JP7474138B2 - Lift-off Method - Google Patents

Description

The present invention relates to a lift-off method for transferring an optical device layer of an optical device wafer, in which an optical device layer is stacked on the other side of an epitaxy wafer via a buffer layer, to a transfer substrate.

For example, as in the technology disclosed in Patent Document 1, Patent Document 2, or Patent Document 3, an optical device layer laminated on an intermediate layer called a buffer layer formed on the surface of a sapphire wafer (epitaxy wafer) is bonded with an adhesive to wiring on a transfer substrate having wiring formed on its surface, and then a laser beam having a wavelength that is transparent to the sapphire wafer and absorbent to the buffer layer is irradiated from the sapphire wafer side to destroy (modify) the buffer layer, and the optical device layer is peeled off from the sapphire wafer to form an optical device substrate.

JP 2013-021225 A JP 2013-229508 A JP 2016-021464 A

A sapphire wafer with an optical device layer formed on the front side has a wafer ID formed on the back side, which is the exposed surface of the sapphire wafer, to preserve the history of the process of forming the optical device layer in epitaxial growth. On the other hand, a transfer substrate with wiring formed on the front side has a substrate ID formed on the back side, which is the exposed surface, to preserve the history of the process of forming the wiring layer. In other words, the bonded substrate formed by bonding the sapphire wafer and transfer substrate has both the wafer ID and substrate ID exposed.

As a result, a laser beam that is irradiated onto the buffer layer from the exposed surface side of the sapphire wafer in order to peel off the sapphire wafer is, for example, scattered by the wafer ID, and sufficient energy is not absorbed by the buffer layer, resulting in the generation of portions of the buffer layer that are insufficiently destroyed, resulting in the problem that the sapphire wafer cannot be properly peeled off.
Therefore, when transferring the optical device layer of the optical device wafer to a transfer substrate, there is a problem in that the sapphire wafer on which the wafer ID is formed can be appropriately peeled off.

The present invention, which aims to solve the above-mentioned problems, is a lift-off method for transferring an optical device layer of an epitaxy wafer, in which an optical device layer is laminated on the other surface of the epitaxy wafer, on which a wafer ID is formed on the outer periphery of one surface, via a buffer layer, to a transfer substrate, the lift-off method including a bonding step of bonding the transfer substrate to the surface of the optical device layer of the optical device wafer via an adhesive to form a bonded workpiece, a holding step of holding the transfer substrate of the bonded workpiece on the holding surface of a chuck table, and a step of grinding the wafer ID formed on the one surface of the epitaxy wafer of the bonded workpiece held on the holding surface with a grinding wheel to connect it to the unground surface of the one surface. The lift-off method includes a wafer ID removal step of forming a ground surface with a curved edge and removing the wafer ID; a polishing step of polishing at least the ground surface ground with the grinding wheel and the boundary between the ground surface and the surface not ground with the grinding wheel; a peeling layer formation step of irradiating a pulsed laser beam having a wavelength that is transparent to the epitaxy wafer and absorbent to the buffer layer from the one side of the epitaxy wafer to form a peeling layer on the buffer layer; and an optical device layer transfer step of applying an external force to the peeling layer after the peeling layer formation step to peel the epitaxy wafer from the transfer substrate and transfer the optical device layer to the transfer substrate.

In the lift-off method according to the present invention, the wafer ID removal process preferably involves rotating the bonded workpiece held on the holding surface about a rotation axis passing through the center of the holding surface, forming a circular surface in the central portion of one side of the epitaxy wafer that is not ground by the grinding wheel, and a ring-shaped ground surface that is connected to the outer periphery of the circular surface.

In the lift-off method according to the present invention, the wafer ID removal step preferably includes a tilt adjustment step of tilting the holding surface with respect to the grinding wheel so that the outer peripheral portion of one side of the epitaxy wafer of the bonded workpiece held on the holding surface contacts the underside of the grinding wheel before the central portion, and a grinding step of rotating the bonded workpiece held on the holding surface while measuring an area of the outer peripheral portion of one side of the epitaxy wafer closer to the center than the wafer ID with a measuring device, and grinding with the grinding wheel until the value of the measuring device changes.

In the lift-off method according to the present invention, the wafer ID removal process preferably includes a tilt adjustment process of tilting the holding surface with respect to the grinding wheel so that the outer peripheral portion of one side of the epitaxy wafer of the bonded workpiece held on the holding surface comes into contact with the underside of the grinding wheel before the central portion, and a grinding process of grinding with the grinding wheel until the magnitude of the load measured by a load measuring means that measures the load applied to the grinding wheel reaches a preset value.

In the lift-off method according to the present invention, it is preferable that one surface of the optical device wafer of the adhesive workpiece has a concave surface with a curved outer periphery, and that the holding step includes a tape application step of applying a tape having an area covering the holding surface to the transfer substrate.

In the lift-off method according to the present invention, it is preferable that one surface of the optical device wafer of the adhesive work forms a concave surface with a warped outer periphery, and the holding step includes a sheet attachment step of supplying liquid resin into a gap between a sheet having an area covering the holding surface and the warped outer periphery of the transfer substrate of the adhesive work placed on the sheet, hardening the resin, and attaching the sheet to the transfer substrate.

The lift-off method according to the present invention, which transfers an optical device layer of an epitaxy wafer having a wafer ID formed on the outer periphery of one side and an optical device layer laminated on the other side of the epitaxy wafer via a buffer layer, to a transfer substrate, grinds only the outer periphery where the wafer ID is formed in the wafer ID removal step to remove the wafer ID while suppressing wear of the grinding wheel, and further polishes the ground surface of the optical device wafer so that the pulsed laser beam can be properly irradiated to the buffer layer, and then in the peeling layer formation step, a peeling layer can be formed on the entire surface of the buffer layer without the wafer ID interfering with the irradiation of the pulsed laser beam to the buffer layer. Therefore, in the optical device layer transfer step, an external force can be applied to the peeling layer formed on the entire surface of the buffer layer to properly peel the epitaxy wafer from the transfer substrate.

In the lift-off method according to the present invention, the wafer ID removal process rotates the bonded workpiece held on the holding surface around a rotation axis passing through the center of the holding surface, forming a circular surface in the center of one side of the epitaxy wafer that is not ground by the grinding wheel and an annular ground surface that is connected to the outer periphery of the circular surface, thereby making it possible to reduce the amount of wear on the grinding wheel when removing the wafer ID.

In the lift-off method according to the present invention, the wafer ID removal process includes a tilt adjustment process in which the holding surface is tilted with respect to the grinding wheel so that the outer peripheral portion of one side of the epitaxy wafer of the bonded workpiece held on the holding surface contacts the underside of the grinding wheel before the central portion, and a grinding process in which the bonded workpiece held on the holding surface is rotated while measuring the area of the outer peripheral portion of one side of the epitaxy wafer closer to the center than the wafer ID with a measuring device, and is ground with the grinding wheel until the value of the measuring device changes, making it possible to grind off only the outer peripheral portion where the wafer ID is formed by the desired amount.

In the lift-off method according to the present invention, the wafer ID removal process includes an inclination adjustment process in which the holding surface is inclined with respect to the grinding wheel so that the outer peripheral portion of one side of the epitaxy wafer of the bonded workpiece held on the holding surface comes into contact with the underside of the grinding wheel before the central portion, and a grinding process in which the grinding wheel is used to grind the wafer until the magnitude of the load measured by a load measuring means that measures the load on the grinding wheel reaches a preset value, thereby making it possible to grind only the outer peripheral portion on which the wafer ID is formed by a desired amount.

In the lift-off method according to the present invention, when one surface of the optical device wafer of the bonded workpiece forms a concave surface with a curved outer periphery, the holding process includes a tape application process in which a tape with an area covering the holding surface is applied to the transfer substrate, making it possible to grind off only the desired amount of the outer periphery where the wafer ID is formed without causing vacuum leaks from the holding surface.

In the lift-off method according to the present invention, when one surface of the optical device wafer of the bonded work forms a concave surface with a warped outer periphery, the holding process includes a sheet attachment process in which liquid resin is supplied into the gap between a sheet with an area covering the holding surface and the warped outer periphery of the transfer substrate of the bonded work placed on the sheet, and hardened to attach the sheet to the transfer substrate. This makes it possible to grind the desired amount of only the outer periphery of the epitaxy wafer on which the wafer ID is formed in a short time without causing vacuum leaks from the holding surface.

FIG. 2 is a perspective view showing an example of a grinding device. 4 is a cross-sectional view showing an example of the structure of a grinding means, a chuck table, a table rotating means, and an inclination adjusting means. FIG. FIG. 2 is a perspective view illustrating an optical device wafer and a transfer substrate. Fig. 4A is a perspective view of a bonded work in which an optical device wafer and a transfer substrate are bonded together, and Fig. 4B is a cross-sectional view showing a part of the bonded work in which an optical device wafer and a transfer substrate are bonded together. 4A to 4C are cross-sectional views illustrating a holding step in the first embodiment. 11A to 11C are cross-sectional views illustrating a holding step in the second embodiment. 13A to 13C are cross-sectional views illustrating a holding step in the third embodiment. 11 is a cross-sectional view illustrating a tilt adjusting step and a grinding step in a wafer ID removing step. FIG. 1 is a cross-sectional view showing a bonded workpiece with a wafer ID removed. FIG. 11A to 11C are cross-sectional views illustrating a grinding step in a wafer ID removal step according to a third embodiment. 13A to 13C are cross-sectional views illustrating a grinding step in a wafer ID removal step according to a fourth embodiment. FIG. 13 is a plan view illustrating a stage at which an in-feed grinding process according to the fifth embodiment is started in the wafer ID removal process. FIG. 13 is a plan view illustrating the stage where the wafer ID is ground in the in-feed grinding process of the fifth embodiment in the wafer ID removal process. FIG. 13 is a plan view illustrating a stage where the in-feed grinding process of the fifth embodiment in the wafer ID removal process is completed. FIG. 13 is a plan view illustrating the stage at which the in-feed grinding process of the fifth embodiment in the wafer ID removal process is started while rotating the bonded workpiece. FIG. 13 is a plan view illustrating the stage where the wafer ID of the rotating bonded workpiece is ground in the in-feed grinding process of the fifth embodiment in the wafer ID removal process. 13 is a plan view illustrating a state in which an annular ground surface is formed upon completion of the in-feed grinding process of the fifth embodiment in the wafer ID removal process. FIG. 4A to 4C are cross-sectional views illustrating a polishing step. 10A to 10C are cross-sectional views illustrating a release layer forming step. 10 is a cross-sectional view illustrating a state in which an external force is applied to the peeling layer in an optical device layer transferring step. FIG. 10 is a cross-sectional view illustrating a state in which the optical device layer has been transferred to a transfer substrate in an optical device layer transfer step. FIG.

The grinding apparatus 1 shown in FIG. 1 is an apparatus that uses a grinding means 16 to grind a workpiece such as a wafer that is suction-held on the holding surface 302 of a chuck table 30. The front (-Y direction side) of the grinding apparatus 1 on the apparatus base 10 is an attachment/detachment area where the workpiece is attached to and detached from the chuck table 30, and the rear (+Y direction side) of the apparatus base 10 is a processing area where the workpiece held on the chuck table 30 is ground by the grinding means 16.
In addition, the grinding device of the present invention is not limited to a grinding device with a single-axis grinding means such as grinding device 1, but may be a two-axis grinding device that is equipped with a rough grinding means and a finish grinding means and can position the workpiece below the rough grinding means or the finish grinding means using a rotating turntable.

The chuck table 30, which has a circular outer shape in a plan view, includes an adsorption unit 300 made of, for example, a porous material or the like, which adsorbs the workpiece to be ground, and a frame 301 which supports the adsorption unit 300. The adsorption unit 300 is connected to a suction source (not shown), such as an ejector mechanism or a vacuum generator, and the suction force generated by the suction source is transmitted to the holding surface 302, which is the exposed surface of the adsorption unit 300, allowing the chuck table 30 to adsorb and hold the workpiece on the holding surface 302. The holding surface 302 is an extremely gentle conical slope with the apex at the center of rotation of the chuck table 30, which is indiscernible to the naked eye.

The chuck table 30 is surrounded by a cover 39 and can rotate about a rotation axis 350 (see FIG. 2) whose axial direction is the Z-axis direction (vertical direction) and passes through the center of the holding surface 302. The horizontal movement means 13 arranged below the cover 39 and the bellows cover 390 connected to the cover 39 and expanding and contracting in the Y-axis direction can move the chuck table 30 back and forth in the Y-axis direction on the device base 10.

The horizontal movement means 13 shown in FIG. 1, which moves the chuck table 30 and the grinding means 16 relatively in the Y-axis direction, includes a ball screw 130 having an axis in the Y-axis direction, a pair of guide rails 131 arranged parallel to the ball screw 130, a motor 132 connected to one end of the ball screw 130 to rotate the ball screw 130, and a movable block 133 whose internal nut is screwed onto the ball screw 130 and whose bottom is in sliding contact with the guide rail 131. When the motor 132 rotates the ball screw 130, the movable block 133 is guided by the guide rail 131 and moves linearly in the Y-axis direction, and the chuck table 30 arranged on the movable block 133 via the table rotation means 35 shown in FIG. 2 can be moved in the Y-axis direction.

The grinding apparatus 1 includes a table rotating means 35 for rotating the chuck table 30. In this embodiment, the table rotating means 35 is a pulley mechanism shown in FIG.
The table rotating means 35 includes a rotating shaft 350 that is connected to the underside of the chuck table 30, extends perpendicular to the chuck table 30, and passes through the center of the chuck table 30. A driving pulley 352 is attached to the shaft of a motor 351 that serves as a drive source for rotating the rotating shaft 350, and an endless belt 354 is wound around the driving pulley 352. A driven pulley 355 is attached to the lower end side of the rotating shaft 350, and the endless belt 354 is also wound around the driven pulley 355. When the motor 351 drives and rotates the driving pulley 352, the endless belt 354 rotates, and the driven pulley 355 and the rotating shaft 350 rotate accordingly. The motor may be directly connected to the lower end side of the rotating shaft 350 via a coupling or the like.

The rotating shaft 350 connected to the chuck table 30 is supported by the chuck base 36 shown in Figs. 1 and 2. For example, the chuck base 36, which is in the shape of a circular ring, is disposed below the cover 39 shown in Fig. 1 and surrounds the periphery of the rotating shaft 350. As shown in Fig. 2, a bearing 363 is disposed on the inner periphery of the chuck base 36, and the chuck base 36 rotatably supports the chuck table 30 via the rotating shaft 350 by the bearing 363.

The chuck base 36 is supported on the upper surface of the movable block 133 of the horizontal moving means 13 by, for example, an inclination adjustment means 37 that adjusts the inclination of the holding surface 302, which is a very gentle conical inclination of the chuck table 30 shown in FIG.
For example, two or more inclination adjustment means 37 are provided at equal intervals in the circumferential direction of the chuck base 36 on the bottom surface side of the chuck base 36. That is, for example, two inclination adjustment means 37 (only one is shown) and support columns 379 for fixing the chuck base 36 are arranged at intervals of 120 degrees in the circumferential direction.

A screw shaft hole 364 extending in the thickness direction is formed in the chuck base 36, and a screw shaft 372 of the tilt adjustment means 37 is screwed into the screw shaft hole 364. The lower end of the screw shaft 372 is connected to a lift motor 374 via a coupling 375. The tilt of the chuck base 36 and the chuck table 30 can be changed by the amount of thrust of the screw shaft 372 by the lift motor 374, thereby adjusting the tilt of the holding surface 302 relative to the grinding surface (lower surface) of the grinding wheel 1641 of the grinding means 16.

In this embodiment, the grinding apparatus 1 shown in FIG. 1 is equipped with a load sensor 33 that detects the load received by the workpiece when the grinding means 16 is pressed from above against the workpiece held by the chuck table 30.
The load sensors 33 are disposed, for example, between the chuck base 36 supporting the chuck table 30 and the movable block 133 of the horizontal moving means 13, at intervals of 120 degrees in the circumferential direction of the chuck table 30, that is, at the vertices of an imaginary equilateral triangle. The three load sensors 33 are the points of application of the load from the grinding means 16, and are constituted, for example, by a thin force sensor manufactured by Kistler using a piezoelectric element such as lead zirconate titanate (PZT). The piezoelectric element is disposed at the above-mentioned location in a state in which a predetermined compression pressure (pre-pressure) is applied and the element is compressed to a certain degree. When the load sensor 33 is compressed by receiving a load during grinding, it generates a positive voltage. This voltage signal indicates the load and is transmitted to the control means 19 shown in FIG. 1, and the control means 19 can recognize the load applied to the workpiece (the sum of the detection values of the three load sensors 33).

In the processing area, a column 11 is erected, and a grinding feed means 17 is disposed on the front surface of the column 11 on the -Y direction side, which moves the chuck table 30 and the grinding means 16 relatively in a direction perpendicular to the holding surface 302 (Z-axis direction). The grinding feed means 17 includes a ball screw 170 whose axial direction is the Z-axis direction, a pair of guide rails 171 disposed parallel to the ball screw 170, a grinding feed motor 172 connected to the upper end of the ball screw 170 and rotating the ball screw 170, and a lift plate 173 whose internal nut is screwed into the ball screw 170 and whose side is in sliding contact with the guide rail 171. When the grinding feed motor 172 rotates the ball screw 170, the lift plate 173 is guided by the guide rail 171 and moves back and forth in the Z-axis direction, and the grinding means 16 fixed to the lift plate 173 is fed for grinding in the Z-axis direction.

For example, the grinding device 1 is equipped with height position detection means 12 that detects the height position of the grinding means 16 that moves up and down by the grinding feed means 17. The height position detection means 12 is equipped with a scale 120 that extends in the Z-axis direction along a pair of guide rails 171, and a reading unit 123 that is fixed to the lift plate 173, moves together with the lift plate 173 along the scale 120, and optically reads the graduations of the scale 120.

The grinding means 16, which grinds the workpiece held on the holding surface 302 of the chuck table 30, includes a rotating shaft 160 whose axial direction is the Z-axis direction, a housing 161 that rotatably supports the rotating shaft 160, a grinding motor 162 that rotates and drives the rotating shaft 160, an annular mount 163 connected to the lower end of the rotating shaft 160, a grinding wheel 164 that is detachably attached to the lower surface of the mount 163, and a holder 165 that supports the housing 161 and is fixed to the lift plate 173 of the grinding feed means 17.

The grinding wheel 164 comprises a wheel base 1640 and a number of grinding stones 1641 of roughly rectangular parallelepiped shape arranged in a ring shape on the bottom surface of the wheel base 1640. The grinding stones 1641 are formed by bonding diamond abrasive grains or the like with an appropriate binder (adhesive), and the lower surface thereof is mainly the grinding surface.

Inside the rotating shaft 160, a flow passage (not shown) that is connected to a grinding water supply source and serves as a passage for grinding water is provided, penetrating the axial direction of the rotating shaft 160. The flow passage (not shown) further passes through the mount 163 and opens at the bottom surface of the wheel base 1640 so that the grinding water can be sprayed toward the grinding wheel 1641.

A thickness measuring means 38 that measures the thickness of the workpiece by contact is disposed adjacent to the grinding means 16 when the grinding means 16 has been lowered to the grinding position. The thickness measuring means 38 may be of a non-contact type.

The thickness measuring means 38 includes, for example, a pair of thickness measuring devices (height gauges), i.e., a table top surface height measuring device 381 for measuring the height position of the top surface of the chuck table 30, and a workpiece top surface height measuring device 382 for measuring the height position of the top surface, which is the grinding surface, of the workpiece held by the chuck table 30.
The table top surface height measuring device 381 and the workpiece top surface height measuring device 382 each have a contact at its tip that moves up and down and contacts each measurement surface. The table top surface height measuring device 381 (workpiece top surface height measuring device 382) is supported so as to be movable up and down, and can be pressed against each measurement surface with an appropriate force. The thickness measuring means 38 detects the height position of the top surface of the frame 301, which serves as a reference surface, with the table top surface height measuring device 381, detects the height position of the top surface of the workpiece with the workpiece top surface height measuring device 382, and calculates the difference between the two detection values, thereby sequentially measuring the thickness of the workpiece during grinding.

The grinding device 1 is equipped with a control means 19 capable of controlling each component of the grinding device 1 described above. The control means 19, which is composed of a CPU and storage elements such as memory, is electrically connected to, for example, the grinding feed means 17, the grinding means 16, and the horizontal movement means 13, and under the control of the control means 19, the grinding feed operation of the grinding means 16 by the grinding feed means 17, the rotation operation of the grinding wheel 164 in the grinding means 16, and the positioning operation of the chuck table 30 relative to the grinding wheel 164 by the horizontal movement means 13 are controlled.

Below, we will explain each step of carrying out the lift-off method according to the present invention using the grinding device 1 shown in Figure 1, etc.

The optical device wafer 90 shown in FIG. 3 includes, for example, an epitaxy wafer 900 made of a flat, disk-shaped sapphire wafer, and an optical device layer 902 laminated on the other surface 901 of the epitaxy wafer 900, which faces upward in FIG. 3 .
The optical device layer 902 is composed of, for example, an n-type gallium nitride semiconductor layer and a p-type gallium nitride semiconductor layer formed by epitaxial growth on the other surface 901 of the epitaxy wafer 900. When the optical device layer 902 having a thickness of, for example, several μm to several tens of μm is laminated on the epitaxy wafer 900, a buffer layer 98 (see FIG. 4B ) having a thickness of, for example, about 1 μm and made of GaN or the like having intermediate properties between the two layers is formed between the other surface 901 of the epitaxy wafer 900 and the p-type gallium nitride semiconductor layer.
For example, as shown in FIG. 3, in an optical device layer 902, optical devices 905 are formed in a plurality of regions partitioned by a plurality of planned division lines 904 formed in a lattice pattern.

In the optical device wafer 90 shown in Figures 3 and 4 (B) , a wafer ID 909 is formed in an area of the outer periphery of one surface 908 facing downward, for example, to record the history of the formation process of the optical device layer 902 in epitaxial growth. The wafer ID 909 is, for example, letters or numbers printed on one surface 908 by laser irradiation, and is a modification of the epitaxy wafer 900.

(1) Bonding Process In the bonding process, a flat circular plate-shaped transfer substrate 91 made of a copper substrate having a thickness of, for example, about 1 mm is bonded to the surface of the optical device layer 902 via an adhesive 93 (only shown in FIG. 4B). The transfer substrate 91 may be made of, for example, Mo (molybdenum), Cu (copper), Si (silicon), or the like, and the adhesive 93 may be made of, for example, a bonding metal such as Au (gold), Pt (platinum), Cr (chromium), In (indium), or Pd (palladium). In the bonding process, the adhesive 93 is evaporated onto the surface of the optical device layer 902 or the lower surface of the transfer substrate 91 in FIG. 3 to form a layer of the adhesive 93 having a thickness of, for example, about 3 μm. Then, the adhesive 93 is placed face-to-face with the lower surface of the transfer substrate 91 or the surface of the optical device layer 902 and pressure-bonded. As a result, a bonded work 9 is formed in which the optical device wafer 90 and the transfer substrate 91 are bonded to each other via the adhesive 93, as shown in FIGS. 4A and 4B.

(2-1) Holding Step 1
First, as shown in Fig. 5, for example, the center of the workpiece 9 to be bonded is approximately aligned with the center of the holding surface 302 of the chuck table 30, and the workpiece 9 to be bonded is placed on the holding surface 302 with one surface 908 facing upward. Then, a suction force generated by the operation of a suction source (not shown) is transmitted to the holding surface 302, and the chuck table 30 sucks and holds the transfer substrate 91 of the workpiece 9 on the holding surface 302. That is, the plate-shaped workpiece 9 to be bonded, which was flat overall before being sucked and held, is sucked and held according to the holding surface 302, which is an extremely gentle conical slope. Note that the adhesive 93 is omitted in Fig. 5.

(2-2) Holding Step 2
The holding step is not limited to the above-mentioned embodiment 1. For example, as shown in Fig. 6, one surface 908 of the optical device wafer 90 of the bonded workpiece 9 may have a concave surface with the outer periphery warped due to the contraction of the adhesive 93 shown in Fig. 4B. The outer periphery of the transfer substrate 91 bonded to the optical device wafer 90 also warps upward. The warp in the outer periphery of the bonded workpiece 9 is gradually lowered from the outer periphery of the bonded workpiece 9 where the transfer substrate 91 is held by the chuck table 30 toward the center.

(Tape application step in the holding step of embodiment 2)
When the bonded workpiece 9 has such a warp in the outer periphery, the holding process includes a tape application process in which a tape 95 having an area covering the holding surface 302 of the chuck table 30 shown in Figure 6 is applied to the transfer substrate 91.

The tape 95 shown in FIG. 6 is circular and has a diameter larger than the holding surface 302 and smaller than the frame body 301, and includes, for example, a base layer made of a polyolefin resin and an adhesive layer made of an adhesive glue.
In the tape adhering process, the adhesive workpiece 9 is placed on the adhesive layer of the tape 95 with the transfer substrate 91 side facing the tape mounter or the like, and the transfer substrate 91 side of the adhesive workpiece 9 is attached to the adhesive layer by a not-shown adhering roller rolling on the tape 95 or by manual work by an operator. Then, for example, the center of the tape 95 and the center of the adhesive workpiece 9 are approximately aligned, and the outer peripheral portion of the adhesive workpiece 9 that is warped toward the upper side is not attached to the tape 95 (floating on the tape 95).

(Holding of adhesive work with tape attached in holding step of embodiment 2)
For example, the bonded workpiece 9 is placed on the chuck table 30 so that the center of the bonded workpiece 9 approximately coincides with the center of the holding surface 302, and the tape 95 covers the entire holding surface 302, and the chuck table 30 suction-holds the tape 95 of the bonded workpiece 9 on the holding surface 302. That is, the bonded workpiece 9 as a whole is suction-held following the holding surface 302, which is an extremely gentle conical slope, and the outer peripheral portion that is warped upward is separated from the holding surface 302. However, since the holding surface 302 is covered by the tape 95, no vacuum leak occurs from the holding surface 302, and the bonded workpiece 9 is appropriately held by the chuck table 30 via the tape 95.

(2-3) Holding Step 3
As described in embodiment 2, when the adhesive workpiece 9 has a warped concave surface formed at the outer periphery of one side 908 of the optical device wafer 90, i.e., when the adhesive workpiece 9 has a warped outer periphery, the holding process may include a sheet attachment process in which liquid resin is supplied into the gap between a sheet 96 having an area covering the holding surface 302 of the chuck table 30 shown in FIG. 6 and the warped outer periphery of the transfer substrate 91 of the adhesive workpiece 9 placed on the sheet 96, and the liquid resin is hardened to attach the sheet 96 to the transfer substrate 91.

(Sheet attachment step in the holding step of the third embodiment)
The sheet 96 is, for example, a polyolefin resin film, and in the third embodiment, does not include an adhesive layer for adhering the workpiece 9. The sheet 96 is circular and has a diameter larger than the holding surface 302 and smaller than the frame 301.
In the sheet adhering process, the sheet 96 is placed so as to cover the entire holding surface 302 of the chuck table 30, and the chuck table 30 suction-holds the sheet 96 on the holding surface 302 without vacuum leakage.

Next, the adhesive workpiece 9 is placed on the sheet 96 with the transfer substrate 91 facing downward. The center of the sheet 96 and the center of the adhesive workpiece 9 are approximately aligned, and a gap of a predetermined size is formed between the sheet 96 and the outer peripheral portion of the adhesive workpiece 9 that is warped upward, i.e., the outer peripheral area of the underside of the transfer substrate 91.

For example, a liquid resin supplying means 34 is disposed near the chuck table 30. The liquid resin supplying means 34 includes a resin supplying nozzle 340 and a resin supply source 343 that communicates with the resin supplying nozzle 340 via a dispenser, a flexible resin tube, or the like.
For example, the resin supply nozzle 340 , which is inverted L-shaped when viewed from the side, has a supply port facing the outer periphery of the chuck table 30 .
In this embodiment, the liquid resin 349 supplied to the resin supply nozzle 340 by the resin supply source 343 is an ultraviolet-curable resin that hardens when irradiated with ultraviolet rays, but it may also be a thermosetting resin that hardens when heat is applied.

The resin supply source 343 sends out liquid resin 349 to the resin supply nozzle 340, and the liquid resin 349 is supplied from the supply port toward the gap between the outer peripheral area of the underside of the transfer substrate 91 placed on the chuck table 30 and the sheet 96. The chuck table 30 also rotates at a low speed, and a predetermined amount of liquid resin 349 is supplied around the entire circumference of the gap. Then, after an amount of liquid resin 349 sufficient to fill the entire circumference of the gap has been supplied, the supply of liquid resin 349 is stopped.

Next, an ultraviolet ray irradiation lamp (not shown) arranged near the chuck table 30 irradiates ultraviolet rays onto the liquid resin 349 filled in the gap. As a result, the liquid resin 349 hardens and adheres the sheet 96 to the transfer substrate 91 by the liquid resin 349. In other words, the adhesive workpiece 9 is sucked and held to the chuck table 30 via the sheet 96 with the outer periphery warped.

For example, it is not necessary to supply the liquid resin 349 using a nozzle as described above. For example, the liquid resin 349 may be supplied in advance to the upper surface of the sheet 96 in a circular shape having a diameter approximately equal to the diameter of the workpiece 9 to be bonded.

The sheet 96 may have an adhesive layer made of a glue layer or the like, and may be adhered to the lower surface of the transfer substrate 91 by the adhesive layer, and then the adhered workpiece 9 to which the sheet 96 is adhered may be transported to the chuck table 30. Thereafter, the liquid resin 349 may be supplied to the gap as described above.
Furthermore, since the polyolefin-based sheet 96 has thermoplasticity, even if it does not have an adhesive layer, it may be partially melted and adhered to the workpiece 9 by heating it to a temperature close to its melting point while being pressed against the transfer substrate 91 of the workpiece 9 under application of a predetermined pressure. Then, the workpiece 9 to which the sheet 96 is adhered may be transported to the chuck table 30. Thereafter, the liquid resin 349 may be supplied to the gap as described above.
Furthermore, the sheet may be rectangular in area covering the holding surface 302. Then, after liquid resin 349 is supplied to the gap and cured, the sheet may be cut into a circle along the outer periphery of the workpiece 9 to be bonded.
Alternatively, the sheet 96 may be placed on a separate placement table, liquid resin 349 may be supplied into the gap, and after being hardened, the sheet 96 may be held on the holding surface 302 of the chuck table 30 .

(3-1) Tilt Adjustment Process in Wafer ID Removal Process For example, after carrying out the holding process of embodiment 1 described using Figure 5, a wafer ID removal process is carried out in which the wafer ID 909 formed on one surface 908 of the epitaxy wafer 900 of the bonded workpiece 9 held on the holding surface 302 of the chuck table 30 is ground with a grinding wheel 1641 shown in Figure 8 to form a ground surface connected to the unground surface of the one surface 908, and the wafer ID 909 is removed.

In the wafer ID removal process in this embodiment, a tilt adjustment process is performed to tilt the holding surface 302 relative to the grinding wheel 1641 so that the outer periphery of the epitaxy wafer 900 of the bonded workpiece 9 held on the holding surface 302 comes into contact with the underside of the grinding wheel 1641 before the central portion.

In the tilt adjustment process, a portion of the outer periphery of the chuck table 30 is raised a predetermined distance by the tilt adjustment means 37 shown in simplified form in FIG. 8 so that it is higher than the other portions, and the outer periphery of one surface 908 of the epitaxy wafer 900 of the bonded workpiece 9, which is held by suction following the holding surface 302, which is a conical inclined surface, is positioned relatively higher than the central portion. When the outer periphery is positioned higher, the height position of the outer periphery is determined, for example, based on data obtained from past test processing and the thickness of the bonded workpiece 9 to be ground.

(3-2) First embodiment of the grinding process in the wafer ID removal process
After the inclination adjustment step is performed, for example, a grinding step according to the embodiment 1 described below is performed. In the grinding step according to the embodiment 1, while measuring an area closer to the center than a wafer ID 909 in an outer peripheral portion of one surface 908 of the epitaxy wafer 900 with a work top surface height measuring device 382 of a thickness measuring means 38, the bonded workpiece 9 held on the holding surface 302 is rotated and ground with a grinding wheel 1641 until the value of the work top surface height measuring device 382 changes.

Specifically, first, the chuck table 30 holding the bonded workpiece 9 moves in the +Y direction to below the grinding means 16. Then, the grinding wheel 1641 of the grinding means 16 is aligned with the bonded workpiece 9 held on the chuck table 30. The alignment is performed, for example, as shown in FIG. 8 , such that the center of rotation of the grinding wheel 164 is horizontally shifted a predetermined distance from the center of rotation of the bonded workpiece 9, and the rotation trajectory of the grinding wheel 1641 passes through the center of the epitaxy wafer 900.
In other words, the inclination of the rotation axis 350 that rotates the holding surface 302 is changed at a position where the grinding wheel 1641 passes through the center of the holding surface 302, so that the outer periphery of the bonded workpiece 9 is brought into contact with the grinding wheel 1641 first.
Further, the workpiece upper surface height gauge 382 of the thickness measuring means 38 is positioned in a region closer to the center than the wafer ID 909 in the outer peripheral portion of one surface 908 of the epitaxy wafer 900, and the workpiece upper surface height gauge 382 comes into contact with that region.

Next, the grinding means 16 is sent in the -Z direction by the grinding feed means 17, and the lower surface of the grinding wheel 1641, which rotates with the rotation of the rotating shaft 160, comes into contact with the outer periphery of the epitaxy wafer 900 of the bonded workpiece 9, on which the wafer ID 909 located at the highest position on one surface 908 of the epitaxy wafer 900 is formed, thereby performing grinding. During grinding, the table rotating means 35 (see FIG. 2) rotates the chuck table 30, for example, in the same direction as the grinding wheel 1641, and the bonded workpiece 9 held on the holding surface 302 also rotates, so that the grinding wheel 1641 first grinds the entire outer periphery of the epitaxy wafer 900. Grinding water is also supplied to the contact portion between the grinding wheel 1641 and the epitaxy wafer 900, and the contact portion is cooled and washed.
In this embodiment, so-called in-feed grinding is used. In-feed grinding is a grinding method in which a grinding wheel 164 is fed in a thrust direction (Z-axis direction) relative to a rotation shaft 160 with respect to the rotating bonded workpiece 9.

The workpiece top surface height measuring device 382 transmits information on the measurement value of the height of the region closer to the center than the wafer ID 909 of the epitaxy wafer 900 to the control means 19. In the initial stage when the grinding process is started, grinding of the region closer to the center than the wafer ID 909 of the outer periphery of one side 908 of the epitaxy wafer 900 measured by the workpiece top surface height measuring device 382 is not performed, and there is no change in the measurement value of the workpiece top surface height measuring device 382 measuring the height of the region closer to the center than the wafer ID 909 of one side 908 of the epitaxy wafer 900.

As the grinding process is performed by the grinding wheel 1641 rotating while descending in the -Z direction, widening the annular ground surface from the outer periphery of the rotating epitaxy wafer 900 gradually toward the center, an annular ground surface 907 shown in Fig. 9 is formed on the epitaxy wafer 900 such that the width widens from the outer periphery toward the inside in the radial direction. Note that Fig. 9 shows the main parts of the bonded workpiece 9 enlarged, and the grinding means 16 and the like are shown in a simplified manner.
Then, the wafer ID 909 is also ground and removed together with the epitaxy wafer 900. After the entire wafer ID 909 is ground and removed, the annular ground surface 907 expands to the position of the workpiece top surface height measuring device 382 shown in Fig. 8, causing a change in the measurement value of the workpiece top surface height measuring device 382. Then, under the control of the grinding feed means 17 by the control means 19 which recognizes the change in the measurement value of the workpiece top surface height measuring device 382, the grinding means 16 is lifted in the +Z direction and the grinding wheel 1641 is separated from the epitaxy wafer 900, thereby completing the grinding of the epitaxy wafer 900.
The workpiece upper surface height measuring device 382 may be of a non-contact type. Also, the measuring device may be a thickness measuring device that measures the thickness of the epitaxy wafer 900.

After grinding is completed, the bonded workpiece 9 has a circular surface 906 that is not ground by the grinding wheel 1641 in the central portion of one side 908 of the epitaxy wafer 900 shown in FIG. 9, and a ring-shaped ground surface 907 that is connected to the outer periphery of the circular surface 906, and the wafer ID 909 has been removed.

As described above, in the lift-off method according to the present invention, the wafer ID removal process rotates the bonded workpiece 9 held on the holding surface 302 around the rotation axis 350 passing through the center of the holding surface 302, forming a circular surface 906 that is not ground by the grinding wheel 1641 in the central portion of one surface 908 of the epitaxy wafer 900, and an annular ground surface 907 that is connected to the outer periphery of the circular surface 906, thereby making it possible to reduce the amount of wear on the grinding wheel 1641 when removing the wafer ID 909.

In addition, in the lift-off method according to the present invention, the wafer ID removal process includes a tilt adjustment process in which the holding surface 302 is tilted relative to the grinding wheel 1641 so that the outer peripheral portion of one side 908 of the epitaxy wafer 900 of the bonded workpiece 9 held on the holding surface 302 contacts the underside of the grinding wheel 1641 before the central portion, and a grinding process in which the bonded workpiece 9 held on the holding surface 302 is rotated while measuring the area of the outer peripheral portion of one side 908 of the epitaxy wafer 900 closer to the center than the wafer ID 909 with the workpiece top surface height measuring device 382, and grinding with the grinding wheel 1641 until the value of the workpiece top surface height measuring device 382 changes. This makes it possible to grind only the outer peripheral portion where the wafer ID 909 is formed by a desired amount, that is, the amount that completely removes the wafer ID 909.

(3-3) Embodiment 2 of Grinding Process in Wafer ID Removal Process
The grinding step in the wafer ID removal step may be performed as in the following embodiment 2 instead of the above embodiment 1.
In the second embodiment, the outer periphery of the epitaxy wafer 900 is ground with the grinding wheel 1641 until the magnitude of the load measured by a load measuring means for measuring the load applied to the grinding wheel 1641 reaches a preset value.

An example of a load measuring means for measuring the load on the grinding wheel 1641 is the motor load measuring means 167 for measuring the load on the grinding motor 162 of the grinding means 16 shown in FIG. 8. The motor load measuring means 167 is electrically connected to the control means 19 and can transmit information about the load current value of the grinding motor 162 to the control means 19.

The chuck table 30 holding the bonded workpiece 9 moves in the +Y direction to below the grinding means 16, and the center of rotation of the grinding wheel 164 is shifted horizontally by a predetermined distance relative to the center of rotation of the bonded workpiece 9, and the grinding wheel 1641 is positioned for grinding so that its rotational trajectory passes through the center of the epitaxy wafer 900.

The grinding means 16 is fed in the -Z direction by the grinding feed means 17, and the lower surface of the grinding wheel 1641, which rotates with the rotation of the rotating shaft 160, is positioned at the highest position of one surface 908 of the epitaxy wafer 900 of the bonded workpiece 9 and abuts against the outer periphery portion on which the wafer ID 909 is formed, thereby performing in-feed grinding. During grinding, for example, the bonded workpiece 9 held on the holding surface 302 is rotated, but the bonded workpiece 9 does not have to be rotated.
As a result, first, the entire outer periphery of the epitaxy wafer 900 is ground by the grinding wheel 1641. When the bonded workpiece 9 is not rotated, the chuck table 30 is rotated in advance by a predetermined angle so that the wafer ID 909 formed on one surface 908 of the epitaxy wafer 900 is positioned directly under the grinding wheel 1641, and one area of the outer periphery where the wafer ID 909 is formed is ground.

As the grinding wheel 1641 grinds the outer peripheral portion of one surface 908 of the epitaxy wafer 900 together with the wafer ID 909, the load on the grinding wheel 1641 increases due to the abrasive grains being worn away, etc. While the grinding wheel 1641 is rotating, power is continuously supplied to the grinding motor 162 from a power source (not shown), and the grinding motor 162 is feedback-controlled so that the grinding wheel 164 rotates at a constant rotation speed even if the load on the grinding wheel 1641 increases. Then, when the control means 19, which continues to receive information about the load current value from the motor load measuring means 167, determines that the load on the grinding wheel 1641, in other words, the load on the increasing grinding motor 162, reaches a predetermined value (load current value), it determines that a predetermined amount of the outer periphery of one surface 908 of the epitaxy wafer 900 has been ground away and the wafer ID 909 has been removed, and controls the grinding feed means 17 to pull the grinding means 16 up in the +Z direction so that the grinding wheel 1641 is separated from the epitaxy wafer 900, thereby completing grinding of the epitaxy wafer 900.
The above-mentioned preset values are preset in a storage section or the like of the control means 19 based on data obtained from past experiments or the like.

Another example of the load measuring means for measuring the load acting on the grinding wheel 1641 shown in FIG. 8 will be described below.
Another example of the load measuring means are the three load sensors 33 shown in Figure 1. As shown in Figure 8, each load sensor 33 (only one shown) is electrically connected to the control means 19 and can transmit information to the control means 19 about the load value received.

After the tilt adjustment process is performed as described above, in-feed grinding of the epitaxy wafer 900 is performed. During in-feed grinding, the grinding means 16 is lowered by the grinding feed means 17, and a load is applied from the grinding means 16 to the bonded workpiece 9. The load sensor 33 detects the load and sends a detection signal to the control means 19, which monitors whether an appropriate load is being applied to the bonded workpiece 9 during grinding.

For example, when grinding of the outer peripheral portion of the epitaxy wafer 900 is started, the control means 19 sequentially sums up the load values sent from the load sensor 33. Then, while the grinding wheel 1641 grinds the outer peripheral portion of one surface 908 of the epitaxy wafer 900 together with the wafer ID 909, when the magnitude of the load applied to the grinding wheel 1641, in other words, the total value of the increasing load values, reaches a preset value, it determines that the outer peripheral portion of one surface 908 of the epitaxy wafer 900 has been ground by a predetermined amount and the wafer ID 909 has been removed, and controls the grinding feed means 17 to lift the grinding means 16 in the +Z direction and separate the grinding wheel 1641 from the epitaxy wafer 900, thereby completing grinding of the epitaxy wafer 900.
The above-mentioned preset values are preset in a storage section or the like of the control means 19 based on data obtained from past experiments or the like.

As described above, in the lift-off method of the present invention, the wafer ID removal process includes a tilt adjustment process of tilting the holding surface 302 relative to the grinding wheel 1641 so that the outer peripheral portion of one surface 908 of the epitaxy wafer 900 of the bonded workpiece 9 held on the holding surface 302 of the chuck table 30 comes into contact with the underside of the grinding wheel 1641 before the central portion, and a grinding process of grinding with the grinding wheel 1641 until the magnitude of the load measured by the above-mentioned example load measuring means or another example load measuring means that measures the load applied to the grinding wheel 1641 reaches a predetermined value, making it possible to completely remove the wafer ID 909 by grinding only the outer peripheral portion where the wafer ID 909 is formed by the desired amount.
During grinding, for example, the bonded workpiece 9 held on the holding surface 302 is rotated, but the bonded workpiece 9 does not have to be rotated.
When the bonded workpiece 9 is not rotated, only the portion where the wafer ID 909 is to be formed is ground.

(3-4) Third embodiment of grinding process in wafer ID removal process
As described above, in the holding step of embodiment 2, one surface 908 of the optical device wafer 90 of the bonded workpiece 9 shown in FIG. 6 forms a concave surface with a curved outer periphery, and when the tape bonding step is performed, the grinding step may be performed as in the following embodiment 3 shown in FIG. 10.
6, which is a stage before the grinding step in this embodiment 3, it is not necessary to carry out an inclination adjustment step of inclining the holding surface 302 with respect to the grinding wheel 1641 so that the outer periphery of one surface 908 of the epitaxial wafer 900 of the bonded workpiece 9 held on the holding surface 302 comes into contact with the underside of the grinding wheel 1641 before the central portion. That is, this is because, at the stage where the holding step in embodiment 2 is carried out, the warped outer periphery of one surface 908 of the epitaxial wafer 900 comes into contact with the underside of the grinding wheel 1641 before the central portion.
In the example shown in Figure 10, the inclination of the chuck table 30 is adjusted by the inclination adjustment means 37 so that the holding surface 302, which is an extremely gently inclined surface, is parallel to the grinding surface (lower surface) of the grinding wheel 1641 of the grinding means 16.

The chuck table 30 holding the bonded workpiece 9 is positioned so that, for example, the rotational trajectory of the grinding wheel 1641 passes through the center of the epitaxy wafer 900 (see FIG. 6). Thereafter, the grinding means 16 shown in FIG. 10 is sent in the -Z direction by the grinding feed means 17, and the lower surface of the rotating grinding wheel 1641 is positioned at the highest position on one surface 908 of the epitaxy wafer 900, and the wafer ID 909 is formed and abuts against the warped outer periphery, thereby performing in-feed grinding. During grinding, for example, the bonded workpiece 9 held on the holding surface 302 is rotated, but the bonded workpiece 9 does not have to be rotated.
When the bonded workpiece 9 is not rotated, only the portion where the wafer ID 909 is to be formed is ground.

As a result, first, the entire outer periphery of the epitaxy wafer 900 is ground by the grinding wheel 1641. Note that the grinding feed speed (lowering speed) of the grinding means 16 is set to be slower than in the past in order to prevent damage to the outer periphery of the bonded workpiece 9, since a gap of a predetermined size is formed between the outer periphery of the bonded workpiece 9 that warps upward, i.e., the outer periphery region of the lower surface of the transfer substrate 91, and the tape 95.
In addition, when the bonded workpiece 9 is not rotated, the chuck table 30 is rotated in advance by a predetermined angle, so that the wafer ID 909 formed on one side 908 of the epitaxy wafer 900 is positioned directly under the grinding wheel 1641, and the outer peripheral portion on which the wafer ID 909 is formed is ground.

The wafer ID 909 is also ground and removed together with the epitaxy wafer 900. Furthermore, after the entire wafer ID 909 is ground and removed, the annular grinding surface 907 spreads to the position of the workpiece top surface height measuring device 382, causing the measurement value of the workpiece top surface height measuring device 382 to change. Then, under the control of the grinding feed means 17 by the control means 19 that recognizes the change in the measurement value of the workpiece top surface height measuring device 382, the grinding means 16 is pulled up in the +Z direction, and the grinding wheel 1641 is separated from the epitaxy wafer 900, and grinding of the epitaxy wafer 900 is completed. In this way, it is possible to reduce the amount of wear of the grinding wheel 1641 by grinding only the desired amount of the outer peripheral portion where the wafer ID 909 is formed.

(3-5) Grinding Process in Wafer ID Removal Process, Embodiment 4
In the holding process of the embodiment 3 described above with reference to Figure 7, one surface 908 of the optical device wafer 90 of the bonded workpiece 9 forms a concave surface with a curved outer periphery, and when the sheet bonding process is performed, the grinding process may be performed as in the embodiment 4 shown in Figure 11 below.
The grinding step of the fourth embodiment is performed in substantially the same manner as the grinding step of the third embodiment, but the outer peripheral portion of the bonded work 9 that is warped upward, i.e., the gap between the outer peripheral region of the lower surface of the transfer substrate 91 and the sheet 96, is filled with the hardened liquid resin 349, and the outer peripheral portion is supported by the liquid resin 349, so that the grinding feed speed of the grinding means 16 can be made faster than that of the grinding step of the third embodiment. That is, even if the grinding feed speed is high, damage to the outer peripheral portion is prevented by the support of the outer peripheral portion by the liquid resin 349. In this way, it is possible to reduce the wear of the grinding wheel 1641 by grinding only the desired amount of the outer peripheral portion where the wafer ID 909 is formed.
In other words, no step is formed at the boundary between the surface ground to remove the wafer ID 909 and the surface that is not ground.

(3-6) Fifth embodiment of the grinding process in the wafer ID removal process
The grinding process is not limited to the in-feed grinding described above, and may be performed by creep feed grinding. Creep feed grinding is a grinding method in which the height position of the grinding means 16 shown in Fig. 1 is fixed, and the bonded workpiece 9 held on the chuck table 30 is fed at a low speed from the radial direction (Y-axis direction) relative to the rotation shaft 160 of the grinding means 16.
Before carrying out the grinding process of the fifth embodiment, the chuck table 30 is rotated by a predetermined angle in advance, and the bonded workpiece 9 is positioned so that the wafer ID 909 faces the grinding wheel 1641 as shown in Fig. 12. Then, the inclination adjustment process described above is carried out, and a part of the outer periphery of the chuck table 30 is raised by a predetermined distance so that it is higher than the other parts, and the outer periphery part on which the wafer ID is formed of one surface 908 of the epitaxy wafer 900 of the bonded workpiece 9 shown in Fig. 12, which is suction-held following the holding surface 302 which is a conical inclined surface as shown in Fig. 1, is positioned at a position relatively higher than the central part.

The grinding means 16 shown in FIG. 1 is fed in the -Z direction by the grinding feed means 17, and the grinding means 16 is positioned at a predetermined height position where the grinding wheel 1641 cuts into the wafer ID 909 on the outer periphery of the epitaxy wafer 900 shown in FIG. 12 so that it can be completely removed. The grinding wheel 1641 is then rotated, for example, in a clockwise direction as viewed from the +Z direction, and the chuck table 30, which holds the bonded workpiece 9 by suction, is moved in the +Y direction at a predetermined feed rate. Then, as shown in FIG. 13, the outer periphery where the wafer ID 909 is formed is ground by the rotating grinding wheel 1641.

Then, as shown in FIG. 14, the chuck table 30 is moved to a predetermined position in the +Y direction, and all of the wafer IDs 909 are removed from the epitaxy wafer 900. After that, the grinding means 16 is raised in the +Z direction and separated from the bonded workpiece 9. As a result, the bonded workpiece 9 after grinding is in a state in which a surface 9088 that is not ground by the grinding wheel 1641 on one surface 908 of the epitaxy wafer 900 shown in FIG. 14 and a ground surface 9087 connected to the surface 9088 are formed.

As shown in Figures 15 and 16, during creep feed grinding, for example, the bonded workpiece 9 held on the holding surface 302 may be rotated and the entire outer periphery of the epitaxy wafer 900 may be ground by the grinding wheel 1641 to remove the wafer ID 909. As a result, as shown in Figure 17, the bonded workpiece 9 after grinding is in a state in which a circular surface 9086 that is not ground by the grinding wheel 1641 on one surface 908 of the epitaxy wafer 900 and an annular ground surface 9085 connected to the circular surface 9086 are formed.

(4) Polishing process After completing the grinding process of embodiment 1, embodiment 2, embodiment 3, embodiment 4, or embodiment 5 as described above, a polishing process is carried out to polish at least the grinding surface of the bonded workpiece 9 ground by the grinding wheel 1641, i.e., for example, the annular grinding surface 907 shown in Figure 9, and the boundary between the grinding surface 907 and the circular surface 906, which is the surface not ground by the grinding wheel 1641.

Specifically, the bonded workpiece 9 is transferred to the chuck table 20 of the polishing apparatus 2 shown in FIG. 18, and is suction-held on the holding surface 200 of the chuck table 20 with the epitaxy wafer 900 facing upward.
The polishing means 22 for polishing the epitaxy wafer 900 of the polishing apparatus 2 includes, for example, a spindle 220 whose axial direction is vertical (Z-axis direction), a motor (not shown) for rotating the spindle 220, a circular plate-shaped mount 223 fixed to the lower end of the spindle 220, and a circular polishing pad 225 detachably attached to the lower surface of the mount 223. The polishing pad 225 is made of, for example, nonwoven fabric such as felt. The diameter of the polishing pad 225 is, for example, larger than the diameter of the bonded workpiece 9. In this embodiment, the polishing pad 225 is used to polish the bonded workpiece 9 in a dry manner, for example.
The polishing pad 225 may have abrasive grains attached thereto with an adhesive, or may be for use in CMP (chemical mechanical polishing) using an abrasive liquid.

First, the chuck table 20 holding the bonded workpiece 9 is positioned below the polishing means 22. For example, the positioning is performed so that the polishing pad 225 covers one side 908 of the epitaxy wafer 900 so that the polishing pad 225 always contacts the entire surface of the one side 908 during polishing. Then, the polishing means 22 is fed in the -Z direction, and the rotating polishing pad 225 contacts one side 908 of the bonded workpiece 9 that rotates along with the rotation of the chuck table 20, thereby performing polishing. In this embodiment, the annular grinding surface 907, the circular surface 906, and the boundary between the grinding surface 907 and the circular surface 906 on one side 908 of the bonded workpiece 9 are polished and mirror-finished for a predetermined time, and the boundary is eliminated, making it possible to appropriately irradiate the pulsed laser beam described below. Then, the polishing means 22 is raised to separate the polishing pad 225 from the bonded workpiece 9.

(5) Peeling layer formation process After the polishing process is performed, the bonded workpiece 9 is transported to the chuck table 80 of the laser beam application device 8 shown in Figure 19, and the epitaxy wafer 900 is suction-held on the holding surface 800 of the chuck table 80 with the epitaxy wafer 900 facing upward.
The chuck table 80 is rotatable about an axis in the vertical direction (Z-axis direction), and is reciprocally movable in the X-axis direction by a processing feed means (not shown).

The pulsed laser beam application means 81 of the laser beam application device 8 can move back and forth in the Y-axis direction by an indexing feed means such as a ball screw mechanism, and the pulsed laser beam oscillated from the laser beam oscillator 819 and having a wavelength that is absorbent for the buffer layer 98 is incident on the focusing lens 817 inside the focusing device 818 via a transmission optical system such as an optical fiber, so that the pulsed laser beam can be accurately focused and irradiated at a predetermined height position of the bonded workpiece 9 held by the chuck table 80. The focal point position of the pulsed laser beam focused by the focusing device 818 can be adjusted in the Z-axis direction by a focal point position adjustment means (not shown).

First, the focal point of the condenser 818 is positioned at a predetermined height inside the buffer layer 98. In the illustrated embodiment, the focal point is positioned at a relatively deep position from the upper surface of the buffer layer 98. Next, while moving the chuck table 80 at a predetermined feed rate in the X-axis direction, a pulsed laser beam is incident on the buffer layer 98 from one surface 908 side of the epitaxy wafer 900. The pulsed laser beam passes through the epitaxy wafer 900 and is absorbed by the buffer layer 98, destroying the buffer layer 98 and forming a peeling layer 983 (see FIG. 20). Then, the chuck table 80 moves so that the pulsed laser beam is irradiated from one outer periphery to the other outer periphery in the X-axis direction of the buffer layer 98 of the bonded workpiece 9 as shown in FIG. 19.

Thereafter, the chuck table 80 is indexed in the Y-axis direction relative to the focal point by a predetermined indexing amount while the pulsed laser beam is applied repeatedly in the same manner as described above, thereby forming a peeling layer 983 over almost the entire surface of the buffer layer 98.
Here, since the wafer ID 909 (see FIG. 8) has already been removed from the epitaxy wafer 900, the wafer ID 909 does not hinder the irradiation of the buffer layer 98 with the pulsed laser beam, and the peeling layer 983 can be formed on the entire surface of the buffer layer 98, that is, it is possible to prevent the occurrence of any portion where the peeling layer 983 is incomplete. Therefore, in the optical device layer transfer step described later, it is possible to apply an external force to the peeling layer 983 formed on the entire surface of the buffer layer 98, thereby appropriately peeling the epitaxy wafer 900 from the transfer substrate 91.

It is not necessary to completely separate the epitaxial wafer 900 and the buffer layer 98 by irradiating the pulsed laser beam, and it is sufficient that a peeling layer 983 is formed in which the entire surface of the buffer layer 98 is destroyed to such an extent that the epitaxial wafer 900 and the buffer layer 98 can be separated by applying an external force in a later optical device layer transfer process. When irradiating the buffer layer 98 with a pulsed laser beam, the condenser 818 may be moved instead of the chuck table 80. The number of times (number of passes) that the same location of the buffer layer 98 is irradiated with the pulsed laser beam may be set arbitrarily. The buffer layer 98 may be irradiated with a pulsed laser beam in a spiral shape in a plan view.

(6) Optical Device Layer Transfer Process After the peeling layer formation process is performed, the bonded workpiece 9 is transported to the chuck table 70 of the peeling device 7 shown in FIG. 20, and the epitaxy wafer 900 is suction-held on the holding surface 700 of the chuck table 70 with the epitaxy wafer 900 facing upward.

For example, the peeling device 7 has an oscillator 73 that generates ultrasonic vibrations, and an ultrasonic horn 75 that is disposed above the chuck table 70 and has an upper end connected to the oscillator 73. The ultrasonic vibrations generated by the oscillator 73 resonate in the ultrasonic horn 75 and are transmitted to the lower end of the ultrasonic horn 75.

When the lower end of the ultrasonic horn 75 is brought into contact with one surface 908 of the epitaxy wafer 900 while ultrasonic vibrations are being generated by the oscillator 73, ultrasonic waves are transmitted to the peeling layer 983. When ultrasonic waves of a predetermined frequency are applied as an external force to the peeling layer 983, the bonded state between the epitaxy wafer 900 and the optical device layer 902 is dissolved, and the epitaxy wafer 900 can be easily separated from the optical device layer 902. For example, the lower end of the ultrasonic horn 75 may be moved in a spiral shape in a plan view or in the vertical and horizontal directions in a plan view so as to follow the entire surface of one surface 908.
The ultrasonic horn 75 is preferably brought into contact with the outer periphery of the epitaxy wafer 900 .

The peeling device 7 further includes a transport arm (not shown) for lifting up the epitaxy wafer 900 after the bonded state between the epitaxy wafer 900 and the optical device layer 902 is released. A suction pad (not shown) is provided at the tip of the transport arm, and the suction pad can suction one surface 908 of the epitaxy wafer 900 by applying negative pressure from a vacuum suction source (not shown) to the lower surface of the suction pad. Then, by lifting up the transport arm, the epitaxy wafer 900 can be peeled off from the optical device layer 902, i.e., the transfer substrate 91 with which the optical device layer 902 is integrated, as shown in FIG. 21. This completes the optical device layer transfer process for transferring the optical device layer 902 to the transfer substrate 91.
In the optical device layer transferring step, the external force applied to the peeling layer 983 is not limited to ultrasonic waves.

It goes without saying that the lift-off method according to the present invention is not limited to the above-mentioned embodiment, and may be implemented in various different forms within the scope of the technical concept. Furthermore, the shapes of the components of the grinding device 1, polishing device 2, laser beam application device 8, and peeling device 7 shown in the attached drawings are not limited to these, and may be modified as appropriate within the scope of the effects of the present invention.

1: Grinding device 10: Device base 30: Chuck table 300: Suction portion 301: Frame 302: Holding surface 39: Cover 390: Bellows cover 35: Table rotation means 350: Rotation shaft
36: Chuck base 363: Bearing 364: Screw shaft hole 37: Tilt adjustment means 372: Screw shaft 374: Lifting motor 379: Support column 33: Load sensor
38: Thickness measuring means 381: Table top surface height measuring device 382: Work top surface height measuring device 13: Horizontal movement means 130: Ball screw 132: Motor 133: Movable block 11: Column 17: Grinding feed means 170: Ball screw Motor: 172
12: Height position detection means 120: Scale 123: Reading unit 16: Grinding means 160: Rotating shaft 162: Grinding motor 164: Grinding wheel 1640: Wheel base 1641: Grinding wheel 19: Control means 9: Bonded workpiece 90: Optical device wafer 900: Epitaxy wafer 908: One surface of epitaxy wafer 909: Wafer ID 901: Other surface of epitaxy wafer 907: Grinding surface 906: Circular surface 902: Optical device layer 98: Buffer layer 983: Peeling layer 91: Transfer substrate 93: Adhesive 95: Tape 96: Sheet
2: Polishing device 20: Chuck table 22: Polishing means 225: Polishing pad 8: Laser beam irradiation device
80: Chuck table 81: Laser beam application means 819: Laser beam oscillator 818: Condenser 817: Condenser lens 7: Peeling device 70: Chuck table 73: Oscillator 75: Ultrasonic horn

Claims (6)

1. A lift-off method for transferring an optical device layer of an optical device wafer, the optical device layer being stacked on one surface of an epitaxy wafer having a wafer ID formed on an outer periphery of the other surface of the epitaxy wafer via a buffer layer, to a transfer substrate, the method comprising:
a bonding step of bonding the transfer substrate to a surface of the optical device layer of the optical device wafer via an adhesive to form a bonded workpiece;
a holding step of holding the transfer substrate of the bonded workpiece on a holding surface of a chuck table;
a wafer ID removing step of grinding the wafer ID formed on the one surface of the epitaxy wafer of the bonded work held on the holding surface with a grinding wheel to form a ground surface connected to the unground surface of the one surface, and removing the wafer ID;
a polishing step of polishing at least the surface to be ground that has been ground with the grinding wheel and a boundary between the surface to be ground and a surface that has not been ground with the grinding wheel;
a separation layer forming step of applying a pulsed laser beam having a wavelength that is transparent to the epitaxial wafer and absorbent to the buffer layer to the one surface side of the epitaxial wafer, thereby forming a separation layer on the buffer layer;
the lift-off method including, after the release layer forming step, an optical device layer transferring step of applying an external force to the release layer to release the epitaxial wafer from the transfer substrate and transferring the optical device layer to the transfer substrate. The wafer ID removing step includes:
2. The lift-off method according to claim 1, wherein the bonded workpiece held on the holding surface is rotated around a rotation axis passing through the center of the holding surface, and a circular surface that is not ground by the grinding wheel is formed in the central portion of one side of the epitaxy wafer, and the annular ground surface is formed so as to connect to the outer periphery of the circular surface. The wafer ID removing step includes:
an inclination adjustment step of inclining the holding surface with respect to the grinding wheel so that an outer peripheral portion of one surface of the epitaxy wafer of the bonded workpiece held on the holding surface contacts the lower surface of the grinding wheel before a central portion of the epitaxy wafer;
3. The lift-off method according to claim 2, further comprising a grinding step of rotating the bonded workpiece held on the holding surface while measuring an area of the outer circumferential portion of one surface of the epitaxy wafer closer to the center than the wafer ID with a measuring device, and grinding with the grinding wheel until the value of the measuring device changes. The wafer ID removing step includes:
an inclination adjustment step of inclining the holding surface with respect to the grinding wheel so that an outer peripheral portion of one surface of the epitaxy wafer of the bonded workpiece held on the holding surface comes into contact with a lower surface of the grinding wheel before a central portion of the one surface of the epitaxy wafer of the bonded workpiece is brought into contact with the lower surface of the grinding wheel;
3. The lift-off method according to claim 1, further comprising a grinding step of grinding with the grinding wheel until the magnitude of the load measured by a load measuring means for measuring the load applied to the grinding wheel reaches a preset value. One surface of the optical device wafer of the bonding work forms a concave surface with a warped outer periphery,
3. The lift-off method according to claim 1, wherein the holding step includes a tape application step of applying a tape having an area covering the holding surface to the transfer substrate. One surface of the optical device wafer of the bonding work forms a concave surface with a warped outer periphery,
The lift-off method according to claim 1 or claim 2, further comprising a sheet attachment step of supplying liquid resin into a gap between a sheet having an area covering the holding surface and the warped outer peripheral portion of the transfer substrate of the adhesive workpiece placed on the sheet, hardening the resin, and attaching the sheet to the transfer substrate.

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