SiC Epitaxial Layer Doping Gradient for Stacking Fault Suppression
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Solution Overview
Problem
Existing silicon carbide epitaxial substrates and semiconductor devices face challenges in suppressing basal plane dislocations from becoming stacking faults, which hinder current flow and increase on-resistance.
Innovation Solution
A silicon carbide epitaxial substrate with a 4H polytype structure, featuring a nitrogen concentration gradient in multiple layers, where the nitrogen concentration increases from the first to the third silicon carbide layer, with specific thickness and concentration relationships to minimize positive holes and convert basal plane dislocations into threading edge dislocations, thereby preventing stacking faults.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional silicon carbide epitaxial substrate structure is used, then the manufacturing process is simple, but basal plane dislocations become stacking faults which increase on-resistance and reduce device performance
Solution Approach 1:
The epitaxial layer is divided into multiple distinct layers (first through fourth silicon carbide layers) with different nitrogen concentration profiles. This segmentation allows each layer to perform specific functions: the first layer provides a transition zone, the second layer creates a gradient to suppress dislocation movement, the third layer maintains low dislocation density, and the fourth layer serves as the functional device layer. This multi-layer structure resolves the contradiction by improving device performance through systematic dislocation control while managing the increased structural complexity.
Solution Approach 2:
Different regions of the epitaxial structure are assigned different nitrogen concentrations and thicknesses to achieve local optimization. Specifically, the second silicon carbide layer has a nitrogen concentration gradient that increases from bottom to top, creating local variations in material properties that suppress basal plane dislocation transformation. This local quality approach allows precise control of dislocation behavior in critical regions while maintaining overall structure feasibility.
2Reliability
If the nitrogen concentration gradient is increased to suppress basal plane dislocations, then stacking fault formation is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The nitrogen concentration gradient is established in advance during the epitaxial growth process, particularly in the second silicon carbide layer. By pre-configuring the nitrogen distribution before device fabrication, the structure is prepared to naturally suppress basal plane dislocation transformation into stacking faults. This preliminary action reduces the need for post-processing adjustments and manages manufacturing precision requirements by incorporating control mechanisms into the growth process itself.
Solution Approach 2:
The invention utilizes controlled changes in nitrogen concentration as a key parameter to suppress dislocation transformation. By systematically varying nitrogen concentration across different layers and positions (particularly the gradient in the second layer), the material properties are tuned to prevent basal plane dislocations from becoming stacking faults. This parameter-based approach provides a controllable method to improve reliability while managing manufacturing precision through established epitaxial growth techniques.
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
The solution effectively reduces the number of positive holes reaching the substrate, suppressing basal plane dislocations from becoming stacking faults, thereby enhancing current flow and reducing on-resistance in silicon carbide semiconductor devices.
Implementation Method 1
convert basal plane dislocations into threading edge dislocations, thereby preventing stacking faults
Implementation Method 2
A nitrogen concentration of the second silicon carbide layer is increased from the first silicon carbide layer toward the third silicon carbide layer
Implementation Method 3
suppressing basal plane dislocations from becoming stacking faults, which hinder current flow
Data Source
AI summary
A silicon carbide epitaxial layer includes a first silicon carbide layer, a second silicon carbide layer, a third silicon carbide layer, and a fourth silicon carbide layer. A nitrogen concentration of the second silicon carbide layer is increased from the first silicon carbide layer toward the third silicon carbide layer. A value obtained by dividing, by a thickness of the second silicon carbide layer, a value obtained by subtracting a nitrogen concentration of the first silicon carbide layer from a nitrogen concentration of the third silicon carbide layer is less than or equal to 6×1023 cm−4. Assuming that the nitrogen concentration of the third silicon carbide layer is N cm−3 and a thickness of the third silicon carbide layer is X μm, X and N satisfy a Formula 1.