SiC Stacked Substrate BPD to TED Conversion via Buffer Layer
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Solution Overview
Problem
The existing manufacturing methods for silicon carbide stacked substrates face issues such as increased resistance due to basal plane dislocations (BPDs) in the epitaxial layer, which are not effectively suppressed, leading to higher substrate resistance and reduced reliability, especially when current flows through regions with BPDs, and the conversion efficiency of BPDs to harmless threading edge dislocations (TEDs) is insufficient.
Innovation Solution
A silicon carbide stacked substrate structure is developed with specific impurity concentration gradients, including a first semiconductor layer with a lower impurity concentration than the second semiconductor layer and the SiC substrate, and a third semiconductor layer with a higher impurity concentration than the second layer, to enhance the conversion efficiency of BPDs to TEDs at the interface between the SiC substrate and the epitaxial layers, thereby reducing substrate resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BPDs are removed by recessing the substrate surface, then BPD density is reduced, but epitaxial layer morphology is deteriorated and leakage current increases
Solution Approach 1:
A buffer layer is formed preliminarily on the substrate surface before forming the main epitaxial layer. This buffer layer serves as an intermediate structure that prevents BPDs from propagating into the main epitaxial layer while maintaining a flat surface for subsequent epitaxial growth, thus avoiding morphology deterioration
Solution Approach 2:
The buffer layer acts as an intermediary between the substrate and the main epitaxial layer. It mediates the interaction by capturing BPDs from the substrate while providing a clean interface for the main epitaxial layer, preventing direct contact between the defective substrate surface and the sensitive main layer
2Reliability
If buffer layer impurity concentration is close to substrate impurity concentration, then manufacturing is simplified, but BPD to TED conversion efficiency is insufficient
Solution Approach 1:
The impurity concentration of the buffer layer is specifically controlled to be lower than that of the substrate (Nd ≤ 1×10^18 cm^-3 versus substrate's 1×10^19 to 1×10^21 cm^-3). This parameter change creates a concentration gradient that drives efficient BPD to TED conversion at the substrate-buffer layer interface
Solution Approach 2:
Different regions of the stacked substrate are assigned different impurity concentrations tailored to their specific functions: the substrate has high concentration for structural stability, the buffer layer has intermediate concentration for BPD conversion, and the main epitaxial layer has low concentration for device performance
Data Source
AI summary
In a silicon carbide stacked substrate, the efficiency of converting the basal plane dislocation (BPD) which is a fault to deteriorate the current-carrying reliability into a threading edge dislocation (TED) which is a harmless fault is improved, thereby improving the reliability of the silicon carbide stacked substrate. As means therefor, in a silicon carbide stacked substrate including a SiC substrate and a buffer layer and a drift layer which are epitaxial layers sequentially formed on the SiC substrate, a semiconductor layer having an impurity concentration lower than those of the SiC substrate and the buffer layer and higher than that of the drift layer is formed between the SiC substrate and the buffer layer so as to be in contact with an upper surface of the SiC substrate.