A method for easily strippable large-area gallium nitride epitaxial growth

Abstract

The present invention discloses a large-area gallium nitride epitaxial growth method that is easy to peel off, which solves the problems of poor quality and difficult peeling of existing epitaxial gallium nitride. The present invention comprises the following steps: Step 1: Prepare Cu <111> Single crystal substrate; Step 2: Cu in step 1 <111> A graphene two-dimensional material layer is grown on a single crystal substrate; step 3: epitaxially grow a GaN film on the graphene two-dimensional material layer grown in step 2; step 4: cool the GaN film obtained in step 3 to room temperature to obtain a flat GaN film. The invention has the advantages of good quality of the generated GaN epitaxial film, low dislocation density, easy peeling, etc.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a large-area gallium nitride epitaxial growth method that is easy to peel off. Background Art

[0002] Gallium nitride (GaN) is a typical wide bandgap direct bandgap semiconductor with advantages such as high electron mobility, wide bandgap width, high breakdown field strength, high thermal conductivity, and stable physical and chemical properties. This makes gallium nitride semiconductors the preferred material for various electronic device applications, including high-frequency and high-power electronic devices such as light-emitting diodes, field-effect transistors, and Schottky diodes. However, the prerequisite for further research and development of gallium nitride devices is to synthesize gallium nitride materials with high crystal quality and low dislocation density. Due to the very large dissociation pressure of nitrogen and the melting point of gallium nitride reaching 2300°C, the use of the traditional melt method requires quite harsh growth conditions. Therefore, the current growth of gallium nitride mainly relies on heteroepitaxial growth, such as the use of molecular beam epitaxy or metal organic chemical vapor deposition methods, which can achieve epitaxial growth on substrates such as sapphire and single crystal silicon. However, during the heteroepitaxial process, gallium nitride and the substrate or buffer layer will produce a large lattice mismatch and thermal mismatch. The gallium nitride epitaxial layer on the heterogeneous substrate has a much higher dislocation density than homoepitaxial, which undoubtedly reduces the comprehensive performance of heteroepitaxial devices. Therefore, in response to the above problems, those skilled in the art have proposed a method for self-supporting gallium nitride substrates. Self-supporting gallium nitride substrates are an effective way to reduce the defect density of the epitaxial layer and improve the quality of the epitaxial layer and the quality of electronic devices.

[0003] At present, laser lift-off technology has been applied to the preparation of gallium nitride self-supporting substrates. Its principle is to use high-power ultraviolet laser to irradiate the interface area between the gallium nitride epitaxial layer and the heterogeneous substrate. The high-energy ultraviolet laser can destroy the strong chemical bond between the substrate and the epitaxial layer at the interface. However, this method has many disadvantages: first, the cost of laser lift-off technology is relatively high, and the size of the stripped gallium nitride is limited, which is not conducive to large-scale promotion; second, the thermal stress introduced by the laser lift-off technology will produce a large number of defects at the interface, causing cracks in the gallium nitride substrate. In addition, the use of laser lift-off technology has certain requirements for the type of substrate. Due to the similar bandgap width of silicon carbide, gallium nitride substrate and epitaxial gallium nitride, it is not suitable to be separated using laser lift-off technology. Therefore, inventing a process that can achieve high-quality gallium nitride epitaxy and easy lift-off has immeasurable practical value for realizing the development of the entire gallium nitride industry.

[0004] Compared to laser lift-off, mechanical lift-off is a simpler technique in principle, requiring neither chemical treatment nor additional transfer equipment. However, mechanical lift-off of heteroepitaxial GaN using conventional methods still results in a large number of defects at the interface.

[0005] The above methods currently used in the industry to strip the epitaxial GaN from the substrate will cause a large number of interface defects, affecting the quality of the epitaxial layer and restricting the development of the GaN industry. Summary of the invention

[0006] The present invention aims to provide a large-area gallium nitride epitaxial growth method that is easy to peel off, so as to solve the problem that the existing epitaxial gallium nitride has poor quality and is not easy to peel off.

[0007] The present invention is achieved through the following technical solutions:

[0008] A method for easily strippable large-area gallium nitride epitaxial growth comprises the following steps:

[0009] Step 1: Prepare Cu <111> Single crystal substrate;

[0010] Step 2: Cu in step 1 <111> Growing a graphene two-dimensional material layer on a single crystal substrate;

[0011] Step 3: epitaxially growing a GaN film on the graphene two-dimensional material layer grown in step 2;

[0012] Step 4: Cool the GaN film obtained in step 3 to room temperature to obtain a flat GaN film.

[0013] The present invention takes into account that due to the lack of GaN homogeneous substrates, most gallium nitride-based devices are mainly prepared on substrates such as sapphire, silicon carbide, and silicon. However, due to the existence of lattice mismatch and thermal mismatch between the substrate and the epitaxial layer during heterogeneous epitaxy, the large residual biaxial stress generated will cause cracks or even fractures in the gallium nitride material, which affects the crystal quality of gallium nitride. In addition, the stripping of the gallium nitride film will also affect the quality of the final gallium nitride film. When the quality and stripping performance of gallium nitride are not good, it is not conducive to the subsequent device preparation. Therefore, it is key to obtain high-quality, low-defect, easy-to-strip gallium nitride.

[0014] Currently, the commonly used stripping technologies are laser stripping technology and mechanical stripping technology. The cost of laser stripping technology is relatively high, and the size of the stripped gallium nitride is limited, which is not conducive to large-scale promotion. Secondly, the thermal stress introduced by laser stripping technology will produce a large number of defects at the interface, causing cracks in the gallium nitride substrate, while the traditional mechanical stripping technology will still cause a large number of defects at the interface when stripping heteroepitaxial gallium nitride.

[0015] In order to solve the problems of GaN quality and stripping, the present invention designs an ideal intermediate material that is easy to strip and can produce a good epitaxial relationship with gallium nitride. Graphene is an ideal layer for mechanically releasing devices from the substrate. Graphene is a two-dimensional material with excellent parameters such as large theoretical specific surface area, ultra-high intrinsic carrier mobility, and high thermal conductivity. The carbon atoms in the graphene monolayer are sp2 hybridized to form a hexagonal honeycomb planar film, and the layers are connected by weak van der Waals forces. For this type of graphene layered material with a van der Waals structure, it can not only be used as an intermediate layer for growing gallium nitride epitaxy to improve the growth quality of the GaN film, but also help to strip the epitaxial layer from the substrate.

[0016] There are many advantages to using copper single crystal substrates with high ductility and high thermal conductivity to achieve epitaxial growth of GaN: first, copper single crystal substrates have no wafer size restrictions and can achieve ultra-large-area GaN epitaxy; second, copper single crystal substrates are low-cost and can effectively reduce the cost of growing GaN; third, copper single crystals can be removed by ferric chloride solution after the reaction, leaving a large area of ​​self-supporting GaN substrate. However, there are large lattice defects between copper single crystal substrates and GaN, and it is difficult to directly epitaxially grow high-quality GaN on copper single crystals. Therefore, using graphite as a buffer layer effectively solves the problem of large lattice mismatch between copper substrates and GaN.

[0017] During the research, the inventors of the present invention also considered the relationship between graphene and the different crystal orientations of the Cu single crystal substrate. Based on the structural characteristics of the Cu crystal surface, the order of the two-dimensional energy barriers from small to large is Cu <111> , Cu <110> , Cu <100> , so Cu <111> The surface two-dimensional energy barrier is the smallest, so Cu <111> The surface roughness decreases faster than Cu <100> Be quick, Cu <111> The surface is more conducive to the growth of graphene two-dimensional materials, so we choose <111> Cu single crystal as substrate.

[0018] The present invention first realizes the <111> Graphene two-dimensional material is grown on a copper single crystal in the direction of the sun, and then placed in a reaction chamber to grow a high-quality gallium nitride epitaxial layer that is easy to peel off.

[0019] The present invention preferably provides a large-area gallium nitride epitaxial growth method that is easy to peel off, and further includes step 5: removing Cu by chemical method <111> GaN epitaxial film is obtained on single crystal substrate.

[0020] The present invention firstly uses Cu single crystal to grow gallium nitride film, and then uses chemical method to remove Cu single crystal substrate, so as to obtain large-area self-supporting gallium nitride.

[0021] The present invention preferably provides a large-area gallium nitride epitaxial growth method that is easy to peel off. The specific method for growing the graphene two-dimensional material layer in step 2 is: using the CVD method, the growth temperature is set to 900°C to 1100°C, the pressure is set to 0.5 to 2Torr, and the growth time is 20min to 60min.

[0022] Preferably, the graphene two-dimensional material layer is a single layer.

[0023] The present invention uses a single-layer graphene as an intermediate layer. The single-layer graphene does not affect the epitaxial guiding effect of the copper substrate on gallium nitride. If multiple layers of graphene are used, the thick intermediate layer will block the guiding effect of the substrate and the gallium nitride epitaxy, resulting in a decrease in the epitaxial quality.

[0024] The present invention preferably provides a large-area gallium nitride epitaxial growth method that is easy to peel off. The specific method of epitaxially growing the GaN film in step 3 is: using a halide vapor phase epitaxial process, setting the growth temperature at 1020°C to 1080°C, setting the pressure at 550 to 800 Torr, and the growth time at 60 min to 180 min.

[0025] The present invention preferably provides a large-area gallium nitride epitaxial growth method that is easy to peel off, wherein the growth temperature in step 3 is set to 1020-1030° C., the pressure is set to 750-800 Torr, and V / III is set to 10-15.

[0026] In order to promote the two-dimensional growth of GaN, the present invention selects a low pressure for pressure control, and in order to promote the migration of Ga atoms, the V / III of the present invention is set to a suitable smaller value.

[0027] The present invention preferably provides a large-area gallium nitride epitaxial growth method that is easy to peel off, wherein the growth rate of the GaN film using the halide vapor phase epitaxial process in step 3 is 50 μm / h to 500 μm / h.

[0028] The present invention preferably provides a large-area gallium nitride epitaxial growth method that is easy to peel off, wherein the cooling time in step 4 is 30 minutes to 120 minutes, and the thickness of the GaN film ranges from 1 μm to 500 μm.

[0029] The method of the invention uses a halide vapor phase epitaxy process to grow gallium nitride on a copper substrate. The gallium nitride grows quickly and can be used to grow high-quality gallium nitride epitaxial films and gallium nitride substrates in various thickness ranges.

[0030] The present invention preferably provides a large-area gallium nitride epitaxial growth method that is easy to peel off, wherein the chemical method in step 5 removes Cu <111> The single crystal substrate is etched chemically, using a ferric chloride solution as a solvent, with a concentration ranging from 0.5 mol / L to 1 mol / L, and an etching time of 20 min to 60 min.

[0031] The present invention preferably provides a large-area gallium nitride epitaxial growth method that is easy to peel off, wherein the Cu <111> The thickness of the single crystal substrate is 5-25 μm.

[0032] The present invention selects Cu <111> The thickness of the single crystal substrate can adjust the rigidity and flexibility of the overall structure. Due to the flexibility and ductility of the copper substrate, the size can be adjusted within a reasonable range according to different needs.

[0033] The present invention has the following advantages and beneficial effects:

[0034] 1. The present invention selects Cu <111> As the substrate, first realize the large area <111> A layer of graphene two-dimensional material is grown on the copper single crystal, and a high-quality gallium nitride epitaxial layer is grown on the graphene two-dimensional material. It is possible to grow gallium nitride epitaxially on a large-area single crystal, that is, using a single layer of graphene as the intermediate layer, a high-quality gallium nitride film is directly obtained by a two-step growth method without the need for transfer, and the gallium nitride film is easy to peel off.

[0035] 2. The present invention mainly adopts the halide vapor phase epitaxy process to grow GaN film. This method has a fast growth rate (speed is 50-500μm / h), good repeatability, more economic advantages, is conducive to the large-scale production of gallium nitride, and can be used to make GaN-based high-power devices and flexible wearable devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0037] Figure 1 It is a flowchart of the preparation process of the present invention.

[0038] Figure 2 This is a schematic diagram of the structure of the product prepared by the present invention.

[0039] Figure 3 This is the XRD spectrum of the GaN film prepared in Example 2 of the present invention.

[0040] Figure 4 This is an AFM height image of the GaN film prepared in Example 2 of the present invention.

[0041] Figure 5 This is an AFM amplitude image of the GaN film prepared in Example 2 of the present invention.

[0042] Figure 6 This is the AFM phase image of the GaN film prepared in Example 2 of the present invention.

[0043] Figure 7This is a cathode fluorescence dislocation density test chart of the GaN film after stripping prepared in Example 2 of the present invention.

[0044] Figure 8 This is a SEM image of the GaN film before peeling off in Example 2 of the present invention.

[0045] Fig. 9 This is a SEM image of the GaN film prepared in Example 2 of the present invention after peeling off.

[0046] Fig.10 This is a Raman spectrum of the single-layer graphene prepared in Example 2 of the present invention.

[0047] Structure names in the attached pictures:

[0048] 1-Cu <111> Single crystal substrate, 2-graphene two-dimensional material layer, 3-GaN film. DETAILED DESCRIPTION

[0049] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0050] Example 1

[0051] A method for easily strippable large-area gallium nitride epitaxial growth comprises the following steps:

[0052] Step 1: Providing a Cu(111) single crystal substrate 1

[0053] The Cu single crystal substrate 1 has a thickness of 10 μm and a size of 1 cm*1 cm.

[0054] Step 2: growing a graphene two-dimensional material layer 2 on the Cu (111) single crystal substrate of step 1;

[0055] Using chemical vapor deposition (CVD) method, the copper substrate was first annealed at 900°C for 1h under 50sccm hydrogen background, and then reacted at 900°C with a gas flux of 30sccm methane and 10sccm hydrogen. The growth temperature was set at 900°C, the pressure was set at 0.5Torr, and the growth time was 20min.

[0056] Step 3: epitaxially growing a GaN film 3 on the graphene two-dimensional material layer 2 grown in step 2;

[0057] A halide vapor phase epitaxy process was used, the growth temperature was set at 1020°C, the background atmosphere was high-purity nitrogen, the pressure in the chamber was maintained at 770 Torr, the V / III ratio was set to 10, the growth time was 60 min, and the HCl flow rate was 60 sccm.

[0058] In the specific implementation of the present invention, the inlet and outlet are designed in an outer tube inner tube structure. Different inner tubes transport different types of reaction gases, and the outlet is designed near the reaction zone. The biggest advantage of this is that it can reduce the spontaneous reaction consumption during the gas flow transportation process and ensure the maximum utilization rate of the reaction raw materials.

[0059] Step 4: Cool the GaN film obtained in step 3 to room temperature to obtain a flat GaN film.

[0060] The cooling time is 60 minutes, the background gas introduced during the cooling process is nitrogen, and the thickness of the epitaxial gallium nitride is in the range of 50 μm.

[0061] Step 5: Remove the Cu(111) single crystal substrate by chemical method to obtain GaN epitaxial film.

[0062] The specific chemical method is: using ferric chloride solution as the processing solvent with a concentration of 0.5 mol / L, the etching time is set at 60 minutes, and after the copper foil is etched, a high-quality GaN epitaxial film with a size of 1 cm*1 cm is obtained.

[0063] Example 2

[0064] The difference between this embodiment and embodiment 1 is that:

[0065] The copper single crystal substrate used in step 1 has a thickness of 25 μm and a size of 5 cm*5 cm.

[0066] In step 2, a graphene two-dimensional material layer 2 is grown on a copper single crystal substrate using a CVD process, with a growth temperature set at 1100° C., a pressure set at 2 Torr, and a growth time of 60 min.

[0067] The high-quality GaN film is epitaxially grown in step 3 using the HVPE process. The growth temperature is set at 1030°C, the background atmosphere is high-purity nitrogen, the pressure in the chamber is maintained at 760 Torr, the V / III ratio is set to 15, and the growth time is 120 minutes.

[0068] The cooling time in step 4 is 120 minutes, and the background gas introduced during the cooling process is nitrogen. The thickness of the epitaxial GaN film is in the range of 100 μm.

[0069] The copper single crystal substrate is removed by the chemical method described in step 5. The concentration of the ferric chloride solution used is 1 mol / L, and the etching time is set at 20 min. After the copper foil is etched, a high-quality GaN epitaxial film with a size of 5 cm*5 cm is obtained.

[0070] The GaN film obtained in Example 2 was subjected to XRD detection, AFM atomic force microscopy detection and cathode fluorescence dislocation density test. The test results are as follows: Figure 3-Figure 7 shown.

[0071] Among them, from Figure 3 It can be seen from the XRD spectrum that the synthesized gallium nitride is oriented along the c-plane with high quality, has good orientation, and has high strength, indicating that the film has high quality and good crystallinity.

[0072] Figure 4-Figure 6 The AFM morphology and size of the GaN epitaxial film surface are given. According to image analysis, the roughness of the sample surface is less than 2nm.

[0073] And from Figure 7 The dislocation density test results of the cathode fluorescence of the stripped GaN epitaxial film show that the dislocation density of the GaN epitaxial film is low, which is 3.6×10 6 / cm 2 , with much lower dislocation density than existing heteroepitaxial methods, showing good crystal quality.

[0074] The GaN film prepared in Example 2 was characterized by SEM before and after peeling. Figure 8 and Fig. 9 As shown, it can be seen that the quality of the GaN film prepared by the present invention is very good both before and after stripping, showing good stripping properties.

[0075] In the present invention, the single-layer graphene is very important. The single-layer graphene of this embodiment is tested by Raman spectroscopy. Fig.10 As shown, it can be seen that graphene is in a single-layer state.

[0076] Example 3

[0077] The difference between this embodiment and embodiment 2 is that the size of the Cu substrate is 6 cm*6 cm, and other growth processes remain unchanged.

[0078] The difference also lies in the step 5, in which the specific method of stripping the GaN epitaxial film adopts mechanical stripping. The GaN film grown by the present invention can be stripped with a force of 50-100N. The specific operation is to directly use wide-mouth tweezers to gently push along the horizontal plane. Due to the effect of the two-dimensional material buffer layer, the epitaxial wafer can be directly stripped from the substrate, and the quality of the GaN epitaxial film after stripping is good.

[0079] Example 4

[0080] The difference between this embodiment and the first embodiment is that the crystal plane of the Cu single crystal substrate 1 is (100), and the GaN film generated thereby has poor uniformity and large roughness.

[0081] Example 5

[0082] like Figure 2 As shown, this embodiment provides a Cu / graphene / GaN structure obtained by the above method, which includes Cu <111> Single crystal substrate 1, graphene two-dimensional material layer 2, GaN film 3.

[0083] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for easily strippable large-area gallium nitride epitaxial growth, characterized in that: The steps include: Step 1: Prepare Cu <111> Single crystal substrate (1); Step 2: Cu in step 1 <111> Growing a graphene two-dimensional material layer (2) on a single crystal substrate (1); Step 3: epitaxially growing a GaN film (3) on the graphene two-dimensional material layer (2) grown in step 2; Step 4: Cool the GaN film obtained in step 3 to room temperature to obtain a flat GaN film.

2. The method for easily strippable large-area GaN epitaxial growth according to claim 1, characterized in that: Also includes step 5: removing Cu by chemical methods <111> GaN epitaxial film is obtained on single crystal substrate.

3. A method for easily strippable large-area gallium nitride epitaxial growth according to claim 1 or 2, characterized in that: The specific method for growing the graphene two-dimensional material layer (2) in step 2 is: using the CVD method, setting the growth temperature to 900° C. to 1100° C., setting the pressure to 0.5 to 2 Torr, and the growth time to 20 min to 60 min.

4. The method for easily strippable large-area GaN epitaxial growth according to claim 1 or 2, characterized in that: The graphene two-dimensional material layer (2) is a single layer.

5. The method for easily strippable large-area gallium nitride epitaxial growth according to claim 1 or 2, characterized in that: The specific method of epitaxially growing the GaN film (3) in step 3 is: using a halide vapor phase epitaxy process, setting the growth temperature at 1020° C. to 1080° C., setting the pressure at 550 to 800 Torr, and the growth time at 60 min to 180 min.

6. The method for easily strippable large-area GaN epitaxial growth according to claim 5, characterized in that: The growth temperature in step 3 is set to 1020-1030° C., the pressure is set to 750-800 Torr, and V / III is set to 10-15.

7. The method for easily strippable large-area GaN epitaxial growth according to claim 5, characterized in that: In the step 3, the growth rate of the GaN film (3) using the halide vapor phase epitaxy process is 50 μm / h to 500 μm / h.

8. The method for easily strippable large-area gallium nitride epitaxial growth according to claim 1 or 2, characterized in that: The cooling time in step 4 is 30 min to 120 min, and the thickness of the GaN film is in the range of 1 μm to 500 μm.

9. The method for easily strippable large-area GaN epitaxial growth according to claim 2, characterized in that: The chemical method in step 5 removes Cu <111> The single crystal substrate is etched chemically, using a ferric chloride solution as a solvent, with a concentration ranging from 0.5 mol / L to 1 mol / L, and an etching time of 20 min to 60 min.

10. The method for easily strippable large-area GaN epitaxial growth according to claim 1 or 2, characterized in that: The Cu <111> The thickness of the single crystal substrate is 5-25 μm.

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