Cobalt Silicide Buffer Layer for Silicon Carbide Lattice Mismatch
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Solution Overview
Problem
The growth of high-quality cubic silicon carbide (3C—SiC) single crystal films on silicon substrates is hindered by significant lattice mismatch, leading to defects and voids due to the large difference in lattice constants between silicon and silicon carbide, which existing buffer layers like cubic boron phosphide fail to adequately address.
Innovation Solution
A semiconductor substrate with a buffer layer composed of cobalt silicide layers having lattice constants between 0.4447 nm and 0.5367 nm, specifically CoSi and CoSi2, is used to reduce lattice mismatch between the silicon substrate and the silicon carbide single crystal film, allowing for continuous or staged composition changes within the buffer layer to minimize defects and enhance crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a cubic boron phosphide (c-BP) buffer layer is inserted to reduce lattice mismatch between silicon substrate and cubic silicon carbide, then the lattice mismatch is reduced to 4.1%, but a huge lattice mismatch of 17.9% remains between silicon substrate and c-BP, causing many defects in the c-BP film itself
Solution Approach 1:
The patent introduces a cobalt silicide buffer layer as an intermediary between the silicon substrate and cubic silicon carbide layer. This intermediate layer has a lattice constant that can be adjusted to match both the silicon substrate and the 3C-SiC layer, serving as a mediator that gradually transitions the lattice structure and prevents direct confrontation between the two mismatched materials.
Solution Approach 2:
The patent utilizes the adjustable lattice constant parameter of cobalt silicide (ranging from 0.4447 nm for CoSi to 0.5367 nm for CoSi2) to optimize the buffer layer composition. By controlling the Co/Si ratio, the lattice constant can be tuned to achieve optimal matching with both the silicon substrate and the cubic silicon carbide layer, thereby minimizing defects.
2Manufacturing precision
If cobalt silicide buffer layer is used to reduce lattice mismatch, then high quality silicon carbide single crystal film can be grown, but the buffer layer composition must be precisely controlled within a specific lattice constant range
Solution Approach 1:
The patent exploits the continuous可调性 (adjustability) of the cobalt silicide lattice constant by varying the stoichiometric ratio. By changing the Co/Si ratio from 1:1 to 1:2, the lattice constant can be continuously adjusted within the range of 0.4447-0.5367 nm, providing flexibility to match different substrate and film requirements without needing multiple different materials.
3Manufacturing precision
If cubic boron phosphide is used as buffer layer, then lattice mismatch with cubic silicon carbide is reduced, but the low melting point of c-BP causes material evaporation and unstable buffer layer growth
Solution Approach 1:
The patent replaces the thermally unstable cubic boron phosphide with cobalt silicide, which has superior thermal stability and can withstand the high temperatures required for stable buffer layer growth and subsequent silicon carbide epitaxy without evaporation or decomposition.
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 use of cobalt silicide buffer layers with controlled lattice constants significantly reduces lattice mismatch, enabling the growth of high-quality silicon carbide single crystal films with fewer defects, facilitating better crystal growth and improving the quality of the semiconductor substrate.
Implementation Method 1
the buffer layer is formed from a cobalt silicide layer primarily containing cobalt silicide having a lattice constant in the range between 0.4447 nm (CoSi) and 0.5367 nm (CoSi2). This buffer layer provides a smaller lattice constant difference (lattice mismatch) with respect to both of the single crystal silicon and the silicon carbide single crystal film.
Data Source
AI summary
A semiconductor substrate includes: a substrate having a single crystal silicon on at least one surface thereof; a buffer layer that is provided on the single crystal silicon and has at least one cobalt silicide layer primarily containing cobalt silicide; and a silicon carbide single crystal film provided on the buffer layer.