Sapphire Substrate Annealing and Grinding for Flatness
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Solution Overview
Problem
Sapphire substrates sliced with a wire saw often exhibit residual stress, leading to warping or bowing issues that hinder achieving high flatness during the flattening process.
Innovation Solution
The method involves annealing the sapphire substrate to remove residual stress, followed by a multi-step grinding process using a liquid resin to flatten both surfaces, ensuring that each surface is ground independently to eliminate warping and achieve high flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a sapphire substrate is sliced with a wire saw, then the substrate can be obtained from the ingot, but residual stress is generated causing warp or bow that prevents high flatness
Solution Approach 1:
The patent applies preliminary action by performing annealing treatment on the sapphire substrate before the flattening process. This preliminary stress relief treatment removes residual stress generated during wire saw slicing, preventing warp or bow from developing during subsequent grinding operations, thereby enabling high flatness to be achieved
2Manufacturing precision
If both sides of the wafer are ground and polished to remove undulation and strain, then flatness is improved, but the process becomes complex and time-consuming
Solution Approach 1:
The patent applies preliminary action by performing annealing treatment on the sapphire substrate before the flattening process. This preliminary stress relief treatment removes residual stress generated during wire saw slicing, preventing warp or bow from developing during subsequent grinding operations, thereby enabling high flatness to be achieved
3Ease of manufacture
If conventional flattening is performed without considering residual stress, then the process is simple, but warp or bow is generated preventing high flatness
Solution Approach 1:
The patent applies preliminary action by performing annealing treatment on the sapphire substrate before the flattening process. This preliminary stress relief treatment removes residual stress generated during wire saw slicing, preventing warp or bow from developing during subsequent grinding operations, thereby enabling high flatness to be achieved
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
This approach effectively suppresses the generation of warp or bow due to residual stress, resulting in high flatness and ultraflat terrace surfaces with consistent crystal orientation, suitable for semiconductor devices.
Implementation Method 1
the viscosity of the liquid resin is lowered by irradiation with ultrasonic waves to thereby restore the undulation of the wafer
Implementation Method 2
mounting said sapphire substrate processed by said annealing step on a stage having a holding surface in a state where a first surface of said sapphire substrate is in contact with said holding surface of said stage through a liquid resin
Implementation Method 3
selectively applying ultrasonic waves to the wafer according to the undulation measured above to thereby partially reduce the viscosity of the liquid resin and restore the undulation of the wafer
Implementation Method 4
curing the liquid resin
Data Source
AI summary
A sapphire substrate flattening method including an ingot slicing step of slicing a sapphire single-crystal ingot to obtain a sapphire substrate, an annealing step of annealing the sapphire substrate, a wafer mounting step of mounting the sapphire substrate processed by the annealing step on a stage having a holding surface in the condition where a first surface of the sapphire substrate is in contact with the holding surface of the stage through a liquid resin, a resin curing step of curing the liquid resin, a first grinding step of grinding a second surface of the sapphire substrate opposite to the first surface, a resin removing step of removing the liquid resin cured on the first surface of the sapphire substrate, and a second grinding step of grinding the first surface of the sapphire substrate.