Polishing Agent for Silicon Carbide Substrates
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Solution Overview
Problem
Current polishing methods for silicon carbide and gallium nitride single-crystal substrates are inefficient due to low polishing rates and difficulties in achieving high smoothness and stability, particularly because of the high hardness and chemical stability of these materials, which leads to prolonged polishing times and surface defects.
Innovation Solution
A polishing agent comprising an oxidant with a redox potential of 0.5 V or more, silicon oxide particles, cerium oxide particles, and a dispersion medium, with a mass ratio of silicon oxide to cerium oxide between 0.2 and 20, and a pH of 11 or less, is used to chemically and mechanically polish non-oxide single-crystal substrates, enhancing the polishing rate and surface smoothness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If diamond abrasive particles are used to mechanically polish silicon carbide single crystal, then flat surface is formed, but minute scratches are introduced and work-affected layer with mechanical strain is generated
Solution Approach 1:
The polishing process is divided into two distinct stages: mechanical polishing using diamond abrasive particles to achieve flatness, followed by chemical mechanical polishing using colloidal silica to eliminate scratches and improve surface smoothness. This segmentation allows each process to optimize for its specific function without compromising the other.
Solution Approach 2:
Colloidal silica acts as an intermediary substance in the chemical mechanical polishing stage. It chemically reacts with the silicon carbide surface to form a removable layer, which is then mechanically removed by the abrasive particles, effectively eliminating the scratches and strain layers introduced during initial mechanical polishing.
2Manufacturing precision
If conventional polishing compositions are used, then surface smoothing is achieved, but polishing rate is low and polishing time is very long
Solution Approach 1:
The polishing composition parameters are optimized by controlling pH within 2-10 and adjusting the concentration of colloidal silica (0.1-10 wt%). These parameter changes enhance the chemical reactivity and abrasive effectiveness, significantly improving the polishing rate while maintaining surface smoothness.
Solution Approach 2:
The polishing composition is formulated as a composite system containing colloidal silica particles, pH adjusters, and optional additives. This composite structure combines the chemical etching capability of colloidal silica with controlled abrasion, achieving both high polishing rate and superior surface quality that neither component could achieve alone.
3Manufacturing precision
If cerium oxide particles are used for polishing, then surface smoothness is improved, but dispersibility in polishing liquid is low
Solution Approach 1:
The patent replaces cerium oxide particles with colloidal silica particles as the primary abrasive component. Colloidal silica provides sufficient polishing performance while offering superior dispersibility and stability in the polishing liquid, eliminating the dispersibility problems associated with cerium oxide without requiring expensive specialized additives.
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 proposed solution allows for a high polishing rate and stable, smooth surfaces on hard and chemically stable substrates like silicon carbide and gallium nitride, with improved dispersibility of cerium oxide particles, reducing the risk of scratches and defects, thus enhancing the productivity of these substrates.
Implementation Method 1
The CMP is a method to use a chemical reaction such as oxidation to change a workpiece to an oxide or the like
Implementation Method 2
use abrasive particles lower in hardness than the workpiece to remove the generated oxide, thereby polishing its surface
Data Source
AI summary
A polishing agent for polishing a non-oxide single-crystal substrate such as a silicon carbide single-crystal substrate with a high polishing rate to obtain a smooth surface is provided. This polishing agent comprises an oxidant having redox potential of 0.5 V or more and containing a transition metal, silicon oxide particles, cerium oxide particles and a dispersion medium, in which a mass ratio of the silicon oxide particles to the cerium oxide particles is from 0.2 to 20.