Wafer Edge Separation Layer for Safe Ultrathin Grinding
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Solution Overview
Problem
Existing wafer processing methods, such as edge trimming using a laser beam, are inadequate as they may leave unremoved outer circumferential excessive regions, cause collisions between radial and inward regions, and damage polishing pads during subsequent polishing steps.
Innovation Solution
A method involving a bonded wafer assembly with a separation layer formed by a laser beam applied radially inward from the outer edge, followed by grinding and detection using measurement light to ensure removal of the excessive region, with optional external force application to complete the removal process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the wafer is ground to thin down to ultrathin configuration, then the wafer thickness is reduced, but the beveled outer circumferential edges are turned into knife edges that chip during grinding
Solution Approach 1:
The patent applies preliminary action by forming a separation layer at a predetermined distance from the outer circumferential edge before the grinding process. This separation layer is created by irradiating the wafer with a laser beam to form a modified layer, which then serves as a predetermined separation line. By preparing this separation structure in advance, the patent prevents knife edge formation during subsequent thin grinding while maintaining device integrity.
2Reliability
If a separation layer is formed by laser irradiation along the outer circumferential edge, then the modified layer prevents chips from reaching devices, but the end part of the outer circumferential excessive region may remain unremoved
Solution Approach 1:
The patent solves the incomplete removal problem by changing the spatial approach from edge-on irradiation to top-down irradiation. The laser beam is applied from above the wafer surface at positions radially outward from the device region, creating a separation layer that extends through the wafer thickness. This dimensional change in laser application allows the separation layer to reach the bottom surface, ensuring complete separation of the excessive region.
3Manufacturing precision
If the focused spot of the laser beam is positioned close to the outer circumferential edge, then the separation layer forms near the edge, but regions radially outwardly and inwardly of the annular modified layer may collide and break
Solution Approach 1:
The patent applies local quality by positioning the laser beam's focused spot at a predetermined distance radially inwardly from the outer circumferential edge, rather than directly at the edge. This creates a separation layer at an optimized location that provides sufficient buffer zone. The separation layer is formed with specific local properties (modified layer structure) that prevent collision between regions while maintaining overall wafer integrity during grinding.
4Reliability
If the outer circumferential excessive region is not completely removed, then the separation layer prevents chip formation, but the excessive region may damage the polishing pad in subsequent polishing steps
Solution Approach 1:
The patent uses preliminary action by forming the separation layer before grinding to ensure complete removal of the excessive region. The separation layer acts as a predetermined guide that ensures the excessive region is completely separated and removed during the subsequent grinding process. This preliminary preparation prevents any residual excessive region from reaching the polishing pad in later steps, eliminating the risk of polishing pad damage while maintaining chip prevention benefits.
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
Effectively removes the outer circumferential excessive region without damaging devices on the wafer, preventing collisions and polishing pad damage during grinding and subsequent processing steps.
Implementation Method 1
a separation layer forming step of 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
Implementation Method 2
applying a laser beam to the outer circumferential excessive region of the first wafer... thereby forming a separation layer shaped as a side surface of a truncated cone
Implementation Method 3
applying measurement light to the outer circumferential excessive region that extends from the separation layer to the outer circumferential edge, and determining whether or not the outer circumferential excessive region has been removed from the first wafer, by detecting at least either light reflected by the outer circumferential excessive region or light reflected by the separation layer
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.