SiC Substrate Evaluation via Photoluminescence
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Solution Overview
Problem
The existing methods for evaluating SiC substrates before epitaxial layer formation are inadequate in identifying specific defects such as bar-shaped stacking faults, which can cause bipolar degradation in SiC devices, especially due to high impurity concentrations and the difficulty in distinguishing defects using photoluminescence methods.
Innovation Solution
A SiC substrate evaluation method involving irradiation with excitation light of specific wavelength ranges (405 nm to 445 nm) and intensities, allowing for the identification of bar-shaped stacking faults before epitaxial layer stacking, which involves determining the suitability of the substrate for further processing based on defect presence and density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photoluminescence method is used to evaluate SiC substrate, then non-destructive inspection is achieved, but defect identification becomes difficult due to high impurity concentration
Solution Approach 1:
The patent changes the photoluminescence measurement parameters by using specific excitation wavelengths (266 nm, 325 nm, or 351 nm) and analyzing specific emission wavelength ranges (370-400 nm, 410-450 nm, 460-500 nm) to distinguish different defect types. This parameter optimization enables defect identification in substrates with high impurity concentrations that previously could not be evaluated.
2Measurement precision
If chemical etching method is used to identify defects, then specific defects can be identified, but the substrate is destroyed and cannot be used for device manufacture
Solution Approach 1:
The patent replaces the chemical etching method with an optimized photoluminescence measurement method. By using specific excitation wavelengths and analyzing characteristic emission spectra, the system can identify stacking faults and other defects non-destructively, eliminating the need for substrate destruction while maintaining defect identification capability.
3Reliability
If photoluminescence method is applied to SiC substrate with high impurity concentration, then non-destructive evaluation is possible, but the photoluminescence spectrum becomes broad and specific defects cannot be distinguished
Solution Approach 1:
The patent optimizes measurement parameters including excitation wavelength selection (266 nm, 325 nm, or 351 nm), emission wavelength range analysis (370-400 nm, 410-450 nm, 460-500 nm), and measurement conditions to resolve the broadening effect of impurities. This enables distinction of specific defect types even in high-impurity substrates.
Solution Approach 2:
The patent uses characteristic photoluminescence emission spectra as an intermediary to indirectly identify defect types. By analyzing the specific wavelength ranges and intensity ratios of emitted light, the system can distinguish stacking faults and other defects without direct observation, overcoming the spectrum broadening issue.
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 enables non-destructive identification of bar-shaped stacking faults in SiC substrates, improving the production yield of high-quality SiC epitaxial wafers by ensuring the selection of substrates with minimal defects, thereby reducing bipolar degradation in SiC devices.
Implementation Method 1
observing a bar-shaped stacking fault by irradiating a first surface of a SiC substrate before stacking an epitaxial layer with excitation light and extracting light having a wavelength range of equal to or greater than 405 nm and equal to or less than 445 nm among photoluminescence light beams emitted from the first surface
Data Source
AI summary
A SiC epitaxial wafer, including: a SiC substrate; and an epitaxial layer stacked on a first surface of the SiC substrate, wherein an area occupied by bar-shaped stacking faults on the first surface of the SiC substrate is identified, and the area occupied by bar-shaped stacking faults on the first surface of the SiC substrate is equal to or less than ¼ of the first surface area of the SiC substrate.