SiC Wafer Back-Surface Finishing for Optical Sensor Detection
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Solution Overview
Problem
The challenge lies in manufacturing high-quality silicon carbide (SiC) wafers with reduced material loss, as SiC is hard and brittle, making it difficult to process, and existing methods struggle to remove the work-affected layer from the entire wafer surface, including outer peripheral portions and notches, leading to defects and increased SORI values during high-temperature annealing.
Innovation Solution
A SiC wafer manufacturing method involving satin finishing and Si vapor pressure etching to create a satin-finished back surface and mirror-finished main surface, using boron carbide or silicon carbide abrasive grains, which reduces material loss and removes the work-affected layer, thereby improving wafer quality and detection rates for optical sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If diamond abrasive grains are used to remove the work-affected layer, then the work-affected layer can be removed, but material loss increases and processing cost increases
Solution Approach 1:
The patent changes the key parameter from abrasive grain hardness to abrasive grain type by using boron carbide (Mohs hardness 9-10) or silicon carbide (Mohs hardness 9-10) instead of diamond (Mohs hardness 10). This parameter change allows effective work-affected layer removal while reducing material loss and processing cost, as these abrasive grains are sufficiently hard to remove the damaged layer but cause less material removal compared to diamond.
Solution Approach 2:
The patent employs disposable abrasive grains made of boron carbide or silicon carbide that can be easily replaced. These abrasive grains are less expensive than diamond and can be used to remove the work-affected layer effectively without the high cost and material loss associated with diamond abrasive grains, aligning with the principle of using cheaper, replaceable materials for single-use or limited-use applications.
2Shape
If the back surface is made into a mirror surface, then the wafer appearance is improved, but optical sensor detection becomes difficult
Solution Approach 1:
The patent applies asymmetry by making the front surface and back surface of the SiC wafer have different surface finishes. The front surface is polished to a mirror finish for device fabrication quality, while the back surface is intentionally left with a satin finish (arithmetic mean roughness Ra of 0.03 μm to 0.3 μm) to enhance optical sensor detection. This asymmetric treatment of opposite surfaces resolves the contradiction between aesthetic/functional surface quality and detectability.
Solution Approach 2:
The patent applies local quality by differentiating the surface finish requirements for different regions of the wafer. The front surface requires high-quality mirror finish for semiconductor device manufacturing, while the back surface requires satin finish for optical detection. This localized quality assignment allows each surface to optimize its function without compromising the other.
3Difficulty of detecting and measuring
If satin finishing is performed on the back surface, then detection rate improves and friction increases, but the work-affected layer remains on the surface
Solution Approach 1:
The patent segments the wafer processing into distinct stages: first performing satin finishing on the back surface to improve detection rate and friction properties, then separately removing the work-affected layer through controlled etching or additional polishing. This segmentation allows each function (detection improvement and defect removal) to be addressed independently in sequence, resolving the contradiction between maintaining surface roughness for detection and removing damaged layers for quality.
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 enhances the detection rate of optical sensors, reduces material loss, and produces high-quality SiC wafers with minimized lattice strains and defects, allowing for more wafers to be produced from a single ingot with improved flatness and reduced processing costs.
Implementation Method 1
an etching technique (hereinafter, also referred to as Si vapor pressure etching) for etching a SiC wafer by heating the SiC wafer under Si vapor pressure
Data Source
AI summary
An object is to provide a SiC wafer in which a detection rate of an optical sensor can improved and a SiC wafer manufacturing method.The method includes: a satin finishing process S141 of satin-finishing at least a back surface 22 of a SiC wafer 20; an etching process 21 of etching at least the back surface 22 of the SiC wafer 20 by heating under Si vapor pressure after the satin finishing process S141; and a mirror surface processing process S31 of mirror-processing a main surface 21 of the SiC wafer 20 after the etching process S21. Accordingly, it is possible to obtain a SiC wafer having the mirror-finished main surface 21 and the satin-finished back surface 22.