SiC Substrate Structure for Uniform 3D Stress Distribution
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Solution Overview
Problem
SiC crystals and substrates suffer from defects such as polycrystalline, polymorphism, micropipes, and dislocations due to imbalances in Si/C ratio and temperature gradients, leading to lattice distortion and non-uniform stress distribution, which affects their quality and limits their use and processing.
Innovation Solution
An SiC substrate with a specific layer structure and stress distribution, including a first and second surface layer and an intermediate layer, with controlled radial stress differences (ΔS1 and ΔS2) between these layers, ensuring uniform stress distribution in three dimensions, and a method for preparing high-quality SiC crystals using a TaC-coated graphite crucible to manage temperature gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional machining methods (laser cutting, wire cutting, grinding, polishing) are used to process SiC substrates, then substrates can be manufactured, but mechanical stress causes microcracks on the surface and introduces damage layers with non-uniform stress distribution
Solution Approach 1:
The patent changes the stress state parameters of the SiC substrate by controlling the radial stress difference between surface and intermediate layers. By specifying that the radial stress difference ΔS satisfies -15 MPa ≤ ΔS ≤ 10 MPa, the substrate achieves uniform three-dimensional stress distribution without requiring conventional machining processes that generate microcracks and damage layers.
2Productivity
If SiC crystals are grown with conventional methods, then crystals can be produced, but defects such as polycrystalline, polymorphism, micropipes, and dislocations are introduced due to Si/C ratio imbalance and temperature gradient changes
Solution Approach 1:
The patent changes the temperature distribution parameters during crystal growth by using a crucible with a specific temperature field distribution. This controls the temperature gradient to prevent lattice distortion and defects while maintaining high crystal growth efficiency.
Solution Approach 2:
The patent introduces a crucible as an intermediary element with specific thermal properties. The crucible acts as a mediator to distribute temperature uniformly during crystal growth, preventing thermal stress and defects in the SiC crystal.
3Productivity
If SiC substrates with non-uniform stress distribution are used for crystal or epitaxial layer growth, then growth can proceed, but stresses are passed to the crystal or epitaxial layer resulting in more defects and uneven quality
Solution Approach 1:
The patent changes the stress parameters of the substrate by controlling the radial stress difference ΔS to satisfy -15 MPa ≤ ΔS ≤ 10 MPa. This ensures uniform three-dimensional stress distribution in the substrate, preventing stress transmission to the epitaxial layer during growth and eliminating the associated defects.
Data Source
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AI summary
The present application belongs to the technical field of SiC production and processing. Disclosed are an SiC substrate having uniform stress distribution in a three-dimensional direction, and an SiC crystal. The SiC substrate comprises a first surface layer, a second surface layer and an intermediate layer, wherein on the same axis, at any plane parallel to a first main surface or a second main surface in the first surface layer, Smax1 represents the maximum value of an absolute value of a radial stress in the first surface layer, Smax2 represents the maximum value of an absolute value of a radial stress in the intermediate layer, Smax3 represents the maximum value of an absolute value of a radial stress in the second surface layer. ΔS1 = Smax2 - Smax1, ΔS2 = Smax2 - Smax3, -15 MPa ≤ ΔS1 ≤ 10 MPa, and -15 MPa ≤ ΔS2 ≤ 10 MPa. The radial stresses in the SiC substrate in all of the first surface layer, the second surface layer and the intermediate layer are relatively low, the stress distribution uniformity among the layers is good, so that the quality of the SiC substrate can be improved, the usage range of the SiC substrate is expanded, and the production and processing of downstream epitaxial wafers and crystals are facilitated.