Wafer processing method

Abstract

To provide a wafer processing method that suppresses damage to a device when dividing an outer peripheral area from a device area of the wafer and dividing the back side from the front side of the device area at the same time, and suppress a decrease in the number of chips that can be manufactured from the wafer.SOLUTION: A first peeling layer such that a first bottom surface is located on the surface side of a wafer, and a second bottom surface having a shorter diameter than the first bottom surface is along the side surface of a truncated cone located inside the wafer, and a second release layer along the upper base surface of the truncated cone are formed inside the wafer. Then, by applying external force to the wafer along the thickness direction of the wafer, the wafer is divided with the first release layer and the second release layer as division starting points.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a wafer processing method. [Background technology]

[0002] Semiconductor device (hereinafter simply referred to as "device") chips are generally manufactured using a disk-shaped wafer made of a semiconductor material such as silicon (Si). Specifically, this wafer is divided by dividing lines set in a grid pattern, and devices are formed on the front surface of each of the multiple regions. Then, chips are manufactured by dividing this wafer along the dividing lines.

[0003] Furthermore, a wafer may be provided with through-silicon vias (TSVs (Through-Silicon Vias)) for the purpose of increasing the integration of a package containing multiple chips. In this package, for example, electrodes included in different chips can be electrically connected via the TSVs.

[0004] For example, TSVs are formed on a wafer in the following order: First, grooves are formed on the front side of the wafer. Then, TSVs are formed in these grooves. Next, the front side of the wafer is bonded to a support wafer. Next, the back side of the wafer is ground until the TSVs are exposed on the back side of the wafer.

[0005] Here, in many cases, the outer peripheral region of a wafer is chamfered for the purpose of preventing cracks, etc. When the back surface side of a wafer with a chamfered outer peripheral region is ground until the thickness of the wafer is reduced to half or less, the back surface side of the outer peripheral region takes on a knife-edge shape.

[0006] In this case, stress may be concentrated on the back surface side of the outer peripheral region during grinding of the wafer, making the wafer more susceptible to cracking and reducing the yield of chips obtained from the wafer. Therefore, it has been proposed to remove a portion of the front surface side of the outer peripheral region (so-called edge trimming) prior to grinding the back surface side of the wafer (see, for example, Patent Document 1).

[0007] As a result, when the remaining portion on the back side of the outer peripheral region is removed by grinding, the side surface of the wafer becomes approximately perpendicular to the front and back surfaces. Therefore, stress concentration does not occur on the back side of the outer peripheral region during wafer grinding, making the wafer less likely to crack. As a result, a decrease in chip yield can be suppressed.

[0008] However, if the backside of the wafer is ground after edge trimming until the TSVs are exposed on the backside of the wafer, the amount of wafer ground increases, and the grinding stone required to grind the wafer wears out, which may increase the cost of the chips or packages manufactured using the wafer and may take longer to process.

[0009] In view of this, a method for dividing a wafer using a laser beam with a wavelength that can pass through the wafer has been proposed (see, for example, Patent Document 2). In this method, first, a region of the wafer where diffuse reflection does not occur when irradiated with the laser beam (specifically, a region inside the chamfered outer peripheral region) is irradiated with a laser beam in a circular pattern with the focal point positioned on the front surface of the wafer.

[0010] This forms a peeling layer (cylindrical peeling layer) whose bottom surface is located on the surface side of the wafer and whose top surface follows the side of a cylinder located inside the wafer. Next, a laser beam is irradiated to the region inside this cylindrical peeling layer with the focal point positioned on the top surface of the cylinder. This forms a peeling layer (disk-shaped peeling layer) that follows the top surface of the cylinder.

[0011] Next, an external force is applied to the wafer to separate it at the cylindrical and disc-shaped separation layers, i.e., the wafer is separated from the region where devices are formed (device region) to the outer periphery region, and also from the front side to the back side of the device region.

[0012] When the wafer is divided in this manner, the amount of wafer grinding required to expose the TSVs on the backside of the wafer can be reduced, and the amount of wear on the grinding stone required to grind the wafer can be reduced, thereby preventing increases in the cost and prolonged processing time of the chips or packages manufactured using the wafer. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-158239 [Patent Document 2] Japanese Patent Publication No. 2020-136442 Summary of the Invention [Problem to be solved by the invention]

[0014] When dividing a wafer at the cylindrical release layer and the disk-shaped release layer as described above, it is necessary to separate the outer peripheral region of the wafer from the device region along the radial direction of the wafer, and also to separate the back side of this device region from the front side along the thickness direction of the wafer.

[0015] That is, the direction of the external force required to separate the outer peripheral region of the wafer from the device region is perpendicular to the direction of the external force required to separate the back side of the device region from the front side, and therefore it is not necessarily easy to simultaneously divide the wafer at the cylindrical peeling layer and the disk-shaped peeling layer by applying an external force along a specific direction to the wafer.

[0016] For example, when dividing a wafer by applying an external force to the wafer along the thickness direction, the side surface of the device region newly exposed by dividing the wafer at the cylindrical peeling layer and the inner surface of the outer peripheral region may come into contact with each other, which may cause cracks to propagate toward the devices formed on the surface side of the device region, resulting in damage to the devices.

[0017] Furthermore, as described above, the cylindrical peeling layer is formed in a region of the wafer where diffuse reflection does not occur when the laser beam is irradiated (specifically, the region inside the chamfered outer peripheral region). Therefore, when the wafer is divided at this cylindrical peeling layer, the region near the inside of the outer peripheral region of the wafer cannot be used to manufacture device chips. In this case, the number of chips that can be manufactured from this wafer may be reduced.

[0018] In view of the above, an object of the present invention is to provide a wafer processing method that can suppress damage to devices when dividing the peripheral region from the device region of the wafer and dividing the back side from the front side of the device region simultaneously, and can suppress a decrease in the number of chips that can be manufactured from the wafer. [Means for solving the problem]

[0019] According to the present invention, a wafer processing method includes irradiating a first wafer having a plurality of devices formed on its front surface side and a chamfered outer peripheral region with a laser beam having a wavelength that passes through the first wafer to form a peeling layer inside the first wafer, and then dividing the first wafer using the peeling layer as a division starting point, the method comprising the steps of: bonding the front surface side of the first wafer to the front surface side of a second wafer; and irradiating a region of the first wafer that is more inward than the outer peripheral region with the laser beam such that the closer the focal point is to the outer peripheral region, the closer it is to the front surface of the first wafer, thereby forming a first bottom surface located on the front surface side of the first wafer and a second bottom surface having a diameter larger than that of the first bottom surface. a first separation layer forming step of forming a first separation layer whose short second bottom surface follows a side surface of a truncated cone located inside the first wafer; a second separation layer forming step of forming a second separation layer that follows the second bottom surface of the truncated cone by irradiating a region of the first wafer that is inside the first separation layer with the laser beam so that the focal point is positioned on the second bottom surface of the truncated cone; and a dividing step of dividing the first wafer using the first separation layer and the second separation layer as dividing starting points by applying an external force to the first wafer along a thickness direction of the first wafer after performing the bonding step, the first separation layer forming step, and the second separation layer forming step. In the first peeling layer forming step, the laser beam is split so as to generate a plurality of focal points aligned along the radial direction of the first wafer in a plan view. A method for processing a wafer is provided. 。

[0020] This wafer processing method may include at least one of the following items (1) to (3): (1) in the dividing step, an external force is applied to the outer peripheral region of the first wafer; (2) the first wafer is made of silicon carbide or gallium nitride; (3) in the dividing step, ultrasonic waves are applied to the first wafer prior to dividing the first wafer; and Preferably, the first release layer forming step is performed before the second release layer forming step is performed. [Effects of the Invention]

[0022] In the present invention, a first release layer is formed inside the wafer, the first bottom surface of which is located on the front surface side of the wafer, and a second bottom surface of which is located inside the wafer and has a diameter smaller than that of the first bottom surface and follows the side surface of the truncated cone, and a second release layer is formed inside the wafer and follows the second bottom surface of the truncated cone.Then, in the present invention, an external force is applied to the wafer along the thickness direction of the wafer, thereby dividing the wafer using the first release layer and the second release layer as division starting points.

[0023] In this wafer, the first separation layer is formed along the side surface of the truncated cone. In this case, when the wafer is divided, the side surface of the region where devices are formed (device region) newly exposed by dividing the wafer at the first separation layer and the inner surface of the outer peripheral region are unlikely to come into contact with each other. Therefore, in the present invention, the probability that cracks will propagate toward the devices formed on the surface side of the device region is also low, and damage to the devices can be suppressed.

[0024] Furthermore, in this wafer, cracks tend to propagate from the first separation layer in a direction along the side surface of the truncated cone. In this case, the probability that the cracks will propagate toward the devices formed on the front surface side of the device region is reduced. Therefore, in the present invention, a decrease in the number of chips that can be manufactured from the wafer can be suppressed. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1(A) is a top view that schematically shows an example of a wafer, and FIG. 1(B) is a cross-sectional view that schematically shows an example of a wafer. [Figure 2] FIG. 2 is a flow chart schematically showing an example of a wafer processing method. [Figure 3] FIG. 3 is a cross-sectional view that schematically shows how the front surface side of the wafer is bonded to the front surface side of the support wafer. [Figure 4] FIG. 4 is a perspective view schematically showing an example of a laser processing device used in the first release layer forming step. [Figure 5]FIG. 5 is a diagram schematically showing how a laser beam travels in a laser beam irradiation unit. [Figure 6] FIG. 6 is a cross-sectional view that schematically shows how a laser beam is irradiated onto a region inside the outer peripheral region of the wafer. [Figure 7] FIG. 7 is a cross-sectional view that schematically shows how a laser beam is irradiated onto a region inside the first separation layer of the wafer. [Figure 8] FIG. 8 is a partial cross-sectional side view that schematically shows how the wafer is divided. DETAILED DESCRIPTION OF THE INVENTION

[0026] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1(A) is a top view schematically showing an example of a wafer, and Fig. 1(B) is a cross-sectional view schematically showing an example of the wafer. The wafer 11 shown in Figs. 1(A) and 1(B) is made of, for example, silicon, and has a front surface 11a and a back surface 11b that are generally parallel.

[0027] This wafer 11 is divided into a plurality of regions by a plurality of planned dividing lines that intersect with each other, and devices 13 such as ICs (Integrated Circuits), LSIs (Large Scale Integration), semiconductor memories, or CMOS (Complementary Metal Oxide Semiconductor) image sensors are formed on the surface 11a side of each region.

[0028] Furthermore, grooves in which TSVs are provided may be formed on the front surface 11a side of the wafer 11. The peripheral region of the wafer 11 is chamfered. That is, the side surface 11c of the wafer 11 is curved so as to be convex outward. Note that no devices 13 are formed in the peripheral region of the wafer 11. That is, the region of the wafer 11 in which the devices 13 are formed (device region) is surrounded by the peripheral region.

[0029] There are no limitations on the material, shape, structure, size, etc. of the wafer 11. The wafer 11 may be made of, for example, a semiconductor material other than silicon (e.g., silicon carbide (SiC) or gallium nitride (GaN)). Similarly, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the devices 13.

[0030] 2 is a flow chart showing a typical example of a wafer processing method. Briefly, in this method, a laser beam having a wavelength that can be transmitted through the wafer 11 is irradiated onto the wafer 11 to form a peeling layer inside the wafer 11, and then the wafer 11 is divided using this peeling layer as the division starting point.

[0031] Specifically, in this method, first, the front surface 11a of the wafer (first wafer) 11 is bonded to the front surface of a support wafer (second wafer) (bonding step: S1). Fig. 3 is a cross-sectional view schematically showing the manner in which the front surface 11a of the wafer 11 is bonded to the front surface of the support wafer.

[0032] The support wafer 15 to be bonded to the wafer 11 has, for example, the same shape as the wafer 11. Similar to the wafer 11, a plurality of devices may be formed on the front surface 15a of the support wafer 15. An adhesive 17 such as an acrylic adhesive or an epoxy adhesive is provided on the front surface 15a of the support wafer 15.

[0033] Then, in the bonding step (S1), while the back surface 15b side of the support wafer 15 is supported, the front surface 11a of the wafer 11 is pressed against the front surface 15a of the support wafer 15 via the adhesive 17. As a result, a bonded wafer is formed in which the front surface 11a side of the wafer 11 is bonded to the front surface 15a side of the support wafer 15.

[0034] Next, a peeling layer (first peeling layer) is formed so that its first bottom surface (lower bottom surface) is located on the surface 11a side of the wafer (first wafer) 11 and its second bottom surface (upper bottom surface) having a diameter shorter than that of the first bottom surface follows the side of the truncated cone located inside the wafer 11 (first peeling layer forming step: S2), and a peeling layer (second peeling layer) follows the upper bottom surface of the truncated cone (second peeling layer forming step: S3).

[0035] Fig. 4 is a perspective view showing a schematic example of a laser processing device used in the first release layer forming step (S2) and the second release layer forming step (S3). Note that the X-axis direction (left-right direction) and the Y-axis direction (front-back direction) shown in Fig. 4 are directions perpendicular to each other on a horizontal plane, and the Z-axis direction (up-down direction) is a direction (vertical direction) perpendicular to the X-axis direction and the Y-axis direction, respectively.

[0036] The laser processing device 2 shown in Fig. 4 has a base 4 that supports each of the components. A horizontal movement mechanism 6 is disposed on the upper surface of the base 4. The horizontal movement mechanism 6 is fixed to the upper surface of the base 4 and has a pair of Y-axis guide rails 8 that extend along the Y-axis direction.

[0037] A Y-axis moving plate 10 is connected to the upper surfaces of the pair of Y-axis guide rails 8 in a manner that allows it to slide along the pair of Y-axis guide rails 8. A screw shaft 12 extending along the Y-axis direction is disposed between the pair of Y-axis guide rails 8. A motor 14 for rotating the screw shaft 12 is connected to the front end (one end) of this screw shaft 12.

[0038] A ball screw is formed by providing a nut portion (not shown) that houses balls that roll on the surface of the rotating screw shaft 12 on the surface of the screw shaft 12 where the spiral groove is formed. That is, when the screw shaft 12 rotates, the balls circulate inside the nut portion, and the nut portion moves along the Y-axis direction.

[0039] Furthermore, this nut portion is fixed to the underside of the Y-axis moving plate 10. Therefore, when the screw shaft 12 is rotated by the motor 14, the Y-axis moving plate 10 moves along the Y-axis direction together with the nut portion. In addition, a pair of X-axis guide rails 16 extending along the X-axis direction are fixed to the upper surface of the Y-axis moving plate 10.

[0040] An X-axis moving plate 18 is connected to the upper surfaces of the pair of X-axis guide rails 16 in a manner that allows it to slide along the pair of X-axis guide rails 16. A screw shaft 20 extending along the X-axis direction is disposed between the pair of X-axis guide rails 16. A motor 22 for rotating the screw shaft 20 is connected to one end of the screw shaft 20.

[0041] Furthermore, a nut portion (not shown) that houses balls that roll on the surface of the rotating screw shaft 20 is provided on the surface of the screw shaft 20 on which the spiral groove is formed, thereby forming a ball screw. That is, when the screw shaft 20 rotates, the balls circulate inside the nut portion, and the nut portion moves along the X-axis direction.

[0042] Furthermore, this nut portion is fixed to the underside of the X-axis moving plate 18. Therefore, when the screw shaft 20 is rotated by the motor 22, the X-axis moving plate 18 moves along the X-axis direction together with the nut portion.

[0043] A cylindrical table base 24 is disposed on the upper surface side of the X-axis moving plate 18. A holding table 26 for holding the above-mentioned bonded wafer is disposed on the upper part of this table base 24. This holding table 26 has, for example, a circular upper surface (holding surface) parallel to the X-axis direction and the Y-axis direction, and a porous plate 26a is exposed on this holding surface.

[0044] A rotary drive source (not shown), such as a motor, is connected to the bottom of the table base 24. When this rotary drive source operates, the holding table 26 rotates around a rotation axis that passes through the center of the holding surface and is parallel to the Z-axis direction. When the above-mentioned horizontal movement mechanism 6 operates, the holding table 26 moves along the X-axis and / or Y-axis directions.

[0045] Furthermore, the porous plate 26a is connected to a suction source (not shown) such as a vacuum pump via a flow path or the like provided inside the holding table 26. When this suction source is activated, a negative pressure is generated in the space near the holding surface of the holding table 26.

[0046] A support structure 30 having side surfaces that are generally parallel to the Y-axis direction and the Z-axis direction is provided on the rear region of the base 4. A vertical movement mechanism 32 is disposed on the side surface of this support structure 30. The vertical movement mechanism 32 is fixed to the side surface of the support structure 30 and has a pair of Z-axis guide rails 34 that extend along the Z-axis direction.

[0047] A Z-axis moving plate 36 is connected to the front surfaces of the pair of Z-axis guide rails 34 in a manner that allows it to slide along the pair of Z-axis guide rails 34. A screw shaft (not shown) extending along the Z-axis direction is disposed between the pair of Z-axis guide rails 34. A motor 38 for rotating the screw shaft is connected to the upper end (one end) of this screw shaft.

[0048] A nut (not shown) that houses balls that roll on the surface of the rotating screw shaft is provided on the surface of the screw shaft where the spiral grooves are formed, forming a ball screw. That is, when the screw shaft rotates, the balls circulate inside the nut, causing the nut to move along the Z-axis direction.

[0049] Furthermore, this nut portion is fixed to the rear surface side of the Z-axis moving plate 36. Therefore, when the screw shaft disposed between the pair of Z-axis guide rails 34 is rotated by the motor 38, the Z-axis moving plate 36 moves along the Z-axis direction together with the nut portion.

[0050] A support 40 is fixed to the front surface side of the Z-axis moving plate 36. This support 40 supports a part of the laser beam irradiation unit 42. Figure 5 is a diagram showing a schematic view of the laser beam LB traveling in the laser beam irradiation unit 42. Note that in Figure 5, some of the components of the laser beam irradiation unit 42 are shown in functional blocks.

[0051] The laser beam irradiation unit 42 has a laser oscillator 44 fixed to the base 4. This laser oscillator 44 has, for example, Nd:YAG or the like as a laser medium, and emits a laser beam LB having a wavelength (for example, 1342 nm) that can be transmitted through the wafer 11. This laser beam LB is, for example, a pulsed laser beam having a frequency of 60 kHz.

[0052] The output of the laser beam LB is adjusted by the attenuator 46, and then the laser beam LB is supplied to the spatial light modulator 48. The laser beam LB is branched in the spatial light modulator 48. For example, the spatial light modulator 48 branches the laser beam LB, which has been adjusted by the attenuator 46, so that the laser beam LB emitted from an irradiation head 52 (described later) forms a plurality of focal points that differ from one another in both positions (coordinates) in a plane parallel to the X-axis direction and the Y-axis direction (XY coordinate plane) and in positions (heights) in the Z-axis direction.

[0053] Furthermore, the laser beam LB branched by the spatial light modulator 48 is reflected by a mirror 50 and guided to an irradiation head 52. This irradiation head 52 houses a condenser lens (not shown) that condenses the laser beam LB, and the like. The laser beam LB condensed by this condenser lens is then emitted toward the holding surface of the holding table 26.

[0054] 4, the irradiation head 52 is provided at the front end of a cylindrical housing 54. A support 40 is fixed to the rear side of the housing 54. Furthermore, an imaging unit 56 is fixed to the front side of the housing 54.

[0055] The imaging unit 56 includes, for example, a light source such as an LED (Light Emitting Diode), an objective lens, and an imaging element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor.

[0056] When the above-described vertical movement mechanism 32 operates, the laser beam irradiation unit 42 and the imaging unit 56 move along the Z-axis direction. Furthermore, a cover (not shown) that covers the above-described components is provided on the base 4. A touch panel 58 is disposed on the front surface of this cover.

[0057] The touch panel 58 is configured by an input device such as a capacitive or resistive touch sensor, and a display device such as a liquid crystal display or an organic EL (Electro Luminescence) display, and functions as a user interface.

[0058] In the laser processing apparatus 2, for example, the first separation layer forming step (S2) and the second separation layer forming step (S3) are performed in the following order: Specifically, first, the bonded wafer is placed on the holding table 26 so that the center of the back surface 15b of the support wafer 15 of the bonded wafer coincides with the center of the holding surface of the holding table 26.

[0059] Next, the suction source communicating with the porous plate 26a is operated so that the bonded wafer is held by the holding table 26. Next, the imaging unit 56 images the back surface 11b side of the wafer 11 of the bonded wafer to form an image.

[0060] Next, with reference to this image, the horizontal movement mechanism 6 is operated so that the irradiation head 52 of the laser beam irradiation unit 42 is positioned directly above an area slightly inside the outer periphery of the wafer 11 .

[0061] Next, the laser beam irradiation unit 42 is operated so that the laser beam LB, which is branched so that the focal point approaches the surface 11a of the wafer 11 as it approaches the outer periphery region, is irradiated onto the wafer 11.

[0062] 6 is a cross-sectional view schematically showing how a laser beam LB is irradiated onto a region inside the outer circumferential region of the wafer 11. This laser beam LB forms a plurality of (e.g., eight) focal points, the positions of which are shifted by 10 μm from each other within the wafer 11, in both the radial direction (direction perpendicular to the Z-axis direction) and thickness direction (Z-axis direction) of the wafer 11.

[0063] In this case, modified regions 19 in which the crystal structure of the material constituting the wafer 11 is disturbed are formed inside the wafer 11, with each of the multiple focal points as the center. That is, multiple modified regions 19 are formed that are aligned linearly along the radial direction of the wafer 11 in a plan view, and the acute angle formed by this line and the surface 11a of the wafer 11 is 45°.

[0064] The acute angle formed between the linearly arranged modified regions 19 and the surface 11a of the wafer 11 is not limited to 45°. In other words, the laser beam LB may be irradiated onto the wafer 11 so as to form a plurality of focal points whose spacing between adjacent focal points in the radial direction of the wafer 11 is different from its spacing in the thickness direction.

[0065] Furthermore, cracks 21 extend from each of the multiple modified regions 19 so as to connect adjacent pairs of modified regions 19. As a result, a delamination layer including the multiple modified regions 19 and the cracks 21 extending from each of the multiple modified regions 19 is formed inside the wafer 11.

[0066] Next, while the laser beam irradiation unit 42 is kept operating, the rotary drive source connected to the lower part of the table base 24 is operated so as to rotate the holding table 26 that holds the bonded wafer at least once.

[0067] As a result, a peeling layer (first peeling layer) is formed in a region inside the outer peripheral region of the wafer 11, with its lower bottom surface located on the surface 11a side of the wafer 11 and its upper bottom surface following the side of the truncated cone located inside the wafer 11.

[0068] Next, the horizontal movement mechanism 6 is operated so that the irradiation head 52 of the laser beam irradiation unit 42 is positioned directly above a region slightly inside the first peeled layer of the wafer 11. Next, the laser beam irradiation unit 42 is operated to irradiate the branched laser beam LB so that all of the focal points are positioned on the upper and bottom surfaces of the truncated cone.

[0069] 7 is a cross-sectional view schematically showing how a laser beam LB is irradiated onto a region inside the first peeling layer of the wafer 11. This laser beam LB is branched so as to form a plurality of (e.g., 2 to 10) focal points arranged at equal intervals (e.g., 5 μm to 15 μm) in a direction perpendicular to the Z-axis direction (the depth direction of the paper in FIG. 7).

[0070] Next, while the laser beam irradiation unit 42 is operating, the horizontal movement mechanism 6 is operated to move the holding table 26 that holds the bonded wafer. For example, when the laser beam LB is branched so as to form a plurality of focusing points that are arranged at equal intervals in the X-axis direction, the horizontal movement mechanism 6 is operated to move the holding table 26 along the Y-axis direction.

[0071] As a result, a peeling layer including a plurality of modified regions 19 and cracks 21 extending from each of the plurality of modified regions 19 is formed in a linear region inside the first peeling layer of the wafer 11. Next, the operation of the laser beam irradiation unit 42 is stopped.

[0072] Next, the horizontal movement mechanism 6 is operated to move the holding table 26 in a direction perpendicular to the linear region where the peeling layer has already been formed. That is, when the laser beam LB is branched to form a plurality of focusing points arranged at equal intervals in the X-axis direction, the horizontal movement mechanism 6 is operated to move the holding table 26 along the X-axis direction.

[0073] Next, the laser beam irradiation unit 42 and the horizontal movement mechanism 6 are operated so that a peeling layer is formed in a linear region parallel to the linear region where the peeling layer has already been formed. Furthermore, the same operation is repeated until a peeling layer is formed from the region on one end side of the wafer 11 inside the first peeling layer to the region on the other end side.

[0074] As a result, a separation layer (second separation layer) that conforms to the upper bottom surface of the truncated cone is formed in a region inside the first separation layer of the wafer 11. This completes the first separation layer formation step (S2) and the second separation layer formation step (S3).

[0075] In the method shown in Figure 3, after performing the first peeling layer formation step (S2) and the second peeling layer formation step (S3), the wafer 11 is divided by applying an external force to the wafer 11 along the thickness direction of the wafer 11, using the first peeling layer and the second peeling layer as the dividing starting points (dividing step: S3).

[0076] Fig. 8 is a partial cross-sectional side view schematically showing how the wafer 11 is divided. The dividing step (S3) is performed, for example, by a dividing apparatus 60 shown in Fig. 8. This dividing apparatus 60 has a holding table 62 that holds a bonded wafer including the wafer 11 on which the first and second separation layers are formed.

[0077] The holding table 62 has a circular upper surface (holding surface), and a porous plate (not shown) is exposed on this holding surface. Furthermore, this porous plate is in communication with a suction source (not shown), such as a vacuum pump, via a flow path or the like provided inside the holding table 62. When this suction source is activated, negative pressure is generated in the space near the holding surface of the holding table 62.

[0078] Moreover, a split unit 64 is provided above the holding table 62. This split unit 64 has a cylindrical support member 66. To the top of this support member 66, for example, a ball screw type lifting mechanism (not shown) is connected, and by operating this lifting mechanism, the split unit 64 moves up and down.

[0079] The lower end of the support member 66 is fixed to the center of the upper part of a disk-shaped gripping claw base 68. A plurality of gripping claws 70 are provided below the outer circumferential region of the gripping claw base 68 at approximately equal intervals along the circumferential direction of the gripping claw base 68. Each gripping claw 70 has a plate-shaped erected portion 70a extending downward.

[0080] The upper end of this standing portion 70a is connected to an actuator such as an air cylinder built into the gripping claw base 68, and by operating this actuator, the gripping claws 70 move along the radial direction of the gripping claw base 68. In addition, on the inner surface of the lower end of this standing portion 70a, a plate-shaped claw portion 70b is provided which extends toward the center of the gripping claw base 68 and becomes thinner the closer it is to the center of the gripping claw base 68.

[0081] In the dividing apparatus 60, the dividing step (S3) is performed, for example, in the following order: Specifically, first, the bonded wafer including the wafer 11 on which the first and second separation layers are formed is placed on the holding table 26 so that the center of the back surface 15b of the support wafer 15 of the bonded wafer coincides with the center of the holding surface of the holding table 26.

[0082] Next, a suction source communicating with the porous plate exposed on the holding surface is operated so that the bonded wafer is held by the holding table 62. Next, an actuator is operated so that each of the plurality of gripping jaws 70 is positioned radially outward of the gripping jaw base 68.

[0083] Next, the lifting mechanism is operated to position the tip of each of the claw portions 70b of the multiple gripping claws 70 at the same height as the adhesive 17 on the bonded wafer. Next, the actuator is operated to bring the claw portions 70b into contact with the bonded wafer. Next, the lifting mechanism is operated to raise the claw portions 70b.

[0084] As a result, an upward external force, i.e., an external force along the thickness direction of the wafer 11, is applied to the outer peripheral region of the wafer 11. As a result, the crack 21 contained in the first separation layer and / or the second separation layer further extends, and the wafer 11 is divided into the front surface 11a side (lower surface side) and the back surface 11b side (upper surface side).

[0085] 2, a first peeling layer is formed inside the wafer 11, the lower surface of which is located on the front surface 11a side of the wafer 11 and the upper surface of which follows the side of a truncated cone located inside the wafer 11, and a second peeling layer is formed along the upper surface of this truncated cone. Then, in this method, an external force is applied to the wafer 11 along the thickness direction of the wafer 11, thereby dividing the wafer 11 using the first peeling layer and the second peeling layer as dividing starting points.

[0086] Here, in this wafer 11, the first separation layer is formed along the side surface of the truncated cone. In this case, when dividing the wafer 11, the side surface of the region where devices are formed (device region) newly exposed by dividing the wafer at the first separation layer and the inner surface of the outer peripheral region are unlikely to come into contact with each other. Therefore, in the method shown in Fig. 2, the probability that cracks will propagate toward the devices 13 formed on the surface side of the device region is also low, and damage to the devices 13 can be suppressed.

[0087] Furthermore, in this wafer 11, cracks tend to propagate from the first separation layer in a direction along the side surface of the truncated cone. In this case, the probability that the cracks will propagate toward the devices 13 formed on the front surface side of the device region is reduced. Therefore, in the method shown in FIG. 2, a decrease in the number of chips that can be manufactured from the wafer 11 can be suppressed.

[0088] The above-described wafer processing method is one embodiment of the present invention, and the present invention is not limited to the above-described method. For example, in the present invention, after the first and second release layers are formed on the wafer 11, the front surface 11a of the wafer 11 may be bonded to the front surface 15a of the support wafer 15. That is, in the present invention, the bonding step (S1) may be performed after the first release layer forming step (S2) and the second release layer forming step (S3) are performed.

[0089] In addition, in the present invention, the order of the first release layer forming step (S2) and the second release layer forming step (S3) is not limited. That is, in the present invention, the first release layer forming step (S2) may be performed after the second release layer forming step (S3).

[0090] Furthermore, in the first peeling layer formation step (S2) of the present invention, it is sufficient to form a peeling layer whose lower bottom surface is located on the surface 11a side of the wafer 11 and whose upper bottom surface follows the side of a truncated cone located inside the wafer 11, and the method for doing so is not limited to the method described above.

[0091] For example, in the first peeling layer forming step (S2) of the present invention, the laser beam LB may be irradiated onto the wafer 11 while operating the horizontal movement mechanism 6 and the vertical movement mechanism 32 in addition to or instead of the rotation drive source connected to the lower part of the table base 24. That is, the laser beam LB may be irradiated onto the wafer 11 not only by rotating the wafer 11 but also by changing the coordinate and height of the focal point on the XY coordinate plane.

[0092] In this case, a non-branched laser beam LB may be used. In other words, even when a laser beam LB having only one focal point is used, by rotating the wafer 11 and irradiating the wafer 11 with the laser beam LB while changing the coordinate and height of the focal point on the XY coordinate plane, it is possible to form a peeling layer on the wafer 11 that follows the side surface of the truncated cone.

[0093] In the first separation layer forming step (S2) of the present invention, the laser beam LB may be irradiated multiple times with the same or adjacent focal points. In this case, the size of the modified region 19 included in the separation layer increases, and the cracks 21 included in the separation layer further extend. Therefore, in this case, the wafer 11 can be more easily divided in the division step (S4).

[0094] Furthermore, in the first separation layer formation step (S2) of the present invention, the laser beam LB may be irradiated onto the wafer 11 so that adjacent modified regions 19 are directly connected to each other rather than being connected via the cracks 21. In this case, the shape of the separation layer can be determined independently of the shape of the cracks 21 propagating from the modified regions 19, thereby enabling stable processing of the wafer 11.

[0095] Furthermore, in the second release layer forming step (S3) of the present invention, it is only necessary to form a release layer that conforms to the upper bottom surface of the truncated cone, and the method for doing so is not limited to the above-mentioned method. For example, in the second release layer forming step (S3) of the present invention, a non-branched laser beam LB may be used.

[0096] Furthermore, in the second separation layer forming step (S3) of the present invention, the laser beam LB may be irradiated onto the wafer 11 while operating a rotary drive source connected to the lower part of the table base 24 in addition to or instead of the horizontal movement mechanism 6. That is, the laser beam LB may be annularly irradiated onto the region of the wafer 11 that is inside the first separation layer.

[0097] Furthermore, in the second peeling layer formation step (S3) of the present invention, similar to the first peeling layer formation step (S2) of the present invention, multiple irradiations of the laser beam LB with the same or close focal points may be carried out, and the laser beam LB may be irradiated onto the wafer 11 so that adjacent modified regions 19 are connected to each other directly rather than via cracks 21.

[0098] Furthermore, in the dividing step (S4) of the present invention, prior to dividing the wafer 11 having the first and second separation layers formed thereon, ultrasonic waves may be applied to the wafer 11. In this case, the cracks 21 contained in the first and second separation layers are extended, making it even easier to divide the wafer 11.

[0099] Furthermore, if it is possible to extend the crack 21 in the dividing step (S4), the first and second peeling layers do not have to be connected. For example, the second peeling layer may be formed at a position slightly farther or closer to the front surface 11a of the wafer 11 than the upper bottom surface of the truncated cone. Similarly, the second peeling layer may be formed in a circular shape with a diameter shorter than the upper bottom surface of the truncated cone.

[0100] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0101] 11: Wafer (first wafer) (11a: front surface, 11b: back surface, 11c: side surface) 13: Device 15: Support wafer (second wafer) (15a: front surface, 15b: back surface) 17: Adhesive 19: Modified area 21: Crack 2: Laser processing equipment 4: Base 6: Horizontal movement mechanism 8: Y-axis guide rail 10: Y-axis moving plate 12: Screw shaft 14: Motor 16: X-axis guide rail 18: X-axis moving plate 20: Screw shaft 22: Motor 24: Table base 26: Chuck table (holding unit) (26a: holding surface) 30:Support structure 32: Vertical movement mechanism 34: Z-axis guide rail 36: Z-axis moving plate 38: Motor 40: Support 42: Laser beam irradiation unit 44: Laser oscillator 46: Attenuator 48: Spatial light modulator 50: Mirror 52: Irradiation head 54: Housing 56: Imaging unit 58: Touch panel 60:Dividing device 62: Holding table 64: Division unit 66: Support member 68: Gripping claw base 70: Gripping claw (70a: standing part, 70b: claw part)

Claims

1. A wafer processing method comprising: forming a peeling layer inside a first wafer, the first wafer having a plurality of devices formed on a front surface side and a chamfered peripheral region, by irradiating the first wafer with a laser beam having a wavelength that is transmitted through the first wafer; and then dividing the first wafer using the peeling layer as a division starting point, a bonding step of bonding the front surface side of the first wafer to the front surface side of a second wafer; a first peeling layer forming step of forming a first peeling layer having a first bottom surface located on the surface side of the first wafer and a second bottom surface having a diameter smaller than that of the first bottom surface and extending along a side surface of a truncated cone located inside the first wafer by irradiating the laser beam onto a region of the first wafer that is more inward than the outer circumferential region so that the closer the focal point is to the outer circumferential region, the closer it is to the surface of the first wafer; a second peeling layer forming step of forming a second peeling layer along the second bottom surface of the truncated cone by irradiating the laser beam onto a region of the first wafer that is inside the first peeling layer so that the focal point is positioned on the second bottom surface of the truncated cone; and a dividing step of dividing the first wafer using the first release layer and the second release layer as dividing starting points by applying an external force to the first wafer along a thickness direction of the first wafer after the bonding step, the first release layer forming step, and the second release layer forming step are performed, A wafer processing method, characterized in that in the first peeling layer forming step, the laser beam is branched so as to generate multiple focal points aligned along the radial direction of the first wafer in a planar view.

2. A wafer processing method as described in claim 1, wherein an external force is applied to the outer peripheral region of the first wafer during the dividing step.

3. A method for processing a wafer as described in claim 1 or 2, wherein the wafer is made of silicon carbide or gallium nitride.

4. A wafer processing method as described in any one of claims 1 to 3, wherein in the dividing step, ultrasonic waves are applied to the first wafer prior to dividing the first wafer.

5. 5. The wafer processing method according to claim 1, wherein the first separation layer forming step is performed before the second separation layer forming step is performed.

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