Wafer Grinding Method for Recessed Portion Depth Control
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Solution Overview
Problem
Existing grinding methods for wafers with devices on the front surface face challenges in forming a recessed portion of predetermined depth on the back surface without compromising the wafer's rigidity and in ensuring proper drainage of chemical solutions, especially when grinding stone wear is not accounted for, leading to shallow recessed portions and residual chemical solutions.
Innovation Solution
A grinding method that involves holding the wafer with its back surface exposed, using a grinding wheel with stones arranged in an annular pattern, and moving the wheel and wafer relative to each other along specific directions to form a recessed portion of predetermined depth, taking into account the expected wear of the grinding stones, to create an obtuse angle between the bottom and side surfaces, facilitating solution drainage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the wafer is ground on the back surface to form a recessed portion without considering grinding stone wear, then the recessed portion depth is insufficient (shallower than predetermined depth), but the grinding process is simple and does not require wear compensation
Solution Approach 1:
The method applies preliminary action by pre-calculating and compensating for the wear amount of grinding stones before the grinding process. The wear amount is determined based on the relationship between grinding amount, wafer outer diameter, and recessed portion depth, allowing the system to achieve the predetermined depth despite stone wear during processing
Solution Approach 2:
The invention changes parameters by adjusting the grinding amount based on the wear amount of grinding stones. The control unit modifies grinding parameters (such as grinding depth or number of passes) to compensate for wear, ensuring the recessed portion reaches the predetermined depth even as stones wear during the process
2Ease of manufacture
If the recessed portion is formed with a right angle between bottom and side surfaces, then the grinding process is simple, but chemical solution drains poorly and remains in the recessed portion
Solution Approach 1:
The invention applies asymmetry by forming the recessed portion with a specific angle (different from 90 degrees) between the bottom surface and side surfaces. This asymmetric angular design allows chemical solutions to drain more effectively from the recessed portion, preventing residue accumulation while maintaining manufacturing simplicity through controlled grinding parameters
3Productivity
If the wafer is thinned by grinding the back surface, then the wafer can be divided into smaller chips, but the wafer rigidity decreases making handling difficult
Solution Approach 1:
The invention applies local quality by forming a recessed portion only in a specific region of the wafer back surface rather than thinning the entire wafer uniformly. This localized grinding approach allows the wafer to be divided into smaller chips while maintaining overall rigidity, as the majority of the wafer structure remains intact and provides structural support
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
This method effectively forms a recessed portion of predetermined depth with an obtuse angle, ensuring proper drainage and maintaining wafer rigidity by accounting for grinding stone wear, thus addressing the issues of shallow recesses and residual chemical solutions.
Implementation Method 1
grinding with a grinding wheel that has multiple grinding stones... the wafer is ground on the side of the back surface thereof
Data Source
AI summary
A second relative speed of a grinding wheel and a wafer along a second direction in a grinding step is set such that a relative movement of the grinding wheel and the wafer along a first direction and a relative movement of the grinding wheel and the wafer along the second direction are concurrently initiated and are concurrently finished. Specifically, this second relative speed is set taking into consideration parameters which are optionally set, and an expected wear thickness of multiple grinding stones as known before or in a course of the grinding step, in other words, the absolute value of an expected variation in thickness of the grinding stones through the grinding step.