing device 1, the control unit 8 (see Fig. 1) controls the drive unit 7 and the actuator 70 to move the focusing position in the imaging unit 4, thereby imaging the inside of the wafer 20 with the imaging unit 4. In such imaging control, the drive unit 7 performs rough alignment of the focusing position related to imaging, and the actuator 70 performs detailed alignment of the focusing position related to imaging. The drive unit 7 is configured to support the entire imaging unit 4 and to move the entire imaging unit 4 in the Z direction. The actuator 70 is attached to the objective lens 43 of the imaging unit 4 and is configured to move the objective lens 43 in the Z direction.

Figure 15 is a diagram for explaining an overview of the movement of the focusing position using the drive unit 7 and the actuator 70. The control unit 8 is configured to execute a first control (see FIG. 15(a)) in which the drive unit 7 is controlled so that the imaging unit 4 moves to a position where the back surface 21a becomes the focusing position, and a second control (see FIG. 15(b)) in which the objective lens 43 moves to a position where at least a part of the first region 28, which is the region between the front surface 21b and the back surface 21a, becomes the focusing position after the first control, and controls the actuator 70 to move to a position where at least a part of the second region 29, which is the region on the opposite side of the back surface 21a from the front surface 21b, becomes the focusing position (see FIG. 5(1c)). Note that the back surface 21a becoming the focusing position may include the vicinity of the back surface 21a (for example, a region within a range of ±10 μm from the back surface 21a) becoming the focusing position.

Furthermore, before executing the first control, the control unit 8 executes a pre-control to control the actuator 70 so that the actuator 70 is fixed (center-fixed) at the center position of the movable range of the actuator 70 in the Z direction. The center position of the operating range may be near the center position of the movable range, and for example, when the movable range of the actuator 70 is 80 μm, it may be a position of 40 μm±10 μm.

In the first control, as shown in FIG. 15(a), in response to the control by the control unit 8, the drive unit 7 moves the entire imaging unit 4 so that the light collection position is on the back surface 21a. That is, the Z axis is dropped near the back surface 21a. As described above, the actuator 70 is fixed at the center in the Z direction. Since the first area 28 and the second area 29, which are the imaging areas, are located symmetrically with respect to the back surface 21a (that is, the back surface 21a is the center of the imaging area in the Z direction), the state in which the actuator 70 is fixed at the center and the light collection position is on the back surface 21a can be said to be a state in which the area in which imaging can be performed by the operation of the actuator 70 is maximized.

In the second control, as shown in FIG. 15(b), the actuator 70 first moves only the objective lens 43 in response to the control by the control unit 8 so that the focusing position is the first region 28. Next, as shown in FIG. 15(c), the actuator 70 moves only the objective lens 43 in response to the control by the control unit 8 so that the focusing position is the second region 29. The control unit 8 may move the objective lens 43 by the actuator 70 so that the entire region of the first region 28 and the entire region of the second region 29 in the Z direction are sequentially focused positions, or may move the objective lens 43 by the actuator 70 so that only a portion of the first region 28 and a portion of the second region 29 are sequentially focused positions. The control unit 8 may also move the objective lens 43 by the actuator 70 so that the second region 29 is first focused and then the first region 28 is focused. By executing the second control, imaging of the inside of the wafer 20 in the first region 28 and the second region 29 is performed.

16 is a diagram for explaining the details of the movement of the focusing position using the drive unit 7 and the actuator 70. As shown in FIG. 16(a), when the thickness of the wafer 20 is different from the expected thickness, it is considered that the focusing position after the first control described above may deviate from the back surface 21a. For this reason, in the second control after the first control, the control unit 8 first controls the actuator 70 so that the position of the objective lens 43 moves in the Z direction with the area near the back surface 21a being the focusing position, and executes a third control to control the actuator 70 so that the objective lens 43 moves to a reference position where the specified detailed position of the back surface 21a is the focusing position based on the light detection result by the light detection unit 44 in this state (see FIG. 16(b)). The area near the back surface 21a here may be an area including the entire range of the focusing position that may deviate from the back surface 21a after the first control.

In the third control, the actuator 70 moves only the objective lens 43 in response to the control by the control unit 8 so that the focusing position after the first control moves in the Z direction. In this way, the focusing position is continuously changed in the Z direction, thereby imaging the vicinity of the back surface 21a. The control unit 8 may detect a device pattern on the back surface 21a based on a signal from the light detection unit 44, which is the imaging result, and identify the detailed position of the back surface 21a based on the device pattern. Alternatively, the control unit 8 may identify the results of direct observation and back surface reflection observation of the cracks 14 from the modified region 12 in the vicinity of the back surface 21a based on the signal from the light detection unit 44, and identify the detailed position of the back surface 21a from the identified information. Then, in response to the control by the control unit 8, the actuator 70 moves the objective lens 43 to a reference position where the detailed position of the back surface 21a becomes the focusing position. By moving the objective lens 43 to the reference position in this way, the fourth control described later can be executed starting from the reference position where the focusing position is appropriately set to the back surface 21a.

The control unit 8 is configured to execute a second control in which the actuator 70 is controlled so that the objective lens 43 moves from the reference position described above to a position where at least a part of the first region 28 is at the focusing position (see FIG. 16(d)), and a fourth control in which the actuator 70 is controlled so that the objective lens 43 moves from the reference position to a position where at least a part of the second region 29 is at the focusing position (see FIG. 16(c)). The control unit 8 may move the objective lens 43 by the actuator 70 so that the entire first region 28 and the entire second region 29 in the Z direction are sequentially at the focusing position, or may move the objective lens 43 by the actuator 70 so that only a part of the first region 28 and a part of the second region 29 are sequentially at the focusing position.

In this manner, in the aspect shown in FIG. 16, the objective lens 43 is moved to the reference position, which is the starting position for imaging, by the first control and the third control, and then an imaging process is performed by the fourth control to image the inside of the wafer 20, and information related to the modified region 12 is derived (e.g., detection of the tip position of the crack 14).

Figure 17 is a flowchart of an example of an observation method performed by the laser processing device 1. Below, an example of the observation method is described with reference to Figures 17 and 16.

As shown in FIG. 17, first, the control unit 8 controls the actuator 70 so that the actuator 70 is fixed at the center position of the movable range of the actuator 70 in the Z direction (step S1: preliminary step). Note that such center fixing of the actuator 70 may be performed manually.

Next, the control unit 8 controls the drive unit 7 so that the imaging unit 4 moves to a position where the back surface 21a becomes the light collecting position, as shown in FIG. 16(a) (step S2: first step).

Then, the control unit 8 controls the actuator 70 so that the position of the objective lens 43 moves in the Z direction with the area near the back surface 21a being the focusing position, and the detailed position of the back surface 21a is identified based on the detection result of the light detection unit 44 in this state, and the actuator 70 is controlled so that the objective lens 43 moves to a reference position where the identified detailed position of the back surface 21a is the focusing position, as shown in FIG. 16(b). That is, the focusing position is corrected based on the detection result (step S3: second process).

Next, the control unit 8 controls the actuator 70 so that the objective lens 43 moves to a position where the second region 29, which is the region on the back surface observation side, becomes the focusing position, as shown in FIG. 16(c) (step S4: second process). Then, the control unit 8 controls the actuator 70 so that the objective lens 43 moves to a position where the first region 28, which is the region on the front surface observation side, becomes the focusing position, as shown in FIG. 16(d) (step S5: second process). This is one example of the observation method.

The observation method performed by the laser processing apparatus 1 is not limited to the aspects shown in FIG. 16 and FIG. 17. FIG. 18 is a diagram for explaining the details of another example of the movement of the focusing position using the drive unit 7 and the actuator 70. In the aspect shown in FIG. 18, the above-mentioned first control is executed (see FIG. 18(a)), and the above-mentioned third control is executed in the second control after the first control (see FIG. 18(b)). In other words, the control shown in FIG. 18(a) corresponds to the control shown in FIG. 16(a), and the control shown in FIG. 18(b) corresponds to the control shown in FIG. 16(b). Here, in the aspect shown in FIG. 16, in the third control (see FIG. 16(b)) that determines the reference position, the imaging result near the back surface 21a is obtained, but the imaging result is used only to determine the reference position, and is not used as information related to the derivation of information related to the modified region 12 of the wafer 20. In this regard, in the embodiment shown in FIG. 18, the imaging results obtained in the vicinity of the back surface 21a in the third control (see FIG. 18(b)) are used not only as information related to deriving the reference position, but also as information related to deriving information related to the modified region 12 of the wafer 20. In this way, by effectively utilizing the imaging results in the third control, it is possible to avoid performing duplicate imaging processes on the same region, and imaging can be performed more efficiently.

Now, suppose that an imaging result of the area A1 (see FIG. 18(c)) near the back surface 21a has been obtained in the third control (see FIG. 18(b)) for determining the reference position. In this case, the control unit 8 executes the fifth control to control the drive unit 7 so that the entire imaging unit 4 moves to a position where at least a part of the unimaged area, which is an area in the first area 28 or the second area 29 that was not set as the light-collecting position when the detailed position of the back surface 21a was specified in the third control, i.e., an area other than the above-mentioned area A1, becomes the light-collecting position. In the example shown in FIG. 18, the unimaged area of the second area 29 is assumed to be an area that does not require imaging. In this case, the control unit 8 controls the drive unit 7 so that the entire imaging unit 4 moves (is pushed up) to a position where the area A2, which is the unimaged area of the first area 28, becomes the light-collecting position. More specifically, the control unit 8 controls the drive unit 7 so that the entire imaging unit 4 moves to a position where the area A2 becomes the light-collecting position by the sixth control described later, which moves the objective lens 43 by the actuator 70, taking into account the movable range of the actuator 70.

Then, the control unit 8 executes a sixth control in which the actuator 70 is controlled to move the objective lens 43 to a position where the area A2, which is included in the unimaged area, becomes the focusing position, with the position of the objective lens 43 of the imaging unit 4 after the fifth control being set as a new reference position. The control unit 8 may move the objective lens 43 by the actuator 70 so that the entire area of the area A2 in the Z direction becomes the focusing position sequentially, or may move the objective lens 43 by the actuator 70 so that only a portion of the area A2 becomes the focusing position sequentially.

In this manner, in the aspect shown in FIG. 18, the imaging results acquired during the third control are used not only as information related to deriving the reference position but also as information related to deriving information related to the modified region 12 of the wafer 20, and imaging can be efficiently performed by performing the fifth control and the sixth control so as to image only the regions for which imaging results could not be acquired in the third control. Furthermore, even if the entire desired imaging region does not fit within the movable range of the actuator 70, for example, the fifth control and the sixth control can be performed (performed multiple times as necessary) to sequentially expand the imaging region and image the entire desired imaging region.

[Action and Effect]
Next, the effects of the laser processing apparatus 1 (observation apparatus) and the observation method according to this embodiment will be described.

The laser processing device 1 according to this embodiment is an observation device for observing a wafer 20 having a front surface 21b and a back surface 21a, in which a modified region 12 is formed by irradiating laser light from the front surface 21b side, and includes an imaging unit 4 having a light source 41 that outputs light that is transparent to the wafer 20, an objective lens 43 that focuses the light output from the light source 41 at a focusing position on the wafer 20, and a light detection unit 44 that detects the light that has propagated through the wafer 20, a drive unit 7 that supports the imaging unit 4 and moves the imaging unit 4 in the Z direction, which is the up-down direction, and a drive unit 8 that is provided on the objective lens 43 and moves the objective lens 43 in the Z direction. The control unit 8 is configured to execute a first control for controlling the drive unit 7 so that the imaging unit 4 moves to a position where the back surface 21a becomes the focusing position, and a second control for controlling the actuator 70 so that after the first control, the objective lens 43 moves to a position where at least a part of the first region 28, which is the region between the back surface 21a and the front surface 21b, becomes the focusing position, and to control the actuator 70 so that the objective lens 43 moves to a position where at least a part of the second region 29, which is the region on the opposite side of the back surface 21a from the front surface 21b, becomes the focusing position.

In such a laser processing device 1, in observing the wafer 20 on which the modified region 12 is formed, the drive unit 7 that moves the imaging unit 4 in the Z direction is controlled so that the imaging unit 4 moves to a position where the back surface 21a of the wafer 20 becomes the focusing position, and then the objective lens 43 moves to a position where the first region 28, which is the region between the back surface 21a and the front surface 21b, becomes the focusing position, and the actuator 70 that moves the objective lens 43 in the Z direction is controlled so that the objective lens 43 moves to a position where the second region 29, which is the region on the opposite side of the back surface 21a from the front surface 21b, becomes the focusing position. In this way, by moving the objective lens 43 so that both the first region 28 and the second region 29 become focusing positions, both direct observation of the cracks 14, etc. from the modified region 12 when the first region 28 is the focusing position, and observation using the back reflection of the cracks 14, etc. when the second region 29 is the focusing position can be appropriately performed. The movement of the objective lens 43, which focuses the first region 28 and the second region 29, is performed by the actuator 70 that moves only the objective lens 43 of the imaging unit 4, so that the focus position can be moved at high speed and vibration after the movement can be suppressed, compared to the case where the entire imaging unit 4 is moved. Here, the laser processing device 1 according to the present embodiment has a drive unit 7 that moves the entire imaging unit 4 in the Z direction and an actuator 70 that moves the objective lens 43 of the imaging unit 4 in the Z direction. By providing both the drive unit 7 and the actuator 70 in this way, it is possible to perform rough alignment by the drive unit 7 and detailed alignment by the actuator 70, for example, and it is possible to perform alignment (focus alignment in the imaging range, etc.) that requires precision with high accuracy while suppressing the device cost compared to the case where all the movement in the Z direction is performed by an actuator capable of detailed alignment. In the laser processing device 1 according to this embodiment, first, the imaging unit 4 is controlled by the drive unit 7 so that the rear surface 21a, which is the boundary surface between the first region 28 and the second region 29, becomes the focusing position, and then the objective lens 43 is controlled by the actuator 70 so that the first region 28 and the second region 29 become the focusing positions. By aligning the focusing position with the rear surface 21a (the boundary surface between the first region 28 and the second region 29) before the control by the actuator 70 is started, the movable range of the actuator 70 can be fully utilized to appropriately perform high-speed movement of the objective lens 43 with the first region 28 and the second region 29 as the focusing positions. As described above, according to the laser processing device 1 according to this embodiment, the focusing position can be moved at high speed, and the tact time can be improved.

Before the first control, the control unit 8 may further execute a pre-control to control the actuator 70 so that the actuator 70 is fixed at the center position of the movable range of the actuator 70 in the Z direction. This allows the second control to be executed in a state where the actuator 70 can be fully movable in both directions (up and down) in the Z direction, and the movable range of the actuator 70 can be fully utilized to appropriately perform high-speed movement of the objective lens 43 with the first region 28 and the second region 29 as focusing positions.

The control unit 8 may be configured to execute a third control in which the actuator 70 is controlled so that the position of the objective lens 43 moves in the Z direction in a state where the area near the back surface 21a is the light-focusing position, the detailed position of the back surface 21a is identified based on the light detection result by the light detection unit 44 in this state, and the actuator 70 is controlled so that the objective lens 43 moves to a reference position where the identified detailed position of the back surface 21a is the light-focusing position, and a fourth control in which the actuator 70 is controlled so that the objective lens 43 moves from the reference position to a position where at least a part of the first area 28 is the light-focusing position, and the actuator 70 is controlled so that the objective lens 43 moves from the reference position to a position where at least a part of the second area 29 is the light-focusing position. Even with the first control, for example, if the thickness of the actual wafer 20 is different from the expected one, it is possible that the light-focusing position will deviate from the back surface 21a. In this case, there is a risk that imaging of the first area 28 and the second area 29 cannot be realized by making the most of the movable range of the actuator 70 described above. In this regard, in the second control, the exact position of the back surface 21a is identified based on the light detection results and is set as the reference position (third control), and the objective lens 43 is moved from the reference position to the imaging range of the first area 28 and the second area 29 by the actuator 70 (fourth control). Even if the light collection position is shifted from the back surface 21a in the first control, the reference position can be appropriately set to realize imaging of the first area 28 and the second area 29 by making the most of the movable range of the actuator 70.

The control unit 8 is configured to execute a third control in which the actuator 70 is controlled so that the position of the objective lens 43 moves in the Z direction in a state where the area near the back surface 21a becomes the light-focusing position, and the actuator 70 is controlled to specify the detailed position of the back surface 21a based on the light detection result by the light detection unit 44 in this state, and the actuator 70 is controlled so that the objective lens 43 moves to a reference position where the specified detailed position of the back surface 21a becomes the light-focusing position. The control unit 8 may further execute a fifth control in which the drive unit 7 is controlled so that the imaging unit 4 moves to a position where at least a part of the unimaged area, which is an area in the first area 28 or the second area 29 and is not set as the light-focusing position when specifying the detailed position of the back surface 21a in the third control, becomes the light-focusing position, and a sixth control in which the actuator 70 is controlled so that the objective lens 43 moves to a position where the area included in the unimaged area becomes the light-focusing position, with the position of the objective lens 43 of the imaging unit 4 after the fifth control being set as a new reference position. According to the third control, imaging of the area near the back surface 21a can be performed in the process of specifying the detailed position of the back surface 21a. Therefore, in this observation device, the drive unit 7 is controlled so that the imaging unit 4 moves to a position where the unimaged region becomes the focusing position in the third control (fifth control), and the position of the objective lens 43 after the fifth control is set as a new reference position, and the actuator 70 is controlled so that the objective lens 43 moves to a position where the unimaged region becomes the focusing position (sixth control). With this configuration, the region that has not been imaged in the third control is controlled to become the focusing position, so that imaging can be performed more efficiently without performing unnecessary imaging. Also, with this configuration, even if the region to be imaged does not fit within the movable range of the actuator 70 at the initial reference position, the region to be imaged can be reliably imaged by changing the reference position.

The observation method according to this embodiment is an observation method for observing a wafer 20 having a front surface 21b and a back surface 21a, in which a modified region 12 is formed inside by irradiating laser light from the front surface 21b side, and includes a first step of moving the imaging unit 4 to a position where the back surface 21a is a focusing position by a drive unit 7 that moves the imaging unit 4 in the Z direction, which is the vertical direction, and a second step of moving the objective lens 43 included in the imaging unit 4 in the Z direction to a position where at least a part of the first region 28, which is the region between the back surface 21a and the front surface 21b, is a focusing position by an actuator 70 that moves the objective lens 43 included in the imaging unit 4 in the Z direction, and moving the objective lens 43 to a position where at least a part of the second region 29, which is the region on the opposite side of the back surface 21a from the front surface 21b, is a focusing position. According to the observation method according to this embodiment, the focusing position can be moved at high speed, thereby improving the tact time.

The observation method may further include a preliminary step of controlling the actuator 70 before the first step so that the actuator 70 is fixed at the center position of the movable range of the actuator 70 in the Z direction. With this configuration, the movable range of the actuator 70 can be fully utilized to appropriately perform high-speed movement of the objective lens 43 with the first region 28 and the second region 29 as focusing positions.

1...laser processing device (observation device), 4...imaging unit (imaging section), 7...driving unit, 8...control section, 12...modified region, 20...wafer, 21a...rear surface (second surface), 21b...front surface (first surface), 28...first region, 29...second region, 41...light source, 43...objective lens (collecting lens), 44...light detection section, 70...actuator.

Claims (6)

1. An observation apparatus for observing a wafer having a first surface and a second surface, the wafer having a modified region formed therein by irradiating the wafer with laser light from the first surface side, the observation apparatus comprising:
an imaging unit including a light source that outputs light that is transparent to the wafer, a condenser lens that condenses the light output from the light source at a condensing position on the wafer, and a light detection unit that detects the light that has propagated through the wafer;
a drive unit that supports the imaging unit and moves the imaging unit in a Z direction that is a vertical direction;
an actuator provided on the condenser lens and configured to move the condenser lens in the Z direction;
A control unit,
The control unit is
a first control for controlling the drive unit so that the imaging unit moves to a position where the second surface is at the light collecting position;
the observation device is configured to execute a second control, which controls the actuator so that, after the first control, the focusing lens moves to a position where at least a portion of a first region, which is a region between the second surface and the first surface, becomes the focusing position, and which controls the actuator so that the focusing lens moves to a position where at least a portion of a second region, which is a region on the opposite side of the second surface from the first surface, becomes the focusing position. The observation device according to claim 1, wherein the control unit further performs a pre-control to control the actuator so that the actuator is fixed at a center position of the movable range of the actuator in the Z direction before the first control. The control unit is
In the second control,
a third control for controlling the actuator so that a position of the condensing lens is moved in the Z direction with a region near the second surface being the condensing position, identifying a detailed position of the second surface based on a detection result of the light by the light detection unit in this state, and controlling the actuator so that the condensing lens is moved to a reference position where the identified detailed position of the second surface is the condensing position;
3. The observation device according to claim 1, wherein the actuator is controlled so that the condensing lens moves from the reference position to a position where at least a portion of the first region becomes the condensing position, and a fourth control is controlled so that the actuator is controlled so that the condensing lens moves from the reference position to a position where at least a portion of the second region becomes the condensing position. The control unit is
In the second control,
a third control is configured to execute a third control of controlling the actuator so that a position of the condensing lens moves in the Z direction in a state where an area near the second surface becomes the condensing position, identifying a detailed position of the second surface based on a light detection result by the light detection unit in this state, and controlling the actuator so that the condensing lens moves to a reference position which is a position of the condensing lens where the identified detailed position of the second surface becomes the condensing position,
a fifth control for controlling the drive unit so that the imaging unit moves to a position where at least a part of an unimaged region, which is a region within the first region or the second region and which was not set as the light-collecting position when a detailed position of the second surface was specified in the third control, becomes the light-collecting position;
and a sixth control for controlling the actuator so that the condenser lens moves to a position where an area included in the unimaged area becomes the condensing position, using a position of the condenser lens of the imaging unit after the fifth control as a new reference position. 1. A method for observing a wafer having a first surface and a second surface, the method comprising:
a first step of moving the imaging unit to a position where the second surface is a light collecting position by a drive unit that moves the imaging unit in a Z direction that is a vertical direction;
a second step of moving the focusing lens by an actuator that moves a focusing lens included in the imaging unit in the Z direction to a position where at least a portion of a first region, which is a region between the second surface and the first surface, is at the focusing position, and moving the focusing lens to a position where at least a portion of a second region, which is a region on the opposite side of the second surface from the first surface, is at the focusing position. The observation method according to claim 5, further comprising a preliminary step of controlling the actuator so that the actuator is fixed at a center position of the movable range of the actuator in the Z direction before the first step.

Images