Wafer processing method

Abstract

To provide a wafer processing method capable of removing an outer peripheral residual region while suppressing damages to a device in a grinding step of a bonded wafer.SOLUTION: A wafer processing method comprises: a plasma activation processing step 101 of executing plasma processing to at least one surface of a first wafer and a second wafer to activate the surface; a bonded wafer formation step 102 of forming a bonded wafer by temporally bonding the first and the second wafers; a modified layer formation step 103 of generating a wrapping of an outer peripheral region by forming an annular modified layer and a crack inside the first wafer by a laser beam; a crimp step 104 of crimping a center region; an annealing processing step 105 of increasing a bonding strength of the bonded wafer by the annealing processing; and a grinding step 106 of grinding the first wafer to thin it down to a finishing thickness.SELECTED DRAWING: Figure 3

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 that a large amount of cutting waste is generated, which may easily contaminate the device. Also, the method of Patent Document 2 has the problem that, when the modified layer is formed inside the bonding region, the end material in the peripheral excess region that should be removed during grinding may not peel off and may remain.

[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 wafer processing method of the present invention includes a plasma activation processing step of performing a plasma treatment on at least one of one surface of the first wafer and one surface of the second wafer to activate the plasma-treated surface in order to bond a first wafer and a second wafer, a bonded wafer forming step of temporarily bonding the one surface of the first wafer and the one surface of the second wafer to form a bonded wafer after performing the plasma activation processing step, and a bonded wafer forming step of annularly irradiating a laser beam having a wavelength that transmits the first wafer along a position a predetermined distance inside an outer circumferential edge of the first wafer, thereby forming an annular modified layer and a modified layer inside the first wafer. a modified layer forming step of forming a crack extending from a modified layer and appearing on the one surface side of the first wafer, thereby causing warping in the modified layer and in the outer peripheral region on the outer edge side from the crack; 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; and a grinding step of grinding the first wafer of the bonded wafer from the other surface side to thin it down to a finish thickness after performing the annealing treatment step, and further comprising a compression step of compressing a central region of the first wafer that is closer to the center than the modified layer after performing the modified layer forming step and before performing the annealing treatment step, or while performing the annealing treatment step.

[0009] In addition, it is preferable that the wafer processing method of the present invention further includes, after carrying out the modified layer formation step, an exposure crack formation step of forming a second modified layer overlapping the modified layer in the thickness direction of the first wafer, and a second crack emerging from the second modified layer to the other side of the first wafer.

[0010] In the wafer processing method of the present invention, the grinding step may include thinning the first wafer to a finishing thickness and removing the outer circumferential region.

[0011] In addition, the wafer processing method of the present invention may further include a peripheral region removal step of removing the peripheral region by applying an external force to the peripheral region on the outer edge side of the modified layer before performing the pressure bonding step.

[0012] Furthermore, in the wafer processing method of the present invention, the modified layer formation step may further include irradiating the outer peripheral region with a laser beam having a wavelength that transmits through the first wafer, to form, within the first wafer, an auxiliary modified layer along a direction parallel to the one surface of the first wafer, and an auxiliary crack extending from the auxiliary modified layer along a direction parallel to the one surface 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 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 a flow of the wafer processing method according to the embodiment. [Figure 4] FIG. 4 is a side view, partly in cross section, showing an example of the plasma activation processing step shown in FIG. [Diagram 5] FIG. 5 is a perspective view showing one state of the bonded wafer forming step shown in FIG. [Figure 6] FIG. 6 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 7] FIG. 7 is a side view, partly in section, showing one state of the modified layer forming step shown in FIG. [Figure 8]FIG. 8 is an enlarged cross-sectional view showing a part of the bonded wafer after the modified layer forming step shown in FIG. [Figure 9] FIG. 9 is a side view, partly in section, showing one state of the crimping step shown in FIG. [Figure 10] FIG. 10 is a side view, partially in cross section, illustrating an example of the annealing step shown in FIG. [Figure 11] FIG. 11 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. [Figure 12] FIG. 12 is a side view, partly in section, showing one state of the grinding step shown in FIG. [Figure 13] FIG. 13 is a flowchart showing the flow of the wafer processing method according to the first modified example. [Figure 14] FIG. 14 is an enlarged cross-sectional view showing a part of the bonded wafer after the exposed crack formation step shown in FIG. [Figure 15] FIG. 15 is a flowchart showing the flow of the wafer processing method according to the second modified example. [Figure 16] FIG. 16 is a side view, partially in cross section, showing an example of the outer periphery region removing step shown in FIG. [Figure 17] FIG. 17 is a plan view showing the bonded wafer after the modified layer forming step according to the third modified example. [Figure 18] FIG. 18 is a plan view showing the bonded wafer after the modified layer forming step according to the fourth modified example. [Figure 19] FIG. 19 is an enlarged cross-sectional view showing a part of the bonded wafer after the modified layer forming step according to the fifth modified example. 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] [Embodiment] A method for processing a wafer 10 according to an 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 in the method for processing a wafer 10 according to the 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 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 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 side 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 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 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 embodiment. As shown in FIG. 3, the processing method of the wafer 10 according to the embodiment includes a plasma activation step 101, a bonded wafer forming step 102, a modified layer forming step 103, a pressure bonding step 104, an annealing step 105, and a grinding step 106. The processing method of the wafer 10 according to the 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 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. 5), 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 in the embodiment as a TSV wafer similar to the first wafer 10-1, but in the present invention, it may be a simple substrate wafer without a pattern.

[0022] (Plasma activation processing step 101) Fig. 4 is a side view showing, in partial cross section, an example of the plasma activation step 101 shown in Fig. 3. The plasma activation step 101 is a step of activating the plasma-treated surfaces by performing plasma treatment on the surfaces to be bonded together in order to bond the first wafer 10-1 and the second wafer 10-2. In the plasma activation step 101, the plasma treatment is performed on at least one of one surface (front surface 13 in the embodiment) of the first wafer 10-1 and one surface (front surface 13 in the embodiment) of the second wafer 10-2.

[0023] In the plasma activation processing step 101 of the embodiment, plasma processing is performed on the surface 13 of the wafer 10 (first wafer 10-1 and second wafer 10-2) by the plasma processing apparatus 30 shown in Fig. 4. The plasma processing 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.

[0024] 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.

[0025] 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).

[0026] 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).

[0027] In the plasma activation processing step 101, 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 surface 13 faces upward. Next, an electrostatic adsorption mechanism (not shown) is driven to electrostatically adsorb the wafer 10 to the holder and hold it. 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 a lifting mechanism (not shown) so that the lower electrode 32 and the upper electrode 34 have a predetermined positional relationship suitable for plasma processing.

[0028] In the plasma activation step 101, next, an exhaust mechanism (not shown) is driven to evacuate (low pressure) the processing space in the chamber 31. Next, while a process gas is supplied from the gas supply source 35 to the processing space in the chamber 31 at a predetermined flow rate, a predetermined high frequency power is supplied from the high frequency power source 36 to the lower electrode 32 and the upper electrode 34, so that a plasma-like gas is supplied 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.

[0029] The plasma activation treatment step 101 in the embodiment is performed on both the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2, but may be performed on either surface. In addition, the method of performing the plasma treatment in the plasma activation treatment step 101 is not limited to the reduced pressure plasma method in which the pressure inside the chamber 31 is reduced to generate plasma as described in the embodiment, 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.

[0030] (Bonded wafer formation step 102) Fig. 5 is a perspective view showing one state of the bonded wafer forming step 102 shown in Fig. 3. Fig. 6 is a cross-sectional view showing a schematic state of the bonding surface of the bonded wafer 20 after the bonded wafer forming step 102 shown in Fig. 3. The bonded wafer forming step 102 is performed after the plasma activation treatment step 101 is performed. The bonded wafer forming step 102 is a step of temporarily bonding the first wafer 10-1 and the second wafer 10-2 to form the bonded wafer 20.

[0031] In the bonded wafer formation step 102, the surface on which OH groups are formed in the plasma activation treatment step 101 is used as a bonding surface. 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.

[0032] In the bonded wafer forming step 102, 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. 5. 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.

[0033] 6, 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.

[0034] (Modified layer forming step 103) Fig. 7 is a side view partially in cross section showing one state of the modified layer forming step 103 shown in Fig. 3. Fig. 8 is a cross-sectional view partially enlargedly showing the bonded wafer 20 after the modified layer forming step 103 shown in Fig. 3. The modified layer forming step 103 is performed after the bonded wafer forming step 102 is performed. The modified layer forming step 103 is a step of forming a ring-shaped modified layer 21 along a position a predetermined distance inside the outer circumferential edge 12 of the first wafer 10-1 and a crack 22 exposed on one surface (in the embodiment, the front surface 13) to cause a warp in the outer circumferential region 16.

[0035] In the modified layer forming step 103, 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. 7. 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.

[0036] In the modified layer forming step 103, 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).

[0037] 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.

[0038] In the modified layer forming step 103, first, the back surface 14 side 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 at 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.

[0039] In the modified layer forming step 103, 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.

[0040] 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. 8, in the modified layer forming step 103, the modified layer 21 is formed by irradiation 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.

[0041] In the modified layer forming step 103, the height of the focal point 44 of the laser beam 43 may be changed and the laser beam 43 may be irradiated multiple times, or a 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 multiple times from the back surface 14 side of the first wafer 10-1, the modified layer 21 is formed in sequence from the front surface 13 side toward the back surface 14 side. Moreover, "perpendicular to the front surface 13 of the first wafer 10-1" indicates that the inclination of an approximate plane that approximates the entire extended crack 22 to a plane with respect to a 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.

[0042] As shown in FIG. 8, due to the formation of a modified layer 21 and a crack 22, the first wafer 10-1 undergoes warping such that the outer peripheral region 16 on the outer peripheral edge 12 side of the modified layer 21 and the crack 22 of the first wafer 10-1 becomes separated from the second wafer 10-2.

[0043] 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 103 is completed.

[0044] (Crimping step 104) Fig. 9 is a side view, partially in cross section, showing one state of the bonding step 104 shown in Fig. 3. The bonding step 104 is performed after the modified layer forming step 103 and before the annealing step 105. In the present invention, the bonding step 104 may be performed while the annealing step 105 is being performed. The bonding step 104 is a step of bonding the central region 15 of the first wafer 10-1, which is closer to the center than the modified layer 21.

[0045] In the pressing step 104 of the embodiment, the central region 15 of the first wafer 10-1 is pressed onto the second wafer 10-2 by a pressing device 50 shown in Fig. 9. The pressing device 50 includes a holding table 51 and a pressing unit 52. The pressing unit 52 faces the holding surface (upper surface) of the holding table 51 and has a pressing surface 53 that is flat and has substantially the same shape as the central region 15. The pressing unit 52 is movable relative to the holding table 51.

[0046] In the pressure bonding step 104, first, the back surface 14 side of the second wafer 10-2 is sucked and held on the holding surface of the holding table 51. Next, the holding table 51 and the pressing unit 52 are aligned so that the pressing surface 53 is located directly above the central region 15 of the first wafer 10-1. Next, the pressing unit 52 is moved close to the holding table 51 to press the first wafer 10-1 from the back surface 14 side. Note that the pressing device 50 may be one in which the holding table 51 rises up relative to the pressing unit 52.

[0047] In the bonded wafer 20, the central region 15 is sandwiched and pressed between the holding surface of the holding table 51 and the pressing surface 53 of the pressing unit 52, so that the central region 15 of the first wafer 10-1 and the second wafer 10-2 are pressure-bonded together. As a result, even if the warpage generated in the outer circumferential region 16 in the modified layer forming step 103 reaches the central region 15 and the bonding in the central region 15 is released, the central region 15 can be bonded again.

[0048] (Annealing step 105) Fig. 10 is a side view partially in cross section showing an example of the annealing step 105 shown in Fig. 3. Fig. 11 is a cross-sectional view typically showing the state of the bonding surface of the bonded wafer 20 after the annealing step 105 shown in Fig. 3. The annealing step 105 is performed after the modified layer forming step 103 is performed. The annealing step 105 of the embodiment is further performed after the pressure bonding step 104 is performed. The annealing step 105 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.

[0049] The annealing step 105 of the embodiment is performed in an annealing apparatus 60 shown in Fig. 10. 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.

[0050] In the annealing step 105 of the 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 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).

[0051] 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.

[0052] In the annealing step 105, 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 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.

[0053] (Grinding step 106) Fig. 12 is a side view, partially in cross section, showing one state of the grinding step 106 shown in Fig. 3. The grinding step 106 is performed after the annealing treatment step 105. The grinding step 106 is a step of grinding the first wafer 10-1 of the bonded wafer 20 from the other surface (in the embodiment, the back surface 14) side to thin it down to a finish thickness 19.

[0054] In the grinding step 106 of the 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. 12. 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.

[0055] In the grinding step 106, 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 down to a predetermined finishing thickness 19.

[0056] At this time, the grinding wheel 74 may apply an external force to press the ground surface of the first wafer 10-1, and the modified layer 21 and the cracks 22 may be used as starting points for splitting to remove the end material of the outer peripheral region 16 of the first wafer 10-1.

[0057] As described above, in the processing method of the wafer 10 according to the embodiment, a pair of wafers 10 are bonded together by temporary bonding using hydrogen bonding, and then in the modified layer forming step 103, the outer circumferential region 16 of the first wafer 10-1 is warped to cause bonding failure, and then the bonding strength is increased by annealing before grinding. This allows the outer circumferential region 16 to be peeled off in a state where the bonding strength is weak, facilitating removal of the outer circumferential region 16 during grinding in the subsequent grinding step 106.

[0058] In addition, after the modified layer forming step 103 and before the annealing step 105, a pressure bonding step 104 is performed to pressure bond the central region 15. As a result, even if the warping force of the outer peripheral region 16 is too strong due to the formation of the modified layer 21 and the central region 15 inside the modified layer 21 is peeled off and the bonding is released, it is possible to bond them again, so that the outer peripheral region 16 can be removed and peeling of the central region 15 can be suppressed. Also, even if a void exists at the formation position of the modified layer 21, the void can be crushed by pressure bonding.

[0059] In addition, in the processing method of the wafer 10 of the embodiment, the step of forming the annular modified layer 21 serving as a dividing starting point for removing the outer peripheral region 16 (modified layer forming step 103) is a step subsequent to the step of bonding the wafers 10 together (bonded wafer forming step 102). This makes it possible to achieve a cleaner process since processing waste from the formation of the modified layer 21 does not scatter onto the bonding surfaces. In addition, since it is not necessary to transport the wafer 10 for bonding after the formation of the modified layer 21, the risk of edge chipping and the like due to transportation can be suppressed.

[0060] [First Modification] A method for processing a wafer 10 according to a first modified example of the present invention will be described with reference to the drawings. Fig. 13 is a flow chart showing the flow of the method for processing a wafer 10 according to the first modified example. As shown in Fig. 13, the method for processing a wafer 10 according to the first modified example includes a plasma activation step 201, a bonded wafer formation step 202, a modified layer formation step 203, an exposed crack formation step 204, a pressure bonding step 205, an annealing step 206, and a grinding step 207.

[0061] In addition, the plasma activation treatment step 201, the bonded wafer formation step 202, the modified layer formation step 203, the bonding step 205, the annealing treatment step 206, and the grinding step 207 in the first modified example are similar to the plasma activation treatment step 101, the bonded wafer formation step 102, the modified layer formation step 103, the bonding step 104, the annealing treatment step 105, and the grinding step 106 in the embodiment, and therefore their explanations are omitted.

[0062] (Exposing crack formation step 204) Fig. 14 is an enlarged cross-sectional view showing a part of the bonded wafer 20 after the exposed crack forming step 204 shown in Fig. 13. The exposed crack forming step 204 is performed after the modified layer forming step 203. The exposed crack forming step 204 is a step of forming a second modified layer 21-1 overlapping the modified layer 21 in the thickness direction of the first wafer 10-1, and a second crack 22-1 exposed from the second modified layer 21-1 to the other surface (back surface 14 in the first modified example) of the first wafer 10-1.

[0063] In the exposed crack forming step 204, the procedure for forming the second modified layer 21-1 and the second crack 22-1 is similar to the procedure for forming the modified layer 21 and the crack 22, except that the height at which the focal point 44 of the laser beam 43 is positioned is changed to the back surface 14 side from the position at which the modified layer 21 is formed. In the exposed crack forming step 204, the laser beam 43 is irradiated so that the second crack 22-1 extending from the second modified layer 21-1 is connected to the crack 22 extending to the back surface 14 side from the modified layer 21 formed closest to the back surface 14 side among the modified layers 21 formed on the first wafer 10-1.

[0064] In addition, the height of the focal point 44 of the laser beam 43 is changed and the laser beam 43 is irradiated multiple times so that the second crack 22-1 appears on the back surface 14 side, or a laser beam 43 having multiple focal points 44 spaced apart in the thickness direction of the first wafer 10-1 is irradiated, thereby forming multiple second modified layers 21-1 overlapping in the thickness direction of the first wafer 10-1. As shown in Fig. 14, the first wafer 10-1 has a division starting point formed from the front surface 13 to the back surface 14 of the first wafer 10-1 in an annular region along a position a predetermined distance inside the outer circumferential edge 12 by forming the second modified layer 21-1 and the second crack 22-1.

[0065] As described above, the processing method of the wafer 10 of the first modified example exposes the crack 22 (second crack 22-1) not only on the front surface 13 side of the first wafer 10-1 but also on the back surface 14 side. In addition to the modified layer 21 and crack 22 formed in the modified layer forming step 203, the second modified layer 21-1 and the second crack 22-1 formed in the exposed crack forming step 204 bulge, causing the first wafer 10-1 to warp such that the outer circumferential region 16 is separated from the second wafer 10-2. As a result, the bond between the front surface 13 of the first wafer 10-1 and the front surface 13 of the second wafer 10-2, which were in a temporarily bonded state, is peeled off at the outer circumferential region 16. At this time, it is easier to remove the outer circumferential region 16 when the crack 22 is exposed on both the front surface 13 and the back surface 14 than when it is exposed only on the front surface 13.

[0066] [Second Modification] A method for processing a wafer 10 according to a second modified example of the present invention will be described with reference to the drawings. Fig. 15 is a flow chart showing the flow of the method for processing a wafer 10 according to the second modified example. As shown in Fig. 15, the method for processing a wafer 10 according to the second modified example includes a plasma activation step 301, a bonded wafer formation step 302, a modified layer formation step 303, an outer peripheral region removal step 304, a bonding step 305, an annealing step 306, and a grinding step 307.

[0067] In addition, the plasma activation treatment step 301, the bonded wafer formation step 302, the modified layer formation step 303, the bonding step 305, the annealing treatment step 306, and the grinding step 307 in the second modified example are similar to the plasma activation treatment step 101, the bonded wafer formation step 102, the modified layer formation step 103, the bonding step 104, the annealing treatment step 105, and the grinding step 106 in the embodiment, and therefore their explanations are omitted.

[0068] (Outer region removal step 304) Fig. 16 is a side view partially in cross section showing an example of the outer peripheral region removing step 304 shown in Fig. 15. The outer peripheral region removing step 304 is performed before the pressing step 305 is performed. The outer peripheral region removing step 304 is a step of removing the outer peripheral region 16 by applying an external force to the outer peripheral region 16 on the outer periphery 12 side of the position where the annular modified layer 21 of the first wafer 10-1 is formed. In the outer peripheral region removing step 304 of the second modified example, the pressing member 80 applies a shear force in the thickness direction of the first wafer 10-1 to remove the outer peripheral region 16.

[0069] The pressing member 80 is movable in the vertical direction, and applies an external force by pressing from above and applying a load to the first wafer 10-1 of the bonded wafer 20. In the outer periphery region removing step 304, first, the bonded wafer 20 is placed so that the first wafer 10-1 is located at the top. Next, the pressing member 80 is lowered downward while facing the outer periphery region 16 of the first wafer 10-1 in the vertical direction, and the pressing member 80 is pressed against the outer periphery region 16 of the first wafer 10-1 to apply a load.

[0070] As a result, a downward external force is applied to the outer circumferential region 16 by the pressing member 80. Then, the central region 15 and the outer circumferential region 16 are divided from each other starting from the modified layer 21 and the cracks 22, and the outer circumferential region 16 of the first wafer 10-1 is removed.

[0071] The method of applying an external force in the outer peripheral region removing step 304 is not limited to the method of applying an external force in the shear direction by pressing the outer peripheral region 16 from above as described in the second modified example shown in Fig. 16, but may be a method of lifting the outer peripheral region 16 to apply an external force in the shear direction, or a method of crushing the outer peripheral region 16 with rollers. Also, the method is not limited to a mechanical external force, but may be ultrasonic vibration or an external force in the radial direction by expanding an expandable tape attached to the back surface 14 of the first wafer 10-1.

[0072] As described above, in the processing method of the wafer 10 of the second modified example, the outer circumferential region removing step 304 is performed after the modified layer forming step 303 and before the pressure bonding step 305 to remove the outer circumferential region 16 of the first wafer 10-1. This makes it possible to remove the outer circumferential region 16 on the outer circumferential edge 12 side of the annular modified layer 21 while the bonding strength is weak.

[0073] [Third Modification] 17 is a plan view showing the bonded wafer 20 after the modified layer forming steps 103, 203, and 303 according to the third modified example. In the modified layer forming steps 103, 203, and 303 of the third modified example, an auxiliary modified layer 23 concentric with the modified layer 21 and an auxiliary crack exposed on the front surface 13 side are formed in the outer peripheral region 16 on the outer peripheral edge 12 side of the ring-shaped modified layer 21 and the crack 22 formed in the first wafer 10-1.

[0074] The procedure for forming the auxiliary modified layer 23 is the same as the procedure for forming the modified layer 21, except that the irradiation position of the laser beam 43 is shifted a predetermined distance toward the outer circumferential edge 12. The auxiliary modified layer 23 may be formed after the modified layer 21 is formed, or may be formed before the modified layer 21 is formed. In addition, the irradiated laser beam 43 is a laser beam having a wavelength that transmits through the first wafer 10-1, and may be the same as or different from the processing conditions in the modified layer forming steps 103, 203, and 303.

[0075] In the outer peripheral region 16, an annular auxiliary modified layer 23 is formed along a position a predetermined distance inside the outer peripheral edge 12 of the first wafer 10-1, and an auxiliary crack extends from the auxiliary modified layer 23. At this time, the auxiliary modified layer 23 is formed by irradiation with a laser beam 43 so that the auxiliary crack extending from the auxiliary modified layer 23 is exposed on the front surface 13 side of the first wafer 10-1. Note that, as in the exposed crack formation step 204 of the first modified example, the auxiliary crack may be exposed not only on the front surface 13 side of the first wafer 10-1 but also on the back surface 14 side.

[0076] The first wafer 10-1 is warped such that the outer peripheral region 16 of the first wafer 10-1 is separated from the second wafer 10-2 due to the expansion of the auxiliary modified layer 23 and the auxiliary cracks. This results in a larger warpage in addition to the warpage caused by the formation of the modified layer 21 and the cracks 22.

[0077] As described above, the processing method of the wafer 10 of the third modified example forms the auxiliary modified layer 23 concentric with the modified layer 21 and the auxiliary cracks in the outer peripheral region 16 of the first wafer 10-1. This can promote warping of the first wafer 10-1 in the outer peripheral region 16, making it easier to remove the outer peripheral region 16.

[0078] [Fourth Modification] 18 is a plan view showing the bonded wafer 20 after the modified layer forming steps 103, 203, 303 according to the fourth modified example. In the modified layer forming steps 103, 203, 303 of the fourth modified example, an auxiliary modified layer 24 and an auxiliary crack are formed to divide the outer circumferential region 16 on the outer circumferential edge 12 side of the ring-shaped modified layer 21 and crack 22 formed in the first wafer 10-1 into at least two or more portions.

[0079] 18, for example, at a predetermined circumferential position in the outer peripheral region 16 of the first wafer 10-1, an auxiliary modified layer 24 is formed in the radial direction between the inner peripheral edge and the outer peripheral edge 12 of the outer peripheral region 16. The procedure for forming the auxiliary modified layer 24 and the auxiliary cracks is similar to the procedure for forming the modified layer 21 and the cracks 22, except that the direction in which the focal point 44 is moved during irradiation of the laser beam 43 is different.

[0080] Specifically, the holding table 41 is moved so that the focal point 44 of the laser beam 43 moves toward the radially outer side of the first wafer 10-1. That is, the auxiliary modified layer 24 is formed along the radial direction by irradiating the outer peripheral region 16 with the laser beam 43 in the radial direction. The laser beam 43 may be irradiated while moving the holding table 41 so that the focal point 44 moves from the radially outer side to the radially inner side of the first wafer 10-1. In this case, the irradiation of the laser beam 43 is stopped when the focal point 44 reaches the modified layer 21.

[0081] The auxiliary modified layer 24 may be formed after the modified layer 21 is formed, or may be formed before the modified layer 21 is formed. The irradiated laser beam 43 is a laser beam having a wavelength that transmits the first wafer 10-1, and may be the same as or different from the processing conditions in the modified layer forming steps 103, 203, and 303. The auxiliary modified layer 24 shown in FIG. 18 divides the outer peripheral region 16 into eight in the circumferential direction, but in the present invention, it may be further divided into 16, for example, and the number of divisions may be appropriately set depending on the diameter of the first wafer 10-1 and the width of the outer peripheral region 16.

[0082] As described above, the processing method of the wafer 10 of the fourth modified example forms the auxiliary modified layer 23 and auxiliary cracks that divide the outer peripheral region 16 of the first wafer 10-1 into at least two or more parts. This forms a division starting point that divides the outer peripheral region 16 in the circumferential direction, making it easier to remove the outer peripheral region 16.

[0083] [Fifth Modification] 19 is an enlarged cross-sectional view of a part of the bonded wafer 20 after the modified layer forming steps 103, 203, and 303 according to the fifth modified example. In the modified layer forming steps 103, 203, and 303 of the fifth modified example, an auxiliary modified layer 25 along a direction parallel to one surface (front surface 13) and an auxiliary crack 26 extending from the auxiliary modified layer 25 along a direction parallel to one surface (front surface 13) are further formed inside the first wafer 10-1. The parallel direction indicates that the inclination of an approximation plane obtained by approximating the entire extended auxiliary crack 26 to a plane with respect to a horizontal plane is within ±5 degrees, preferably within ±2 degrees.

[0084] In the modified layer forming steps 103, 203, 303 of the fifth modified example, the auxiliary modified layer 25 and the auxiliary crack 26 may be formed before or after forming the modified layer 21 and the crack 22 described above. The procedure for forming the auxiliary modified layer 25 may be similar to the procedure for forming the modified layer 21, except that the irradiation position of the laser beam 43 is changed to a position along a direction parallel to one face (surface 13).

[0085] In the modified layer forming steps 103, 203, and 303 of the fifth modified example, for example, the laser beam 43 is irradiated so that multiple focal points 44 of the laser beam 43 branched in the radial direction move in a ring shape along the outer peripheral region 16. After processing the outer peripheral region 16 once, the positions of the multiple focal points 44 are moved in the radial direction, and processing is performed in a similar concentric shape until the entire outer peripheral region 16, which is annular in plan view, is processed. As a result, an annular auxiliary modified layer 25 is formed over the entire outer peripheral region 16. At this time, an auxiliary crack 26 extends from the auxiliary modified layer 25 along a direction parallel to the surface 13 of the first wafer 10-1, and extends over the entire outer peripheral region 16 in plan view.

[0086] As described above, the processing method of the wafer 10 of the fifth modified example forms the auxiliary modified layer 25 and the auxiliary crack 26 along a direction parallel to one surface (front surface 13) of the first wafer 10-1 in the outer peripheral region 16 of the first wafer 10-1. That is, a layer that separates the front surface 13 side and the back surface 14 side is formed in the outer peripheral region 16 of the first wafer 10-1.

[0087] The bulging of the auxiliary modified layer 25 and the auxiliary crack 26 causes the first wafer 10-1 to warp such that the outer peripheral region 16 on the outer peripheral edge 12 side of the modified layer 21 and the crack 22 separates from the second wafer 10-2. As a result, the bond between the surface 13 of the first wafer 10-1 and the surface 13 of the second wafer 10-2, which was in a temporarily bonded state, peels off at the outer peripheral region 16. At this time, since the outer peripheral region 16 can be warped more than when only the modified layer 21 and the crack 22 are formed, it is easier to remove the outer peripheral region 16 in the subsequent process.

[0088] It should be noted that the present invention is not limited to the above-described embodiment and modifications, and can be practiced in various forms without departing from the spirit of the present invention. [Explanation of symbols]

[0089] 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 21-1 Second modified layer 22 Crack 22-1 The Second Crack 23, 24, 25 Auxiliary modification layer 26 Auxiliary Crack 43 Laser Beam 44 Focus point

Claims

1. A wafer processing method comprising the steps of: a plasma activation step of performing a plasma treatment on at least one of one surface of the first wafer and one surface of the second wafer to activate the surface that has been subjected to the plasma treatment, in order to bond the first wafer and the second wafer; a bonded wafer forming step of temporarily bonding the one surface of the first wafer and the one surface of the second wafer to form a bonded wafer after performing the plasma activation treatment step; a modified layer forming step in which, after carrying out the bonded wafer forming step, a laser beam having a wavelength that transmits through the first wafer is annularly irradiated along a position a predetermined distance inside the outer periphery of the first wafer to form an annular modified layer inside the first wafer and cracks that extend from the modified layer and are exposed on the one surface side of the first wafer, thereby causing warping in an outer periphery region on the outer periphery side due to the modified layer and the cracks; 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 the first wafer to a finish thickness after the annealing step is performed; Equipped with After the modified layer forming step is performed and before the annealing step is performed, or during the annealing step, The method further includes a step of compressing a central region of the first wafer that is closer to the center than the modified layer. A wafer processing method comprising the steps of:

2. After performing the modified layer forming step, The method further includes an exposure crack forming step of forming a second modified layer overlapping the modified layer in the thickness direction of the first wafer, and a second crack exposed from the second modified layer to the other surface side of the first wafer.

2. The wafer processing method according to claim 1 .

3. In the grinding step, Thinning the first wafer to a finishing thickness and removing the peripheral region.

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

4. Prior to carrying out the crimping step, The method further includes a peripheral region removing step of removing the peripheral region by applying an external force to the peripheral region on the outer periphery side of the modified layer.

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

5. In the modified layer forming step, A laser beam having a wavelength that is transmitted through the first wafer is irradiated onto the outer peripheral region, and an auxiliary modified layer is formed inside the first wafer along a direction parallel to the one surface of the first wafer, and an auxiliary crack is formed extending from the auxiliary modified layer along a direction parallel to the one surface of the first wafer.

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

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