SiC Substrate Resistivity Uniformity for Laser Processing
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Solution Overview
Problem
Existing SiC substrate processing methods using laser technology often result in rough cut surfaces and unexpected cracks due to variations in resistivity distribution, particularly outside the device acquisition region.
Innovation Solution
The SiC substrate is processed to ensure a uniform resistivity distribution by controlling the resistivity difference between measurement points within specific regions, including those outside the device acquisition area, to be 2 mΩ·cm or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If laser processing is used to cut SiC substrate, then cutting loss is reduced compared to wire saw processing, but rough cut surfaces and unexpected cracks occur due to non-uniform resistivity distribution
Solution Approach 1:
The patent applies preliminary action by controlling the resistivity distribution uniformity before laser processing occurs. Specifically, the SiC substrate is manufactured with controlled resistivity uniformity (difference of 5 mΩ·cm or less among measurement points in the outer 5mm region) prior to laser cutting, which prevents the occurrence of rough surfaces and cracks during the subsequent laser processing step. This pre-conditioning of the material properties eliminates the need for post-processing corrections.
2Reliability
If resistivity distribution is controlled only within device acquisition region, then device characteristics are improved, but processing success rate decreases due to non-uniform resistivity in outer regions
Solution Approach 1:
The patent applies local quality by differentiating the resistivity control requirements for different regions of the SiC substrate. The device acquisition region (inner region) and the outer region (within 5mm of the circumferential end) have different measurement point configurations and acceptance criteria. This localized quality control ensures that each region meets its specific requirements, with the outer region specifically optimized for laser processing success while the inner region maintains device performance.
3Measurement precision
If measurement points are densely distributed to accurately assess resistivity uniformity, then measurement precision improves, but device acquisition area is reduced
Solution Approach 1:
The patent applies partial action by implementing measurement points only in specific critical regions rather than uniformly across the entire substrate. Measurement points are strategically placed in the outer region (within 5mm of the circumferential end) and at the center, with specific spacing requirements (10mm or more between points). This selective measurement approach provides sufficient assessment of resistivity uniformity where it matters most for laser processing, while preserving maximum device acquisition area in the inner region.
Data Source
AI summary
In a SiC substrate, when resistivities at a plurality of first measurement points that are in a region inside a boundary located 5 mm inward from an outer circumferential end thereof and that include a center and a plurality of measurement points separated by 10 mm from each other in the [11-20] direction or the [−1-120] direction from the center, and at two second measurement points that are located 1 mm inward from the outer circumferential end and located in each of the [11-20] direction from the center and the [−1-120] direction from the center are measured, a difference between the maximum resistivity and the minimum resistivity among the resistivities of each of the plurality of first measurement points and the two second measurement points is 0.5 mΩ·cm or less, and the diameter is 149 mm or more.