A method for growing GaN thick films

Abstract

The present invention relates to a method for growing a GaN thick film, belonging to the technical field of optoelectronic power devices. The present invention is based on an AIXTRON MOCVD device, grows a GaN material of a certain thickness on one side of a double-polished sapphire substrate, and then grows a GaN material of the same thickness on the other side of the double-polished sapphire substrate. The GaN thickness on both sides of the sapphire substrate is the same, thereby achieving the purpose of reducing thermal expansion, reducing warpage and reducing stress, thereby growing a flat GaN thick film, solving the problem that heteroepitaxial thick films cannot be grown due to high stress, providing a thick film for the preparation of a GaN self-supporting substrate, and being applied to homoepitaxial power devices, blue lasers, etc., to meet the application needs of high-efficiency, new-type, high-power power electronics, optoelectronics and other fields.

Description

Technical Field

[0001] The present invention relates to a technology for preparing high-efficiency, high-power gallium nitride devices and blue lasers and other optoelectronic power devices using heteroepitaxial materials, and specifically to a method for growing GaN thick films, belonging to the technical field of optoelectronic power devices. Background Art

[0002] GaN materials are ideal for optoelectronic devices, particularly blue-green LEDs and LDs. These light sources offer broad applications and enormous market potential in high-density optical information storage, high-speed laser printing, full-color dynamic high-brightness displays, solid-state lighting, high-brightness signal detection, and communications. Furthermore, GaN semiconductor materials are ideal for high-temperature, high-frequency, and high-power devices. GaN, a representative nitride material, is a member of the III-V compound semiconductor family with an excellent wide-bandgap performance and is one of the world's most advanced semiconductor materials.

[0003] Due to the large difference in lattice matching and expansion coefficient between the nitride material and the substrate material, the stress in the epitaxially grown nitride is large, cracks are generated at the interface during growth, and as the thickness increases, the cracks will spread to the surface, thereby affecting the performance of the material. To reduce the stress in the growing nitride thick film, people have adopted the method of making a void structure on the heterogeneously grown GaN and then growing the nitride thick film to release the stress. There are also studies that use electrochemical corrosion to etch nano-scale micro-defect pits on GaN, and then grow GaN thick films through metal organic chemical vapor deposition to release heterojunction stress. However, the above effects are not obvious, and thicker GaN epitaxial layers cannot be grown because the stress is mainly generated at the heterojunction interface. In view of this, the present invention provides another method for growing GaN thick films. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention proposes a method for growing GaN thick films. Based on AIXTRON MOCVD equipment, the present invention grows a certain thickness of GaN material on one side of a double-polished sapphire substrate, and then grows the same thickness of GaN material on the other side of the same double-polished sapphire substrate. The GaN thickness on both sides of the sapphire substrate is the same, thereby achieving the purpose of reducing thermal expansion, reducing warping and reducing stress, thereby growing a flat GaN thick film, solving the problem that heteroepitaxial growth cannot grow thick films due to high stress, providing thick films for the preparation of GaN self-supporting substrates, and being applied to homoepitaxial power devices, blue light lasers, etc., to meet the application needs of high-efficiency new high-power power electronics, optoelectronics and other fields.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for growing a GaN thick film comprises the following steps:

[0007] (1) Prepare double-polished sapphire substrate and grow it using AIXTRON MOCVD;

[0008] (2) Place the double-polished sapphire substrate into the MOCVD reaction chamber and grow the buffer layer, rough layer, and recovery layer according to the conventional LED procedure. The growth rate conditions are the same as those for conventional LEDs.

[0009] (3) Then growing a uGaN layer, the growth rate of the uGaN layer is between 15um / h and 22um / h, and the growth thickness of the uGaN layer is 200um to 220um;

[0010] (4) After the uGaN growth on one side of the double-polished sapphire substrate is completed, the grown epitaxial wafer is taken out, and a tray that has been baked clean is replaced. The double-polished sapphire substrate is placed with the other side facing up and the side on which the GaN has grown facing the tray, and is placed into the replaced tray slot. The substrate is then re-transferred into the MOCVD reaction chamber and grown according to steps (2) and (3). Except for the uGaN layer, the growth conditions of other layers are the same as those of conventional mass-produced LEDs.

[0011] (5) Growth step: Repeat the conditions of steps (2) and (3). After the outermost uGaN layers on both sides of the double-polished sapphire substrate are grown, the GaN layers on both sides and the sapphire substrate are cut and separated using diamond wire to obtain two GaN thick films with the same thickness of 200um-220um. Figure 1 Then, place any 200um-220um GaN thick film after cutting on a clean tray after baking, with the side not cut by diamond wire facing up, and transfer it into the MOCVD reaction chamber to continue homogeneous growth of GaN. This time, the bottom buffer\rough\recovery layer will no longer be grown, and the uGaN layer will be directly grown. The growth rate is the same as step (3) at 20um / h-22um / h. A certain growth time is set, the growth time is 15h, and other growth conditions are the same as the previous stage, to obtain a GaN super thick film with a thickness of 500-520um. Since GaN material continues to grow on GaN material, it is homogeneous epitaxial growth. The stress and expansion during growth are very small, the interface is very smooth, and the crystal quality is very high. The two cut pieces can each be grown separately into a 500-520um GaN super thick film.

[0012] Preferably, in step (1), GaN is grown on both sides of a double-polished sapphire substrate with a 001 crystal orientation, and MOCVD is used to grow the GaN thick film.

[0013] In step (2), the growth rate and growth conditions of the buffer\rough\recovery bottom layer of the growth structure of the present invention are the same as those of conventional LEDs, and the subsequent uGaN growth rate is increased.

[0014] Preferably, in step (2), the growth material of the buffer layer is GaN / AlGaN, the growth material of the rough layer is GaN, and the growth material of the recovery layer is GaN.

[0015] Preferably, in step (3), the growth rate of the uGaN layer is set by one or a combination of the following methods:

[0016] a. The total amount of H2 / N2 in the reaction chamber remains unchanged, and the TMGa flow rate and NH3 flow rate are increased. The TMGa flow rate is 800-1400cc, and the NH3 flow rate is 8-12L;

[0017] b. Maintain the flow rates of TMGa and NH3 unchanged and increase the total amount of H2 / N2 in the reaction chamber to 100L-130L.

[0018] Further preferably, in step (3), the TMGa flow rate is 1200cc and the NH3 flow rate is 10L.

[0019] Further preferably, in step (3), the total amount of H2 / N2 is increased to 120L.

[0020] Preferably, in step (3), when the organic chemical vapor deposition method is adopted, the growth pressure is controlled between 50-100 mbar, the molar ratio of group V / group III is between 50-300, and the growth temperature is controlled between 1000-1100°C.

[0021] While keeping the total amount of H2 / N2 in the reaction chamber constant, increasing the TMGa flow rate from 200cc to 1200cc and the NH3 flow rate from 2L to 10L can increase the uGaN growth rate from the original 5um / h-6um / h to 12um / h-22um / h. Furthermore, adjusting the total amount of H2 in the reaction chamber can also increase the growth rate. That is, while keeping the TMGa and NH3 flows constant, increasing the total amount of H2 from 80L to 120L increases the uGaN growth rate from the original 5um / h-6um / h to 13um / h-18um / h. Combining these two methods, based on the mass-produced LED structure, increasing the TMGa flow rate from 200cc to 1000cc, the NH3 flow rate from 2L to 10L, and the total amount of H2 from 80L to 100L, the uGaN growth rate is increased from the original 5um / h-6um / h of mass-produced LEDs to 15um / h-22um / h. At the same time, the uGaN growth time for mass-produced LEDs was extended from 1h to 10h, and the uGaN growth thickness was increased from the original 2um-3um to 200um-220um.

[0022] In step (4), the sapphire substrate is no longer grown on a single side. Because a 200um GaN film is grown on a single side of the sapphire, the warpage of the entire epitaxial wafer reaches an astonishing 700um-800um. In this case, the epitaxial wafer is too severely curved and cannot be cut using diamond wire. The inventors also experimented with peeling using a wet etching method. Due to the large warpage and high stress, some GaN fragments broke after etching, and a whole GaN thick film could not be obtained. To address the problem of large warpage, the present invention grows GaN films of the same thickness on both sides, and the warpage of the entire epitaxial wafer is controlled at 80-100um. Such a warpage can meet the diamond wire cutting conditions and can achieve complete peeling of the GaN thick film.

[0023] In addition, the growth method of the present invention will not cause adverse effects on other processes, such as subsequent laser lift-off and other related processes.

[0024] Where the present invention is not exhaustive, existing technologies may be used.

[0025] The beneficial effects of the present invention are:

[0026] The present invention provides a method for growing a GaN thick film. The method uses MOCVD equipment to grow GaN thick films on both sides of a double-polished sapphire substrate. GaN thick films of equal thickness and growth rate are grown on both sides of the sapphire substrate. Since the GaN thick film is grown on one side, the significant difference in thermal expansion coefficients between sapphire and GaN leads to significant warpage of the epitaxial wafer. By growing the same GaN thick film on both sides of the sapphire substrate, the warpage and stress issues are resolved, achieving the goal of growing the GaN thick film. A flat GaN thick film with a thickness of 200-220 μm is obtained on one side, resolving the problem of heteroepitaxial thick film growth being unable to grow due to high stress. This method provides a thick film for the preparation of GaN self-supporting substrates. The unique feature of this growth method is that the GaN thick film is grown on both sides of the double-polished sapphire substrate. By using the same material, thermal expansion coefficient, and stress on both sides of the sapphire substrate, the epitaxial wafer warpage is minimized, providing favorable conditions for GaN thick film growth. By using this growth method, the heteroepitaxially grown GaN thick film is free of cracks, thus providing a thick film for the preparation of a GaN self-supporting substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a diagram of the physical composition of the GaN thick film of the present invention. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, the present invention is further described below through embodiments and in conjunction with the accompanying drawings, but is not limited thereto. Matters not fully described in the present invention are based on conventional techniques in the art.

[0029] Example 1:

[0030] A method for growing a GaN thick film, such as Figure 1 As shown, the following steps are included:

[0031] (1) GaN was grown using a 001 double-polished sapphire substrate in MOCVD.

[0032] (2) Place the double-polished sapphire substrate into the MOCVD reaction chamber and grow the buffer layer, rough layer, and recovery layer according to the conventional LED procedure. The growth material is GaN and the rate growth conditions are the same as those of conventional LEDs.

[0033] (3) Then, a uGaN layer is grown in an H2 environment. The TMGa flow rate is adjusted to 1000cc, the NH3 flow rate is adjusted to 10L, and the H2 flow rate is adjusted to 100L. The uGaN growth rate is 20um / h and the growth time is 10 hours. The GaN thick film epitaxial growth structure is shown in Table 1. Through the adjustment of step (3), the molar ratio of group V / group III in the uGaN growth layer is 150, TMGa is used as the group III source, and NH3 is used as the group V source.

[0034] (4) After the uGaN growth on one side of the double-polished sapphire substrate is completed, the grown epitaxial wafer is taken out, and the tray that has been baked clean is replaced. The sapphire substrate side of the epitaxial wafer with GaN grown on it is placed upwards and placed into the replaced tray slot, and then re-transferred into the MOCVD reaction chamber to grow according to steps (2) and (3). Except for the uGaN layer, the growth conditions of other layers are the same as those of conventional mass-produced LEDs.

[0035] (5) Growth step: Repeat the conditions of steps (2) and (3). After the outermost uGaN layers on both sides of the double-polished sapphire substrate are grown, the GaN layers on both sides and the sapphire substrate are cut and separated using diamond wire to obtain two GaN thick films of the same thickness. Figure 1 Then, place any piece of GaN thick film after cutting on a clean tray after baking, with the side not cut by diamond wire facing up, and transfer it into the MOCVD reaction chamber to continue homogeneous growth of GaN. This time, the bottom buffer\rough\recovery layer is no longer grown, and the uGaN layer is directly grown. The growth rate is the same as step (3), which is 20um / h, and the growth time is 15h. Other growth conditions are the same as the previous stage, and a GaN super thick film with a thickness of 500-520um is obtained.

[0036] Table 1 GaN thick film epitaxial growth structure of the present invention

[0037] layer Growth materials High-speed uGaN GaN recovery GaN rough GaN buffer GaN / AlGaN Double polished sapphire substrate Al2O3 buffer GaN / AlGaN rough GaN recovery GaN High-speed uGaN GaN

[0038] Example 2:

[0039] A method for growing a GaN thick film, as described in Example 1, except that:

[0040] In step (2), the buffer layer is grown using AlGaN;

[0041] In step (3), the uGaN growth environment is an N2 environment with a flow rate of 100 L; the TMGa flow rate is adjusted to 800 cc, the NH3 flow rate is adjusted to 10 L, and the N2 flow rate is adjusted to 100 L, resulting in a uGaN growth rate of 15 μm / h and a growth time of 15 hours; the molar ratio of group V / group III in the uGaN growth layer is 180.

[0042] Example 3:

[0043] A method for growing a GaN thick film is as described in Example 1, except that in step (3), the total amount of H2 / N2 in the reaction chamber remains unchanged, and the TMGa flow rate and NH3 flow rate are increased, the TMGa flow rate is 1400cc, and the NH3 flow rate is 8L.

[0044] Example 4:

[0045] A method for growing a GaN thick film is as described in Example 1, except that in step (3), the total amount of H2 / N2 in the reaction chamber remains unchanged, and the TMGa flow rate and NH3 flow rate are increased, the TMGa flow rate is 800cc, and the NH3 flow rate is 12L.

[0046] Example 5:

[0047] A method for growing a GaN thick film is as described in Example 1, except that in step (3), the total amount of H2 / N2 in the reaction chamber remains unchanged, and the TMGa flow rate and NH3 flow rate are increased, the TMGa flow rate is 1200cc, and the NH3 flow rate is 10L.

[0048] Example 6:

[0049] A method for growing a GaN thick film is as described in Example 1, except that in step (3), the flow rates of TMGa and NH3 are maintained unchanged, and the total amount of H2 / N2 in the reaction chamber is increased to 130L.

Claims

1. A method for growing a GaN thick film, characterized in that: The following steps are involved: (1) Prepare a double-polished sapphire substrate and grow it using MOCVD; (2) Place the double-polished sapphire substrate in the MOCVD reaction chamber and grow the buffer layer, roughening layer, and recovery layer according to the conventional LED procedure. The growth rate conditions are the same as those of conventional LEDs. The growth material of the buffer layer is GaN / AlGaN, the growth material of the roughening layer is GaN, and the growth material of the recovery layer is GaN. (3) Then, a uGaN layer is grown. The growth rate of the uGaN layer is 15 μm / h-22 μm / h, and the thickness of the uGaN layer is 200 μm-220 μm. The growth rate of the uGaN layer is set by one or a combination of the following methods: a. The total amount of H2 / N2 in the reaction chamber remains unchanged, and the TMGa flow rate and NH3 flow rate are increased. The TMGa flow rate is 800-1400cc, and the NH3 flow rate is 8-12L; b. Maintaining the flow rates of TMGa and NH3 unchanged, increase the total amount of H2 / N2 in the reaction chamber to 100L-130L; (4) After the uGaN growth on one side of the double-polished sapphire substrate is completed, the grown epitaxial wafer is taken out, and a tray that has been baked clean is replaced. The other side of the double-polished sapphire substrate is facing upwards, and the side on which the GaN has been grown is facing the tray. It is placed in the replaced tray slot and re-introduced into the MOCVD reaction chamber to continue growth according to steps (2) and (3); (5) Growth step: Repeat the conditions of steps (2) and (3). After the outermost uGaN layers on both sides of the double-polished sapphire substrate are grown, use diamond wire to cut and separate the GaN layers on both sides and the sapphire substrate to obtain two GaN thick films of the same thickness. Then, any one of the cut GaN thick films is placed on a clean tray after baking, with the side not cut by the diamond wire facing up, and is passed into the MOCVD reaction chamber to continue the homogeneous growth of GaN. This time, the bottom buffer layer, roughening layer, and recovery layer are no longer grown, and the uGaN layer is directly grown. The growth rate is the same as step (3). A certain growth time is set to obtain a GaN super thick film with a thickness of 500-520um.

2. The method for growing a GaN thick film according to claim 1, wherein: In step (1), GaN is grown on both sides of a double-polished sapphire substrate with a 001 surface, and MOCVD is used to grow the GaN thick film.

3. The method for growing a GaN thick film according to claim 1, wherein: In step (3), the TMGa flow rate is 1200cc and the NH3 flow rate is 10L.

4. The method for growing a GaN thick film according to claim 1, wherein: In step (3), the total amount of H2 / N2 is increased to 120L.

5. The method for growing a GaN thick film according to claim 1, wherein: In step (3), the growth pressure is controlled between 50-100 mbar, the molar ratio of group V / group III is between 50-300, and the growth temperature is controlled between 1000-1100°C.

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