JP2015204367A - Processing method of optical device wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a processing method of an optical device wafer capable of destroying a buffer layer by efficiently transmitting a laser beam from a rear face of an epitaxy substrate without processing the rear face of the epitaxy substrate into a mirror surface.SOLUTION: The processing method of the optical device wafer in which an optical device layer is laminated on a front face of the epitaxy substrate via the buffer layer, includes: a transfer substrate bonding step of bonding a transfer substrate to a front face of the optical device layer of the optical device wafer via a bonding material; a buffer layer destruction step of destroying the buffer layer by irradiating the buffer layer with a pulse laser beam of a wavelength having transmissivity for the epitaxy substrate and absorptivity for the buffer layer from a rear face side of the epitaxy substrate of the optical device wafer; and an optical device layer transfer step of transferring the optical device layer to the transfer substrate by exfoliating the epitaxy substrate from the optical device layer after the buffer layer destruction step is implemented. Before implementing the buffer layer destruction step, a resin coating step is implemented for flattening the rear face of the epitaxy substrate by coating the rear face of the epitaxy substrate with a resin through which the laser beam is transmissive.

Description

  The present invention relates to a method for processing an optical device wafer in which 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 with a buffer layer transferred to a transfer substrate.

  In the optical device manufacturing process, GaN (gallium nitride) or INGaP (indium gallium phosphorus) or ALGaN (aluminum Optical devices such as light-emitting diodes and laser diodes in a plurality of regions partitioned by a plurality of streets formed by laminating optical device layers composed of n-type semiconductor layers and p-type semiconductor layers composed of gallium nitride) To form an optical device wafer. Each optical device is manufactured by dividing the optical device wafer along the streets (see, for example, 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 to the transfer substrate of molybdenum (Mo), copper (Cu), and silicon (Si) via a bonding material such as AuSn (gold tin), and the buffer layer passes through the epitaxy substrate 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 irradiating a laser beam having an absorbed wavelength to break the buffer layer and peeling the epitaxy substrate from the optical device layer. ing.

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

Thus, the lift-off described above is performed by irradiating the buffer layer (GaN absorption edge: 365 nm) with a laser beam having a wavelength that is transmissive to the epitaxy substrate from the back side of the epitaxy substrate. This is done by breaking the layer.
However, in order to efficiently transmit the laser beam from the back surface of the epitaxy substrate and destroy the buffer layer, it is necessary to polish the back surface of the epitaxy substrate and process it into a mirror surface without unevenness (pear surface), which means that productivity is poor. There's a problem.

  The present invention has been made in view of the above facts, and its main technical problem is to destroy the buffer layer by efficiently transmitting a laser beam from the back surface of the epitaxy substrate without processing the back surface of the epitaxy substrate into a mirror surface. It is an object to provide a method for processing an optical device wafer.

In order to solve the main technical problem, according to the present invention, there is provided an optical device wafer processing method in which an optical device layer is laminated on a surface of an epitaxy substrate via a buffer layer,
A transfer substrate bonding step of bonding the transfer substrate to the surface of the optical device layer of the optical device wafer via a bonding material;
Breaking the buffer layer by irradiating the buffer layer from the back side of the epitaxy substrate of the optical device wafer with a pulsed laser beam having a wavelength that is transmissive to the epitaxy substrate and absorbing the buffer layer Process,
An optical device layer transfer step of peeling the epitaxy substrate from the optical device layer and transferring the optical device layer to the transfer substrate after performing the buffer layer breaking step,
Before carrying out the buffer layer breaking step, a resin coating step is carried out to coat and flatten the back surface of the epitaxy substrate with a resin that transmits laser light.
An optical device wafer processing method is provided.

  The epitaxy substrate is made of a sapphire substrate, the wavelength of the laser beam used in the buffer layer destruction step is an ultraviolet wavelength band, and the resin used in the resin coating step is a methylpentene polymer.

  In the processing method of an optical device wafer according to the present invention, a pulsed laser beam having a wavelength having transparency to the epitaxy substrate and absorption to the buffer layer from the back surface side of the epitaxy substrate of the optical device wafer. Before the buffer layer destruction process is performed to destroy the buffer layer, a resin coating process is performed in which the back surface of the epitaxy substrate is coated with a resin that transmits a laser beam and planarized, and the back surface of the epitaxy substrate is uneven. Even if it is flattened by resin coating, the buffer layer can be destroyed by efficiently transmitting the laser beam from the back surface of the epitaxy substrate without processing the back surface of the epitaxy substrate into a mirror surface. Therefore, it is not necessary to polish the back surface of the epitaxy substrate and process it into a mirror surface, so that productivity can be improved.

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 processing method of the optical device wafer 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. Explanatory drawing which shows 1st Embodiment of the resin coating process in the processing method of the optical device wafer by this invention. Explanatory drawing which shows 2nd Embodiment of the resin coating process in the processing method of the optical device wafer by this invention. The perspective view of the laser processing apparatus for implementing the buffer layer destruction process in the processing method of the optical device wafer by this invention. Explanatory drawing of the buffer layer destruction process in the processing method of the optical device wafer by this invention. Explanatory drawing which shows the optical device layer transfer process in the processing method of the optical device wafer 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. 2A, 2B, and 2C, 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 material 4 made of gold tin (AuSn). The transfer substrate 3 can be made of molybdenum (Mo), copper (Cu), silicon (Si) or the like, and the bonding material 4 can be made of AuSn (gold tin), gold (Au), platinum (Pt). Further, chromium (Cr), indium (In), palladium (Pd), or the like can be used. In this transfer substrate bonding step, the bonding material 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 a bonding metal layer having a thickness of about 3 μm. Then, the bonding metal layer and the surface 3a of the transfer substrate 3 or the surface 22a of the optical device layer 22 are brought into contact with each other and pressed, so that the surface of the transfer substrate 3 is applied to the surface 22a of the optical device layer 22 constituting the optical device wafer 2. 3a is bonded via a bonding material to form a composite substrate 200.

Next, a resin coating step is performed in which the back surface of the epitaxy substrate 21 is coated with a resin that transmits a laser beam and planarized. A first embodiment of this resin coating step will be described with reference to FIG.
That is, as shown in FIGS. 3A and 3B, the resin film 5 made of polyolefin-based methylpentene polymer is coated on the back surface 21b of the epitaxy substrate 21 constituting the composite substrate 200. In addition, as a resin film which consists of a methyl pentene polymer, the brand name: Opuran (trademark) manufactured and sold by Mitsui Chemicals Tosero Co., Ltd. can be used. When the back surface 21b of the epitaxy substrate 21 is thus coated with the resin film 5 made of polyolefin-based methylpentene polymer, the resin film 5 is heated to about 50 ° C. by the heater 6 as shown in FIG. By doing so, the unevenness of the back surface 21b of the epitaxy substrate 21 is absorbed and planarized.
As the resin film, NCF (non-conductive film) made of an epoxy resin provided by Nagase ChemteX Corporation or Nitto Denko Corporation can be used. Since NCF (non-conductive film) has little absorption in UV (wavelength: 257.5 nm) and good UV transmittance, it can be used as a resin film in the resin coating process of the present invention.

Next, a second embodiment of a resin coating process for coating and flattening the back surface of the epitaxy substrate 21 with a resin that transmits a laser beam will be described with reference to FIG.
As shown in FIGS. 4A and 4B, a predetermined amount of a resin solution 50 that transmits a laser beam is dropped and applied to the center of the back surface 21b of the epitaxy substrate 21 constituting the composite substrate 200, whereby the resin layer 51 is formed. Form.

  As described above, if the resin coating step of coating and flattening the back surface of the epitaxy substrate 21 with a resin that transmits a laser beam is performed, from the back surface side of the epitaxy substrate 21 of the optical device wafer 2 to which the transfer substrate 3 is bonded. The buffer layer is destroyed by irradiating the buffer layer 23 with a pulsed laser beam having a wavelength that is transmissive to the epitaxy substrate 21 and absorbable to the buffer layer 23. This buffer layer destruction step is performed using a laser processing apparatus 7 shown in FIG. A laser processing apparatus 7 shown in FIG. 5 includes a chuck table 71 that holds a workpiece, and a laser beam irradiation unit 72 that irradiates the workpiece held on the chuck table 71 with a laser beam. The chuck table 71 is configured to suck and hold a workpiece. The chuck table 71 is moved in a processing feed direction indicated by an arrow X in FIG. 5 by a processing feed means (not shown), and in FIG. 5 by an index feed means (not shown). It can be moved in the index feed direction indicated by the arrow Y.

  The laser beam application means 72 includes a cylindrical casing 721 arranged substantially horizontally. In the casing 721, pulse laser beam oscillating means including a pulse laser beam oscillator and repetition frequency setting means (not shown) are arranged. A condenser 722 for condensing the pulse laser beam oscillated from the pulse laser beam oscillating means is attached to the tip of the casing 721. The laser beam irradiating unit 72 includes a condensing point position adjusting unit (not shown) for adjusting the condensing point position of the pulse laser beam collected by the condenser 722.

In order to perform the buffer layer destruction step using the laser processing apparatus 7, the transfer substrate 3 side of the composite substrate 200 is placed on the upper surface (holding surface) of the chuck table 71 as shown in FIG. Then, the composite substrate 200 is sucked and held on the chuck table 71 by a suction means (not shown) (wafer holding step). Accordingly, the composite substrate 200 held on the chuck table 71 has the resin film 5 or the resin layer 51 coated on the back surface 21b of the epitaxy substrate 21 constituting the optical device wafer 2 on the upper side. When the composite substrate 200 is sucked and held on the chuck table 71 as described above, the machining feed means (not shown) is operated to bring the chuck table 71 into the condenser 722 of the laser beam irradiation means 72 as shown in FIG. Is moved to the laser beam irradiation region where is positioned, and one end (the left end in FIG. 6A) is positioned directly below the condenser 722 of the laser beam irradiation means 72. Then, as shown in FIG. 6B, the spot (S) in the defocused state of the pulse laser beam irradiated from the condenser 722 is aligned with the buffer layer 23. Next, the chuck table 71 is moved at a predetermined processing feed speed in the direction indicated by the arrow X1 in FIG. 6A while irradiating the pulsed laser beam from the condenser 722 by operating the laser beam irradiation means 72. Then, as shown in FIG. 6C, when the other end of the epitaxy substrate 21 (the right end in FIG. 6C) reaches the irradiation position of the condenser 722 of the laser beam irradiation means 72, the pulse laser beam is irradiated. The movement of the chuck table 71 is stopped while stopping. This laser beam irradiation step is performed on a region corresponding to the entire surface of the buffer layer 23.
In the buffer layer destruction step, the light collector 722 is positioned on the outermost periphery of the epitaxy substrate 21, and the chuck table 71 is rotated while moving toward the light collector 722. You may irradiate a laser beam.

The buffer layer destruction step is performed, for example, under the following processing conditions.
<Processing conditions: 1>
Light source: Excimer laser Wavelength: 248nm
Repetition frequency: 50 kHz
Average output: 0.08W
Pulse width: 10 ns
Spot diameter: 400 μm
Defocus: 1.0 (collection of laser beams on the back surface of the epitaxy substrate 21
1 mm epitaxy of light collector 722 with light spot positioned
-Move closer to the substrate 21. )
Processing feed rate: 20 mm / sec

<Processing conditions: 2>
Light source: YAG laser Wavelength: 257 nm
Repetition frequency: 50 kHz
Average output: 0.12W
Pulse width: 100ps
Spot diameter: 70 μm
Defocus: 1.0 (collection of laser beams on the back surface of the epitaxy substrate 21
1 mm epitaxy of light collector 722 with light spot positioned
-Move closer to the substrate 21. )
Processing feed rate: 600 mm / sec

  Before performing the above-described buffer layer destruction step, a resin coating step is performed in which the back surface of the epitaxy substrate 21 is coated with a resin that transmits a laser beam and is flattened. Since it is flattened by the resin coating (resin film 5 or resin layer 51), the buffer layer 23 is destroyed by efficiently transmitting the laser beam from the back surface of the epitaxy substrate 21 without processing the back surface of the epitaxy substrate 21 into a mirror surface. can do. Therefore, it is not necessary to polish the back surface of the epitaxy substrate 21 and process it into a mirror surface, so that productivity can be improved.

If the buffer layer destruction process described above is performed, an optical device layer transfer process is performed in which the epitaxy substrate 21 is peeled from the optical device layer 22 and the optical device layer 22 is transferred to the transfer substrate 3.
In this optical device layer transfer step, as shown in FIG. 7, the epitaxy substrate 21 is easily lifted from the optical device layer 22 because the buffer layer 23 is destroyed by pulling the epitaxy substrate 21 away from the transfer substrate 3. Can be peeled off.

2: Optical device wafer 21: Epitaxy substrate 22: Optical device layer 23: Buffer layer 3: Transfer substrate 4: Bonding material 5: Resin film 200: Composite substrate 6: Heater 7: Laser processing device 71: Chuck table of laser processing device 72: Laser beam irradiation means

Claims (2)

An optical device wafer processing method in which an optical device layer is laminated on a surface of an epitaxy substrate via a buffer layer,
A transfer substrate bonding step of bonding the transfer substrate to the surface of the optical device layer of the optical device wafer via a bonding material;
Breaking the buffer layer by irradiating the buffer layer from the back side of the epitaxy substrate of the optical device wafer with a pulsed laser beam having a wavelength that is transmissive to the epitaxy substrate and absorbing the buffer layer Process,
An optical device layer transfer step of peeling the epitaxy substrate from the optical device layer and transferring the optical device layer to the transfer substrate after performing the buffer layer breaking step,
Before carrying out the buffer layer breaking step, a resin coating step is carried out to coat and flatten the back surface of the epitaxy substrate with a resin that transmits laser light.
An optical device wafer processing method characterized by the above.   The method for processing an optical device wafer according to claim 1, wherein the epitaxy substrate is a sapphire substrate, the wavelength of the laser beam used in the buffer layer breaking step is an ultraviolet wavelength band, and the resin used in the resin coating step is a methylpentene polymer. .

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