SiC Epitaxial Layer Dislocation Removal via Graphite Capping
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Solution Overview
Problem
Basal plane dislocations in silicon carbide epitaxial layers lead to stacking faults and forward voltage degradation in minority carrier devices, with conventional growth techniques resulting in high BPD densities and no known methods to mitigate them post-growth while preserving surface morphology.
Innovation Solution
High temperature annealing of post-growth silicon carbide epitaxial layers capped with a graphite cap at temperatures of 1750° C. or greater under nitrogen overpressure of 60-110 psi to remove basal plane dislocations without surface degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high temperature annealing is performed to remove basal plane dislocations, then dislocation density is reduced, but surface morphology deteriorates due to silicon sublimation
Solution Approach 1:
A graphite cap is introduced as an intermediary substance between the SiC epilayer and the ambient environment. The graphite cap prevents silicon sublimation from the epilayer surface during high temperature annealing, thereby eliminating surface degradation while allowing the annealing process to proceed at temperatures sufficient to remove basal plane dislocations
Solution Approach 2:
The annealing process is performed under nitrogen overpressure (60-110 psi) to create an inert atmosphere that prevents silicon sublimation. The nitrogen pressure environment suppresses the sublimation of silicon from the SiC epilayer surface, preserving surface morphology while enabling high temperature treatment to eliminate dislocations
2Productivity
If conventional growth techniques are used, then epitaxial layers are formed, but basal plane dislocation density remains high at 100 cm−2 or more
Solution Approach 1:
The graphite cap is applied to the SiC epilayer before the high temperature annealing process. This preliminary action of capping prepares the epilayer for subsequent dislocation removal by protecting the surface from degradation, enabling the annealing process to focus on eliminating basal plane dislocations without causing surface damage
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
Effectively eliminates basal plane dislocations while preserving surface morphology, enhancing device reliability and performance for high power and high voltage applications.
Implementation Method 1
higher temperature annealing (in excess of 1750° C.) of SiC material can be used with no silicon sublimation from the surface, which prevents surface degradation
Implementation Method 2
annealing the capped silicon carbon epilayers at a temperature of 1750° C. or greater
Implementation Method 3
annealing the capped silicon carbon epilayers at a temperature of 1750° C. or greater with a nitrogen overpressure of 60-110 psi
Data Source
AI summary
A method to remove basal plane dislocations in post growth silicon carbide epitaxial layers by capping post growth silicon carbide epilayers with a graphite cap and annealing the capped silicon carbon epilayers at a temperature of 1750° C. or greater with a nitrogen overpressure of 60-110 psi, wherein basal plane dislocations in the epilayers are removed while surface morphology is preserved. Also disclosed is the related silicon carbide substrate material made by this method.