Silicon carbide composite substrate for preparing nitride single crystal thin film

Abstract

The present invention relates to a silicon carbide composite substrate for preparing a nitride single crystal thin film. The composite substrate is provided with a silicon nitride layer with a flat surface on the surface of the silicon carbide substrate, so as to well flatten the uneven surface of the silicon carbide substrate, so that the substrate surface becomes smooth and flat, which is conducive to the subsequent epitaxial growth of high-quality nitride single crystal thin films. In addition, the silicon carbide substrate of the present invention does not need to be thinned, and has a large thickness, which is conducive to the processing of the subsequent process, thereby further improving the quality of the entire finished product, improving the yield of the entire production process, reducing the scrap rate, and saving production costs.

Description

Technical Field

[0001] The invention relates to the technical field of new silicon carbide materials, and in particular to a silicon carbide composite substrate for preparing a nitride single crystal film. Background Art

[0002] Silicon carbide, as a semiconductor material used in light-emitting device transistors and semiconductor device manufacturing, has a larger band gap than commonly used single-crystal silicon. In addition, the lattice matching between silicon carbide substrate and nitride semiconductor is good. These characteristics make nitride semiconductor materials made of silicon carbide substrate have the advantages of high breakdown voltage, good thermal conductivity, low on-resistance, etc., and have broad market application prospects.

[0003] In order to produce high-quality nitride single crystal thin films, a silicon carbide substrate with good physical properties and appearance flatness is required. The existing technology mainly uses physical grinding processes to obtain silicon carbide substrates with smooth and flat surfaces. However, due to factors such as the grinding pressure, grinding speed, polishing liquid concentration and pH value of the grinder, the silicon carbide substrate obtained by this process is often not flat enough, which in turn affects the quality of the nitride single crystal thin film. In addition, the physical grinding process will also cause the silicon carbide substrate to become thinner, especially for reprocessed products, which will become thinner and thinner. The thinning of the substrate increases the difficulty of later process processing.

[0004] Therefore, it is necessary to develop a silicon carbide substrate with a smooth and flat surface and a large thickness for preparing nitride single crystal thin films. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a silicon carbide composite substrate for preparing a nitride single crystal thin film. The composite substrate is provided with a silicon nitride layer with a flat surface on the surface of the silicon carbide substrate, which well flattens the uneven surface of the silicon carbide substrate, so that the substrate surface becomes smooth and flat, which is conducive to the subsequent epitaxial growth of high-quality nitride single crystal thin films. In addition, the silicon carbide substrate of the present invention does not need to be thinned, and has a large thickness, which is conducive to the processing of the later process, thereby further improving the quality of the entire finished product, improving the yield of the entire production process, reducing the scrap rate, and saving production costs.

[0006] Another object of the present invention is to provide a method for preparing the silicon carbide composite substrate.

[0007] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0008] A silicon carbide composite substrate for preparing a nitride single crystal thin film, comprising:

[0009] Silicon carbide substrate; and

[0010] A silicon nitride layer is arranged on the upper surface of the silicon carbide substrate, the silicon nitride layer has a flat upper surface, and a distance D from the highest point of the upper surface of the silicon carbide substrate to the upper surface of the silicon nitride layer is greater than 0 and less than or equal to 10 μm.

[0011] Preferably, the distance D is > 0 and ≤ 3 μm, preferably > 100 nm and ≤ 3 μm, and more preferably > 500 nm and ≤ 3 μm. If the silicon nitride layer is too thick, it will affect a series of physical properties of the silicon carbide substrate, such as electrical conductivity and thermal conductivity, so that the characteristics cannot be prominently displayed; if the silicon nitride layer is too thin (i.e., the upper surface of the silicon nitride layer is lower than the highest point of the upper surface of the silicon carbide substrate), it will not be able to make the substrate surface smooth and flat.

[0012] The present invention also provides a method for preparing the silicon carbide composite substrate, comprising:

[0013] A silicon carbide substrate is placed in a reaction chamber, and the distance between the highest point on the upper surface of the silicon carbide substrate and the top wall of the reaction chamber is controlled to be >0 and ≤10 μm. After evacuation, SiO gas and nitrogen gas are introduced to heat the silicon carbide substrate, thereby forming a silicon nitride layer on the upper surface of the silicon carbide substrate to obtain a silicon carbide composite substrate.

[0014] In the present invention, SiO gas and nitrogen gas may undergo the following chemical reaction.

[0015] 6SiO+4N 2 =2Si 3 N 4 +3O 2

[0016] Preferably, the flow ratio of SiO gas to nitrogen gas is 1.5:(1-2), preferably 1.5:(1-1.5), and more preferably 1.5:(1-1.2).

[0017] Preferably, after evacuation, the pressure in the reaction chamber is 1*10 -6 Pa-1*10 -5 Pa.

[0018] Preferably, when p(O 2 ) / pθ≤10 -19 ,p(SiO) / pθ≥6.0*10 1.0 , that is, when the SiO partial pressure p(SiO) ≥ 6.0MPa (where p(O 2 ) is the oxygen partial pressure, pθ is the standard atmospheric pressure), stop introducing SiO gas and nitrogen, which is the optimal condition for SiO gas and nitrogen to fully react. At this time, introducing SiO gas and nitrogen again will cause unnecessary waste. Then, the silicon carbide substrate is heated to a certain temperature to react with SiO gas and nitrogen to generate Si 3 N4 .

[0019] The purity of the nitrogen used in the present invention is 99.999%, which also contains 0.001% of O 2 , that is, p(O 2 ) / pθ=1.0*10 -5 . With SiO gas and N 2 After being continuously charged with the atmosphere in the reaction chamber, it mixes with the atmosphere in the reaction chamber. 2 ) / pθ≤10 -19 ,p(SiO) / pθ≥6.0*10 1.0 , that is, when the SiO partial pressure p(SiO) ≥ 6.0MPa, SiO gas and nitrogen begin to react to generate Si 3 N 4 .

[0020] Preferably, the heating temperature is 1450-2000° C. SiO gas and N 2 The reaction is preferably carried out under isothermal conditions.

[0021] Preferably, Si powder is placed in the reaction chamber and heated to above 300°C. 2 The O generated by the reaction 2 Under high temperature conditions, it can react with Si powder to generate SiO. The newly produced SiO can continue to react with N 2 The reaction generates the Si required by the present invention 3 N 4 The advantage of adding Si powder is that the O generated by the reaction can be used 2 To generate more Si 3 N 4 , making Si 3 N 4 The extraction rate is higher, the utilization rate of the gas introduced is higher, and the Si 3 N 4 The layer is more complete and thick. By placing Si powder in the reaction chamber, the amount of SiO gas used can be reduced, thereby reducing production costs.

[0022] Preferably, the silicon carbide substrate is plasma cleaned before being placed in the reaction chamber. If a single hydrogen gas is used as the cleaning gas, the surface of the substrate will be rough after cleaning. This is because the hydrogen plasma is relatively active and the degree of ionization is relatively high after electron cyclotron resonance (ECR) discharge, causing the substrate to be excessively reduced by hydrogen active ions, resulting in amorphous products gathering on the substrate surface. In order to avoid the above problems, the present invention adds nitrogen to the hydrogen cleaning gas. Nitrogen active particles can effectively inhibit the excessive occurrence of reduction reactions, making the surface of the silicon carbide substrate initially smooth and flat.

[0023] Preferably, in a filled H 2 and N 2 Plasma cleaning is performed in the chamber, H 2 and N 2 The flow ratio is (3-15): (1-5), preferably (3-7): (1:2). The cleaning temperature is 1000-1500°C, preferably 1000-1200°C. The microwave power is 500-1500w, preferably 800-1000w. The cleaning time is more than 60min.

[0024] Preferably, the surface of the substrate cleaned under the following process conditions is the smoothest and flattest and will not affect or change other physical properties of the substrate. The cleaning process conditions are: the flow ratio of hydrogen to nitrogen is (3-7): (1:2); the microwave power is 800-1000w; the cleaning temperature is 1000-1200℃; and the cleaning time is more than 60min.

[0025] The present invention controls the thickness of the formed silicon nitride layer by controlling the distance between the highest point on the upper surface of the silicon carbide substrate and the top wall in the reaction chamber.

[0026] In some specific embodiments, the cleaned silicon carbide substrate is placed on a lifting platform in a reaction chamber. The lifting platform has a fine-tuning function. The distance can be accurately controlled to the micron level through the fine-tuning digital display. Therefore, by adjusting the lifting platform, the distance between the highest point on the upper surface of the silicon carbide substrate and the top wall in the reaction chamber can be accurately controlled, thereby controlling the thickness of the silicon nitride layer formed.

[0027] Preferably, the preparation method of the present invention further comprises: grinding the upper surface of the obtained silicon carbide composite substrate. After the silicon carbide composite substrate is taken out from the reaction chamber, the upper surface of the substrate is processed and ground according to a normal grinding process to finally obtain a substrate product with a smoother and flatter surface.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention provides a silicon carbide composite substrate for preparing a nitride single crystal thin film. The composite substrate flattens the uneven surface of the silicon carbide substrate by arranging a silicon nitride layer with a flat surface on the surface of the silicon carbide substrate, so that the substrate surface becomes smooth and flat, which is conducive to the subsequent epitaxial growth of high-quality nitride single crystal thin films. In addition, the silicon carbide substrate of the present invention does not need to be thinned, and has a large thickness, which is conducive to the processing of the later process, thereby further improving the quality of the entire finished product, improving the yield of the entire production process, reducing the scrap rate, and saving production costs.

[0030] 2. The reaction of the present invention is a gas phase reaction, and the reaction contact is relatively sufficient, so the reaction efficiency is relatively high, which can relatively accelerate the reaction rate and shorten the entire production cycle.

[0031] 3. The present invention can remove the useless substances (O 2 ) recycling, making Si 3 N 4 The extraction rate is higher and the utilization rate of the input gas is higher, which can speed up the entire reaction cycle and have more mass production advantages in the production development process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic structural diagram of the silicon carbide composite substrate of the present invention.

[0033] Description of reference numerals:

[0034] 1 is a silicon carbide substrate; 2 is a silicon nitride layer. DETAILED DESCRIPTION

[0035] In order to make the content of the present invention easier to understand, the technical scheme of the present invention is further described below in conjunction with specific embodiments, but the present invention is not limited thereto. All technologies realized based on the above content of the present invention are included in the scope that the present invention is intended to protect. Unless otherwise specified, the raw materials and reagents used in the examples are all commercially available products. The reagents, instruments or operating procedures not recorded herein are all contents that can be routinely determined by a person of ordinary skill in the art.

[0036] Example 1

[0037] First, the silicon carbide substrate was plasma cleaned. A hydrogen and nitrogen mixed gas was introduced into the cleaning chamber, with a hydrogen to nitrogen flow ratio of 3:1; the microwave power was 800w; the cleaning temperature was 1000°C; and the cleaning time was 60min.

[0038] Place the cleaned silicon carbide substrate on the lifting platform in the reaction chamber, and adjust the height of the lifting platform so that the distance between the highest point on the upper surface of the silicon carbide substrate and the top wall of the reaction chamber is 5 μm. Then, evacuate the reaction chamber to a pressure of 1*10 -6 After Pa, SiO gas and N with a flow ratio of 3:2 were introduced. 2 , when p(O 2 ) / pθ=10 -19 , p(SiO) / pθ=6.0*10 1.0 , that is, when the SiO partial pressure p(SiO) = 6.0MPa (where p(O 2 ) is the oxygen partial pressure, pθ is the standard atmospheric pressure), the introduction of SiO gas and nitrogen is stopped, and then the silicon carbide substrate is heated to 2000°C to cause the following chemical reaction:

[0039] 6SiO+4N 2 =2Si3 N 4 +3O 2

[0040] Si generated by the reaction 3 N 4 Cover the upper surface of the silicon carbide substrate to make the uneven surface of the substrate flat.

[0041] The silicon powder was placed in the chamber at the beginning. During the heating process to 2000℃, when it was heated to 300℃, the silicon powder and a small amount of O in the chamber 2 The reaction begins, at which time p(O 2 ) / pθ=10 -19 , the following reaction occurs:

[0042] 2Si+O 2 =2SiO

[0043] The silicon carbide substrate (ie, silicon carbide composite substrate) with the surface covered with the silicon nitride layer is taken out, and the upper surface of the substrate is processed and ground by a grinding process, so as to finally obtain a finished substrate with a smoother and flatter upper surface.

[0044] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a silicon carbide composite substrate for preparing a nitride single crystal thin film, characterized in that: The silicon carbide composite substrate comprises a silicon carbide substrate and a silicon nitride layer, wherein the silicon nitride layer is arranged on the upper surface of the silicon carbide substrate, the silicon nitride layer has a flat upper surface, and a distance D from the highest point of the upper surface of the silicon carbide substrate to the upper surface of the silicon nitride layer is greater than 0 and less than or equal to 10 μm; The preparation method comprises: Plasma cleaning is performed on a silicon carbide substrate in a chamber filled with H2 and N2, wherein the ratio of H2 to N2 is (3-15):(1-5) and the cleaning temperature is 1000-1500°C. Si powder is placed in a reaction chamber, and a silicon carbide substrate is placed in the reaction chamber. The distance between the highest point on the upper surface of the silicon carbide substrate and the top wall in the reaction chamber is controlled to be >0 and ≤10μm. After evacuation, SiO gas and nitrogen are introduced to heat the silicon carbide substrate and the Si powder. The SiO gas and nitrogen react to generate Si3N4 and O2. The O2 generated by the reaction of SiO and N2 reacts with the Si powder under high temperature conditions to generate SiO. The newly produced SiO continues to react with N2 to generate the required Si3N4, thereby forming a silicon nitride layer on the upper surface of the silicon carbide substrate to obtain a silicon carbide composite substrate.

2. The preparation method according to claim 1, characterized in that: The flow ratio of SiO gas to nitrogen gas is 1.5:(1-2).

3. The preparation method according to claim 1 or 2, characterized in that: The heating temperature is 1450℃-2000℃.

4. The preparation method according to claim 1 or 2, characterized in that: Also includes: The upper surface of the obtained silicon carbide composite substrate was polished.

5. The preparation method according to claim 1, characterized in that: The distance D>0 and ≤3 μm.

6. The preparation method according to claim 5, characterized in that: The distance D is >100 nm and ≤3 μm.

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