SiC Epitaxial Substrate Dislocation Conversion
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Solution Overview
Problem
Silicon carbide semiconductor devices experience energized deterioration due to the propagation of basal plane dislocations during bipolar operations, which is not adequately suppressed by existing methods, leading to increased forward voltage drop and device degradation.
Innovation Solution
A silicon carbide epitaxial substrate is designed with a layered structure comprising a silicon carbide single-crystal substrate, a first silicon carbide layer with a lower impurity concentration, a second silicon carbide layer with a higher impurity concentration, and a third silicon carbide layer with a lower impurity concentration, where the second layer hinders the extension of basal plane dislocations, converting them into threading edge dislocations and preventing their propagation into the third layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon carbide single-crystal substrate with high crystal quality is used, then device reliability is improved, but manufacturing cost and complexity increase due to the difficulty of producing large-diameter substrates with low dislocation density
Solution Approach 1:
The epitaxial layer is divided into multiple layers with different impurity concentrations (first layer with lower impurity concentration, second layer with higher impurity concentration, third layer with lower impurity concentration). This segmentation allows each layer to perform specific functions: the first layer converts basal plane dislocations to threading edge dislocations, the second layer suppresses dislocation propagation, and the third layer provides the active device region with low dislocation density.
Solution Approach 2:
Different regions of the epitaxial structure are given different impurity concentrations tailored to their specific functions. The first layer has lower impurity concentration optimized for dislocation conversion, the second layer has higher impurity concentration optimized for dislocation suppression, and the third layer has low impurity concentration optimized for device performance. This local quality differentiation resolves the contradiction by optimizing each region for its specific purpose rather than requiring uniform high quality throughout.
2Reliability
If the impurity concentration in the active layer is reduced to increase withstand voltage, then device withstand voltage increases, but manufacturing precision requirements increase to maintain uniform low impurity concentration throughout the layer
Solution Approach 1:
The impurity concentration parameter is changed systematically across different layers. The first layer uses lower impurity concentration (optimized for dislocation conversion), the second layer uses higher impurity concentration (optimized for dislocation suppression), and the third layer uses low impurity concentration (optimized for withstand voltage). This parameter differentiation resolves the contradiction by allowing the active layer to achieve low impurity concentration for high withstand voltage while the other layers provide compensating functions that reduce manufacturing precision requirements.
3Ease of manufacture
If basal plane dislocations are present in the substrate, then substrate manufacturing becomes easier, but device performance deteriorates due to energized deterioration during bipolar operations
Solution Approach 1:
The invention converts the harmful basal plane dislocations into beneficial threading edge dislocations through the first epitaxial layer with lower impurity concentration. This conversion transforms a harmful defect that causes energized deterioration into a less harmful defect that does not propagate into the active layer, thereby allowing the use of substrates with basal plane dislocations while maintaining device performance.
Solution Approach 2:
The first epitaxial layer with lower impurity concentration acts as an intermediary between the substrate containing basal plane dislocations and the active layer requiring low dislocation density. This intermediary layer converts the dislocation type and suppresses their propagation, thereby mediating between the ease of manufacturing substrates with dislocations and the need for high device performance.
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 configuration effectively suppresses energized deterioration by converting basal plane dislocations into threading edge dislocations and preventing their extension, thereby enhancing the reliability and performance of silicon carbide semiconductor devices during bipolar operations.
Implementation Method 1
the second layer hinders the extension of basal plane dislocations, converting them into threading edge dislocations and preventing their propagation into the third layer
Implementation Method 2
This configuration effectively suppresses energized deterioration by converting basal plane dislocations into threading edge dislocations and preventing their extension
Data Source
AI summary
A silicon carbide epitaxial substrate includes a silicon carbide single-crystal substrate of one conductivity type, a first silicon carbide layer of the above-mentioned one conductivity type, a second silicon carbide layer of the above-mentioned one conductivity type, and a third silicon carbide layer of the above-mentioned one conductivity type. The silicon carbide single-crystal substrate has first impurity concentration. The first silicon carbide layer is provided on the silicon carbide single-crystal substrate, and has second impurity concentration that is lower than the first impurity concentration. The second silicon carbide layer is provided on the first silicon carbide layer, and has third impurity concentration that is higher than the first impurity concentration. The third silicon carbide layer is provided on the second silicon carbide layer, and has fourth impurity concentration that is lower than the second impurity concentration.