JP2016060675A - Method for separating group 13 element nitride layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress cracks of a nitride layer during separation without the step of joining a composite substrate to a base and separating from the base when irradiating a supporting substrate with a laser beam to separate a group 13 element nitride layer.SOLUTION: A method for separating a group 13 element nitride layer comprises: sandwiching a composite substrate 1A including a supporting substrate 2A and a nitride layer 3A provided on the supporting substrate 2A and having a warp between a base 5 and a laser-beam permeable plate 7; arranging the supporting substrate 2A on the side of the laser-beam permeable plate 7; and decomposing the crystal lattice bonding of an interface between the supporting substrate 2A and the nitride layer 3A by applying a stress between the base 5 and the laser-beam permeable plate 7 and irradiating the laser-beam permeable plate 7 with a laser beam in the state of binding the composite substrate 1A between the base and the laser-beam permeable plate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for separating a group 13 element nitride layer from a support substrate.

  A self-standing GaN crystal can be obtained by growing a GaN crystal on a support substrate such as a sapphire substrate or a GaN template to obtain a composite substrate, and then separating the GaN crystal from the support substrate by a method such as laser lift-off. Are known. In this case, conventionally, the composite substrate is temporarily bonded to a separate base such as a metal substrate, and laser light is irradiated in that state (Non-Patent Document 1). In Non-Patent Document 1, after a gallium nitride film is grown on a sapphire substrate by HVPE, the gallium nitride film is attached to a heater using a metal binder and heated to about 600 ° C. to reduce warpage. Then, the sapphire substrate is irradiated with laser light to separate the gallium nitride film from the sapphire substrate.

  In addition, since the composite substrate warps due to the difference in thermal expansion coefficient between the sapphire substrate and the gallium nitride film, in order to reduce the warp, the composite substrate is heated to a temperature of 600 ° C. or more to reduce the warp. The laser beam was irradiated (Patent Document 1). This is because the stress generated at the interface between sapphire and gallium nitride is reduced to suppress non-uniform fluctuation during peeling. At this time, it is preferable that the polycrystalline gallium nitride formed on the outer periphery of the sapphire substrate is removed and the laser light is irradiated.

  In addition, when the gallium nitride layer is provided on the sapphire substrate, the present applicant has succeeded in suppressing cracks at the time of laser lift-off by providing an inclusion-containing layer at the initial growth stage of the gallium nitride layer (Patent Document 2). .

JJAP 38 (1999) 1347-4065_3A_L217

Patent 4227315 WO 2013/021804 A JP2009-111423

  As described in Non-Patent Document 1, when a gallium nitride layer is bonded to a base with a metal bonding agent or the like and separated by irradiating laser light from the sapphire substrate side, the gallium nitride layer is used as the base. Therefore, it is necessary to join the substrate, and it is necessary to separate the gallium nitride layer from the base after laser processing. Furthermore, it is necessary to remove the metal binder adhering to the gallium nitride layer. There is a method of using a resin instead of a metal binder, but there is a similar problem.

  In the method described in Patent Document 1, a gallium nitride layer is formed by heating the composite substrate to 600 to 1000 ° C. to reduce warpage and irradiating the sapphire substrate with laser light without bonding the composite substrate to the base. Is separated from the sapphire substrate. For this reason, the process which adhere | attaches a composite substrate with respect to a base, or isolate | separates from a base becomes unnecessary.

  However, as a result of further detailed examination by the present inventor, the following problem has been clarified. That is, even when the laser lift-off method is applied after heat treating the composite substrate, the gallium nitride layer may crack when the gallium nitride layer is peeled off from the support substrate, particularly near the end of the gallium nitride layer. There were many cracks. This crack was a cause of yield reduction.

  An object of the present invention is to eliminate the step of bonding the composite substrate to the base or separating the base from the base when the support substrate is irradiated with laser light to separate the group 13 element nitride layer. And to suppress cracks in the group 13 element nitride layer during separation.

  In the method according to the present invention, a support substrate and a group 13 element nitride layer provided on the support substrate are provided, and a warped composite substrate is placed between the base and the laser light transmitting plate. In this case, a support substrate is disposed on the laser light transmitting plate side, and stress is applied between the base and the laser light transmitting plate to restrain the composite substrate between the base and the laser light transmitting plate. By irradiating the laser light transmitting plate with laser light in a state, the crystal lattice bond at the interface between the support substrate and the group 13 element nitride layer is decomposed.

  The inventor investigated the cause of cracks in the gallium nitride layer when the gallium nitride layer was peeled off from the support substrate even when the laser lift-off method was applied after the composite substrate was heat-treated. Many cracks were observed at the periphery of the gallium nitride layer.

  About this cause, it estimated as follows. This will be described with reference to the schematic diagram of FIG. That is, when the composite substrate 1 is manufactured by forming the group 13 element nitride layer 3 on the surface 2 a of the support substrate 2, the composite substrate 1 has a warp due to a difference in thermal expansion coefficient. Here, laser light is irradiated in order from the outer peripheral side, and the group 13 element nitride layer 3 is peeled off. P is an irradiated region and N is an unirradiated region. The peeling proceeds in order from the irradiated region P. 14 is a void formed by peeling.

  However, when peeling from the irradiated region on the outer peripheral side of the group 13 element nitride layer, the peeled portion 13 of the group 13 element nitride layer 3 has a twiman effect due to damage by the laser beam due to the Twiman effect. Warpage occurs in the direction opposite to warpage. On the other hand, the influence of the Twiman effect is small in the peeling portion 12 of the support substrate 2. As a result, in the group 13 element nitride layer 3, the curvature near the boundary between the peeled portion 13 and the unpeeled portion becomes large, and the bending strength is concentrated. It is considered that a crack is generated in the portion 15 that cannot withstand this concentrated bending strength.

Based on this knowledge, the present inventor sandwiched a composite substrate having warpage between the base and the laser light transmissive plate, and applied stress between the base and the laser light transmissive plate to form a composite substrate. Is constrained between the base and the laser light transmissive plate, and the laser light transmissive plate is irradiated with laser light to bond the crystal lattice at the interface between the support substrate and the group 13 element nitride layer. Disassembled.
That is, at the interface between the support substrate and the group 13 element nitride layer, the crystal lattice constituting the support substrate and the group 13 element nitride lattice form a crystal lattice bond. By irradiating the support substrate side with laser light, the group 13 element nitride is decomposed into group 13 element metal and nitrogen, and the crystal lattice bond is decomposed. As a result, the group 13 element nitride layer is constrained when decomposition of crystal lattice bonds at the interface occurs in the group 13 element nitride layer, particularly at the periphery thereof, by irradiation with laser light. It can be suppressed that the group element nitride is spatially separated from the support substrate and warped in the reverse direction by the Twiman effect. By releasing the restraint after this, the group 13 element nitride layer can be spatially separated from the support substrate. As a result, the present inventors have succeeded in preventing cracks caused by warping in the reverse direction due to the Twiman effect, and reached the present invention.

(A) is a schematic diagram which shows the composite substrate 1, (b) is a schematic diagram which shows the state which set the composite substrate 1 to the holding | maintenance apparatus 4. FIG. It is a schematic diagram which shows the state restrained, pressing a composite substrate with the holding | maintenance apparatus 4 and correcting curvature. (A) is a schematic diagram which shows the state which set the composite substrate 1 to the holding | maintenance apparatus 4A which concerns on other embodiment, (b) is the state restrained without correcting the curvature of the composite substrate 1 with the holding | maintenance apparatus 4A. It is a schematic diagram which shows. It is a schematic diagram explaining the principle that a crack 15 is generated in the group 13 element nitride layer when the group 13 element nitride layer 3 is peeled off from the support substrate 1 by laser light irradiation. (A) is a schematic diagram for demonstrating the measuring method of the curvature of a composite substrate, and shows the case where curvature is a plus. (B) is a schematic diagram for demonstrating the measuring method of the curvature of a composite substrate, and shows the case where curvature is minus. It is a schematic diagram which shows the state which is irradiating a laser beam in the state which restrained and hold | maintained the composite substrate at the holding | maintenance apparatus. An example of the scanning pattern of the laser beam with respect to a composite substrate is shown.

(Composite substrate)
In the present invention, a composite substrate having a warp and including a support substrate and a group 13 element nitride layer provided on the support substrate is used.
In the example shown in FIG. 1A, the composite substrate 1 has a support substrate 2 and a group 13 element nitride layer 3 provided on the surface 2 a of the support substrate 2.

The material constituting the support substrate is not limited, but sapphire, AlN template, GaN template, GaN free-standing substrate, silicon single crystal, SiC single crystal, MgO single crystal, spinel (MgAl ₂ O ₄ ), LiAlO ₂ , LiGaO ₂ , LaAlO ₃ , perovskite complex oxides such as LaGaO ₃ and NdGaO ₃ , SCAM (ScAlMgO ₄ ). The composition formula _{[A 1-y (Sr 1-} x Ba x) y ] _{[(Al 1-z Ga z)} 1-u · D u ] _O 3 (A is a rare earth element; D is niobium and One or more elements selected from the group consisting of tantalum; y = 0.3-0.98; x = 0-1; z = 0-1; u = 0.15-0.49; x + z = 0 .1 to 2) cubic perovskite structure composite oxides can also be used.

  Although the group 13 element nitride layer 3 can be directly formed on the surface 2a of the support substrate 2, a seed crystal film may be formed on the surface 2a, and the group 13 element nitride layer 3 may be formed on the seed crystal film. it can. The seed crystal film and the group 13 element nitride layer 3 may be integrated with the same material.

The seed crystal is not particularly limited as long as the group 13 element nitride crystal layer can be grown. The group 13 element referred to here is a group 13 element according to the periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like. This group 13 element nitride is particularly preferably GaN, AlN, or GaAlN.
The seed crystal film may be a single layer, or may include a buffer layer on the support substrate side.

  As a method for forming the seed crystal film, a vapor deposition method is preferable, but a metal organic chemical vapor deposition (MOCVD) method, a hydride vapor deposition (HVPE) method, a pulsed excitation deposition (PXD) method, MBE Method and sublimation method. Metalorganic chemical vapor deposition is particularly preferred. The growth temperature is preferably 950 to 1200 ° C.

  The growth direction of the group 13 element nitride crystal layer may be the normal direction of the c-plane of the wurtzite structure, or may be the normal direction of the a-plane and the m-plane.

The dislocation density on the surface of the seed crystal is desirably low from the viewpoint of reducing the dislocation density of the group 13 element nitride crystal layer provided on the seed crystal. From this viewpoint, the dislocation density of the seed crystal is preferably 7 × 10 ⁸ cm ⁻² or less, and more preferably 5 × 10 ⁸ cm ⁻² or less. Further, the lower the dislocation density of the seed crystal, the better from the viewpoint of quality, so there is no particular lower limit, but generally it is often 5 × 10 ⁷ cm ⁻² or more.

  Although the manufacturing method of the group 13 element nitride layer is not particularly limited, metal organic chemical vapor deposition (MOCVD) method, hydride vapor deposition (HVPE) method, pulse excitation deposition (PXD) method, MBE method Examples thereof include gas phase methods such as a sublimation method and liquid phase methods such as a flux method.

  In the group 13 element nitride constituting the crystal layer, the group 13 element is a group 13 element according to a periodic table established by IUPAC. The group 13 element is specifically gallium, aluminum, indium, thallium, or the like. This group 13 element nitride is particularly preferably GaN, AlN, or GaAlN. Examples of the additive include carbon, low melting point metals (tin, bismuth, silver, gold) and high melting point metals (transition metals such as iron, manganese, titanium, and chromium).

  In a preferred embodiment, the group 13 element nitride crystal layer is grown by a flux method. At this time, the type of the flux is not particularly limited as long as the group 13 element nitride can be generated. In a preferred embodiment, a flux containing at least one of an alkali metal and an alkaline earth metal is used, and a flux containing sodium metal is particularly preferred.

  For the flux, a raw material of a group 13 element is mixed and used. As the raw material, a single metal, an alloy, or a compound can be applied, but a single metal of a group 13 element is preferable from the viewpoint of handling.

  From the viewpoint of the present invention, the ratio (mol ratio) of Group 13 element nitride / flux (for example, sodium) in the melt is preferably increased, preferably 18 mol% or more, and more preferably 25 mol% or more. However, if this ratio becomes too large, the crystal quality tends to deteriorate, so 40 mol% or less is preferable.

(Compound substrate warpage)
In the composite substrate 1 obtained in this way, warping due to film formation by cooling, for example, and cooling occurs. In general, as shown in FIG. 1A, the warp often has a convex shape on the lower side when the support substrate is on the upper side. It has been found that such warping is not eliminated by heating, but cracks are generated in the group 13 element nitride layer by the Twiman effect when irradiated with laser light.

  The warpage of the composite substrate is a value measured by the method described in Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2009-111423).

The warping will be described with reference to FIG.
Here, in the example shown in FIG. 5A, the composite substrate is warped so that the bottom surface 2b of the support substrate 2 of the composite substrate 1 is concave and the surface 3a of the group 13 element nitride layer 3 is convex. Yes. This warpage is positive (indicated by a + sign). In the example shown in FIG. 5B, the composite substrate is warped so that the bottom surface 2b of the support substrate 2 of the composite substrate 1 is convex and the surface 3a of the group 13 element nitride layer 3 is concave. . This warpage is negative (indicated by a symbol “−”). A curved surface formed by the bottom surface 2b of the composite substrate 1 is referred to as a “curved curved surface”.

  A plane that minimizes the average distance between the curved curved surface 2b and the plane is assumed, and this plane is defined as the optimum plane H. Then, the distance between the warped curved surface 2b and the optimum plane H is measured. That is, for a predetermined measurement range, a point on the optimal plane H in the bottom surface 2b is set as zp. Further, the point farthest from the optimum plane H in the bottom surface 2b is defined as zv. The distance between the point zv and the optimum plane H is warp W (R). 21 and 22 are gaps between the sample and the optimum plane H. Reference numeral 20 denotes a surface plate.

  In other words, the warpage W (R) is the difference in height between the point zp closest to the optimum plane H and the point zv farthest from the bottom surface 2b.

  In many cases, the absolute value of the warp of the composite substrate at 25 ° C. is +300 to +700 μm per 5 cm in length.

  The warpage of the composite wafer can be measured by a laser displacement meter. The laser displacement meter is a device that measures the displacement of the back surface by irradiating the bottom surface of the composite wafer with laser light. The laser wavelength is 633 nm, and a laser focus method or an optical interference method can be used as a measurement method according to the surface roughness.

(Composite board setting)
In the present invention, the warped composite substrate is sandwiched between the base and the laser light transmitting plate. At this time, a support substrate is arranged on the laser light transmitting plate side, stress is applied between the surface of the base and the surface of the laser light transmitting plate, and the composite substrate is placed between the base and the laser light transmitting plate. The state is constrained to. In this state, laser irradiation is performed to decompose the crystal lattice bond at the interface between the group 13 element nitride layer and the support substrate.

  Here, stress is applied between the base and the laser light transmissive plate so that the composite substrate is constrained between the base and the laser light transmissive plate. This is the bottom surface of the support substrate of the composite substrate. And a surface of the group 13 element nitride layer are stressed, which means that the composite substrate is fixed in a state in which the composite substrate is not deformed by the stress. At this time, it is not necessary to join the composite substrate and the base, and it is not necessary to join the composite substrate and the laser light transmitting plate. In addition, applying stress between the base and the laser light transmissive plate means that mechanical stress is applied between the laser light transmissive plate and the substrate, excluding the weight of the laser light transmissive plate and the composite substrate. It means to apply.

  In a preferred embodiment, stress is applied between the base and the laser light transmitting plate to hold the composite substrate in a corrected state. FIG. 1B and FIG. 2 relate to this embodiment.

  In the present embodiment, the holding device 4 is used. In the holding device 4, the base 5 and the laser light transmitting plate 7 are attached to the jig 18. The cushion material 6 is placed on the surface 5a of the base 5, and the composite substrate 1 is placed thereon. The composite substrate and the base 5 are not joined. Then, a laser light transmissive plate 7 is placed on the composite substrate 1. At this time, the surface 3 a of the group 13 element nitride layer 3 faces the base 5, and the bottom surface 2 b of the support substrate 2 faces the surface 7 a of the laser light transmitting plate 7.

  The composite substrate 1 is warped, for example, as shown in FIG. On the other hand, the surface 5a of the base 5 and the surface 7a of the laser light transmitting plate 7 are flat surfaces. For this reason, in the state before pressurization, a gap 15A is formed between the surface 7a of the laser light transmitting plate 7 and the bottom surface 2b of the support substrate 2, and the surface 3a of the group 13 element nitride layer 3 A gap 15 </ b> B is also formed between the cushion material 6.

  Next, as indicated by an arrow A in FIG. 2, the laser light transmissive plate 7 is moved toward the base 5. At this time, the base 5 may be moved toward the laser light transmissive plate 7 without moving the laser light transmissive plate 7, or both the laser light transmissive plate 7 and the base 5 may be moved. May be. As a result, the distance between the surfaces 5a and 7a is reduced, and the composite substrate is compressed in the thickness direction.

  Here, since the surface 7a of the laser light transmissive plate 7 and the surface 5a of the base 5 are flat, the warpage of the composite substrate 1 is corrected accordingly, and the warpage is reduced, resulting in a state of the composite substrate 1A. As a result, the composite substrate 1A is constrained by the laser light transmissive plate 7 base 5 so as not to be deformed.

  In holding, the warping of the composite substrate 1 is corrected by restraining and holding the composite substrate 1 to obtain a state of the composite substrate 1A. At this time, it is not necessary to completely correct the warpage of the composite substrate to make the warpage zero, and partial correction may be used. That is, it is only necessary that the warpage at the time of restraint is smaller than the warp before restraint.

  Since cracks are less likely to occur when the warpage of the composite substrate is smaller, (absolute value of warpage of composite substrate during restraint) / (absolute value of warpage of composite substrate before restraint) is preferably 0.5 or less. More preferably, it is 0.25 or less. Further, (the absolute value of the warp of the composite substrate when restrained) is preferably 300 μm or less, more preferably 150 μm or less per 5 cm length.

  Moreover, in this embodiment which correct | amends the curvature of a composite board | substrate, both the surface 7a of the laser beam transparent board and the surface 5a of the base 5 are flat surfaces. However, the surface of the laser light transmitting plate and the surface of the base may not be flat, and protrusions and recesses may be formed. In this case, it is sufficient that the warpage of the composite substrate is partially corrected during pressurization.

  In a preferred embodiment, the laser light transmitting plate is irradiated with laser light in a state where the composite substrate is restrained without correcting the warpage of the composite substrate. 3A and 3B relate to this embodiment.

  In the present embodiment, the holding device 4A is used. In the holding device 4A, a base 5A and a laser beam transmitting plate 7A are attached to a jig 18. The cushion material 6 is placed on the surface 5a of the base 5A, and the composite substrate 1 is placed thereon. The composite substrate and the base 5A are not joined. Then, a laser light transmitting plate 7A is placed on the composite substrate 1. At this time, the surface 3 a of the group 13 element nitride layer 3 faces the base 5, and the bottom surface 2 b of the support substrate 2 faces the surface 7 a of the laser light transmitting plate 7.

  The composite substrate 1 is warped, for example, as shown in FIG. A protrusion 11 is formed on the surface 7a of the laser light transmitting plate 7A, and a recess 9 is formed on the surface 5a of the base 5A. Each of the protrusions 11 and the recesses 9 has a shape that can absorb the warp of the composite substrate. In this example, since the cushion material 6 is placed on the laser light transmissive plate, a gap 10 is formed between the cushion material 6 and the base surface 5a.

  Next, as indicated by an arrow A in FIG. 3B, the laser light transmitting plate 7A is moved toward the base 5A. At this time, the base 5A may be moved toward the laser light transmissive plate 7A without moving the laser light transmissive plate 7A, or both the laser light transmissive plate 7A and the base 5A are moved. May be. As a result, the distance between the surfaces 5a and 7a is reduced.

  Here, a protrusion 11 is provided on the surface 7 a of the laser light transmitting plate 7, and a recess 9 is provided on the surface 5 a of the base 5. And the protrusion 11 and the recessed part 9 are each formed in the same form as the curvature of a composite substrate. As a result, in this example, the warpage of the composite substrate 1 is not corrected and does not change from before pressurization, or the change in warpage is small. In this state, the composite substrate 1 that has not been warped is restrained from being deformed by the laser light transmitting plate 7A and the base 5A. Even if the warp is not corrected, deformation of the composite substrate 1 is suppressed as a result of pressurizing the entire bottom surface 2b and surface 3a of the composite substrate 1.

  As described above, in the present invention, as a result of the composite substrate being pressurized and restrained so as not to be deformed, as shown in FIG. 4, when a partial region P of the composite substrate is irradiated with laser light. The deformation due to the Twiman effect of the peripheral portion (irradiated region) 13 of the group 13 element nitride layer 3 and the peripheral portion 12 of the support substrate is suppressed, and as a result, the crack 15 is suppressed.

  The material of the base is not particularly limited, but alumina or SiC ceramic is preferable.

  The laser light transmissive plate is preferably a plate having a linear transmittance of 50% or more with respect to laser light having a wavelength used in the laser lift-off method, and more preferably a plate having 75% or more. The material of the laser light transmissive plate is preferably synthetic quartz glass or sapphire.

  In a preferred embodiment, a cushioning material is sandwiched between the group 13 element nitride layer and the surface of the base. This prevents the surface of the group 13 element nitride layer from being damaged during pressurization. Examples of such cushion materials include glass fiber wool, fluoro rubber (Viton), and Teflon (Kalrez).

  Further, when the composite substrate is held, the warp can be reduced or the stress accompanying the correction of the warp can be reduced by heating the composite substrate. As such heating temperature, 100-500 degreeC is preferable and 200-300 degreeC is still more preferable. However, such heating is not essential and can be performed at room temperature.

(Laser irradiation)
While holding the composite substrate as described above, laser light is irradiated from the laser light transmitting plate side to decompose the crystal lattice bond at the interface between the group 13 element nitride and the support substrate.

  The wavelength of the laser beam is appropriately selected according to the material of the group 13 element nitride to be peeled, but is generally 380 nm or less, preferably 150 to 380 nm. ArF excimer laser, KrF excimer laser, XeCl excimer laser, third harmonic Nd: YAG laser, etc. can be used.

For example, in order to peel the following materials, it is preferable to use laser light having the following wavelengths.
GaN: 200 to 360 nm
AlN: 150-200 nm
GaAlN: 200 to 250 nm

  A method for performing laser lift-off is not particularly limited. For example, a laser beam emitted from a laser oscillator is converted into a condensed laser beam through a beam expander, a columnar lens or a convex lens, a dichroic mirror, and a condenser lens, and is irradiated onto a composite substrate on an XY stage. By combining a columnar lens and a condensing lens, the focal length can be made different between the x direction and the y direction. For example, an elliptical laser beam that is strongly focused in the x direction and defocused in the y direction can be formed. it can.

  A laser lift-off device using a beam scanner can also be used. That is, the laser beam emitted from the laser oscillator is converted into a focused laser beam via a beam expander, a columnar lens or a convex lens, a reflecting mirror, a galvano scanner, and an fθ lens, and is irradiated onto a moving composite substrate on an XY stage.

  In the example of FIG. 6, the laser beam 26A oscillated from the laser light source 25 is passed through the pinhole 27 and the light beam 26B is focused. Next, the light beam 26B is condensed by the lens 28 into a beam 26C, reflected by the reflecting plate 29, and the reflected light 26D is irradiated toward the laser light transmitting plate as indicated by an arrow B. This light passes through the laser light transmitting plate 7 and enters the composite substrate 1A.

  The laser beam to be used can be irradiated while scanning the entire bottom surface of the composite substrate. Alternatively, the bottom surface of the composite substrate can be scanned by fixing the position of the laser beam and moving the holding device 4.

  For example, in the example of FIG. 7, the laser beam spot 29 is moved vertically and horizontally as indicated by the arrow C on the composite substrate 1A for scanning. Here, the diameter of each spot 29 is preferably 1 to 5 mm. The moving speed of the spot 29 is preferably 10 to 50 mm / sec, although it depends on the repetition frequency of the pulse laser.

  When the laser beam spot is moved on the composite substrate, it is preferable that the adjacent spots 29 overlap each other, so that an unirradiated region can be eliminated.

The power of the laser beam depends on the object to be processed, temperature, laser oscillation wavelength, pulse width, etc., but can generally be 0.1 to 0.5 J / cm ² .

Example 1
The laser lift-off method was performed by the method described with reference to FIGS. 1, 2, 6, and 7.
Specifically, a gallium nitride layer 3 was grown to a thickness of 350 microns on a support substrate 2 made of sapphire having a diameter of 55 mm (FIG. 1). The warp of the obtained composite substrate 1 was +300 μm.

  The composite substrate 1 was set on the holding device 4. The cushion material 6 was a natural rubber cushion, the base 5 was made of stainless steel, and the surface 5a of the base 5 was a flat surface. The laser light transmitting plate 7 was a sapphire plate having a thickness of 3 mm. The laser light transmitting plate was pressed with a jig and pressed to fix (see FIG. 2). The warp of the composite substrate at this time is about 150 μm.

In this state, the holding device 4 is arranged on the drive stage, and the pulse of the third harmonic (ultraviolet laser beam having a wavelength of 355 nm) of the flash lamp excitation Q-switched Nd: YAG laser (repetition frequency: 10 Hz, pulse width: 5 ns) is raised. The stage was moved while irradiating and scanning was performed in order from the end of the composite substrate (see FIG. 7). The beam size of the laser light was shaped and condensed using a pinhole and a convex lens, and adjusted to be a circle having a diameter of 3.0 mm on the composite substrate (FIG. 7). The energy of one pulse was 0.25 mJ / cm ² . Scanning was performed so that one shot of the pulse slightly overlapped. That is, the speed was 27 mm / sec.

After the scan was completed, the composite substrate was immersed in hot water at 40 ° C. to dissolve the metal gallium (melting point: 29 ° C.) generated at the interface between sapphire and gallium nitride, and a sapphire and gallium nitride were separated. Neither the gallium nitride layer nor the sapphire substrate was cracked.
Thereafter, the outer peripheral portion of the separated gallium nitride layer was beveled and polished on both sides to obtain a self-standing GaN wafer having a diameter of 2 inches (50.8 mm) and a thickness of 300 μm.

(Example 2)
In the same manner as in Example 1, the gallium nitride layer was separated from the support substrate.
However, in this example, as shown in FIG. 3A, by providing the projection 11 and the recess 9 corresponding to the warp of the composite substrate, the warp of the composite substrate is accommodated when the composite substrate is pressed, and the warp Restrained without correction.

After the scan was completed, the composite substrate was immersed in hot water at 40 ° C. to dissolve the metal gallium (melting point: 29 ° C.) generated at the interface between sapphire and gallium nitride, and a sapphire and gallium nitride were separated. Neither the gallium nitride layer nor the sapphire substrate was cracked.
Thereafter, the outer peripheral portion of the separated gallium nitride layer was beveled and polished on both sides to obtain a self-standing GaN wafer having a diameter of 2 inches (50.8 mm) and a thickness of 300 μm.

(Comparative Example 1)
When the composite substrate 1 is set on the holding device 4 as shown in FIG. 1B, the laser light transmissive plate 7 is disposed on the composite substrate 1, but stress is applied from the laser light transmissive plate 7 to the composite substrate. I set it without it. As a result, a gap 15A remains between the laser light transmissive plate 7 and the composite substrate, and a gap 15B remains between the cushion material 6 and the composite substrate 1. Otherwise, the gallium nitride layer was separated from the support substrate in the same manner as in Example 1.

  After the scan was completed, the composite substrate was immersed in hot water at 40 ° C. to dissolve the metal gallium (melting point: 29 ° C.) generated at the interface between sapphire and gallium nitride, and a sapphire and gallium nitride were separated. Although separation was possible, cracks occurred in the outer peripheral portions of both the gallium nitride layer and the support substrate. The reason is considered to be due to the Twiman effect described with reference to FIG.

(Comparative Example 2)
The laser lift-off method was performed by the method described in Patent Document 1 (Patent 4227315). Specifically, a composite substrate 1 was obtained as in Example 1. A heat resistant cushion 6 made of glass wool was installed on the flat surface 5a of the base 5, and the composite substrate 1 was installed thereon. Next, the laser light transmissive plate 7 was placed on the composite substrate 1, but it was set without applying stress from the laser light transmissive plate 7 to the composite substrate. As a result, a gap 15A remains between the laser light transmissive plate 7 and the composite substrate, and a gap 15B remains between the cushion material 6 and the composite substrate 1. It heated to 600 degreeC in this state. Otherwise, the gallium nitride layer was separated from the support substrate in the same manner as in Example 1.

After the scan was completed, the composite substrate was immersed in hot water at 40 ° C. to dissolve the metal gallium (melting point: 29 ° C.) generated at the interface between sapphire and gallium nitride, and a sapphire and gallium nitride were separated. Although separation was possible, cracks occurred in the outer peripheral portions of both the gallium nitride layer and the support substrate. The reason is considered to be due to the Twiman effect described with reference to FIG.

Claims (7)

  A support substrate and a group 13 element nitride layer provided on the support substrate are provided, and a warped composite substrate is sandwiched between a base and a laser beam transmitting plate, and at this time, the laser beam The support substrate is disposed on the transmissive plate side, and stress is applied between the base and the laser light transmissive plate to restrain the composite substrate between the base and the laser light transmissive plate. The group 13 element nitride is characterized by decomposing a crystal lattice bond at an interface between the support substrate and the group 13 element nitride layer by irradiating the laser beam transmitting plate with a laser beam in a state. Layer separation method.   The method according to claim 1, wherein the warp of the composite substrate is corrected by applying the stress between the base and the laser light transmitting plate.   The method according to claim 1, wherein a surface of the base on the side of the composite substrate and a surface of the laser light transmissive plate on the side of the composite substrate are flat surfaces.   2. The method according to claim 1, wherein the laser light transmitting plate is irradiated with the laser light in a state where the composite substrate is restrained without correcting the warp of the composite substrate.   5. The method according to claim 4, wherein a protrusion or a recess is formed on at least one of the surface of the base on the side of the composite substrate and the surface of the laser light transmissive plate on the side of the composite substrate.   The method according to any one of claims 1 to 5, wherein a cushioning material is sandwiched between the group 13 element nitride layer and the base. The method according to claim 1, wherein the composite substrate is scanned with the laser beam.

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