Wafer Grinding with Unevenness-Absorbing Pad and Concavity
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Solution Overview
Problem
Thinned wafers after grinding face handling difficulties due to reduced rigidity, uneven rear surfaces matching the front surfaces, and low die strength, making them challenging to remove from grinding machines and transport between process steps.
Innovation Solution
A method involving a grinding apparatus with a chuck table and a rotatable grindstone, using an unevenness-absorbing pad with a porous resin sheet and adhesive layer to form a concavity on the wafer's rear surface, surrounded by an annular reinforcing portion, preventing unevenness transfer and improving handling and die strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the wafer thickness is reduced by grinding to enable reduction in size and weight of electronic machines, then the weight and size are reduced, but the wafer loses rigidity and handling becomes difficult
Solution Approach 1:
The wafer rear surface is divided into two functional zones: a thinned device region (50-150 μm) for weight reduction and a thickened reinforcing portion (200-500 μm) for structural strength. This segmentation allows the wafer to simultaneously achieve reduced weight while maintaining handling rigidity through the annular reinforcing ring surrounding the device region.
Solution Approach 2:
Different thicknesses are applied to different regions of the wafer rear surface. The device region is thinned to reduce weight, while the reinforcing portion is maintained at greater thickness to provide structural support. This local quality variation resolves the contradiction between overall weight reduction and local rigidity requirements.
2Volume of moving object
If the wafer is ground to reduce thickness, then size and weight are reduced, but the rear surface develops unevenness matching the front surface, reducing die strength
Solution Approach 1:
An unevenness-absorbing pad is introduced as an intermediary element between the chuck table and the wafer front surface. This pad absorbs the surface unevenness of the thinned wafer during grinding, preventing the transfer of front surface irregularities to the rear surface. The pad acts as a mediator that decouples the grinding process from the wafer's inherent surface variations.
Solution Approach 2:
The unevenness-absorbing pad is placed on the chuck table before the wafer is positioned for grinding. This beforehand cushioning prepares the support surface to compensate for wafer unevenness, ensuring that the grinding process produces a flat rear surface despite variations in wafer thickness and front surface irregularities.
3Length of moving object
If the wafer thickness is reduced to enable miniaturization, then electronic machine size is reduced, but handling and transportation become difficult
Solution Approach 1:
The wafer is segmented into a thin device region for miniaturization and a thick reinforcing portion for handling. This segmentation enables the wafer to be thin enough for electronic machine miniaturization while the annular reinforcing ring provides the mechanical strength needed for easy handling and transportation.
Solution Approach 2:
The wafer exhibits local quality variation in thickness: thin (50-150 μm) in the device region for miniaturization, and thick (200-500 μm) in the reinforcing portion for handling. This local differentiation resolves the contradiction between overall thickness reduction and handling ease.
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 facilitates easy removal and handling of wafers, prevents low die strength, and maintains device quality by absorbing unevenness and reinforcing the wafer's rear surface, ensuring improved flatness and die strength.
Implementation Method 1
The unevenness-absorbing pad disposed between the device region of the wafer and the chuck table absorbs the unevenness of the wafer on its front surface and thereby prevents any corresponding unevenness from being formed on its rear surface
Implementation Method 2
The unevenness-absorbing pad preferably has an adhesive layer formed on one surface thereof to allow the wafer to adhere to the pad
Implementation Method 3
causing the wafer held by the chuck table to be rotated and ground, while having the grindstone kept in contact with the rear surface of the wafer
Data Source
AI summary
To facilitate handling of a wafer with its thickness reduced by grinding its rear surface, and prevent any protrusions and depressions matching those of the front surface from being formed on its rear surface, the method including the steps of disposing an unevenness absorbing pad between a chuck table and a device region of the wafer for absorbing unevenness of the device region, and causing the wafer held by the chuck table to be rotated and ground, while having a grindstone kept in contact with rear surface of the wafer at center of rotation of the wafer, and out of contact with a portion of its rear surface opposite from the outer excess region, thereby forming a concavity in the portion of the rear surface of the wafer opposite from the device region, and forming an annular reinforcing portion including the outer excess region around the concavity.