SiC Substrate BPD Removal via High-Temp Annealing
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Solution Overview
Problem
Basal plane dislocations in silicon carbide (SiC) substrates lead to forward voltage degradation in high power devices, as they form stacking faults during device operation, and existing methods for reducing BPD density in SiC epilayers are inefficient and can damage the surface morphology.
Innovation Solution
A method involving the addition of a protective carbon layer on the SiC substrate, followed by high-temperature annealing to embed basal plane dislocations below the surface, allowing subsequent epilayer growth without further BPD suppression, thereby converting BPDs to threading edge dislocations and preventing their propagation into the epilayer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional methods are used to reduce BPD density in SiC epilayers, then BPD density is reduced, but surface morphology is damaged
Solution Approach 1:
The patent applies preliminary action by performing substrate annealing at high temperature (1850-2000°C) before epilayer growth to convert BPDs to threading dislocations. This pre-treatment eliminates the need for subsequent BPD suppression measures during growth, and crucially, avoids the surface damage caused by conventional post-growth annealing methods. The protective carbon cap is also applied beforehand to prevent surface degradation during the high-temperature annealing process.
Solution Approach 2:
The patent changes the temperature parameter to extremely high values (1850-2000°C) for substrate annealing, which is sufficient to convert BPDs to threading dislocations without damaging the eventual epilayer surface. This temperature parameter change, combined with the protective carbon cap, resolves the contradiction by enabling effective BPD removal while preserving surface morphology.
2Reliability
If high temperature annealing is performed without protective layer, then BPDs are embedded below surface, but surface morphology deteriorates
Solution Approach 1:
The protective carbon cap layer serves as an intermediary between the SiC substrate surface and the high-temperature annealing environment. This carbon cap prevents direct oxidation and degradation of the substrate surface during the 1850-2000°C annealing process, while still allowing the thermal energy to penetrate and convert BPDs to threading dislocations. After annealing, the carbon cap is removed to reveal the intact surface morphology.
3Reliability
If multiple annealing steps are used to remove BPDs, then BPD density is reduced, but process complexity increases
Solution Approach 1:
The patent merges the BPD removal function into a single substrate annealing step performed before epilayer growth, eliminating the need for separate post-growth annealing steps. This consolidation achieves complete BPD suppression (converting them to threading dislocations) in one process, significantly reducing process complexity while maintaining or improving effectiveness.
Solution Approach 2:
By performing the annealing treatment preliminarily on the substrate before epilayer growth, the patent eliminates the need for subsequent annealing steps that would be required if growth were performed first. This preliminary action simplifies the overall process flow and reduces the number of manufacturing steps.
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 results in BPD-free epilayers of any desired thickness, preserving surface morphology and eliminating the need for additional annealing steps, which enhances the reliability and performance of high power SiC devices by mitigating BPD-induced defects.
Implementation Method 1
adding a protective layer on the surface of the substrate; annealing the substrate at a temperature approximately greater or equal to 1850° C.
Implementation Method 2
annealing the substrate at a temperature approximately greater or equal to 1850° C., wherein the annealing embeds the basal plane dislocations within the substrate and below the surface of the substrate
Implementation Method 3
growing a first epilayer on the substrate after the removing of the protective layer, wherein the first epilayer is grown without attempting to prevent the basal plane dislocations to propagate in the first epilayer
Data Source
AI summary
A method and device including adding a protective layer on the surface of a substrate, annealing the substrate at a temperature approximately greater or equal to 1850° C., removing the protective layer from the surface of the substrate after the annealing, and growing a first epilayer on the substrate after the removing of the protective layer, wherein the first epilayer is grown without attempting to prevent the basal plane dislocations to propagate in the first epilayer when growing the first epilayer, and wherein the first epilayer is free of the basal plane dislocations.