Eddy Current Sensor Signal Processing Circuit

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Solution Overview

Problem

Conventional eddy current sensors for film thickness measurement in semiconductor wafer polishing are sensitive to changes in ambient environment, leading to decreased measurement accuracy due to temperature changes and stray capacitance variations.

Innovation Solution

A detection signal processing apparatus and method that digitize the analog signals from the detection coils and perform synchronous detection using a digital signal processing circuit, with optional features like phase difference correction, oversampling, and differential signal processing to reduce noise and improve stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional bridge circuit is used for signal processing, then the circuit can cancel out detection signal and dummy signal to achieve balance, but the zero point easily shifts due to temperature changes and stray capacitance variations, causing decreased measurement accuracy

Engineering Contradiction:

Improvefilm thickness measurement accuracyVSAvoidstability of zero point

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces the conventional analog bridge circuit with a digital signal processing system. The detection signal and dummy signal are converted to digital signals and processed by a signal processing unit that calculates the difference between them, eliminating the need for physical bridge balancing components that are sensitive to temperature and stray capacitance changes.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the processing method from analog voltage balancing to digital signal subtraction. By converting signals to digital domain and performing arithmetic operations, the system achieves environmental stability while maintaining measurement precision.

Inventive Principle:

Principle #35Parameter changes

2Power

If the bridge circuit output signal is largely amplified, then the output signal level is sufficient, but noise increases significantly

Engineering Contradiction:

Improveoutput signal levelVSAvoidnoise

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

The patent replaces analog amplification with digital signal processing. Instead of using amplifiers that introduce noise, the system converts signals to digital domain and performs mathematical operations (subtraction and scaling) that can be done without adding significant noise, thus achieving sufficient output signal level with minimal noise increase.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of manufacture

If analog signal processing is used, then the circuit implementation is straightforward, but the processing is sensitively influenced by ambient environment changes

Engineering Contradiction:

Improvecircuit implementation simplicityVSAvoidambient environment influence

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the analog circuit implementation with a digital signal processing system. The signal processing unit performs digital subtraction of detection and dummy signals, which is insensitive to temperature changes, stray capacitance variations, and other ambient environmental factors that affect analog circuits.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 proposed solution significantly reduces the impact of ambient environment changes, enhancing the measurement accuracy and stability of film thickness detection in semiconductor wafer polishing.

Implementation Method 1

an eddy current sensor having an excitation coil configured to form an eddy current in an object to be detected

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

a first detection coil configured to detect the eddy current formed in the object to be detected

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS12241738B2Detection signal processing apparatus and detection signal processing method for eddy current sensor

Publication Date: 2025.03.04 EBARA CORP

AI summary

There is provided a detection signal processing circuit and a detection signal processing method for an eddy current sensor that are less easily influenced by a change in ambient environment than conventional technologies. A detection signal processing apparatus includes a converter configured to convert a first analog signal output by a detection coil into a first digital signal, a converter configured to convert a second analog signal output by a dummy coil into a second digital signal, and a detector which is a digital signal processing circuit configured to detect the first digital signal and the second digital signal.