A growth method for improving material quality of MOCVD growth and application thereof

Abstract

The application relates to the technical field of semiconductor epitaxial growth, in particular to a growth method for improving the material quality of MOCVD growth and application thereof. Before high-temperature H treatment of a substrate or before annealing and N treatment after high-temperature H treatment, a certain amount of third main group metal organic source is pre-passed, and the fifth main group gas or source reacting with the third main group metal organic source is prohibited from being passed, so that the substrate is pretreated, the effective surface immersion film is formed by high migration rate and low adhesion of atoms, the surface is pre-reconstructed, the non-uniform steps and damage of the substrate interface are improved, uncontrollable chaotic nucleation caused by high-temperature non-uniform thermal erosion of the ALN coating film is avoided, the nucleation crystal direction is relatively single and consistent, the subsequent pre-film diffusion structure is assisted, the buffer immersion and high-temperature resistance are improved, high-quality crystal nucleus is obtained through annealing, and the defect density of GaN single crystal material is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor epitaxial growth technology, specifically a growth method for improving the quality of MOCVD grown materials and its application. Background Technology

[0002] The buffer growth technology for GaN is one of the most crucial and challenging aspects of its epitaxial process. Due to the lack of homogeneous, low-cost, and large-size GaN single-crystal substrates, GaN devices are almost entirely grown on heterogeneous substrates (such as sapphire, SiC, and Si). The role of the buffer layer is to lay the foundation for subsequent high-quality GaN epitaxial layers on these "mismatched" substrates. Its core objective is to grow a GaN initiation layer with low dislocation density, flatness, and the required electrical properties (often high resistivity) on heterogeneous substrates with severe mismatches in lattice constant and thermal expansion coefficient.

[0003] Disadvantages of existing technology:

[0004] 1. Existing GaN epitaxial buffers are usually rapidly deposited on the surface of a substrate (such as sapphire) in a random and disordered manner under low temperature conditions (600~900℃) to form an amorphous or polycrystalline microcrystalline layer. This low-temperature nucleation layer cannot serve as a self-supporting structure for the subsequent formal growth of GaN materials. It is subsequently recrystallized by high-temperature annealing.

[0005] 2. Buffer annealing nucleation is based on the fact that crystal nuclei with a preferred orientation that matches the substrate (for the C-plane of sapphire, it is the direction of GaN) are more thermodynamically stable and resistant to high temperatures, while mismatched parasitic crystal nuclei are more likely to decompose, shrink or disappear under high temperature conditions.

[0006] 3. At low temperatures, the deposited atoms (Ga, N) have almost no long-range diffusion capability, the temperature tolerance of the grown buffer layer is poor, the annealing temperature is limited, the self-assembled ordered structure of the crystal nuclei after annealing is not ideal, and the furnace environment causes wide fluctuations in the defect density of batch epitaxial GaN materials.

[0007] 4. Interface steps and micro-mechanical damage from pattern etching or planar polishing can also affect the uniformity of buffer nucleation and stress-strain, leading to the formation of high-density penetrating dislocations, defect clusters, and microcracks. Summary of the Invention

[0008] The purpose of this invention is to provide a growth method and its application for improving the quality of MOCVD grown materials, thereby solving the problems mentioned in the background art. Before the high-temperature H-treatment of the substrate or before the N-treatment after annealing and cooling following the high-temperature H-treatment, a certain amount of a Group III metal-organic source is pre-passed through the substrate, while the introduction of a Group V gas or source that reacts with it is prohibited. This pretreatment of the substrate facilitates the formation of an effective surface-wetting film due to its high atomic mobility and low adhesion. Surface pre-reconstruction improves the non-uniform steps and damage at the substrate interface and the uncontrollable disordered nucleation caused by the non-uniform thermal erosion of the ALN coating at high temperatures. This makes the nucleation crystal orientation more consistent than a single crystal orientation, assisting in the subsequent pre-growth of the film diffusion structure, improving buffer wetting and high-temperature tolerance, and obtaining high-quality crystal nuclei after annealing to reduce the defect density of GaN single crystal materials.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0010] A growth method for improving the quality of MOCVD grown materials includes the following steps:

[0011] S1. Substrate pretreatment: The substrate is sent into the MOCVD reaction chamber and conventional substrate surface cleaning is completed.

[0012] S2. Metal film preparation: Before the high-temperature hydrogen annealing and cleaning repair treatment of the substrate, or after the high-temperature hydrogen annealing followed by annealing and before the nitriding treatment, a certain amount of group III metal organic source is pre-introduced into the reaction chamber. The introduction of group V gas or source that can react with group III metal is prohibited throughout the process, so that metal atoms can be fully spread and diffused on the substrate surface, completely covering all surface areas of the substrate, forming a uniform thin metal wetting film.

[0013] S3. Synergistic high-temperature treatment: Hydrogen gas is introduced to carry out high-temperature H-chemical synergistic surface treatment. The atomic migration characteristics of the metal wetting film under high temperature environment are utilized, and the decomposition atomic migration of the pre-set thin-layer epitaxial diffusion film is combined to repair the non-uniform steps and micro-mechanical damage on the substrate surface. At the same time, the non-uniform thermal erosion problem on the AlN vapor-deposited thin film surface is improved, and the pre-reconstruction of the substrate surface is completed.

[0014] S4. Buffer layer growth: A conventional low-temperature buffer layer is grown on the surface of the pre-reconstructed substrate.

[0015] Preferably, the metal source in step S2 is a Group 3 metal source, and in the GaN epitaxial system, the metal source includes one or more of TMAl, TEAl, SiH4, TMGa, and TMin.

[0016] Preferably, in step S2, a metal source is introduced simultaneously or sequentially before the high-temperature hydrogen ionization cleaning and repair treatment of the substrate, and the introduction of other sources or gases that react with it is prohibited. The growth temperature is 600-900℃ and the time is 5S-1min.

[0017] Preferably, in step S2, after the high-temperature hydrogen H-treatment followed by annealing and before the nitriding treatment, a metal source is introduced simultaneously or sequentially. It is prohibited to introduce group V gases or sources that react with it. The duration of the metal source introduction is 5s to 1min.

[0018] Preferably, in step S2, after the metal source is stopped, a post-diffusion film can be grown or an auxiliary diffusion film can be grown at intervals of 10s-1min.

[0019] Preferably, the auxiliary diffusion film is a diffused GaN layer, which is combined with the metal layer to form a metal film diffused GaN layer composite film structure. The growth conditions are 900-1000℃, and a Ga source or Ga source and other metal sources are introduced, wherein the Ga source <20slm, other metal sources <20slm, NH3 <10slm, and the time is 5-20s.

[0020] Preferably, the thickness of the auxiliary diffusion film is 2~15 nm.

[0021] Preferably, the thickness of the metal immersion film in step S2 is 1~5 nm.

[0022] The application of growth methods for improving the quality of MOCVD growth materials in epitaxial structures that enhance the uniformity of epitaxial buffer nucleation and improve the quality of the underlying crystals through high recrystallization temperatures.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0024] This invention utilizes a single Group 3 metal source to pre-pass a thin metal film wetting layer on the substrate surface before the formal growth of the buffer layer in epitaxial growth. This provides a surface environment with high atomic mobility and balanced surface tension in two dimensions for subsequent buffer growth. With the assistance of a thin film diffusion layer and high-temperature H-type synergistic surface treatment, a surface nucleation structure with high temperature tolerance is obtained. This allows the buffer to recrystallize under higher temperature baking conditions, thereby significantly improving the quality of the crystal nuclei. The balanced two-dimensional surface tension and affinity wetting surface make the crystal plane orientation of the crystal regions in the subsequent epitaxial growth of the nuclei more concentrated and reduce the interfacial energy of the merging and dissolution of different crystal regions, thus improving the crystal quality of the epitaxial layer.

[0025] Significantly improves crystal quality: The XRD 002 half-width of the epitaxial layer can be reduced by more than 12 arcsec, the penetration dislocation density is greatly reduced, and the defect clusters and microcracks in the epitaxial layer are effectively reduced.

[0026] Improve the temperature tolerance of the buffer layer: The substrate surface modified with metal wetting film can support the buffer layer to complete annealing and recrystallization at higher temperatures, greatly improving the crystal orientation consistency of the crystal nuclei and almost eliminating the parasitic crystal nuclei with random orientation.

[0027] Reduced batch performance fluctuations: The surface modification of single metal atom thin films has significantly improved the uniformity of epitaxial thickness between wafers, increased the warpage dispersion between wafers, and significantly improved the performance consistency of products from different batches.

[0028] Strong process compatibility: No hardware modification is required for existing MOCVD equipment; it can be achieved simply by adjusting the precursor feed timing. It can be directly adapted to the conventional process flow of existing production lines, resulting in extremely low promotion costs. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the invention and form part of the specification. In the drawings:

[0030] Figure 1 This is a schematic diagram of an epitaxial structure embodiment for improving the quality of MOCVD grown materials using the method of the present invention.

[0031] In the figure: 001, substrate; 002, AlN vapor-deposited thin film; 003, metal film; 004, buffer layer; 005, GaN 3D transition layer; 006, U-GaN recapping layer. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention pre-circulates a metal source before nitriding during buffer growth, prohibiting the introduction of group V reaction sources, thus allowing for sufficient diffusion coverage of the entire substrate surface. This metal film reconstructs the substrate surface, improving the uniformity of buffer layer growth affected by substrate surface and material lattice differences, and reducing internal defects caused by multi-directional unbalanced stretching surface tension. The pre-circulation of the metal film before nitriding, supplemented by a thin epitaxial film as the subsequent diffusion film structure, allows for the synergistic repair and high-temperature nucleation of single crystals by the decomposition and migration of atoms in the diffusion film and the partial migration of atoms in the metal film when the substrate surface is treated with high-temperature hydrogen. This provides high-quality crystallization centers for the buffer, improving its temperature tolerance, thereby obtaining a high-quality 3D crystal nucleus structure under higher temperature recrystallization conditions.

[0034] Example 1

[0035] After the substrate undergoes high-temperature H-treatment (high-temperature hydrogen purification and repair treatment) and before annealing and cooling and N-treatment (NH3 treatment), taking the GaN epitaxial system as an example, the annealing temperature of this system is not lower than 1050℃. At the same time or in sequence, a group III metal source is introduced. In the GaN epitaxial system, the group III metal source is one or more of TMAl, TEAl, SiH4, TMGa, and TMin. It is forbidden to introduce group V gas or metal source that reacts with it. During the subsequent cooling process, no metal source is introduced until the epitaxial growth begins and the reaction source is required. The duration is 5s-1min. Finally, a metal wetting film is formed on the substrate surface.

[0036] Example 2

[0037] Before the substrate hematization process, a metal source, which can be one or more group III metal sources, is introduced simultaneously or sequentially. The introduction of other metal sources or gases that react with the substrate is prohibited. The temperature is 600℃-900℃, and the time is 5 seconds to 1 minute. Other procedures are the same as in Example 1. A metal wetting film is ultimately formed on the substrate surface. Subsequently, high-temperature hematization is used to perform "atomic-level cleaning" and "surface reconstruction" on the substrate surface, laying the foundation for subsequent high-quality epitaxial growth. The high-temperature hematization temperature is above 1050℃, the H2 flow rate is not less than 300 L / min, and the time is 1 minute to 10 minutes.

[0038] Example 3

[0039] Based on Example 1 or Example 2, after the introduction of the group III metal source is stopped, a post-assisted diffusion film can be grown or an auxiliary diffusion film can be grown at intervals of 10s-1min. The growth conditions are 900℃-1000℃. A Ga source or Ga source and other metal sources are introduced, with Ga source <20slm, other metal sources <20slm, NH3 <10slm, and the time is 5s-20s; thus forming a metal film diffusion GaN layer composite film structure.

[0040] In Example 3, an auxiliary diffusion film and the metal film formed in Example 1 or Example 2 constitute a metal-film diffused GaN layer composite film structure. The auxiliary diffusion film, leveraging the high mobility of the metal film, achieves extremely uniform extension, allowing the subsequent GaN reactants to form a highly planar film structure. Then, high-quality crystal nuclei are generated under H2 high-temperature treatment conditions. After buffer growth and baking, the probability of nucleation at low-temperature unstable parasitic sites can be effectively reduced, thus lowering the defect density.

[0041] In Examples 1 to 3, a metal-wetting film is formed on the surface of the substrate. A conventional low-temperature buffer layer is then grown on the pre-reconstructed substrate surface. Subsequently, a GaN 3D transition layer and a U-GaN recapping layer are grown sequentially to complete the fabrication of a complete GaN epitaxial structure.

[0042] The table below shows X-ray diffraction (XRD) data, which mainly compares the diffraction peak positions (2θ angle, in degrees) of the experimental group and the reference group on specific crystal planes (002) and (102). The experimental group is a GaN LED structure with a thickness of micrometers grown under the process conditions of this application, and the reference group is an epitaxial structure that has not been improved by the method of this application.

[0043]

[0044] As can be seen from Table 1, the experimental group showed a decrease in the full width at half maximum (FWHM) of XRD 002, indicating that the crystal integrity of the epitaxial layer of this application was significantly improved and the dislocation density (especially screw dislocations / mixed dislocations that are sensitive to device leakage and breakdown characteristics) was effectively suppressed.

[0045] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A growth method for improving the quality of MOCVD grown materials, characterized in that: Includes the following steps: S1. Substrate pretreatment: The substrate is sent into the MOCVD reaction chamber and conventional substrate surface cleaning is completed. S2. Metal film preparation: Before the high-temperature hydrogen annealing and cleaning repair treatment of the substrate, or after the high-temperature hydrogen annealing followed by annealing and before the nitriding treatment, a certain amount of group III metal organic source is pre-introduced into the reaction chamber. The introduction of group V gas or source that can react with group III metal is prohibited throughout the process, so that metal atoms can be fully spread and diffused on the substrate surface, completely covering all surface areas of the substrate, forming a uniform thin metal wetting film. S3. Synergistic high-temperature treatment: Hydrogen gas is introduced to carry out high-temperature H-chemical synergistic surface treatment. The atomic migration characteristics of the metal wetting film under high temperature environment are utilized, and the decomposition atomic migration of the pre-set thin-layer epitaxial diffusion film is combined to repair the non-uniform steps and micro-mechanical damage on the substrate surface. At the same time, the non-uniform thermal erosion problem on the AlN vapor-deposited thin film surface is improved, and the pre-reconstruction of the substrate surface is completed. S4. Buffer layer growth: A conventional low-temperature buffer layer is grown on the surface of the pre-reconstructed substrate.

2. The growth method for improving the quality of MOCVD grown materials according to claim 1, characterized in that: In step S2, the metal source is a Group 3 metal source. In the GaN epitaxial system, the metal source includes one or more of TMAl, TEAl, SiH4, TMGa, and TMin.

3. The growth method for improving the quality of MOCVD grown materials according to claim 1, characterized in that: In step S2, a metal source is introduced simultaneously or sequentially before the high-temperature hydrogen ionization cleaning and repair treatment of the substrate. It is prohibited to introduce other sources or gases that react with it. The growth temperature is 600-900℃ and the time is 5S-1min.

4. The growth method for improving the quality of MOCVD grown materials according to claim 1, characterized in that: In step S2, after the high-temperature hydrogen H-treatment followed by annealing and before the nitriding treatment, a metal source is introduced simultaneously or sequentially. It is prohibited to introduce group V gases or sources that react with it. The duration of the metal source introduction is 5s to 1min.

5. A growth method for improving the quality of MOCVD grown materials according to claim 3 or 4, characterized in that: In step S2, after the metal source is shut off, a post-aided diffusion film can be grown or an auxiliary diffusion film can be grown at intervals of 10s-1min.

6. The growth method for improving the quality of MOCVD grown materials according to claim 5, characterized in that: The auxiliary diffusion film is a diffused GaN layer, which is combined with a metal layer to form a metal-film diffused GaN layer composite film structure. Its growth conditions are 900-1000℃, and a Ga source or Ga source and other metal sources are introduced. Among them, the Ga source <20slm, other metal sources <20slm, NH3 <10slm, and the time is 5-20s.

7. The growth method for improving the quality of MOCVD grown materials according to claim 5, characterized in that: The thickness of the auxiliary diffusion film is 2~15nm.

8. The growth method for improving the quality of MOCVD grown materials according to claim 1, characterized in that: The thickness of the metal immersion film in step S2 is 1~5 nm.

9. The growth method for improving the quality of MOCVD growth materials according to any one of claims 1-8 is used in epitaxial structures to improve the uniformity of epitaxial buffer nucleation and the quality of the underlying crystals by increasing the recrystallization temperature.

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