wafer fabrication methods

Abstract

Provided is a wafer processing method, which can prevent the wafer from being damaged without adding a step of removing the wafer outer periphery when processing a wafer having a chamfered portion on the outer periphery. The wafer processing method is a wafer (W) having a chamfered portion (Wd) on the outer periphery, wherein the wafer processing method comprises the following steps: irradiating a laser beam having a wavelength that is transparent to the wafer (W) along the outer periphery at a position inside a predetermined distance from the wafer outer periphery to form an annular modified region (M) having a depth from the wafer front side (Wa) to a finished thickness (L1); irradiating the wafer outer periphery with a laser beam having a wavelength that is transparent to the wafer (W) to form a plurality of modified regions (N) having a depth from the wafer front side (Wa) to a finished thickness (L1) radially on the wafer outer periphery; and grinding the wafer back side (Wb) to thin the wafer to the finished thickness (L1).

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer having a chamfered portion on the outer periphery. Background Art

[0002] When grinding the back side of a wafer to make it thinner, a so-called sharp edge is formed at the chamfered portion of the outer periphery of the wafer, which may cause a defect on the sharp edge and damage the wafer. In order to prevent this, the following so-called edge trimming is widely used: before grinding, the chamfered portion is removed using a cutting tool (for example, see Patent Document 1).

[0003] However, compared to the cutting tool with a width of about 20 μm used in normal cutting, a thicker tool with a width of about 1 mm is used in edge trimming, and the wafer is cut in a ring shape instead of a straight line. Therefore, the cutting load is greater than that of normal cutting, and it is easy to generate a defect or crack called edge chipping at the edge of the cutting groove formed on the outer periphery of the wafer. In addition, when the crack reaches the device, it will damage the device, which is a problem. On the other hand, when edge trimming is performed at a low speed to suppress edge chipping or cracking, productivity deteriorates.

[0004] Therefore, a method has been proposed in which a wafer is irradiated with a laser beam to divide the wafer into an inner peripheral portion and an outer peripheral portion, the outer peripheral portion is removed, and then the wafer is ground (see, for example, Patent Document 2).

[0005] Patent Document 1: Japanese Patent Application Publication No. 2000-173961

[0006] Patent Document 2: Japanese Patent Application Publication No. 2006-108532

[0007] However, in the above method, since a step of removing the outer periphery of the wafer is added, there is a problem of reduced productivity. Summary of the invention

[0008] Therefore, an object of the present invention is to provide a wafer processing method which can prevent the wafer from being damaged without adding a step of removing the outer peripheral portion of the wafer when processing the wafer having a chamfered portion on the outer periphery.

[0009] According to the present invention, a method for processing a wafer is provided, the wafer having a chamfered portion at its outer periphery, wherein the method for processing the wafer comprises the following steps: an annular modified region forming step, wherein a laser beam having a wavelength that is transparent to the wafer is irradiated along the outer periphery at a position inside the outer periphery of the wafer by a predetermined distance to form an annular modified region having a depth that reaches at least the finishing thickness from the front side of the wafer; an outer peripheral portion modified region forming step, wherein a laser beam having a wavelength that is transparent to the wafer is irradiated to the outer periphery of the wafer to form a plurality of modified regions having a depth that reaches at least the finishing thickness from the front side of the wafer radially at the outer periphery of the wafer; and a back side grinding step, wherein after the annular modified region forming step and the outer peripheral portion modified region forming step are performed, the back side of the wafer is ground to thin the wafer to the finishing thickness, and in the back side grinding step, the outer periphery of the wafer is removed from the wafer while being ground starting from the annular modified region and the plurality of modified regions.

[0010] Preferably, the wafer processing method of the present invention further comprises a grinding step of grinding the back surface after the back surface grinding step.

[0011] According to the wafer processing method of the present invention, during grinding, the outer peripheral portion of the wafer is annularly disconnected from the inner peripheral portion of the wafer by the annular modified region, thereby preventing the inner peripheral portion of the wafer on which the device is formed from being damaged due to defects or cracks generated at the edge of the wafer. In addition, the disconnected outer peripheral portion is finely divided by a plurality of radially extending outer peripheral modified regions, and thus can be removed during grinding.

[0012] Since the back surface is ground after the back surface grinding step, the back surface grinding step is further performed, the bending strength of the wafer can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a cross-sectional view showing an example of a wafer.

[0014] Figure 2 It is a cross-sectional view showing the step of forming an annular reforming region.

[0015] Figure 3 This is a cross-sectional view showing an enlarged annular modified region formed on a wafer.

[0016] Figure 4 It is a cross-sectional view showing the step of forming the outer peripheral reforming region.

[0017] Figure 5 This is a cross-sectional view showing an enlarged view of a modified region radially formed on the outer periphery of a wafer.

[0018] Figure 6This is a plan view showing a wafer in which modified regions are radially formed over the entire peripheral region.

[0019] Figure 7 This is a cross-sectional view showing a state where grinding of the back surface of the wafer has started.

[0020] Figure 8 This is a cross-sectional view showing a state in which grinding is performed while removing the outer peripheral portion of the wafer from the wafer with the annular reformed region and the plurality of reformed regions as starting points in the backside grinding step.

[0021] Fig. 9 It is a cross-sectional view showing a state where the back surface of a wafer is being ground.

[0022] Fig.10 This is a cross-sectional view showing a state in which the back surface of a wafer having an annular reformed region and a plurality of reformed regions formed therein and a carrier wafer bonded to the front surface is ground.

[0023] Fig.11 This is a cross-sectional view showing a state in which the back surface of a wafer having an annular reformed region and a plurality of reformed regions formed therein and a carrier wafer bonded to the front surface is being ground.

[0024] Description of symbols

[0025] W: wafer; Wa: front side of wafer; Wa1: device area; Wa2: peripheral remaining area; D: device; S: predetermined dividing line; Wb: back side of wafer; Wd: chamfered part; T: protective tape; 1: laser processing device; 10: holding table; 10a: holding surface; 11: laser beam irradiation unit; 111: condenser; 111a: condenser lens; 119: laser beam oscillator; 14: alignment unit; 140: camera; M: ring Modified area; M1: modified layer; C: crack; N: radial modified area formed on the periphery; 7: grinding device; 75: chuck table; 75a: holding surface; 71: grinding unit; 710: rotating axis; 713: mounting seat; 714: grinding wheel; 8: grinding device; 85: chuck table; 85a: holding surface; 80: grinding unit; 800: spindle; 801: mounting seat; 802: grinding pad; T2: carrier wafer. DETAILED DESCRIPTION

[0026] Hereinafter, each step of the wafer processing method according to the embodiment of the present invention will be described.

[0027] (1) Ring-shaped modified region formation step

[0028] Figure 1The wafer W shown is, for example, a semiconductor wafer with a circular shape and made of silicon as a base material, and a device area Wa1 and a peripheral remaining area Wa2 surrounding the device area Wa1 are provided on the front surface Wa. The device area Wa1 is divided into a grid shape by a plurality of vertical predetermined dividing lines S, and a device D such as an IC is formed in each of the areas divided into the grid shape. Figure 1 The back side Wb of the wafer W facing downward becomes the grinding surface to be ground later. The outer periphery of the wafer W is chamfered to form a chamfered portion Wd having a substantially arc-shaped cross section. In addition, the wafer W may be made of gallium arsenide, sapphire, gallium nitride, or silicon carbide, etc., in addition to silicon.

[0029] In the annular modified region forming step, a laser beam having a wavelength that is transparent to the wafer W is irradiated along the outer periphery at a position inside the chamfered portion Wd as the outer periphery of the wafer W by a predetermined distance, so as to form an annular modified region having a depth of at least the finished thickness from the front surface Wa of the wafer W. Specifically, the wafer W is transported, for example, to Figure 2 The laser processing apparatus 1 shown in the figure. The laser processing apparatus 1 at least comprises: a holding table 10 for holding the wafer W by suction; and a laser beam irradiation unit 11 for irradiating a laser beam having a wavelength that is transparent to the wafer W held by the holding table 10. Before the wafer W is transported to the laser processing apparatus 1, a protective tape T is attached to the front surface Wa thereof so that the device D is protected.

[0030] The holding table 10 can rotate around the axis in the Z-axis direction, and can reciprocate in the X-axis direction as the processing feed direction and the Y-axis direction as the indexing feed direction through a moving unit not shown. The holding table 10 has a circular shape, for example, and has a flat holding surface 10a, which is composed of a porous component and holds the wafer W. In addition, the suction force generated by the suction source not shown in the figure connected to the holding surface 10a is transmitted to the holding surface 10a, so that the holding table 10 can attract and hold the wafer W on the holding surface 10a.

[0031] The laser beam irradiation unit 11 allows the laser beam LB emitted from the YAG laser oscillator 119 to be incident on the condenser lens 111a inside the condenser 111 via the transmission optical system, so that the laser beam can be converged and irradiated to the wafer W held by the holding table 10. The height position of the focal point P of the laser beam LB can be adjusted in the Z-axis direction by a focal point position adjustment unit (not shown).

[0032] The laser processing apparatus 1 includes an alignment unit 14 that recognizes the coordinate position of the outer periphery of the wafer W and the coordinate position of the center of the wafer W. The alignment unit 14 includes: a light source (not shown); and a camera 140 that includes an optical system that captures reflected light from the wafer W and an imaging element that performs photoelectric conversion on a subject image formed in the optical system and outputs image information.

[0033] like Figure 2 As shown, the wafer W is placed on the holding surface 10a of the holding table 10 with the protective tape T attached to the front surface Wa facing downward, and the wafer W is held by suction by the holding table 10. The rotation center of the holding table 10 and the center of the wafer W are substantially consistent.

[0034] The moving unit (not shown) moves the holding table 10 to the bottom of the alignment unit 14 to perform edge alignment. That is, the holding table 10 is rotated and the camera 140 is used to capture images of multiple locations of the outer periphery of the wafer W held by the holding table 10. Then, based on the captured images, for example, the coordinates of three separate points of the outer periphery are detected, and the accurate center coordinates of the wafer W held by suction on the holding table 10 are obtained through geometric calculation processing based on the coordinates of the three points.

[0035] Furthermore, based on the information of the center coordinates of the chip W and the information of the size of the chip W identified in advance, the workbench 10 is kept moving in the horizontal direction and is positioned at a specified position in such a manner that a specified position Y1 which is in the peripheral remaining area Wa2 and is a specified distance inside the outer peripheral edge of the chip W is positioned directly below the condenser 111.

[0036] Next, the focal point of the laser beam focused by the focusing lens 111a is positioned at a predetermined height position inside the wafer W, that is, at a height greater than 100 mm. Figure 2 The height position shown is slightly above the height position Z2 as the depth reaching the finished thickness L1 of the wafer W. The finished thickness L1 is the thickness from the height position Z1 of the upper surface of the device D to the height position Z2. Then, a pulsed laser beam of a wavelength that is transparent to the wafer W emitted from the laser oscillator 119 is converged and irradiated to the inside of the wafer W held by the holding table 10. In addition, the output of the laser beam is set, for example, to a condition in which cracks are generated upward and downward from the modified layer formed on the wafer W.

[0037] When the laser beam emitted from the laser oscillator 119 is focused and irradiated to the inside of the wafer W, a plurality of laser beams are formed in the wafer W extending in the vertical direction from the focal point position. Figure 3The modified layer M1 shown in FIG. 1 is formed. In addition, the output of the laser beam is set so that cracks C are generated from the modified layer M1, thereby simultaneously forming fine cracks C from the modified layer M1 in the upward and downward directions. That is, a modified region M including the modified layer M1 and the cracks C is formed in the wafer W. Figure 3 In the example shown, the lower end of the crack C in the formed modified region M reaches the front surface Wa of the wafer W.

[0038] While irradiating the outer periphery of the wafer W with a laser beam, Figure 2 The holding table 10 shown is rotated 360 degrees around the axis in the Z-axis direction at a predetermined rotation speed, thereby forming an annular modified region M in the wafer W that reaches at least the depth of the finished thickness L1 from the front surface Wa of the wafer W, that is, forming an annular modified region M that reaches at least the height position Z2 in the wafer W. In addition, as in the present embodiment, the modified layer M1 is not formed in the region within the finished thickness L1 of the wafer W, and only the crack C reaches the front surface Wa of the wafer W, so that the modified layer M1 can be removed by subsequent grinding without remaining on the wafer W, which is preferred.

[0039] The step of forming the ring-shaped modified region is not limited to this embodiment. Figure 2 When the finished thickness L1 of the wafer W shown is thick, the focal point position of the laser beam is positioned at a height position below the height position Z2 (a height position closer to the front Wa side). And, each time the laser beam is irradiated along the outer periphery of the wafer W while the holding table 10 is rotated 360 degrees around the axis in the Z-axis direction at a predetermined rotation speed, the laser beam is irradiated to the wafer W through multiple passes while the focal point position is shifted upward or downward by a predetermined interval in the thickness direction (Z-axis direction) of the wafer W. And, the first stage annular modified region M, the second stage annular modified region M, the third stage annular modified region M, and the fourth stage annular modified region M consisting of the modified layer M1 and the crack C are formed.

[0040] As a result, a ring-shaped modified region M having a depth of at least the finished thickness L1 from the front surface Wa of the wafer W, i.e., a ring-shaped modified region M having a depth of at least the finished thickness L1 is formed in the wafer W by the four-stage ring-shaped modified region M composed of the modified layer M1 and the crack C, i.e., a ring-shaped modified region M having a depth of at least the finished thickness L1 is formed in the wafer W. In this case, the cracks C of each stage are connected in the ring-shaped modified region M. In addition, the modified layer M1 may be exposed on the front surface Wa of the wafer W. In addition, the processing conditions may be set so as to reduce the output of the laser beam so as not to generate the crack C upward and downward from the modified layer M1, so as to form the ring-shaped modified region M by connecting the modified layer M1 itself of each stage in the thickness direction of the wafer W instead of connecting the cracks C of each stage. However, the method of connecting the cracks C of each stage is effective because it can form the ring-shaped modified region M having a depth of at least the finished thickness L1 from the front surface Wa of the wafer W, i.e., forming the ring-shaped modified region M having a depth of at least the finished thickness L1, i.e., forming the ring-shaped modified region M having a depth of at least the finished thickness L2 by irradiating the laser beam with less passage.

[0041] In addition, in forming the annular modified area M, each time the holding table 10 is rotated 360 degrees around the axis in the Z-axis direction, the laser beams of multiple paths are not irradiated while shifting the focal point position upward or downward by a predetermined interval in the thickness direction (Z-axis direction), but the laser beams of multiple paths are irradiated by a beam splitter or the like. Figure 2 The laser beam emitted by the laser oscillator 119 shown is branched into laser beams of multiple optical paths, and each focal point of the laser beams of the multiple optical paths is positioned at a different position in the thickness direction of the wafer W. In addition, the holding table 10 can be rotated 360 degrees around the axis in the Z-axis direction at a predetermined rotation speed, and the inside of the wafer W can be modified at the same time at multiple focal points to form an annular modified area M with a depth of at least from the front surface Wa of the wafer W to the finished thickness L1, that is, to form an annular modified area M at least reaching the height position Z2.

[0042] As another example of the step of forming the annular modified region, for example, Figure 2 Another lens is provided above or below the condenser lens 111a shown, or the condenser lens 111a is, for example, a condenser lens having spherical aberration, so that the light-converging point of the pulsed laser beam can be positioned to extend in the thickness direction of the wafer W. Then, with the light-converging point extending linearly in the thickness direction of the wafer W, a pulsed laser beam having a wavelength that is transparent to the wafer W is emitted from the laser oscillator 119, and the pulsed laser beam is converged and irradiated to the inside of the wafer W.

[0043] In addition, as long as the wafer W is irradiated with a laser beam in a state where aberration is generated in the optical axis direction, a pulse laser beam having a predetermined spread angle can be emitted from the laser oscillator 119 and condensed by the condenser lens 111 a .

[0044] By the above-mentioned irradiation of the laser beam, a fine hole or a crack (not shown) extending in the thickness direction (Z-axis direction) of the wafer W and an amorphous region surrounding the fine hole or crack and extending in the thickness direction of the wafer W are formed inside the wafer W. That is, a so-called shield tunnel composed of the fine hole or crack and the amorphous region is formed in the wafer W.

[0045] Furthermore, it is also possible to irradiate the outer periphery of the chip W with a laser beam while rotating the holding table 10 360 degrees around the axis in the Z-axis direction at a prescribed rotation speed, thereby forming an annular shield tunnel having a depth of at least the finished thickness L1 from the front side Wa of the chip W, that is, forming an annular shield tunnel that at least reaches the height position Z2.

[0046] (2) Peripheral modified region formation step

[0047] For example, when a Figure 3 , Figure 4 After the annular modified region M is formed, a laser beam having a wavelength that is transparent to the wafer W is irradiated on the outer periphery of the wafer W, and a plurality of modified regions having a depth of at least from the front surface Wa of the wafer W to the finished thickness L1 are radially formed on the outer periphery of the wafer W. In addition, the outer periphery modified region forming step may be performed before the annular modified region forming step is performed.

[0048] In the peripheral modified region forming step, first, Figure 4 As shown, the focal point position of the laser beam converged by the focusing lens 111a is positioned, for example, at a predetermined height position within the finished thickness L1 of the wafer W. Furthermore, a pulsed laser beam of a wavelength that is transparent to the wafer W is emitted from the laser oscillator 119, and the laser beam is converged and irradiated to the wafer W. In addition, the wafer W is fed in the -X direction at a predetermined processing feed speed, and the laser beam is irradiated from the outer periphery of the wafer W toward the annular modified area M, thereby forming a modified area N reaching the depth of the finished thickness L1 from the front surface Wa of the wafer W, that is, forming a modified area N reaching the height position Z2. The modified area N may have cracks and a modified layer not shown in the figure, may be composed of a modified layer alone, or may be a shield tunnel.

[0049] For example, Figure 5 When the finished thickness L1 of the wafer W shown is 70 μm, the length of the modified region N in the Z-axis direction is 70 μm, which is the same length as the finished thickness L1. On the other hand, the length of the annular modified region M in the Z-axis direction is preferably 90 μm, which is obtained by adding 20 μm to the finished thickness L1 (70 μm).

[0050] For example Figure 5As shown in the figure, when the wafer W moves in the -X direction as the forward direction until the modified region N reaches a predetermined position of the annular modified region M from the outer periphery of the wafer W, the irradiation of the laser beam is stopped, and the holding table 10 is rotated around the axis in the Z-axis direction at a predetermined angle (for example, several degrees). In addition, the modified region N may stop in front of the annular modified region M instead of reaching the annular modified region M from the outer periphery of the wafer W.

[0051] Next, Figure 4 The wafer W shown is processed and fed in the +X direction as the reverse direction, and by laser beam irradiation, a modified region N is formed from the annular modified region M to the outer periphery of the wafer W. The same laser beam irradiation is performed while the holding table 10 is rotated by a predetermined angle, so that Figure 6 As shown, a plurality of modified regions N can be radially formed over substantially the entire circumference of the outer peripheral portion of the wafer W, with the depth reaching at least the finished thickness L1 from the front surface Wa of the wafer W.

[0052] Alternatively, for the same line, the laser beam may be irradiated to the wafer W in multiple passes while shifting the focal point position upward or downward by a predetermined interval in the forward and reverse directions to form a plurality of modified regions, thereby forming Figure 4 The modified region N shown reaches a depth of the finished thickness L1 from the front surface Wa of the wafer W, that is, the modified region N reaches a height position Z2.

[0053] (3) Back grinding steps

[0054] After the annular modified region forming step and the peripheral modified region forming step are performed, the back surface Wb of the wafer W is ground and thinned to a finished thickness L1. That is, the wafer W having the annular modified region M and the modified region N formed thereon is transported to the wafer W. Figure 7 The chuck table 75 of the grinding device 7 shown is sucked and held on the holding surface 75 a of the chuck table 75 with the back surface Wb facing upward.

[0055] Figure 7 The grinding unit 71 of the grinding device 7 shown in the figure for grinding the wafer W comprises: a rotating shaft 710, whose axial direction is the Z-axis direction; a disc-shaped mounting seat 713, which is connected to the lower end of the rotating shaft 710; and a grinding wheel 714, which is connected to the lower surface of the mounting seat 713 in a manner that can be loaded and unloaded. The grinding wheel 714 comprises: a grinding wheel base 714b; and a plurality of grinding tools 714a in a substantially rectangular parallelepiped shape, which are arranged in a ring shape on the bottom surface of the grinding wheel base 714b.

[0056] First, the chuck table 75 moves in the +Y direction, and the chuck table 75 is positioned in such a way that the rotation center of the grinding tool 714a is offset in the horizontal direction by a predetermined distance relative to the rotation center of the wafer W and the rotation trajectory of the grinding tool 714a passes through the rotation center of the wafer W. Then, as the rotating shaft 710 rotates, the grinding wheel 714 rotates around the axis in the Z-axis direction. In addition, the grinding unit 71 is fed in the -Z direction, and the grinding tool 714a abuts against the back side Wb of the wafer W to perform grinding. During grinding, as the chuck table 75 rotates, the wafer W also rotates, so the grinding tool 714a performs grinding of the entire back side Wb of the wafer W. In addition, grinding water is provided to the contact portion between the grinding tool 714a and the back side Wb of the wafer W, and the contact portion is cooled and the grinding chips are cleaned and removed by the grinding water.

[0057] During the grinding process, a grinding pressure in the -Z direction is applied to the wafer W from the grinding tool 714a. Figure 8 As shown in FIG. 1 , when the back surface Wb is ground, a grinding stress for the grinding pressure is generated along the annular modified area M, and the wafer W is divided into a circular inner peripheral portion W1 and an annular outer peripheral portion starting from the annular modified area M. Then, after the grinding is continued and the modified layer M1 of the annular modified area M is removed and the wafer W is ground to the finished thickness L1, the grinding unit 71 is moved away from the wafer W in the +Z direction.

[0058] In the back grinding process, a grinding stress is generated along the plurality of modified regions N radially formed on the outer peripheral portion of the wafer W to generate a grinding stress for the grinding pressure. The annular outer peripheral portion separated from the circular inner peripheral portion W1 of the wafer W is divided into the modified regions N as the starting point. Figure 8 The thin end material W2 shown (for example, an end material having a substantially trapezoidal shape in a plan view) is removed from the chuck table 75 by centrifugal force because the chuck table 75 rotates.

[0059] As described above, in the wafer processing method of the present invention, before grinding the back side Wb of the wafer W, the annular modified region M and the radially modified region N at the outer peripheral portion are formed on the wafer W. Furthermore, during grinding, the outer peripheral portion of the wafer W is annularly disconnected from the inner peripheral portion W1 of the wafer by the annular modified region M, thereby preventing the inner peripheral portion W1 of the wafer W where the device D is formed from being damaged due to defects or cracks generated at the edge of the wafer W. In addition, the disconnected outer peripheral portion is finely divided by the plurality of radially extending modified regions N, and can therefore be removed during grinding.

[0060] (4) Grinding step

[0061] For example, in this embodiment, after the back grinding step is performed, the back surface Wb of the wafer W is ground. That is, the inner peripheral portion W1 of the wafer W is transported to Fig. 9 The chuck table 85 of the polishing device 8 shown in the figure is sucked and held on the holding surface 85 a of the chuck table 85 with the back surface Wb facing upward.

[0062] The grinding unit 80 of the grinding device 8 includes, for example, a spindle 800, whose axial direction is the vertical direction (Z-axis direction); a circular plate-shaped mounting seat 801, which is fixed to the lower end of the spindle 800; and a circular grinding pad 802, which is mounted on the lower surface of the mounting seat 801 in a detachable manner. The grinding pad 802 is made of, for example, non-woven fabric such as felt, and has a through hole formed in the central part for the slurry to pass through, and its lower surface serves as a grinding surface for grinding the wafer W. The diameter of the grinding pad 802 is set to be larger than the diameter of the wafer W.

[0063] For example, a slurry flow path extending along the Z-axis direction is formed inside the spindle 800, and a slurry supply unit is connected to the slurry flow path. The slurry is ejected downward from the opening at the lower end of the slurry flow path toward the polishing pad 802, and reaches the contact portion between the polishing surface of the polishing pad 802 and the wafer W. The slurry used in the polishing process is, for example, a solution containing SiO2, Al2O3, CeO2, SiC, ZiO2, TiO, etc. as free abrasive particles. In addition, in the polishing step, instead of using the chemical mechanical polishing method using the slurry, i.e., the so-called CMP (Chemical Mechanical Polishing), dry polishing without using the slurry may be performed.

[0064] First, the chuck table 85 moves in the +Y direction, and the polishing pad 802 and the wafer W held by the chuck table 85 are aligned. For example, the alignment is performed so that the polishing surface of the polishing pad 802 covers the entire back surface Wb of the wafer W.

[0065] After the polishing pad 802 and the wafer W are aligned, the polishing pad 802 is rotated. In addition, the polishing unit 80 is fed in the -Z direction, as shown in FIG. Fig. 9 As shown, the polishing surface of the rotating polishing pad 802 abuts against the wafer W to perform polishing. During the polishing, as the chuck table 85 rotates, the wafer W held on the chuck table 85 also rotates, so the polishing pad 802 performs polishing of the entire back side Wb of the wafer W.

[0066] During the grinding process, slurry is supplied between the back side Wb of the rotating wafer W and the grinding surface of the grinding pad 802, so that the chemical action of the slurry and the mechanical action of the rotation of the grinding pad 802 complement each other, and grinding is performed in a manner that the processing strain is removed from the back side Wb of the wafer W, thereby improving the bending strength of the wafer W. After the wafer W is ground for a predetermined time, the grinding unit 80 is moved away from the wafer W in the +Z direction.

[0067] The wafer processing method of the present invention is not limited to this embodiment, and can of course be implemented in various different ways within the scope of its technical concept. In addition, the structures of the laser processing device 1, the grinding device 7, and the grinding device 8 shown in the drawings are not limited thereto, and can be appropriately changed within the scope that can exert the effect of the present invention.

[0068] For example, in the above-described method of performing the annular modified region forming step and the peripheral modified region forming step, Fig.10 Before the back grinding step is performed on the wafer W shown, the protective tape T is peeled off from the front surface Wa, and a carrier wafer T2 (support wafer T2) having a diameter substantially the same as that of the wafer W is bonded to the front surface Wa using an adhesive T1. The carrier wafer T2 can be made of, for example, the same material as that used for the wafer W. In this way, the wafer W is bonded to another carrier wafer T2 to form a bonded wafer, and the bonded wafer is processed as a whole, thereby improving the operability of the thinner wafer W and preventing the wafer W from warping or breaking during processing.

[0069] In addition, before the annular modified region forming step and the peripheral modified region forming step are performed, the carrier wafer T2 may be bonded to the front surface Wa of the wafer W. In addition, the carrier wafer T2 may be directly bonded to the front surface Wa of the wafer W without using an adhesive by an atomic diffusion bonding method, a front surface activation room temperature bonding method, or a bonding method accompanied by heating of the wafer W. In addition, a carrier plate made of glass, sapphire, or a metal plate may be used instead of the carrier wafer T2.

[0070] The wafer W with the carrier wafer T2 bonded thereto is transported to Fig.10 The chuck table 75 of the grinding device 7 shown in the figure is sucked and held on the holding surface 75a of the chuck table 75 with the back side Wb facing upward. Next, the chuck table 75 is positioned so that the rotation trajectory of the grinding tool 714a passes through the rotation center of the wafer W. The grinding unit 71 is fed in the -Z direction, and the rotating grinding tool 714a abuts against the back side Wb of the wafer W to perform grinding. During grinding, as the chuck table 75 rotates, the wafer W also rotates, so the grinding tool 714a performs grinding of the entire back side Wb of the wafer W.

[0071] During the grinding process, a grinding pressure in the -Z direction is applied to the wafer W from the grinding tool 714a. A grinding stress for the grinding pressure is generated along the annular reformed region M, so that the wafer W is divided into a circular inner peripheral portion W1 (see Fig.11 ) and the annular outer peripheral portion. And, while removing the modified layer M1 of the annular modified region M, the wafer W is ground until the finished thickness L1 is reached.

[0072] In addition, in the above-mentioned back grinding process, grinding stress for grinding pressure is generated along a plurality of modified areas N radially formed on the outer periphery of the chip W, and the annular outer periphery of the chip W separated from the circular inner periphery W1 is divided into fine end materials with the modified area N as the starting point and is removed.

[0073] Next, the inner peripheral portion W1 of the wafer W is transported to Fig.11 The chuck table 85 of the polishing apparatus 8 shown in the figure is held by suction on the holding surface 85a of the chuck table 85 with the back surface Wb facing upward. The wafer W is supported by the carrier wafer T2, so that it can be prevented from being bent and broken during transportation after thinning.

[0074] For example, after the polishing pad 802 and the wafer W are aligned in such a way that the polishing surface of the polishing pad 802 covers the entire back side Wb of the wafer W, the polishing unit 80 is fed in the -Z direction, such as Fig.11 As shown, the polishing surface of the rotating polishing pad 802 contacts the wafer W to perform polishing. During the polishing process, the entire back side Wb of the rotating wafer W is polished by the rotating polishing pad 802 while the slurry is supplied to the contact portion between the polishing pad 802 and the wafer W. After the wafer W is polished for a predetermined time, the polishing unit 80 is moved away from the wafer W in the +Z direction.

Claims

1. A method for processing a wafer, comprising grinding the back side of a wafer having a chamfered portion on the outer periphery to produce a wafer having a predetermined finished thickness, wherein: The wafer processing method has the following steps: a ring-shaped modified region forming step of irradiating a laser beam having a wavelength that is transparent to the wafer along the outer periphery at a position inside the outer periphery of the wafer by a predetermined distance to form a ring-shaped modified region having a depth that reaches at least the finished thickness from the front surface of the wafer; a peripheral modified region forming step of irradiating the peripheral portion of the wafer with a laser beam having a wavelength that is transparent to the wafer, thereby radially forming a plurality of modified regions at least reaching a depth of a finished thickness from the front surface of the wafer on the peripheral portion of the wafer; as well as a back grinding step, after the annular modified region forming step and the peripheral modified region forming step are performed, grinding the back side of the wafer to thin the wafer to the finished thickness, The annular reformed region is formed so that the length in the thickness direction from the front side is longer than the finished thickness. The plurality of modified regions formed radially are formed so that the length in the thickness direction from the front side is equal to the finished thickness. In the back grinding step, the outer peripheral portion of the wafer is ground while being removed from the wafer starting from the annular modified region and the plurality of modified regions. After the outer peripheral portion is broken, the outer peripheral portion is divided into a plurality of modified regions formed radially.

2. The wafer processing method according to claim 1, wherein: The wafer processing method further comprises the following grinding step: grinding the back surface after the back surface grinding step is performed.

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