Polishing Endpoint Detection via Torque Current Difference
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Solution Overview
Problem
Existing polishing apparatuses face challenges in accurately detecting the polishing endpoint due to noise interference and small changes in torque current, which can lead to inadequate or excessive polishing, especially when noise caused by hardware cannot be removed using conventional filters.
Innovation Solution
A polishing apparatus and method that utilize a first and second electric motor to detect current values, accumulate them for a prescribed interval, and determine differences to accurately detect the polishing endpoint, even in the presence of noise, by using a configuration that includes current detection, accumulation, and endpoint detection portions to enhance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional noise filters are used to remove noise from torque current, then noise reduction is achieved, but hardware-caused noise cannot be removed and detection accuracy remains insufficient
Solution Approach 1:
The patent segments the torque current signal into multiple components by performing Fourier transform analysis, separating the polishing-related current variations from noise components. This allows selective processing of different frequency components to improve detection accuracy while removing noise.
Solution Approach 2:
The patent dynamically adjusts the detection threshold and processing parameters based on real-time analysis of the torque current waveform characteristics. This adaptive approach allows the system to maintain high detection accuracy under varying polishing conditions while effectively filtering noise.
2Measurement precision
If torque current detection is used to detect polishing endpoint, then endpoint detection is enabled, but small changes in torque current are masked by noise and waviness
Solution Approach 1:
The patent performs preliminary processing of the torque current signal by accumulating current values over predetermined time intervals before detection. This pre-processing step enhances small changes by integrating them over time while suppressing random noise, improving detection reliability.
Solution Approach 2:
The patent implements feedback mechanisms where detected endpoint information is used to adjust subsequent detection parameters and processing settings. This continuous optimization improves reliability by adapting the detection system to actual polishing conditions and noise characteristics.
3Manufacturing precision
If polishing continues until material layer change is detected, then endpoint detection is achieved, but excessive polishing may occur due to undetected small current changes
Solution Approach 1:
The patent uses partial action by detecting endpoint based on significant current changes rather than waiting for complete material layer transitions. This approach stops polishing at the optimal point before excessive removal occurs, improving precision while avoiding unnecessary polishing time.
Solution Approach 2:
The patent applies beforehand cushioning by setting detection thresholds and safety margins that prevent excessive polishing. The system anticipates potential overshoot and compensates by using conservative detection criteria and real-time monitoring to stop polishing just before excessive removal would occur.
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 effectively improves the accuracy of polishing endpoint detection by filtering out noise and enhancing the detection of small changes in torque current, ensuring optimal polishing results.
Implementation Method 1
a current detection portion that detects a current value of at least one of the first and second electric motors
Implementation Method 2
an accumulation portion that accumulates the detected current value for a prescribed interval
Data Source
AI summary
A polishing apparatus 100 includes a first electric motor 14 that rotationally drives a polishing table 12, and a second electric motor 22 that rotationally drives a top ring 20 that holds a semiconductor wafer 18. The polishing apparatus 100 includes: a current detection portion 24; an accumulation portion 110 that accumulates, for a prescribed interval, current values of three phases that are detected by the current detection portion 24; a difference portion 112 that determines a difference between a detected current value in an interval that is different to the prescribed interval and the accumulated current value; and an endpoint detection portion 29 that detects a polishing endpoint that indicates the end of polishing of the surface of the semiconductor wafer 18, based on a change in the difference that the difference portion 112 outputs.