Wafer processing method

Abstract

To provide a wafer processing method capable of removing an outer peripheral excessive region while suppressing damages to a device in a grinding step of a bonded wafer.SOLUTION: A wafer processing method comprises: a bonded wafer forming step 201 of forming a bonded wafer by temporally bonding a first wafer and a second wafer; a modified layer formation step 202 of forming an annular modified layer and a crack extended from the modified layer into an internal part of the first wafer by a laser beam; an anneal processing step 203 of increasing a bonding strength of the bonded wafer by annealed processing; an outer peripheral region removing step 204 of positioning a cutting blade in an annular region of the first wafer, and removing an outer peripheral region on an outer peripheral edge side from the modified layer and the crack by cutting up to a depth that does not reach the second wafer from the other surface side and cutting it along an annular region; and a grinding step 205 of grinding the first wafer from the other surface side to reduce it to a finishing thickness.SELECTED DRAWING: Figure 12

Description

[Technical field]

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

[0002] In recent years, the development of 3D stacked semiconductor wafers has progressed in line with the trend toward lower profile and higher integration of device chips. For example, TSV (Through-Silicon Via) wafers enable the connection of electrodes between two chips by bonding them together using through-hole electrodes.

[0003] Such wafers are ground and thinned while bonded to a support wafer (silicon, glass, ceramics, etc.) that serves as a base. Normally, the outer edge of a wafer is chamfered, so when the wafer is ground to an extremely thin thickness, the outer edge becomes a so-called knife edge, and the edge is likely to chip during grinding. This may cause the chip to extend to the device, leading to damage to the device.

[0004] As a countermeasure against the knife edge, a so-called edge trimming technique has been developed in which the outer periphery on the front surface side of the wafer is cut into an annular shape (see Patent Document 1). Also, an edge trimming method has been devised in which after bonding the wafers together, a laser beam is irradiated along the outer periphery of the device to form an annular modified layer, thereby preventing edge chipping of the wafer that occurs during grinding from extending into the device (see Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4895594 [Patent Document 2] JP 2020-057709 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method of Patent Document 1 has the problem that chipping may reach the device during cutting, damaging the device, and a large amount of cutting waste is generated, which makes the device susceptible to contamination. In addition, the method of Patent Document 2 has the problem that, when the modified layer is formed inside the bonding area, the end material of the peripheral surplus area that should be removed during grinding may not peel off and may remain. Even if it can be peeled off during grinding, the end material of the peripheral surplus area may get caught between the grinding wheel and the wafer, causing scratches on the wafer.

[0007] The present invention has been made in consideration of such problems, and its object is to provide a wafer processing method that can remove the outer peripheral excess region while suppressing damage to the device in the grinding process of the bonded wafer. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, a first aspect of a wafer processing method of the present invention includes a bonded wafer forming step of temporarily bonding one surface of a first wafer and one surface of a second wafer to form a bonded wafer in order to bond a first wafer and a second wafer, a modified layer forming step of irradiating a laser beam having a wavelength that transmits the first wafer onto an annular region a predetermined distance inside an outer circumferential edge of the first wafer after the bonded wafer forming step, thereby forming an annular modified layer and cracks extending from the modified layer inside the first wafer, and a modified layer forming step of performing a modified layer forming step on the bonded wafer after the modified layer forming step. The method includes an annealing step of increasing the bonding strength between the first wafer and the second wafer by performing an annealing treatment, and a grinding step of grinding the first wafer of the bonded wafer from the other surface side to thin it to a finish thickness after performing the annealing step, and further includes a peripheral region removal step of positioning a cutting blade in the annular region of the first wafer after performing the modified layer formation step and before performing the grinding step, cutting from the other surface side of the first wafer to a depth not reaching the second wafer and cutting along the annular region, thereby removing the modified layer and the peripheral region on the outer periphery side of the crack.

[0009] A second aspect of the wafer processing method of the present invention includes a bonded wafer forming step of bonding one surface of a first wafer and one surface of a second wafer to form a bonded wafer, a modified layer forming step of irradiating a laser beam having a wavelength that transmits the first wafer onto an annular region a predetermined distance inside an outer periphery of the first wafer after the bonded wafer forming step is performed, and forming an annular modified layer and cracks extending from the modified layer inside the first wafer. and a peripheral region removing step of, after performing a modified layer forming step, positioning a cutting blade in the annular region of the first wafer, cutting from the other surface side of the first wafer to a depth not reaching the second wafer and cutting along the annular region to remove the modified layer and the peripheral region on the outer edge side of the crack, and a grinding step of, after performing the peripheral region removing step, grinding the first wafer of the bonded wafer from the other surface side to thin it to a finishing thickness.

[0010] In addition, in the wafer processing method of the present invention, it is preferable that the outer peripheral region removal step involves cutting from the other surface side of the first wafer to a depth that does not reach the modified layer and cutting along the annular region.

[0011] In the wafer processing method of the present invention, in the outer peripheral region removing step, the center in the thickness direction of the cutting blade may be positioned radially outward of the first wafer relative to the annular region.

[0012] In the wafer processing method of the present invention, in the outer peripheral region removing step, the center in the thickness direction of the cutting blade may be positioned radially inward of the annular region of the first wafer. Effect of the Invention

[0013] The present invention is capable of removing the outer circumferential excess region while suppressing damage to devices in a grinding process of a bonded wafer. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing an example of a wafer to be processed by the wafer processing method according to the first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view taken along the line II-II shown in FIG. [Diagram 3] FIG. 3 is a flowchart showing the flow of the wafer processing method according to the first embodiment. [Figure 4] FIG. 4 is a perspective view showing one state of the bonded wafer forming step shown in FIG. [Diagram 5] FIG. 5 is a side view, partly in section, showing one state of the modified layer forming step shown in FIG. [Figure 6] FIG. 6 is an enlarged cross-sectional view showing a part of the bonded wafer after the modified layer forming step shown in FIG. [Figure 7] FIG. 7 is a side view, partially in section, showing one state of the outer periphery region removing step shown in FIG. [Figure 8] FIG. 8 is a cross-sectional view showing an example of positioning of the cutting blade in FIG. [Figure 9] FIG. 9 is a cross-sectional view showing an example of positioning of the cutting blade in FIG. [Figure 10] FIG. 10 is a cross-sectional view showing an example of positioning of the cutting blade in FIG. [Figure 11] FIG. 11 is a side view, partly in section, showing one state of the grinding step shown in FIG. [Figure 12] FIG. 12 is a flowchart showing the flow of the wafer processing method according to the second embodiment. [Figure 13] FIG. 13 is a side view, partly in section, showing one state of the bonded wafer forming step shown in FIG. [Figure 14] FIG. 14 is a cross-sectional view that typically shows a state of the bonding surface of the bonded wafer after the bonded wafer forming step shown in FIG. [Figure 15] FIG. 15 is a side view, partially in cross section, illustrating an example of the annealing step shown in FIG. [Figure 16] FIG. 16 is a cross-sectional view that typically shows the state of the bonding surface of the bonded wafer after the annealing treatment step shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The form (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. Furthermore, the components described below include those that a person skilled in the art can easily imagine and those that are substantially the same. Furthermore, the configurations described below can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the configurations can be made without departing from the gist of the present invention.

[0016] [First embodiment] A method for processing a wafer 10 according to a first embodiment of the present invention will be described with reference to the drawings. First, the wafer 10 to be processed will be described. Fig. 1 is a perspective view showing an example of the wafer 10 to be processed by the method for processing a wafer 10 according to the first embodiment. Fig. 2 is a cross-sectional view taken along the line II-II shown in Fig. 1.

[0017] 1 and 2 is a wafer such as a disk-shaped semiconductor wafer or an optical device wafer, with silicon (Si), sapphire (Al2O3), gallium arsenide (GaAs), silicon carbide (SiC), or the like, as a substrate 11, and in the first embodiment, is a silicon wafer. As shown in Fig. 2, the wafer 10 has a chamfered outer periphery 12 such that the center in the thickness direction protrudes most toward the outer periphery, and the cross section from the front surface 13 to the back surface 14 of the substrate 11 is arc-shaped.

[0018] 1, the wafer 10 has a device layer including a central region 15 on the surface 13 side of the substrate 11 and an outer periphery region 16 surrounding the central region 15. The central region 15 has a plurality of planned division lines 17 set in a lattice pattern on the surface 13 of the substrate 11, and devices 18 formed in each region partitioned by the planned division lines 17. The outer periphery region 16 is a region surrounding the central region 15 all around and in which no devices 18 are formed.

[0019] In the first embodiment, the device 18 constitutes a 3D NAND flash memory and includes an electrode pad and a through electrode connected to the electrode pad. The through electrode penetrates the back surface 14 of the substrate 11 when the substrate 11 is thinned and the devices 18 are individually separated from the wafer 10. That is, the wafer 10 of the first embodiment is a so-called TSV wafer in which the individually separated devices 18 have through electrodes. Note that the wafer 10 of the present invention is not limited to a TSV wafer having through electrodes as in the first embodiment, and may be a device wafer without through electrodes.

[0020] Next, the flow of the processing method of the wafer 10 will be described. FIG. 3 is a flow chart showing the flow of the processing method of the wafer 10 according to the first embodiment. As shown in FIG. 3, the processing method of the wafer 10 according to the first embodiment includes a bonded wafer forming step 101, a modified layer forming step 102, an outer peripheral region removing step 103, and a grinding step 104. The processing method of the wafer 10 according to the first embodiment is a method in which one surface side of a pair of wafers 10 is bonded to each other, a division starting point for removing the outer peripheral region 16 is formed, and then one wafer 10 (first wafer 10-1) is thinned to a predetermined finishing thickness 19. In the first embodiment, the one surface is the front surface 13.

[0021] In the following description, when distinguishing between the wafers 10 of the pair of wafers 10, one wafer 10 will be referred to as a first wafer 10-1 and the other wafer 10 will be referred to as a second wafer 10-2 (see FIG. 4), and when no distinction is required, the wafers will be simply referred to as wafers 10. The other, second wafer 10-2, which is not thinned, will be described as a TSV wafer similar to the first wafer 10-1 in the first embodiment, but in the present invention, it may be a simple substrate wafer without a pattern.

[0022] (Bonded wafer formation step 101) Fig. 4 is a perspective view showing one state of the bonded wafer forming step 101 shown in Fig. 3. The bonded wafer forming step 101 is a step of forming a bonded wafer 20 by bonding one surface (front surface 13 in the first embodiment) of a first wafer 10-1 and one surface (front surface 13 in the first embodiment) of a second wafer 10-2 together.

[0023] In the bonded wafer forming step 101, first, the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2 are opposed to each other with a gap therebetween, as shown in Fig. 4. Next, the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2 are bonded together. In this way, the bonded wafer 20 is formed.

[0024] In this case, when a bonding layer is provided between the first wafer 10-1 and the second wafer 10-2, the bonding layer is laminated on one of the front surface 13 of the first wafer 10-1 and the front surface 13 of the second wafer 10-2, and then the front surface 13 of the first wafer 10-1 and the front surface 13 of the second wafer 10-2 are bonded together via the bonding layer. The bonding layer may be a double-sided tape having an adhesive layer laminated on the front and back surfaces of a base layer, an oxide film, or a layer formed by applying an adhesive containing a resin or the like.

[0025] Also, the first wafer 10-1 and the second wafer 10-2 may be directly bonded together without using a bonding layer. Also, in the embodiment, the front surface 13 side of the first wafer 10-1 and the front surface 13 side of the second wafer 10-2 are bonded together, but when the second wafer 10-2 is a substrate wafer, the front surface 13 side of the first wafer 10-1 and the front surface 13 side of the second wafer 10-2 may be bonded together.

[0026] (Modified layer forming step 102) Fig. 5 is a side view partially in cross section showing one state of the modified layer forming step 102 shown in Fig. 3. Fig. 6 is a cross-sectional view partially enlargedly showing the bonded wafer 20 after the modified layer forming step 102 shown in Fig. 3. The modified layer forming step 102 is performed after the bonded wafer forming step 101 is performed. The modified layer forming step 102 is a step of irradiating a laser beam 43 having a wavelength that transmits the first wafer 10-1 onto an annular region 23 located a predetermined distance inside the outer circumferential edge 12 of the first wafer 10-1, to form an annular modified layer 21 and cracks 22 extending from the modified layer 21 inside the first wafer 10-1.

[0027] In the modified layer forming step 102, a modified layer 21 and cracks 22 are formed inside the first wafer 10-1 by stealth dicing using a laser processing device 40 shown in FIG. 5. The laser processing device 40 includes a holding table 41 and a laser beam irradiation unit 42. The holding table 41 holds the wafer 10 on a holding surface and is rotatable around a vertical axis. The laser beam irradiation unit 42 irradiates a laser beam 43 onto the wafer 10 held on the holding table 41. The laser processing device 40 further includes a moving unit (not shown) that moves the holding table 41 and the laser beam irradiation unit 42 relatively, an imaging unit (not shown) that images the wafer 10 held on the holding table 41, and the like.

[0028] In the modified layer forming step 102, a laser beam 43 is irradiated from the back surface 14 side of the first wafer 10-1 along a position a predetermined distance inside the outer circumferential edge 12 of the first wafer 10-1, thereby forming an annular modified layer 21 inside the first wafer 10-1. Specifically, the position a predetermined distance inside the outer circumferential edge 12 is the boundary between the central region 15 and the outer circumferential region 16. The laser beam 43 is a laser beam with a wavelength that is transparent to the first wafer 10-1, for example, infrared rays (IR).

[0029] The modified layer 21 refers to a region in which the density, refractive index, mechanical strength or other physical properties are different from those of the surrounding area as a result of irradiation with the laser beam 43. The modified layer 21 is, for example, a melting process region, a crack region, a dielectric breakdown region, a refractive index change region, a region in which these regions are mixed, etc. The modified layer 21 has a lower mechanical strength, etc. than other parts of the first wafer 10-1.

[0030] In the modified layer forming step 102, first, the back surface 14 of the second wafer 10-2 is sucked and held on the holding surface (upper surface) of the holding table 41. Next, the first wafer 10-1 and the condenser of the laser beam irradiation unit 42 are aligned. Specifically, the holding table 41 is moved to an irradiation area below the laser beam irradiation unit 42 by a moving unit (not shown). Next, the first wafer 10-1 is photographed and aligned by an imaging unit (not shown), so that the irradiation part of the laser beam irradiation unit 42 is vertically opposed to a position a predetermined distance inside the outer circumferential edge 12 of the first wafer 10-1, and then the focusing point 44 of the laser beam 43 is set inside the first wafer 10-1.

[0031] In the modified layer forming step 102, next, while rotating the holding table 41 about a vertical axis, a pulsed laser beam 43 is emitted from a laser beam irradiation unit 42 to the back surface 14 of the first wafer 10-1. That is, the laser beam 43 is annularly irradiated along a position a predetermined distance inside the outer circumferential edge 12 of the first wafer 10-1.

[0032] As a result, an annular modified layer 21 is formed on the first wafer 10-1 along a position a predetermined distance inward from the outer circumferential edge 12, a crack 22 extends from the modified layer 21, and a split starting point is formed at a position a predetermined distance inward from the outer circumferential edge 12 of the first wafer 10-1 by connecting the modified layer 21 and the crack 22. As shown in Fig. 6, in the modified layer forming step 102, it is preferable to form the modified layer 21 by irradiating with a laser beam 43 so that the crack 22 extending from the modified layer 21 is exposed on the front surface 13 side of the first wafer 10-1.

[0033] In the modified layer forming step 102, the height of the focal point 44 of the laser beam 43 may be changed to irradiate the laser beam 43 multiple times, or the laser beam 43 having multiple focal points 44 spaced apart in the thickness direction of the first wafer 10-1 may be irradiated to form multiple modified layers 21 overlapping in the thickness direction of the first wafer 10-1. When the laser beam 43 is irradiated from the back surface 14 side of the first wafer 10-1 multiple times, the modified layer 21 is formed in sequence from the front surface 13 side to the back surface 14 side. Moreover, "perpendicular to the front surface 13 of the first wafer 10-1" indicates that the inclination of the approximation plane obtained by approximating the entire extended crack 22 to a plane with respect to the vertical plane is within ±5 degrees, preferably within ±2 degrees. Moreover, the laser beam 43 branched in the traveling direction of the laser beam 43 may be used, or the laser beam 43 branched in a direction perpendicular to the traveling direction may be used, or an elliptical laser beam 43 having a major axis in the traveling direction and a minor axis in a direction perpendicular to the traveling direction may be used.

[0034] As shown in FIG. 6, in the first wafer 10-1, due to the formation of a modified layer 21 and a crack 22, a warp occurs in which the surface 13 side is convex in the outer peripheral region 16 on the outer peripheral edge 12 side of the modified layer 21 and the crack 22.

[0035] The warpage of the outer peripheral region 16 releases the bond between the first wafer 10-1 and the second wafer 10-2. The release of the bond due to the warpage is not limited to the interface between the device layer on the front surface 13 side of the first wafer 10-1 and the device layer on the front surface 13 side of the second wafer 10-2, but may be at the interface between the substrate 11 of the first wafer 10-1 and the device layer, or at the interface between the substrate 11 of the second wafer 10-2 and the device layer. When the modified layer 21 and the cracks 22 are formed in an annular shape along the entire circumference of the first wafer 10-1, the modified layer forming step 102 is completed.

[0036] (Outer region removal step 103) 7 is a side view partially in cross section showing one state of the outer circumferential region removing step 103 shown in FIG. The outer circumferential region removing step 103 is performed after the modified layer forming step 102 is performed. The outer circumferential region removing step 103 is a step in which a cutting blade 53 is positioned in the annular region 23 of the first wafer 10-1, and cutting is performed along the annular region 23 by cutting into the other surface (in the first embodiment, from the back surface 14 side) of the first wafer 10-1 to a depth not reaching the second wafer 10-2, thereby removing the outer circumferential region 16 on the outer circumferential edge 12 side of the modified layer 21 and the crack 22. In the first embodiment, the cutting is performed to a depth not reaching the modified layer 21.

[0037] In the outer peripheral region removing step 103 of the first embodiment, cutting is performed along the annular region 23 to a predetermined depth by a cutting device 50 shown in FIG. 7. The cutting device 50 includes a holding table 51 and a cutting unit 52. The cutting unit 52 includes a cutting blade 53, a spindle 54, and a spindle housing 55. The cutting blade 53 has an annular cutting grindstone, and is attached to the spindle 54 so that its axis coincides with the axis of the spindle 54. The spindle 54, which is a rotating shaft member, rotates about a rotation axis parallel to the holding surface of the holding table 51. The spindle housing 55 holds the spindle 54 rotatably around the rotation axis. The cutting device 50 further includes a moving unit (not shown) that moves the holding table 51 and the cutting blade 53 relatively, an imaging unit (not shown), and a cutting water supply unit (not shown) that supplies cutting water to the processing point of the cutting blade 53.

[0038] In the outer peripheral region removing step 103, first, the back surface 14 side of the second wafer 10-2 is suction-held on the holding surface of the holding table 51. Next, the first wafer 10-1 and the cutting blade 53 are aligned. Specifically, the holding table 51 is moved to the processing region below the cutting blade 53 by a moving unit (not shown). Next, the first wafer 10-1 is photographed and aligned by an imaging unit (not shown), thereby aligning the processing point of the cutting blade 53 with the annular region 23 of the first wafer 10-1.

[0039] In the outer peripheral region removing step 103, next, a cutting water supply unit (not shown) starts to supply cutting water toward the front surface 13 of the first wafer 10-1. Next, a moving unit (not shown) cuts the cutting blade 53 and rotates the holding table 51 around a vertical axis. Then, the cutting blade 53 cuts into the first wafer 10-1 from the front surface 13 side to a predetermined depth.

[0040] The predetermined depth is at most a depth that does not reach the second wafer 10-2. The predetermined depth is preferably a depth that reaches the crack 22 formed in the modified layer forming step 102, but does not necessarily have to reach the position of the crack 22 at the time of its formation in the modified layer forming step 102 because the crack 22 extends due to the stress load by the cutting blade 53. For example, when the thickness of the first wafer 10-1 is 775 μm and the formation position of the modified layer 21 closest to the back surface 14 is 600 μm deep, the predetermined depth is 580 μm.

[0041] In the outer peripheral region removing step 103, the annular region 23 is cut to a predetermined depth, whereby a stress load is applied by the cutting blade 53 and a crack propagates between the front surface 13 side of the first wafer 10-1 and the crack 22. As a result, the end material of the outer peripheral region 16 is removed, with the modified layer 21, the crack 22, and the cut groove serving as division starting points.

[0042] 8 to 10 are cross-sectional views showing examples of positioning of the cutting blade 53 in FIG. 7. In the example shown in FIG. 8, the center in the thickness direction of the cutting blade 53 is positioned radially outward of the first wafer 10-1 relative to the annular region 23. In the example shown in FIG. 9, the center in the thickness direction of the cutting blade 53 is positioned radially inward of the first wafer 10-1 relative to the annular region 23. In the example shown in FIG. 10, the entire thickness direction of the cutting blade 53 is positioned radially inward of the first wafer 10-1 relative to the annular region 23.

[0043] 8, when the center of the cutting blade 53 in the thickness direction is positioned radially outward of the annular region 23 of the first wafer 10-1, a load is applied directly to the outer circumferential region 16 itself, so that the outer circumferential region 16 can be removed by just bringing the cutting blade 53 into contact with the back surface 14 of the first wafer 10-1 without increasing the cutting depth. Therefore, while the amount of cutting can be reduced and cutting debris can be reduced, there is a possibility that the outer circumferential region 16 will easily scatter within the device.

[0044] 9 and 10, when the center in the thickness direction of the cutting blade 53 is positioned radially inward of the annular region 23, no load is directly applied to the outer circumferential region 16 itself, so scattering of the outer circumferential region 16 into the apparatus can be suppressed. Therefore, it is preferable to appropriately set the center depending on the size and material of the first wafer 10-1 to be processed, the size of the outer circumferential region 16, etc.

[0045] (Grinding step 104) Fig. 11 is a side view, partially in cross section, showing one state of the grinding step 104 shown in Fig. 3. The grinding step 104 is performed after the outer circumferential region removing step 103 is performed. The grinding step 104 is a step of grinding the first wafer 10-1 of the bonded wafer 20 from the other surface (back surface 14 in the first embodiment) side to thin it down to a finish thickness 19.

[0046] In the grinding step 104 of the first embodiment, the back surface 14 side of the first wafer 10-1 is ground to a predetermined finish thickness 19 by a grinding device 70 shown in Fig. 11. The grinding device 70 includes a holding table 71, a spindle 72 which is a rotating shaft member, a grinding wheel 73 attached to the lower end of the spindle 72, a grinding stone 74 attached to the lower surface of the grinding wheel 73, and a grinding fluid supply unit (not shown). The grinding wheel 73 rotates on an axis parallel to the axis of the holding table 71.

[0047] In the grinding step 104, first, the back surface 14 side of the second wafer 10-2 is suction-held on the holding surface of the holding table 71. Next, while the holding table 71 is rotated about its axis, the grinding wheel 73 is rotated about its axis. Grinding fluid is supplied to the processing point by a grinding fluid supply unit (not shown), and the grinding wheel 74 of the grinding wheel 73 is brought close to the holding table 71 at a predetermined feed speed, whereby the back surface 14 of the first wafer 10-1 is ground by the grinding wheel 74 to be thinned to a predetermined finishing thickness 19.

[0048] Second Embodiment A method for processing a wafer 10 according to a second embodiment of the present invention will be described with reference to the drawings. The wafer 10 to be processed in the second embodiment is similar to the wafer 10 to be processed in the first embodiment, and therefore a description thereof will be omitted. In addition, in the description of the second embodiment, the same elements as those in the first embodiment are denoted by the same reference numerals, and a description thereof will be omitted as appropriate.

[0049] The flow of the processing method for the wafer 10 according to the second embodiment will be described. Fig. 12 is a flowchart showing the flow of the processing method for the wafer 10 according to the second embodiment. As shown in Fig. 12, the processing method for the wafer 10 according to the second embodiment includes a bonded wafer forming step 201, a modified layer forming step 202, an annealing step 203, an outer peripheral region removing step 204, and a grinding step 205.

[0050] In addition, since the modified layer forming step 202, the outer peripheral region removing step 204, and the grinding step 205 in the second embodiment are similar to the modified layer forming step 102, the outer peripheral region removing step 103, and the grinding step 104 in the first embodiment, their explanations are omitted.

[0051] (Bonded wafer formation step 201) Fig. 13 is a side view partially in cross section showing one state of the bonded wafer forming step 201 shown in Fig. 12. Fig. 14 is a cross-sectional view typically showing the state of the bonding surface of the bonded wafer 20 after the bonded wafer forming step 201 shown in Fig. 12. The bonded wafer forming step 201 of the second embodiment is a step of forming the bonded wafer 20 by temporarily bonding one surface (front surface 13 in the second embodiment) of the first wafer 10-1 and one surface (front surface 13 in the second embodiment) of the second wafer 10-2 to bond the first wafer 10-1 and the second wafer 10-2.

[0052] In the bonded wafer forming step 201 of the second embodiment, at least one of the surfaces to be bonded of the first wafer 10-1 and the second wafer 10-2 is subjected to plasma treatment to activate the surfaces, and then bonded together for temporary bonding. Note that the temporary bonding strength is increased by performing annealing treatment in the annealing treatment step 203 described later.

[0053] In the bonded wafer formation step 201 of the second embodiment, a plasma treatment is performed on the front surface 13 of the wafer 10 (first wafer 10-1 and second wafer 10-2) by a plasma treatment apparatus 30 shown in Fig. 13. The plasma treatment apparatus 30 includes a chamber 31, a lower electrode 32, an upper electrode 34, a gas supply source 35, a high-frequency power source 36, and an electrostatic adsorption mechanism, a lifting mechanism, a loading / unloading port, and an exhaust mechanism, all of which are not shown.

[0054] A lower electrode 32 and an upper electrode 34 are arranged vertically facing each other within the chamber 31. The lower electrode 32 is made of a conductive material and has a disk-shaped holder that holds the wafer 10. An electrostatic adsorption mechanism (not shown) is formed inside the holder. When the electrostatic adsorption mechanism is driven, the wafer 10 placed on the upper surface of the holder can be fixed by electrostatic adsorption.

[0055] The upper electrode 34 is made of a conductive material and has a disk-shaped gas outlet that covers the upper side of the wafer 10 held by the holder of the lower electrode 32. The gas outlet is connected to a gas supply source 35. The gas supply source 35 supplies a process gas such as argon (Ar), nitrogen (N2), or oxygen (O2) into the chamber 31 through the gas outlet. The upper electrode 34 can be raised and lowered relative to the lower electrode 32 by a lifting mechanism (not shown).

[0056] The lower electrode 32 and the upper electrode 34 have an insulating member (not shown) between them and the chamber 31, and are insulated from the chamber 31. The lower electrode 32 and the upper electrode 34 are connected to a high-frequency power supply 36. The high-frequency power supply 36 supplies a predetermined high-frequency power to the lower electrode 32 and the upper electrode 34 based on a control signal output from a control device (not shown).

[0057] In the bonded wafer forming step 201, first, the wafer 10 is carried into the chamber 31 through an entrance (not shown) and placed on the holder of the lower electrode 32 so that the front surface 13 faces upward. Next, an electrostatic adsorption mechanism (not shown) is driven to electrostatically adsorb and hold the wafer 10 on the holder. The entrance (not shown) is also closed to seal the processing space in the chamber 31. Furthermore, the height position of the upper electrode 34 is adjusted by an elevation mechanism (not shown) so that the lower electrode 32 and the upper electrode 34 have a predetermined positional relationship suitable for plasma processing.

[0058] In the bonded wafer forming step 201, next, an exhaust mechanism (not shown) is driven to evacuate (low pressure) the processing space in the chamber 31. Next, a process gas is supplied from the gas supply source 35 to the processing space in the chamber 31 at a predetermined flow rate, while a predetermined high frequency power is supplied from the high frequency power source 36 to the lower electrode 32 and the upper electrode 34, thereby supplying a plasma gas to the surface 13 of the wafer 10. By carrying out such plasma processing, surface impurities such as organic matter adsorbed on the surface 13 of the wafer 10 are removed, and a clean surface is exposed. Furthermore, hydroxyl groups (OH groups) are bonded to the Si dangling species on the exposed clean surface 13. That is, OH groups are formed on the surface 13 of the wafer 10 activated by the plasma processing.

[0059] In the bonded wafer forming step 201, the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2 are opposed to each other with a gap therebetween, similarly to the bonded wafer forming step 101 of the first embodiment shown in Fig. 4. Next, the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2 are bonded together. In this way, the bonded wafer 20 is formed.

[0060] At this time, as shown in Fig. 14, the hydrogen atom (H) of the OH group formed on the surface 13 side of the first wafer 10-1 forms a hydrogen bond with the oxygen atom (O) of the OH group formed on the surface 13 side of the second wafer 10-2. Also, the hydrogen atom (H) of the OH group formed on the surface 13 side of the second wafer 10-2 forms a hydrogen bond with the oxygen atom (O) of the OH group formed on the surface 13 side of the first wafer 10-1. As a result, the first wafer 10-1 and the second wafer 10-2 are attracted to each other by the hydrogen bond and are temporarily bonded.

[0061] The plasma treatment in the bonded wafer forming step 201 is performed on both the front surface 13 of the first wafer 10-1 and the front surface 13 of the second wafer 10-2, but may be performed on either one of the surfaces. Furthermore, the method of performing the plasma treatment in the bonded wafer forming step 201 is not limited to the reduced pressure plasma method described in the second embodiment in which the pressure inside the chamber 31 is reduced to generate plasma, but may be an open atmospheric pressure plasma method in which a plasma generating electrode is scanned in-plane while the wafer 10 is placed on the chamber and in standby.

[0062] (Annealing step 203) Fig. 15 is a side view partially in cross section showing an example of the annealing treatment step 203 shown in Fig. 12. Fig. 16 is a cross-sectional view typically showing the state of the bonding surface of the bonded wafer 20 after the annealing treatment step 203 shown in Fig. 12. The annealing treatment step 203 is performed after the modified layer forming step 202 and before the outer periphery region removing step 204. The annealing treatment step 203 is a step for increasing the bonding strength between the first wafer 10-1 and the second wafer 10-2 by performing an annealing treatment on the bonded wafer 20.

[0063] The annealing step 203 of the second embodiment is performed in an annealing apparatus 60 shown in Fig. 15. The annealing apparatus 60 includes a chamber 61, a holding table 62, and a heating source 63. The holding table 62 is disposed in the chamber 61. The holding table 62 is capable of suction-holding the bonded wafer 20 on its holding surface. The inside of the chamber 61 is heated by the heating source 63. The heating source 63 includes, for example, an infrared lamp. The holding table 62 may have an internal heating source, and the holding table 62 may heat the bonded wafer 20 held on its holding surface.

[0064] In the annealing step 203 of the second embodiment, first, the bonded wafer 20 is carried into the chamber 61 through a carry-in port (not shown) and held by the holding table 62. Next, the heating source 63 is driven to heat the inside of the chamber 61. The wafer 10 of the second embodiment is a silicon wafer, and therefore easily absorbs infrared rays. Therefore, the bonded wafer 20 heated by the heating source 63 including an infrared lamp is heated rapidly. This heating method is called RTA (Rapid Thermal Anneal).

[0065] A dehydration condensation reaction occurs at the bonding surfaces between the first wafer 10-1 and the second wafer 10-2 of the heated bonded wafer 20. That is, water (H2O) is lost from the OH groups formed on the surface 13, resulting in covalent bonds via oxygen atoms (O), thereby improving the bond strength between the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2.

[0066] In the annealing step 203, the method of annealing the bonded wafer 20 is not limited to the single-wafer RTA in which the bonded wafer 20 is rapidly heated one by one inside the chamber 61 described in the second embodiment, and may be, for example, a batch type in which a plurality of bonded wafers 20 arranged in a quartz furnace tube are heated from the outside by a heater and simultaneously heat-treated. In addition, the method is not limited to infrared heating, and may be a method of heating with a hot plate.

[0067] As described above, the method of processing the wafer 10 in each embodiment involves irradiating a laser beam 43 to an annular region 23 located a predetermined distance inside the outer peripheral edge 12 of the bonded wafer 20 to form a modified layer 21 and a crack 22 extending from the modified layer 21, and then cutting along the annular region 23 with a cutting blade 53.

[0068] This makes it possible to reliably remove the end material of the outer peripheral region 16 starting from the modified layer 21, and prevents the end material from being pinched between the grinding wheel 73 and the first wafer 10-1 during grinding and being damaged. In addition, cutting waste can be reduced compared to the case where the thickness of the annular region 23 is processed by simply cutting only.

[0069] It should be noted that the present invention is not limited to the above-described embodiments, and can be practiced in various modified forms without departing from the gist of the present invention.

[0070] For example, in the modified layer forming steps 102, 202, an auxiliary modified layer may be formed at a predetermined circumferential position in the outer peripheral region 16 of the first wafer 10-1 between the inner peripheral edge and the outer peripheral edge 12 of the outer peripheral region 16. This promotes warping and peeling in the outer peripheral region 16. Also, the auxiliary modified layer divides the outer peripheral region 16 into multiple regions, making it easier to remove the outer peripheral region 16.

[0071] In the second embodiment, the outer periphery region removing step 204 may be performed before performing the annealing treatment step 203. This makes it possible to remove the outer periphery region 16 in a state where the bonding strength is weak. [Explanation of symbols]

[0072] 10 wafers 10-1 First wafer 10-2 Second wafer 11 Substrate 12 Outer rim 13 Surface 14 Back side 15 Central area 16 Outer area 17 Division line 18 Devices 19 Finished thickness 20 Bonded wafer 21 Modification layer 22 Crack 23 Annular Region 43 Laser Beam 44 Focus point 53 Cutting blade

Claims

1. A wafer processing method comprising the steps of: a bonded wafer forming step of temporarily bonding one surface of the first wafer and one surface of the second wafer to form a bonded wafer in order to bond the first wafer and the second wafer; a modified layer forming step of irradiating a laser beam having a wavelength that transmits through the first wafer onto an annular region located a predetermined distance inside an outer periphery of the first wafer, and forming an annular modified layer and cracks extending from the modified layer inside the first wafer, after the bonded wafer forming step is performed; an annealing step of increasing the bonding strength between the first wafer and the second wafer by performing an annealing treatment on the bonded wafer after performing the modified layer forming step; a grinding step of grinding the first wafer of the bonded wafer from the other surface side to thin it to a finish thickness after the annealing step is performed; Equipped with After performing the modified layer forming step and before performing the grinding step, a cutting blade is positioned in the annular region of the first wafer, and the cutting blade cuts from the other surface side of the first wafer to a depth not reaching the second wafer, thereby cutting along the annular region, thereby removing the modified layer and the peripheral region on the outer periphery side of the crack. A wafer processing method comprising the steps of:

2. A wafer processing method comprising the steps of: a bonded wafer forming step of bonding one surface of the first wafer and one surface of the second wafer together to form a bonded wafer; a modified layer forming step of irradiating a laser beam having a wavelength that transmits through the first wafer onto an annular region located a predetermined distance inside an outer periphery of the first wafer, and forming an annular modified layer and cracks extending from the modified layer inside the first wafer, after the bonded wafer forming step is performed; an outer circumferential region removing step of, after carrying out the modified layer forming step, positioning a cutting blade in the annular region of the first wafer, cutting from the other surface side of the first wafer to a depth not reaching the second wafer and cutting along the annular region, thereby removing the modified layer and the outer circumferential region on the outer circumferential edge side of the crack; a grinding step of grinding the first wafer of the bonded wafer from the other surface side to thin the first wafer to a finish thickness after the outer periphery region removing step is performed; Equipped A wafer processing method comprising the steps of:

3. In the outer periphery region removing step, The first wafer is cut from the other surface side to a depth not reaching the modified layer and cut along the annular region.

3. The wafer processing method according to claim 1 or 2.

4. In the outer periphery region removing step, The center of the cutting blade in the thickness direction is positioned radially outward of the first wafer relative to the annular region.

3. The wafer processing method according to claim 1 or 2.

5. In the outer periphery region removing step, The center of the cutting blade in the thickness direction is positioned radially inward of the first wafer relative to the annular region.

3. The wafer processing method according to claim 1 or 2.

Images