Silicon Carbide Substrate Vapor Phase Etching for Flat Surface
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Solution Overview
Problem
The existing methods for manufacturing silicon carbide semiconductor substrates using vapor phase etching with a mixed gas of hydrogen and propane at high substrate temperatures are inefficient in removing foreign matters and defects, leading to a rough surface and increased manufacturing costs.
Innovation Solution
Performing vapor phase etching on a silicon carbide seed substrate using only hydrogen, followed by supplying a carbon-atom containing gas during the etching process to balance the composition ratio and promote flat epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If vapor phase etching is performed using a mixed gas of hydrogen and propane at high substrate temperature to remove foreign matters and defects, then the surface cleaning effect is improved, but the surface roughness increases and manufacturing cost increases
Solution Approach 1:
The patent segments the vapor phase etching process into two distinct stages: a first etching stage using hydrogen gas to remove foreign matters and defects, followed by a second etching stage using a carbon-containing gas to smooth the surface. This segmentation allows each stage to perform its specific function optimally without the harmful effects of combining both gases throughout the entire process.
Solution Approach 2:
The patent maintains continuous vapor phase etching action throughout the process by transitioning from hydrogen gas to carbon-containing gas without interrupting the etching environment. This continuous action ensures that the surface remains under controlled etching conditions, preventing oxidation and maintaining surface quality while transitioning between different gas types.
2Manufacturing precision
If vapor phase etching is performed using a mixed gas of hydrogen and propane at high substrate temperature, then foreign matters are removed, but the etching efficiency decreases for certain types of foreign matters
Solution Approach 1:
The patent divides the etching process into two sequential stages with different gas compositions. The first stage uses hydrogen gas specifically for removing organic foreign matters and defects, while the second stage uses carbon-containing gas for inorganic foreign matters and surface smoothing. This segmentation optimizes etching efficiency for different types of contaminants.
Solution Approach 2:
The patent changes the chemical composition parameter of the etching gas from hydrogen to carbon-containing gas between stages. This parameter change allows the process to adapt to different etching requirements: hydrogen for organic contaminant removal and carbon-containing gas for inorganic contaminant removal and surface planarization.
3Manufacturing precision
If mechanical polishing or chemical polishing is performed on the silicon carbide single crystal substrate before epitaxial growth, then the surface flatness is improved, but polishing marks and roughness are introduced
Solution Approach 1:
The patent replaces mechanical polishing methods with a chemical vapor phase etching process. Instead of using mechanical abrasion that creates polishing marks and surface roughness, the patent uses controlled chemical reactions to remove material uniformly, achieving surface flatness without introducing mechanical damage or polishing artifacts.
Solution Approach 2:
The patent utilizes hydrogen gas as a reactive etching medium that chemically reacts with carbon and silicon on the substrate surface to form volatile compounds. This chemical etching process provides precise control over material removal and produces a clean, mark-free surface compared to mechanical polishing 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
This method effectively removes foreign matters and defects, resulting in a silicon carbide semiconductor substrate with a highly flat surface at a lower cost by optimizing the surface preparation for epitaxial growth.
Implementation Method 1
Hydrogen reacts with carbon and silicon constituting the main surface of the silicon carbide single crystal substrate, and produces hydrocarbon and silicane in the vapor phase. Therefore, by exhausting the hydrocarbon and silicane, it is possible to remove foreign matters of carbide or silicide adhered to or deposited on the main surface of the silicon carbide single crystal substrate and to remove defects formed on the main surface of the silicon carbide single crystal substrate.
Implementation Method 2
Hydrogen reacts with carbon and silicon constituting the main surface of the silicon carbide single crystal substrate, and produces hydrocarbon and silicane in the vapor phase.
Implementation Method 3
the carbon atoms and the silicon atoms differ from each other in terms of a rate of reaction with the hydrogen atoms, with the result that the main surface of the silicon carbide single crystal substrate may become rough after the vapor phase etching.
Implementation Method 4
Silicon carbide is epitaxially grown on a silicon carbide single crystal substrate serving as a seed substrate.
Data Source
AI summary
A method for manufacturing a silicon carbide semiconductor substrate is provided to offer a silicon carbide semiconductor substrate having a highly flat surface at low cost. The method includes: a step of preparing a silicon carbide substrate as a seed substrate; a step of performing vapor phase etching onto a main surface of the silicon carbide substrate; and a step of epitaxially growing silicon carbide on the main surface. A carbon-atom containing gas is supplied to silicon carbide substrate from a point of time in the step of performing the vapor phase etching.