Bonded Wafer Edge Separation Using Laser-Induced Warpage
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Solution Overview
Problem
The existing methods for processing semiconductor wafers with a three-dimensionally stacked structure face challenges in removing the outer circumferential region without causing breakage during grinding, as the edge chipping can extend to the device and lead to device breakage.
Innovation Solution
A processing method that involves bonding a first wafer to a second wafer, forming an annular modified layer inside the first wafer using a laser beam, detecting warpage in the outer circumferential region, determining if bonding has been released, and grinding the wafer from the back surface when sufficient warpage is achieved to thin it to a finished thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the wafer is ground extremely thinly to reduce height and increase integration, then the wafer thickness is reduced, but the outer circumferential edge becomes a knife edge and chipping is likely to occur
Solution Approach 1:
The patent applies preliminary action by forming an annular modified layer at the outer circumferential edge of the wafer before the grinding process. This modified layer is created through laser irradiation that modifies the material structure in advance, providing reinforcement to prevent chipping during subsequent thin grinding operations. The modified layer acts as a preventive measure that prepares the edge region to withstand the stresses of extreme thinning without developing knife-edge conditions.
2Reliability
If an annular modified layer is formed inside the first wafer to suppress edge chipping, then edge chipping is suppressed, but the outer circumferential region may remain without being separated
Solution Approach 1:
The patent introduces an intermediary mechanism by forming cracks that extend from the annular modified layer toward the front surface of the wafer. These cracks act as a mediator that connects the modified layer to the outer circumferential region, enabling controlled separation. The cracks serve as stress concentration points that facilitate the detachment of the outer circumferential region after the modified layer has provided chipping suppression during grinding, thus resolving the contradiction between edge protection and region separation.
3Strength
If the outer circumferential edge is beveled to prevent knife edge formation, then edge strength is improved, but device breakage may still occur during extreme thin grinding
Solution Approach 1:
The patent applies local quality by creating a localized annular modified layer at the outer circumferential edge region rather than uniformly treating the entire wafer. This localized modification concentrates the structural reinforcement exactly where the knife-edge problem occurs during extreme thinning, while leaving the device regions unaffected. The modified layer provides enhanced edge strength and chipping resistance precisely at the critical boundary zone, preventing device breakage during grinding without interfering with device integrity.
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 outer circumferential region while minimizing the risk of device breakage during grinding, ensuring the integrity of the semiconductor wafer.
Implementation Method 1
executing irradiation with a laser beam with such a wavelength as to be transmitted through the first wafer from the back surface side of the first wafer along a position separate inward from the outer circumferential edge by a predetermined distance in an annular manner and forming, inside the first wafer, an annular modified layer
Data Source
AI summary
A wafer processing method includes forming a bonded wafer by bonding a first wafer to a second wafer, irradiating a laser beam along a position separate inward from an outer circumferential edge by a predetermined distance in an annular manner and forming, inside the first wafer, an annular modified layer and cracks that extend from the modified layer toward a front surface side to cause warpage in the outer circumferential region. The method also includes detecting the amount of warpage of the outer circumferential region, determining whether or not bonding between the first wafer and the second wafer has been released on the basis of the amount of warpage of the outer circumferential region, deciding whether or not to execute a grinding step, and if so, grinding the first wafer from a back surface side.