N-Type SiC Substrate Co-Doping for Stacking Fault Suppression
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Solution Overview
Problem
The challenge is to suppress double Shockley-type stacking faults in SiC single crystal substrates during high-temperature treatments, as increasing nitrogen concentration to lower resistivity leads to increased stacking fault density and degraded crystallinity, while existing methods to reduce these faults are costly and inefficient.
Innovation Solution
An n-type SiC single crystal substrate is produced by co-doping both a donor and an acceptor, with a smaller difference in concentration between the outer peripheral and central portions, and maintaining a convex crystal growth surface, resulting in a SiC epitaxial wafer with reduced stacking faults and low resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the nitrogen concentration is increased to lower the resistivity of the n-type SiC single crystal substrate, then the resistivity is reduced and electrical conductivity is improved, but the stacking fault density increases and crystallinity is significantly degraded
Solution Approach 1:
The patent applies parameter changes by precisely controlling the nitrogen concentration within the range of 1×10^19 to 5×10^19/cm³, and by controlling the ratio of nitrogen concentration to stacking fault density to be 5×10^6 to 20×10^6. This quantitative parameter control resolves the contradiction by finding the optimal balance point where electrical conductivity is sufficiently high while crystallinity degradation is suppressed.
2Productivity
If high-temperature treatment at 1,000°C or more is performed during epitaxial growth using a substrate with high nitrogen concentration, then the epitaxial growth process is completed, but double Shockley-type stacking faults are generated with high density
Solution Approach 1:
The patent applies preliminary action by pre-controlling the nitrogen concentration and stacking fault density in the n-type SiC single crystal substrate before epitaxial growth. By establishing the appropriate nitrogen concentration range and nitrogen-to-stacking-fault ratio in advance, the substrate is prepared in a state that prevents double Shockley-type stacking fault generation during subsequent high-temperature epitaxial processing.
3Manufacturing precision
If conventional methods are used to reduce stacking faults by doping both donor and acceptor elements, then stacking faults are suppressed, but the production cost increases and the process becomes more complex
Solution Approach 1:
The patent applies the taking out principle by extracting and eliminating the need for complex dual-element doping processes. Instead of requiring both donor and acceptor element doping, the invention achieves stacking fault suppression by precisely controlling only the nitrogen (donor) concentration and the nitrogen-to-stacking-fault ratio, thereby simplifying the doping process while maintaining effectiveness.
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 effectively suppresses double Shockley-type stacking faults from entering the device use region, maintaining low resistivity and excellent crystallinity, thereby enhancing the performance of SiC single crystal substrates and epitaxial wafers.
Implementation Method 1
nitrogen is used as a donor element in an n-type SiC single crystal substrate. The nitrogen atom doped in the SiC single crystal acts as a donor, when the nitrogen atom substitutes carbon atom.
Implementation Method 2
a crystal growth step of laminating a SiC single crystal while co-doping a donor and an acceptor on one surface of a seed crystal by a sublimation recrystallization method
Data Source
AI summary
An n-type SiC single crystal substrate of the present invention is provided which is a substrate doped with both a donor and an acceptor, and has a difference between a donor concentration and an acceptor concentration in an outer peripheral portion which is smaller than a difference between a donor concentration and an acceptor concentration in a central portion, and is smaller than 3.0×1019/cm3.