Wafer Edge Separation Layer for Safe Excess Region Removal
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Solution Overview
Problem
Existing methods for processing wafers, such as the edge trimming method disclosed in JP 2020-057709A, fail to effectively remove the outer circumferential excessive region during grinding, leading to potential damage to devices on the wafer and issues with incomplete removal or collision of wafer regions.
Innovation Solution
A method involving a separation layer forming step using a laser beam to create a truncated cone-shaped separation layer radially inward from the outer circumferential edge, followed by a grinding step to thin the wafer, and a detecting step to ensure complete removal of the excessive region, using light reflection to monitor the process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a laser beam is applied to form an annular modified layer along the outer circumferential edge to prevent chipping, then device protection is improved, but unremoved excessive regions may remain and polishing pads may be damaged
Solution Approach 1:
The patent extracts the harmful outer circumferential excessive region from the wafer by forming a separation layer that enables selective removal of this region through grinding, while preserving the device region. The separation layer acts as a boundary that allows the excessive region to be separated and removed independently.
Solution Approach 2:
The patent performs preliminary action by forming the separation layer through laser irradiation before the grinding step. This pre-formed separation layer guides the subsequent grinding process to remove only the excessive region without affecting the device region, preventing both chipping and excessive region retention.
2Productivity
If the wafer is ground to thin down to ultrathin configuration, then integration density is improved, but knife edges develop and chipping occurs
Solution Approach 1:
The patent converts the harmful knife edge effect into a beneficial feature by forming a separation layer that guides crack propagation. The laser-induced separation layer creates a controlled path for stress release, transforming the potential chipping hazard into a controlled separation mechanism that protects the device region.
Solution Approach 2:
The separation layer acts as an intermediary between the outer circumferential edge and the device region. It serves as a buffer zone that absorbs stress and prevents direct transmission of mechanical loads that would cause chipping, while still allowing the wafer to be thinned to ultrathin configurations.
3Reliability
If the focused spot is positioned closer to the outer circumferential edge to improve separation layer effectiveness, then chipping prevention is improved, but regions may collide and break
Solution Approach 1:
The patent applies local quality by positioning the laser focused spot at a specific distance from the outer circumferential edge to create a separation layer with optimal properties. This localized positioning ensures the separation layer is formed at the precise location needed to prevent chipping while maintaining sufficient distance to avoid structural collision and breakage.
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 allows for the safe removal of the outer circumferential excessive region while preventing damage to devices on the wafer, ensuring complete removal and reducing the risk of collisions or polishing pad damage.
Implementation Method 1
applying a laser beam to the outer circumferential excessive region of the first wafer while positioning a focused spot of the laser beam in a region spaced a predetermined distance radially inwardly from the outer circumferential edge, on an inclined plane that is progressively closer to the one of the opposite surfaces of the first wafer toward the outer circumferential edge, thereby forming a separation layer shaped as a side surface of a truncated cone
Implementation Method 2
detecting whether or not the outer circumferential excessive region that extends from the separation layer to the outer circumferential edge has been removed from the first wafer
Data Source
AI summary
A method of processing a wafer includes forming a bonded wafer assembly by bonding one of opposite surfaces of a first wafer to a second wafer, the first wafer having a device region and an outer circumferential excessive region, applying a laser beam to the first wafer while positioning a focused spot of the laser beam radially inwardly from the outer circumferential edge of the first wafer, on an inclined plane that is progressively closer to the one of the opposite surfaces of the first wafer toward the outer circumferential edge, thereby forming a separation layer shaped as a side surface of a truncated cone, grinding the first wafer from the other one of the opposite surfaces thereof to thin down the first wafer to a predetermined thickness, and detecting whether or not the outer circumferential excessive region has been removed from the first wafer.