Method for processing bonded wafers

Abstract

To provide a method for processing bonded wafers that can improve productivity. [Solution] The present invention relates to a method for transferring a first device to a second wafer by peeling off the first substrate side from a bonded wafer (300) formed by bonding a first wafer (100), on which a first device (131) is formed on the surface (111) side of a first substrate (110), to a second wafer (200). The method involves a laser processing step in which a laser beam (LB) having a wavelength that is transparent to the first substrate is irradiated from the back surface (102) of the first wafer and focused into the first substrate near the bonding surface (301) between the first wafer and the second wafer to form a planar processed layer (303) in the first wafer, and a separation step in which the processed layer is used to separate the first substrate side from the second wafer while the first device of the first wafer remains bonded to the second wafer.

Description

Technical Field

[0006] , , ,

[0001] The present invention relates to a method for processing a bonded wafer that transfers devices from one wafer to another wafer.

Background Art

[0002] Patent Document 1 discloses a method of grinding one wafer of a bonded wafer in which two wafers are bonded with a bonding film and transferring the devices of one wafer to the other wafer. In the grinding process performed by this method, the wafer may remain about 10 μm, and the thickness of the laminated wafer to which the devices are transferred becomes thick. In addition, there is a problem that about 760 μm is often removed by the grinding process of the wafer, and the processing time becomes long.

[0003] Here, Patent Document 2 discloses a method of forming a release layer in a buffer layer by a laser beam and peeling off one wafer. In Patent Document 2, the grinding process performed in Patent Document 1 can be omitted, and the processing time can be shortened.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in Patent Document 2, in order to prevent the devices of the wafer from being damaged by the transmitted light of the irradiated laser beam, it is necessary to thicken the bonding film, which causes a problem of reducing productivity.

[0006] This invention has been made in view of the above, and one of its objectives is to provide a method for processing bonded wafers that can improve productivity. [Means for solving the problem]

[0007] A bonding wafer processing method according to one aspect of the present invention is a bonding wafer processing method in which a first wafer having a first device formed on the surface side of a first substrate is bonded to a second wafer, and the first device is transferred to the second wafer by peeling off the first substrate side from the bonding wafer, comprising: a laser processing step of irradiating the first wafer from the back surface of the first wafer with a laser beam having a wavelength that is transparent to the first substrate and focusing it into the first substrate near the bonding surface between the first wafer and the second wafer to form a processing layer in a planar manner within the first wafer; and a separation step of separating the first substrate side from the second wafer by separating it at the processing layer, while the first device of the first wafer remains bonded to the second wafer. [Effects of the Invention]

[0008] According to the present invention, a processed layer is formed in a planar manner within the first wafer and then separated, and the first device of the first wafer remains bonded to the second wafer while the first substrate side is separated. This eliminates the need for laser processing of the bonding layer, bonding film, or bonding member before such separation. As a result, productivity can be improved by eliminating the need to form a thick bonding film to prevent damage to the device due to light leakage from the laser beam irradiated onto the bonding film, etc., as in the past. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1A is an explanatory diagram of each step in the manufacturing method of a stacked wafer according to the first embodiment, where Figure 1A is the preparation step, Figure 1B is the bonding step, Figure 1C is the laser processing step, and Figure 1D is the separation step. [Figure 2] This is a schematic perspective view of a laser processing device. [Figure 3] Figures 3A and 3B are explanatory diagrams illustrating processing marks formed by the laser processing process. [Figure 4]Figures 4A, 4B, and 4C are explanatory diagrams illustrating processing marks formed by the laser processing process. [Figure 5] This is an explanatory cross-sectional view showing the state during the laser processing step in which a processed layer is being formed. [Figure 6] This is an explanatory diagram of the processing layer treatment process in the manufacturing method of stacked wafers. [Figure 7] This is an explanatory diagram of each step in the manufacturing method of a stacked wafer according to the second embodiment, similar to Figure 1. [Figure 8] This is an explanatory diagram of each step in the manufacturing method of a stacked wafer according to the third embodiment, similar to Figure 1. [Figure 9] This is a cross-sectional view similar to Figure 5 of the laser processing step according to the third embodiment. [Figure 10] This is an explanatory diagram of each step in the manufacturing method of a stacked wafer according to the fourth embodiment, similar to Figure 1. [Figure 11] This is an explanatory diagram of each step in the manufacturing method of a stacked wafer according to the fifth embodiment, similar to Figure 1. [Figure 12] This is a cross-sectional view similar to Figure 5 of the laser processing process according to the fifth embodiment. [Figure 13] This is a cross-sectional view similar to Figure 5 of the laser processing process according to the fifth embodiment. [Modes for carrying out the invention]

[0010] [First Embodiment] The manufacturing method of a laminated wafer, including the processing method for the bonded wafer according to the first embodiment, will be described below with reference to the attached drawings. Figure 1A shows the preparation step, Figure 1B shows the bonding step, Figure 1C shows the laser processing step, and Figure 1D shows the separation step. Note that the steps shown in each figure in the first embodiment are merely examples and are not limited to this configuration. Also, in each figure, including Figure 1, the hatching in the cross-section of the first substrate 110, which will be described later, has been omitted.

[0011] [Preparation process] The preparation process is for preparing the bonding wafer 300 (see FIG. 1B) and the stacked wafer 500 (see FIG. 1D). As shown in FIG. 1A, a disk-shaped first wafer 100 and a second wafer 200 are prepared. The first wafer 100 includes a front surface 101 and a back surface 102 that are surfaces orthogonal to the thickness direction. The front surface 101 is arranged downward in FIG. 1A, and the back surface 102 is arranged upward in FIG. 1A. Also, the second wafer 200 includes a front surface 201 and a back surface 202 that are surfaces orthogonal to the thickness direction. The front surface 201 is arranged upward in FIG. 1A, and the back surface 202 is arranged downward in FIG. 1A.

[0012] The first wafer 100 includes a first substrate 110 (substrate) made of silicon, an insulating film 120 formed on a front surface 111 which is one surface in the thickness direction of the first substrate 110, and a first device layer 130 formed on the surface of the insulating film 120 (the lower surface in FIG. 1). The back surface 102 of the first wafer 100 is formed by the back surface 112 of the first substrate 110. The insulating film 120 is an interlayer insulating film laminated between the first substrate 110 and the first device layer 130. The insulating film 120 is any one of a silicon oxide film (SiO2 film), a silicon carbide film (SiC film), a silicon nitride film (SiN film), and a silicon carbonitride film (SiCN film).

[0013] The first device layer 130 includes a plurality of first devices 131 (devices) and a first surface film 132 formed as an insulating film. The front surface 101 of the first wafer 100 is formed by the front surface 133 of the first surface film 132 in the first device layer 130, and the first devices 131 are formed on the front surface 101 side of the first wafer 100.

[0014] Each of the plurality of first devices 131 includes, for example, elements for constituting an IC, a semiconductor memory, or an image sensor. The plurality of first devices 131 are formed in a plurality of regions partitioned by a plurality of streets 134 formed in a grid pattern.

[0015] The first surface film 132 is made of any one of a silicon oxide film (SiO2 film), a silicon carbide film (SiC film), a silicon nitride film (SiN film), and a silicon carbonitride film (SiCN film).

[0016] The second wafer 200 has an outer shape corresponding to the first wafer 100, and is formed, for example, in a disc shape having the same shape as the first wafer 100. For the second wafer 200, for example, the same one as the first wafer 100 before the formation of the first device layer 130 can be used. However, the second wafer 200 is not limited to this. That is, the second wafer 200 may have a device layer formed thereon in the same manner as the first wafer 100.

[0017] In the preparation step, as preparation for the bonding step by plasma-activated bonding, preparation is carried out to make it possible to bond the surface 201 of the second wafer 200 to the surface 101 (the surface 133 of the first surface film 132) of the first wafer 100.

[0018] In the preparation step, for example, the surface 133 of the first surface film 132 of the first wafer 100 and the surface 201 of the second wafer 200 are each irradiated with plasma of a rare gas generated using the rare gas and high-frequency power. Thereby, the surface 101 (the surface 133 of the first surface film 132) of the first wafer 1 and the surface 201 of the second wafer 200 are activated, and in the bonding step, the respective surfaces 101 and 201 can function as bonding members.

[0019] [Bonding step] After the preparation step is completed, as shown in FIG. 1B, a bonding step is carried out by plasma-activated bonding. In the bonding step, after holding the back surface 202 of the second wafer 200 downward on the chuck table 11, the surface 101 on the side of the first device layer 130 of the first wafer 100 is made to face the surface 201 of the second wafer 200.

[0020] Subsequently, the surface 101 of the first wafer 100 is pressed against the surface 201 of the second wafer 200. This joins the surfaces 101 and 201 of the first wafer 100 and the second wafer 200, which function as bonding members, and forms a bonded wafer 300. Here, the surfaces 101 and 201 of the first wafer 100 and the second wafer 200 that are joined to each other are formed as the bonding surface 301 of the bonded wafer 300. Note that the joining of the first wafer 100 and the second wafer 200 is not limited to direct bonding such as surface activation bonding, but may also be bonded using an intermediate layer such as adhesive bonding or glass fit bonding.

[0021] [Laser processing process] After the bonding process is completed, the laser processing process is performed by the laser processing apparatus 20. Figure 2 is a schematic perspective view of the laser processing apparatus. The laser processing apparatus will be described below with reference to Figure 2. Note that the laser processing apparatus can be any configuration capable of performing the laser processing process of this embodiment, and is not limited to the configuration shown in Figure 2.

[0022] As shown in Figure 2, the laser processing apparatus 20 is configured to laser process the bonded wafer 300 by relatively moving a laser irradiation unit 40 that irradiates a laser beam LB (see Figure 1C) and a holding table 34 that holds the bonded wafer 300.

[0023] A holding table moving mechanism 22 is provided on the base 21 of the laser processing apparatus 20 for moving the holding table 34 in the X-axis and Y-axis directions. The holding table moving mechanism 22 has a pair of guide rails 23 arranged on the base 21 and parallel to the X-axis direction, and a motor-driven X-axis table 24 that is slidably mounted on the pair of guide rails 23. The holding table moving mechanism 22 also has a pair of guide rails 25 arranged on the upper surface of the X-axis table 24 and parallel to the Y-axis direction, and a motor-driven Y-axis table 26 that is slidably mounted on the pair of guide rails 25.

[0024] Nut portions (not shown) are formed on the back sides of the X-axis table 24 and the Y-axis table 26, respectively, and ball screws 27 and 28 are screwed into these nuts. Drive motors 29 and 30, connected to one end of the ball screws 27 and 28, are rotationally driven, causing the holding table 34 to move along the guide rails 23 and 25 in the X-axis and Y-axis directions.

[0025] Furthermore, the holding table moving mechanism 22 further includes a rotating mechanism 31 provided on the Y-axis table 26. The rotating mechanism 31 supports the holding table 34 from below, and the rotating mechanism 31 and the holding table 34 move together with the Y-axis table 26 in the X-axis and Y-axis directions. The rotating mechanism 31 also includes a rotating bearing (not shown), a drive motor, and a pulley mechanism, and the holding table 34 rotates around the Z-axis. A holding surface 35 for suction holding of the bonded wafer 300 is formed on the upper surface of the holding table 34.

[0026] An arm portion 38 is provided protruding from the rear vertical wall portion 37 of the holding table 34, and a laser irradiation unit 40 and an imaging camera 41 are provided at the tip of the arm portion 38 so as to face the holding table 34 in the vertical direction. The laser irradiation unit 40 irradiates the bonded wafer 300 held on the holding table 34 with a laser beam LB (see Figure 1C) emitted from an oscillator (not shown). The imaging camera 41 is provided to the side of the laser irradiation unit 40 and images the surface of the bonded wafer 300 held on the holding table 34.

[0027] Using the laser processing apparatus 20, the laser processing process shown in Figure 1C is performed. In the laser processing process, the bonded wafer 300 is transported to and held on the holding table 34 via a transport mechanism (not shown). Subsequently, a laser beam LB having a wavelength that is transparent to the first substrate 110 of the first wafer 100 is pulsed and irradiated from the laser irradiation unit 40 towards the bonded wafer 300 from the back surface 102 of the first wafer 100. In other words, the laser beam LB irradiated from the laser irradiation unit 40 is irradiated from the first substrate 110 side (back surface 102 side) of the first wafer 100.

[0028] The irradiated laser beam LB is adjusted by the focusing lens of the laser irradiation unit 40 to focus into the first wafer 100 near the bonding surface 301 between the first wafer 100 and the second wafer 200. More specifically, the focusing position of the laser beam LB in the bonded wafer 300 is inside the first substrate 110 in the first wafer 100, and is located near the surface 111 of the first substrate 110, while being displaced from the surface 111 toward the back surface 112. Furthermore, this focusing position is adjusted so that, in the thickness direction of the first wafer 100, the distance to the surface 101 of the first wafer 100 is shorter than the distance to the back surface 102 of the first wafer 100.

[0029] When the laser beam LB is focused within the thickness of the first substrate 110 of the first wafer 100, a portion of the first substrate 110 in the area where the laser beam LB is focused is modified from a single crystal to a polycrystalline material, causing its volume to expand and forming a processed layer 303 (processing mark 304) within the first substrate 110 of the first wafer 100.

[0030] The laser beam LB used in the laser processing process has a wavelength λ set within the range of 1000 nm to 3000 nm, and more preferably, the wavelength λ is set to 1342 nm. By setting the wavelength λ to this value, the energy of the laser beam LB can be efficiently absorbed at the focusing position while allowing transmission of the laser beam LB through the first substrate 110 of the first wafer 100.

[0031] In the laser processing process, while irradiating with a laser beam LB, the holding table 34 that holds the bonded wafer 300 is moved relative to the laser irradiation unit 40 along the horizontal direction (a direction parallel to the XY plane in Figure 2). As a result, the entire bonded wafer 300 is irradiated with the laser beam LB when viewed from the thickness direction. Due to this irradiation with the laser beam LB, a processing mark 304 is formed in the first substrate 110 of the first wafer 100, and a first crack 305 and a second crack 306 extend from the volume-expanded processing mark 304, forming a processed layer 303 in a planar manner within the thickness of the first wafer 100.

[0032] Figures 3A, 3B, 4A, 4B, and 4C are explanatory diagrams illustrating a view of the processing marks 304 caused by laser irradiation in the laser processing process, as seen from above the first wafer 100. In the laser processing process, the laser irradiation unit 40 moves relative to the bonded wafer 300 held on the holding table 34, so that the laser beam LB is irradiated along the trajectory shown by the dashed line in Figures 3A, 3B, 4A, 4B, and 4C, and processing marks 304 are formed where the irradiation occurred, forming a planar processing layer 303 within the first wafer 100.

[0033] In the laser processing process, when forming the planar processed layer 303 shown in Figure 3A, the laser beam LB is irradiated along multiple concentric circles centered on the center of the first wafer 100. Specifically, the laser beam LB is first irradiated along the trajectory of the circle closest to the outermost circumference of the first wafer 100, and then the laser beam LB is irradiated sequentially along the trajectories of concentric circles while gradually decreasing the diameter of the circle. This irradiation of the laser beam LB forms multiple concentric processed marks 304 as the processed layer 303. Furthermore, the irradiation of the laser beam LB forms ellipsoidal processed marks 304 in cross-sectional view (see Figure 5). More specifically, the processed marks 304 are ellipsoids with their lower end inclined towards the outer circumference and their upper end inclined towards the center. The multiple concentric processed marks 304 formed by the irradiation of the laser beam LB are formed sequentially from the largest circular processed marks 304 to the smallest circular processed marks 304. In other words, by irradiation with the laser beam LB, circular processing marks 304 are sequentially created on the first substrate 110 (first wafer 100) from the outer edge, which is one direction in the planar direction, toward the center, which is the other direction, thereby forming a planar processing layer 303.

[0034] Figure 5 is an explanatory cross-sectional view showing the state during the laser processing step in which the processed layer is being formed. In the processed layer 303, as shown in Figure 5, during the process of forming concentric processing marks 304 when viewed from above, a first crack 305 extends and forms in the first substrate 110 from the lower end of the processing marks 304 toward the insulating film 120 in the thickness direction of the first substrate 110, and diagonally toward the outer circumference.

[0035] Furthermore, the second crack 306 of the processed layer 303 is formed by extending planarly along the planar direction of the surface 111 of the first substrate 110 once the first crack 305 reaches the insulating film 120. Specifically, the first crack 305 that reaches the insulating film 120 becomes the second crack 306 and extends radially toward the outer circumference of the first wafer 100 at the boundary between the first substrate 110 and the insulating film 120. Also, in the circumferential direction of the first wafer 100, the second cracks 306 that have extended from adjacent processing marks 304 are connected. Then, multiple second cracks 306 extend parallel to the bonding surface, which is the boundary between the first substrate 110 and the insulating film 120, and are formed planarly in the planar direction of the first wafer 100. In other words, the first wafer 100 forms a planar second crack 306 along the bonding surface, which is the boundary between the first substrate 110 and the insulating film 120, where the bond is weaker than the intermolecular bonding force of the silicon in the first substrate 110.

[0036] In the laser processing process, when forming the planar processed layer 303 shown in Figure 3B, the laser beam LB is irradiated along a spiral shape centered on the center of the first wafer 100. This irradiation with the laser beam LB forms a spiral-shaped processing mark 304 as the processed layer 303. This processing mark 304 is formed from the outer periphery, which is one side of the planar direction of the first wafer 100, toward the center, which is the other side, and is an ellipsoid in cross-sectional view with its lower end inclined toward the outer periphery and its upper end inclined toward the center (see Figure 5). Then, in the process of forming the spiral-shaped processing mark 304, a first crack 305 is formed diagonally from the processing mark 304 within the first substrate 110, similar to when forming multiple concentric processing marks 304 as described above (see Figure 5). Furthermore, the first crack 305 that reaches the insulating film 120 becomes a second crack 306, as described above, and extends and connects to the boundary between the first substrate 110 and the insulating film 120, forming a planar second crack 306 along the bonding surface which is the boundary between the first substrate 110 and the insulating film 120. When forming concentric or spiral-shaped machining marks 304, the machining marks 304 are formed at equal intervals in the circumferential direction.

[0037] In the laser processing process, when forming the planar processed layer 303 shown in Figures 4A, 4B, and 4C, the laser beam LB is irradiated along multiple parallel lines (straight lines). Irradiation with this laser beam LB forms multiple linearly aligned processed marks 304 as the processed layer 303 when viewed from above. The processed marks 304 are ellipsoids in cross-sectional view, with their lower end inclined towards the outer periphery and their upper end inclined towards the center (see Figure 5). The linear processed marks 304 are formed sequentially from one side of the planar direction of the first wafer 100 toward the other. More specifically, the linear processed marks 304 are formed sequentially, with one outer periphery of the diameter perpendicular to the direction of alignment of the processed marks 304 being one side of the planar direction of the first wafer 100, and the other outer periphery being the other side of the planar direction of the first wafer 100.

[0038] During the process of forming the processing mark 304, a first crack 305 is formed within the first substrate 110 from the tip (lower end) of the inclined processing mark 304 toward the insulating film 120. When the first crack 305 reaches the insulating film 120, it becomes a second crack 306 and extends radially toward the outer circumference of the first wafer 100 at the boundary between the first substrate 110 and the insulating film 120. In the circumferential direction of the first wafer 100, adjacent second cracks 306 are connected. Multiple second cracks 306 then extend parallel to the bonding surface, which is the boundary between the first substrate 110 and the insulating film 120, forming a planar structure in the planar direction of the first wafer 100.

[0039] In the bonded wafer 300 shown in Figure 4A, multiple linearly aligned processing marks 304 are formed in the diametrical direction connecting the notch 103 of the first wafer 100 to its center. When forming a single linear processing mark 304, the laser beam LB may be irradiated from either one side of the linear direction to the other, or vice versa.

[0040] In the bonded wafers 300 shown in Figures 4B and 4C, the multiple linear processing marks 304 are formed in a diametrical direction inclined at 45 degrees to the diameter connecting the notch 103 and the center of the first wafer 100. In the bonded wafers 300 shown in Figures 4B and 4C, the processed layer 303 is formed by creating processing marks 304, a first crack 305, and a second crack 306, similar to the processed layer 303 formed on the bonded wafer 300 in Figure 4A. In Figures 4B and 4C, the direction of the multiple linear processing marks 304, which are inclined at 45 degrees to the diameter connecting the notch 103 and the center of the first wafer 100, is reversed.

[0041] As shown in Figure 5, during the laser processing process, the first crack 305 and the second crack 306 expand in volume due to the formation of processing marks 304, and as a result of the impact, each crack 305 and 306 extends toward the area with weaker bonding force.

[0042] The processing marks 304 of the processed layer 303 can be formed by dividing the focusing position 307 into multiple parts in the laser irradiation unit 40 and irradiating them with the laser beam LB. The processing marks 304 are formed as an ellipsoid with the direction of extension being the direction connecting the multiple focusing positions 307 in a cross-sectional view. The extension direction of these processing marks 304 is adjusted to be inclined with respect to the thickness direction of the first wafer 100. The direction of this inclination is from the back surface 102, which is the non-bonding surface opposite to the bonding surface 301 of the first wafer 100, toward the bonding surface 301, and is oblique in the plane direction of the bonding surface 301 from one side to the other. Here, the direction from the back surface 102 toward the bonding surface 301 is the direction from top to bottom in Figure 5, and for example, when the laser beam LB is irradiated as in Figures 3A and 3B, the direction from one side to the other in the plane direction of the bonding surface 301 is the direction from left to right in Figure 5. Therefore, the diagonal extension direction of the processing mark 304 is considered to be the direction of displacement from left to right, as shown in Figure 5, from top to bottom.

[0043] [Separation process] After the laser processing is completed, a separation process is performed as shown in Figure 1D. In the separation process, the bonded wafer 300 is transported and held on the chuck table 55 of the separation device 50 via a transport mechanism (not shown). Next, the back surface 102 of the first wafer 100 on the bonded wafer 300 is held by an adsorption pad 53 connected to a suction source 51, which generates negative pressure on the holding surface 52. Then, the adsorption pad 53 is raised via a lifting mechanism 54, applying a force that separates the first wafer 100 from the second wafer 200. As a result, in the bonded wafer 300, the first substrate 110 is separated from the first device layer 130 of the first wafer 100 by a planar second crack 306 in the processed layer 303.

[0044] In the separation process, the portion of the first wafer 100 that is on the back surface 102 side of the separation cross-section 309 is separated from the second wafer 200 by the separation at the second crack 306 in the processed layer 303. At the same time, the portion of the first wafer 100 that is on the front surface 101 side of the separation cross-section 309, i.e., the first device layer 130 including the first device 131, remains bonded to the second wafer 200.

[0045] During the separation process, the first wafer 100 side is peeled off from the bonded wafer 300, and the first device layer 130 of the first wafer 100, which includes the first device 131, is transferred to the second wafer 200. Due to the separation at the processed layer 303 during the separation process, a laminated wafer 500 is formed in which the first device 131 has been transferred to the second wafer 200. The manufacturing method of the laminated wafer 500 of this embodiment has been described above, but as a processing method for the bonded wafer 300, at least the laser processing step and the separation step are performed from the above-described steps.

[0046] According to the first embodiment described above, since the processed layer 303 is formed and divided within the first wafer 100, laser processing of the bonding layer, bonding film, and bonding member, as in the conventional method, becomes unnecessary. As a result, the occurrence of stray light from the laser beam LB irradiated onto the bonding film, etc., is eliminated, and damage to the first device 131 due to irradiation with the laser beam LB can be suppressed. Therefore, the conventional process of forming a thick bonding film becomes unnecessary, and productivity can be improved.

[0047] In the manufacturing method of the stacked wafer 500 according to the first embodiment described above, after the separation step, a processing layer treatment step may be performed to flatten the cross-sectional area 309 of the processed layer 303 on the second wafer 200 side. Figure 6 is an explanatory diagram of the processing layer treatment step.

[0048] [Processing layer treatment process] In the processing layer treatment process performed after the separation process, polishing is carried out by the polishing mechanism 60, as shown in Figure 6. In this polishing process, wet polishing and CMP may be performed, or dry polishing may be performed, to the extent that the cross-sectional area 309 of the processed layer 303 can be flattened.

[0049] The processing layer treatment process involves holding the back surface 202 of the second wafer 200 of the stacked wafer 500 facing downwards on the chuck table 61 of the polishing mechanism 60, and then bringing the polishing pad 62 of the polishing mechanism 60 face the cross-section 309 of the processing layer 303 that was exposed by the separation process. Then, while rotating the chuck table 61 and the polishing pad 62 around their respective vertical axes, the lower surface of the polishing pad 62 is pressed against the cross-section 309 of the exposed processing layer 303 of the stacked wafer 500, thereby polishing the cross-section 309. This polishing removes the irregularities on the upper surface (one side in the thickness direction) of the stacked wafer 500 formed by the cross-section 309, and flattens the cross-section 309.

[0050] In addition, during the processing layer treatment process, instead of the polishing process described above, the irregularities of the cross-section 309 may be removed by plasma etching. By performing a processing layer treatment, a wafer equipped with a device is bonded again to the flattened surface, and the devices are stacked to manufacture a stacked wafer.

[0051] Next, embodiments of the present invention other than those described above will be described. In the following description, the same reference numerals may be used for components that are the same as or equivalent to those described in embodiments described before the embodiment being described, and the description may be omitted or simplified.

[0052] [Second Embodiment] Next, a second embodiment of the present invention will be described with reference to Figure 7. Figure 7 is an explanatory diagram of each step in the manufacturing method of a stacked wafer according to the second embodiment, where Figure 7A shows the preparation step, Figure 7B shows the bonding step, Figure 7C shows the laser processing step, and Figure 7D shows the separation step. In the second embodiment, the configuration of the second wafer 200 is changed compared to the first embodiment. Note that the steps shown in each figure in the second embodiment are merely examples and are not limited to this configuration.

[0053] The second wafer 200 of the second embodiment is configured in the same way as the first wafer 100. Therefore, in the second wafer 200, if the configuration corresponding to the first wafer 100 is described as "first", it is changed to "second", the hundreds digit of the reference numeral is changed from "1" to "2", and the specific explanation is omitted. As shown in Figure 7A, the second wafer 200 has a second device 231 (device) formed on the surface 201 side, similar to the first wafer 100.

[0054] [Preparation process] In the preparation step of the second embodiment, for example, the surface 133 of the first surface film 132 of the first wafer 100 and the surface 233 of the second surface film 232 of the second wafer 200 are irradiated with a rare gas plasma generated using a rare gas and high-frequency power. This activates the respective surfaces 133 and 233 of the first surface film 132 and the second surface film 232, so that in the bonding step, the first surface film 132 and the second surface film 232 can function as bonding members.

[0055] [Bonding process] In the bonding process of the second embodiment, as shown in Figure 7B, when the surface 101 of the first wafer 100, which is on the side of the second device layer 130, is brought into contact with the surface 201 of the second wafer 200, which is on the side of the second device layer 230, the horizontal alignment of the devices 131 and 231 on the first wafer 100 and the second wafer 200 is performed. Subsequently, by pressing the surface 101 of the first wafer 100 against the surface 201 of the second wafer 200, the first surface film 132 of the first wafer 100, which functions as a bonding member, and the second surface film 232 of the second wafer 200 are bonded by plasma-activated bonding. This bonding forms a bonded wafer 300, and the surfaces 101 and 201 of the first wafer 100 and the second wafer 200 are formed as the bonding surface 301 of the bonded wafer 300.

[0056] [Laser processing process] In the second embodiment, as shown in Figure 7C, the laser processing step is similar to the first embodiment in which a laser beam LB is pulsed and irradiated from the back surface 102 of the first wafer 100 toward the bonded wafer 300. The focusing position of the irradiated laser beam LB is the same as in the first embodiment, located inside the first wafer 100, and the processed layer 303 is formed in a planar manner, similar to the first embodiment.

[0057] [Separation process] In the second embodiment, as shown in Figure 7D, the separation step involves applying a force to pull the first wafer 100 away from the second wafer 200, similar to the first embodiment, so that the first substrate 110 of the first wafer 100 is separated by the second crack 306 of the processed layer 303. Then, when the first wafer 100 side is separated from the bonded wafer 300, the first device layer 130 is moved so that the first device 131 of the first wafer 100 overlaps the second device 231 of the second wafer 200. In the second embodiment as well, a processed layer processing step may be performed to manufacture the stacked wafer.

[0058] [Third Embodiment] Next, a third embodiment of the present invention will be described with reference to Figures 8 and 9. Figure 8 is an explanatory diagram of each step in the manufacturing method of a stacked wafer according to the third embodiment, where Figure 8A shows the preparation step, Figure 8B shows the bonding step, Figure 8C shows the laser processing step, and Figure 8D shows the separation step. Figure 9 is a cross-sectional view of the laser processing step according to the third embodiment, similar to Figure 5. In the third embodiment, the configuration of the first wafer 100 is changed compared to the first embodiment.

[0059] As shown in Figure 8, the first wafer 100 of the third embodiment is configured without the insulating film 120 (see Figure 1) of the first wafer 100 in the first embodiment. Therefore, in the first wafer 100 of the third embodiment, the first device layer 130 is formed by laminating it on the surface 111 of the first substrate 110. As a result, the first device 131 is formed on the surface 111 of the first substrate 110.

[0060] In the laser processing step of the third embodiment, similar to the first embodiment, a laser beam LB having a wavelength that is transparent to the first substrate 110 of the first wafer 100 is pulsed and irradiated from the laser irradiation unit 40 from the back surface 102 of the first wafer 100 (see Figure 8C). Irradiation with this laser beam LB forms a planar processed layer 303 within the thickness of the first wafer 100. As shown in Figure 9, this processed layer 303 consists of a processed mark 304 formed planarly within the first substrate 110 by irradiation with the laser beam LB, and a third crack 308 extending from the processed mark 304. The third crack 308 is formed within the thickness of the first substrate 110 so as to connect adjacent processed marks 304 or the processed marks 304 and the outer edge of the first substrate 110 in a direction parallel to the planar direction of the first substrate 110.

[0061] In the laser processing step of the third embodiment, the spacing between adjacent processing marks 304 is set narrower than in the first embodiment. As a result, adjacent processing marks 304 are connected by a third crack 308 and are formed to extend planarly along the planar direction of the first substrate 110. In Figure 9, the processing marks 304 are shown as oblique ellipsoids, but the processing marks 304 may be formed as ellipsoids or spheres extending parallel to the planar or thickness direction of the first substrate 110, and the third crack 308 may be formed to connect these processing marks 304. The third crack 308 is formed when the processing marks 304 are formed and that portion expands in volume.

[0062] In the separation step of the third embodiment, by applying a force to pull the first wafer 100 away from the second wafer 200, the first substrate 110 of the first wafer 100 is separated by the processing marks 304 of the processed layer 303 and the third crack 308.

[0063] Here, similar to the first embodiment, in the laser processing step, the focusing position of the laser beam LB for forming the processing marks 304 is set such that the distance from the surface 101 of the first wafer 100 is shorter than the distance from the back surface 102. As a result, when comparing the thickness of the first wafer 100 on the surface 101 side and the back surface 102 side from the division point, the surface 101 side is thinner and the back surface 102 side is thicker. In the separation step, the thicker portion of the first wafer 100 on the back surface 102 side from the division cross-section 309 is separated from the second wafer 200 by the division at the processing layer 303. At the same time, the thinner portion of the first wafer 100 on the surface 101 side from the division cross-section 309 remains bonded to the second wafer 200 together with the first device layer 130 including the first device 131.

[0064] During the separation process, the first wafer 100 side is peeled off from the bonded wafer 300, and the first device layer 130 of the first wafer 100, which includes the first device 131, is transferred to the second wafer 200. During the separation process, the processing marks 304 and the third crack 308 in the processed layer 303 separate, forming a laminated wafer 500 on the second wafer 200 with the first device 131 transferred to it. In the third embodiment, the separation at the processing marks 304 and the third crack 308 leaves a small portion of the first substrate 110 remaining on the cross-section 309 side of the laminated wafer 500.

[0065] [Fourth Embodiment] Next, a fourth embodiment of the present invention will be described. Figure 10 is an explanatory diagram of each step in the method for manufacturing a stacked wafer according to the fourth embodiment. Figure 10A shows the preparation step, Figure 10B shows the bonding step, Figure 10C shows the laser processing step, and Figure 10D shows the separation step.

[0066] In the fourth embodiment, the configurations of wafers 100 and 200 are modified compared to the second embodiment. The modification of the configuration of the first wafer 100 in the fourth embodiment is the same as in the third embodiment, in that the insulating film 120 (see Figure 7) is not formed. Similarly, the modification of the configuration of the second wafer 200 in the fourth embodiment is the same as in the first wafer 100, in that the insulating film 220 (see Figure 7) is not formed.

[0067] In the fourth embodiment, the laser processing and separation processes can be carried out in the same manner as in the third embodiment. Therefore, even in the first and second wafers 100 and 200 which do not have insulating films 120 and 220 as in the third and fourth embodiments, laser processing of the bonding layer, bonding film, and bonding member can be made unnecessary as in the conventional method. As a result, the occurrence of stray light from the laser beam LB irradiated onto the bonding film, etc., can be eliminated, and damage to the first device 131 due to irradiation with the laser beam LB can be suppressed. Therefore, the conventional process of forming a thick bonding film can be eliminated, and productivity can be improved.

[0068] [Fifth Embodiment] Next, a fifth embodiment of the present invention will be described with reference to Figure 11. Figure 11 is an explanatory diagram of each step in the manufacturing method of a stacked wafer according to the fifth embodiment, with Figure 5A showing the preparation step, Figure 5B showing the bonding step, Figure 5C showing the laser processing step, and Figure 5D showing the separation step. In the fifth embodiment, the configuration of the first wafer 100 is changed compared to the fourth embodiment.

[0069] The first wafer 100 in Figure 11 of the fifth embodiment is configured to have a light-shielding film 310 instead of the insulating film 120 of the first wafer 100 in Figure 7 of the second embodiment. Although not shown, the light-shielding film 310 may be provided between the insulating film 120 and the first device layer 130 of the first wafer 100 in Figure 7 of the second embodiment, or between the first device layer 130 and the first substrate 110 of the first wafer 100 in Figure 10 of the fourth embodiment. As shown in Figures 11A and 11B, the light-shielding film 310 is provided in a planar manner within the first substrate 110 of the first wafer 100 at a location near the surface 111.

[0070] The light-shielding film 310 plays a role in shielding the light that passes through the first substrate 110 when the laser beam LB irradiated during the laser processing process is focused into the first substrate 110 to form a processing mark 304, and is formed of a porous film 320 such as a porous oxide film or nitride film, or a metal film 330. Figures 12 and 13 are cross-sectional views similar to those in Figure 5 of the laser processing process according to the fifth embodiment. Note that the insulating film 220 and the second device layer 230 on the second wafer 200 are not shown in Figures 12 and 13.

[0071] When the light-shielding film 310 is formed from a porous film 320, the silicon of the first substrate 110 is porousd by an anodic oxidation reaction, and then gas oxidation is performed to form it. When the light-shielding film 310 is a porous film 320, the bonding force in the porous film 320 is weaker than the bonding force in the first substrate 110. Therefore, as shown in the enlarged view of Figure 12, after focusing the laser beam LB to form a processing mark 304 in the first substrate 110, a first crack 305 is formed from the processing mark 304 toward the porous film 320 in the thickness direction of the first substrate 110. When the lower end of the first crack 305 reaches the porous film 320, a second crack 306 is extended horizontally within the porous film 320, forming the second crack 306 in a planar shape.

[0072] When the light-shielding film 310 is formed from a metal film 330, examples of materials include aluminum and nickel, and it can be formed by vapor deposition or sputtering. When the light-shielding film 310 is a metal film 330, as shown in the enlarged view of Figure 13, a laser beam LB is focused to form a processing mark 304 in the first substrate 110, a first crack 305 is formed from the processing mark 304, and when the lower end of the first crack 305 reaches the boundary with the metal film 330, a second crack 306 is extended to the boundary between the first substrate 110 and the metal film 330, forming the second crack 306 in a planar manner.

[0073] By forming a light-shielding film 310 on the first wafer 100, even if the laser beam LB passes through the processing layer 303 and causes stray light, the light-shielding film 310 can block the stray light. This better suppresses damage to each device 131, 231 and eliminates the need for the conventional process of forming a thick bonding film, thereby improving productivity. In addition, in the fifth embodiment, even if wafers 100, 200 are configured to have insulating films 120, 220 (see Figure 7) formed on them, similar to the second embodiment, the same processing as described above is possible. When the light-shielding film 310 is formed from a metal film 330, the metal film 330 blocks the escaping light. As a result, the metal film 330 is irradiated with escaping light and heated, causing thermal expansion which facilitates the peeling of the first substrate 110.

[0074] Furthermore, the present invention is not limited to the embodiments described above, and can be implemented with various modifications. In the embodiments described above, the size, shape, etc., shown in the accompanying drawings are not limited thereto, and can be appropriately modified within the scope that allows the present invention to exert its effects. In addition, the present invention can be implemented with appropriate modifications as long as it does not deviate from the scope of its objectives.

[0075] In the formation of the processing marks 304 on the processed layer 303 described above, the laser beam LB was irradiated by dividing the focusing position 307 into multiple parts, but this is not the only method. For example, the laser beam LB may be irradiated at the focusing position 307 having a width in the direction of extension of the processing marks 304, or the laser beam LB may be irradiated in multiple steps along the direction of extension of the processing marks 304 to create multiple focusing positions 307.

[0076] Furthermore, the processing marks 304 of the planar processed layer 303 are not limited to the shape shown above in Figures 3 and 4, but may be changed. For example, the processing marks 304 may be formed radially, extending in multiple linear directions from the center of the first wafer 100. Such radial processing marks 304 are formed by irradiation with a laser beam LB during the laser processing process, moving from the outer periphery, which is one direction in the planar direction of the first wafer 100, toward the center of the first wafer 100, which is the other direction.

[0077] Furthermore, after performing the processing layer treatment process described above, another wafer may be stacked on the cross-section 309 of the processed layer 303 of the stacked wafer 500 to transfer the device. In this case, the cross-section 309 of the planarized processed layer 303 and one side of the other wafer to be stacked are activated in the same manner as described above, and bonding is performed by activation bonding of these sides. Then, by performing the laser processing process and separation process on the other wafer as described above, the device from the other wafer can be transferred to the stacked wafer 500. This device transfer may be repeated further. [Industrial applicability]

[0078] As described above, the present invention has the effect of forming a planar processed layer within the first wafer of a bonded wafer, thereby separating and detaching it, eliminating the need to form a thick bonded film and improving productivity. [Explanation of symbols]

[0079] 100: First wafer 101: Surface 102: Back side 110: First board 111 :Surface 120: Insulating film 131: First device 200: Second wafer 201 :Surface 231: Second device 300: Bonded wafer 301: Joint surface 303: Processing layer 304: Machining marks 305: First Crack 306: Second Crack 308: Third Crack 309: Cutting plane 310: Light-shielding film 320: Porous film 330: Metal film LB: Laser beam

Claims

1. A method for processing a bonded wafer, comprising transferring the first device to the second wafer by peeling off the first substrate side from a bonded wafer formed by bonding a first wafer, on which a first device is formed on the surface side of a first substrate, to a second wafer, A laser processing step comprising: irradiating the first wafer with a laser beam having a wavelength that is transparent to the first substrate from the back surface of the first wafer and focusing the beam into the first substrate near the bonding surface between the first wafer and the second wafer, thereby forming a processed layer in a planar manner within the first wafer; A method for processing a bonded wafer, comprising: a separation step of separating the first substrate side from the second wafer while the first device of the first wafer remains bonded to the second wafer by the processing layer.

2. The first wafer includes an insulating film formed planarly between the surface of the first substrate and the first device. The processed layer consists of a processing mark formed planarly within the first substrate by irradiation with the laser beam, a first crack extending from the processing mark toward the insulating film in the thickness direction of the first substrate, and a second crack that extends planarly along the surface direction of the first substrate once the first crack reaches the insulating film. The method for processing a bonded wafer according to claim 1, wherein the wafer is separated at the second crack during the separation step.

3. The processed layer consists of a processing mark formed planarly within the first substrate by irradiation with the laser beam, and a third crack formed within the first substrate by connecting adjacent processing marks in a direction parallel to the surface direction of the first substrate. A method for processing a bonded wafer according to claim 1, wherein the wafer is separated by the processing mark and the third crack in the separation step.

4. The method for processing a bonded wafer according to claim 1, wherein the second wafer has a second device formed on its surface side.

5. After the separation process, A method for processing a bonded wafer according to claim 1, comprising a processing layer treatment step for flattening the cross-section of the second wafer.

6. The method for processing a bonded wafer according to claim 2 or 3, wherein in the laser processing step, the processing marks are formed diagonally from the non-bonded surface of the first wafer opposite to the bonding surface toward the bonding surface, and from one side toward the other in the plane direction of the bonding surface.

7. The method for processing a bonded wafer according to any one of claims 1 to 5, wherein in the laser processing step, the planar processed layer is formed from one plane direction of the first wafer toward the other.

8. The method for processing a bonded wafer according to claim 7, wherein in the laser processing step, the planar processed layer is formed in a plurality of concentric circles, spirals, or lines centered on the center of the first wafer, with the outer circumference of the first wafer being one of the processing layers and the center of the first wafer being the other.

9. The method for processing a bonded wafer according to claim 7, wherein in the laser processing step, the planar processed layer is formed in a plurality of linear shapes, with one diameter of the first wafer being the first and the other diameter of the first wafer being the other.

10. The method for processing a bonded wafer according to claim 1, wherein the first wafer irradiated with the laser beam is provided with a light-shielding film between the processed layer formed in the laser processing step and the bonded surface that blocks the light from passing through the laser beam.

11. The method for processing a bonded wafer according to claim 10, wherein the light-shielding film is a porous film.

12. The method for processing a bonded wafer according to claim 10, wherein the light-shielding film is a metal film.

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