Method for producing group III nitride semiconductor

Abstract

The present invention provides a method for manufacturing a group III nitride semiconductor. The method for manufacturing a group III nitride semiconductor comprises the following steps: a step of preparing a group III nitride substrate having a first group III nitride layer and a second group III nitride layer stacked in sequence from the back to the surface, wherein the first group III nitride layer has a transmittance of 60% or more at a predetermined wavelength of 400 nm to 700 nm, and the second group III nitride layer has a transmittance of 1×10 20 cm ‑3 The method further comprises the following steps: a step of forming a device structure on the surface side of the above-mentioned group III nitride substrate, wherein the device structure comprises oxygen as an impurity at a concentration above 0.1% and has a transmittance of 0.1% or less for the above-mentioned specified wavelength, and is disposed on the above-mentioned first group III nitride layer. The method further comprises the following steps: a step of focusing the laser light on the above-mentioned first group III nitride layer on the back side of the above-mentioned group III nitride substrate, which is closer to the front of the above-mentioned second group III nitride layer, forming an internal modified layer in the above-mentioned first group III nitride layer by multiphoton absorption, and dividing the above-mentioned group III nitride substrate by using the above-mentioned internal modified layer as a boundary.

Description

Technical Field

[0001] The present application relates to a method for manufacturing a Group III nitride semiconductor. Background Art

[0002] Single crystal III-nitride semiconductor substrates (GaN substrates are shown below as an example) are used as materials for white lighting LEDs with blue wavelengths, laser diodes with ultraviolet to blue wavelengths used as light sources for blue light (Blu-Ray) reading and welding processing, and power devices used for frequency conversion in power systems or motor control.

[0003] The thickness of a GaN substrate is usually 300 to 700 μm, and the shape is a circle with a diameter of 50 to 150 mm. Generally speaking, a GaN substrate has a transmittance of more than 60% and is a substrate that is transparent to visible light.

[0004] On the other hand, an example of a method for manufacturing a device structure from a GaN substrate is shown in Figure 5-1 to Figure 5-6 . Figure 5-1 to Figure 5-6 The schematic cross-sectional views show the respective steps in a method of manufacturing an example of a device from a GaN substrate.

[0005] (1) First, prepare the GaN substrate 32 ( Figure 5-1 ).

[0006] (2) Next, a functional layer 14 is stacked on the surface of the GaN substrate by using a metal organic vapor phase epitaxy method (hereinafter referred to as MOCVD method). Figure 5-2 ).

[0007] (3) Next, a non-transparent insulating film and an electrode 15 are formed on the functional layer 14 ( Figure 5-3 ), forming multiple segmentation grooves ( Figure 5-4 ).

[0008] (4) Then, the GaN substrate 32 having a plurality of device structures formed on its surface is thinned and polished to a thickness of 50 to 100 μm.

[0009] (5) If necessary, an electrode 33 is also formed on the back surface of the GaN substrate. Figure 5-5 ).

[0010] (6) Next, the GaN substrate 32 is divided into individual devices 34 by cutting and cleaving ( Figure 5-6 ).

[0011] The divided devices 34 are connected to wiring, and are inspected for appearance, electrical characteristics, and reliability. The devices 34 that have passed the inspection are widely used according to various uses.

[0012] GaN substrates are expensive compared to semiconductor materials such as Si and GaAs. Therefore, in order to process the obtained GaN crystals into GaN substrates without waste, Patent Document 1 for preventing cracks caused by segmentation and improving the yield rate and Patent Document 2 for reducing material loss in a segmentation method using laser irradiation are disclosed as known technologies for manufacturing GaN substrates.

[0013] SiC substrates are expensive substrates like GaN substrates. Therefore, Patent Document 3 discloses a method for manufacturing reusable SiC substrates by dividing a SiC substrate having a functional layer and an electrode on its surface.

[0014] Prior art literature

[0015] Patent Literature

[0016] Patent Document 1: Japanese Patent Application Publication No. 2014-84263

[0017] Patent Document 2: Japanese Patent Application Publication No. 2017-183600

[0018] Patent Document 3: Japanese Patent Application Publication No. 2017-28072 Summary of the invention

[0019] Problems to be solved by the invention

[0020] Patent Document 1 describes a method of growing a first layer and a second layer having different impurity concentrations on a substrate, irradiating the substrate with laser light having a wavelength of 8 to 12 μm, and dividing the substrate using absorption heat generated in the second layer.

[0021] However, if the laser is irradiated from the back side of a substrate having a device structure on the surface using this method, the heat generated is large relative to the high incident energy, and sometimes the heat even reaches the device structure on the surface. Therefore, there is a possibility that the device with the thermal history cannot obtain a device with the desired characteristics, and the reliability is damaged, which makes it difficult to apply.

[0022] Patent Document 2 describes a method of forming a modified layer inside a crystal by utilizing a multiphoton absorption phenomenon caused by focusing laser light on one point instead of division based on absorption heat, and dividing the crystal using the modified layer as a boundary.

[0023] However, if the substrate having the device structure is irradiated with laser light from the back side using this method, the laser light with focus deviation and part of the unprocessed laser light will reach the device structure on the surface. The laser light reaching the device structure is converted into heat by non-transparent materials such as electrodes and insulating films, causing heat generation. As a result, the functional layer and the electrode film are affected by the heat, so as described in Patent Document 1, it causes problems with the device and is difficult to apply.

[0024] Patent Document 3 is applied to a SiC substrate, and there is no description of the influence on the device structure on the substrate surface. It is considered that in this manner, as described in Patent Document 2, the device structure generates heat.

[0025] The purpose of the present application is to solve the problem of applying heat to the device when dividing a substrate having a device structure on its surface by laser, and to provide a method for manufacturing a Group III nitride semiconductor capable of dividing a substrate having a device structure on its surface by laser irradiation.

[0026] Solutions to Solve Problems

[0027] The method for manufacturing a group III nitride substrate of the present application for achieving the above-mentioned object comprises the following steps: preparing a group III nitride substrate having a first group III nitride layer and a second group III nitride layer stacked in sequence from the back to the surface, wherein the first group III nitride layer has a transmittance of 60% or more at a predetermined wavelength of 400 nm to 700 nm, and the second group III nitride layer has a transmittance of 1×10 20 cm -3 The above concentration contains oxygen as an impurity, has a transmittance of 0.1% or less for the above specified wavelength, and is provided on the above first group III nitride layer;

[0028] A step of forming a device structure on the surface side of the III-nitride substrate; and

[0029] A process of focusing the laser light at a position forward of the first III-nitride layer from the back side of the III-nitride substrate relative to the second III-nitride layer, forming an internal modified layer in the first III-nitride layer by utilizing multi-photon absorption, and dividing the III-nitride substrate with the internal modified layer as a boundary.

[0030] Effects of the Invention

[0031] According to the method for manufacturing a group III nitride semiconductor described in the present application, a second group III nitride layer having a low laser transmittance is provided on the back side. Therefore, when laser light is irradiated from the back side, the laser light transmitted to the front side can be converted into heat in the second group III nitride layer. Thus, the deterioration of the characteristics of the device structure formed on the front side can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1-1 This is a schematic cross-sectional view showing one step of the method for producing a group III nitride semiconductor according to Embodiment 1.

[0033] Figure 1-2 This is a schematic cross-sectional view showing one step of the method for producing a group III nitride semiconductor according to Embodiment 1.

[0034] Figure 1-3 This is a schematic cross-sectional view showing one step of the method for producing a group III nitride semiconductor according to Embodiment 1.

[0035] Figure 1-4 This is a schematic cross-sectional view showing one step of the method for producing a group III nitride semiconductor according to Embodiment 1.

[0036] Figure 2 This is a schematic diagram schematically showing the structure of the dividing device described in Embodiment 1.

[0037] Figure 3 The diagram illustrates the difference in transmittance between the first group III nitride layer, the third group III nitride layer, and the second group III nitride layer of the GaN substrate in terms of transmittance with respect to the wavelength of light.

[0038] Figure 4-1 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0039] Figure 4-2 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0040] Figure 4-3 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0041] Figure 4-4 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0042] Figure 4-5This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0043] Figure 4-6 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0044] Figure 4-7 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0045] Figure 4-8 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0046] Figure 4-9 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0047] Figure 4-10 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0048] Figure 4-11 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0049] Figure 4-12 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0050] Figure 4-13 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0051] Figure 4-14 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0052] Figure 4-15 This is a schematic cross-sectional view of one step of the method for manufacturing the GaN substrate having the transparent layer and the light-to-heat conversion layer described in Embodiment 1.

[0053] Figure 5-1 This is a schematic cross-sectional view showing one step in an example manufacturing method of a device from a GaN substrate.

[0054] Figure 5-2This is a schematic cross-sectional view showing one step in an example manufacturing method of a device from a GaN substrate.

[0055] Figure 5-3 This is a schematic cross-sectional view showing one step in an example manufacturing method of a device from a GaN substrate.

[0056] Figure 5-4 This is a schematic cross-sectional view showing one step in an example manufacturing method of a device from a GaN substrate.

[0057] Figure 5-5 This is a schematic cross-sectional view showing one step in an example manufacturing method of a device from a GaN substrate.

[0058] Figure 5-6 This is a schematic cross-sectional view showing one step in an example manufacturing method of a device from a GaN substrate.

[0059] Figure 6 This is a graph showing the relationship between the oxygen concentration and transmittance of a nitride crystal.

[0060] Description of Reference Numerals

[0061] 10 Group III Nitride Substrates

[0062] 11. First III-nitride layer

[0063] 12 Second III-nitride layer

[0064] 13. Group III Nitride Layer

[0065] 14 Functional layer

[0066] 15 Non-transparent materials for insulating films and electrodes

[0067] 16 Objective lens

[0068] 17 Laser

[0069] 18 Modified layer (internal modified layer)

[0070] 19 Spotlight

[0071] 20 Laser

[0072] 21 GaN substrate

[0073] 22 GaN substrate

[0074] 23 Drive Abutment

[0075] 24 Laser Oscillator

[0076] 25 Mirror

[0077] 26 substrates

[0078] 27 First III-nitride layer

[0079] 28 First III-nitride layer

[0080] 29 Second III-nitride layer

[0081] 30 Second III-nitride layer

[0082] 31 Group III nitride layer

[0083] 32 GaN substrate

[0084] 34 Equipment

[0085] 40 Splitting device

[0086] 41 Ultra-high vacuum chamber

[0087] 42 Wafer process jig of bonding device (upper side)

[0088] 43 Wafer process jig of bonding device (lower side)

[0089] 44 Ion beam electrode

[0090] 45 Ion Beam

[0091] 46 Amorphous layer

[0092] 47 Bonding interface DETAILED DESCRIPTION

[0093] The method for manufacturing a group III nitride semiconductor according to the first embodiment comprises the following steps: preparing a group III nitride substrate formed by laminating a first group III nitride layer and a second group III nitride layer in sequence from the back side to the front side, wherein the first group III nitride layer has a transmittance of 60% or more at a predetermined wavelength of 400 nm to 700 nm, and the second group III nitride layer has a transmittance of 1×10 20 cm -3 The above concentration contains oxygen as an impurity, has a transmittance of 0.1% or less for the above specified wavelength, and is provided on the above first group III nitride layer;

[0094] A step of forming a device structure on the surface side of the III-nitride substrate; and

[0095] A process of focusing the laser light at a position forward of the first III-nitride layer from the back side of the III-nitride substrate relative to the second III-nitride layer, forming an internal modified layer in the first III-nitride layer by utilizing multi-photon absorption, and dividing the III-nitride substrate with the internal modified layer as a boundary.

[0096] Regarding the method for manufacturing a group III nitride semiconductor according to the second embodiment, in the first embodiment, the step of preparing the group III nitride substrate may include the following steps:

[0097] The process of preparing a seed substrate;

[0098] A step of performing crystal growth of the first group III nitride layer on the seed substrate;

[0099] A step of separating the seed substrate;

[0100] A step of mirror-finishing the surface of the first group III nitride layer by grinding and polishing;

[0101] A step of growing the second Group III nitride layer on the seed substrate by oxide vapor phase epitaxy;

[0102] A step of separating the seed substrate;

[0103] a step of grinding and polishing the surface of the second group III nitride layer; and

[0104] and bonding the separated first group III nitride layer and the second group III nitride layer together.

[0105] Regarding the method for manufacturing a group III nitride semiconductor according to the third embodiment, in the second embodiment, the step of preparing the group III nitride substrate may further include the following steps:

[0106] A step of crystal-growing a third group III nitride layer having a transmittance of 60% or more with respect to the predetermined wavelength is performed on the second group III nitride layer.

[0107] Regarding the method for manufacturing a group III nitride semiconductor described in the fourth embodiment, in any of the first to third embodiments, the device structure may include a functional layer, an electrode, and an insulating film.

[0108] Regarding the method for producing a group III nitride semiconductor according to the fifth aspect, in any of the first to fourth aspects, the group III nitride substrate may be made of GaN.

[0109] (About the Background of the Method for Manufacturing the Group III Nitride Semiconductor Described in the Present Application)

[0110] In this application, "transmittance" is defined as the ratio of light transmission when irradiated with light having a wavelength of 400-700nm, which is longer than the absorption end wavelength of GaN. In addition, "transparency" is also defined as having a transmittance of 60% or more when irradiated with light having a specified wavelength of 400-700nm.

[0111] GaN substrates, which are an example of group III nitride substrates, are usually grown independently using a single crystal growth method such as the hydride vapor phase epitaxy method (hereinafter referred to as HVPE method). Therefore, it is difficult to manufacture a GaN substrate having multiple layers with significantly different transmittances by adjusting the growth conditions, such as the flow rates of group V and group III raw material gases, or changing the impurity doping method.

[0112] This is because when a plurality of different GaN crystal growth methods are combined to produce a self-standing GaN substrate, there is a problem of cracks and breakages occurring due to differences in the lattice constants of the crystals.

[0113] However, with the recent development of GaN crystal growth technology mainly based on oxide vapor phase epitaxy (hereinafter referred to as OVPE), it has been found that practical GaN substrates free of cracks and fissures can be realized even by combining crystal growth methods having characteristics of significantly different transmittances.

[0114] The OVPE method is a method of blowing a gas containing an oxide of a group III element and a gas containing a nitride onto a seed substrate, causing the two to react and grow a group III nitride crystal on the seed substrate. 2 O 3 The powder reacts with carbon powder at high temperature to generate oxide gas of group III elements, Ga 2 O gas, so that the generated Ga 2 O gas and ammonia gas on the seed substrate based on the reaction formula Ga 2 O+2NH 3 →2GaN+H 2 O+2H 2 A reaction occurs, thereby allowing GaN crystals to grow.

[0115] The inventors of the present invention have repeatedly conducted intensive research and have come to the following conclusion: GaN crystals produced by combining different crystal growth methods have Figure 3Such a transmittance difference can be used as a means to obtain reusable GaN substrates by dividing the GaN substrate having the device structure on the surface. Thus, the method for producing a group III nitride semiconductor described in the present application is realized.

[0116] Hereinafter, a method for producing a group III nitride semiconductor according to an embodiment will be described with reference to the accompanying drawings. It should be noted that in the accompanying drawings, substantially the same components are denoted by the same reference numerals.

[0117] (Implementation method 1)

[0118] Figure 1-1 to Figure 1-4 Schematic cross-sectional views showing the respective steps of the method for producing a group III nitride semiconductor according to the first embodiment.

[0119] The method for manufacturing a group III nitride semiconductor according to the first embodiment includes the steps of: preparing a group III nitride substrate in which a first group III nitride layer 11, a second group III nitride layer 12, and a third group III nitride layer 13 are stacked in this order from the back side to the front side ( Figure 1-1 ); a step of forming a device structure on the surface side of the group III nitride substrate ( Figure 1-2 ); and a step of irradiating the first group III nitride layer on the back side of the group III nitride substrate with laser light to split the group III nitride substrate ( Figure 1-3 and Figure 1-4 The first group III nitride layer 11 has a transmittance of 60% or more for a predetermined wavelength of 400 nm to 700 nm. The second group III nitride layer is formed on the first group III nitride layer at a thickness of 1×10 20 cm -3 The above concentration contains oxygen as an impurity, and the transmittance for the specified wavelength is 0.1% or less. The third group III nitride layer 13 has a transmittance of 60% or more for the specified wavelength. In addition, in the process of dividing the group III nitride substrate, the focal point of the laser is concentrated at a position further in front of the second group III nitride layer, and an internal modified layer is formed by multiphoton absorption, and the group III nitride substrate is divided with the internal modified layer as the starting point.

[0120] According to the method for manufacturing a group III nitride semiconductor described in Embodiment 1, the second group III nitride layer 12 having a low laser transmittance is provided on the back side of the third group III nitride layer 13 forming the device structure on the surface side. Therefore, when the focal point of the laser light is focused on the front side of the second group III nitride layer from the back side, the laser light transmitted to the surface side can be converted into heat in the second group III nitride layer, and the deterioration of the characteristics of the device structure formed on the surface of the third group III nitride layer on the surface side can be suppressed.

[0121] Hereinafter, each step of the method for producing the group III nitride semiconductor will be described.

[0122] (Regarding the process of preparing a group III nitride substrate ( Figure 1-1 )

[0123] Figure 4-1 to Figure 4-15 The present invention is a schematic cross-sectional view of each step of a method for manufacturing a group III nitride semiconductor, i.e., a GaN substrate, having a first group III nitride layer 11 as a transparent layer, a second group III nitride layer 12 as a light-to-heat conversion layer, and a third group III nitride layer 13 as described in Embodiment 1. The group III nitride substrate 10 is formed by stacking the first group III nitride layer 11, the second group III nitride layer 12, and the third group III nitride layer 13 in this order from the back side to the front side. For the step of preparing the group III nitride substrate, a method of manufacturing a group III nitride substrate is used. Figure 4-1 to Figure 4-15 Provide explanation.

[0124] (1) Prepare sapphire, ScAlMgO 4 , GaN, etc. as a seed substrate 26 ( Figure 4-1 ).

[0125] (2) Next, a first group III nitride layer 27 as a first transparent layer having a transmittance of 60% or more was crystal-grown on the seed substrate 26 with a thickness of 440 μm by HVPE ( Figure 4-2 ). The material and shape of the seed substrate 26 are not particularly limited. Regarding the growth method, in addition to the HVPE method, the liquid phase method or the ammonothermal method known in the Na flux method can also be used. By doping the first group III nitride layer 27 with 1×10 18 cm -3 With about 100% Si as an impurity, the first group III nitride layer 27 can be made into an N-type semiconductor layer.

[0126] (3) Next, the GaN substrate 28, which is an example of a group III nitride substrate having the seed substrate 26 and the first group III nitride layer 27, is separated by a known method such as etching or lift-off. Figure 4-3 ).

[0127] (4) The front and back surfaces of the separated first group III nitride layer 27 are subjected to mirror finishing such as grinding and polishing by 20 μm, respectively, to obtain a parallel and flat GaN substrate 28 having a thickness of 400 μm ( Figure 4-4 ).

[0128] (5) On the other hand, sapphire, ScAlMgO 4, GaN, etc. as another substrate 26 ( Figure 4-5 ).

[0129] (6) Next, a second group III nitride layer 29 having a transmittance of 0.1% or less and functioning as a light-to-heat conversion layer was crystal-grown on the seed substrate 26 with a thickness of 120 μm by OVPE ( Figure 4-6 The material and shape of the substrate 26 are not particularly limited. The details of the second group III nitride layer functioning as a light-to-heat conversion layer are as follows.

[0130] (7) Next, the group III nitride substrate having the seed substrate 26 and the second group III nitride layer 29 is separated by a known method such as etching or stripping. Figure 4-7 ).

[0131] (8) The front and back surfaces of the separated second group III nitride layer 29 are mirror-finished by grinding or polishing to a thickness of, for example, 10 μm, to obtain a parallel and flat group III nitride layer 30 having a thickness of 100 μm ( Figure 4-8 ).

[0132] It should be noted that the manufacturing method of the III-nitride layer 30 can also be to crystal-grow a second III-nitride layer 29 having a transmittance of less than 0.1% and functioning as a light-to-heat conversion layer on a seed substrate 26 with a thickness of, for example, 2000 μm, and after separating the seed substrate, cut it into multiple pieces using known methods such as a wire saw and laser, and then grind / polish it on both sides to a thickness of 100 μm.

[0133] (9) Figure 4-4 The GaN substrate 28 obtained in Figure 4-8 First, a wafer process jig (upper side) 42 and a wafer process jig (lower side) 43 of the bonding device are respectively provided in a chamber of a bonding device corresponding to ultra-high vacuum, so that the bonding surfaces of the GaN substrate 28 and the III-nitride layer 30 face each other with a certain interval. Figure 4-9 ).

[0134] To enhance the bonding strength between the GaN substrate 28 and the group III nitride layer 30 , the main surface is preferably polished to a mirror surface (eg, a mirror surface having an arithmetic mean roughness Ra of 10 nm or less as specified in JIS B 0601:2001).

[0135] (10) Next, the bonding surface is irradiated with an ion beam such as Ar or an atomic beam 45 ( Figure 4-10). At this time, not only the oxide film and adsorption layer on the bonding surface are removed, but also the bonding surface itself is activated to form an active particle film.

[0136] (11) By beam irradiation, an amorphous layer 46 is formed on the bonding surface ( Figure 4-11 ).

[0137] (12) These bonding surfaces are brought into contact, and a certain load is applied as appropriate to bond / integrate the amorphous layers 3 to each other, and bonding is performed with the bonding interface 47 formed by the amorphous layers interposed therebetween ( Figure 4-12 ).

[0138] (13) Complete the bonding of substrates ( Figure 4-13 ).

[0139] It should be noted that the bonding interface 47 is formed by an amorphous layer with a thickness of less than 10nm. The higher the irradiation energy of the beam and the longer the irradiation time, the thicker the amorphous layer becomes, but at the same time, it is difficult to bond due to the increased surface roughness. Therefore, the thickness of the bonding interface 47 is preferably less than 10nm. In fact, it can be seen that the interface has sufficient bonding strength with a thickness of several nm. In addition, the amorphous layer constituting the bonding interface 47 contains metal components containing Ti, Cr, Ni, Fe, Al or their alloys. They are generated by irradiating the interior of the chamber and the conveyor plate when the beam is irradiated and cutting their surfaces, thereby moving to the surface of the wafer as metal components.

[0140] As bonding methods other than this method, there is no particular limitation as long as they are suitable for forming the amorphous layer. For example, it is preferable to apply a known bonding method, which is a direct bonding method in which the bonding surface is cleaned and directly bonded, and then the temperature is raised to about 600°C to 1200°C for bonding; a surface activation method in which the bonding surface is cleaned and activated by plasma, ions, etc., and then bonding is performed at a low temperature of about room temperature (e.g., 25°C) to about 400°C.

[0141] (14) On the flat second group III nitride layer 30 of the GaN substrate, a third group III nitride layer 31 is crystal-grown to a thickness of 120 μm as a third transparent layer by using the HVPE method or the like in the same manner as the first group III nitride layer 27 ( Figure 4-14 The third group III nitride layer 31 is preferably doped with 1×10 18 cm -3 The Si on the GaN substrate is made into an N-type semiconductor layer.

[0142] (15) Next, the surface of the third group III nitride layer 31 is ground and polished by 20 μm, so that the group III nitride substrate 10, i.e., the GaN substrate ( Figure 4-15 ).

[0143] Through the above steps, a GaN substrate as the group III nitride substrate 10 can be obtained.

[0144] (Step of forming a device structure on the surface side of the group III nitride substrate) Figure 1-2 )

[0145] Next, a functional layer is stacked on the surface of the III-nitride substrate 10, such as a GaN substrate, by MOCVD. Next, a non-transparent electrode, an insulating film, etc. are formed on the functional layer to form a plurality of predetermined dividing lines ( Figure 1-2 ). Thus, a process of forming a device structure on the surface of the group III nitride substrate 10 is performed. Here, the device structure includes, for example, a functional layer 14, an electrode, and an insulating film 15.

[0146] (Step of dividing a group III nitride substrate having a device structure on its surface) Figure 1-3 )

[0147] Next, the back side of the III-nitride substrate, such as a GaN substrate, having a device structure on the surface is used as the upper surface. Figure 2 As shown, it is arranged in the dividing device 40. The back surface of the GaN substrate has been mirror-finished.

[0148] <Division device>

[0149] Figure 2 This is a schematic diagram showing the structure of the dividing device described in Embodiment 1. The dividing device 40 includes a driving base 23 for fixing the group III nitride substrate, a laser oscillator 24 for oscillating laser light, and optical systems 25 and 16 for guiding the laser light to the group III nitride substrate.

[0150] <Drive base>

[0151] The driving base 23 of the dividing device has a hole for sucking the GaN substrate, for example, although not shown, and the GaN substrate can be fixed by making the hole negatively pressurized by a vacuum pump, etc. Furthermore, the base 23 is configured to be movable in three axes: xyz.

[0152] <Laser Oscillator>

[0153] Figure 3 1 is a diagram illustrating the difference in transmittance of the first, third, and second group III nitride layers of the GaN substrate in terms of transmittance to the wavelength of light. Figure 3 The difference in transmittance between the first III-nitride layer, the third III-nitride layer and the second III-nitride layer is used as a reference, and a laser having a wavelength of, for example, 532 nm can be oscillated. In addition, by exchanging control signals with the drive base 23 (not shown), the laser can be turned on / off at a desired position.

[0154] <Optical System>

[0155] The optical system for guiding the laser light to the group III nitride substrate includes, for example, the mirror 25 and the objective lens 16 .

[0156] The mirror 25 is a mirror that reflects 90% or more of the laser light emitted from the laser oscillator 24 and transmits it to the GaN substrate, and is composed of, for example, a multilayer dielectric film mirror that reflects light of a wavelength of 532 nm.

[0157] (Regarding the formation of the internal modified layer)

[0158] The focal point 19 of the laser 17 transmitted through the objective lens 16 can be set to a position 380 μm from the back surface of the GaN substrate using the z-axis setting of the driving base. In this embodiment, a microscope objective lens with spherical aberration correction having a transmission wavelength of 532 nm, i.e., an objective lens 16 with NA=0.85, f=2 mm, and 100 times magnification is used.

[0159] The laser 17 is capable of extremely short pulse oscillation of 25 ps (picoseconds) or less. Therefore, multiphoton absorption occurs in the focal point 19 inside the first group III nitride layer 11, and the inside of the first group III nitride layer 11 is modified, and a modified layer 18 is formed at a thickness of 20 μm at a distance of 380 μm from the back surface, for example. It should be noted that the modified layer 18 is formed to the inside of the first group III nitride layer 11, and therefore, it is sometimes referred to as an internal modified layer.

[0160] The thickness of the modified layer 18 is determined by the laser irradiation conditions. The in-plane deviation of the modified layer is determined by the movement accuracy of the z-axis of the base, the vibration of the device, and the surface accuracy of the GaN substrate. Therefore, it is better to have a high device accuracy, less vibration, and high surface accuracy. In this way, the in-plane deviation of the modified layer can be reduced.

[0161] The modified layer 18 can be formed on the entire surface of the GaN substrate by setting the laser frequency to 100 kHz and the scanning speed to 100 mm / s so that the lateral width of the modified layer 18 formed per laser pulse is 3 to 5 μm.

[0162] What is important here is that even if the aberration correction based on the above-mentioned objective lens is implemented with high precision in laser processing using multiphoton absorption, a certain proportion of laser light that is not focused at the focal point 19 and laser light 20 that is not used for modification processing may sometimes penetrate the surface side of the GaN substrate.

[0163] Therefore, in the method for manufacturing a group III nitride semiconductor described in Embodiment 1, the laser light 20 transmitted to the surface side is Figure 4-6 The heat is converted into heat by the second III-nitride layer 12 of the GaN substrate prepared in the process. This is because the transmittance of the second III-nitride layer 12 to the laser wavelength of 400~700nm is less than 0.1%. It should be noted that when the transmittance exceeds 0.1%, the proportion of the irradiated laser penetrating to the device structure side increases, and the possibility of deteriorating the reliability of the device becomes extremely high. Therefore, from the perspective of ensuring the reliability of the device, a transmittance exceeding 0.1% is not preferred. Heat generation only occurs inside the second III-nitride layer 12 of the GaN substrate, and its influence does not affect the device structure on the surface.

[0164] <Regarding the Second Group III Nitride Layer as a Light-to-Heat Conversion Layer>

[0165] Here, a method for producing the second group III nitride layer 12 having a transmittance of 0.1% or less for laser light having a wavelength of 400 to 700 nm and functioning as a light-to-heat conversion layer will be described in detail.

[0166] The second group III nitride layer 12 is obtained by the OVPE method. In the OVPE method, oxide is used as a raw material, so the grown second group III nitride layer 12 may contain oxygen as an impurity. Figure 6 In this way, the transmittance changes depending on the oxygen concentration contained in the second group III nitride layer 12 .

[0167] Figure 6 is a graph showing the relationship between the oxygen concentration and transmittance of the nitride crystal. As described above, in order to suppress the influence of the second group III nitride layer on the device structure on the surface side, the transmittance of the second group III nitride layer to the laser with a wavelength of 400 to 700 nm needs to be set to 0.1% or less. In order to achieve this transmittance, for example, Figure 6 As shown in FIG. 1 , the oxygen concentration of the second group III nitride layer is set to 1×10 20 cm -3Above, preferably 1×10 21 cm -3 That’s all.

[0168] In order to set the oxygen concentration contained in the second group III nitride layer 12 to 1×10 20 cm -3 In the above, the V group raw material gas, such as NH 3 The number of N moles is relative to the group III source gas, such as Ga 2 The ratio of the number of moles of Ga to O is set to 100 or less, preferably 10 or less, and the crystal growth is performed at a substrate temperature of 1200°C.

[0169] It should be noted that the value of oxygen concentration is obtained by secondary ion mass spectrometry (SIMS). The oxygen concentration of the first group III nitride layer having a transmittance of 60% or more is as follows: Figure 6 As shown, it is 1×10 19 cm -3 the following.

[0170] Here, the difference between the first and third group III nitride layers and the second group III nitride layer is based on the orientation difference of crystal growth. Specifically, the first group III nitride layer has a strong element of growth parallel to the (0001) plane, but the second group III nitride layer has a strong element of growth parallel to a small crystal plane including {10-1m} and {11-2n} planes (m is an integer other than 0, and n is an even number). The two have this difference.

[0171] In addition, in the above processing method, the second group III nitride layer 12 having a characteristic of low transmittance in the wavelength range of the above laser light is provided in the GaN substrate by the OVPE method. As a result, it is found that the laser light 20 that is not completely focused and passes through the surface side can be converted into heat in the second group III nitride layer 12, thereby suppressing the heat generation in the device structure.

[0172] (Group III nitride substrate with device structure on the surface after segmentation) Figure 1-4 )

[0173] After the modified layer 18 is formed by laser irradiation, the GaN substrate 21 having the device structure on the surface and the GaN substrate 22 having the modified layer 18 and the first transparent layer can be easily separated by using a physical external force (not shown) with the modified layer 18 formed in a planar shape as a starting point. Figure 1-4 ).

[0174] The separated GaN substrate 21 with the device structure on the surface is taken out from the splitting device, and the back surface is ground or polished to a thickness of less than 100 μm. At this time, the second III-nitride layer 12 and the bonding interface 47 are polished and disappear. Next, if, for example, Figure 5-5 , Figure 5-6 By forming and dividing the back electrode as shown, it is possible to obtain a device similar to the conventional manufacturing method.

[0175] Furthermore, the separated GaN substrate 22 having only the first group III nitride layer with a thickness of 390 μm can be used as a GaN substrate by grinding and polishing its surface by 20 μm. Therefore, the expensive material of the GaN substrate can be effectively utilized.

[0176] As described above, an example of an embodiment has been described. The described embodiment is constructed by one division, but is not limited thereto. For example, a plurality of GaN substrates having light-to-heat conversion layers sandwiched by transparent layers may be prepared, and the embodiment may be constructed by repeatedly dividing the substrate a plurality of times.

[0177] In addition, in this embodiment, GaN crystal is used as an example of group III nitride crystal, but any material can be used as long as the crystal system is the same. For example, it goes without saying that AlGaInN or AlN can be used as crystal and the same effect can be obtained by using the same embodiment.

[0178] It should be noted that the first group III nitride layer 11 may be sapphire, ScAlMgO 4 In other words, the first III-nitride layer 11 can be a substrate having a transmittance of 60% or more for a predetermined wavelength of 400 nm to 700 nm. In addition, the second III-nitride layer 12 can be a substrate having a transmittance of 1×10 20 cm -3 The above concentration may be used as a Group III nitride layer having oxygen as an impurity and a transmittance of 0.1% or less at the above-mentioned predetermined wavelength.

[0179] In addition, the focal point 19 of the laser 17 may be located inside the second group III nitride layer 12. That is, the laser 17 may be irradiated from the substrate on the back side of the group III nitride layer to form an internal modified layer 18 by multiphoton absorption, and the device 34 and the substrate may be separated by using the internal modified layer 18 as a boundary.

[0180] It should be noted that the device 34 may be formed on the second group III nitride layer 12 without providing the third group III nitride layer 13. This is because: the second group III nitride layer 12 is 1×10 20 cm-3 The above concentration contains oxygen as an impurity, and thus exhibits high conductivity, thereby enabling the formation of high-quality devices.

[0181] It should be noted that the present application includes a solution formed by appropriately combining any of the various embodiments and / or examples described above, which can bring out the effects of each embodiment and / or example.

[0182] Industrial Applicability

[0183] The method for producing a group III nitride semiconductor according to the present invention can be applied to a method for producing a group III nitride semiconductor that requires a reduction in production cost.

Claims

1. A method for producing a group III nitride semiconductor, comprising the following steps: A process for preparing a group III nitride substrate having a first group III nitride layer and a second group III nitride layer sequentially stacked from the back side to the front side, wherein the first group III nitride layer has a transmittance of 60% or more at a predetermined wavelength of 400 nm to 700 nm, and the second group III nitride layer has a transmittance of 1×10 20 cm -3 The semiconductor layer contains oxygen as an impurity at a concentration of 0.1% or less and has a transmittance of 0.1% or less at the predetermined wavelength and is disposed on the first group III nitride layer; A step of forming a device structure on the surface side of the group III nitride substrate; and A process of focusing the laser light at a position forward of the first III-nitride layer from the back side of the III-nitride substrate relative to the second III-nitride layer, forming an internal modified layer in the first III-nitride layer by utilizing multi-photon absorption, and dividing the III-nitride substrate with the internal modified layer as a boundary.

2. The method for producing a Group III nitride semiconductor according to claim 1, wherein: The process of preparing the group III nitride substrate includes the following steps: The process of preparing a seed substrate; A step of performing crystal growth of the first group III nitride layer on the seed substrate; A step of separating the seed substrate; A step of mirror-finishing the surface of the first group III nitride layer by grinding and polishing; a step of performing crystal growth of the second group III nitride layer on the seed substrate by oxide vapor phase epitaxy; A step of separating the seed substrate; a step of grinding and polishing the surface of the second group III nitride layer; and The separated first group III nitride layer and the second group III nitride layer are bonded together.

3. The method for producing a Group III nitride semiconductor according to claim 2, wherein: The step of preparing the group III nitride substrate further comprises the following steps: A step of crystal-growing a third group III nitride layer having a transmittance of 60% or more with respect to the predetermined wavelength is performed on the second group III nitride layer.

4. The method for producing a Group III nitride semiconductor according to claim 1 or 2, wherein: The device structure includes functional layers, electrodes and insulating films.

5. The method for producing a Group III nitride semiconductor according to claim 1 or 2, wherein: The group III nitride substrate is formed of GaN.

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