Polishing End Point Detector Signal Processing

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Solution Overview

Problem

Existing polishing apparatuses face challenges in accurately detecting the polishing end point due to small changes in polishing frictional force, often resulting in misdetection due to noise interference.

Innovation Solution

The polishing apparatus incorporates an end point detector that removes noise from signals by moving-average, differentiates, and exponentiates them with an exponent greater than 1 to enhance the detection of the polishing end point, using signals from motor currents or acoustic/ultrasonic sensors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the change in polishing frictional force is small, then the polishing end point detection becomes difficult, but noise interference increases causing misdetection

Engineering Contradiction:

Improvepolishing end point detection accuracyVSAvoidnoise interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies preliminary action by performing moving average processing and differentiation on the frictional force signal before exponentiation. These preprocessing steps prepare the signal by reducing noise and highlighting trends, making the subsequent exponentiation more effective at amplifying the end-point signal while suppressing noise interference.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent applies parameter changes by using exponentiation with an exponent greater than 1 to transform the frictional force signal. This non-linear transformation amplifies the magnitude of the signal change at the polishing end point while suppressing smaller noise variations, effectively changing the parameter scale to improve detection accuracy.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If noise removal processing is applied to the signal, then detection accuracy improves, but the signal processing complexity increases

Engineering Contradiction:

Improvepolishing end point detection accuracyVSAvoidsignal processing complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent merges multiple signal processing operations (moving average, differentiation, and exponentiation) into a unified processing pipeline within the end point detector. By combining these functions into a single integrated system, the patent reduces overall system complexity while maintaining the benefits of each individual processing step.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent replaces complex mechanical or hardware-based noise filtering systems with software-based signal processing algorithms. The moving average, differentiation, and exponentiation operations are implemented as computational processes, simplifying the physical system while achieving effective noise removal and end-point detection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentUS20240342854A1Polishing apparatus and polishing end point detection method in polishing apparatus

Publication Date: 2024.10.17 EBARA CORP

AI summary

To accurately detect a polishing end point even if a change in a polishing frictional force is small. A polishing apparatus includes a polishing table for holding a polishing pad, a holder for holding a polishing target object such that the polishing target object faces the polishing pad, and an end point detector that detects, based on a signal indicating a state of polishing of the polishing target object by the polishing pad, a polishing end point indicating an end of the polishing. The end point detector is configured to remove noise of the signal, exponentiate the signal subjected to the noise removal with an exponent greater than 1, and detect the polishing end point based on the exponentiated signal.