A method for epitaxial growth of gallium nitride and a method for preparing a gallium nitride epitaxial layer

Abstract

The application discloses a gallium nitride epitaxial growth method and a gallium nitride epitaxial layer preparation method. The gallium nitride epitaxial growth method comprises the following steps: growing a porous aluminum oxide mask layer on a substrate; nanoholes in the porous aluminum oxide mask layer penetrate through the porous aluminum oxide mask layer; growing an aluminum nitride filling layer in the nanoholes in the porous aluminum oxide mask layer; removing the aluminum oxide mask layer; growing a gallium nitride buffer layer in the aluminum nitride filling layer and on the aluminum nitride filling layer; and growing a gallium nitride epitaxial layer on the gallium nitride buffer layer. In the method, a large number of dislocations are terminated at the interface between the aluminum nitride filling layer and the gallium nitride buffer layer, and the quality of the gallium nitride epitaxial layer grown on the gallium nitride buffer layer is improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for epitaxial growth of gallium nitride and a method for preparing gallium nitride epitaxial layers. Background Technology

[0002] With the development and application of silicon, germanium, gallium arsenide, and indium phosphide semiconductor materials, efficient and reliable application scenarios depend on the superior performance of semiconductor materials. In order to realize applications under extreme conditions such as high temperature, high frequency, high power, strong radiation, and full wavelength, the research and application of third-generation semiconductor materials, namely wide-bandgap semiconductors (WBGS), is a hot topic in the semiconductor industry.

[0003] Gallium nitride (GaN), as a wide bandgap semiconductor material, has the characteristics of a large adjustable bandgap, high breakdown field strength, low dielectric constant, high electron saturation, high drift velocity, strong radiation resistance, and excellent chemical stability. High electron mobility field-effect transistors and photodetectors fabricated with GaN as the core are widely used in high-tech fields such as microelectronics, power electronics, and optoelectronics, as well as in the defense industry, information industry, electromechanical industry, and energy industry. It is also a key basic material for the continued development of these pillar industries in the 21st century.

[0004] Silicon carbide (SiC) and gallium nitride (GaN) substrates, due to their low lattice and thermal mismatch rates with GaN, can grow high-quality epitaxial layers. However, commercially available SiC and GaN substrates are expensive. Currently, commercially available GaN is typically grown on sapphire or silicon substrates, especially silicon substrates, because they are mass-producible and can be grown in large sizes. Therefore, epitaxial growth of GaN devices on silicon substrates can significantly increase the number of devices and effectively reduce the epitaxial cost of GaN-based devices. However, there is a large difference in lattice constant and thermal mismatch between the silicon substrate and the epitaxial layer, resulting in high dislocation density and high stress in the GaN epitaxial material. This makes it difficult to grow high-crystallinity, thick, crack-free silicon-based GaN epitaxial layers. Therefore, the most mainstream method currently is to use an AlGaN buffer layer to introduce compressive stress and prevent silicon-based GaN material from cracking due to thermal stress during the cooling process. However, through-dislocations in the silicon-based gallium nitride material system will climb and tilt under compressive stress, thus forming vertically growing mismatched dislocations. This weakens the compressive stress introduced by the AlGaN buffer layer, resulting in insufficient compressive stress compensation during the cooling process, and the gallium nitride epitaxial layer is still prone to cracking. Summary of the Invention

[0005] Therefore, the present invention provides a gallium nitride epitaxial growth method that can effectively filter through dislocations conducted from the substrate, reduce the possibility of cracking in the epitaxially grown gallium nitride layer, and improve its quality, and further provides a method for preparing gallium nitride epitaxial layers that can achieve high-quality gallium nitride epitaxial layer preparation.

[0006] According to a first aspect, the present invention provides a method for epitaxial growth of gallium nitride, comprising the following steps:

[0007] A porous alumina mask layer is grown on a substrate; nanopores within the porous alumina mask layer penetrate the porous alumina mask layer.

[0008] An aluminum nitride filling layer is grown within the nanopores of a porous alumina mask layer;

[0009] Remove the alumina mask layer;

[0010] Gallium nitride buffer layers are grown inside and on the aluminum nitride filler layer;

[0011] Gallium nitride epitaxial layers are grown in gallium nitride buffer layers.

[0012] In one possible implementation, the step of growing a porous alumina mask layer on the substrate specifically includes:

[0013] Aluminum thin films are grown on substrates;

[0014] Anodizing the aluminum thin film yields a first alumina mask layer with a blind hole array.

[0015] The first alumina mask layer is anodized to make the blind holes extend toward the substrate, thus obtaining a porous alumina mask layer.

[0016] In one possible implementation, prior to the step of anodizing the first alumina mask layer to extend the blind holes toward the substrate and obtain the porous alumina mask layer, the method further includes:

[0017] The first alumina mask layer is subjected to surface chemical etching treatment.

[0018] In one possible implementation, the step of growing a gallium nitride buffer layer within and on the aluminum nitride filling layer includes:

[0019] Gallium nitride buffer layers are grown sequentially in a chemical vapor deposition apparatus under first preset growth conditions and second preset growth conditions, within an aluminum nitride filling layer and on top of the aluminum nitride filling layer; the first growth temperature in the first preset growth conditions is lower than the second growth temperature in the second preset growth conditions, and the first growth pressure in the first preset growth conditions is greater than the second growth pressure in the second preset growth conditions.

[0020] In one possible implementation, the step of growing a gallium nitride epitaxial layer in the gallium nitride buffer layer specifically includes:

[0021] Under the second preset growth conditions, a gallium nitride epitaxial layer on a gallium nitride buffer layer is grown in a chemical vapor deposition apparatus.

[0022] In one possible implementation, the first growth temperature is between 600℃ and 800℃, the second growth temperature is between 900℃ and 1300℃, the first growth pressure is between 300 torr and 500 torr, and the second growth pressure is between 150 torr and 250 torr.

[0023] According to a second aspect, the present invention also provides a method for preparing a gallium nitride epitaxial layer, comprising the following steps:

[0024] The gallium nitride epitaxial layer is grown using the gallium nitride epitaxial growth method in any of the embodiments of the first aspect described above.

[0025] Separate the substrate and gallium nitride epitaxial layer from the aluminum nitride filler layer, and remove the aluminum nitride filler layer and gallium nitride buffer layer on the gallium nitride epitaxial layer.

[0026] The technical solution provided by this invention has the following advantages:

[0027] 1. The gallium nitride epitaxial growth method provided by the present invention involves growing a porous alumina mask layer with nanopores penetrating the substrate on a substrate, and then growing an aluminum nitride filling layer within the nanopores of the porous alumina mask layer to obtain an aluminum nitride filling layer with the same porous structure (the porous structure within the aluminum nitride filling layer is complementary to the nanopores within the alumina mask layer). This aluminum nitride filling layer is used as the nucleation point for gallium nitride growth. A gallium nitride buffer layer is grown within and on the aluminum nitride mask layer. The porous structure increases the contact area between gallium nitride and aluminum nitride and enriches the growth directions of gallium nitride. This makes gallium nitride growth no longer the traditional bottom-up growth on a plane. Dislocation climb and annihilation occur in various directions, terminating a large number of dislocations at the interface between the aluminum nitride filling layer and the gallium nitride buffer layer. This effectively reduces the penetrating dislocations penetrating from the substrate to the epitaxial layer, thereby improving the quality of the gallium nitride epitaxial layer grown on the gallium nitride buffer layer.

[0028] 2. The gallium nitride epitaxial growth method provided by the present invention first grows a gallium nitride buffer layer under a first preset growth condition with relatively low temperature and relatively high pressure, and then transforms it into a second preset growth condition with relatively high temperature and relatively low pressure. This achieves a rapid transformation of three-dimensional gallium nitride growth to two-dimensional growth mode, thereby further introducing nanopores in the gallium nitride buffer layer (different from nanopores generated based on the pore structure in the aluminum nitride filling layer). This facilitates the subsequent lift-off process, reduces the damage to the gallium nitride epitaxial layer caused by the subsequent lift-off process, and achieves high-quality gallium nitride epitaxial growth. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 A flowchart of a gallium nitride epitaxial growth method provided in an embodiment of the present invention;

[0031] Figures 2A-2D These are schematic diagrams of the devices fabricated through steps S100, S200, S400, and S500, respectively.

[0032] Figure 3 for Figure 1 Flowchart of the specific steps in step S100;

[0033] Figure 4 This is a schematic diagram of the structure of the first alumina mask layer. Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0035] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] Example 1

[0037] Figure 1 A flowchart illustrating a gallium nitride epitaxial growth method provided in this embodiment is shown. Figure 1 As shown, the method includes the following steps:

[0038] S100: A porous alumina mask layer is grown on a substrate.

[0039] In this embodiment, as Figure 2A As shown, the nanopores in the porous alumina mask layer penetrate the porous alumina mask layer.

[0040] In this embodiment, the substrate can be an SOI substrate, or a composite substrate with a silicon carbide top structure formed by heat treatment, carbonization, or epitaxial growth of the top layer, such as a SiC-on-Si substrate, a SiC-on-SOI substrate, or a SiC substrate. Furthermore, the substrate in this step can be a directly obtained finished substrate, or it can be grown before performing this step.

[0041] In practice, the thickness of the alumina mask layer can be set between 50nm and 1000nm.

[0042] S200: An aluminum nitride filling layer is grown in the nanopores within a porous alumina mask layer.

[0043] The semiconductor structure prepared through this step is as follows: Figure 2B As shown.

[0044] In this embodiment, the aluminum nitride filler layer can be grown using a magnetron sputtering process; in specific implementation, the temperature during the growth process can be set between 80°C and 600°C, and the pressure between 1 mtorr and 3 mtorr.

[0045] S300: Removes the alumina mask layer.

[0046] In this embodiment, an alkaline NaOH solution or KOH solution can be used for wet etching to remove the aluminum oxide mask layer, thereby obtaining an aluminum nitride filling layer that also has a porous structure extending through the substrate (this porous structure is complementary to the porous structure in the aluminum oxide mask layer).

[0047] S400: Gallium nitride buffer layers are grown inside and on the aluminum nitride filling layer.

[0048] The semiconductor structure prepared through this step is as follows: Figure 2C As shown.

[0049] In this embodiment, a gallium nitride buffer layer can be grown using a metal-organic source chemical vapor deposition (MOCVD) process.

[0050] In this embodiment, the thickness of the portion of the gallium nitride buffer layer located on the aluminum nitride filling layer (distinct from the portion located within the aluminum nitride filling layer) can be set according to the needs of specific application scenarios, with the surface flatness meeting the growth requirements of the gallium nitride epitaxial layer in the specific application scenario. In specific implementation, the thickness of the gallium nitride buffer layer can be set between 1 μm and 2 μm.

[0051] S500: Gallium nitride epitaxial layer is grown in gallium nitride buffer layer.

[0052] The semiconductor structure prepared through this step is as follows: Figure 2D As shown.

[0053] Specifically, the gallium nitride epitaxial layer can be an unintentionally doped gallium nitride layer or an N-doped gallium nitride layer; its doping configuration can be set according to the needs of specific application scenarios, and there are no restrictions here.

[0054] Specifically, gallium nitride epitaxial layers can be grown using metal-organic source chemical vapor deposition (MOCVD) technology.

[0055] In summary, the gallium nitride epitaxial growth method in this embodiment involves growing a porous alumina mask layer with nanopores penetrating the substrate on the substrate, followed by growing an aluminum nitride filling layer within the nanopores of the porous alumina mask layer. This results in an aluminum nitride filling layer with the same porous structure (the porous structure within the aluminum nitride filling layer is complementary to the nanopores within the alumina mask layer). This aluminum nitride filling layer is then used as a nucleation point for gallium nitride growth. A gallium nitride buffer layer is grown within and on the aluminum nitride mask layer. The porous structure increases the contact area between gallium nitride and aluminum nitride, enriches the growth directions of gallium nitride, and makes gallium nitride growth no longer the traditional bottom-up growth on a plane. Dislocation climb and annihilation occur in various directions, terminating a large number of dislocations at the interface between the aluminum nitride filling layer and the gallium nitride buffer layer. This effectively reduces penetrating dislocations penetrating from the substrate into the epitaxial layer, thereby improving the quality of the gallium nitride epitaxial layer grown on the gallium nitride buffer layer.

[0056] In one specific implementation of this embodiment, such as Figure 3 As shown, step S100 above may specifically include the following steps:

[0057] S101: Growing aluminum thin film on a substrate.

[0058] In this embodiment, an aluminum thin film can be grown using a magnetron sputtering process. Specifically, the temperature during the growth process can be set between 50°C and 200°C, the pressure between 0.1Pa and 5Pa, and the thickness of the aluminum thin film can be set between 50nm and 1000nm.

[0059] In this embodiment, the substrate can be cleaned before growth begins to remove the oxide layer on the substrate surface.

[0060] S102: The aluminum film is anodized to obtain a first aluminum oxide mask layer with a blind hole array.

[0061] The structure of the aluminum thin film prepared through this step is as follows: Figure 4 As shown.

[0062] In this embodiment, the anodic oxidation of the filter module can be completed in the electrolytic cell, and the electrolyte in the electrolytic cell is set to a 0.3 mol / L oxalic acid solution.

[0063] In this embodiment, in order to improve the surface smoothness of the finally grown alumina mask layer, a second step S104 can be performed after this step:

[0064] S104: Perform surface chemical etching treatment on the first alumina mask layer.

[0065] In practice, a mixed solution of 0.1 mol / L chromic acid (H2CrO4) and 0.4 mol / L phosphoric acid (H3PO4) can be placed in a water bath at 55°C to perform surface chemical etching treatment on the first alumina mask layer.

[0066] S103: The first alumina mask layer is anodized to make the blind holes extend toward the substrate, thus obtaining a porous alumina mask layer.

[0067] The structure of the aluminum thin film prepared through this step is as follows: Figure 2A As shown.

[0068] In this embodiment, the process of anodizing the first alumina mask layer can be the same as the process of anodizing the aluminum thin film, and by adjusting the time, holes with consistent pore size that penetrate into the substrate can be obtained.

[0069] In one specific embodiment of this example, as shown in FIG2, step S400 may specifically include the following steps:

[0070] S401: Under the first preset growth conditions and the second preset growth conditions, gallium nitride buffer layers are grown in the aluminum nitride filling layer and on the aluminum nitride filling layer in a chemical vapor deposition apparatus.

[0071] In this embodiment, the first growth temperature in the first preset growth condition is lower than the second growth temperature in the second preset growth condition, and the first growth pressure in the first preset growth condition is greater than the second growth pressure in the second preset growth condition.

[0072] Specifically, the first growth temperature is between 600℃ and 800℃, the second growth temperature is between 900℃ and 1300℃, the first growth pressure is between 300 torr and 500 torr, and the second growth pressure is between 150 torr and 250 torr.

[0073] Specifically, the thickness of the gallium nitride buffer layer grown under the first preset growth condition and the thickness of the gallium nitride buffer layer grown under the second preset growth condition can be set according to the needs of specific application scenarios. As long as the conversion from the first preset growth condition to the second preset growth condition is completed during the entire growth process of the gallium nitride buffer layer, realizing the rapid conversion of three-dimensional gallium nitride growth to two-dimensional growth, and the surface of the gallium nitride buffer layer has high flatness, it is sufficient. At this time, nanopores can be introduced into the gallium nitride buffer layer (different from the nanopores generated by the pore structure in the aluminum nitride filling layer), which is conducive to the subsequent lift-off process, can reduce the damage of the gallium nitride epitaxial layer to the gallium nitride epitaxial layer in the subsequent lift-off process, and realize the epitaxial growth of high-quality gallium nitride epitaxial layer.

[0074] In this embodiment, step S500 specifically includes:

[0075] S501: Under the second preset growth conditions, a gallium nitride epitaxial layer on a gallium nitride buffer layer is grown in a chemical vapor deposition apparatus.

[0076] Example 2

[0077] This embodiment provides a method for preparing a gallium nitride epitaxial layer, the method comprising the following steps:

[0078] S10: The gallium nitride epitaxial layer is grown using the gallium nitride epitaxial growth method in any of the embodiments of Example 1 described above.

[0079] S20: Separate the substrate and gallium nitride epitaxial layer from the aluminum nitride filling layer, and remove the aluminum nitride filling layer and gallium nitride buffer layer on the gallium nitride epitaxial layer.

[0080] The method in this embodiment can prepare a high-quality gallium nitride epitaxial layer.

[0081] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for epitaxial growth of gallium nitride, characterized in that, Includes the following steps: A porous alumina mask layer is grown on a substrate; the nanopores in the porous alumina mask layer penetrate the porous alumina mask layer. An aluminum nitride filling layer is grown within the nanopores of the porous alumina mask layer; Remove the alumina mask layer; A gallium nitride buffer layer is grown within and on the aluminum nitride filling layer; A gallium nitride epitaxial layer is grown in the gallium nitride buffer layer; The step of growing a gallium nitride buffer layer within and on the aluminum nitride filling layer includes: Gallium nitride buffer layers are grown sequentially within the aluminum nitride filler layer and on the aluminum nitride filler layer in a chemical vapor deposition apparatus under first preset growth conditions and second preset growth conditions. The first growth temperature in the first preset growth conditions is lower than the second growth temperature in the second preset growth conditions, and the first growth pressure in the first preset growth conditions is greater than the second growth pressure in the second preset growth conditions. The first growth temperature is between 600°C and 800°C, the second growth temperature is between 900°C and 1300°C, the first growth pressure is between 300 torr and 500 torr, and the second growth pressure is between 150 torr and 250 torr. The step of growing a gallium nitride epitaxial layer in the gallium nitride buffer layer specifically includes: Under the second preset growth conditions, a gallium nitride epitaxial layer on the gallium nitride buffer layer is grown in a chemical vapor deposition apparatus; The step of growing a porous alumina mask layer on the substrate specifically includes: An aluminum thin film is grown on the substrate; The alumina mask layer is subjected to surface chemical etching treatment; The aluminum film is subjected to anodizing treatment to obtain an aluminum oxide mask layer with a blind hole array; The alumina mask layer is anodized to make the blind holes extend toward the substrate, thus obtaining the porous alumina mask layer.

2. A method for preparing a gallium nitride epitaxial layer, characterized in that, Includes the following steps: The gallium nitride epitaxial layer is grown using the gallium nitride epitaxial growth method described in claim 1. Separate the substrate and the gallium nitride epitaxial layer from the aluminum nitride filler layer, and remove the aluminum nitride filler layer and the gallium nitride buffer layer on the gallium nitride epitaxial layer.

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