Localized Wafer Laser Thinning to Reduce Warpage and Breakage
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Solution Overview
Problem
Conventional wafer thinning methods, such as grinding, result in high breakage ratios and warpage issues, especially when thinning wafers to less than 100µm, making handling and subsequent processes difficult, particularly in applications like VCSEL and SiC MOSFETs.
Innovation Solution
A method and system for localized wafer thinning using a laser process, involving image recognition and localized laser thinning based on die features to selectively thin specific regions of the wafer, reducing warpage and breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional grinding methods are used to thin the entire backside of the wafer, then the wafer thickness can be reduced, but the wafer will warp and break easily
Solution Approach 1:
The patent applies localized laser thinning to specific regions of the wafer backside rather than grinding the entire surface. The laser processing is confined to defined processing regions that exclude certain areas, allowing thickness reduction in needed locations while preserving structural integrity in critical areas, thus eliminating warpage and breakage issues
Solution Approach 2:
The patent replaces conventional mechanical grinding with laser-based processing. This substitution eliminates mechanical contact and associated stresses that cause warpage, while achieving precise thickness control through controlled material removal via laser ablation
2Manufacturing precision
If the wafer is thinned to a thickness smaller than 100μm, then the device performance can be improved, but the handling difficulty and breakage ratio increase significantly
Solution Approach 1:
The patent selectively thins only specific regions of the wafer to the required thin dimensions while leaving other regions at greater thickness. This creates a thickness gradient where handled areas remain thick and robust, while functional areas achieve the required thinness for device performance
Solution Approach 2:
The patent preserves thicker material in strategic locations before the wafer needs to be handled or processed further. This remaining material acts as a mechanical cushion or support structure that prevents breakage during handling, while still allowing the thinned regions to achieve their target thickness
3Manufacturing precision
If conventional grinding methods are used on SiC wafers for power devices, then the wafer can be thinned to less than 150μm, but the breakage ratio is 3% to 5%
Solution Approach 1:
The patent replaces mechanical grinding with laser-based processing for SiC wafer thinning. This eliminates mechanical stresses and contact forces that cause breakage during grinding, while achieving the required thickness reduction through controlled laser ablation, reducing breakage from 3-5% to near zero
Solution Approach 2:
The patent changes the physical mechanism of material removal from mechanical abrasion to thermal ablation. By controlling laser parameters such as power, pulse duration, and scanning speed, the process achieves precise thickness control without the mechanical stresses that cause SiC wafer breakage
4Reliability
If the middle portion of the backside of the wafer is thinned using a smaller grinding wheel, then the wafer warpage can be reduced, but the supporting stress in the middle portion becomes insufficient
Solution Approach 1:
The patent applies laser thinning with precise spatial control to create different thickness profiles in different regions. By selectively removing material only where needed and preserving thicker sections in supporting areas, the process reduces warpage in thinned regions while maintaining structural strength and supporting stress in critical areas
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 effectively thins wafers locally, minimizing warpage and breakage, allowing for precise thickness control and improved handling of wafers, enhancing device performance and reducing material waste.
Implementation Method 1
performing localized laser thinning processing on a bottom surface of the wafer within the at least one to-be-thinned starting region of each of the plurality of dies by a laser apparatus
Data Source
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AI summary
A method for localized wafer thinning, comprising following steps of: providing a wafer including a plurality of dies; for each of the plurality of dies, determining at least one interested feature related to at least one device formed on a top surface of the wafer and at least one to-be-thinned starting region according to the at least one interested feature; capturing at least one image of each of the plurality of dies; performing image recognition on the at least one image to recognize the at least one interested feature of each of the plurality of die; and performing localized laser thinning processing on a bottom surface of the wafer within the at least one to-be-thinned starting region of each of the plurality of dies, such that the wafer is locally thinned.