JP5996254B2 - 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 laminated on a surface of an epitaxy substrate such as a sapphire substrate or silicon carbide via a buffer layer to a transfer substrate.

  In the optical device manufacturing process, GaN (gallium nitride), INGaP (indium gallium phosphorus), or ALGaN (aluminum nitridation) is formed on the surface of a substantially disk-shaped epitaxial substrate such as a sapphire substrate or silicon carbide via a buffer layer. Optical devices such as light-emitting diodes and laser diodes are formed in multiple areas partitioned by multiple streets formed by laminating optical device layers consisting of n-type semiconductor layers and p-type semiconductor layers composed of gallium). An optical device wafer is formed. Each optical device is manufactured by dividing the optical device wafer along the street. (For example, refer to Patent Document 1.)

  In addition, as a technology for improving the brightness of optical devices, light consisting of an n-type semiconductor layer and a p-type semiconductor layer stacked on the surface of an epitaxial substrate such as a sapphire substrate or silicon carbide constituting an optical device wafer via a buffer layer The device layer is bonded through a bonding metal layer such as AuSu (gold tin), and the buffer layer is irradiated by irradiating a laser beam having a wavelength (for example, 248 nm) that is transmitted through the epitaxy substrate and absorbed by the buffer layer from the back side of the epitaxy substrate. Patent Document 2 below discloses a manufacturing method called lift-off in which an optical device layer is transferred to a transfer substrate by breaking and peeling the epitaxy substrate from the optical device layer.

JP-A-10-305420 JP 2004-72052 A

Thus, when the focal point is positioned on the buffer layer from the back side of the epitaxy substrate and irradiated with a laser beam, GaN or INGaP or ALGaN constituting the buffer layer decomposes into gases such as Ga and N _2, so that the buffer layer becomes Although it is destroyed, there are areas where GaN or INGaP or ALGaN decomposes into gases such as Ga and N ₂ and areas that do not decompose, causing unevenness in the destruction of the buffer layer, and properly separating the epitaxy substrate There is a problem that you can not.
In addition, when unevenness is formed on the surface of the epitaxy substrate in order to improve the quality of the optical device, the laser beam is blocked by the uneven wall, so that the destruction of the buffer layer is suppressed and peeling of the epitaxy substrate becomes difficult. There is a problem.

  The present invention has been made in view of the above-described facts, and a main technical problem thereof is to provide a lift-off method capable of reliably peeling the epitaxy substrate.

In order to solve the above main technical problem, according to the present invention, an optical device layer of an optical device wafer in which an optical device layer is laminated on a surface of an epitaxy substrate through a buffer layer made of a Ga-containing compound is transferred to a transfer substrate. A lift-off method that transfers to
A transfer substrate bonding step of bonding the transfer substrate to the surface of the optical device layer of the optical device wafer via the bonding metal layer;
Epitaxy substrate is irradiated with a pulsed laser beam having a wavelength that is transparent to the epitaxy substrate and absorbing to the buffer layer from the back side of the epitaxy substrate of the optical device wafer to which the transfer substrate is bonded. A gas layer forming step of forming a gas layer on the interface between the buffer layer and
A gas layer detection step of detecting a region of the gas layer located on the outermost side of the gas layer formed on the boundary surface between the epitaxy substrate and the buffer layer by the gas layer formation step;
An epitaxy substrate adsorption step of adsorbing the epitaxy substrate by positioning a suction pad in a region where the outermost gas layer detected by the gas layer detection step in the epitaxy substrate is located;
An optical device layer transfer step of moving the suction pad that has adsorbed the epitaxy substrate in a direction away from the epitaxy substrate, peeling the epitaxy substrate, and transferring the optical device layer to the transfer substrate;
A lift-off method is provided.

  The lift-off method according to the present invention includes the transfer substrate bonding step, the gas layer formation step, the gas layer detection step, the epitaxy substrate adsorption step, and the optical device layer transfer step. In the optical device layer transfer step, the epitaxy substrate, the buffer layer, The gas layer located on the outermost surface of the outermost layer is adsorbed by the suction pad and moved in a direction away from the epitaxy substrate to peel the epitaxy substrate. The entire epitaxy substrate is peeled off smoothly from the layer region.

The perspective view and principal part expanded sectional view of the optical device wafer in which the optical device layer transferred to a transfer board | substrate by the lift-off method by this invention was formed. Explanatory drawing of the transfer board | substrate joining process which joins a transfer board | substrate to the surface of the optical device layer of the optical device wafer shown in FIG. The perspective view of the laser processing apparatus for implementing the buffer layer destruction process in the lift-off method by this invention. Explanatory drawing which shows the Ga layer formation process in the buffer layer destruction process of the lift-off method by this invention. Sectional drawing which expands and shows the principal part of the optical device wafer in which the Ga layer formation process shown in FIG. 4 was implemented. Explanatory drawing of the gas layer detection process in the lift-off method by this invention. Explanatory drawing which shows the state which located the area | region of the gas layer selected as the gas layer located in the outermost side directly under an imaging means. Explanatory drawing of the epitaxy board | substrate adsorption | suction process in the lift-off method by this invention. Explanatory drawing of the optical device layer transfer process in the lift-off method by this invention.

  Hereinafter, preferred embodiments of a lift-off method according to the present invention will be described in detail with reference to the accompanying drawings.

FIGS. 1A and 1B show a perspective view and an enlarged cross-sectional view of an essential part of an optical device wafer on which an optical device layer transferred to a transfer substrate by a lift-off method according to the present invention is formed.
An optical device wafer 2 shown in FIGS. 1A and 1B includes an n-type gallium nitride semiconductor layer 221 and a surface 21a of an epitaxy substrate 21 made of a sapphire substrate having a disk shape with a diameter of 50 mm and a thickness of 600 μm. An optical device layer 22 made of a p-type gallium nitride semiconductor layer 222 is formed by an epitaxial growth method. When the optical device layer 22 including the n-type gallium nitride semiconductor layer 221 and the p-type gallium nitride semiconductor layer 222 is stacked on the surface of the epitaxy substrate 21 by the epitaxial growth method, the surface 21a of the epitaxy substrate 21 and the optical device layer 22 are formed. Between the n-type gallium nitride semiconductor layer 221 to be formed, a buffer layer 23 made of gallium nitride (GaN) and having a thickness of, for example, 1 μm is formed. In the optical device wafer 2 configured in this manner, the thickness of the optical device layer 22 is, for example, 10 μm in the illustrated embodiment. In the optical device layer 22, as shown in FIG. 1A, optical devices 224 are formed in a plurality of regions partitioned by a plurality of streets 223 formed in a lattice shape.

  As described above, in order to peel the epitaxy substrate 21 in the optical device wafer 2 from the optical device layer 22 and transfer it to the transfer substrate, a transfer substrate bonding step of bonding the transfer substrate to the surface 22a of the optical device layer 22 is performed. . That is, as shown in FIGS. 2 (a), (b) and (c), the surface 22a of the optical device layer 22 formed on the surface 21a of the epitaxy substrate 21 constituting the optical device wafer 2 has a thickness of 1 mm. The transfer substrate 3 made of a copper substrate is joined via a joining metal layer 4 made of gold tin (AuSu). The transfer substrate 3 can be made of molybdenum (Mo), silicon (Si) or the like, and the bonding metal forming the bonding metal layer 4 can be gold (Au), platinum (Pt), or chromium (Cr). Indium (In), palladium (Pd), or the like can be used. In the transfer substrate bonding step, the bonding metal is deposited on the surface 22a of the optical device layer 22 formed on the surface 21a of the epitaxy substrate 21 or the surface 3a of the transfer substrate 3 to form the bonding metal layer 4 having a thickness of about 3 μm. Then, the bonding metal layer 4 and the surface 3a of the transfer substrate 3 or the surface 22a of the optical device layer 22 are faced to each other and bonded to the surface 22a of the optical device layer 22 constituting the optical device wafer 2 by pressing. The composite substrate 200 is formed by bonding the surfaces 3a of the two through the bonding metal layer 4.

  As described above, if the composite substrate 200 is formed by bonding the surface 3a of the transfer substrate 3 to the surface 22a of the optical device layer 22 constituting the optical device wafer 2 via the bonding metal layer 4, the transfer substrate 3 is bonded. The buffer layer 23 is irradiated from the back side of the epitaxy substrate 21 of the optical device wafer 2 with a pulse laser beam having a wavelength that is transmissive to the epitaxy substrate and absorbable to the buffer layer. A gas layer forming step of forming a gas layer on the interface with the buffer layer 23 is performed. This gas layer forming step is performed using a laser processing apparatus shown in FIG. A laser processing apparatus 5 shown in FIG. 3 includes a stationary base 50 and a chuck table mechanism that is disposed on the stationary base 50 so as to be movable in a machining feed direction (X-axis direction) indicated by an arrow X and holds a workpiece. 6, a laser beam irradiation unit support mechanism 7 disposed on the stationary base 50 so as to be movable in an indexing feed direction (Y axis direction) indicated by an arrow Y orthogonal to the X axis direction, and the laser beam irradiation unit support mechanism 7 And a laser beam irradiation unit 8 disposed so as to be movable in the condensing point position adjustment direction (Z-axis direction) indicated by an arrow Z.

  The chuck table mechanism 6 is disposed on the stationary base 50 in parallel along the X-axis direction, and guide rails 61 and 61 are disposed on the guide rails 61 and 61 so as to be movable in the X-axis direction. A first sliding block 62; a second sliding block 63 disposed on guide rails 621 and 621 disposed on the upper surface of the first sliding block 62 so as to be movable in the Y-axis direction; A cover table 65 supported by a cylindrical member 64 on the second sliding block 63 and a chuck table 66 as a workpiece holding means are provided. The chuck table 66 includes a suction chuck 661 formed of a porous material, and holds, for example, a disk-shaped semiconductor wafer as a workpiece on the upper surface (holding surface) of the suction chuck 661 by suction means (not shown). It is supposed to be. The chuck table 66 configured as described above is rotated by a pulse motor (not shown) disposed in the cylindrical member 64. The illustrated chuck table mechanism 6 includes a processing feed means 67 for moving the first slide block 62 in the X-axis direction along the guide rails 61 and 61, and a second slide block 63 for the guide rails 621 and 621. The first index feeding means 68 is provided along the Y axis direction. The processing feed means 67 and the first index feed means 68 are configured by a known ball screw mechanism.

  The laser beam irradiation unit support mechanism 7 is movable in the Y-axis direction on a pair of guide rails 71, 71 disposed in parallel along the Y-axis direction on the stationary base 50. The movable support base 72 is provided. The movable support base 72 includes a moving support portion 721 movably disposed on the guide rails 71 and 71, and a mounting portion 722 attached to the moving support portion 721. By a ball screw mechanism. The second index feed means 73 configured is moved along the guide rails 71 and 71 in the Y-axis direction.

  The illustrated laser beam irradiation unit 8 includes a unit holder 81 and laser beam irradiation means 82 attached to the unit holder 81. The unit holder 81 is supported so as to be movable in the Z-axis direction along guide rails 723 and 723 provided on the mounting portion 722 of the movable support base 72. Thus, the unit holder 81 supported so as to be movable along the guide rails 723 and 723 is moved in the Z-axis direction by the condensing point position adjusting means 83 constituted by a ball screw mechanism.

  The illustrated laser beam application means 8 includes a cylindrical casing 82 fixed to the unit holder 81 and extending substantially horizontally. In the casing 82, pulse laser beam oscillation means including a pulse laser beam oscillator and repetition frequency setting means (not shown) are arranged. A condenser 84 for condensing the pulse laser beam oscillated from the pulse laser beam oscillating means is attached to the tip of the casing 82. At the front end of the casing 82, an image pickup means 85 for picking up an image of the workpiece held on the chuck table 66 by the laser beam irradiation means 8 is disposed. The imaging means 85 is composed of optical means such as a microscope and a CCD camera, and sends the captured image signal to a control means (not shown).

  The illustrated laser processing apparatus 5 includes a peeling mechanism 9 for peeling the epitaxy substrate 21 constituting the optical device wafer 2 from the optical device layer 22. The peeling mechanism 9 supports a suction means 91 that sucks the epitaxy substrate 21 in a state where the optical device wafer 2 held on the chuck table 66 is positioned at the peeling position, and the suction means 91 is movably supported in the vertical direction. It comprises support means 92 and is arranged on one side of the chuck table mechanism 6. The suction means 91 includes a holding member 911 and a plurality of (three in the illustrated embodiment) suction pads 912a, 912b, and 912c attached to the lower side of the holding member 911. The suction pads 912a, 912b and 912c are connected to suction means (not shown). Of the three suction pads, the suction pad 912a is disposed on the same axis line as the imaging means 85 in the X-axis direction.

From the back side of the epitaxy substrate 21 of the optical device wafer 2 to which the transfer substrate 3 is bonded using the laser processing apparatus 5, the buffer layer 23 is transparent to the epitaxy substrate and absorbable to the buffer layer. In order to perform a gas layer forming step of forming a gas layer on the interface between the epitaxy substrate 21 and the buffer layer 23 by irradiating a pulsed laser beam having a wavelength of Place 3 side. Then, the composite substrate 200 is sucked and held on the chuck table 66 by a suction means (not shown) (wafer holding step). Accordingly, in the composite substrate 200 held on the chuck table 66, the back surface 21b of the epitaxy substrate 21 constituting the optical device wafer 2 is on the upper side. When the composite substrate 200 is sucked and held on the chuck table 66 in this way, the processing feed means 67 is operated to move the chuck table 66 to the laser beam irradiation region where the condenser 84 of the laser beam irradiation means 8 is located. Then, as shown in FIG. 4A, one end of the epitaxy substrate 21 constituting the optical device wafer 2 of the composite substrate 200 held on the chuck table 66 (the left end in FIG. 4A) is connected to the laser beam irradiation means 8. It is positioned directly below the light collector 84. Next, the laser beam irradiating means 8 is operated to irradiate the buffer layer 23 with a pulsed laser beam having a wavelength that is transparent to sapphire and absorbable to gallium nitride (GaN). The chuck table 66 is moved at a predetermined processing feed speed in the direction indicated by the arrow X1 in FIG. When the other end of the epitaxy substrate 21 (the right end in FIG. 4C) reaches the irradiation position of the condenser 84 of the laser beam irradiation means 8 as shown in FIG. 4C, the pulse laser beam is irradiated. At the same time, the movement of the chuck table 66 is stopped. This laser beam irradiation step is performed on a region corresponding to the entire surface of the buffer layer 23.
In the Ga layer forming step, the light collector 84 is positioned on the outermost periphery of the epitaxy substrate 21, and the chuck table 66 is rotated toward the light collector 84 while rotating the chuck table 66 so that the entire surface of the buffer layer 23 is pulsed. You may irradiate a laser beam.

The processing conditions for performing the gas layer forming step using an excimer laser are set as follows, for example.
Light source: excimer laser wavelength: 193 nm or 248 nm
Repetition frequency: 50Hz
Average output: 0.08W
Pulse width: 10 ns
Spot type: 400μm
Processing feed rate: 20 mm / sec

Further, the processing conditions for performing the gas layer forming step using a YAG laser are set as follows, for example.
Light source: YAG laser Wavelength: 257 nm or 266 nm
Repetition frequency: 200 kHz
Average output: 1.0W
Pulse width: 10 ns
Spot diameter: φ30μm
Processing feed rate: 100 mm / sec

  By performing the gas layer forming step under the above processing conditions, a plurality of gas layers 230 are formed on the boundary surface between the epitaxy substrate 21 and the buffer layer 23 as shown in FIG. The plurality of gas layers 230 are formed in an island shape.

  If the gas layer forming process described above is performed, the gas for detecting the region of the gas layer located on the outermost side of the gas layer 230 formed on the boundary surface between the epitaxy substrate 21 and the buffer layer 23 by the gas layer forming process. A layer detection step is performed. In order to perform this gas layer detection step, the chuck table 66 holding the composite substrate 200 is moved to the imaging region of the imaging means 85 from the state where the gas layer formation step has been performed, and the composite substrate as shown in FIG. The outer peripheral portion of the epitaxy substrate 21 constituting the 200 optical device wafer 2 is positioned directly below the imaging means 85. Then, the image pickup means 85 is operated and the chuck table 66 is rotated once in the direction indicated by the arrow 66a, and the image pickup means 85 sends an image signal picked up during this time to a control means (not shown). A control unit (not shown) detects a gas layer region located on the outermost side based on an image signal from the imaging unit 85. In the embodiment shown in FIG. 6, the gas layer 230a is selected to be the outermost gas layer.

  If the region of the gas layer 230a located on the outermost side among the gas layers 230 formed on the boundary surface between the epitaxy substrate 21 and the buffer layer 23 is detected by performing the gas layer detection step described above, the chuck table is detected. The region of the gas layer 230a selected to be the outermost gas layer by rotating 66 is positioned immediately below the imaging means 85 as shown in FIG. As a result, the region of the gas layer 230a located on the outermost side is positioned on the same axis line in the X axis direction as the suction pads 912a of the three suction pads 912a, 912b, and 912c constituting the suction means 91 of the peeling mechanism 9. It will be.

  Next, the chuck table 66 is moved to the peeling position where the peeling mechanism 9 is disposed, and the optical device wafer 2 of the composite substrate 200 held by the chuck table 66 is configured as shown in FIG. The region of the outermost gas layer 230a formed at the boundary surface between the epitaxy substrate 21 and the buffer layer 23 is positioned directly below the suction pad 912a. Then, as shown in FIG. 8 (b), the suction means 91 is lowered to bring the suction pad 912a into contact with the region where the outermost gas layer 230a is located on the back surface 21b of the epitaxy substrate 21, and the suction pad. The back surface 21b of the epitaxy substrate 21 is adsorbed by 912b and 912c (epitaxy substrate adsorption step).

  If the above-described epitaxy substrate adsorption process is performed, the suction pads 912a, 912b, and 912c that adsorb the epitaxy substrate 21 are moved away from the epitaxy substrate 21, the epitaxy substrate 21 is peeled off, and the optical device layer 22 is transferred. An optical device layer transfer step of transferring to the substrate 3 is performed. That is, the epitaxy substrate 21 is peeled from the optical device layer 22 by moving the adsorption means 91 upward as shown in FIG. 9 from the state where the epitaxy substrate adsorption step is performed as shown in FIG. Is done. As a result, the optical device layer 22 is transferred to the transfer substrate 3. In this optical device layer transfer step, the region of the gas layer 230a located on the outermost surface formed on the boundary surface between the epitaxy substrate 21 and the buffer layer 23 is adsorbed by the suction pad 912a and separated from the epitaxy substrate 21. Since the epitaxy substrate 21 is moved and peeled off, it is peeled off from the region of the gas layer 230a located on the outermost side that is most easily peeled off, and the entire epitaxy substrate 21 is smoothly peeled off.

2: Optical device wafer 21: Epitaxy substrate 22: Optical device layer 23: Buffer layer 230: Gas layer 3: Transfer substrate 4: Bonding metal layer 200: Composite substrate 5: Laser processing device 6: Chuck table mechanism 66: Chuck table 67 : Processing feed means 7: Laser beam irradiation unit support mechanism 72: Movable support base 8: Laser beam irradiation unit 83: Focusing point position adjusting means 84: Light collector 85: Imaging means 9: Peeling mechanism 91: Adsorption means 912a, 912b 912c: Suction pad

Claims (1)

A lift-off method of transferring an optical device layer of an optical device wafer in which an optical device layer is laminated via a buffer layer made of a Ga compound containing Ga on the surface of an epitaxy substrate to a transfer substrate,
A transfer substrate bonding step of bonding the transfer substrate to the surface of the optical device layer of the optical device wafer via the bonding metal layer;
Epitaxy substrate is irradiated with a pulsed laser beam having a wavelength that is transparent to the epitaxy substrate and absorbing to the buffer layer from the back side of the epitaxy substrate of the optical device wafer to which the transfer substrate is bonded. A gas layer forming step of forming a gas layer on the interface between the buffer layer and the buffer layer;
A gas layer detection step of detecting a region of the gas layer located on the outermost side of the gas layer formed on the boundary surface between the epitaxy substrate and the buffer layer by the gas layer formation step;
An epitaxy substrate adsorption step of adsorbing the epitaxy substrate by positioning a suction pad in a region where the outermost gas layer detected by the gas layer detection step in the epitaxy substrate is located;
An optical device layer transfer step of moving the suction pad that has adsorbed the epitaxy substrate in a direction away from the epitaxy substrate, peeling the epitaxy substrate, and transferring the optical device layer to the transfer substrate;
A lift-off method characterized by that.

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