Silicon Carbide Wafer Flatness Control via Seed Crystal Preparation
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Solution Overview
Problem
Silicon carbide wafers often exhibit warping and bowing due to low angle grain boundaries caused by basal plane dislocation defects, leading to defects and reduced flatness, which existing methods fail to effectively control or eliminate.
Innovation Solution
A method for fabricating silicon carbide wafers that involves using a seed crystal with balanced basal plane dislocation defects and low impurity silicon carbide powder for crystal growth, ensuring minimal low angle grain boundaries within specific edge ranges, followed by grinding and polishing to achieve high flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional crystal growth process is used with seed crystal having uneven surface or BPD defects, then crystal growth can proceed, but low angle grain boundaries form causing warping and bowing of wafers
Solution Approach 1:
The patent applies preliminary action by carefully selecting and preparing the seed crystal before the crystal growth process. The seed crystal is chosen to have specific properties (controlled BPD density, proper orientation) to prevent the formation of low angle grain boundaries during subsequent growth, thereby ensuring wafer flatness from the outset rather than correcting defects later
Solution Approach 2:
The patent changes critical parameters of the crystal growth process including temperature gradients, growth rates, and seed crystal orientation to control the behavior of basal plane dislocations. By optimizing these parameters, the method prevents BPD clustering that leads to low angle grain boundaries, thus maintaining wafer flatness while achieving productive crystal growth
2Productivity
If low angle grain boundaries are present in the crystal, then crystal growth can proceed, but strain stress cannot disperse resulting in large warping and bowing
Solution Approach 1:
The patent converts the potentially harmful effect of basal plane dislocations into a beneficial outcome by controlling their distribution and density. Instead of allowing BPDs to cluster and form harmful low angle grain boundaries, the method guides them to distribute uniformly, transforming a defect into a controlled feature that does not compromise wafer integrity
Solution Approach 2:
The patent applies local quality by ensuring uniform distribution of dislocations throughout the crystal structure rather than allowing localized clustering. This uniform distribution prevents the formation of concentrated stress regions (low angle grain boundaries) while maintaining overall crystal growth, thereby preserving local and global structural integrity
3Ease of manufacture
If seed crystal surface is uneven or damaged, then crystal growth can initiate, but different crystal growth directions result in more defects
Solution Approach 1:
The patent applies preliminary action by thoroughly characterizing and selecting seed crystals with appropriate surface quality and orientation before growth initiation. This pre-selection ensures that the crystal growth starts from a controlled, uniform base, preventing divergent growth directions and associated defects while maintaining ease of manufacture
Solution Approach 2:
The patent changes the surface preparation parameters of the seed crystal, including surface polishing quality and orientation alignment, to ensure uniform crystal growth initiation. By optimizing these parameters, the method enables easy growth initiation while maintaining precise crystal orientation throughout the growth process
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
The method results in silicon carbide wafers with reduced or no low angle grain boundaries, achieving bowing and warping within ideal ranges of less than 15 μm and 30 μm respectively, thereby ensuring high flatness and reducing strain stress.
Implementation Method 1
A raw material of silicon carbide powder is used to contact the seed crystal to perform a crystal growth process
Data Source
AI summary
A silicon carbide wafer is provided, wherein within a range area of 5 mm from an edge of the silicon carbide wafer, there are no low angle grain boundaries formed by clustering of basal plane dislocation defects, and the silicon carbide wafer has a bowing of less than 15 μm.