SiC Substrate Grinding with Tribo-Catalytic Metallic Oxide Abrasives
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Solution Overview
Problem
Current methods for machining single crystal SiC substrates are limited by high machining loads and the generation of small scratches, making them unsuitable for mass production and practical use in power semiconductor devices, especially for larger diameters.
Innovation Solution
A surface machining method using a grinding plate with a soft pad and a hard pad sequentially attached to a base metal, where abrasive grains made of metallic oxides softer than SiC are fixed to the hard pad, employing tribo-catalytic action to reduce scratches and facilitate efficient machining, with specific conditions for coolant usage, rotation speeds, and segmentation of the hard pad.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If diamond abrasive grains are used for grinding, then machining speed is improved, but small scratches are generated on the surface
Solution Approach 1:
The invention changes the material parameter of abrasive grains from diamond to metallic oxide (such as cerium oxide, aluminum oxide, or silicon oxide) that is softer than SiC. This parameter change resolves the contradiction by eliminating scratch generation while maintaining acceptable machining speed through the softening effect that prevents aggressive cutting and scratch formation on the SiC substrate surface.
Solution Approach 2:
The invention replaces the purely mechanical removal mechanism of diamond abrasives with a combined mechano-chemical polishing mechanism. The metallic oxide abrasive grains, being softer than SiC, do not mechanically scratch the surface but instead facilitate chemical reactions that remove material, thereby eliminating scratches while maintaining productivity.
2Ease of operation
If resin bond grindstone is used, then machining is facilitated, but small scratches cannot be avoided
Solution Approach 1:
The invention changes the abrasive material parameter from diamond to metallic oxide with hardness lower than SiC. This parameter change fundamentally alters the interaction mechanism between abrasive and substrate, enabling easy machining through chemical reactions while preventing mechanical scratches that would otherwise be inevitable with harder abrasives like diamond or resin bond grindstones.
3Productivity
If high machining load is applied, then machining speed is improved, but surface quality deteriorates with increased scratches
Solution Approach 1:
The invention changes the abrasive material parameter to metallic oxide softer than SiC, which fundamentally alters the machining mechanism from mechanical removal to mechano-chemical polishing. This parameter change resolves the contradiction by enabling surface oxidation and removal through chemical reactions rather than mechanical force, thereby maintaining surface quality even at higher machining loads and speeds.
Solution Approach 2:
The invention utilizes metallic oxide abrasive grains that promote oxidation of the SiC substrate surface. The oxidation reaction converts SiC into SiO2.nH2O and CO/CO2, which are then removed by the abrasive grains. This oxidation mechanism allows for efficient material removal at higher loads without generating scratches, as the chemical reaction occurs before mechanical contact removes the oxidized layer.
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 enables mass production of mirror-finish single crystal SiC substrates with reduced scratches and increased machining speed, suitable for existing grinders, by effectively generating active species for oxidation and removal of SiO2.nH2O, achieving uniform surface finishing.
Implementation Method 1
energy is supplied due to mechanical rubbing between abrasive grains made of a material having a bandgap and a substance to be machined, and electrons on the surfaces of the abrasive grains are excited, thereby generating electron-hole pairs. Therefore, by the same mechanism as that for a photocatalyst material, active species having an extremely strong oxidation power such as a superoxide anion, a hydroxyl radical, or atomic oxygen are generated and the surface of the specimen is oxidized.
Implementation Method 2
SiO2.nH2O is removed using abrasive grains, whereby the surfaces of a single crystal SiC substrate can be machined to a mirror finish.
Data Source
AI summary
A surface machining method for a single crystal SiC substrate, including: a step of mounting a grinding plate which includes a soft pad and a hard pad sequentially attached onto a base metal having a flat surface, a step of generating an oxidation product by using the grinding plate, and a step of grinding the surface while removing the oxidation product, wherein abrasive grains made of at least one metallic oxide that is softer than single crystal SiC and has a bandgap are fixed to the surface of the hard pad.