Wafer processing methods

Abstract

A wafer processing method in which a wafer (W) having a component region (W1) in which a plurality of components (D) are formed in regions defined by a plurality of streets (S) formed in a lattice arrangement on a front surface (WS), and having a peripheral excess region (W2) surrounding the component region (W1), is held on a holding surface (10a) of a chuck table (10), and a region on a rear surface (WR) corresponding to the component region (W1) is ground by a grinding means (24, 34) to adjust the thickness of the component region to a predetermined final thickness (T), the wafer processing method comprising: a first grinding step of moving a first grinding means (24) in a processing feed direction, which is a direction perpendicular to the holding surface (10a), and grinding the wafer (W) to form a first circular recess (R1) on the rear surface (WR) of the wafer (W); and a second grinding step of moving a second abrasive (34) formed of finer abrasive grains than the first abrasive (24) downward in an inclined direction from one side of the center of the wafer toward the periphery of the wafer and grinding the first circular recess (R1) after the first grinding step has been performed, wherein in the second grinding step, an outer tip periphery (34a) of the second grinding means (34) is moved inclined downward to a position which is closer to an inner side by a predetermined distance than an inner peripheral wall (I1) of the first circular recess (R1) and closer to an upper side by a predetermined distance than a lower surface (B1) of the first circular recess (R1), and a part of a curved surface part (C1) connecting the inner peripheral wall (I1) and the lower surface (B1) of the first circular recess is ground, and the wafer processing method further includes a third grinding step of moving the second grinding means (34) in the processing feed direction and grinding the lower surface of the first circular recess (R1) to adjust the thickness of the device region to a predetermined final thickness after the second grinding step is performed.

Description

Background of the inventionField of the invention

[0001] The present invention relates to a wafer processing method and in particular to a so-called TAIKO grinding method. Description of the state of the art

[0002] As a processing method for improving the handling ease of a semiconductor wafer during grinding the semiconductor wafer to a very fine thickness, a grinding method is known in which the back surface of the semiconductor wafer corresponding to a device region is ground to form a circular recess and leave an annular protrusion at the peripheral part (see, for example, JP 2009-176896 A and JP 2008-42081 A). In the present specification, this grinding method is defined as TAIKO grinding. In TAIKO grinding, after the circular recess is roughly formed by rough grinding, fine grinding is further performed on the bottom surface of the circular recess with a fine-grain abrasive for the purpose of increasing the bending strength of the device region.

[0003] When the fine grinding abrasive collides with the inner peripheral wall of the circular recess formed by rough grinding, the fine grinding abrasive wears or causes a crack in the inner peripheral wall. Therefore, the fine grinding abrasive moves downward slightly within the inner peripheral wall and grinds the lower surface at a fine grinding speed from above at a predetermined distance from the lower surface. Since the fine grinding abrasive does not perform grinding, the fine grinding abrasive moves downward at a high speed to the position above the lower surface at the predetermined distance, thus shortening the machining time.

[0004] US 2013 / 0 001 766 A1 and DE 35 05 102 A1 disclose further prior art. Summary of the invention

[0005] The component area (the number of chips) is determined by the position of the fine grinding abrasive relative to the inner peripheral wall of the circular recess. Therefore, it is necessary to arrange the fine grinding abrasive at a position as close as possible to the inner peripheral wall. The corner connecting the inner peripheral wall and the bottom surface of the circular recess has a curved surface shape due to deformation resulting from the wear of the coarse grinding abrasive. Therefore, as the fine grinding abrasive is brought closer to the outer periphery, a larger area of ​​the curved surface part must be ground by the fine grinding abrasive. The volume of the curved surface part is small.However, when machining is performed at high speed, the deformation due to wear of the fine grinding abrasive is increased. As a result, the area obtained as the component area becomes smaller due to an increase in the curved surface portion after fine machining. For this reason, the inner side of the curved surface portion is conventionally ground by the fine grinding abrasive, and the area corresponding to the separation of the fine grinding abrasive from the curved surface portion toward the inner side and the area that is not successfully ground due to the deformation of the fine grinding abrasive are areas where components cannot be manufactured.

[0006] Therefore, research has been conducted on grinding the curved surface portion to expand the area obtained as the component area. Furthermore, research has been conducted on a method in which the fine grinding abrasive also moves downward at a fine grinding speed when passing through the curved surface portion. However, this method poses the following problem. Specifically, when the height of the curved surface portion is approximately 200 μm, for example, 200 μm is added as the distance of depression during which machining is performed at the fine grinding speed, thus resulting in a very long machining time.

[0007] Therefore, it is an object of the present invention to provide a wafer processing method that enables expansion of the device area while preventing an increase in processing time.

[0008] The present invention is defined by the wafer processing method according to the features of independent claim 1.

[0009] According to one aspect of the present invention, there is provided a wafer processing method in which a wafer having a device region in which devices are formed in regions defined by a plurality of streets formed on a front surface in a lattice arrangement and having a circumferential excess region surrounding the device region is held on a holding surface of a chuck table, and a region on a rear surface corresponding to the device region is ground by an abrasive to adjust the thickness of the device region to a predetermined final thickness.The wafer processing method includes a first grinding step of moving a first abrasive in a processing feed direction, which is a direction perpendicular to the holding surface, and grinding the wafer to form a first circular recess in the back surface of the wafer, and a second grinding step of moving a second abrasive formed of finer abrasive grains than the first abrasive downward in an inclined direction from the side of the center of the wafer toward the periphery of the wafer and grinding the first circular recess.

[0010] Preferably, in the second grinding step, an outer tip periphery of the second abrasive is moved inclined downward to a position slightly inside an inner peripheral wall of the first circular recess and slightly above a lower surface of the first circular recess, and a portion of a curved surface connecting the inner peripheral wall and the lower surface of the first circular recess is ground. Preferably, the wafer processing method according to the present invention includes a third grinding step of moving the second abrasive in the processing feed direction and grinding the lower surface of the first circular recess to adjust the thickness of the device region to a predetermined final thickness after the second grinding step is performed.

[0011] In the wafer processing method according to the invention of the present application, when the second grinding medium is moved downward, it is moved downward at an inclination from an upper side on the wafer center side toward the wafer periphery. This provides the effect of expanding the flat area on the back surface of the wafer corresponding to the device area while preventing an increase in processing time.

[0012] The above and other objects, features and advantages of the present invention and the mode for carrying them out will become more apparent and the invention itself will be best understood by studying the following description and the appended claims with reference to the accompanying drawings which show some preferred embodiments of the invention. Short description of the drawings Fig. 1 is a perspective view of a wafer to be processed by a wafer processing method according to a first embodiment; Fig. 2 is a perspective view showing a holding member arranging step of the wafer processing method according to the first embodiment; Fig. 3 is a perspective view of the main part of a grinding apparatus for performing the wafer processing method according to the first embodiment; Fig. 4 is a side view showing the outline of a first grinding step of the wafer processing method according to the first embodiment; Fig. 5 is a side view showing the outline of a second grinding step of the wafer processing method according to the first embodiment; Fig. 6 is a side view showing a state in which second abrasives of the second grinding step of the wafer processing method according to the first embodiment are brought into contact with the lower surface of a first circular recess; Fig. 7 is an enlarged side view showing Part VII in Fig. 6 shows; Fig. 8 is an enlarged side view showing a state in which grinding to a final thickness of the second grinding step of the wafer processing method according to the first embodiment is performed; Fig. 9 is a side view showing the outline of a second grinding step of a wafer processing method according to a second embodiment; Fig. 10 is a side view showing the representation of the state after the second grinding step of the wafer processing method according to the second embodiment; Fig. 11 is an enlarged side view showing part XI in Fig. 10 shows; Fig. 12 is an enlarged side view showing the outline of a third grinding step of the wafer processing method according to the second embodiment; and Fig. 13 is an enlarged side view showing the representation of the state after the third grinding step of the wafer processing method according to the second embodiment. Detailed description of the preferred embodiments

[0013] Preferred embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. Furthermore, in the components described below, what can be easily conceived by those skilled in the art and what is substantially the same is included. Furthermore, it is possible to appropriately combine the structures described below. Furthermore, various forms of omission, substitution, or modification of the structures can be made without departing from the gist of the present invention. [First embodiment]

[0014] A wafer processing method according to a first embodiment will be described based on drawings. Fig. 1 is a perspective view of a wafer to be processed by the wafer processing method according to the first embodiment. The wafer processing method according to the first embodiment (hereinafter referred to simply as the processing method) is a method for processing a wafer in Fig. 1 shown wafer W.

[0015] The wafer W to be processed by the processing method according to the first embodiment is a semiconductor wafer or an optical device wafer having a circular plate shape and made of silicon, sapphire, gallium, or the like as its matrix material. As shown in Fig. 1, the wafer W has a device region W1 in which devices D are formed in regions defined by a plurality of streets S formed on a front surface WS in a lattice arrangement, and a peripheral excess region W2 surrounding the device region W1. Although the boundary between the device region W1 and the peripheral excess region W2 is shown for the sake of simplicity in Fig. 1 is shown by a one-dotted dashed line, in practice there is no line at the border.

[0016] The processing method of the first embodiment is a method in which the wafer W is held on a holding surface 10a of a chuck table 10 of a grinding apparatus 1 (in Fig. 3) and an area on a rear surface WR corresponding to the component area W1 is ground by abrasives 24 and 34 (in Fig. 4 and Fig. 5) is ground to reduce the thickness of the component area W1 to a predetermined final thickness T (in Fig. 8). As shown in Fig. 3, the grinding apparatus 1 includes the chuck table 10 holding the wafer W, a first grinding unit 20 performing a first grinding step on the wafer W held by the chuck table 10, and a second grinding unit 30 (in Fig. 5), which performs a second grinding step on the wafer W held by the chuck table 10.

[0017] The chuck table 10 has a circular disk shape, in which the part constituting the holding surface 10a is formed of porous ceramic or the like. The chuck table 10 is connected to a vacuum suction source (not shown) via a vacuum suction path (not shown) and sucks the wafer W placed on the holding surface 10a to hold the wafer W. The chuck table 10 is provided so as to be able to rotate around the shaft center parallel to the Z-axis along the vertical direction by a rotation drive source (not shown). Further, at least one chuck table 10 is provided on a turntable (not shown) rotatably provided around the shaft center of the grinding apparatus 1.

[0018] As in Fig. As shown in Fig. 3, the first grinding unit 20 is composed of a spindle (not shown) rotated about the shaft center parallel to the Z-axis along the vertical direction, and a grinding wheel 22 attached to the lower end of the spindle. The spindle is rotatably provided in a spindle housing 21 and is rotated about the shaft center by a motor 26. Further, the spindle, i.e., the first grinding unit 20, is provided so that it can move in the Z-axis direction by a machining feed unit (not shown) and can move in the Y-axis direction parallel to the horizontal direction by a horizontal moving unit (not shown).

[0019] The grinding wheel 22 is used in the machining process and includes a first abrasive base 23 having a circular disk shape and a plurality of first abrasives 24, as shown in Fig. 3. The first abrasive base 23 is attached to a flange portion 25 provided at the tip of the spindle by bolts. The first abrasives 24 are attached to the lower surface of the first abrasive base 23 in a circular ring arrangement. The diameter of the circle formed by the outer peripheral edges of the plurality of first abrasives 24 is set to be smaller than the radius of the wafer W. The first abrasives 24 are abrasives for rough grinding formed of bonded resin abrasive grains or bonded vitrified abrasive grains whose abrasive grain size is, for example, approximately #32 to 600.

[0020] The second grinding unit 30 is arranged on the downstream side of the first grinding unit 20 in the direction of rotation of the turntable. As shown in Fig. As shown in Fig. 5, the second grinding unit 30 is composed of a spindle (not shown) that rotates around the shaft center parallel to the Z-axis direction along the vertical direction, and a grinding wheel 32 attached to the lower end of the spindle. The spindle is rotatably provided in a spindle housing (not shown) and is rotated around the shaft center by a motor (not shown). Further, the spindle, that is, the second grinding unit 30, is provided so that it can move in the Z-axis direction by a machining feed unit (not shown) and can move in the Y-axis direction by a horizontal movement unit (not shown).

[0021] The grinding wheel 32 is used in the machining process and includes a second abrasive base 33 having a circular disk shape and a plurality of second abrasives 34, as shown in Fig. 5. The second abrasive base 33 is attached to a flange portion 35 provided at the tip of the spindle by bolts. The second abrasives 34 are attached to the lower surface of the second abrasive base 33 in a circular ring arrangement. The diameter of the circle formed by the outer peripheral edges of the plurality of second abrasives 34 is set to be smaller than the radius of the wafer W. The second abrasives 34 are abrasives for fine grinding, which are formed, for example, from abrasive grains finer than the abrasive grains of the first abrasives 24.

[0022] The processing procedure includes a Fig. 2 shown holding element arrangement step, one in Fig. 4 shown first grinding step and one in Fig. 5. In the holding element arrangement step, as shown in Fig. 2, a holding member P having substantially the same size as the wafer W and a circular plate shape is adhered to the front surface WS of the wafer W. Thereafter, the processing proceeds to the first grinding step. As the holding member P, a component obtained by applying an adhesive material having a thickness of approximately 5 to 20 µm to a single surface of a soft base layer of polyolefin or the like having a thickness of approximately 70 to 200 µm is used.

[0023] In the first grinding step, first, the holding member P adhered to the front surface WS of the wafer W is placed on the holding surface 10a of the chuck table 10, and the front surface WS side of the wafer W is held on the chuck table 10 by suction with the holding member P interposed therebetween. Thereafter, the chuck table 10 is rotated about the shaft center, and the first abrasives 24 of the first grinding unit 20 are rotated about the shaft center. Further, the rotary table is rotated, and the outer peripheral edges of the first abrasives 24 of the grinding wheel 22 are positioned opposite the position corresponding to the inner peripheral edge of the rear surface of the peripheral excess portion W2 of the wafer W and the center of the wafer W.

[0024] Afterwards, as in Fig. 4, the first abrasives 24 are moved (i.e., moved downward) by the processing feed unit in the processing feed direction parallel to the Z-axis along the direction perpendicular to the holding surface 10a, and the wafer W is ground to form a first circular recess R1 corresponding to the device region W1 in the back surface WR of the wafer W. In the first grinding step, the processing feed (i.e., the downward movement) is performed at a comparatively high speed until the first abrasives 24 abut against the back surface WR of the wafer W. After the first abrasives 24 abut against the back surface WR of the wafer W, the processing feed (i.e., the downward movement) is performed at a speed lower than the speed used until the abutment.Further, in the first grinding step, the first grinding unit 20 is moved upward when the thickness of the lower part of the first circular recess R1 of the wafer W becomes a predetermined thickness. After that, the processing proceeds to the second grinding step.

[0025] The first circular recess R1 is formed in a circular shape as its surface shape and is formed as a recess from the rear surface WR of the wafer W. As shown in Fig. 6 and Fig. As shown in Fig. 7, the first circular recess R1 consists of a bottom surface B1 that is parallel to the support surface 10a and flat, a curved surface part C1 that is continuous with the outer edge of the bottom surface B1, and an inner peripheral wall 11 that is continuous with the curved surface part C1 and perpendicular to the support surface 10a. The curved surface part C1 connects the inner peripheral wall 11 to the bottom surface B1 and is formed as such a curved surface that no edge line is formed between the curved surface part C1 and the bottom surface B1, nor between the curved surface part C1 and the inner peripheral wall 11.

[0026] In the second grinding step, the rotary table is rotated to position the second grinding means 34 of the second grinding unit 30 above the first circular recess R1 of the wafer W held by the chuck table 10. In addition, the second grinding means 34 of the second grinding unit 30 are rotated around the shaft center. Thereafter, as shown in Fig. 5, the second grinding means 34 are moved downward by the processing feeding unit and the horizontal moving unit in an inclined direction intersecting the holding surface 10a and directed from the center side of the wafer W toward the periphery of the wafer W, and the second grinding means 34 are pressed against the inside of the first circular recess R1 to grind the inside of the first circular recess R1.

[0027] Specifically, in the second grinding step, the second abrasives 34 are moved downward in the inclined direction from the center side of the wafer W toward the periphery of the wafer W, and the second abrasives 34 are brought to abut against the outer edge part of the lower surface B1 of the first circular recess R1 close to the inner peripheral wall I1, as shown in Fig. 6 and Fig. 7. Thereafter, the second grinding means 34 are moved further downward in the inclined direction from the side of the center of the wafer W toward the periphery of the wafer W. As shown in Fig. 8, the curved surface part C1 is thereby ground by outer tip peripheries 34a of the second abrasives 34, and the lower surface B1 of the first circular recess R1 is ground by the second abrasives 34. When the thickness of the device region W1 of the wafer W has been adjusted to the final thickness T, as shown in Fig. 8, the second grinding unit 30 is moved upward. Also in the second grinding step, the machining feed (i.e., the downward movement) is performed at a comparatively high speed until the second abrasives 34 abut against the lower surface B1 of the first circular recess R1. After the second abrasives 34 abut against the lower surface B1 of the first circular recess R1, the machining feed (i.e., the downward movement) is performed at a speed lower than the speed used until the abutment.It is preferable that the machining feed speed of the second grinding means 34 in the Z-axis direction after the abutment of the second grinding means 34 against the bottom surface B1 of the first circular recess R1 is set to a speed corresponding to a conventional machining feed speed at which machining feed of the second grinding means 34 is performed only in the Z-axis direction.

[0028] As in Fig. As shown in Fig. 8, a second circular recess R2 is formed within the first circular recess R1 in the wafer W after the second grinding step. The second circular recess R2 is formed in a circular shape as its surface shape and is formed as a recess from the bottom surface B1 of the first circular recess R1. As shown in Fig. 8, the second circular recess R2 consists of a second lower surface B2 that is parallel to the holding surface 10a and flat, a second curved surface part C2 that is continuous with the outer edge of the second lower surface B2, and an inner peripheral surface I2 that is continuous with the second curved surface part C2 and perpendicular to the holding surface 10a. The inner peripheral surface I2 is continuous with the curved surface part C1 of the first circular recess R1. The second curved surface part C2 connects the inner peripheral surface I2 to the second lower surface B2 and is formed as such a curved surface that no edge line is formed between the second curved surface part C2 and the second lower surface B2, nor between the second curved surface part C2 and the inner peripheral surface I2.The second curved surface part C2 is formed with a radius of curvature that is smaller than that in the case where the second grinding means 34 are moved downward parallel to the Z-axis.

[0029] Thereafter, in the grinding apparatus 1, the rotary table is rotated, and the wafer W for which the second grinding step has been performed is removed from the chuck table 10. Thereafter, the wafer W for which the first grinding step and the second grinding step have not yet been performed is held on the chuck table 10, and the first grinding step and the second grinding step are performed sequentially as in the previous method.

[0030] According to the machining method of the first embodiment, when the second abrasives 34 are moved downward to the lower surface B1 at a position as close as possible to the inner peripheral wall I1 of the first circular recess R1, the second abrasives 34 are moved downward in an inclined direction from the center side of the wafer W toward the circumference. Therefore, the outer tip peripheries 34a of the second abrasives 34 are pressed against the curved surface part C1 in the inclined direction from the center side of the wafer W toward the circumference.For this reason, compared with the case where the second abrasives 34 are moved downward parallel to the Z-axis, the wear (deformation) of the second abrasives 34 is suppressed even if the second abrasives 34 are moved downward at a comparatively high speed until they come into contact with the lower surface B1, and the curved surface part C1 is slightly ground by the second abrasives 34. Therefore, the radius of curvature of the second curved surface part C2 of the second circular recess R2 can be made smaller than in the case where the second abrasives 34 are moved downward parallel to the Z-axis.Therefore, the machining method according to the first embodiment provides the effect that the second lower surface B2 of the second circular recess R2 formed after fine grinding is set wide, and thus the flat area on the back surface of the wafer W corresponding to the device area W1 of the wafer W (ie, the second lower surface B2) can be expanded, preventing an increase in the machining time. [Second embodiment]

[0031] A wafer processing method according to a second embodiment will be described based on the drawings. The wafer processing method according to the second embodiment (hereinafter referred to simply as the processing method) includes a holder arrangement step and a first grinding step, which are the same as those in the processing method of the first embodiment, a Fig. 9 and so on, and a second grinding step shown in Fig. 12 shown third grinding step.

[0032] In the second grinding step of the machining method according to the second embodiment, similar to the first embodiment, a rotary table is rotated to arrange the second grinding means 34 of the second grinding unit 30 above the first circular recess R1 of the wafer W held by the chuck table 10. In addition, the second grinding means 34 of the second grinding unit 30 are rotated around the shaft center. Thereafter, as shown in Fig. 9, the second grinding means 34 are moved downward by the processing feeding unit and the horizontal moving unit in an inclined direction intersecting the holding surface 10a and directed from the center side of the wafer W toward the periphery of the wafer W, and the second grinding means 34 are pressed against the inside of the first circular recess R1 to grind the inside of the first circular recess R1.

[0033] Specifically, in the second grinding step according to the second embodiment, the outer tip peripheries 34a of the second grinding means 34 are moved inclined downward from the side of the center of the wafer W toward the periphery of the wafer W to a position slightly inside the inner peripheral wall I1 of the first circular recess R1 and slightly above the bottom surface B1 of the first circular recess R1. As shown in Fig. 10 and Fig. 11, a part of the curved surface portion C1 connecting the inner peripheral wall I1 and the bottom surface B1 of the first circular recess R1 is thereby ground by the outer tip peripheries 34a of the second abrasives 34. Thereafter, the machining process proceeds to the third grinding step. Also in the second grinding step of the machining process according to the second embodiment, the machining feed (i.e., downward movement) is performed at a comparatively high speed until the second abrasives 34 grind the curved surface portion C1 of the first circular recess R1.

[0034] In the third grinding step, after the second grinding step is performed, the second grinding means 34 are moved by the machining feed unit in the machining feed direction parallel to the Z-axis, and thereby the curved surface part C1 of the first circular recess R1 is further ground by the outer tip peripheries 34a of the second grinding means 34, as shown in Fig. 12. In addition, the lower surface B1 of the first circular recess R1 is ground by the second grinding means 34. Thereafter, when the curved surface part C1 and the lower surface B1 of the first circular recess R1 have been ground and the thickness of the component region W1 is reduced to the predetermined final thickness T (in Fig. 13), the second grinding unit 30 is moved upward. Also, in the third grinding step, the machining feed (ie, the downward movement) is performed at a speed lower than the speed used until the second grinding means 34 grinds the curved surface portion C1 of the first circular recess R1 in the second grinding step.

[0035] As in Fig. As shown in Figure 13, after the third grinding step, a second circular recess R2 is formed within the first circular recess R1 in the wafer W. The second circular recess R2 is formed in a circular shape as its surface shape and is formed as a recess from the bottom surface B1 of the first circular recess R1. As shown in Fig.13, the second circular recess R2 consists of a second lower surface B2 that is parallel to the holding surface 10a and flat, a second curved surface part C2 that is continuous with the outer edge of the second lower surface B2, and an inner peripheral surface I2 that is continuous with the second curved surface part C2 and perpendicular to the holding surface 10a. The inner peripheral surface I2 is continuous with the curved surface part C1 of the first circular recess R1. The second curved surface part C2 connects the inner peripheral surface I2 to the second lower surface B2 and is formed as such a curved surface that no edge line is formed between the second curved surface part C2 and the second lower surface B2, nor between the second curved surface part C2 and the inner peripheral surface I2.The second curved surface part C2 is formed with a radius of curvature smaller than that in the case where the second grinding means 34 are moved downward parallel to the Z-axis.

[0036] Thereafter, in the grinding apparatus 1, the rotary table is rotated, and the wafer W for which the third grinding step has been performed is removed from the chuck table 10. Thereafter, the wafer W for which the first grinding step, the second grinding step, and the third grinding step have not yet been performed is held on the chuck table 10, and the first grinding step, the second grinding step, and the third grinding step are sequentially performed as in the previous method.

[0037] According to the machining method of the second embodiment, when the second grinding means 34 are moved downward toward the curved surface part C1 at a position as close as possible to the inner peripheral wall I1 of the first circular recess R1, the second grinding means 34 are moved downward in an inclined direction from the center side of the wafer W toward the circumference. Therefore, the outer tip peripheries 34a of the second grinding means 34 are pressed against the curved surface part C1 in the inclined direction from the center side of the wafer W toward the circumference.For this reason, even if the second abrasives 34 are moved downward at a comparatively high speed until they come into contact with the lower surface B1 and the curved surface part C1 is slightly ground by the second abrasives 34, the wear (deformation) of the second abrasives 34 is suppressed compared to the case where the second abrasives 34 are moved downward in parallel with the Z-axis. Moreover, the machining feed of the second abrasives 34 in the third grinding step is performed in parallel with the Z-axis. Therefore, the radius of curvature of the second curved surface part C2 of the second circular recess R2 can be made smaller than in the case where the second abrasives 34 are moved downward in parallel with the Z-axis.Therefore, the machining method according to the second embodiment provides the effect that the second lower surface B2 of the second circular recess R2 formed after fine grinding is set wide, and therefore the flat area on the back surface of the wafer W corresponding to the device area W1 of the wafer W (ie, the second lower surface B2) can be expanded, preventing an increase in the machining time.

[0038] Subsequently, the inventor of the present invention examined the effects of the processing methods according to the above-described first embodiment and the above-described second embodiment. For this examination, the first circular recesses R1 were formed to each have the inner peripheral wall I1 with a thickness of 2.5 mm in the rear surfaces WR of the wafers W having a diameter of 200 mm. Thereafter, the second circular recesses R2 were formed by the second abrasives 34 by the processing methods of the present invention product 1 (product according to the first embodiment), the present invention product 2 (product according to the second embodiment), and a comparative example (product according to the prior art) in such a manner that the thickness of the device regions W1 was 50 μm.Next, the diameters of the second lower surfaces B2 and the radii of curvature of the second curved surface portions C2 in the second circular recesses R2 were measured. For the present invention product 1, the present invention product 2, and the comparative example, the second abrasives 34 formed from the same bonded vitrified abrasive grains were used, respectively. As a result, an expansion of the diameter of the second lower surface B2 by 0.7 mm in the present invention product 1 (product corresponding to the first embodiment) and by 1 mm in the present invention product 2 (product corresponding to the second embodiment) relative to the comparative example (product corresponding to the prior art) was confirmed.

[0039] Therefore, it became clear that the wear of the outer tip peripheries 34a of the second abrasives 34 is suppressed and an expansion of the device area W1 is enabled by moving the second abrasives 34 in an inclined direction from the center side of the wafer W toward the periphery in the second grinding step.

[0040] The present invention is not limited to the details of the preferred embodiments described above. The scope of the invention is defined by the appended claims.

Claims

[1] A wafer processing method in which a wafer (W) having a device region (W1) in which a plurality of devices (D) are formed in regions defined by a plurality of streets (S) formed on a front surface (WS) in a lattice arrangement, and having a peripheral excess region (W2) surrounding the device region (W1), is held on a holding surface (10a) of a chuck table (10), and a region on a rear surface (WR) corresponding to the device region (W1) is ground by a grinding means (24, 34) to adjust the thickness of the device region to a predetermined final thickness (T), the wafer processing method comprising: a first grinding step of moving a first grinding means (24) in a processing feed direction, which is a direction perpendicular to the holding surface (10a), and grinding the wafer (W) to form a first circular recess (R1) on the rear surface (WR) of the wafer (W); and a second grinding step of moving a second abrasive (34) formed of finer abrasive grains than the first abrasive (24) downward in an inclined direction from one side of the center of the wafer toward the periphery of the wafer and grinding the first circular recess (R1) after the first grinding step has been performed, wherein in the second grinding step, an outer tip periphery (34a) of the second grinding means (34) is moved inclined downward to a position which is closer to an inner side by a predetermined distance than an inner peripheral wall (I1) of the first circular recess (R1) and closer to an upper side by a predetermined distance than a lower surface (B1) of the first circular recess (R1), and a part of a curved surface part (C1) connecting the inner peripheral wall (I1) and the lower surface (B1) of the first circular recess is ground, and the wafer processing method further includes a third grinding step of moving the second grinding means (34) in the processing feed direction and grinding the lower surface of the first circular recess (R1) to adjust the thickness of the device region to a predetermined final thickness after the second grinding step is performed.

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