Wafer Edge Removal Using Laser-Induced Warping Before Thinning
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Solution Overview
Problem
Existing wafer processing methods face issues such as chipping and contamination of devices due to annular cutting of the outer circumferential edge, and incomplete removal of the outer circumferential region leading to potential damage during grinding.
Innovation Solution
A method involving the formation of multiple annular and radial modified layers using laser beams to create cracks and warps in the wafer, allowing for precise removal of the outer circumferential region without damaging the devices, followed by grinding to achieve the desired thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the outer circumferential edge of the wafer is annularly cut at the front surface, then the outer circumferential region can be removed, but chipping occurs that damages devices and contaminates with chips
Solution Approach 1:
The patent applies laser beams to form modified layers and induce warping in the outer circumferential region before bonding. This preliminary action creates controlled stress distribution that prevents chipping during subsequent grinding, eliminating the need for aggressive annular cutting that causes device damage and contamination.
Solution Approach 2:
The patent replaces mechanical annular cutting with laser-based modified layer formation. The laser induces controlled warping and stress distribution in the outer circumferential region, which allows for safe removal during grinding without the chipping and contamination problems associated with direct mechanical cutting.
2Object-affected harmful factors
If the outer circumferential region is not completely removed, then device damage is prevented, but the remaining region causes strike between inner and outer regions damaging devices and polishing pad
Solution Approach 1:
The patent forms modified layers and induces warping in the outer circumferential region before bonding to the support wafer. This preliminary action creates controlled stress distribution that allows complete removal of the outer region during grinding without causing strike damage to devices or polishing pad, as the stress is already managed through the modified layer structure.
3Length of moving object
If the wafer is ground to very small thickness, then three-dimensional semiconductor wafer stacks with reduced height are achieved, but the outer circumferential edge becomes a knife edge that is prone to cutting
Solution Approach 1:
The patent forms modified layers and induces controlled warping in the outer circumferential region before thinning the wafer to small thickness. This preliminary action prevents the formation of knife edges by creating stress distribution that maintains edge integrity even when the wafer is ground to very small thickness for three-dimensional semiconductor wafer stacks.
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 removes the unnecessary outer circumferential region while minimizing damage to the devices, ensuring complete and controlled grinding of the wafer stack.
Implementation Method 1
emitting, onto a first wafer having a plurality of devices formed on a front surface thereof and having a chamfered outer circumferential edge, a laser beam at a wavelength capable of transmitting the first wafer such that the laser beam is applied along an annular line that is a predetermined distance inward of the outer circumferential edge of the first wafer to form, in the first wafer, an annular first modified layer
Data Source
AI summary
A wafer processing method includes emitting a laser beam along an annular line that is a predetermined distance inward of the outer circumferential edge of the first wafer to form, in the first wafer, an annular first modified layer and a first crack extending from the first modified layer to make an appearance on the front surface, thereby causing the first wafer to become warped at an outer circumferential region thereof that lies closer to the outer circumferential edge than does the first modified layer and the first crack; bonding the front surface of the first wafer to a second wafer to form a bonded wafer stack; and grinding a rear surface of the first wafer of the bonded wafer stack to thin the first wafer to a finish thickness.