Wafer Thinning via Laser-Formed Annular Modified Layer
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Solution Overview
Problem
Existing wafer processing methods for TSV wafers face issues with edge chipping during grinding, leading to device breakage and contamination from swarf generation.
Innovation Solution
A wafer processing method that involves bonding a chamfered wafer to a support wafer, followed by a modified layer formation using a laser beam to create an annular modified layer or groove, which prevents edge chipping by rupturing at the modified layer during grinding, thereby protecting the device region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a wafer is ground to be extremely thin, then the wafer thickness is reduced to the finished thickness, but the periphery becomes a knife edge and chipping of the edge is liable to occur during grinding
Solution Approach 1:
An annular groove is formed at the peripheral edge portion of the wafer before the grinding step. This preliminary action creates a stress relief feature that prevents chipping from propagating into the device region during subsequent grinding operations, thereby protecting the wafer edges while enabling thin grinding.
Solution Approach 2:
The peripheral edge portion is separated from the device region by forming an annular groove. This segmentation creates a distinct boundary that isolates the stress concentration at the edge, preventing chipping from extending into the device region while allowing the device region to be ground to the required thin thickness.
2Reliability
If edge trimming technology is applied to cut the peripheral edge, then edge chipping is reduced, but a large amount of swarf is generated leading to easy contamination of the devices
Solution Approach 1:
The mechanical cutting process is replaced with a grinding process that utilizes the annular groove as a stress relief feature. Instead of mechanically cutting the edge (which generates swarf), the wafer is ground with the groove in place, allowing the groove to rupture and absorb stress without generating contaminating swarf that would affect the devices.
3Manufacturing precision
If the wafer is ground to be extremely thin, then the finished thickness is achieved, but chipping may extend to devices leading to breakage of the devices
Solution Approach 1:
The annular groove is formed at the peripheral edge before the grinding step, creating a preliminary stress relief structure. This preliminary action ensures that when the wafer is ground to extremely thin dimensions, any chipping that occurs will be contained at the groove location and will not propagate into the device region, thereby protecting the devices from breakage.
Solution Approach 2:
The annular groove acts as an intermediary stress relief feature between the peripheral edge and the device region. It serves as a buffer zone that absorbs and redirects stresses during grinding, preventing direct stress transmission to the devices while enabling the wafer to be ground to the required thin finished thickness.
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 restrains breakage of devices during grinding and reduces swarf generation, ensuring precise thinning of wafers without contamination.
Implementation Method 1
applying along a boundary between the device region and the peripheral surplus region of the first wafer a laser beam of such a wavelength as to be transmitted through the first wafer, to form an annular modified layer inside the first wafer
Data Source
AI summary
A wafer processing method includes: a bonding step of bonding a front surface side of a first wafer chamfered at a peripheral edge portion thereof to a front surface side of a second wafer; a grinding step of holding a back surface side of the second wafer by a chuck table and grinding a back surface of the first wafer to thin the first wafer to a finished thickness, after the bonding step; and a modified layer forming step of applying along a boundary between a device region and a peripheral surplus region of the first wafer a laser beam of such a wavelength as to be transmitted through the first wafer to form an annular modified layer inside the first wafer in the vicinity of the front surface of the first wafer, before the grinding step.