SiC Substrate In-Situ Etch for BPD Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in SiC epitaxial growth is the high density of basal plane dislocations (BPDs) that lead to forward voltage drift and degrade device performance, particularly in high-power devices, as existing techniques either introduce adverse defects or are costly and difficult to control.
Innovation Solution
A method involving an off-axis silicon carbide substrate etched with a dry gas, hydrogen, or inert gas before epitaxial growth to convert BPDs into threading edge dislocations (TEDs), optimizing etch conditions such as temperature and pressure to achieve a low BPD density in the active region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If standard epitaxial growth is performed on SiC substrate, then epitaxial layer is formed, but high BPD density (100-1000 cm−2) remains causing forward voltage drift
Solution Approach 1:
The patent applies preliminary action by performing surface patterning (groove formation) and selective etching before epitaxial growth to convert BPDs into TEDs at the substrate surface. This pre-treatment modifies the substrate surface morphology and dislocation structure prior to growth, enabling BPD conversion without requiring post-growth processing. The grooves are formed at specific locations where BPDs are expected to emerge, and selective etching removes material at these groove locations to promote dislocation conversion before the epitaxial layer is deposited.
Solution Approach 2:
The patent applies segmentation by dividing the substrate surface into patterned regions with grooves and non-groove regions. The grooves are selectively formed at specific locations to target BPD emergence points, creating segmented treatment zones. During epitaxial growth, different regions of the substrate receive different treatments, allowing selective conversion of BPDs in groove regions while maintaining control over the overall epitaxial structure.
2Manufacturing precision
If KOH etching method is used to reduce BPD density, then BPD conversion is improved, but additional processing steps and cost increase
Solution Approach 1:
The patent merges multiple functions into a single integrated process. The surface patterning and selective etching steps are combined with the epitaxial growth process itself, eliminating the need for separate KOH etching and repolishing steps. The selective etching is performed in-situ during the epitaxial growth process, combining defect conversion and layer formation into one continuous operation, thereby reducing process complexity and cost.
Solution Approach 2:
The patent applies self-service by using the epitaxial growth process itself to facilitate BPD conversion through the pre-formed grooves and selective etching patterns. The growth conditions and surface morphology work together to automatically convert BPDs into TEDs during the growth process, without requiring external intervention or additional processing steps after growth.
3Manufacturing precision
If offcut angle is lowered to convert BPDs to TEDs, then BPD density decreases, but 3C inclusions are introduced degrading device performance
Solution Approach 1:
The patent applies local quality by creating localized grooves at specific positions on the substrate surface rather than changing the overall offcut angle of the entire wafer. The grooves are formed only at locations where BPDs are expected to emerge, providing local modification of the surface morphology to promote dislocation conversion. This localized approach allows BPD conversion without introducing 3C inclusions across the entire epitaxial layer, maintaining high device performance.
Solution Approach 2:
The patent changes specific parameters (surface morphology through groove formation and selective etching) rather than changing the fundamental substrate offcut angle. By modifying the surface topology locally through grooves and selective material removal, the patent achieves BPD conversion while maintaining the original offcut angle, thereby avoiding the formation of 3C inclusions that would result from lowering the overall offcut angle.
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 process effectively reduces BPD density to <1 cm−2, enhancing device performance and reliability by burying BPDs in a thin doped buffer layer, making it manufacturable for high-voltage bipolar devices while avoiding defects like 3C inclusions.
Implementation Method 1
etching the surface of the substrate with a dry gas, hydrogen, or an inert gas
Data Source
AI summary
A method of: providing an off-axis silicon carbide substrate, and etching the surface of the substrate with a dry gas, hydrogen, or an inert gas.