Bonded Wafer Thinning With Laser Warpage Edge Release
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Solution Overview
Problem
Existing wafer processing methods face issues with edge chipping and contamination during grinding, where chipping can lead to device breakage and surplus material is not effectively removed, and the formation of modified layers can result in offcuts being left behind.
Innovation Solution
A method involving the formation of annular modified layers and cracks on the wafer using a laser beam, which generates warpage in the peripheral region, allowing for the cancellation of bonding between wafers and enabling the removal of the peripheral surplus region during grinding without breaking the devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the wafer is ground to an extremely small thickness, then the finished thickness is achieved, but the peripheral edge becomes a knife edge causing chipping that extends to devices
Solution Approach 1:
The method applies preliminary action by forming modified layers and cracks in the peripheral region before the grinding step. This preliminary modification creates controlled warpage that prevents knife edge formation during subsequent thin grinding, thereby avoiding device breakage while achieving the required thickness precision.
Solution Approach 2:
The method implements preliminary anti-action by generating controlled warpage through laser-induced modified layers and cracks before grinding. This pre-generated warpage counteracts the tendency of the wafer edge to form a knife edge during grinding, thereby preventing chipping from extending to the devices.
2Reliability
If edge trimming is performed by cutting the peripheral edge, then the knife edge is removed, but chipping reaches devices and a large amount of swarf contaminates devices
Solution Approach 1:
The method replaces the mechanical cutting system with a laser-based system. Instead of using a mechanical blade to cut the peripheral edge (which generates swarf), a laser beam is used to form modified layers and cracks, eliminating mechanical contact and swarf generation while still removing the knife edge effect.
Solution Approach 2:
The method changes the physical state and properties of the peripheral material through laser irradiation. By controlling laser parameters (wavelength, power, scanning speed) to create modified layers with specific thermal and mechanical properties, the material is transformed in a controlled manner without generating harmful swarf.
3Reliability
If a modified layer is formed on the inner side than the bonding region, then edge chipping is restrained, but offcuts of the peripheral surplus region are not peeled off during grinding
Solution Approach 1:
The method segments the modified region into multiple concentric modified layers at different positions in the peripheral region. This segmentation, combined with creating cracks that extend to the front surface, allows differential warpage control that enables both device protection and effective peeling off of peripheral offcuts during grinding.
Solution Approach 2:
The method applies local quality by creating different modified layer configurations in different zones of the peripheral region. The first modified layer is formed at a first position and a second modified layer is formed at a second position, with each zone having tailored properties to achieve both chipping prevention and offcut removal in its respective area.
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 method effectively removes the peripheral surplus region while minimizing the risk of device breakage and contamination, ensuring the successful thinning of wafers without extending edge chipping to the devices.
Implementation Method 1
applying a laser beam having a wavelength transmittable through the first wafer, from a back surface side of the first wafer in an annular pattern along positions on an inner side than the peripheral edge by a predetermined distance to form in an inside of the first wafer an annular first modified layer and a first crack
Implementation Method 2
The bonding of the first wafer and the second wafer to each other is canceled by the warpages generated in the peripheral region in the first modified layer forming step and the second modified layer forming step
Data Source
AI summary
A wafer processing method includes bonding a front surface of a first wafer to a second wafer, applying a laser beam along positions on the inner side other than a peripheral edge of the first wafer by a predetermined distance to form an annular first modified layer and a first crack exposed on the front surface side, thereby generating a warpage in a peripheral region of the first wafer, applying a laser beam to the peripheral region to form a plurality of annular second modified layers and a plurality of second cracks exposed on the front surface side, thereby generating a warpage in the peripheral region, and grinding the first wafer from a back surface side to thin the first wafer to a finished thickness. The bonding of the first wafer and the second wafer to each other is canceled by the warpages in the peripheral region.