SiC Epitaxial Wafer Nitrogen Profile for FT-IR Thickness Measurement
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Solution Overview
Problem
The challenge in manufacturing high-quality SiC epitaxial wafers lies in accurately measuring the film thickness of the epitaxial layer, particularly when a buffer layer with high impurity concentration is present, as it leads to overlapping interference waveforms in Fourier transform infrared spectroscopy (FT-IR) measurements, making it difficult to separate the desired interference waveform and resulting in inaccurate film thickness determination.
Innovation Solution
The SiC epitaxial wafer structure comprises a substrate with specific nitrogen concentration ranges for each layer, including a first layer with lower nitrogen concentration to convert basal plane dislocations into threading edge dislocations, a second high-concentration layer to suppress carrier recombination, and a third layer for drift current, allowing for controlled nitrogen concentration and refractive index to prevent interference waveform overlap, enabling accurate film thickness measurement by FT-IR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a buffer layer with high impurity concentration is formed between the SiC substrate and the semiconductor layer, then the BPD expansion is suppressed, but the film thickness measurement accuracy deteriorates due to overlapping interference waveforms
Solution Approach 1:
The patent applies parameter changes by carefully controlling the nitrogen concentration in the buffer layer within a specific range (1×10^18 to 1×10^19 atoms/cm³) rather than using high impurity concentration. This parameter optimization allows the buffer layer to suppress BPD expansion while maintaining distinct interference waveforms for accurate FT-IR measurement.
Solution Approach 2:
The patent implements local quality by creating a buffer layer with specific nitrogen concentration distribution between the substrate and device layer. The buffer layer has intermediate impurity concentration - higher than the substrate (6×10^18 to 1.5×10^19 atoms/cm³) but lower than typical high-concentration buffer layers, providing localized defect suppression without compromising measurement accuracy.
2Reliability
If the nitrogen concentration of the buffer layer is increased to suppress BPD expansion, then the reliability improves, but the interference waveform separation becomes difficult
Solution Approach 1:
The patent resolves this contradiction by changing the nitrogen concentration parameter to an optimal intermediate range (1×10^18 to 1×10^19 atoms/cm³). This parameter selection provides sufficient defect suppression while maintaining refractive index differences that enable clear interference waveform separation in FT-IR measurements.
3Reliability
If a buffer layer is formed to prevent BPD expansion, then the device reliability improves, but the film thickness measurement becomes inaccurate
Solution Approach 1:
The patent applies parameter changes by optimizing the nitrogen concentration in the buffer layer to an intermediate range that balances both reliability and manufacturing precision. This allows accurate FT-IR measurement of film thickness while maintaining the buffer layer's function of preventing BPD expansion.
Solution Approach 2:
The patent replaces the mechanical/physical approach of using high impurity concentration buffer layers with a chemically optimized approach using controlled nitrogen concentration. This substitution enables both reliable defect suppression and accurate optical measurement through proper refractive index management.
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 precise measurement of the epitaxial layer thickness and suppresses basal plane dislocation expansion, enhancing the reliability of SiC devices by eliminating interference waveform overlap and ensuring accurate thickness determination, thereby improving device performance.
Implementation Method 1
a first layer, a second layer and a third layer in order from the SiC substrate side, the nitrogen concentration of the SiC substrate is 6.0×10^18 cm^−3 or more and 1.5×10^19 cm^−3 or less, the nitrogen concentration of the first layer is 1.0×10^17 cm^−3 or more and 1.5×10^18 cm^−3 or less
Implementation Method 2
FT-IR measures film thickness by Fourier transform from the interference waveform between surface reflection and interface reflection
Implementation Method 3
FT-IR measures film thickness by Fourier transform from the interference waveform
Implementation Method 4
The BPD has a property of expanding while forming stacking faults when minority carriers recombine in the vicinity thereof
Data Source
AI summary
A SiC epitaxial wafer includes a SiC substrate and an epitaxial layer laminated on the SiC substrate, wherein the epitaxial layer comprises a first layer, a second layer and a third layer in order from the SiC substrate side, the nitrogen concentration of the SiC substrate is 6.0×1018 cm−3 or more and 1.5×1019 cm−3 or less, the nitrogen concentration of the first layer is 1.0×1017 cm−3 or more and 1.5×1018 cm−3 or less, the nitrogen concentration of the second layer is 1.0×1018 cm−3 or more and 5.0×1018 cm−3 or less, and the nitrogen concentration of the third layer is 5.0×1013 cm−3 or more and 1.0×1017 cm−3 or less.