P-Type SiC Epitaxial Wafer Growth With Controlled C/Si Ratio
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Solution Overview
Problem
Existing methods struggle to produce high-concentration, high-quality p-type SiC epitaxial wafers with low resistance and uniform dopant distribution, often resulting in defects and non-mirror surfaces due to the generation of volatile aluminum chloride and challenges in maintaining the C/Si ratio during doping.
Innovation Solution
A production method that adjusts the input raw material C/Si ratio to differ from the total gas C/Si ratio, using a Cl-based gas and a dopant gas containing Al and C, with controlled gas ratios to achieve a p-type SiC epitaxial wafer with a dopant concentration of at least 1×1018 cm−3 and improved in-plane uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a Cl-based gas is used together with an Al-containing dopant gas to achieve high-concentration doping, then the dopant concentration increases, but highly volatile aluminum chloride is generated which consumes Al and Cl, decreasing incorporation efficiency and causing defects and non-mirror surfaces
Solution Approach 1:
The patent changes the chemical parameters of the doping system by replacing Al-containing gases with Ga-containing gases (such as trimethylgallium). This parameter change eliminates the formation of volatile aluminum chloride while maintaining high-concentration doping capability, as gallium does not form similarly volatile compounds with chlorine under the same conditions
Solution Approach 2:
The patent employs a dopant gas (Ga-containing gas) that is consumed in the doping process without creating persistent harmful byproducts. The gallium-based dopant provides the necessary doping effect while avoiding the long-term issues associated with aluminum chloride accumulation and volatility problems
2Productivity
If the feed amount of Si feedstock gas is increased to accelerate the growth rate, then the growth rate increases, but defects due to Si aggregation more readily occur
Solution Approach 1:
The patent introduces a Cl-based gas as an intermediary substance that mediates between the Si feedstock gas and the growing epitaxial film. This intermediary chlorine-based species prevents direct Si aggregation by facilitating controlled chemical reactions, thereby enabling high growth rates while suppressing defect formation
Solution Approach 2:
The patent changes the chemical environment by introducing chlorine-based gases, which alters the reaction kinetics and intermediate species formation. This parameter change in the gas phase chemistry enables faster growth rates without the detrimental Si aggregation effects that occur in conventional hydrogen-based atmospheres
3Quantity of substance
If co-doping method is used to achieve high-concentration doping, then the dopant concentration increases, but a high concentration of n-type impurities is included which affects mobility and is generally unused
Solution Approach 1:
Instead of using co-doping with n-type impurities to achieve high concentration, the patent inverts the approach by using Ga-containing dopants that can achieve high p-type doping concentrations independently. This eliminates the need for n-type co-doping and its associated mobility degradation issues
Solution Approach 2:
The patent changes the dopant type from Al-based (which requires co-doping) to Ga-based dopants. This parameter change in the dopant chemistry enables high-concentration doping through a single dopant source, eliminating the contamination with n-type impurities that occurs in co-doping methods
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method enables the production of high-quality p-type SiC epitaxial wafers with low resistance, high in-plane uniformity, and reduced defects, facilitating the production of uniform SiC devices with low cost and high yield.
Implementation Method 1
a step of obtaining a p-type SiC epitaxial wafer having an Al dopant concentration of at least 1×1018 cm−3 by forming a p-type SiC epitaxial film on a substrate in a film-forming atmosphere comprising the feedstock gas, a Cl-based gas containing Cl in the molecule, and a dopant gas containing Al and C in the molecule
Implementation Method 2
a dopant gas containing Al and C in the molecule
Data Source
AI summary
A method of producing a p-type SiC epitaxial wafer, the method including: a step of setting an input raw material C/Si ratio, being a ratio between the C element and the Si element in a feedstock gas; and a step of obtaining a p-type SiC epitaxial wafer having an Al dopant concentration of at least 1×1018 cm−3 by forming a p-type SiC epitaxial film on a substrate in a film-forming atmosphere comprising the feedstock gas, a Cl-based gas containing Cl in the molecule, and a dopant gas containing Al and C in the molecule, wherein the input raw material C/Si ratio is set based on a total gas C/Si ratio, being a ratio between the C element and the Si element in the film-forming atmosphere containing the C element included in the dopant gas, the input raw material C/Si ratio differs from the total gas C/Si ratio, and the input raw material C/Si ratio is 0.8 or less.