Silicon Carbide Substrate Polishing for Carrot Defect Reduction
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Solution Overview
Problem
The generation of carrot defects in silicon carbide epitaxial layers is a challenge due to threading screw dislocations and polishing damage, such as blind scratches, which are difficult to inhibit using existing manufacturing methods.
Innovation Solution
A silicon carbide substrate with controlled threading screw dislocations and blind scratches is manufactured using chemical mechanical polishing with colloidal silica abrasive grains, where the grain size distribution is optimized, and a cushioning member with high Shore A hardness and compression ratio is used to minimize polishing damage, thereby reducing the area density of blind scratches and carrot defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If chemical mechanical polishing is performed on silicon carbide substrate, then surface flatness is improved, but blind scratches are generated
Solution Approach 1:
The patent applies parameter changes by carefully controlling the grain size distribution of colloidal silica abrasive grains. Specifically, it sets the D50 value between 0.5-2.0 μm and the D90 value between 1.5-3.0 μm, optimizing the balance between polishing effectiveness and damage reduction. This parameter optimization resolves the contradiction by achieving surface flatness while minimizing blind scratch generation
Solution Approach 2:
The patent applies local quality by controlling the distribution and characteristics of abrasive grains at different locations and depths during polishing. By managing the grain size distribution (with D10, D50, D90 parameters) and ensuring uniform colloidal silica application, the process achieves effective surface flattening while limiting the severity and density of local polishing damage, thus resolving the contradiction between surface quality improvement and damage minimization
2Productivity
If threading screw dislocations are present in silicon carbide substrate, then crystal growth is facilitated, but carrot defects are generated in epitaxial layer
Solution Approach 1:
The patent applies preliminary action by performing chemical mechanical polishing with optimized colloidal silica parameters before epitaxial growth. This pre-treatment process reduces the area density of blind scratches and modifies the surface condition, thereby preventing the formation of carrot defects during subsequent epitaxial growth while maintaining the beneficial threading screw dislocations for crystal growth
Solution Approach 2:
The patent converts the potentially harmful effect of threading screw dislocations (which can cause carrot defects) into a beneficial outcome by optimizing the surface condition through controlled polishing. The optimized colloidal silica treatment creates a surface state where threading dislocations promote growth without generating excessive carrot defects, thus converting a harmful factor into a beneficial one
3Object-generated harmful factors
If area density of blind scratches is reduced, then carrot defect generation is suppressed, but polishing time increases
Solution Approach 1:
The patent resolves this time-quality contradiction by optimizing the grain size distribution parameters of colloidal silica. By setting D50 between 0.5-2.0 μm and D90 between 1.5-3.0 μm, the process achieves efficient material removal and surface flattening while minimizing blind scratch generation, thereby reducing the need for extended polishing time and achieving both quality improvement and time efficiency
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 approach effectively suppresses the generation of carrot defects in silicon carbide epitaxial layers by reducing the area density of blind scratches and threading screw dislocations, enhancing the substrate's quality and reducing defect rates during epitaxial growth.
Implementation Method 1
Chemical mechanical polishing is performed on the silicon carbide single-crystal substrate using colloidal silica as abrasive grains
Data Source
AI summary
A silicon carbide substrate includes a first main surface, a second main surface, a threading screw dislocation, and a blind scratch. The second main surface is located opposite to the first main surface. The threading screw dislocation extends to each of the first main surface and the second main surface. The blind scratch is exposed at the first main surface and extends linearly as viewed in a direction perpendicular to the first main surface. A value obtained by dividing an area density of the blind scratch by an area density of threading screw dislocation is smaller than 0.13.