SiC Substrate BPD Conversion and Hole Injection Prevention
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Solution Overview
Problem
Silicon carbide (SiC) substrates face challenges with high basal plane dislocation (BPD) density, leading to increased element resistance and reduced reliability due to stacking faults, especially during surge currents or unbalanced operations, as existing methods do not effectively convert BPDs to threading edge dislocations (TEDs) or prevent hole injection into the substrate.
Innovation Solution
A silicon carbide substrate structure comprising a first substrate, a first semiconductor layer with a lower impurity concentration than the substrate, a second semiconductor layer with a higher impurity concentration, and a third semiconductor layer, where the impurity concentration and thickness of the second semiconductor layer are optimized to satisfy specific equations related to rated voltage or current density, enhancing the conversion of BPDs to TEDs and reducing substrate hole injection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an epitaxial film is formed on the SiC substrate to convert BPD to TED, then the conversion efficiency improves, but the stacking fault still expands into the epitaxial layer causing increased element resistance
Solution Approach 1:
The patent applies preliminary action by forming a first semiconductor layer with a specific impurity concentration range (1×10^16 to 1×10^18 cm^-3) before forming the drift layer. This preliminary layer is designed to prevent hole injection into the substrate during element operation, thereby preventing stacking fault expansion from the outset while maintaining effective BPD conversion to TED.
Solution Approach 2:
The patent applies local quality by creating a semiconductor layer with locally optimized impurity concentration that differs from both the substrate and the drift layer. This intermediate layer has specific electrical properties tailored to block hole injection locally at the substrate interface while allowing the drift layer to maintain its low resistance characteristics for current conduction.
2Object-generated harmful factors
If the impurity concentration of the drift layer is increased to reduce ON resistance, then the element resistance decreases, but the breakdown voltage may be compromised
Solution Approach 1:
The patent applies local quality by creating distinct regions with different impurity concentrations: the drift layer has low impurity concentration (1×10^14 to 1×10^16 cm^-3) optimized for high breakdown voltage, while the first semiconductor layer has higher impurity concentration (1×10^16 to 1×10^18 cm^-3) optimized for blocking hole injection. Each layer's properties are locally optimized for its specific function.
Solution Approach 2:
The patent applies segmentation by dividing the semiconductor structure into functionally distinct layers: the substrate, the first semiconductor layer for hole injection prevention, and the drift layer for voltage blocking and current conduction. This segmentation allows each layer to be independently optimized for its specific function without compromising overall performance.
3Reliability
If the thickness of the first semiconductor layer is increased to improve BPD conversion, then the conversion efficiency improves, but the element resistance increases
Solution Approach 1:
The patent applies parameter changes by optimizing the impurity concentration of the first semiconductor layer to a specific range (1×10^16 to 1×10^18 cm^-3) that balances two competing requirements: sufficient thickness for effective BPD conversion to TED, and low enough resistance to minimize impact on element performance. This parameter optimization resolves the contradiction between conversion efficiency and resistance.
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 improves the reliability of SiC semiconductor substrates by reducing element resistance and preventing stacking fault expansion, ensuring stable operation under varying conditions such as surge currents and unbalanced element operations.
Implementation Method 1
the BPD is converted to TED (Threading Edge Dislocation) by formation of a first semiconductor layer (first epitaxial layer) having an impurity concentration of 1 × 10^17 to 1 × 10^19 [cm^-3]
Implementation Method 2
preventing the hole from being injected into the substrate during the element operation
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
In a silicon carbide substrate including: a SiC substrate; and a first semiconductor layer, a second semiconductor layer and a drift layer that are epitaxial layers sequentially formed on the SiC substrate, an impurity concentration of the first semiconductor layer is lower than impurity concentrations of the SiC substrate and the second semiconductor layer, and the second semiconductor layer is formed to have a high impurity concentration or a large thickness.