Gallium nitride epitaxial layer and method for forming the same

Abstract

The present invention discloses a gallium nitride epitaxial layer and a method for forming the same. The method comprises: first, in a same reaction chamber, cleaning the surface of a gallium nitride substrate with hydrogen under heating conditions, then bombarding the surface of the gallium nitride substrate with inert gas plasma; then, in the reaction chamber, continuing to grow a gallium nitride nucleation layer on the surface of the gallium nitride substrate, then growing a dense gallium nitride layer on the gallium nitride nucleation layer, and finally growing a gallium nitride epitaxial layer on the dense gallium nitride layer. The present invention can significantly reduce the film formation time of the gallium nitride epitaxial layer, improve its production efficiency, and eliminate contamination during the transfer of the gallium nitride substrate. In addition, it can obtain a high-quality gallium nitride epitaxial layer, which is beneficial to the large-scale production and promotion and application of gallium nitride materials.

Description

Technical Field

[0001] The present invention specifically relates to a gallium nitride epitaxial layer and a method for forming the same, and belongs to the technical field of semiconductor materials. Background Art

[0002] To date, obtaining large-scale bulk GaN single crystals remains a key concern in this field. Currently, high-quality GaN materials are generally obtained through epitaxial growth on heterogeneous substrates. High-quality epitaxial thin films generally require substrates that meet the requirements of lattice constant matching, thermal expansion coefficient matching, scalability, and affordability. However, existing techniques often result in poor uniformity and consistency in epitaxial wafers, resulting in poor stability and reliability in the resulting electronic devices, hindering widespread application.

[0003] Gallium nitride materials produced using gallium nitride homoepitaxial growth technology, that is, continuing to grow a gallium nitride layer on an existing gallium nitride substrate, exhibit advantages such as low dislocation density, low current collapse, high reliability and high breakdown voltage, and are therefore increasingly favored by the industry.

[0004] However, in existing GaN homoepitaxial growth processes, since the GaN substrate is typically formed heteroepitaxially, certain dislocations will exist. Furthermore, the GaN substrate often needs to be peeled off from the supporting substrate and cleaned before it can be transported to the deposition chamber. Impurities can easily remain on the surface of the GaN substrate during cleaning, and contamination may also occur during transportation. These factors can lead to a decrease in the quality of the homoepitaxially grown GaN layer. Furthermore, although the GaN layer formed by homoepitaxial growth contains fewer dislocations than the GaN layer formed by heteroepitaxial growth, certain dislocations are unavoidable in the GaN substrate, which can still have a certain negative impact on the quality of the GaN epitaxial layer formed on the GaN substrate. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for forming a gallium nitride epitaxial layer to overcome the deficiencies in the prior art.

[0006] Another object of the present invention is to provide a gallium nitride epitaxial layer.

[0007] To achieve the aforementioned object of the invention, the technical solutions adopted by the present invention include:

[0008] One aspect of the present invention provides a method for forming a gallium nitride epitaxial layer, comprising the following steps:

[0009] S1. placing a gallium nitride substrate into a reaction chamber and cleaning the surface of the gallium nitride substrate;

[0010] S2. bombarding the surface of the gallium nitride substrate with an inert gas plasma in the reaction chamber to at least remove impurities on the surface of the gallium nitride substrate and to etch a pit structure at a surface defect of the gallium nitride substrate;

[0011] S3, introducing a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to be a second temperature and a second pressure, so as to grow a gallium nitride nucleation layer on the surface of the gallium nitride substrate;

[0012] S4, continuing to input a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to a third temperature and a third pressure, wherein the third temperature is higher than the second temperature and the third pressure is higher than the second pressure, thereby growing a dense gallium nitride layer on the gallium nitride nucleation layer;

[0013] S5. Growing a gallium nitride epitaxial layer on the dense gallium nitride layer.

[0014] In some embodiments, step S1 includes: placing a gallium nitride substrate into a reaction chamber, and cleaning the surface of the gallium nitride substrate with hydrogen gas under heating conditions.

[0015] In some embodiments, step S2 includes: introducing an inert gas into the reaction chamber, converting at least a portion of the inert gas into plasma, and applying an acceleration voltage to bombard the surface of the gallium nitride substrate with the plasma, thereby further removing impurities remaining on the surface of the gallium nitride substrate, and etching defects on the surface of the gallium nitride substrate, particularly dislocation defects, to form pit structures.

[0016] The embodiment of the present invention further provides a gallium nitride epitaxial layer manufactured by the above method.

[0017] Compared with the prior art, the beneficial effects of the present invention include at least:

[0018] (1) In the method for forming a gallium nitride epitaxial layer provided, the gallium nitride substrate surface cleaning step and the gallium nitride epitaxial layer growth step are completed in the same reaction chamber. There is no need to transfer the gallium nitride substrate after the cleaning step is completed, which can greatly save the film formation time of the gallium nitride epitaxial layer and improve its production efficiency. In particular, it can also eliminate contamination during the transfer process of the gallium nitride substrate.

[0019] (2) In the method for forming a gallium nitride epitaxial layer provided, after the surface of the gallium nitride substrate is cleaned using hydrogen or the like, the gallium nitride substrate is subjected to plasma bombardment treatment using an inert gas plasma in the same reaction chamber. On the one hand, the residual impurities on the surface of the gallium nitride substrate can be further removed. On the other hand, pit structures, such as V-shaped pits or irregular pits, can be etched at the defects on the surface of the gallium nitride substrate, especially the dislocation defects. These pit structures can relieve the stress in other epitaxial structure layers in subsequent processes. Moreover, compared with the dense gallium nitride layer, the gallium nitride layer can be formed into a plurality of gallium nitride epitaxial layers. The gallium nitride nucleation layer is formed at a relatively low temperature and presents a dispersed columnar or island-shaped nucleation material structure. These dispersed columnar or island-shaped structures have gaps. At the same time, the aforementioned pit structure is distributed on the surface of the gallium nitride substrate. In this way, when epitaxially growing a dense gallium nitride layer or a gallium nitride epitaxial layer, GaN will grow along the sidewalls of the pits or gaps. When the epitaxial lateral growth film merges, the threading dislocation will be correspondingly lateral truncated, and dislocations will only appear on a small part of the hole wall, greatly reducing the density of threading dislocations, thereby obtaining high-quality gallium nitride epitaxial films. In addition, because the method of the present invention uses gas for cleaning and bombarding the substrate instead of using liquid phase reagents, it can avoid the liquid phase and / or solid phase impurity residues caused by the cleaning or etching process using liquid phase reagents, and eliminate the defects of increased contamination of the epitaxial wafer during the transfer process and the difficulty in removing residual impurities, thereby effectively ensuring the performance of the epitaxial wafer.

[0020] (3) In the provided method for forming a gallium nitride epitaxial layer, before forming the gallium nitride epitaxial layer, a dense gallium nitride layer is first formed on the gallium nitride nucleation layer. When the dense gallium nitride layer is formed, the temperature, pressure, flow rate, etc. are controlled, especially under high pressure and high temperature conditions, so that the gallium nitride formed is more dense and has higher crystal quality. Then, with the dense gallium nitride layer as the bottom layer, a gallium nitride epitaxial layer is formed on it. Since the dense gallium nitride layer has fewer defects and higher crystal quality, the formation speed of the gallium nitride epitaxial layer can be increased without reducing the quality of the gallium nitride epitaxial layer, and the production efficiency can be improved, which can better meet the needs of practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 is a flow chart of a method for forming a gallium nitride epitaxial layer in one embodiment of the present invention;

[0023] Figure 2 is a cross-sectional view of a gallium nitride substrate after hydrogen cleaning treatment in one embodiment of the present invention;

[0024] Figure 3 is a cross-sectional view of a gallium nitride substrate after being bombarded by an inert gas plasma in one embodiment of the present invention;

[0025] Figure 4 yes Figure 3 A partial enlarged view of part A;

[0026] Figure 5 corresponds to Figure 3 A partial enlarged top view of part A in the middle;

[0027] Figure 6 is a cross-sectional view of a gallium nitride substrate having a gallium nitride nucleation layer formed on the surface thereof according to one embodiment of the present invention;

[0028] Figure 7 is a cross-sectional view of a gallium nitride substrate having a gallium nitride nucleation layer and a dense gallium nitride layer formed on the surface thereof in one embodiment of the present invention;

[0029] Figure 8 It is a cross-sectional view of a gallium nitride substrate having a gallium nitride nucleation layer, a dense gallium nitride layer and a gallium nitride epitaxial layer formed on the surface in one embodiment of the present invention. DETAILED DESCRIPTION

[0030] In view of the shortcomings of the prior art, the inventors of this case, after long-term research and extensive practice, have proposed the technical solution of the present invention. The following will further explain this technical solution, its implementation process and principles.

[0031] Some embodiments of the present invention provide a method for forming a gallium nitride epitaxial layer, the method comprising the following steps:

[0032] S1. placing a gallium nitride substrate into a reaction chamber and cleaning the surface of the gallium nitride substrate;

[0033] S2. bombarding the surface of the gallium nitride substrate with an inert gas plasma in the reaction chamber to at least remove impurities on the surface of the gallium nitride substrate and to etch a pit structure at a surface defect of the gallium nitride substrate;

[0034] S3, introducing a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to be a second temperature and a second pressure, so as to grow a gallium nitride nucleation layer on the surface of the gallium nitride substrate;

[0035] S4, continuing to input a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to a third temperature and a third pressure, wherein the third temperature is higher than the second temperature and the third pressure is higher than the second pressure, thereby growing a dense gallium nitride layer on the gallium nitride nucleation layer;

[0036] S5. Growing a gallium nitride epitaxial layer on the dense gallium nitride layer.

[0037] In step S1, the gallium nitride substrate can be a gallium nitride substrate commonly used in the art, such as a gallium nitride substrate formed by a heteroepitaxial process. This type of gallium nitride substrate is generally prepared through the following process, including: first forming a buffer layer on a sapphire substrate, the buffer layer can mainly alleviate the lattice mismatch between the sapphire substrate and gallium nitride, the material of the buffer layer is mainly AlGaN material, and then epitaxially forming a gallium nitride layer on the buffer layer, and separating the gallium nitride layer from the buffer layer through a stripping process to form a gallium nitride support layer. The stripping process usually adopts a laser stripping process. Although there is a buffer layer between the sapphire substrate and the gallium nitride support layer (that is, the gallium nitride epitaxial layer), there are still a large number of dislocations in the formed gallium nitride support layer, and the dislocation density may be as high as 10 8 / cm 2 Such a high dislocation density can seriously affect the dislocation density of the GaN epitaxial structure formed on it. Excessive dislocations in GaN can affect the luminous efficiency and service life of the resulting laser or LED. However, the technical solution of the present invention can significantly reduce the dislocation density in the GaN epitaxial structure formed on it while using a common GaN substrate without increasing costs, significantly improving the quality of the resulting GaN epitaxial layer.

[0038] Furthermore, step S1 includes: placing a gallium nitride substrate into a reaction chamber, removing impurity gases from the reaction chamber, then introducing hydrogen into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to a first temperature and a first pressure, thereby cleaning the surface of the gallium nitride substrate. Preferably, the first temperature is 800-1000°C and the first pressure is 50-80 torr. Preferably, the hydrogen flow rate can be controlled to be 50-300 sccm. In step S1, using hydrogen to clean the surface of the gallium nitride substrate under heating conditions can effectively remove contaminants and impurities on the surface of the gallium nitride substrate, thereby cleaning the surface of the gallium nitride substrate.

[0039] Furthermore, step S2 includes introducing an inert gas into the reaction chamber, converting at least a portion of the inert gas into plasma, and applying an acceleration voltage to bombard the surface of the gallium nitride substrate with the plasma to at least remove impurities from the surface of the gallium nitride substrate and to etch pit structures at surface defects of the gallium nitride substrate. Preferably, the inert gas flow rate can be controlled to be 80-300 sccm, the acceleration voltage to be 400-600 keV, and the bombardment time to be 30-80 seconds.

[0040] In step S2, since the surface of the gallium nitride substrate has many dislocation structures, such as edge dislocations and mixed dislocations, these dislocations are mainly defects formed by displacement between the crystal lattices during the formation of the gallium nitride crystal. The crystal arrangement in the dislocated area is unstable and is more fragile than the dislocation-free area. Therefore, when bombarding with inert gas plasma, on the one hand, it can further remove impurities remaining on the surface of the gallium nitride substrate that have not been removed by hydrogen cleaning, and on the other hand, it will etch scattered pits in the dislocation concentrated area. The depth and diameter of these pits are both at the nanometer level, generally tens to hundreds of nanometers, for example, the depth and diameter are both 60-150nm. By controlling the bombardment time, the diameter and depth of the pits can be controlled. Due to different dislocation types, the shape of the pits formed can be regular (such as V-shaped grooves) or irregular. The size of the pit is also related to the number of dislocation defects in the corresponding area. Generally speaking, the more defects there are in the area corresponding to the pit on the GaN substrate surface, the larger the pit; conversely, the fewer defects there are in the area corresponding to the pit, the smaller the pit. These pits can subsequently relieve stress, and during subsequent epitaxial growth, GaN will grow along the sidewalls of the pit. When the epitaxially grown films merge, threading dislocations will be laterally truncated, resulting in dislocations only on a small portion of the pit sidewalls. This greatly reduces the density of threading dislocations and ensures the production of high-quality GaN epitaxial films.

[0041] Moreover, the cleaning and bombardment operations of the aforementioned steps S1 and S2 are all performed in the same reaction chamber, without involving the transfer of the wafer, and the etching uses a plasma bombardment method. Compared with wet etching and other methods, it can avoid secondary contamination and reduced production efficiency caused by wafer transfer, and can also eliminate defects such as reduced quality of epitaxial wafers caused by residual wet etching reagents and the like adhering to the wafer surface and being difficult to remove.

[0042] Furthermore, in step S3, by growing a gallium nitride nucleation layer at a relatively low temperature, a dispersed columnar or island-shaped nucleation material structure can be formed. As previously described, after processing in step S2, the surface of the gallium nitride substrate already has dispersed pits, and in the gallium nitride nucleation layer formed in step S3, there are also gaps between the dispersed columnar or island-shaped structures. In this way, during the subsequent epitaxial growth of gallium nitride, GaN will grow along the sidewalls of the aforementioned pits and gaps. Furthermore, when the epitaxially grown thin films merge, threading dislocations can be correspondingly lateral-truncate, significantly reducing the density of threading dislocations and significantly improving the quality of the gallium nitride epitaxial film. More preferably, in step S3, the second temperature can be controlled to be 600-800°C and the second gas pressure to be 300-450 torr. In addition, the flow rate of the nitrogen source can be controlled to be 80-150 sccm and the flow rate of the gallium source can be controlled to be 100-150 sccm. In addition, the growth time of the gallium nitride nucleation layer can be controlled to be 30-50s.

[0043] Furthermore, the stage of forming a dense gallium nitride layer in step S4 requires controlling the reaction chamber to be in a high temperature and high pressure state, so that a higher quality gallium nitride layer can be formed on the low-temperature grown gallium nitride nucleation layer, wherein the gaps and dislocation density between the gallium nitride crystals are smaller and more dense, thereby further reducing the stress between the epitaxial layer above it and the layer structure below, and improving the overall quality of the epitaxial gallium nitride. The growth mechanism of gallium nitride at this stage is as described above, that is, gallium nitride will grow along the gallium nitride nucleation layer and the sidewalls of the pit. When the epitaxially grown film merges, the threading dislocation will be correspondingly lateral truncated, and at most dislocations will only appear on a small part of the gap or the sidewall of the pit. The threading dislocation density is significantly reduced, and the quality of the corresponding gallium nitride epitaxial film is significantly improved. Furthermore, when gallium nitride is continued to be epitaxially grown on the formed dense gallium nitride layer, the high-density, high-crystalline gallium nitride is used as the bottom layer for growth, which can improve the quality of the gallium nitride epitaxial layer and reduce the defects of the epitaxial layer. Preferably, in step S4, the third temperature can be controlled to 1100-1200°C, the third gas pressure to 500-550 Torr, the nitrogen source flow rate to 100-300 sccm, and the gallium source flow rate to 150-200 sccm. Furthermore, the growth rate of the dense gallium nitride layer can be controlled to 10-20 nm / min.

[0044] Furthermore, in step S5, epitaxial growth can continue on the dense gallium nitride layer to form a gallium nitride epitaxial layer using methods known in the art, and a gallium nitride epitaxial layer with significantly improved quality can be obtained. For example, step S5 includes: continuing to input a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to a fourth temperature and a fourth pressure, thereby growing a gallium nitride epitaxial layer on the dense gallium nitride layer, wherein the fourth temperature is lower than the third temperature and higher than the second temperature, and the fourth pressure is lower than the third pressure. More preferably, the fourth temperature can be controlled to be 1020-1070°C and the fourth pressure can be controlled to be 200-350 torr. In addition, the flow rates of the gallium source and the nitrogen source can be controlled to be 280-350 sccm. Furthermore, the growth rate of the gallium nitride epitaxial layer can be controlled to be 30-50 nm / min.

[0045] In the aforementioned steps S4 and S5, by setting the temperature for forming the GaN epitaxial layer lower than the temperature for forming the dense GaN layer, the growth rate of the GaN epitaxial layer is greater than the growth rate of the dense GaN layer, thereby reducing the time required to form the GaN epitaxial layer (because the thickness of the epitaxial layer is generally in the micron range, a too slow growth rate would seriously affect production efficiency). Furthermore, since the dense GaN layer is formed below the GaN epitaxial layer, the dense GaN layer has high crystalline quality and low defect density. Therefore, when the GaN epitaxial layer is rapidly formed above it, the crystalline quality of the epitaxial layer above it can also be ensured not to be affected.

[0046] Furthermore, the reaction chamber is a reaction chamber of a plasma enhanced chemical vapor deposition device, such as a reaction chamber of a plasma enhanced MOCVD (metal organic chemical vapor deposition) device, but is not limited thereto.

[0047] Furthermore, the gallium source includes trimethylgallium, but is not limited thereto.

[0048] Furthermore, the nitrogen source includes ammonia, but is not limited thereto.

[0049] Preferably, the gallium nitride nucleation layer has a thickness of 20-40 nm.

[0050] Preferably, the thickness of the dense gallium nitride layer is 50-80 nm.

[0051] Preferably, the gallium nitride epitaxial layer has a thickness of 1-1.5 μm.

[0052] In some more specific embodiments of the present invention, reference Figure 1 As shown, a method for forming a gallium nitride epitaxial layer specifically includes the following steps:

[0053] S1, placing the gallium nitride substrate into the reaction chamber of the plasma enhanced chemical vapor deposition equipment, and evacuating the reaction chamber until the impurity gas in the reaction chamber is removed, then introducing hydrogen into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to be the first temperature and the first pressure to clean the surface of the gallium nitride substrate. The structure of the gallium nitride substrate after the treatment in step S1 is as follows Figure 2 shown.

[0054] S2, stop feeding hydrogen into the reaction chamber, and feed inert gas into the reaction chamber instead, and convert at least part of the inert gas into plasma using a plasma discharge module, and apply an acceleration voltage to bombard the surface of the gallium nitride substrate with the plasma, so as to at least remove impurities on the surface of the gallium nitride substrate and etch the surface defects of the gallium nitride substrate to form pit structures. Figure 3-Figure 5 After the processing in step S2, the surface of the gallium nitride substrate is etched to form a plurality of pits of different sizes and shapes. These pits can be regular (such as V-shaped) or irregular.

[0055] S3, stop feeding the inert gas into the reaction chamber, and feed the nitrogen source and gallium source into the reaction chamber, and control the temperature and pressure in the reaction chamber to the second temperature and the second pressure, so as to grow a gallium nitride nucleation layer on the surface of the gallium nitride substrate. After the processing in step S3, a gallium nitride nucleation layer is formed on the surface of the gallium nitride substrate, and the gallium nitride nucleation layer includes a dispersed columnar or island-shaped nucleation material structure, see Figure 6 shown.

[0056] S4, continue to input nitrogen source and gallium source into the reaction chamber, and control the temperature and pressure in the reaction chamber to be the third temperature and the third pressure, so as to grow a dense gallium nitride layer on the gallium nitride nucleation layer. After the processing of step S4, a dense gallium nitride layer is formed on the gallium nitride nucleation layer, see Figure 7 shown.

[0057] S5, continue to input nitrogen source and gallium source into the reaction chamber, and control the temperature and pressure in the reaction chamber to be the fourth temperature and the fourth pressure, so as to grow the dense gallium nitride layer to form a gallium nitride epitaxial layer. After the processing of step S4, a dense gallium nitride layer is formed on the gallium nitride nucleation layer, such as Figure 8 shown.

[0058] The first temperature is higher than the second temperature and the first pressure is lower than the second pressure. The third temperature is higher than the second temperature and the third pressure is higher than the second pressure. The fourth temperature is lower than the third temperature and higher than the second temperature and the fourth pressure is lower than the third pressure.

[0059] The raw materials and process conditions used in steps S1-S5 may all be the same as those listed above, and will not be described in detail here.

[0060] Some embodiments of the present invention also provide a gallium nitride epitaxial layer, produced using the aforementioned method. Compared to gallium nitride epitaxial layers produced using existing homoepitaxial processes, the gallium nitride epitaxial layer obtained by the present invention has significantly improved crystal quality, effectively guaranteeing the performance of various semiconductor devices fabricated therewith. For example, it significantly improves the stability and reliability of corresponding electronic devices.

[0061] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the technical solutions of the present invention are further described in detail below with reference to the accompanying drawings and several preferred embodiments. It is apparent that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0062] Example 1 A method for forming a gallium nitride epitaxial layer comprises the following steps:

[0063] S1. Place a commercially available gallium nitride substrate into the reaction chamber of a plasma-enhanced metal-organic chemical vapor deposition (MOCVD) device. The gallium nitride substrate is grown and exfoliated on a sapphire substrate using a heteroepitaxial process. The reaction chamber of the plasma-enhanced MOCVD device has multiple gas inlet lines, each of which can be used to introduce different gases. The reaction chamber is first evacuated to remove impurities. Hydrogen is then introduced, maintaining a pressure of approximately 80 Torr, a temperature of approximately 800°C, and a hydrogen flow rate of approximately 150 sccm. This removes contaminants and impurities from the surface of the gallium nitride substrate, resulting in a clean gallium nitride substrate.

[0064] S2. After step S1 is completed, the pipeline for introducing hydrogen into the reaction chamber is closed, and argon gas is introduced into another pipeline. The argon gas is converted into plasma by the plasma discharge module in the plasma-enhanced MOCVD equipment, and then the plasma is accelerated to bombard the surface of the gallium nitride substrate under an acceleration voltage, wherein the acceleration voltage is controlled to be about 500 KeV, the inert gas flow rate is about 200 sccm, and the bombardment time is about 50 s.

[0065] S3. After step S2 is completed, the introduction of the inert gas is stopped, and ammonia gas is first introduced into the reaction chamber to reduce the temperature in the reaction chamber to about 600° C. using the ammonia gas. Then, ammonia gas as a nitrogen source and trimethylgallium as a gallium source are introduced together. The nitrogen source flow rate is controlled to be about 80 sccm and the gallium source flow rate is controlled to be about 100 sccm. The temperature in the reaction chamber is maintained at about 600° C., the gas pressure is about 300 torr, and the growth time is about 30 seconds. A gallium nitride nucleation layer with a thickness of about 20 nm is grown.

[0066] S4. After step S3 is completed, the temperature in the reaction chamber is increased to about 1100° C., and the gallium source and nitrogen source are continued to be introduced, with the nitrogen source flow rate being controlled to be about 100 sccm and the gallium source flow rate being about 180 sccm. The gas pressure in the reaction chamber is about 550 Torr, and the growth rate of the dense gallium nitride layer is about 10 nm / min, until a dense gallium nitride layer with a thickness of about 50 nm is grown.

[0067] S5. After step S4 is completed, the temperature in the reaction chamber is lowered to about 1020° C., and the gallium source and the nitrogen source are continued to be introduced, and the flow rates of the gallium source and the nitrogen source are controlled to be about 300 sccm. The gas pressure in the reaction chamber is controlled to be about 300 Torr, and the gallium nitride growth rate is about 30 nm / min, until a gallium nitride epitaxial layer with a thickness of about 1 μm is grown.

[0068] Example 2 A method for forming a gallium nitride epitaxial layer comprises the following steps:

[0069] S1. This step is basically the same as step S1 of Example 1, except that the pressure in the reaction chamber is controlled to be about 60 torr, the temperature is about 900° C., and the hydrogen flow rate is about 300 sccm.

[0070] S2. This step is basically the same as step S2 of Example 1, except that the acceleration voltage is controlled to be about 400 KeV, the inert gas flow rate is about 300 sccm, and the bombardment time is about 80 s.

[0071] S3. This step is basically the same as step S3 of Example 1, except that: the temperature in the reaction chamber is controlled to be maintained at 700°C, the gas pressure is 400 torr, the nitrogen source flow rate is about 150 sccm, the gallium source flow rate is about 130 sccm, the growth time is 40 seconds, and a gallium nitride nucleation layer with a thickness of about 30 nm is grown.

[0072] S4. This step is basically the same as step S4 in Example 1, except that: the nitrogen source flow rate is controlled to be approximately 250 sccm, the gallium source flow rate is controlled to be approximately 200 sccm, the temperature in the reaction chamber is approximately 1150° C., the gas pressure is approximately 500 torr, and the growth rate of the dense gallium nitride layer is approximately 12 nm / min, until a dense gallium nitride layer with a thickness of approximately 60 nm is grown.

[0073] S4. This step is basically the same as step S4 of Example 1, except that: the flow rates of the gallium source and the nitrogen source are both controlled to be 280 sccm, the temperature in the reaction chamber is about 1070°C, the gas pressure is 200 torr, and the gallium nitride growth rate is 35 nm / min, until a gallium nitride epitaxial layer with a thickness of about 1.2 μm is grown.

[0074] Example 3 A method for forming a gallium nitride epitaxial layer comprises the following steps:

[0075] S1. This step is basically the same as step S1 of Example 1, except that the pressure in the reaction chamber is controlled to be about 50 torr, the temperature is about 1000° C., and the hydrogen flow rate is about 50 sccm.

[0076] S2. This step is basically the same as step S2 of Example 1, except that the acceleration voltage is controlled to be about 600 KeV, the inert gas flow rate is about 80 sccm, and the bombardment time is about 30 s.

[0077] S3. This step is basically the same as step S3 of Example 1, except that: the temperature in the reaction chamber is controlled to be maintained at 800°C, the gas pressure is 450 torr, the nitrogen source flow rate is about 120 sccm, the gallium source flow rate is about 150 sccm, the growth time is 50 seconds, and a gallium nitride nucleation layer with a thickness of about 40 nm is grown.

[0078] S4. This step is basically the same as step S3 of Example 1, except that: the nitrogen source flow rate is controlled to be approximately 300 sccm, the gallium source flow rate is controlled to be approximately 180 sccm, the temperature in the reaction chamber is controlled to be approximately 1200° C., the gas pressure is controlled to be approximately 550 torr, and the growth rate of the dense gallium nitride layer is controlled to be approximately 20 nm / min, until a dense gallium nitride layer with a thickness of approximately 80 nm is grown.

[0079] S5. After step S4, the temperature in the reaction chamber is lowered to about 1050° C., and the gallium source and the nitrogen source are continued to be introduced, and the flow rates of the gallium source and the nitrogen source are controlled to be about 350 sccm. The gas pressure in the reaction chamber is controlled to be about 350 Torr, and the gallium nitride growth rate is about 50 nm / min, until a gallium nitride epitaxial layer with a thickness of about 1.5 μm is grown.

[0080] Comparative Example 1 The method for forming a gallium nitride epitaxial layer provided in this comparative example is basically the same as that of Example 1, except that step S2 is omitted.

[0081] Comparative Example 2 The method for forming a gallium nitride epitaxial layer provided in this comparative example is basically the same as that in Example 1, except that: before step S1, the surface of the GaN substrate is wet-etched with a NaOH solution with a concentration of about 5 mol / L for about 5 minutes to form a plurality of pits on the surface of the GaN substrate, and then the substrate is thoroughly cleaned and dried with deionized water, etc., and then the operation of step S1 is performed, and step S2 is omitted.

[0082] The products obtained in Examples 1-3 and Comparative Examples 1-2 were observed using a scanning electron microscope (SEM) and other equipment. It can be seen that the gallium nitride epitaxial layers in the products obtained in Examples 1-3 have high crystallinity and dense crystals without warping. The dislocation density is 5×10 3 / cm 2 The crystallinity of the GaN epitaxial layer in the product of Comparative Example 1 is acceptable, but due to the large stress in the formed epitaxial wafer, the formed GaN epitaxial wafer is warped. The crystallinity of the GaN epitaxial layer in the product of Comparative Example 2 is low. After further analysis, it was found that the Na + and OH - and H in water + After cleaning, there are still some residues. These residual ions will adhere to the surface of the crystal core layer, affecting the crystal quality of GaN. There are also many dislocation defects, and the defect density reaches 8×10 5 / cm 2 .

[0083] Although the present invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions, and / or additions may be made and that substantial equivalents may be substituted for elements of the described embodiments without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from the scope of the invention. Therefore, it is not intended that the present invention be limited to the specific embodiments disclosed for carrying out the invention, but it is intended that the invention encompass all embodiments falling within the scope of the appended claims.

Claims

1. A method for forming a gallium nitride epitaxial layer, characterized in that: The method comprises the following steps: S1. placing a gallium nitride substrate into a reaction chamber, and cleaning the surface of the gallium nitride substrate with hydrogen under heating conditions; S2. Bombarding the surface of the gallium nitride substrate with an inert gas plasma in the reaction chamber to at least remove impurities on the surface of the gallium nitride substrate and to etch a pit structure at a surface defect of the gallium nitride substrate, wherein the depth and diameter of the pit structure are both in the nanometer range; S3, introducing a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to a second temperature and a second pressure, thereby growing a gallium nitride nucleation layer on the surface of the gallium nitride substrate, wherein the gallium nitride nucleation layer exhibits a dispersed columnar or island-shaped nucleation material structure; S4, continuing to input a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to a third temperature and a third pressure, wherein the third temperature is higher than the second temperature and the third pressure is higher than the second pressure, thereby growing a dense gallium nitride layer on the gallium nitride nucleation layer; S5. Growing a gallium nitride epitaxial layer on the dense gallium nitride layer.

2. The method according to claim 1, characterized in that Step S1 includes placing a gallium nitride substrate into a reaction chamber, removing impurity gases in the reaction chamber, introducing hydrogen into the reaction chamber, and controlling the pressure and temperature in the reaction chamber to a first pressure and a first temperature, with a hydrogen flow rate of 50-300 sccm, the first temperature being 800-1000° C., and the first pressure being 50-80 Torr, thereby cleaning the surface of the gallium nitride substrate.

3. The method according to claim 1, characterized in that Step S2 includes: introducing an inert gas into the reaction chamber, converting at least a portion of the inert gas into plasma, and applying an acceleration voltage to bombard the surface of the gallium nitride substrate with the plasma, wherein the inert gas flow rate is controlled to be 80-300 sccm, the acceleration voltage is controlled to be 400-600 KeV, and the bombardment time is controlled to be 30-80 seconds.

4. The method according to claim 1, wherein: In step S3, the second temperature is 600-800° C., and the second pressure is 300-450 Torr.

5. The method according to claim 1, wherein: In step S3, the flow rate of the nitrogen source is 80-150 sccm, and the flow rate of the gallium source is 100-150 sccm.

6. The method according to claim 1, wherein: The growth time of the gallium nitride nucleation layer in step S3 is controlled to be 30-50s.

7. The method according to claim 1, wherein: In step S4, the third temperature is 1100-1200° C., and the third gas pressure is 500-550 Torr.

8. The method according to claim 1, wherein: The growth rate of the dense gallium nitride layer in step S4 is controlled at 10-20 nm / min.

9. The method according to claim 1, wherein: In step S4, the flow rate of the nitrogen source is 100-300 sccm, and the flow rate of the gallium source is 150-200 sccm.

10. The method according to claim 1, characterized in that Step S5 includes: continuing to input a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to a fourth temperature and a fourth pressure, thereby growing a gallium nitride epitaxial layer on the dense gallium nitride layer, wherein the fourth temperature is lower than the third temperature and higher than the second temperature, and the fourth pressure is lower than the third pressure.

11. The method according to claim 10, characterized in that: In step S5, the fourth temperature is 1020-1070° C., and the fourth gas pressure is 200-350 Torr.

12. The method according to claim 10, wherein: In step S5, the flow rates of the gallium source and the nitrogen source are both 280-350 sccm.

13. The method according to claim 10, wherein: In step S5, the growth rate of the gallium nitride epitaxial layer is controlled at 30-50 nm / min.

14. The method according to claim 1, wherein: The reaction chamber is a reaction chamber of a plasma enhanced chemical vapor deposition device.

15. The method according to claim 1, wherein: The gallium source includes trimethylgallium.

16. The method according to claim 1, wherein: The nitrogen source includes ammonia.

17. The method according to claim 1, wherein: The thickness of the gallium nitride nucleation layer is 20-40 nm.

18. The method according to claim 1, wherein: The thickness of the dense gallium nitride layer is 50-80 nm.

19. The method according to claim 1, wherein: The thickness of the gallium nitride epitaxial layer is 1-1.5 μm.

20. A method for forming a gallium nitride epitaxial layer, characterized in that: The method comprises the following steps: S1, placing the gallium nitride substrate into the reaction chamber of the plasma enhanced chemical vapor deposition equipment, and evacuating the reaction chamber until the impurity gas in the reaction chamber is removed, and then inputting hydrogen into the reaction chamber, and controlling the Description The temperature in the reaction chamber is a first temperature, and the pressure is a first pressure, so as to clean the surface of the gallium nitride substrate; S2. Stop feeding hydrogen into the reaction chamber, feed an inert gas into the reaction chamber instead, convert at least a portion of the inert gas into plasma using a plasma application module, and apply an acceleration voltage to bombard the surface of the gallium nitride substrate with the plasma to at least remove impurities on the surface of the gallium nitride substrate and etch a pit structure at a surface defect of the gallium nitride substrate, wherein the depth and diameter of the pit structure are both in the nanometer range; S3, stopping the supply of the inert gas into the reaction chamber, supplying a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to a second temperature and a second pressure, thereby growing a gallium nitride nucleation layer on the surface of the gallium nitride substrate, wherein the gallium nitride nucleation layer presents a dispersed columnar or island-shaped nucleation material structure; S4, continuing to input a nitrogen source and a gallium source into the reaction chamber, and controlling the temperature and pressure in the reaction chamber to be a third temperature and a third pressure, thereby growing a dense gallium nitride layer on the gallium nitride nucleation layer; S5, continue to input nitrogen source and gallium source into the reaction chamber, and control the Description The temperature in the reaction chamber is a fourth temperature, and the pressure in the reaction chamber is a fourth pressure, so that a gallium nitride epitaxial layer is grown on the dense gallium nitride layer; The first temperature is higher than the second temperature and the first pressure is lower than the second pressure. The third temperature is higher than the second temperature and the third pressure is higher than the second pressure. The fourth temperature is lower than the third temperature and higher than the second temperature and the fourth pressure is lower than the third pressure.

21. The method according to claim 20, characterized in that: In step (1), the first gas pressure is 50-80 torr and the first temperature is 800-1000°C.

22. The method according to claim 20, wherein: In step (1), the hydrogen flow rate is controlled to be 50-300 sccm.

23. The method according to claim 20, wherein: In step (2), the inert gas flow rate is controlled to be 80-300 sccm, the acceleration voltage is controlled to be 400-600 KeV, and the bombardment time is controlled to be 30-80 s.

24. The method according to claim 20, wherein: In step S3, the second temperature is 600-800° C., and the second pressure is 300-450 Torr.

25. The method according to claim 20, wherein: In step S3, the flow rate of the nitrogen source is 80-150 sccm, and the flow rate of the gallium source is 100-150 sccm.

26. The method according to claim 20, wherein: The growth time of the gallium nitride nucleation layer in step S3 is controlled to be 30-50s.

27. The method according to claim 20, wherein: In step S4, the third temperature is 1100-1200° C., and the third gas pressure is 500-550 Torr.

28. The method according to claim 20, wherein: The growth rate of the dense gallium nitride layer in step S4 is controlled at 10-20 nm / min.

29. The method according to claim 20, wherein: In step S4, the flow rate of the nitrogen source is 100-300 sccm, and the flow rate of the gallium source is 150-200 sccm.

30. The method according to claim 20, wherein: In step S5, the fourth temperature is 1020-1070° C., and the fourth pressure is 200-350 Torr.

31. The method according to claim 20, wherein: In step S5, the flow rates of the gallium source and the nitrogen source are both 280-350 sccm.

32. The method according to claim 20, wherein: In step S5, the growth rate of the gallium nitride epitaxial layer is controlled at 30-50 nm / min.

33. The method according to claim 20, wherein: The gallium source includes trimethylgallium.

34. The method according to claim 20, wherein: The nitrogen source includes ammonia.

35. The method according to claim 20, wherein: The thickness of the gallium nitride nucleation layer is 20-40 nm.

36. The method according to claim 20, wherein: The thickness of the dense gallium nitride layer is 50-80 nm.

37. The method according to claim 20, wherein: The thickness of the gallium nitride epitaxial layer is 1-1.5 μm.

38. A gallium nitride epitaxial layer, characterized in that: The gallium nitride epitaxial layer is prepared by the method according to any one of claims 1 to 37.

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