JP7724138B2 - Laser processing device and laser processing method - Google Patents

Description

This disclosure relates to a laser processing device and a laser processing method.

Patent Document 1 describes a laser processing device that includes a holding mechanism that holds a workpiece and a laser irradiation mechanism that irradiates the workpiece held by the holding mechanism with laser light. In the laser processing device described in Patent Document 1, the laser irradiation mechanism having a focusing lens is fixed to a base, and the holding mechanism moves the workpiece in a direction perpendicular to the optical axis of the focusing lens.

Patent No. 5456510

For example, in the manufacturing process of semiconductor devices, trimming is sometimes performed to remove unnecessary portions from the outer edge of a semiconductor wafer. That is, to remove the outer edge of an object, the focused area of the laser light is moved relatively along a line that extends in an annular shape inside the outer edge of the object, thereby forming a modified area along the line. In particular, there is currently a demand for performing the above-mentioned trimming process on bonded wafers, which are formed by bonding a semiconductor wafer to another member (e.g., another wafer) via the device layer of the semiconductor wafer.

Here, in bonded wafers, stress may occur inside the semiconductor wafer. This stress may occur, for example, when warped semiconductor wafers or separate components are bonded together, or when the device layer is peeled away from the separate component at the periphery of the device layer. If such stress occurs inside the semiconductor wafer, when a modified region for trimming is formed in the semiconductor wafer, the stress may cause cracks extending from the modified region toward the device layer (separate component) to propagate in unintended directions. Such crack propagation in unintended directions can cause a decrease in the quality of the trimming process.

The present disclosure therefore aims to provide a laser processing device and a laser processing method that can suppress deterioration in the quality of trimming processing of bonded wafers.

The laser processing apparatus according to the present disclosure is a laser processing apparatus for forming a modified region on a wafer that includes a first surface and a second surface opposite the first surface, by irradiating a wafer bonded to a separate member on the first surface side with laser light using the second surface as an incident surface. The laser processing apparatus includes a support unit for supporting the wafer, an irradiation unit for irradiating the laser light toward the wafer supported on the support unit, a movement unit for moving the focused region of the laser light relative to the wafer, and a control unit for controlling the irradiation unit and the movement unit. The first surface has a device layer formed thereon that includes a plurality of chips and is bonded to a separate member. The device layer has an active area including the plurality of chips, and a surface area of the active area that is defined by a Z direction intersecting the first surface. The control unit controls the irradiation unit and the movement unit to irradiate the wafer with laser light while relatively moving the focusing area of the laser light along a first line that extends annularly on the preprocessing area when viewed in the Z direction, thereby forming a first modified region as a modified region along the first line, and performing a first processing process to form a first crack that extends obliquely from the outside of the boundary between the preprocessing area and the bonding area toward the boundary as it moves from the second surface toward the first surface.

The laser processing method according to the present disclosure includes a laser processing step for forming a modified region in a wafer that includes a first surface and a second surface opposite the first surface, the wafer being bonded to a separate member on the first surface side by irradiating the wafer with laser light using the second surface as an incident surface, the first surface having a device layer formed thereon that includes a plurality of chips and is bonded to a separate member, the device layer including an active area including the plurality of chips and a peripheral portion located outside the active area so as to surround the active area when viewed in a Z direction intersecting the first surface, the peripheral portion being the outer edge of the device layer. The laser processing step includes a first processing step in which a laser beam is irradiated onto the wafer while relatively moving the focusing area of the laser beam along a first line that extends circularly on the preprocessing area when viewed in the Z direction, thereby forming a first modified region as a modified region along the first line, and forming a first crack that extends obliquely from the outside of the boundary between the preprocessing area and the bonding area toward the boundary from the second surface toward the first surface from the first modified region.

This device and method perform laser processing by irradiating a wafer bonded to another member via a device layer with laser light. The device layer includes an active area containing multiple chips and a peripheral portion located outside the active area and surrounding the active area. In laser processing, laser light is irradiated onto the wafer along a first line extending annularly on this peripheral portion, thereby forming a first modified region along the first line. This makes it possible to use the first modified region and the first crack extending from the first modified region to perform trimming, removing unnecessary portions from the outer edge of the wafer.

In particular, this apparatus and method forms a preprocessing region around the peripheral edge of the device layer, weakening the bond with the separate component. When a preprocessing region is formed in this manner, there is a risk of stress being generated inside the wafer, as described above. The stress inside the wafer caused by the formation of the preprocessing region can be alleviated by forming a modified region on the preprocessing region. Therefore, this apparatus and method forms a first modified region by irradiating a laser beam at a position above the preprocessing region, thereby alleviating the stress inside the wafer caused by the formation of the preprocessing region and allowing the first crack to extend obliquely from the first modified region in the intended direction. Therefore, this apparatus and method can prevent a decrease in the quality of the trimming process for bonded wafers.

In the laser processing apparatus according to the present disclosure, in the first processing step, the control unit may perform a first oblique processing step in which the position of the light collection area is set to a first Y position in the Y direction from the center of the wafer toward the outer edge and a first Z position in the Z direction, and laser light is applied to the first oblique processing step to form a first Z modified area as the first modified area; and after the first oblique processing step, the control unit may perform a second oblique processing step in which the position of the light collection area is set to a second Y position closer to the outer edge of the wafer than the first Y position in the Y direction and a second Z position closer to the second surface than the first Z position in the Z direction, and laser light is applied to the second Z position, and laser light is applied to the second Z position closer to the second surface than the first Z position in the Z direction, and a second Z modified area as the first modified area is formed closer to the second surface and toward the outer edge of the wafer as the first modified area, and the first crack extends obliquely from the first Z modified area toward the boundary. In this way, by sequentially forming at least two modified areas arranged diagonally, it is possible to more effectively form an oblique crack.

In the laser processing apparatus according to the present disclosure, in the first processing process, the control unit may perform a vertical processing process after the second oblique processing process, in which the control unit positions the focusing region at multiple Z-direction positions closer to the second surface than the second Z-position at the second Y-position and irradiates the laser light to form multiple first modified regions arranged along the Z-direction at the second Y-position, and extends cracks vertically across the multiple first modified regions. In this case, the first oblique processing process and the second oblique processing process are performed at Z-positions farther (deeper) from the second surface, which is the incident surface of the laser light, and then the vertical processing process is performed at a shallower position. Therefore, in either process, it is possible to form new modified regions without being affected by modified regions that have already been formed.

In the laser processing apparatus according to the present disclosure, in the first processing process, the control unit may perform a vertical processing process in which, prior to the first oblique processing process, the control unit positions the focusing region at multiple Z-direction positions closer to the second surface than the second Z-position at the second Y-position and irradiates the laser light, thereby forming multiple first modified regions arranged along the Z-direction at the second Y-position, and extending a crack vertically across the multiple first modified regions. In this case, with stress inside the wafer alleviated by the first modified regions formed in the vertical processing process, it is possible to form a first crack extending obliquely in the first oblique processing process and the second oblique processing process.

In the laser processing apparatus according to the present disclosure, the control unit may, after the first processing step, control the irradiation unit and the movement unit to irradiate the wafer with laser light while relatively moving the focusing region along a second line extending from the outer edge of the wafer to the first line on the peripheral portion as viewed in the Z direction, thereby performing a second processing step to form a second modified region as a modified region along the second line. In this case, the wafer is irradiated with laser light along the second line extending from the outer edge of the wafer to the first line on the peripheral portion of the device layer, and the second modified region is formed along the second line. This makes it possible to easily divide the outer edge portion of the wafer into multiple parts in the circumferential direction by utilizing the second modified region and cracks extending from the second modified region. Particularly in this case, the second processing step is performed after the first processing step. As a result, the extension of cracks extending from the second modified region can be prevented by the first modified region already formed along the first line and the cracks extending from the first modified region. This prevents a decrease in processing quality.

In the laser processing apparatus according to the present disclosure, the control unit may control the irradiation unit and movement unit before the first processing step to irradiate the wafer with laser light while moving the focusing region relative to the first unit along a second line extending from the outer edge of the wafer to the first line on the peripheral portion as viewed in the Z direction, thereby performing a second processing step to form a second modified region as a modified region along the second line. In this case, as in the above case, the second modified region and cracks extending from the second modified region can be used to easily divide the outer edge portion of the wafer into multiple parts in the circumferential direction for trimming. Particularly in this case, the second processing step is performed before the first processing step. Therefore, the second modified region formed in the second processing step further relaxes stress within the wafer, making it possible to form a first crack extending diagonally in the first processing step.

In the laser processing apparatus according to the present disclosure, the control unit may perform a third processing process before the first processing process, in which a third modified region is formed as a modified region by irradiating the wafer with laser light while positioning a focusing region at a position different from the first and second lines on the peripheral edge when viewed from the Z direction. In this case, the third modified region formed in the third processing process makes it possible to form a first crack extending diagonally in the first processing process while further alleviating stress within the wafer.

The laser processing apparatus according to the present disclosure is a laser processing apparatus for forming a modified region on a wafer that includes a first surface and a second surface opposite the first surface, by irradiating the wafer with laser light using the second surface as an incident surface on the wafer that is bonded to a separate member on the first surface side. The laser processing apparatus includes a support unit for supporting the wafer, an irradiation unit for irradiating the laser light toward the wafer supported on the support unit, a movement unit for moving the focused region of the laser light relative to the wafer, and a control unit for controlling the irradiation unit and the movement unit. The first surface has a device layer formed thereon that includes a plurality of chips and is bonded to a separate member. The device layer has an active area that includes the plurality of chips, and a substrate surrounding the active area when viewed from a Z direction that intersects with the first surface. The control unit controls the irradiation unit and movement unit to irradiate the wafer with laser light while relatively moving the focusing region of the laser light along a first line that extends annularly on the peripheral portion as viewed in the Z direction, thereby performing a first processing process to form a first modified region as a modified region along the first line and form a first crack from the first modified region to the first surface; and a stress relaxation process to form a modified region to relieve stress generated inside the wafer by positioning the focusing region at a position on the peripheral portion as viewed in the Z direction and irradiating the wafer with laser light. The control unit performs the stress relaxation process before extending the first crack to the first surface.

This equipment performs laser processing by irradiating a wafer bonded to another member via a device layer with laser light. The device layer includes an active area containing multiple chips and a peripheral portion located outside the active area and surrounding the active area. During laser processing, laser light is irradiated onto the wafer along a first line extending annularly on this peripheral portion, thereby forming a first modified region along the first line. This makes it possible to use the first modified region and the first crack extending from the first modified region to perform trimming, removing unnecessary portions from the outer edge of the wafer.

In particular, this device forms a modified region to relieve stress within the wafer before the first crack extending from the first modified region is propagated to the first surface. This prevents the first crack from propagating in an unintended direction due to stress within the wafer. Therefore, this device can prevent a decrease in the quality of the bonded wafer trimming process.

This disclosure provides a laser processing device and a laser processing method that can suppress deterioration in the quality of trimming of bonded wafers.

FIG. 1 is a schematic diagram showing the configuration of a laser processing apparatus according to one embodiment. FIG. 2 is a schematic diagram showing the configuration of the irradiation unit shown in FIG. FIG. 3 is a diagram showing the 4f lens unit shown in FIG. FIG. 4 is a diagram showing the spatial light modulator shown in FIG. FIG. 5 is a cross-sectional view of an object for explaining the knowledge of oblique crack formation. FIG. 6 is a cross-sectional view of an object for explaining the knowledge of oblique crack formation. FIG. 7 is a diagram showing the beam shape of the focused region of the laser light. FIG. 8 is a diagram showing the offset of the modulation pattern. FIG. 9 is a cross-sectional photograph showing the state of formation of the diagonal crack. FIG. 10 is a diagram showing an example of a modulation pattern. FIG. 11 is a diagram showing the intensity distribution on the entrance pupil plane of the condenser lens and the beam shape in the condensed region. FIG. 12 is a diagram showing the beam shape in the focused area and the observed intensity distribution in the focused area. FIG. 13 is a diagram showing an example of a modulation pattern. FIG. 14 is a diagram showing another example of an asymmetric modulation pattern. FIG. 15 is a diagram showing the intensity distribution on the entrance pupil plane of the condenser lens and the beam shape in the condensed region. FIG. 16 is a diagram showing an example of a modulation pattern and the formation of a light-collecting region. FIG. 17 is a cross-sectional view showing an object to be processed according to this embodiment. 18A and 18B are diagrams showing an object to be processed according to this embodiment, in which (a) is a plan view and (b) is a cross-sectional view. 19A and 19B are diagrams showing one step of the laser processing method according to this embodiment, in which (a) is a plan view and (b) is a cross-sectional view. 20A and 20B are diagrams showing one step of the laser processing method according to this embodiment, in which (a) is a plan view and (b) is a cross-sectional view. 21A and 21B are diagrams showing one step of the laser processing method according to this embodiment, in which (a) is a plan view and (b) is a cross-sectional view. FIG. 22 is a cross-sectional view showing one step of the first processing step. FIG. 23 is a cross-sectional view showing one step of the first processing step. FIG. 24 is a cross-sectional view showing one step of the first processing step. FIG. 25 is a cross-sectional view showing one step of the first processing step. 26A and 26B are diagrams showing one step of the laser processing method according to this embodiment, in which (a) is a plan view and (b) is a cross-sectional view. FIG. 27 is a cross-sectional view for explaining a modified example. FIG. 28 is a plan view for explaining a modified example. FIG. 27 is a cross-sectional view for explaining a modified example. FIG. 30 is a plan view showing an example of the first wafer. 31A and 31B are views showing an object to be processed according to this embodiment, in which (a) is a plan view and (b) is a cross-sectional view. 32A and 32B are diagrams showing one step of the laser processing method according to this embodiment, in which (a) is a plan view and (b) is a cross-sectional view. FIG. 33 is a cross-sectional view showing one step of the laser processing method according to this embodiment. FIG. 34 is a cross-sectional view showing one step of the laser processing method according to this embodiment. FIG. 35 is a cross-sectional view showing one step of the laser processing method according to this embodiment. FIG. 33 is a cross-sectional view showing one step of the laser processing method according to this embodiment.

An embodiment will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and redundant explanations may be omitted. Each drawing may also show a Cartesian coordinate system defined by an X-axis, a Y-axis, and a Z-axis.
[Outline of laser processing device and laser processing]

Figure 1 is a schematic diagram showing the configuration of a laser processing device according to one embodiment. As shown in Figure 1, the laser processing device 1 includes a stage (support unit) 2, an irradiation unit 3, movement units 4 and 5, and a control unit 6. The laser processing device 1 is a device for forming 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 holding a film attached to the object 11. The stage 2 is rotatable around an axis parallel to the Z direction. The stage 2 may also be movable along both the X and Y directions. The X and Y directions are first and second horizontal directions that intersect (are perpendicular to) each other, and the Z direction is the vertical direction.

The 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 focused region C of the laser light L (e.g., the center Ca described below), forming a modified region 12 inside the object 11. The focused region C, which will be described in detail later, is the position where the beam intensity of the laser light L is highest or an area within a predetermined range from the center of gravity of the beam intensity.

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 regions 12 include melt-processed regions, crack regions, dielectric breakdown regions, and refractive index change regions. The modified region 12 can be formed so that cracks extend from the modified region 12 to the incident side of the laser light L and to the opposite side. Such modified regions 12 and cracks are used, for example, to cut the object 11.

As an example, when the stage 2 is moved along the X direction and the focusing region 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 movement speed of the focusing region C with respect to the object 11 and the repetition frequency of the laser light L.

The moving unit 4 includes a first moving unit 41 that moves the stage 2 in one direction within a plane intersecting (orthogonal to) the Z direction, and a second moving unit 42 that moves the stage 2 in another direction within the plane intersecting (orthogonal to) the Z direction. As an example, the first moving unit 41 moves the stage 2 along the X direction, and the second moving unit 42 moves the stage 2 along the Y direction. The moving unit 4 also rotates the stage 2 around an axis parallel to the Z direction. The moving unit 5 supports the irradiation unit 3. The moving unit 5 moves the irradiation unit 3 along the X, Y, and Z directions. By moving the stage 2 and/or the irradiation unit 3 while the focusing region C of the laser light L is formed, the focusing region C moves relative to the object 11. That is, the moving units 4 and 5 move at least one of the stage 2 and the irradiation unit 3 to move the focusing region C of the laser light L relative to the object 11.

The control unit 6 controls the operation of the stage 2, irradiation unit 3, and movement units 4 and 5. The control unit 6 has a processing unit, a memory unit, and an input reception unit (not shown). The processing unit is configured as a computer device including a processor, memory, storage, communication devices, etc. In the processing unit, the processor executes software (programs) loaded into memory, etc., and controls the reading and writing of data in the memory and storage, as well as communication via communication devices. The memory unit is, for example, a hard disk, and stores various types of data. The input reception unit is an interface unit that displays various types of information and receives input of various types of information from the user. The input reception unit constitutes a GUI (Graphical User Interface).

Figure 2 is a schematic diagram showing the configuration of the irradiation unit shown in Figure 1. Figure 2 shows an imaginary line A indicating the planned laser processing area. As shown in Figure 2, the irradiation unit 3 has a light source 31, a spatial light modulator (shaping unit) 7, a condensing lens 33, and a 4f lens unit 34. The light source 31 outputs laser light L, for example, using a pulse oscillation method. Note that the irradiation unit 3 may not have the light source 31 and may instead be configured to introduce laser light L from outside the irradiation unit 3. The spatial light modulator 7 modulates the laser light L output from the light source 31. The condensing lens 33 condenses the laser light L modulated by the spatial light modulator 7 and output from the spatial light modulator 7 toward the target object 11.

As shown in Figure 3, the 4f lens unit 34 has a pair of lenses 34A, 34B arranged on the optical path of the laser light L traveling from the spatial light modulator 7 to the condenser lens 33. The pair of lenses 34A, 34B form a double-telecentric optical system in which the modulation surface 7a of the spatial light modulator 7 and the entrance pupil plane (pupil plane) 33a of the condenser lens 33 are in an imaging relationship. As a result, the image of the laser light L on the modulation surface 7a of the spatial light modulator 7 (the image of the laser light L modulated by the spatial light modulator 7) is transferred (imaged) onto the entrance pupil plane 33a of the condenser lens 33. Note that Fs in the figure indicates the Fourier plane.

As shown in Figure 4, the spatial light modulator 7 is a reflective liquid crystal (LCOS: Liquid Crystal on Silicon) spatial light modulator (SLM). The spatial light modulator 7 is constructed by stacking a drive circuit layer 72, a pixel electrode layer 73, a reflective film 74, an alignment film 75, a liquid crystal layer 76, an alignment film 77, a transparent conductive film 78, and a transparent substrate 79 in this order on a semiconductor substrate 71.

The semiconductor substrate 71 is, for example, a silicon substrate. The drive circuit layer 72 forms an active matrix circuit on the semiconductor substrate 71. The pixel electrode layer 73 includes a plurality of pixel electrodes 73a arranged in a matrix along the surface of the semiconductor substrate 71. Each pixel electrode 73a is formed from a metal material such as aluminum. A voltage is applied to each pixel electrode 73a by the drive circuit layer 72.

The reflective film 74 is, for example, a dielectric multilayer film. The alignment film 75 is provided on the surface of the liquid crystal layer 76 facing the reflective film 74, and the alignment film 77 is provided on the surface of the liquid crystal layer 76 opposite the reflective film 74. Each alignment film 75, 77 is formed from, for example, a polymer material such as polyimide, and the contact surfaces of each alignment film 75, 77 with the liquid crystal layer 76 are subjected to, for example, a rubbing treatment. The alignment films 75, 77 align the liquid crystal molecules 76a contained in the liquid crystal layer 76 in a fixed direction.

The transparent conductive film 78 is provided on the surface of the transparent substrate 79 facing the alignment film 77, and faces the pixel electrode layer 73 with the liquid crystal layer 76 and other layers sandwiched between them. The transparent substrate 79 is, for example, a glass substrate. The transparent conductive film 78 is formed from a light-transmitting and conductive material such as ITO. The transparent substrate 79 and transparent conductive film 78 transmit laser light L.

In the spatial light modulator 7 configured as described above, when a signal indicating a modulation pattern is input from the control unit 6 to the drive circuit layer 72, a voltage corresponding to the signal is applied to each pixel electrode 73a, and an electric field is formed between each pixel electrode 73a and the transparent conductive film 78. When this electric field is formed, the alignment direction of the liquid crystal molecules 76a in the liquid crystal layer 76 changes for each region corresponding to each pixel electrode 73a, and the refractive index changes for each region corresponding to each pixel electrode 73a. This state is when a modulation pattern is displayed on the liquid crystal layer 76. The modulation pattern is used to modulate the laser light L.

In other words, with a modulation pattern displayed on the liquid crystal layer 76, laser light L enters the liquid crystal layer 76 from the outside via the transparent substrate 79 and transparent conductive film 78, is reflected by the reflective film 74, and is emitted from the liquid crystal layer 76 to the outside via the transparent conductive film 78 and transparent substrate 79. The laser light L is modulated according to the modulation pattern displayed on the liquid crystal layer 76. In this way, the spatial light modulator 7 allows modulation of the laser light L (e.g., modulation of the intensity, amplitude, phase, polarization, etc. of the laser light L) by appropriately setting the modulation pattern displayed on the liquid crystal layer 76. The modulation surface 7a shown in FIG. 3 is, for example, the liquid crystal layer 76.

As described above, the laser light L output from the light source 31 is incident on the condenser lens 33 via the spatial light modulator 7 and the 4f lens unit 34, and is then focused by the condenser lens 33 within the object 11, thereby forming a modified region 12 and a crack extending from the modified region 12 in the object 11 in the focused region C. Furthermore, the control unit 6 controls the moving units 4 and 5 to move the focused region C relative to the object 11, thereby forming the modified region 12 and a crack along the movement direction of the focused region C.
[Explanation of findings regarding diagonal crack formation]

Here, the direction of relative movement of the focusing area C (processing progress direction) at this time is defined as the X direction. Furthermore, the direction intersecting (orthogonal to) the second surface 11a, which is the incident surface of the laser light L on the object 11, is defined as the Z direction. Furthermore, the direction intersecting (orthogonal to) the X and Z directions is defined as the Y direction. The X and Y directions are directions along the second surface 11a. Note that the Z direction may be defined as the optical axis of the focusing lens 33, or the optical axis of the laser light L focused toward the object 11 via the focusing lens 33.

As shown in Figure 5, there is a requirement to form a diagonal crack along a line RA inclined with respect to the Z and Y directions (here, a line RA inclined at a predetermined angle θ from the Y direction) within an intersecting plane (YZ plane S including the Y and Z directions) that intersects with the X direction, which is the machining direction. Knowledge about the formation of such diagonal cracks will be explained using machining examples.

Here, modified regions 12a and 12b are formed as modified region 12. As a result, crack 13a extending from modified region 12a and crack 13b extending from modified region 12b are connected to form crack 13 extending diagonally along line RA. First, as shown in FIG. 6, a focusing region C1 is formed with the second surface 11a of object 11 as the incident surface for laser light L. Meanwhile, focusing region C2 is formed on the second surface 11a side of focusing region C1, with the second surface 11a also as the incident surface for laser light L. At this time, focusing region C2 is shifted by a distance Sz in the Z direction from focusing region C1 and a distance Sy in the Y direction from focusing region C1. Distances Sz and Sy correspond, for example, to the slope of line RA.

On the other hand, as shown in FIG. 7 , by modulating the laser light L using the spatial light modulator 7, the beam shape in the YZ plane S of the focusing region C (at least the focusing region C2) is made into an inclined shape that is inclined in the shift direction (here, the negative Y direction) with respect to the Z direction at least on the second surface 11a side of the center Ca of the focusing region C. In the example of FIG. 7 , the beam shape is inclined in the negative Y direction with respect to the Z direction on the second surface 11a side of the center Ca, and is also an arc shape that is inclined in the negative Y direction with respect to the Z direction on the first surface 11b side opposite the second surface 11a from the center Ca. Note that the beam shape of the focusing region C in the YZ plane S refers to the intensity distribution of the laser light L in the focusing region C in the YZ plane S.

In this way, by shifting at least two focusing regions C1 and C2 in the Y direction and tilting the beam shape of at least focusing region C2 (here, both focusing regions C1 and C2), it is possible to form a diagonally extending crack 13, as shown in Figure 9(a). Note that if the object 11 is relatively thin in the Z direction or if processing is performed closer to the first surface 11b, forming only the modified region 12a may result in the crack 13a extending from the modified region 12a reaching the first surface 11b. In this case, by tilting the beam shape of the focusing region C1 used to form the modified region 12a, at least closer to the second surface 11a than the center Ca of the focusing region C, to a tilt shape that corresponds to the tilt direction of the desired crack 13a relative to the Z direction, it is possible to form a diagonal crack (crack 13a) reaching the first surface 11b without forming the modified region 12b. Furthermore, for example, by controlling the modulation pattern of the spatial light modulator 7, the laser light L can be split to simultaneously form the focusing regions C1 and C2, thereby forming the modified region 12 and the crack 13 (multi-focal processing), or the modified region 12a and the crack 13a can be formed by forming the focusing region C1, and then the modified region 12b and the crack 13b can be formed by forming the focusing region C2 (single-pass processing).

Furthermore, by forming another light-collecting region between light-collecting region C1 and light-collecting region C2, another modified region 12c can be interposed between modified region 12a and modified region 12b, as shown in Figure 9(b), thereby forming a longer, diagonally extending crack 13.

Next, we will explain the knowledge required to form an inclined beam shape in the YZ plane S of the focusing region C. First, we will specifically define the focusing region C. Here, the focusing region C is a region within a predetermined range from the center Ca (for example, a range of ±25 μm from the center Ca in the Z direction). As described above, the center Ca is the position where the beam intensity is highest, or the center of gravity of the beam intensity. The center of gravity of the beam intensity is the position on the optical axis of the laser light L when no modulation is performed using a modulation pattern that shifts the optical axis of the laser light L, such as a modulation pattern for branching the laser light L. The position where the beam intensity is highest and the center of gravity of the beam intensity can be obtained as follows. That is, the laser light L is irradiated onto the object 11 with the output of the laser light L set low enough (below the processing threshold) to prevent the formation of a modified region 12 in the object 11. At the same time, the reflected light of the laser light L from the surface of the object 11 opposite the incident surface of the laser light L (here, the first surface 11b) is captured by a camera at multiple positions F1 to F7 in the Z direction shown in Figure 12, for example. This makes it possible to obtain the position where the beam intensity is highest and the center of gravity based on the obtained images. The modified region 12 is formed near this center Ca.

One way to tilt the beam shape in the focusing area C is to offset the modulation pattern. More specifically, the spatial light modulator 7 displays various patterns, such as a distortion correction pattern for correcting wavefront distortion, a grating pattern for branching the laser light, a slit pattern, an astigmatism pattern, a coma aberration pattern, and a spherical aberration correction pattern (a pattern in which these are superimposed is displayed). Of these, as shown in Figure 8, the beam shape in the focusing area C can be adjusted by offsetting the spherical aberration correction pattern Ps.

In the example of FIG. 8, on the modulation plane 7a, the center Pc of the spherical aberration correction pattern Ps is offset by an offset amount Oy1 to the negative side in the Y direction relative to the center Lc (of the beam spot) of the laser light L. As described above, the modulation plane 7a is imaged onto the entrance pupil plane 33a of the condenser lens 33 by the 4f lens unit 34. Therefore, the offset on the modulation plane 7a becomes an offset to the positive side in the Y direction on the entrance pupil plane 33a. In other words, on the entrance pupil plane 33a, the center Pc of the spherical aberration correction pattern Ps is offset by an offset amount Oy2 to the positive side in the Y direction from the center Lc of the laser light L and the center of the entrance pupil plane 33a (which here coincides with the center Lc).

In this way, by offsetting the spherical aberration correction pattern Ps, the beam shape of the laser light L in the focusing region C is deformed into an arc-like tilted shape as shown in FIG. 7. Offsetting the spherical aberration correction pattern Ps as described above is equivalent to imparting coma aberration to the laser light L. Therefore, by including a coma aberration pattern for imparting coma aberration to the laser light L in the modulation pattern of the spatial light modulator 7, the beam shape of the focusing region C can be made tilted. Note that the coma aberration pattern can be a pattern equivalent to the ninth term of the Zernike polynomial (the Y component of third-order coma aberration), which generates coma aberration in the Y direction.

Note that the control of the beam shape to form such an obliquely extending crack 13 is not limited to the above example. Next, another example for forming an inclined beam shape will be described. As shown in FIG. 10(a), the laser light L may be modulated using a modulation pattern PG1 that is asymmetric with respect to the axis Ax along the X direction, which is the processing direction, to form an inclined beam shape in the focused region C. The modulation pattern PG1 includes a grating pattern Ga on the negative side of the Y direction from the axis Ax along the X direction passing through the center Lc of the beam spot of the laser light L in the Y direction, and also includes a non-modulated region Ba on the positive side of the axis Ax in the Y direction. In other words, the modulation pattern PG1 includes the grating pattern Ga only on the positive side of the axis Ax in the Y direction. Note that FIG. 10(b) shows the modulation pattern PG1 of FIG. 10(a) inverted to correspond to the entrance pupil plane 33a of the focusing lens 33.

(a) in Figure 11 shows the intensity distribution of the laser light L on the entrance pupil plane 33a of the focusing lens 33. As shown in (a) in Figure 11, by using such a modulation pattern PG1, the portion of the laser light L incident on the spatial light modulator 7 that is modulated by the grating pattern Ga does not enter the entrance pupil plane 33a of the focusing lens 33. As a result, as shown in (b) in Figure 14 and Figure 15, the beam shape of the focusing region C in the YZ plane S can be made into an inclined shape in which the entire beam is inclined in one direction with respect to the Z direction.

In other words, in this case, the beam shape of the focusing area C is tilted toward the negative Y direction with respect to the Z direction on the side of the second surface 11a from the center Ca of the focusing area C, and is tilted toward the positive Y direction with respect to the Z direction on the side of the first surface 11b, opposite the second surface 11a from the center Ca of the focusing area C. Note that each diagram in Figure 12(b) shows the intensity distribution in the XY plane of the laser light L at each position F1 to F7 in the Z direction shown in Figure 12(a), and is the result of actual observation by a camera. Even when the beam shape of the focusing area C is controlled in this way, a crack 13 extending diagonally can be formed, as in the above example.

Furthermore, modulation patterns PG2, PG3, and PG4 shown in Figure 13 can also be used as modulation patterns asymmetric with respect to the axis Ax. Modulation pattern PG2 includes non-modulation regions Ba and grating patterns Ga arranged in order in a direction away from the axis Ax on the negative side of the Y direction from the axis Ax, and includes a non-modulation region Ba on the positive side of the Y direction from the axis Ax. In other words, modulation pattern PG2 includes a grating pattern Ga in part of the region on the negative side of the Y direction from the axis Ax.

Modulation pattern PG3 includes non-modulation regions Ba and grating patterns Ga arranged in order in the direction away from the axis Ax on the negative side of the axis AX in the Y direction, and also includes non-modulation regions Ba and grating patterns Ga arranged in order in the direction away from the axis Ax on the positive side of the axis Ax in the Y direction. Modulation pattern PG3 is made asymmetric with respect to the axis Ax by varying the proportions of non-modulation regions Ba and grating patterns Ga on the positive side of the axis Ax in the Y direction and the negative side of the axis Ax in the Y direction (by making the non-modulation regions Ba relatively narrower on the negative side of the Y direction).

Modulation pattern PG4, like modulation pattern PG2, includes a grating pattern Ga in part of the region on the negative side of the axis Ax in the Y direction. Modulation pattern PG4 also includes a region in the X direction where grating pattern Ga is provided. That is, modulation pattern PG4 includes a non-modulation region Ba, a grating pattern Ga, and a non-modulation region Ba arranged in order in the X direction in the region on the negative side of the axis Ax in the Y direction. Here, grating pattern Ga is arranged in a region including axis Ay along the Y direction that passes through the center Lc of the beam spot of laser light L in the X direction.

Using any of the above modulation patterns PG2 to PG4, the beam shape in the light collection area C can be made to be an inclined shape that is inclined toward the negative Y direction with respect to the Z direction at least on the second surface 11a side of the center Ca. In other words, to control the beam shape in the light collection area C so that it is inclined toward the negative Y direction with respect to the Z direction at least on the second surface 11a side of the center Ca, it is possible to use modulation patterns PG1 to PG4 or, in addition to modulation patterns PG1 to PG4, an asymmetric modulation pattern including a grating pattern Ga.

Furthermore, the asymmetric modulation pattern for tilting the beam shape in the focusing region C is not limited to one that uses a grating pattern Ga. Figure 14 is a diagram showing another example of an asymmetric modulation pattern. As shown in Figure 14(a), the modulation pattern PE includes an elliptical pattern Ew on the negative side of the axis Ax in the Y direction, and an elliptical pattern Es on the positive side of the axis Ax in the Y direction. Note that Figure 14(b) is the modulation pattern PE of Figure 14(a) inverted to correspond to the entrance pupil plane 33a of the focusing lens 33.

As shown in (c) of Figure 14, the elliptical patterns Ew and Es are both patterns for making the beam shape of the focusing area C in the XY plane, which includes the X and Y directions, an elliptical shape with the X direction as the longitudinal direction. However, the modulation intensity differs between the elliptical patterns Ew and Es. More specifically, the modulation intensity by the elliptical pattern Es is greater than the modulation intensity by the elliptical pattern Ew. In other words, the focusing area Cs formed by the laser light L modulated by the elliptical pattern Es is an elliptical shape that is longer in the X direction than the focusing area Cw formed by the laser light L modulated by the elliptical pattern Ew. Here, a relatively strong elliptical pattern Es is arranged on the negative side of the Y direction from the axis Ax.

As shown in Figure 15(a), by using such a modulation pattern PE, the beam shape of the focusing area C in the YZ plane S can be made to be an inclined shape that is inclined toward the negative Y direction with respect to the Z direction on the side of the second surface 11a closer to the center Ca. In particular, in this case, the beam shape of the focusing area C in the YZ plane S is also inclined toward the negative Y direction with respect to the Z direction on the side opposite the second surface 11a from the center Ca, resulting in an arc shape overall. Note that each diagram in Figure 15(b) shows the intensity distribution in the XY plane of the laser light L at each position H1 to F8 in the Z direction shown in Figure 15(a), and is the result of actual observation by a camera.

Furthermore, the modulation pattern for tilting the beam shape of the focal region C is not limited to the asymmetric pattern described above. One example of such a modulation pattern is a pattern shown in FIG. 16 , in which focal points CI are formed at multiple positions within the YZ plane S, and the laser light L is modulated so that the focal points CI together form a focal region C with a tilted shape (including the multiple focal points CI). Such a modulation pattern can be formed based on an axicon lens pattern, for example. When such a modulation pattern is used, the modified region 12 itself can also be formed at an angle within the YZ plane S. Therefore, in this case, an angled crack 13 can be accurately formed according to the desired angle. On the other hand, when such a modulation pattern is used, the length of the crack 13 tends to be shorter than in the other examples described above. Therefore, by using various modulation patterns according to requirements, desired processing can be achieved.

The focal point CI is, for example, the point at which unmodulated laser light is focused. As described above, according to the inventor's findings, by shifting at least two modified regions 12a, 12b in the Y and Z directions within the YZ plane S and by tilting the beam shape of the focal region C within the YZ plane S, it is possible to form a crack 13 that extends obliquely so as to be inclined in the Y direction relative to the Z direction.

In controlling the beam shape, using an offset of a spherical aberration correction pattern, using a coma aberration pattern, or using an elliptical pattern enables processing with higher energy than using a diffraction grating pattern to cut off part of the laser light. These methods are also effective when prioritizing the formation of cracks. Furthermore, when using a coma aberration pattern, it is possible to make only the beam shape of a part of the focusing area an inclined shape in the case of multi-focus processing. Furthermore, when using an axicon lens pattern, using other patterns is more effective than other patterns when prioritizing the formation of a modified area.
[First embodiment of laser processing]

Next, we will explain laser processing according to the first embodiment. Here, trimming processing is performed. Trimming processing is processing to remove unnecessary portions of the object 11. Figures 17 and 18 are diagrams showing the object to be processed according to this embodiment. Figures 17(a) and (b) and Figure 18(b) are cross-sectional views, and Figure 18(a) is a plan view. Hereinafter, to make it easier to understand, hatching may be omitted in the cross-sectional views.

As shown in Figures 17 and 18, the object 11 includes a first wafer (wafer) 100 and a second wafer (separate member) 200. The first wafer 100 includes a first surface 101 and a second surface 102 opposite the first surface 101. The first wafer 100 and the second wafer 200 may be any wafer, such as a semiconductor wafer (e.g., a silicon wafer).

The first wafer 100 is bonded to the second wafer 200 on the first surface 101 side. More specifically, a device layer 150 is formed on the first surface 101 of the first wafer 100, and this device layer 150 is bonded to the second wafer 200. Note that here, a device layer 250 is also formed on the second wafer 200, and the device layer 150 and the device layer 250 are bonded to each other. Thus, in this embodiment, the object 11 is a bonded wafer formed by bonding the first wafer 100 to the second wafer 200, which is a separate member, via the device layers 150 and 250.

The device layer 150 includes chips of multiple functional elements, such as light-receiving elements such as photodiodes, light-emitting elements such as laser diodes, and circuit elements such as memories. The device layer 150 includes an active area 160 that includes a central portion of the device layer when viewed from the Z direction intersecting (orthogonal to) the first surface 101 and the second surface 102, and an annular peripheral portion 170 located outside the active area 160 and surrounding the active area 160 when viewed from the Z direction. The active area 160 is an area that includes the multiple chips described above.

The peripheral edge 170 includes a portion removed by trimming. The peripheral edge 170 is a region that includes the outer edge 153 of the device layer 150, and includes a pre-processing region 172 where the bond with the second wafer 200 has been weakened. The peripheral edge 170 is also located inside the pre-processing region (on the active area 160 side) when viewed in the Z direction, and includes a bonding region where the bond with the second wafer 200 is maintained. In the peripheral edge 170 of the device layer 150, the bonding region 171 and the pre-processing region 172 are in contact with each other, forming a boundary B12 between them.

The pre-processing region 172 may be formed, for example, by pre-processing, such as by etching, to roughen the bonding surfaces before bonding the first wafer 100 and the second wafer 200. In this case, when bonding the first wafer 100 and the second wafer 200, the entire pre-processing region 172 may not be bonded, or it may be partially bonded, but the bond will be weaker overall (the bond strength will be lower) than in other areas.

The pre-processing region 172 can also be formed by pre-processing, in which, after bonding the first surface 101 and the second wafer 200, laser light is irradiated, which passes through the first wafer 100 and is absorbed by the bonded portion, to form cracks extending in a plane intersecting the Z direction. In this case, cracks may form throughout the entire pre-processing region 172, causing delamination throughout the entire pre-processing region 172, or the bond may be maintained in parts, but the bond overall will be weaker than in other areas (the bond strength will be lower).

In the laser processing according to this embodiment, a trimming process is performed by irradiating the region corresponding to the peripheral edge 170 with laser light L as described above while suppressing irradiation of the region corresponding to the active area 160 of the first wafer 100 with laser light L, thereby removing the removal region E of the first wafer 100 and leaving the effective region R. To achieve this, the laser processing according to this embodiment performs the following steps: a first process along a first line A1 that extends annularly (here, annularly) on the peripheral edge 170 as viewed in the Z direction; a second process along multiple (here, four) second lines A2 that extend linearly from the outer edge 103 of the first wafer 100 to the first line A1 on the peripheral edge 170 as viewed in the Z direction; and a third process at a position on the peripheral edge 170 different from the first line A1 and second line A2 as viewed in the Z direction.

In this embodiment, the third processing is performed along a third line A3 that extends in an annular (here, circular) shape on the peripheral portion 170 when viewed in the Z direction. The third line A3 is set between the first line A1 and the outer edge 103, more specifically, between the boundary B12 and the outer edge 103. In other words, the third line A3 is located on the pre-processing region 172. Note that in this embodiment, the first line A1 is set closer to the active area 160 than the boundary B12. In other words, the first line A1 is located on the bonding region 171.

Next, the laser processing method (laser processing step) according to this embodiment, including each processing step, will be described in detail. Note that in the following description, the Z direction is the direction intersecting (or perpendicular to) the first surface 101 and second surface 102 of the first wafer 100, the X direction is the tangential direction (or circumferential direction) of the outer edge 103 of the first wafer 100 when viewed from the Z direction, and the Y direction is the radial direction from the center of the first wafer 100 toward the outer edge 103 when viewed from the Z direction.

As shown in FIG. 19 , in the laser processing method according to this embodiment, the third processing is first performed (step S101: third processing step). More specifically, in step S101, the object 11 is supported on the stage 2 so that the first surface 101 of the first wafer 100 faces the stage 2. Therefore, in the following steps, including step S101, the second surface 102 of the first wafer 100 faces the irradiation unit 3. Then, the second surface 102 is used as the incident surface for the laser light L, and the laser light L is irradiated onto the first wafer 100, thereby forming a modified region 12 in the first wafer 100 and a crack 13 extending from the modified region 12.

In step S101, the control unit 6 controls the movement units 4 and 5 to adjust the relative positions of the stage 2 and the irradiation unit 3, thereby positioning the irradiation unit 3 above the first wafer 100. In particular, in step S101, the focusing area C of the laser light L is positioned directly below the third line A3 inside the first wafer 100. In this state, the control unit 6 controls the irradiation unit 3 to irradiate the first wafer 100 with the laser light L, and controls the movement unit 4 to rotate the stage 2. As a result, the focusing area C of the laser light L is moved relative to the first wafer 100 along the third line A3, while the laser light L is irradiated onto the first wafer 100. As a result, a third modified region 123 is formed as the modified region 12 inside the first wafer 100 (see FIG. 20 ).

That is, in step S101, the control unit 6 controls the irradiation unit 3 and the movement units 4 and 5 to perform a third processing step in which the first wafer 100 is irradiated with laser light L while positioning the light collection region C at a position different from the first line A1 and the second line A2 on the peripheral portion 170 as viewed in the Z direction, thereby forming a third modified region 123 as the modified region 12. In particular, in step S101, as the third processing step, the control unit 6 irradiates the first wafer 100 with laser light L while moving the light collection region C relatively along the third line A3, thereby forming the third modified region 123 along the third line A3. As described above, the third line A3 is set on the preprocessing region 172. Therefore, in the third processing step, the control unit 6 positions the light collection region C above the preprocessing region 172 and irradiates the first wafer 100 with laser light L, thereby forming the third modified region 123 on the preprocessing region 172.

In addition, in step S101, as shown in FIG. 20, the control unit 6 positions the light collection area C at multiple positions in the Z direction and irradiates the laser light L in the same manner, thereby forming multiple third modified areas 123 along the Z direction. In this example, a third crack 133 is then formed that extends across the multiple third modified areas 123 along the Z direction, and the third crack 133 reaches the second surface 102.

21, the laser processing method according to this embodiment then performs the first processing (step S102: first processing step). More specifically, in step S102, the control unit 6 controls the moving units 4 and 5 to adjust the relative positions of the stage 2 and the irradiation unit 3, thereby positioning the focused area C of the laser light L below the first line A1 within the first wafer 100. In this state, the control unit 6 controls the irradiation unit 3 to irradiate the first wafer 100 with the laser light L, and controls the moving unit 4 to rotate the stage 2. As a result, the laser light L is irradiated onto the first wafer 100 while the focused area C of the laser light L is moved along the first line A1 relative to the first wafer 100. This forms a first modified region 121 as a modified region 12 within the first wafer 100 (see FIG. 26, etc.).

That is, in step S102, the control unit 6 controls the irradiation unit 3 and the movement units 4 and 5 to irradiate the first wafer 100 with laser light L while relatively moving the light collection area C along a first line A1 that extends annularly on the peripheral portion 170 when viewed in the Z direction, thereby performing a first processing process to form a first modified area 121 as a modified area 12 along the first line A1.

Here, in step S102 (first processing), diagonal cracks and vertical cracks are formed. This point will be explained in more detail. In step S102, diagonal cracks are formed first. To achieve this, as shown in FIG. 22, the position of the light-focusing region C is set to a first Y position Y1 in the Y direction from the center toward the outer edge 103 of the first wafer 100 and a first Z position Z1 in the Z direction, and laser light L is irradiated along a first line A1. Note that the first Y position Y1 is the position closest to the boundary B12 among multiple Y-direction positions at which the light-focusing region C is positioned when forming multiple first modified regions 121. Furthermore, the first Z position Z1 is the position closest to the first surface 101 among multiple Z-direction positions at which the light-focusing region C is positioned when forming multiple first modified regions 121. This forms a first Z-modified region 121a as the first modified region 121 and a first crack 131 as the crack 13 extending from the first Z-modified region 121a, as shown in FIG. 23.

Then, the position of the light collection region C is set to a second Y position Y2, which is closer to the boundary B12 in the Y direction than the first Y position Y1 (i.e., closer to the center of the first wafer 100), and is set to a second Z position Z2, which is closer to the second surface 102 than the first Z position Z1 in the Z direction. Laser light L is then irradiated along the first line A1. As a result, as shown in FIG. 24, a second Z modified region 121b is formed as the first modified region 121, closer to the second surface 102 than the first Z modified region 121a and opposite the outer edge 103 of the first wafer 100. When these first Z modified region 121a and second Z modified region 121b are formed, as shown in the findings regarding oblique crack formation described above, the light collection region C has an inclined shape that slopes in the Z direction from the first Y position Y1 toward the second Y position Y2 (shift direction) at least on the second surface 102 side of the center Ca. This causes the first crack 131 to extend obliquely from the second Z-modified region 121b to the first Z-modified region 121a and from the first Z-modified region 121a toward the boundary B12, reaching the first surface 101 (particularly the boundary B12).

As described above, in step S102 (first processing), the control unit 6 positions the focusing area C at multiple Z-direction positions and irradiates the laser light L, thereby forming multiple first modified areas 121 (first Z modified area 121a and second Z modified area 121b) along the Z direction, and forming a first crack 131 from the first modified area 121 (first Z modified area 121a) located closest to the first surface 101 among the multiple first modified areas 121 to the first surface 101.

Furthermore, in step S102 (first processing), the control unit 6 forms multiple first modified regions 121 (first Z modified regions 121a and second Z modified regions 121b) so that the first cracks 131 extend toward the boundary B12 between the pre-processing region 172 and the joining region 171. In particular, in step S102 (first processing), the control unit 6 forms multiple first modified regions 121 (first Z modified regions 121a and second Z modified regions 121b) so that the first cracks 131 extend obliquely from the joining region 171 toward the boundary B12 as they move from the second surface 102 toward the first surface 101.

More specifically, in step S102 (first processing), the control unit 6 performs a first oblique processing process in which the position of the light collection region C is set to a first Y position Y1 in the Y direction and a first Z position Z1 in the Z direction, thereby irradiating the laser light L to form a first Z modified region 121a. After the first oblique processing process, the control unit 6 performs a second oblique processing process in which the position of the light collection region C is set to a second Y position Y2, which is closer to the outer edge 103 of the first wafer 100 than the first Y position Y1 in the Y direction, and is irradiated with laser light L at a second Z position Z2, which is closer to the second surface 102 than the first Z position Z1 in the Z direction, thereby forming a second Z modified region 121b closer to the second surface 102 than the first Z modified region 121a and closer to the outer edge 103 of the first wafer 100, and extending the first crack 131 obliquely from the first Z modified region 121a toward the boundary B12.

Next, in step S102, vertical cracks are formed. To this end, as shown in FIG. 24, the position of the focus area C of the laser light L is set to the second Y position Y2 in the Y direction, and set to a third Z position Z3 closer to the second surface 102 than the second Z position Z2 in the Z direction. Laser light L is then applied along the first line A1. This results in the formation of a third Z modified region 121c as the first modified region 121, as shown in FIG. 25. Here, by similarly applying laser light L to multiple third Z positions Z3, multiple third Z modified regions 121c are formed along the Z direction, and a third crack (vertical crack) 131b extending along the Z direction across the multiple third Z modified regions 121c is formed. At this time, the third crack 131b can be extended to reach the second surface 102.

In this way, in step S102 (first processing), the control unit 6 controls the irradiation unit 3 and movement units 4 and 5 to position the light collection area C at multiple third Z positions Z3 closer to the second surface 102 than the second Z position Z2 at the second Y position Y2, and irradiates the laser light L along the first line A1 to form multiple third Z modified areas 121c arranged along the Z direction at the second Y position Y2, thereby performing a vertical processing process in which the third cracks 131b extend vertically across the multiple third Z modified areas 121c.

26, the laser processing method according to this embodiment then performs a second processing step (step S103, second processing step). More specifically, in step S103, the control unit 6 controls the moving units 4 and 5 to adjust the relative positions of the stage 2 and the irradiation unit 3, thereby positioning the focused area C of the laser light L below the second line A2 within the first wafer 100. In this state, the control unit 6 controls the irradiation unit 3 to irradiate the first wafer 100 with the laser light L, and controls at least one of the moving units 4 and 5 to move the stage 2 along the Y direction. As a result, the laser light L is irradiated onto the first wafer 100 while the focused area C of the laser light L is moved along the second line A2 relative to the first wafer 100. This forms a second modified region 122 as a modified region 12 within the first wafer 100 (see FIG. 26, etc.).

In this way, in step S103, the control unit 6 controls the irradiation unit 3 and movement units 4 and 5 to irradiate the first wafer 100 with laser light L while moving the focusing area C relatively along the second line A2 that extends linearly from the outer edge 103 of the first wafer 100 to the first line A1 on the peripheral portion 170 when viewed in the Z direction, thereby performing a second processing process to form a second modified area 122 as a modified area 12 along the second line A2.

The second modified region 122 and the crack extending from the second modified region 122 formed in the second step described above are formed so as to extend from the outer edge 103 of the first wafer 100 to the first modified region 121 and the first crack 131 formed along the first line A1. This makes it possible to divide the removal region E of the first wafer 100 circumferentially by the number of second lines A2 (here, four).

Then, using a specified jig or device, the removal area E is removed from the first wafer 100, leaving the effective area R bonded to the second wafer 200 via the device layers 150, 250. This completes the trimming process for the object 11. After that, a process of grinding and thinning the effective area R from the second surface 102 side is performed, after which another wafer can be further bonded to the thinned effective area R and the above series of processes can be repeated.

As described above, in the laser processing method and laser processing apparatus 1 according to this embodiment, laser processing is performed by irradiating laser light L onto the first wafer 100 bonded to the second wafer 200 via the device layers 150, 250. The device layer 150 includes an active area 160 including multiple chips and a peripheral edge portion 170 located outside the active area 160 and surrounding the active area 160. In laser processing, laser light L is irradiated along a first line A1 extending annularly on the peripheral edge portion 170, thereby forming a first modified region 121 along the first line A1. This makes it possible to use the first modified region 121 and the first crack 131 extending from the first modified region 121 to perform trimming, removing the outer edge portion of the wafer as an unnecessary portion (removal region E).

In particular, in the laser processing method and laser processing apparatus 1 according to this embodiment, laser light is applied along a second line A2 that extends from the outer edge 103 of the first wafer 100 to the first line A1 on the peripheral portion 170 of the device layer 150, thereby forming a second modified region 122 along the second line A2. This makes it possible to easily divide the removal region E of the first wafer 100 into multiple parts in the circumferential direction by utilizing the second modified region 122 and cracks extending from the second modified region 122.

Furthermore, in the laser processing method and laser processing apparatus 1 according to this embodiment, a third modified region 123 is formed by irradiating the peripheral edge 170 of the device layer 150 with laser light L at a position different from the first line A1 and the second line A2. Such a third modified region 123 relieves stress generated within the first wafer 100. Therefore, by forming this third modified region 123 before extending the first crack 131 extending from the first modified region 121 to the first surface 101, the first crack 131 is prevented from extending in an unintended direction due to stress within the first wafer 100. This makes it possible to prevent a decrease in the quality of the trimming process of the bonded wafer.

The modified region 12 (here, the third modified region 123) formed before the first crack 131 extending from the first modified region 121 is extended to reach the first surface 101 (for example, before the first processing step) functions as a modified region for alleviating stress within the first wafer 100 to prevent the first crack 131 from extending in an unintended direction.

From this perspective, in the laser processing apparatus 1, the control unit 6 controls the irradiation unit 3 and movement units 4 and 5 to position the focusing area C at a position on the peripheral edge 170 when viewed from the Z direction, and irradiate the first wafer 100 with laser light L, thereby performing a stress relaxation process to form a modified area 12 for relieving stress generated inside the first wafer 100. In particular, the control unit 6 performs the stress relaxation process before extending the first crack 131 extending from the first modified area 121 to reach the first surface 101 (for example, before the first processing process).

In the laser processing method and laser processing apparatus 1 according to this embodiment, multiple first modified regions 121 are formed in the Z direction along the first line A1. This enables trimming to remove the outer edge of the wafer as unnecessary portions (removal regions E) using the multiple first modified regions 121 and the first cracks 131 extending from the first modified regions 121. The third modified region 123 is formed before processing to extend the first crack 131 extending from the first Z modified region 121a, which is located closest to the first surface 101 of the first wafer 100 (i.e., the device layer 150 side), to the first surface 101. This prevents the first crack 131 from extending in an unintended direction due to stress within the first wafer 100. This prevents degradation of the quality of the bonded wafer trimming process. In this case, the processing for extending the first crack 131 extending from the first Z modified region 121a, which is located closest to the first surface 101 of the first wafer 100 among the multiple first modified regions 121, to reach the first surface 101 is processing for forming the second Z modified region 121b.

Therefore, in the laser processing apparatus 1 according to this embodiment, the control unit 6 performs a stress relaxation process before forming the first modified region 121 (here, the second Z modified region 121b) to extend the first crack 131 among the multiple first modified regions 121 so that it reaches the first surface 101 (for example, before the first processing process).

Furthermore, in the laser processing device 1 according to this embodiment, the control unit 6 executes the third processing process before the first processing process. This makes it possible to more reliably form the third modified region 123 before the first crack 131 extends to reach the first surface 101.

In addition, in the laser processing apparatus 1 according to this embodiment, the peripheral portion 170 includes the outer edge 153 of the device layer 150 and includes a pre-processing region 172 where the bond with the second wafer 200 is weakened, and a bonding region 171 located inside the pre-processing region 172 when viewed from the Z direction. In the first processing step, the control unit 6 forms the first modified region 121 so that the first crack 131 extends toward the boundary B12 between the pre-processing region 172 and the bonding region 171. Thus, when the device layer 150, which is the bonding portion of the first wafer 100, includes the pre-processing region 172 where the bond is weakened, stress is likely to occur inside the first wafer 100. Therefore, as described above, forming the third modified region 123 to alleviate stress is more effective. In this case, the first crack 131 is prevented from unintentionally extending into the pre-processing region 172, thereby preventing quality degradation.

Furthermore, in the laser processing apparatus 1 according to this embodiment, in the first processing step, the control unit 6 forms the first modified region 121 so that the first crack 131 extends obliquely from the bonding region 171 toward the boundary B12 as it moves from the second surface 102 toward the first surface 101. Therefore, because the first crack 131 becomes an oblique crack, the first crack 131 is prevented from crossing the device layer 150 and reaching the second wafer 200.

Furthermore, in the laser processing apparatus 1 according to this embodiment, in the third processing step, the control unit 6 positions the focusing area C above the preprocessing area 172 and irradiates the laser light L, thereby forming a third modified area 123 on the preprocessing area 172. This makes it possible to reliably relieve stress inside the first wafer 100 caused by the preprocessing area 172.

Furthermore, in the laser processing apparatus 1 according to this embodiment, in the third processing step, the control unit 6 irradiates the laser light L while moving the focusing area C relatively along a third line A3 that extends annularly on the pre-processing area 172 when viewed in the Z direction, thereby forming a third modified area 123 along the third line A3. This makes it possible to alleviate stress along the entire circumference of the first wafer 100.

Furthermore, in the laser processing apparatus 1 according to this embodiment, in the third processing step, the control unit 6 positions the light collection area C at multiple positions in the Z direction and irradiates the laser light L, thereby forming multiple third modified areas 123 along the Z direction and causing third cracks 133 extending across the multiple third modified areas 123 to reach the second surface 102. This not only relieves stress inside the first wafer 100, but also makes it possible to suppress warping of the first wafer 100.
[Modification of the first embodiment]

Next, a modified example of the first embodiment will be described. In the laser processing apparatus 1 according to the first embodiment, in step S101 (third processing step, third processing process), the control unit 6 positions the focusing area C at multiple Z-direction positions and irradiates the laser light L, thereby forming multiple third modified regions 123 along the Z direction and causing a third crack 133 extending across the multiple third modified regions 123 to reach the second surface 102. However, in step S101, a single third modified region 123 may be formed while causing the third crack 133 to reach the second surface 102. That is, in step S101, the control unit 6 may form the third modified region 123 while causing the third crack 133 extending from the third modified region 123 to reach the second surface 102. Furthermore, in the first embodiment described above, an example was described in which, in step S101 (third processing step, third processing treatment), multiple third modified regions 123 are formed so that the third cracks 133 reach the second surface 102 of the first wafer 100, but do not reach the first surface 101 of the first wafer 100.

27(a), in step S101, multiple third modified regions 123 may be formed so that the third crack 133 does not reach either the first surface 101 or the second surface 102 (the number of third modified regions 123 may be one). That is, in the third processing step, the control unit 6 irradiates the laser light L while positioning the light collection region C at a position on the peripheral portion 170 that is different from the first line A1 and the second line A2, thereby forming the third modified region 123 so that the third crack 133 extending from the third modified region 123 does not reach the first surface 101 or the second surface 102. In this case, it is possible to suppress cracking of the wafer due to the third modified region or cracks extending from the third modified region.

Furthermore, as shown in (b) of Figure 27, when forming the third modified region 123 in step S101 so that the third crack 133 does not reach the first surface 101 or the second surface 102, the third modified region 123 may be formed at a deeper position (closer to the first surface 101). In this case, the Z-direction position of the third modified region 123 (light collection region C when forming the third modified region 123) can be at least a position closer to the first surface 101 than the center of the Z-direction of the first wafer 100.

In this example, in the first processing step, the control unit 6 positions the focusing region C at multiple Z-direction positions and irradiates the laser light L to form multiple first modified regions 121 along the Z direction. The control unit 6 then positions the focusing region C at a first Z position Z1, which is the Z-direction position of the focusing region C when forming the first modified region 121 closest to the first surface 101 among the multiple first modified regions 121, to form the third modified region 123. That is, in the third processing step, the control unit 6 may position the focusing region C at the first Z position Z1, which is the Z-direction position of the focusing region C when forming the first modified region 121 closest to the first surface 101 among the multiple first modified regions 121, and irradiate the laser light L to form the third modified region 123. In this case, cracking of the first wafer 100 due to the third modified region 123 or a third crack 133 extending from the third modified region 123 can be suppressed. In particular, in this case, since the third modified region 123 is formed directly above the pre-treatment region 172, it is possible to effectively relieve stress caused by the pre-treatment region 172.

In the above example, step S101 forms one row of third modified regions 123 in the Y direction, but multiple rows of third modified regions 123 may be formed in the Y direction. For example, by setting multiple third lines A3 concentrically on the peripheral portion 170 and irradiating laser light L along each of the third lines A3, it is possible to form multiple rows of third modified regions 123 in the Y direction.

In addition, in the above first embodiment, an example was described in which, in step S103 (second processing step, second processing treatment), laser light L is irradiated all at once along a single second line A2 extending from the outer edge 103 of the first wafer 100 to the first line A1. However, laser light L may be irradiated along the second line A2 in multiple batches.

More specifically, as shown in FIG. 28, the second line A2 includes a first portion A2a extending from the outer edge 103 of the first wafer 100 to the third line A3, and a second portion A2b extending from the third line A3 to the first line A1, and each portion can be irradiated with laser light L. As an example, irradiation of the laser light L along the first portion A2a can be performed before the first step S101, and irradiation of the laser light L along the second portion A2b can be performed after the first step S101.

In other words, in the second processing step, the control unit 6 performs a first partial processing step in which the second modified region 122 is formed along the first portion A2a of the second line A2 by irradiating the laser light L while moving the light collection region C relatively along the first portion A2a, and a second partial processing step in which the second modified region 122 is formed along the second portion A2b of the second line by irradiating the laser light L while moving the light collection region C relatively along the second portion A2b, and the control unit 6 can perform at least the first partial processing step before the first processing step.

In this case, before the first crack 131 extends to the first surface 101, the second modified region 122 formed in the first portion A2a of the second line A2 in addition to the third modified region 123 makes it possible to relieve stress inside the first wafer 100. In this case, in addition to the third modified region 123, the second modified region 122 formed in the first partial processing also functions as a modified region 12 for relieving stress generated inside the first wafer 100. Therefore, the control unit 6 performs the stress relaxation processing simultaneously with the first partial processing.

Furthermore, in this case, the control unit 6 can also perform both the first partial treatment and the second partial treatment before the first processing treatment. In this case, before the first crack 131 extends to the first surface 101, stress inside the first wafer 100 can be relieved by the second modified region 122 formed in the first portion A2a and the second portion A2b of the second line A2 in addition to the third modified region 123. In this case, in addition to the third modified region 123, the second modified region 122 formed by the first partial treatment and the second partial treatment also function as modified regions 12 for relieving stress generated inside the first wafer 100. Therefore, the control unit 6 performs the stress relief treatment simultaneously with the first partial treatment and the second partial treatment.

On the other hand, the control unit 6 can also perform the first partial processing before the first processing, and the second partial processing after the first processing. In this case, when the second modified region 122 is formed in the second portion A2b of the second line A2 that reaches the first line A1, the first modified region 121 has already been formed in the first line A1, and therefore the extension of cracks extending horizontally from the second modified region 122 is stopped by the first modified region 121. In either case, the order of step S101 (third processing step, third processing) is arbitrary.

Furthermore, steps S101 and S102 may be performed at least partially simultaneously. More specifically, as shown in FIG. 29 , when forming the first Z modified region 121a in step S101 (during the first oblique processing), the laser beam L is split into multiple (here, two) laser beams L1 and L2. The focus region C of the laser beam L1 is positioned at the first Z position Z1 and the first Y position Y1, while the focus region C of the laser beam L2 is positioned at the first Z position Z1 and the third Y position Y3. By irradiating the laser beams L1 and L2, the first Z modified region 121a and the third modified region 123 can be simultaneously formed at the respective positions. The third Y position Y3 is located closer to the outer edge 153 than the Y-direction position of the boundary B12. To simultaneously form multiple third modified regions 123 in the Y direction and the first Z modified region 121a, the laser beam L may be split into three or more beams.

In the above example, a case where a diagonal crack (first crack 131) is formed in step S102 (first processing step, first processing treatment) has been described. However, only vertical cracks may be formed in step S102. That is, a first crack 131 extending in the Z direction from the first modified region 121 may be formed so as to reach the first surface 101 (particularly boundary B12). Alternatively, a first crack 131 extending in the Z direction from the first modified region 121 closest to the first surface 101 among the multiple first modified regions 121 may be formed so as to reach the first surface 101 (particularly boundary B12).

In the above example, in step S101 (third processing step, third processing treatment), laser light L was irradiated along the third line A3, which was annular when viewed from the Z direction, to form the third modified region 123 along the third line A3. However, the third modified region 123 only needs to be formed in an area on at least the peripheral portion 170 of the first wafer 100, and is not limited to being formed along the entire annular third line A3. In other words, in step S101, the third modified region 123 may be formed only in a portion of the third line A3.

Figure 30 is a plan view showing an example of a first wafer. In the example of Figure 30, the first wafer 100 is a silicon wafer. The first wafer 100 has a second surface 102 that is a (100) surface, and has a crystal structure that includes one (110) surface, another (110) surface, a first crystal orientation K1 that is perpendicular to the one (110) surface, and a second crystal orientation K2 that is perpendicular to the other (110) surface. Note that the third crystal orientation K3 and the fourth crystal orientation K4 are both crystal orientations that are perpendicular to the (100) surface.

The points where the second crystal orientation K2 and the third line A3 intersect at right angles are defined as 0° and 180°, the points where the first crystal orientation K1 and the third line A3 intersect at right angles are defined as 90° and 270°, the midpoint on the third line A3 between 0° and 90° is defined as 45°, the midpoint between 90° and 180° is defined as 135°, the midpoint between 180° and 270° is defined as 225°, and the midpoint between 270° and 0° is defined as 315°. The points of 45° and 225° are the points where the third crystal orientation K3 and the third line A3 intersect at right angles. The points of 135° and 315° are the points where the fourth crystal orientation K4 and the third line A3 intersect at right angles. The first wafer 100 has a notch 100n at the 0° position.

When forming the third modified region 123 only in a portion of the third line A3 in step S101 and forming only vertical cracks in step S102, it is effective to irradiate the third line A3 with laser light L in a first angle range of 5° to 15° and a second angle range of 75° to 85° in accordance with the above angle definitions to partially form the third modified region 123. This is because stress relaxation is more effective in the first and second angle ranges, where it is relatively difficult to control vertical cracks. Note that the first and second angle ranges each include ranges obtained by adding an integer multiple of 90° to the above values.

Furthermore, when forming the third modified region 123 only in a portion of the third line A3 in step S101 and forming an oblique crack in step S102 (as in the first embodiment described above), it is effective to irradiate the laser light L in a third angle range that includes 45° of the third line A3 (e.g., 40° to 50°) to partially form the third modified region 123. This is because the third angle range is a range in which it is relatively difficult to control oblique cracks, and therefore stress relaxation works more effectively. Note that the third angle range also includes the range obtained by adding an integer multiple of 90° to the above values.

In the above modification, the third modified region 123 is formed in a portion of the annular third line A3. However, the third modified region 123 may be formed in any manner, not limited to an annular shape. Furthermore, the position and number of the third modified region 123 may also be arbitrary. For example, the third modified region 123 may be formed closer to the center of the first wafer 100 than the first modified region 121 on the peripheral portion 170, or may be formed on both sides of the first modified region 121.
[Second embodiment of laser processing]

Next, laser processing according to the second embodiment will be described. Here, trimming processing is performed in the same manner as in the first embodiment. Figure 31 shows an object to be processed according to this embodiment. (a) of Figure 31 is a plan view, and (b) of Figure 31 is a cross-sectional view. The object 11 shown in Figure 31 is the same as the object 11 of the first embodiment shown in Figure 17, etc. That is, in this embodiment, the object 11 is also a bonded wafer formed by bonding a first wafer 100 to a second wafer 200, which is a separate member, via device layers 150, 250.

In the laser processing according to this embodiment, as in the first embodiment, the laser beam L is suppressed from being irradiated onto the region corresponding to the active area 160 of the first wafer 100, while the laser beam L is irradiated onto the region corresponding to the peripheral edge 170, thereby performing trimming to remove the removal region E of the first wafer 100 and leave the effective region R. However, in the laser processing according to this embodiment, a first process is performed along a first line A1 that extends annularly (here, annularly) on the peripheral edge 170 as viewed from the Z direction, and a second process is performed along multiple (here, four) second lines A2 that extend linearly from the outer edge 103 of the first wafer 100 to the first line A1. In other words, in the laser processing according to this embodiment, compared to the first embodiment, a third process is not performed at a position different from the first line A1 and the second line A2 as viewed from the Z direction on the peripheral edge 170 (the third process is not required). Furthermore, in this embodiment, the first line A1 is set on the pre-processing region 172 as viewed from the Z direction.

The laser processing method (laser processing step) according to this embodiment, including each process, will now be described in detail. As shown in FIG. 32 , in the laser processing method according to this embodiment, the first process is first performed (step S201: first processing step). More specifically, in step S101, the control unit 6 controls the moving units 4 and 5 to adjust the relative positions of the stage 2 and the irradiation unit 3, thereby positioning the focusing area C of the laser light L below the first line A1 within the first wafer 100. In this state, the control unit 6 controls the irradiation unit 3 to irradiate the first wafer 100 with the laser light L, and controls the moving unit 4 to rotate the stage 2. As a result, the laser light L is irradiated onto the first wafer 100 while the focusing area C of the laser light L is moved along the first line A1 relative to the first wafer 100. This forms a first modified region 121 as a modified region 12 within the first wafer 100 (see FIG. 36 , etc.).

That is, in step S201, the control unit controls the irradiation unit 3 and the movement units 4 and 5 to irradiate the first wafer 100 with laser light L while relatively moving the light collection area C along a first line A1 that extends in a ring shape on the peripheral portion 170 when viewed in the Z direction, thereby performing a first processing process to form a first modified area 121 as a modified area 12 along the first line A1.

Here, in step S201 (first processing), diagonal cracks and vertical cracks are formed. This will be explained in more detail. In step S201, diagonal cracks are formed first. To achieve this, as shown in FIG. 33 , the position of the light collection region C is set to a first Y position Y1 in the Y direction from the center toward the outer edge 103 of the first wafer 100 and a first Z position Z1 in the Z direction, and laser light L is irradiated along a first line A1. Note that the first Y position Y1 is the position closest to the boundary B12 among multiple Y-direction positions at which the light collection region C is positioned when forming multiple first modified regions 121. Furthermore, the first Z position Z1 is the position closest to the first surface 101 among multiple Z-direction positions at which the light collection region C is positioned when forming multiple first modified regions 121.

Also, as an example, the first Z position Z1 here is the same as the first Z position Z1 in the first embodiment, and the first Y position Y1 is different from the first Y position Y1 in the first embodiment. That is, in the first embodiment, the first Y position Y1 was a position closer to the active area 160 than the boundary B12, but here it is a position closer to the outer edges 103 and 153 than the boundary B12. As a result, as shown in FIG. 34, a first Z modified region 121a as the first modified region 121 and a first crack 131 as a crack 13 extending from the first Z modified region 121a are formed. Here, the first Z modified region 121a and the first crack 131 are formed closer to the outer edges 103 and 153 than the boundary B12 in accordance with the first Y position Y1 as described above. That is, in this embodiment, the first Z modified region 121a and the first crack 131 are formed in an area on the pre-processing region 172 of the first wafer 100.

Then, the position of the light collection region C is set to a second Y position Y2 closer to the outer edge 103, 153 than the first Y position Y1 in the Y direction, and to a second Z position Z2 closer to the second surface 102 than the first Z position Z1 in the Z direction, and laser light L is irradiated along the first line A1. As a result, as shown in FIG. 35, a second Z modified region 121b is formed as the first modified region 121 closer to the second surface 102 and closer to the outer edge 103 of the first wafer 100 than the first Z modified region 121a. When these first Z modified region 121a and second Z modified region 121b are formed, as shown in the findings regarding the formation of oblique cracks described above, the light collection region C has an inclined shape that slopes in the Z direction from the first Y position Y1 toward the second Y position Y2 (shift direction) on the second surface 102 side of the center Ca of the light collection region C, even if there is no light collection region C. This causes the first crack 131 to extend obliquely from the second Z-modified region 121b to the first Z-modified region 121a and from the first Z-modified region 121a toward the boundary B12, reaching the first surface 101 (particularly the boundary B12).

As described above, in step S201 (first processing), the control unit 6 positions the focusing area C at multiple Z-direction positions on the pre-processing area 172 when viewed from the Z direction, and irradiates the laser light L to form multiple first modified areas 121 (first Z modified area 121a and second Z modified area 121b) along the Z direction. A first crack 131 is formed extending obliquely from the outside of the boundary B12 toward the boundary B12 as it moves from the second surface 102 toward the first surface 101, starting from the first modified area 121 (first Z modified area 121a) of the multiple first modified areas 121 that is located closest to the first surface 101.

More specifically, in step S201 (first processing process), the control unit 6 performs a first oblique processing process to form a first Z modified area 121a as the first modified area 121 by setting the position of the light collection area C to a first Y position Y1 in the Y direction and a first Z position Z1 in the Z direction and irradiating the laser light L thereto. Then, after the first oblique processing process, the control unit 6 sets the position of the light collection region C to a second Y position Y2 that is closer to the outer edge 103 of the first wafer 100 in the Y direction than the first Y position Y1, and to a second Z position Z2 that is closer to the second surface 102 than the first Z position Z1 in the Z direction, and irradiates the laser light L to form a second Z modified region 121b as the first modified region 121 closer to the second surface 102 and the outer edge 103 of the first wafer 100 than the first Z modified region 121a, and performs a second oblique processing process that extends the first crack 131 obliquely from the first Z modified region 121a toward the boundary B12.

The second Z-modified region 121b of the multiple first modified regions 121 serves to extend the first crack 131 so that it reaches the first surface 101. The first Z-modified region 121a is formed on the pre-processing region 172 and contributes to stress relaxation within the first wafer 100. Therefore, in step S201, the control unit 6 performs a stress relaxation process to form a modified region 12 (first Z-modified region 121a) for relieving stress generated within the first wafer 100 by positioning the focusing region C at a position on the peripheral portion 170 as viewed from the Z direction and irradiating the first wafer 100 with laser light L. This process is performed before forming the first modified region 121 (second Z-modified region 121b) for extending the first crack 131 of the multiple first modified regions 121 so that it reaches the first surface 101. In other words, the first oblique processing process can be considered a stress relaxation process.

Next, in step S201, vertical cracks are formed. To this end, as shown in FIG. 35, the position of the focus area C of the laser light L is set to the second Y position Y2 in the Y direction, and set to the third Z position Z3 closer to the second surface 102 than the second Z position Z2 in the Z direction. Laser light L is then applied along the first line A1. This results in the formation of a third Z modified region 121c as the first modified region 121, as shown in FIG. 36. Here, by similarly applying laser light L to multiple third Z positions Z3, multiple third Z modified regions 121c are formed along the Z direction, and a third crack (vertical crack) 131b extending along the Z direction across the multiple third Z modified regions 121c is formed. At this time, the third crack 131b can be extended to reach the second surface 102.

In this way, in step S201 (first processing process), after the second oblique processing process, the control unit 6 performs a vertical processing process in which, at the second Y position Y2, the focusing area C is positioned at multiple Z-direction positions closer to the second surface 102 than the second Z position Z2, and the laser light L is irradiated, thereby forming multiple first modified areas 121 (third Z modified areas 121c) arranged along the Z direction at the second Y position Y2, and extending the third crack 131b vertically across the multiple first modified areas 121.

Next, as in the first embodiment, the laser processing method according to this embodiment also performs a second processing (step S202, second processing step). More specifically, in step S202, the control unit 6 controls the moving units 4 and 5 to adjust the relative positions of the stage 2 and the irradiation unit 3, thereby positioning the focused area C of the laser light L below the second line A2 within the first wafer 100 (see FIG. 26). In this state, the control unit 6 controls the irradiation unit 3 to irradiate the first wafer 100 with the laser light L, and controls at least one of the moving units 4 and 5 to move the stage 2 along the Y direction. As a result, the laser light L is irradiated onto the first wafer 100 while the focused area C of the laser light L is moved along the second line A2 relative to the first wafer 100. As a result, a second modified region 122 is formed as the modified region 12 within the first wafer 100 (see FIG. 26).

In this way, in step S202, the control unit 6 controls the irradiation unit 3 and movement units 4 and 5 to irradiate the first wafer 100 with laser light L while moving the focusing area C relatively along the second line A2 that extends linearly from the outer edge 103 of the first wafer 100 to the first line A1 on the peripheral portion 170 when viewed in the Z direction, thereby performing a second processing process to form a second modified area 122 as a modified area 12 along the second line A2.

The second modified region 122 and the crack extending from the second modified region 122 formed in the second step described above are formed so as to extend from the outer edge 103 of the first wafer 100 to the first modified region 121 and the first crack 131 formed along the first line A1. This makes it possible to divide the removal region E of the first wafer 100 circumferentially by the number of second lines A2 (here, four).

Then, using a specified jig or device, the removal area E is removed from the first wafer 100, leaving the effective area R bonded to the second wafer 200 via the device layers 150, 250. This completes the trimming process for the object 11. After that, a process of grinding and thinning the effective area R from the second surface 102 side is performed, after which another wafer can be further bonded to the thinned effective area R and the above series of processes can be repeated.

As described above, in the laser processing method and laser processing apparatus 1 according to this embodiment, laser processing is performed by irradiating laser light L onto the first wafer 100 bonded to the second wafer 200 via the device layers 150, 250. The device layer 150 includes an active area 160 including multiple chips and a peripheral edge portion 170 located outside the active area 160 and surrounding the active area 160. In laser processing, laser light L is irradiated along a first line A1 extending annularly on the peripheral edge portion 170, thereby forming a first modified region 121 along the first line A1. This makes it possible to use the first modified region 121 and the first crack 131 extending from the first modified region 121 to perform trimming, removing the outer edge portion of the wafer as an unnecessary portion (removal region E).

In particular, in the laser processing method and laser processing apparatus 1 according to this embodiment, a preprocessing region 172 is formed on the peripheral edge 170 of the device layer 150, weakening the bond with the second wafer 200. When the preprocessing region 172 is formed in this manner, stress may be generated within the first wafer 100, as described above. The stress within the first wafer 100 caused by the formation of the preprocessing region 172 can be alleviated by forming a modified region 12 on the preprocessing region 172. Therefore, in the laser processing method and laser processing apparatus 1 according to this embodiment, laser light L is irradiated at a position above the preprocessing region 172 to form a first modified region 121, thereby alleviating the stress within the first wafer 100 caused by the formation of the preprocessing region 172 and allowing the first crack 131 to extend obliquely from the first modified region 121 in the intended direction. Therefore, the laser processing method and laser processing apparatus 1 according to this embodiment can suppress degradation in the trimming process of bonded wafers.

In addition, in the laser processing apparatus 1 according to this embodiment, in the first processing process, the control unit 6 performs a first oblique processing process in which the position of the light collection area C is set to a first Y position Y1 in the Y direction and is irradiated with laser light L at a first Z position Z1 in the Z direction, thereby forming a first Z modified area 121a as the first modified area 121; and after the first oblique processing process, the control unit 6 performs a second oblique processing process in which the position of the light collection area C is set to a second Y position Y2 closer to the outer edge 103 than the first Y position Y1 in the Y direction and is irradiated with laser light L at a second Z position Z2 closer to the second surface 102 than the first Z position Z1 in the Z direction, thereby forming a second Z modified area 121b as the first modified area 121 closer to the second surface 102 and outer edge 103 than the first Z modified area 121a, thereby extending the first crack 131 obliquely from the first Z modified area 121a toward the boundary B12. In this way, by sequentially forming at least two diagonally aligned modified regions 12, it is possible to more effectively form diagonal cracks.

Furthermore, in the laser processing apparatus 1 according to this embodiment, in the first processing step, after the second oblique processing step, the control unit 6 performs a vertical processing step in which, at the second Y position Y2, the control unit 6 positions the focusing area C at multiple Z-direction positions closer to the second surface 102 than the second Z position Z2 and irradiates the laser light L, thereby forming multiple first modified regions 121 (third Z modified regions 121c) arranged along the Z direction at the second Y position Y2, and extending the third crack 131b vertically across the multiple first modified regions 121. In this way, after the first oblique processing step and the second oblique processing step are performed at Z positions farther (deeper) from the second surface 102, which is the incident surface of the laser light L, the vertical processing step is performed at a shallower position. Therefore, in either process, it is possible to form a new modified region 12 without being affected by the modified region 12 that has already been formed.

In addition, in the laser processing apparatus 1 according to this embodiment, after the first processing operation, the control unit 6 controls the irradiation unit 3 and the movement units 4 and 5 to irradiate the first wafer 100 with laser light L while moving the focusing area C relative to the first wafer 100 along a second line A2 extending from the outer edge 103 of the first wafer 100 to the first line A1 on the peripheral portion 170 as viewed in the Z direction. This performs a second processing operation to form a second modified area 122 as a modified area 12 along the second line A2. This makes it possible to easily divide the outer edge portion (removal area E) of the first wafer 100 into multiple parts in the circumferential direction by utilizing the second modified area 122 and cracks extending from the second modified area 122. Particularly in this case, the second processing operation is performed after the first processing operation. As a result, the propagation of cracks extending from the second modified region 122 can be stopped by the first modified region 121 already formed along the first line A1 and the cracks extending from the first modified region 121. This prevents a decrease in processing quality.

In addition, in the laser processing apparatus 1 according to this embodiment, the control unit 6 controls the irradiation unit 3 and the movement units 4 and 5 to position the focusing area C at a position on the peripheral edge 170 as viewed from the Z direction, and irradiate the first wafer 100 with laser light L, thereby performing a stress relaxation process (first oblique processing process) to form a modified area 12 (first Z modified area 121a) to relieve stress generated inside the first wafer 100. In particular, the control unit 6 performs the stress relaxation process before extending the first crack 131 to reach the first surface 101.

In this way, with the laser processing apparatus 1 according to this embodiment, a modified region 12 (first Z modified region 121a) is formed to relieve stress within the first wafer 100 before the first crack 131 extending from the first modified region 121 is extended to reach the first surface 101. This prevents the first crack 131 from extending in an unintended direction due to stress within the first wafer 100. Therefore, with the laser processing apparatus 1 according to this embodiment, it is possible to prevent a decrease in the quality of the trimming process of the bonded wafer.

In the laser processing apparatus 1 according to this embodiment, multiple first modified regions 121 are formed in the Z direction along the first line A1. This makes it possible to use the multiple first modified regions 121 and the first cracks 131 extending from the first modified regions 121 to perform trimming, removing the outer edge portion of the wafer as unnecessary portions (removal regions E). The control unit 6 then performs a stress relaxation process before forming the first modified region 121 (second Z modified region 121b) to extend at least the first cracks 131 of the multiple first modified regions 121 so that they reach the first surface 101.

In this way, in the laser processing apparatus 1 according to this embodiment, a first crack 131 extending from the first modified region 121 (first Z modified region 121a) located closest to the first surface 101 of the first wafer 100 (i.e., the device layer 150 side) among the plurality of first modified regions 121 is formed to relieve stress inside the first wafer 100 before processing to extend the first crack 131 to the first surface 101. This prevents the first crack 131 from extending in an unintended direction due to stress inside the first wafer 100. Therefore, the laser processing apparatus 1 according to this embodiment can prevent a decrease in the quality of the trimming process of the bonded wafer.
[Modification of the second embodiment]

Next, a modified example of the second embodiment will be described. First, in the second embodiment, the case where the third processing step for forming the third modified region 123 is not performed has been described. However, in the second embodiment, the third processing step may also be performed, as in the first embodiment. That is, before step S201 (first processing step, first processing step), the control unit 6 may perform the third processing step to form the third modified region 123 as the modified region 12 by irradiating the first wafer 100 with laser light L while positioning the light collection region C at a position different from the first line A1 and the second line A2 on the peripheral portion 170 as viewed in the Z direction. The timing and specific processing content of the third processing step can be the same as in the first embodiment. Furthermore, when the third processing step is performed in the second embodiment, it is also possible to adopt a modification similar to that of the modified example of the first embodiment.

In the second embodiment described above, an example was described in which step S202 (second processing step, second processing treatment) was performed after step S201 (first processing step, first processing treatment) to form the second modified region 122 along the second line A2. However, this order can be changed. This point will be explained in more detail below.

In other words, in the laser processing apparatus 1 according to the second embodiment, the control unit 6 may control the irradiation unit 3 and the movement units 4 and 5 before the first processing process to irradiate the first wafer 100 with laser light L while relatively moving the focusing area C along the second line A2, thereby performing a second processing process to form a second modified area 122 as a modified area 12 along the second line A2. In this case, as in the above case, the second modified area 122 and cracks extending from the second modified area 122 can be used to easily divide the removal area E of the first wafer 100 into multiple parts in the circumferential direction for trimming. In particular, in this case, the second processing process is performed before the first processing process. Therefore, the second modified area 122 formed in the second processing process further relieves stress within the first wafer 100, allowing the first crack 131 extending obliquely to be formed during the first processing process.

On the other hand, in the second embodiment, as in the first embodiment, in the second processing step, the control unit 6 performs a first partial processing step in which the control unit 6 irradiates the laser light L while moving the light collection area C relatively along the first portion A2a of the second line A2, thereby forming the second modified region 122 along the first portion A2a, and a second partial processing step in which the control unit 6 irradiates the laser light L while moving the light collection area C relatively along the second portion A2b of the second line, thereby forming the second modified region 122 along the second portion A2b, and the control unit 6 can perform at least the first partial processing step before the first processing step.

In this case, before the first crack 131 extends to reach the first surface 101, the second modified region 122 formed in the first portion A2a of the second line A2 in addition to the third modified region 123 makes it possible to relieve stress inside the first wafer 100. In this case, the second modified region 122 formed in the first partial processing also functions as a modified region 12 for relieving stress generated inside the first wafer 100. Therefore, the control unit 6 performs the stress relaxation processing simultaneously with the first partial processing.

Furthermore, in this case, the control unit 6 can also perform both the first partial processing and the second partial processing before the first processing. In this case, before the first crack 131 extends to the first surface 101, the second modified region 122 formed in the first portion A2a and the second portion A2b of the second line A2 can relieve stress inside the first wafer 100. In this case, the second modified region 122 formed in the first partial processing and the second partial processing also functions as a modified region 12 for relieving stress generated inside the first wafer 100. Therefore, the control unit 6 performs the stress relaxation processing simultaneously with the first partial processing and the second partial processing.

On the other hand, in the second embodiment, the control unit 6 can also perform the first partial treatment before the first processing treatment and the second partial treatment after the first processing treatment. In this case, when the second modified region 122 is formed in the second portion A2b of the second line A2 that reaches the first line A1, the first modified region 121 has already been formed in the first line A1, so that the extension of cracks extending horizontally from the second modified region 122 is stopped by the first modified region 121.
[Modification common to the first and second embodiments]

In the first and second embodiments described above, an example was described in which the first oblique machining process for forming oblique cracks, the second oblique machining process, and the vertical machining process for forming vertical cracks were performed in this order in steps S102 and S201. However, this order can be changed. More specifically, the control unit 6 may perform the vertical machining process before the first oblique machining process and the second oblique machining process in steps S102 and S201.

That is, in the first processing process, the control unit 6 performs a vertical processing process in which, prior to the first oblique processing process, at the second Y position Y2, the control unit 6 positions the focusing area C at multiple Z-direction positions closer to the second surface 102 than the second Z position Z2 and irradiates the laser light L to form multiple first modified regions 121 (third Z modified regions 121c) arranged along the Z direction at the second Y position Y2, and the third crack 131b extends vertically across the multiple first modified regions 121. In this case, the first oblique processing process and the second oblique processing process can form first cracks 131 extending obliquely in a state in which stress inside the wafer is relieved by the first modified regions 121 formed in the vertical processing process.

In addition, in the first and second embodiments described above, the modified region 12 was formed by irradiating laser light L in the first processing process, the second processing process, and the third processing process, but it is also possible to use different laser light in each process.

In the above first and second embodiments, the control unit 6 controls the irradiation unit 3 and the movement units 4 and 5 to position the focusing area C at multiple Z-direction positions and irradiate the laser light L, thereby forming multiple first modified areas 121 along the Z direction. However, if the object 11 is relatively thin in the Z direction or if processing is performed closer to the first surface 101, the first processing can form a first crack 131 extending from the first Z modified area 121a to the first surface 101 by forming the first Z modified area 121a (without forming the second Z modified area 121b). This is true whether the first crack 131 is an oblique crack inclined relative to the Z direction or a vertical crack extending along the Z direction.

Furthermore, in the above first and second embodiments, the second line A2 extends linearly from the outer edge 103 of the first wafer 100 to the first line A1. However, the second line A2 may be curved as long as it extends from the outer edge 103 to the first line A1. As an example, the second line A2 may be a (partial) spiral curve generated by a combination of rotational movement of the stage 2 around a rotation axis along the Z axis and linear movement of the irradiation unit 3 in the Y direction.

Furthermore, the object 11 in the first and second embodiments is a bonded wafer formed by bonding a first wafer 100 to a second wafer 200. However, the separate member to which the first wafer 100 is bonded is not limited to the second wafer 200.

1...laser processing device, 2...stage (supporting part), 3...irradiation part, 4, 5...moving part, 6...control part, 12...modified area, 13...crack, 100...first wafer (wafer), 101...first surface, 102...second surface, 103...outer edge, 121...first modified area, 121a...first Z modified area, 121b...second Z modified area, 121c...third Z modified area, 122...second modified area, 123...third modified area, 131...first crack, 131b...third crack, 150...device layer, 153...outer edge, 160...active area, 170...periphery, 171...bonding area, 172...pre-processing area, A1...first line, A2...second line, A3...third line, B12...boundary.

Claims (9)

A laser processing apparatus for forming a modified region in a wafer, the laser processing apparatus including a first surface and a second surface opposite to the first surface, the wafer being bonded to another member on the first surface side by irradiating the wafer with laser light using the second surface as an incident surface,
a support for supporting the wafer;
an irradiation unit for irradiating the laser light toward the wafer supported by the support unit;
a moving unit for moving a focused region of the laser light relative to the wafer;
a control unit for controlling the irradiation unit and the movement unit;
Equipped with
a device layer including a plurality of chips and bonded to the separate member is formed on the first surface;
the device layer includes an active area including the plurality of chips, and a peripheral portion located outside the active area so as to surround the active area when viewed from a Z direction intersecting the first surface,
the peripheral portion includes a pre-processing region that includes an outer edge of the device layer and in which the bonding with the separate member is weakened, and a bonding region that is located inside the pre-processing region when viewed from the Z direction;
The control unit controls the irradiation unit and the movement unit to irradiate the wafer with the laser light while relatively moving the focusing area of the laser light along a first line extending in a ring shape on the pre-processing area as viewed in the Z direction, thereby performing a first processing process to form a first modified area as the modified area along the first line, and to form a first crack extending obliquely from the first modified area toward the boundary from the outside of the boundary between the pre-processing area and the bonding area as it moves from the second surface toward the first surface.
Laser processing equipment. In the first processing process, the control unit
a first oblique processing process in which the position of the light collection region is set to a first Y position in a Y direction from the center of the wafer toward the outer edge, and a first Z position in the Z direction, and the laser light is irradiated to form a first Z modified region as the first modified region;
a second oblique processing process in which, after the first oblique processing process, the position of the light collection region is set to a second Y position that is closer to the outer edge of the wafer than the first Y position in the Y direction, and the laser light is irradiated at a second Z position that is closer to the second surface than the first Z position in the Z direction, thereby forming a second Z modified region as the first modified region closer to the second surface and to the outer edge of the wafer than the first Z modified region, and extending the first crack obliquely from the first Z modified region toward the boundary;
To execute
The laser processing device according to claim 1 . In the first processing process, the control unit, after the second oblique processing process, performs a vertical processing process in which the control unit positions the light collection region at a plurality of positions in the Z direction that are closer to the second surface than the second Z position at the second Y position and irradiates the laser light, thereby forming a plurality of the first modified regions arranged along the Z direction at the second Y position, and extending a crack vertically across the plurality of first modified regions.
The laser processing device according to claim 2. In the first processing process, the control unit, before the first oblique processing process, positions the light-collecting region at a plurality of positions in the Z direction that are closer to the second surface than the second Z position at the second Y position, and irradiates the laser light, thereby forming a plurality of the first modified regions arranged along the Z direction at the second Y position, and performs a vertical processing process that extends a crack vertically across the plurality of first modified regions.
The laser processing device according to claim 2. the control unit controls the irradiation unit and the movement unit after the first processing step to irradiate the wafer with the laser light while relatively moving the light collection area along a second line extending from the outer edge of the wafer to the first line on the peripheral portion as viewed in the Z direction, thereby performing a second processing step to form a second modified area as the modified area along the second line.
The laser processing device according to any one of claims 1 to 4. the control unit controls the irradiation unit and the movement unit before the first processing step to irradiate the wafer with the laser light while relatively moving the light collection area along a second line extending from the outer edge of the wafer to the first line on the peripheral portion as viewed in the Z direction, thereby performing a second processing step to form a second modified region as the modified region along the second line.
The laser processing device according to any one of claims 1 to 4. the control unit performs a third processing process to form a third modified region as the modified region by irradiating the wafer with the laser light while positioning the light collection region at a position different from the first line and the second line on the peripheral portion as viewed from the Z direction, before the first processing process.
7. The laser processing device according to claim 5 or 6. a laser processing step of irradiating a wafer including a first surface and a second surface opposite to the first surface, the wafer being bonded to another member on the first surface side with laser light using the second surface as an incident surface to form a modified region in the wafer;
a device layer including a plurality of chips and bonded to the separate member is formed on the first surface;
the device layer includes an active area including the plurality of chips, and a peripheral portion located outside the active area so as to surround the active area when viewed from a Z direction intersecting the first surface,
the peripheral portion is a region including an outer edge of the device layer, and includes a pre-processing region where the bond with the separate member is weakened, and a bonding region located inside the pre-processing region;
The laser processing step includes a first processing step of irradiating the wafer with the laser light while relatively moving a focusing area of the laser light along a first line extending in an annular shape on the pre-processing area as viewed from the Z direction, thereby forming a first modified area as the modified area along the first line, and forming a first crack extending obliquely from the first modified area so as to extend from outside the boundary between the pre-processing area and the bonding area toward the boundary as it moves from the second surface toward the first surface.
Laser processing method. A laser processing apparatus for forming a modified region in a wafer, the laser processing apparatus including a first surface and a second surface opposite to the first surface, the wafer being bonded to another member on the first surface side by irradiating the wafer with laser light using the second surface as an incident surface,
a support for supporting the wafer;
an irradiation unit for irradiating the laser light toward the wafer supported by the support unit;
a moving unit for moving a focused region of the laser light relative to the wafer;
a control unit for controlling the irradiation unit and the movement unit;
Equipped with
a device layer including a plurality of chips and bonded to the separate member is formed on the first surface;
the device layer includes an active area including the plurality of chips, and a peripheral portion located outside the active area so as to surround the active area when viewed from a Z direction intersecting the first surface,
The control unit controls the irradiation unit and the movement unit,
a first processing step of irradiating the wafer with the laser light while relatively moving the light focusing region along a first line extending annularly on the peripheral edge portion as viewed in the Z direction, thereby forming a first modified region as the modified region along the first line and forming a first crack from the first modified region to the first surface;
a second processing step of irradiating the wafer with the laser light while relatively moving the light focusing region along a second line extending from the outer edge of the wafer to the first line on the peripheral portion as viewed in the Z direction, thereby forming a second modified region as the modified region along the second line;
a stress relaxation process in which the laser beam is irradiated onto the wafer by positioning the light collection region at a position different from the first line and the second line on the peripheral portion as viewed from the Z direction, thereby forming the modified region for relaxing stress generated inside the wafer;
Run
the control unit performs the stress relaxation treatment before extending the first crack to the first surface ,
the peripheral portion includes a pre-processing region that includes an outer edge of the device layer and in which the bonding with the separate member is weakened, and a bonding region that is located inside the pre-processing region when viewed from the Z direction;
In the stress relaxation process, the control unit positions the light collection region on at least the pretreatment region and irradiates the laser light, thereby forming the modified region for relaxing the stress on at least the pretreatment region.
Laser processing equipment.