Biaxial SiC Substrate Structure for Crack-Resistant Processing
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Solution Overview
Problem
SiC substrates are difficult to process due to high hardness, leading to yield loss from breakings and cracks during grinding, polishing, and cutting, primarily caused by uneven distribution of basal plane dislocations.
Innovation Solution
A SiC substrate with a biaxially oriented SiC layer where basal plane dislocations (BPDs) are evenly distributed, reducing strains and minimizing continuous regions of high BPD density to prevent cracks during processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If SiC substrate is processed through grinding, polishing, and cutting, then the substrate can be manufactured, but breakings and cracks occur due to high hardness and uneven BPD distribution
Solution Approach 1:
The patent applies local quality by creating a specific layer structure where the first SiC layer has a controlled, lower BPD density compared to the second SiC layer. This local differentiation in dislocation density allows the substrate to maintain overall structural integrity while enabling processing in the more defect-tolerant first layer, thereby improving yield without sacrificing manufacturability
Solution Approach 2:
The patent employs preliminary action by pre-controlling the BPD distribution during the epitaxial growth process. The first SiC layer is grown with controlled BPD density before subsequent processing steps, so that the substrate is pre-prepared to resist breakings and cracks during grinding, polishing, and cutting operations
2Productivity
If BPDs are unevenly distributed in SiC substrate, then crystal growth can proceed, but strains accumulate leading to breakings and cracks during processing
Solution Approach 1:
The patent implements local quality by establishing a gradient in BPD distribution across different layers. The first SiC layer maintains lower BPD density to preserve structural integrity, while the second SiC layer can have higher BPD density, allowing crystal growth efficiency to be maintained overall while preventing strain accumulation in critical processing regions
Solution Approach 2:
The patent applies parameter changes by controlling the BPD density as a key parameter during epitaxial growth. By adjusting growth conditions to achieve specific BPD density ranges in different layers, the patent optimizes both crystal growth efficiency and structural integrity, preventing strain-induced breakings and cracks
3Quantity of substance
If SiC substrate has high BPD density regions, then material can be grown, but continuous high density regions cause cracks during processing
Solution Approach 1:
The patent applies local quality by spatially separating BPD density characteristics across layers. The first SiC layer is engineered with controlled BPD density to ensure substrate quality for processing, while the second SiC layer accommodates higher BPD density to maintain material growth quantity, thus resolving the contradiction between material growth and processing quality
Data Source
AI summary
There is provided a SiC substrate including a biaxially oriented SiC layer, wherein, in an XRT image obtained by subjecting the biaxially oriented SiC layer to X-ray topography (XRT) measurement, when the entire XRT image is divided into a lattice pattern giving a region of 4 mm longitudinal length×4 mm lateral length×28 μm depth per square and an average value of a volume density of basal plane dislocations (BPDs) per square is defined as X (cm/cm3), regions having 5X (cm/cm3) or more per square do not extend for 10 or more continuous squares in a straight line in either a longitudinal or lateral direction.