Method for improving doping uniformity and reproduction stability of silicon carbide epitaxial wafer

Abstract

The invention discloses a method for improving doping uniformity and reproduction stability of a silicon carbide epitaxial wafer, which comprises the following steps of: (1) placing a silicon carbide substrate on a graphite carrying disc in a reaction chamber, and introducing carrier gas; (2) carrying out epitaxial growth, adjusting the temperature in the reaction chamber to a growth temperature, introducing a carbon source and a silicon source as growth sources, synthesizing a growth film through chemical reaction, introducing ammonia gas as an n-type doping source in the growth process, and growing to a target doping concentration and a target thickness; and (3) closing the carbon source, the silicon source and the n-type doping source, and cooling to obtain the silicon carbide epitaxial wafer. According to the invention, by using the doped source ammonia gas, the doped ammonia gas can promote the thermal chemical reaction during deposition of the silicon carbide film, and is beneficial to the stability during doping and the reproducibility between wafers, so that the yield and consistency of epitaxial wafers are effectively improved, the productivity is improved, the yield is increased, and the economic benefit is increased.

Description

Technical Field

[0001] The invention relates to the field of semiconductors, and in particular to a method for improving the doping uniformity and reproducibility stability of a silicon carbide epitaxial wafer. Background Art

[0002] As an excellent third-generation semiconductor material, silicon carbide (SiC) has a bandgap width of 2.3-3.3eV, a breakdown electric field strength ten times that of silicon, and a thermal conductivity three times that of silicon, making it applicable to high-power and high-temperature devices. The wide bandgap characteristics and high thermal stability of silicon carbide allow certain types of silicon carbide devices to operate indefinitely at junction temperatures of 300°C or higher, making silicon carbide a key material for the preparation of high-end power semiconductor devices.

[0003] The thickness and doping concentration uniformity of silicon carbide epitaxial materials, and the repeatability and stability between wafers (Run to Run) are all important performance manifestations of silicon carbide epitaxial equipment. Good material uniformity and reproducibility can not only reduce the discreteness of device performance, but also improve the reliability of the device. Therefore, one of the current hot topics of research at home and abroad is how to improve the thickness and doping concentration uniformity of silicon carbide epitaxial wafers, and the repeatability and stability between wafers. This is also a key technology that needs to be broken through and mastered in silicon carbide epitaxy. The methods for optimizing doping concentration uniformity reported in existing literature and patents are mainly aimed at optimizing key process parameters such as chlorine-silicon ratio, carbon-silicon ratio, main hydrogen flow, growth temperature, and carrier gas ratio of various gas nozzles. However, changes in such parameters will also bring about changes in important indicators of epitaxial wafers such as background concentration, surface morphology, and defect density.

[0004] The n-type doping source currently used in epitaxial equipment is nitrogen, which has the advantages of low cost and high safety. However, the stable reproducibility of doping requires a large degree of monitoring and debugging to the required concentration of doping, which will affect commercial production efficiency and production yield. Summary of the invention

[0005] Purpose of the invention: The present invention aims to provide a method that can effectively improve the doping uniformity and reproducibility stability of silicon carbide epitaxial wafers without changing the key epitaxial process parameters.

[0006] Technical solution: The method for improving the doping uniformity and reproducibility stability of silicon carbide epitaxial wafers provided by the present invention comprises the following steps:

[0007] (1) placing a silicon carbide substrate on a graphite carrier in a reaction chamber and introducing a carrier gas;

[0008] (2) performing epitaxial growth, adjusting the temperature in the reaction chamber to the growth temperature, introducing a carbon source and a silicon source as growth sources, synthesizing a growing film through a chemical reaction, and introducing ammonia as an n-type doping source during the growth process to grow to a target doping concentration and a target thickness;

[0009] (3) Turn off the carbon source, silicon source and n-type doping source, and cool down to obtain a silicon carbide epitaxial wafer.

[0010] Furthermore, in step (1), the pressure in the reaction chamber is 20 kPa-30 kPa, and the carrier gas is H 2 .

[0011] Furthermore, in step (2), the growth temperature is 1600° C.-1660° C.; the silicon source is silane, and the carbon source is propane.

[0012] Furthermore, in step (2), the purity of the ammonia is 100%; the ammonia is stored in a liquid ammonia tank in the form of liquid ammonia, and enters the reaction chamber in the form of gas through an ammonia purifier.

[0013] Furthermore, the pure ammonia gas is used in a double dilution flow control method to perform the doping process, which can effectively improve the doping efficiency. That is, the effective equivalent ammonia gas can obtain a high doping effect and improve the concentration stability and reproducibility between slices.

[0014] Furthermore, in step (2), the equivalent of the ammonia gas and the n-type doping concentration in the silicon carbide epitaxial wafer have a syntenic growth relationship.

[0015] Preferably, the equivalent of the ammonia gas is 0.005-25 sccm, and the n-type doping concentration in the obtained silicon carbide epitaxial wafer is 1E16 / cm 3 -5E18 / cm 3 .

[0016] More preferably, when the doping concentration is 5E18 / cm 3 When the ammonia equivalent of this method is 20.0-25.0sccm; when the doping concentration is 1E18 / cm 3 When the ammonia equivalent of this method is 4.0-5.0sccm; when the doping concentration is 2E16 / cm 3 When the ammonia equivalent of this method is 0.05-1.0sccm; when the doping concentration is 1E16 / cm 3 The ammonia equivalent of this method is 0.005-0.1sccm.

[0017] Principle of the invention: Based on the existing technical framework (Nuflare silicon carbide epitaxial equipment), the present invention uses ammonia instead of nitridation as the n-type doping gas source and its excellent thermochemical reaction characteristics, so that when n-type doping, continuous growth can be achieved, and a highly consistent doping concentration performance can be achieved without debugging.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: By using ammonia as a doping source, the present invention can promote the thermochemical reaction during the deposition of silicon carbide thin films, which is beneficial to the stability during doping and the reproducibility between wafers, thereby effectively improving the yield and consistency of epitaxial wafers, improving production capacity and yield and increasing economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the silicon carbide epitaxial wafer in Example 1;

[0020] Figure 2 is a schematic structural diagram of the epitaxial device used in Example 1;

[0021] Figure 3 This is a schematic diagram of double dilution flow control of the epitaxial device used in Example 1;

[0022] Figure 4 This is a test result diagram of Example 1 using pure ammonia as the n-type doping source;

[0023] Figure 5 This is a test result diagram of Comparative Example 1 using nitrogen as the n-type doping source. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with specific embodiments and drawings.

[0025] Example 1: Figure 1 As shown, the silicon carbide epitaxial wafer provided in this embodiment includes a silicon carbide substrate, an N-type buffer layer and an N-type drift layer from bottom to top, and the preparation method adopts a high-speed rotating device for growing a silicon carbide epitaxial film (hereinafter referred to as an epitaxial device) and an epitaxial structure as shown in FIG. Figure 2 As shown, the specific steps are as follows: The main gas sources for the silicon carbide epitaxial film include: (1) hydrogen (H 2 ) is used as carrier gas, (2) silane is used as Si source for silicon carbide, (3) propane is used as carbon gas source, and (4) ammonia (NH 3 )supply.

[0026] First, the silicon carbide substrate is placed on a graphite carrier in a low-pressure 26.7KPa chamber and heated to 1650 degrees with a resistive heater. The chamber is filled with hydrogen as the carrier gas. Silane and propane are introduced to produce a chemical reaction. After high temperature, SiH 4 and C3 H 8 Chemical synthesis produces SiC epitaxial thin films. During the film growth process, 100% pure ammonia is introduced (ammonia is stored in a liquid ammonia tank in liquid form and enters the reaction chamber in gaseous form through an ammonia purifier) ​​to form an n-type doped silicon carbide epitaxial thin film. After the required film doping concentration and thickness conditions are achieved, it can be made into a silicon carbide device through device manufacturing.

[0027] During the preparation process, 100% pure ammonia is used in the epitaxial equipment to control the doping process with a double dilution flow rate, which can effectively improve the doping efficiency, that is, the effective equivalent ammonia can obtain a high doping effect, and can improve the concentration stability and reproducibility between wafers. Figure 3 As shown, the dual dilute flow controller uses a dilute flow meter to adjust the flow over a wide range. Its flow combination needs to be configured with three single flow meters. The settings are source, push, and dilute. The output flow (equivalent) formula = [source / (source+push)]*dilute. This configuration can obtain the required equivalent output with more diverse changes than a single MFC; it is also less limited by the limitation of a single MFC head.

[0028] Comparative Example 1: The difference from Example 1 is that nitrogen is used as the n-type doping source.

[0029] The silicon carbide epitaxial wafers prepared in Example 1 and Comparative Example 1 were tested for content. The results are as follows: Figure 4 and Figure 5 shown.

[0030] Figure 4 For the continuous growth of 16 slices, no concentration adjustment statistical control chart is made. It can be seen that the use of ammonia as the gas source for n-type doping in the present invention completely achieves no need for adjustment between slices, that is, n-type doping concentration results with high stability and reproducibility can be obtained. Therefore, it is concluded that when ammonia is used as the n-type doping, the doping of slices is almost the same, and the production results with high repeatability can be achieved, and the stability and reproducibility are excellent. At the same time, the production efficiency and yield are also improved. The economic benefits are significantly improved.

[0031] Figure 5 Because nitrogen is used as the gas source for n-type doping, the doping concentration of a monolithic epitaxial cavity will vary greatly when growing silicon carbide films from slice to slice (Run to Run) due to its poor thermochemical reaction. If the concentration cannot be corrected and adjusted in time, the concentration may not reach the expected target. Therefore, it is concluded that when nitrogen is used as n-type doping, the doping variation between slices is large and the stability and reproducibility are poor.

Claims

1. A method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers, characterized in that: The following steps are involved: (1) placing a silicon carbide substrate on a graphite carrier in a reaction chamber and introducing a carrier gas; (2) performing epitaxial growth, adjusting the temperature in the reaction chamber to the growth temperature, introducing a carbon source and a silicon source as growth sources, synthesizing a growing film through a chemical reaction, and introducing ammonia as an n-type doping source during the growth process to grow to a target doping concentration and a target thickness; (3) Turn off the carbon source, silicon source and n-type doping source, and cool down to obtain a silicon carbide epitaxial wafer.

2. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step (1), the pressure in the reaction chamber is 20 kPa-30 kPa.

3. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step (1), the carrier gas is H2.

4. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step (2), the growth temperature is 1600°C-1660°C.

5. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step (2), the silicon source is silane and the carbon source is propane.

6. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step (2), the purity of the ammonia gas is 100%.

7. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 6, characterized in that: The ammonia is stored in a liquid ammonia tank in the form of liquid ammonia, and enters the reaction chamber in the form of gas through an ammonia purifier.

8. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 7, characterized in that: The pure ammonia gas is doped using a double dilution flow control method.

9. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 1, characterized in that: In step (2), the equivalent of the ammonia gas and the n-type doping concentration in the silicon carbide epitaxial wafer have a syntenic growth relationship.

10. The method for improving doping uniformity and reproducibility stability of silicon carbide epitaxial wafers according to claim 9, characterized in that: The equivalent of the ammonia gas is 0.005-25 sccm, and the n-type doping concentration in the obtained silicon carbide epitaxial wafer is 1E16 / cm 3 -5E18 cm 3 .

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