SiC Seed Offset Angle and Facet Control
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Solution Overview
Problem
Conventional methods for growing SiC single crystal wafers struggle to reliably suppress the occurrence of different polytypes and crystal defects, especially when using seeds with low screw dislocation densities, leading to issues with facet position control and defect outflow during crystal growth.
Innovation Solution
A SiC single crystal seed with a main surface offset angle of 2° to 20° relative to the {0001} plane and an initial facet formation surface on the offset upstream side, having an inclination angle less than 2°, is used, which includes a screw dislocation starting point within a prescribed region, to control facet formation and dislocation density, thereby suppressing polytype occurrence and defect outflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If crystal growth is performed using a seed with extremely low screw dislocation density, then the number of screw dislocations in the wafer can be reduced to not more than 10/cm2, but different polytypes tend to occur
Solution Approach 1:
The invention applies local quality by creating a specific region on the seed crystal surface with controlled screw dislocation density. The seed crystal has a first surface with a first region having a first screw dislocation density and a second region having a second screw dislocation density different from the first. This allows different areas to serve different functions: one region controls polytype occurrence while the other maintains low overall dislocation density in the final wafer.
Solution Approach 2:
The seed crystal surface is segmented into multiple regions with different screw dislocation densities. The first region and second region are spatially separated, allowing independent control of their dislocation characteristics. This segmentation enables the system to simultaneously achieve polytype control (through the first region) and low defect density (through the second region).
2Stability of the object's composition
If a c-face facet is formed during crystal growth, then the crystal structure can be preserved, but if no screw dislocation exists within the facet, then island growth occurs and different polytypes tend to develop
Solution Approach 1:
The invention applies preliminary action by pre-forming a c-face facet on the seed crystal surface before the actual crystal growth process. The seed crystal is specifically prepared with a c-face facet having controlled screw dislocation density, so that when growth begins, the facet is already in place and ready to control the polymorphic inheritance. This preliminary preparation ensures that screw dislocations are present in the facet from the start, preventing island growth and polytype development.
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 effectively reduces the occurrence of different polytypes and crystal defects, ensuring high-quality SiC ingots and wafers by maintaining screw dislocation density within a controlled range and stabilizing facet growth during crystal growth.
Implementation Method 1
the initial facet formation surface has a screw dislocation starting point
Implementation Method 2
growing a SiC epitaxial film that functions as the active region of a SiC semiconductor device on a SiC single crystal wafer
Data Source
AI summary
A SiC single crystal seed of the present invention has a main surface with an offset angle of at least 2° but not more than 20° relative to the {0001} plane, and at least one sub-growth surface, wherein the sub-growth surface includes an initial facet formation surface that is on the offset upstream side of the main surface and has an inclination angle θ relative to the {0001} plane with an absolute value of less than 2° in any direction, and the initial facet formation surface has a screw dislocation starting point.