Wafer Grinding End Point Detection Using Reflectivity
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Solution Overview
Problem
Existing grinding technologies in integrated circuit manufacturing face inaccuracies in detecting the optimal end point for exposing copper posts in fan-out wafers, leading to yield loss due to over-grinding or incomplete exposure.
Innovation Solution
A method using wheel currents or reflectivity measurements to determine the optimal end point of the grinding process by correlating different material stages with specific wheel loadings or reflectivity levels, allowing for precise control of the grinding process to avoid over-grinding and ensure complete copper post exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a gauge is used to detect total thickness during grinding, then the grinding process can be monitored, but the detection accuracy is insufficient leading to yield loss
Solution Approach 1:
The patent replaces the mechanical gauge-based thickness measurement system with an optical detection system that measures reflectivity. The optical system uses light sources and photodetectors to detect changes in reflected light intensity, which correlate with the exposure of copper posts during grinding. This substitution provides more precise and reliable end point detection without the limitations of mechanical contact measurement.
Solution Approach 2:
The patent utilizes optical reflectivity changes (analogous to color changes) to detect the grinding end point. As the grinding removes dielectric materials and exposes copper posts, the reflectivity of the wafer surface changes. The optical detection system monitors these reflectivity variations to determine when copper posts are fully exposed, providing accurate end point detection without mechanical contact.
2Manufacturing precision
If grinding continues to ensure complete copper post exposure, then exposure completeness improves, but over-grinding occurs causing yield loss
Solution Approach 1:
The patent implements a feedback control system where the optical detection system continuously monitors reflectivity during grinding and provides real-time feedback to the grinding control system. When the reflectivity signal indicates that copper posts are fully exposed, the system automatically stops or adjusts the grinding process. This closed-loop feedback prevents over-grinding by stopping the process at the precise end point, ensuring complete copper post exposure without excessive material removal.
Solution Approach 2:
The patent applies partial action by using the optical detection system to identify the precise moment when copper post exposure is complete, then stopping the grinding process at that point rather than continuing with excessive material removal. The system performs just enough grinding to achieve the desired exposure without going beyond the necessary amount.
3Ease of manufacture
If traditional thickness-based detection is used, then the process is simple to implement, but it cannot accurately detect the optimal end point
Solution Approach 1:
The patent replaces the simple mechanical gauge system with an optical detection system that measures reflectivity. While the optical system is more complex than a mechanical gauge, it provides accurate end point detection by monitoring reflectivity changes that occur when copper posts are exposed. The system uses light sources, optical paths, and photodetectors to convert optical signals into electrical signals for processing and control.
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 approach enables accurate detection of the optimal end point, significantly reducing yield loss by ensuring complete exposure of copper posts without over-grinding, thereby improving the manufacturing efficiency and reliability of fan-out wafers.
Implementation Method 1
a grinding wheel is placed over a wafer. The grinding wheel and the wafer both rotate, so that the thickness of the wafer is reduced due to the removal of the surface layers by the grinding wheel
Implementation Method 2
In another embodiment, a reflectivity of the wafer is measured during the wafer grinding process
Data Source
AI summary
A method for performing grinding includes selecting a target wheel loading for wafer grinding processes, and performing a grinding process on a wafer. With the proceeding of the grinding process, wheel loadings of the grinding process are measured. The grinding process is stopped after the target wheel loading is reached. The method alternatively includes selecting a target reflectivity of wafer grinding processes, and performing a grinding process on a wafer. With a proceeding of the grinding process, reflectivities of a light reflected from a surface of the wafer are measured. The grinding process is stopped after one of the reflectivities reaches the target reflectivity.