A method for preparing a self-supporting GaN single crystal substrate on a sapphire substrate

Abstract

The present invention belongs to the technical field of semiconductor optoelectronic material preparation, and relates to a method for preparing a self-supporting GaN single crystal substrate on a sapphire substrate. Before growing GaN on the sapphire substrate, the sapphire substrate is nitrided by a hydride vapor phase epitaxy system to form a high-density AlN x O 1‑x Then, GaN nanocolumns, low-temperature GaN buffer layers, and high-temperature GaN layers are formed on the sapphire substrate, and finally a GaN single crystal substrate is obtained. x O 1‑x The protrusion can reduce the formation energy of GaN on the sapphire substrate, facilitating the epitaxial growth of GaN. The low-temperature GaN buffer layer can relieve the stress caused by the lattice mismatch between the sapphire substrate and GaN, and can avoid the occurrence of cracks.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor photoelectric material preparation, and relates to a method for preparing a self-supporting GaN single crystal substrate on a sapphire substrate. Background Art

[0002] Compared with the first-generation semiconductor materials represented by Si and the second-generation semiconductor materials represented by GaAs, the third-generation semiconductor materials represented by GaN and other III-V nitrides have higher breakdown field strength, electron saturation rate, thermal conductivity and wider band gap, and are more suitable for the preparation of high-frequency, high-power, radiation-resistant and corrosion-resistant electronic devices, optoelectronic devices and light-emitting devices.

[0003] Due to the difficulty in preparing bulk GaN materials, it is difficult to obtain large-size, high-quality bulk GaN single crystal substrates, so GaN single crystal substrates are still relatively scarce. At present, the epitaxial growth of GaN is still mainly based on heteroepitaxial growth represented by sapphire and GaAs substrates. However, due to the large lattice constant mismatch and thermal expansion coefficient mismatch between the heterogeneous substrate and GaN, heteroepitaxial growth using GaN epitaxial growth technologies such as hydride vapor phase epitaxy (HVPE), metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) will cause strong stress in the epitaxial layer, leading to the appearance of defects such as cracks, affecting the crystal quality of the epitaxial material, deteriorating the relevant performance of the device, and restricting the development of GaN related fields. The use of porous / loose GaN layers can alleviate the stress caused by the lattice mismatch between the heterogeneous substrate and the GaN epitaxial layer during heteroepitaxial growth and avoid the generation of cracks.

[0004] The porous / loose GaN substrates currently used are all obtained by reprocessing after MOCVD epitaxial growth on heterogeneous substrates, which has a long cycle and low efficiency, restricting the market development of single crystal substrates obtained by HVPE growth. Therefore, how to more simply and efficiently form porous / loose GaN layers on heterogeneous substrates such as sapphire and directly prepare self-supporting GaN single crystal substrates has become an urgent problem to be solved in the preparation of GaN single crystals. Summary of the invention

[0005] In view of the problems existing in the existing GaN single crystal substrate preparation technology, the present invention provides a novel method for preparing a self-supporting GaN single crystal substrate on a sapphire substrate. The self-supporting GaN single crystal substrate is directly obtained on the sapphire substrate through HVPE, which overcomes the problem of multiple furnace loading due to additional processing in the sapphire epitaxial growth GaN substrate process, can save time and improve production efficiency.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A method for preparing a self-supporting GaN single crystal substrate on a sapphire substrate, comprising the following steps:

[0008] Step S1: Raise the temperature of the sapphire substrate to 1080 °C using a hydride vapor phase epitaxy system, and introduce NH3 for nitridation to form AlN x O 1-x (0 < x ≤ 1) protrusions, the growth atmosphere is N2 atmosphere, and the growth pressure is atmospheric pressure;

[0009] Step S2: After nitridation is completed, lower the temperature of the sapphire substrate to 850 °C, introduce GaCl and NH3 for three-dimensional vertical growth of GaN to obtain a GaN nanocolumn layer, the growth atmosphere is N2 atmosphere, and the growth pressure is atmospheric pressure;

[0010] Step S3: Stop introducing GaCl and NH3, introduce HCl to etch the GaN grown in Step S2 and the sapphire substrate to form an etched GaN nanocolumn layer on the sapphire substrate;

[0011] Step S4: Raise the temperature of the sapphire substrate to 850 - 950 °C, and introduce GaCl and NH3 again to form a low-temperature GaN buffer layer on the sapphire substrate;

[0012] Step S5: Continue to raise the temperature of the sapphire substrate to 1030 - 1050 °C, and grow a high-temperature GaN layer on the low-temperature GaN buffer layer, the growth atmosphere is N2 atmosphere, and the growth pressure is atmospheric pressure;

[0013] Step S6: Laser lift-off to remove the sapphire substrate, remove the low-temperature GaN buffer layer and the GaN nanocolumn layer, and the obtained high-temperature GaN layer is the self-supporting GaN single crystal substrate.

[0014] In Step S1, the sapphire substrate is nitrided with NH3 at 1080 °C to form AlN x O 1-x The purpose of the protrusions is to reduce the formation energy of GaN on the sapphire surface and facilitate the subsequent formation and growth of GaN.

[0015] Preferably, in Step S1, the nitridation time of the sapphire is 30 minutes, and the NH3 flow rate is 1500 sccm.

[0016] Preferably, in Step S1, the AlN x O 1-x The density of the protrusions on the sapphire substrate is (2 - 4) × 10 9 cm -2 , and the diameter of the AlN x O 1-x protrusions is 150 - 250 nm.

[0017] Preferably, in step S2, the three-dimensional longitudinal growth of GaN is controlled by adjusting the flow rates of GaCl and NH3 to form GaN columns on the surface of the sapphire substrate, thereby obtaining a GaN nanocolumn layer; GaCl is generated by the reaction of HCl with Ga in a Ga boat, the HCl flow rate is 40-60sccm, the NH3 flow rate is 1200-1600sccm, and the total V / III is 30-60; the growth time is 5-10min.

[0018] Preferably, in step S2, the GaN nanocolumn layer has a thickness of 300-600 nm.

[0019] In step S3, the introduction of GaCl and NH3 is stopped, and HCl is introduced through other pipelines to separate some of the GaN columns that are adhered and contacted, and the grown GaN and the sapphire substrate are etched to obtain GaN nanocolumns uniformly dispersed on the sapphire substrate. The GaN nanocolumns on the sapphire substrate constitute the etched GaN nanocolumn layer.

[0020] Preferably, in step S3, the HCl flow rate is 30 sccm, and the HCl introduction time is 5 minutes.

[0021] Preferably, in step S4, the temperature of the sapphire substrate is 850-950°C, and the lateral growth of GaN is promoted by adjusting the flow rates of GaCl and NH3 at this relatively low temperature, and a flat low-temperature GaN buffer layer is formed on the GaN nanocolumns, and the low-temperature GaN buffer layer serves as an epitaxial base layer for the high-temperature GaN layer. The loose GaN nanocolumns under the low-temperature GaN buffer layer can relieve the stress caused by the lattice mismatch between the GaN layer and the sapphire substrate; GaCl is generated by the reaction of HCl with Ga in the Ga boat, the HCl flow rate is 50-70sccm, the NH3 flow rate is 1300-1500sccm, and the growth time is 15-25 minutes.

[0022] Preferably, in step S4, the thickness of the low-temperature GaN buffer layer is 30-50 μm.

[0023] Preferably, in the growth of high-temperature GaN in step S5, the temperature is 1035-1050°C, GaCl is generated by the reaction of HCl and Ga in the Ga boat, the HCl flow rate is 40-60sccm, the NH3 flow rate is 800-1200sccm, the growth time is 4-6h, and the thickness of the high-temperature GaN layer is 400-600μm; compared with the growth of the low-temperature GaN buffer layer, the temperature is increased, the GaCl (Ga boat pipeline HCl) and NH3 flow rates are both reduced, and the total V / III is reduced.

[0024] In step S6, the GaN nanocolumns between the sapphire substrate and the low-temperature GaN buffer layer are decomposed by laser lift-off, thereby achieving the effect of separating the sapphire substrate.

[0025] Preferably, in step S6, the low-temperature GaN buffer layer and the GaN nanocolumn layer are removed by grinding, thinning or cutting to complete the preparation of the self-supporting GaN single crystal substrate.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] (1) In the method of the present invention, before growing GaN on the sapphire substrate, the sapphire substrate is nitrided by a hydride vapor phase epitaxy system to form a high-density AlN x O 1-x The protrusions can reduce the formation energy of GaN on the sapphire substrate and facilitate the epitaxial growth of GaN.

[0028] (2) In the method of the present invention, GaN nanocolumns and a low-temperature GaN buffer layer are formed on a sapphire substrate, thereby alleviating the stress caused by the lattice mismatch between the sapphire substrate and GaN, avoiding the occurrence of cracks, and obtaining a complete crack-free self-supporting GaN substrate.

[0029] (3) In the method of the present invention, all growth steps involving chemical reactions are completed in a hydride vapor phase epitaxy system, which can avoid multiple furnace loading, save time, and improve efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the process of preparing a self-supporting GaN single crystal substrate on a sapphire substrate according to the present invention;

[0031] Figure 2 This is a schematic diagram of the layered structure of a self-supporting GaN single crystal substrate prepared on a sapphire substrate of the present invention;

[0032] Among them: 1. Sapphire substrate; 2. AlN x O 1-x protrusion; 3.GaN nanocolumn layer; 4.Low-temperature GaN buffer layer; 5.High-temperature GaN layer;

[0033] Figure 3 This is a microscopic picture of a crack-free self-supporting GaN substrate in Example 1;

[0034] Figure 4 This is a microscopic picture of a crack-free self-supporting GaN single crystal substrate in Example 2;

[0035] Figure 5 This is an appearance diagram of the GaN substrate obtained in Comparative Example 1;

[0036] Figure 6 This is an appearance diagram of the GaN substrate obtained in Comparative Example 2;

[0037] Figure 7This is an appearance diagram of the GaN substrate obtained in Comparative Example 3;

[0038] Figure 8 This is the appearance of the GaN substrate obtained in Comparative Example 4. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, the embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0040] Example 1

[0041] A method for preparing a self-supporting GaN single crystal substrate on a sapphire substrate comprises the following steps:

[0042] Step S1. The temperature of the sapphire substrate is raised to 1080°C by using a conventional hydride vapor phase epitaxy system, and 1500 sccm of NH3 is introduced to nitride the sapphire substrate 1 for 30 min to form a 200 nm, 3×10 9 cm -2 High density AlN x O 1-x For protrusion 2, the growth atmosphere is N2 atmosphere and the growth pressure is atmospheric pressure.

[0043] Step S2. Epitaxially grow a GaN nanocolumn layer 3 with a thickness of 400 nm on the nitrided sapphire substrate, supply HCl to the gallium boat to provide a gallium source, the growth temperature is 850°C, the growth atmosphere is N2 atmosphere, the carrier gas is N2, and the growth pressure is atmospheric pressure. During the growth process, the NH3 flow rate is 1600sccm, the HCl flow rate is 50sccm, the total V / III is 32, and the growth time is 5 minutes

[0044] Step S3. After the GaN nanocolumn layer 3 is grown, the NH3 and HCl in the gallium boat pipeline are turned off, and HCl is introduced into other pipelines to etch the GaN nanocolumn layer 3 and the sapphire substrate 1. The HCl flow rate is 30 sccm, and the HCl introduction time is 5 minutes.

[0045] Step S4. Stop the supply of HCl in other pipelines, introduce NH3 and HCl in the Ga boat pipeline, and grow a 30 μm thick low-temperature GaN buffer layer 4 on the etched GaN nanocolumn layer 3 at a growth temperature of 900° C. During the growth process, the NH3 flow rate is 1400 sccm, the HCl flow rate is 60 sccm, and the growth time is 20 minutes.

[0046] Step S5. A high-temperature GaN layer 5 with a thickness of 500 μm is grown on the low-temperature GaN buffer layer 4. The growth atmosphere is N2 atmosphere, the N source is NH3, the Ga source is GaCl generated by the reaction of HCl and Ga, the growth temperature is 1050°C, the growth pressure is atmospheric pressure, the NH3 flow rate is 1100 sccm, the HCl flow rate is 55 sccm, and the growth time is 4 hours.

[0047] Step S6. Use laser lift-off to separate GaN from the sapphire substrate 1, and use a grinding and polishing device to remove the GaN nanocolumn layer 3 and the low-temperature GaN buffer layer 4 to prepare a high-temperature GaN layer 5, that is, a crack-free self-supporting GaN single crystal substrate. Figure 3 As shown, a microscopic picture of a crack-free self-supporting GaN substrate has a smooth native growth surface and no pits or microcracks.

[0048] Example 2

[0049] The difference between Example 2 and Example 1 is that the thickness of the low-temperature GaN buffer layer 4 is 50 μm, the NH3 flow rate is 1500 sccm, the HCl flow rate is 55 sccm, and the growth time is 25 minutes; the thickness of the high-temperature GaN layer 5 is 600 μm, the NH3 flow rate is 1200 sccm, the HCl flow rate is 50 sccm, and the growth time is 4.5 hours. The sapphire substrate, the GaN nanocolumn layer and the low-temperature GaN buffer layer are directly removed by single-wire cutting to prepare a crack-free self-supporting GaN single crystal substrate. The obtained substrate micrograph is shown in FIG. Figure 4 As shown. The thicker the low-temperature GaN buffer layer, the less stress the subsequently grown high-temperature GaN layer will have. The thickness of the low-temperature GaN buffer layer and the high-temperature GaN layer can be adjusted according to the process; the subsequent removal of the sapphire substrate, GaN nanocolumns and the low-temperature GaN buffer layer can be adjusted accordingly according to the equipment conditions and process, thereby obtaining a crack-free self-supporting GaN single crystal substrate.

[0050] Comparative Example 1

[0051] When GaN is grown directly on a sapphire substrate at 1050°C, in a N2 atmosphere, with N2 as the carrier gas and atmospheric pressure, the quality of the GaN grown is poor. Figure 5 As shown, there are a large number of pit defects and dense cracks. After laser lift-off, it is impossible to obtain a complete high-quality self-supporting GaN substrate. During the growth process, the NH3 flow rate is 1200sccm, the HCl flow rate is 50sccm, and the growth time is 5h.

[0052] The present invention first forms a high-density AlN by nitriding the sapphire substrate x O 1-xThe protrusions reduce the formation energy of GaN and serve as epitaxial points for GaN nanocolumns. The GaN nanocolumn layer is formed by the longitudinal growth of GaN and the etching of HCl. As an intermediate medium, it reduces dislocations on the one hand and relieves the stress caused by the lattice mismatch of the sapphire substrate on the other hand. The defects are further reduced by merging the lateral epitaxial growth on the GaN nanocolumns to form a low-temperature GaN buffer layer, release stress, and obtain a high-quality self-supporting GaN single crystal substrate.

[0053] Comparative Example 2

[0054] Compared with Example 1, the difference is that the temperature for preparing the low-temperature GaN buffer layer is 800°C. Figure 6 As shown, the high-temperature GaN layer finally obtained has no cracks caused by stress, but has dense pits, darker color, and poorer quality, and it is impossible to obtain a high-quality self-supporting GaN single crystal substrate.

[0055] Comparative Example 3

[0056] Compared with Example 2, the difference is that the temperature for preparing the low-temperature GaN buffer layer is 1000°C. Figure 7 As shown, the obtained high-temperature GaN layer is bright in color and has a smooth surface, but has large internal stress and dense cracks, making it impossible to obtain a high-quality self-supporting GaN single crystal substrate.

[0057] Comparative Example 4

[0058] Compared with Example 1, the difference lies in the growth time of the low-temperature GaN buffer layer, that is, the thickness of the low-temperature GaN buffer layer. The growth time is 1.5h. Figure 8 As shown, the obtained low-temperature GaN buffer layer is thick enough, the stress is fully released, and the high-temperature GaN layer has no cracks (cracks); however, because the low-temperature GaN buffer layer is too thick, the pits in the low-temperature mode will extend to the high-temperature GaN layer, appearing as densely distributed pits.

Claims

1. A method for preparing a self-supporting GaN single crystal substrate on a sapphire substrate, characterized in that: The following steps are involved: Step S1: Use a hydride vapor phase epitaxy system to raise the temperature of the sapphire substrate to 1080 °C, and introduce NH3 for nitridation to form AlN x O 1−x protrusions, where 0 < x ≤ 1, the growth atmosphere is an N2 atmosphere, and the growth pressure is atmospheric pressure; Step S2: After the nitridation is completed, the temperature of the sapphire substrate is lowered to 850°C, and GaCl and NH3 are introduced to perform three-dimensional longitudinal growth of GaN to form a GaN nanocolumn layer on the surface of the sapphire substrate. The growth atmosphere is N2 atmosphere and the growth pressure is atmospheric pressure. Step S3: Stop passing GaCl and NH3, and pass HCl to etch the GaN grown in step S2 and the sapphire substrate, so as to obtain an etched GaN nanocolumn layer on the sapphire substrate; Step S4: raising the temperature of the sapphire substrate to 850-950° C., introducing GaCl and NH 3 again, and forming a low-temperature GaN buffer layer on the sapphire substrate; Step S5: the temperature of the sapphire substrate is further increased to 1030-1050° C., the flow rates of GaCl and NH 3 are reduced, and a high-temperature GaN layer is grown on the low-temperature GaN buffer layer, the growth atmosphere is N 2 atmosphere, and the growth pressure is atmospheric pressure; Step S6: removing the sapphire substrate by laser stripping, removing the low-temperature GaN buffer layer and the GaN nanocolumn layer, and obtaining a high-temperature GaN layer, which is a self-supporting GaN single crystal substrate.

2. The method according to claim 1, characterized in that In step S1, the nitridation time of sapphire is 30 minutes, and the NH3 flow rate is 1500 sccm.

3. The method according to claim 1, characterized in that In step S1, AlN x O 1−x The density of the protrusions on the sapphire substrate is (2~4)×10 9 cm −2 , AlN x O 1−x The diameter of the protrusions is 150-250 nm.

4. The method according to claim 1, characterized in that In the step S2, the three-dimensional longitudinal growth of GaN is controlled by adjusting the flow rates of GaCl and NH3 to form GaN columns on the surface of the sapphire substrate. GaCl is generated by the reaction of HCl with Ga in the Ga boat. The HCl flow rate is 40-60 sccm, the NH3 flow rate is 1200-1600 sccm, and the total V / III is 30-60. The growth time is 5-10 min.

5. The method according to claim 1, characterized in that In the step S2, the thickness of the GaN nanocolumn layer is 300-600 nm; in the step S3, the HCl flow rate is 30 sccm, and the HCl introduction time is 5 minutes.

6. The method according to claim 1, characterized in that In the step S4, GaCl is generated by the reaction of HCl with Ga in the Ga boat, the HCl flow rate is 50-70 sccm, the NH3 flow rate is 1300-1500 sccm, and the growth time is 15-25 minutes.

7. The method according to claim 1, characterized in that In the step S4, the thickness of the low-temperature GaN buffer layer is 30-50 μm.

8. The method according to claim 1, characterized in that: In the step S5, GaCl is generated by the reaction of HCl with Ga in the Ga boat, the HCl flow rate is 40-60 sccm, the NH3 flow rate is 800-1200 sccm, and the growth time is 4-6 hours.

9. The method according to claim 1, characterized in that: In the step S5, the thickness of the high temperature GaN layer is 400-600 μm.

10. The method according to claim 1, characterized in that In the step S6, the low-temperature GaN buffer layer and the GaN nanocolumn layer are removed by grinding, thinning or cutting.

Images