InP Wafer Edge Geometry for Crack-Resistant Back Lapping
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Solution Overview
Problem
During back lapping to reduce the thickness of an indium phosphide substrate after epitaxial growth, the sharp edges of the wafer are further sharpened, leading to a higher risk of cracking.
Innovation Solution
The indium phosphide substrate is designed with specific angles (0°<θ≤110°) and a rounded edge with a radius of curvature (Rf) of 200 to 350 μm on the main surface side, which suppresses the sharpness of the wafer edge during back surface polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If back surface polishing (back lapping) is used to reduce substrate thickness, then the thickness is decreased to the desired range, but the wafer edge becomes sharper and more prone to cracking
Solution Approach 1:
The patent applies preliminary action by forming a rounded edge (edge round) on the wafer before back surface polishing. This pre-formed radius of curvature (200-350 μm) prevents the edge from becoming sharp during subsequent polishing, thereby avoiding cracking while still allowing thickness reduction to occur.
Solution Approach 2:
The patent applies spheroidality by introducing a curved edge geometry (edge round) with a specific radius of curvature (200-350 μm) on the wafer. This curvature distributes stress away from the edge during polishing, preventing the formation of sharp edges that would lead to cracking, while still permitting the necessary thickness reduction.
2Productivity
If the wafer edge is sharp, then the cutting and slicing process is efficient, but the edge becomes more susceptible to damage during polishing
Solution Approach 1:
The patent applies preliminary action by pre-forming the edge round (200-350 μm radius) before back surface polishing operations. This preliminary shaping protects the edge from damage during subsequent polishing while maintaining the efficiency of earlier slicing operations.
Solution Approach 2:
The patent applies local quality by modifying only the edge region of the wafer (creating edge round) while leaving the bulk material and main surfaces unchanged. This localized modification protects the vulnerable edge area without affecting the overall productivity of slicing or the quality of the main wafer surfaces.
Data Source
AI summary
Provided is an indium phosphide substrate which has suppressed sharpness of a wafer edge when polishing is carried out from the back surface of the wafer by a method such as back lapping. An indium phosphide substrate, wherein when planes A each parallel to a main surface are taken in a wafer, the phosphide substrate has an angle θ on the main surface side of 0°<θ≤110° for all of the planes A where a distance from the main surface is 100 μm or more and 200 μm or less, wherein the angle θ is formed by a plane B, the plane B including an intersection line of an wafer edge with each of the planes A and being tangent to the wafer edge, and an plane of each of the planes A extending in a wafer outside direction, and wherein in a cross section orthogonal to the wafer edge, the indium phosphide substrate has an edge round at least on the main surface side, and the edge round on the main surface side has a radius of curvature Rf of from 200 to 350 μm.