SiC Single Crystal Lattice Strain Evaluation via Raman Shift Comparison
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Solution Overview
Problem
Current methods lack an efficient and reproducible way to evaluate the lattice strain in bulk silicon carbide (SiC) single crystals, which is crucial for preventing cracking and warpage in SiC devices, due to the small Raman shift caused by internal stress and the influence of measurement environment and equipment fluctuations.
Innovation Solution
A method using a reference SiC single crystal to measure and compare Raman shifts of bulk SiC single crystals, determining differences to relative evaluate lattice strains, which helps in identifying and mitigating strain-related issues such as cracking and warpage during processing and epitaxial film growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Raman spectroscopy is used to measure lattice strain in bulk SiC single crystals, then measurement speed and ease of operation are improved, but measurement precision deteriorates due to small Raman shift and equipment fluctuations
Solution Approach 1:
The patent introduces a reference SiC single crystal as an intermediary standard for comparison. By measuring the Raman shift of the reference crystal (which has known, minimal strain) and comparing it with the Raman shift of the bulk SiC single crystal under evaluation, the method eliminates equipment fluctuations and environmental variations from the measurement error. This differential measurement approach enables precise lattice strain evaluation while maintaining the speed and ease of Raman spectroscopy.
2Measurement precision
If X-ray diffraction is used to precisely measure lattice constants, then measurement precision is improved, but device complexity and loss of time worsen due to expensive equipment and long measurement periods
Solution Approach 1:
The patent replaces the complex X-ray diffraction system with a simpler Raman spectroscopy system. By using Raman spectroscopy with a reference crystal comparison method, the patent achieves sufficient lattice strain measurement precision without requiring expensive X-ray equipment or highly skilled operators. The substitution maintains measurement capability while dramatically reducing device complexity and measurement time.
3Ease of manufacture
If temperature gradient is applied during sublimation recrystallization to grow SiC single crystal, then crystal growth is enabled, but thermal stress remains in the grown crystal causing cracking
Solution Approach 1:
The patent applies preliminary annealing treatment to the grown SiC single crystal before cutting and processing. This preliminary action removes or reduces the thermal stress accumulated during crystal growth by heating the crystal to a high temperature (around 2000°C) in a controlled atmosphere, allowing stress relaxation without causing deformation or damage. This prevents subsequent cracking during cutting and processing operations.
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 approach allows for accurate and reproducible evaluation of lattice strains in SiC single crystals, preventing cracking during processing and warpage in epitaxial film growth, even when measurements are taken at different times and with varying equipment, thereby improving the quality and yield of SiC devices.
Implementation Method 1
measuring a Raman shift of a reference silicon carbide single crystal; measuring respective Raman shifts of a plurality of bulk-shaped silicon carbide single crystals
Data Source
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AI summary
Provided are a method by which the degrees of the strains of lattices in a plurality of bulk SiC single crystals can be relatively evaluated, and a reference SiC single crystal to be used in the method. Specifically provided are an evaluation method for bulk-shaped silicon carbide single crystals, including: measuring a Raman shift Rref of a reference silicon carbide single crystal to be used as a standard; measuring respective Raman shifts Rn of a plurality of bulk-shaped silicon carbide single crystals serving as objects to be evaluated; determining differences between each of the Raman shifts Rn and the Raman shift Rref; and relatively comparing the differences, to thereby relatively evaluate magnitudes of strains of lattices in the plurality of bulk-shaped silicon carbide single crystals serving as objects to be evaluated, and a reference silicon carbide single crystal to be used in the method, having a size of 5 mm square or more and 50 mm square or less and a thickness of 100 µm or more and 2, 000 µm or less, having a surface roughness Ra of 1 nm or less, and having a micropipe density of 1.0/cm2 or less and a dislocation density of 5×103/cm2 or less.