Eddy Current Sensor Output Circuit for Stable Film Thickness Sensing

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Solution Overview

Problem

Eddy current sensors used in semiconductor wafer polishing face challenges with signal accuracy due to susceptibility to environmental changes and noise interference, leading to inaccurate film thickness measurements, especially when detecting fine interconnects.

Innovation Solution

The implementation of an eddy current sensor assembly with an output signal processing circuit that includes a mixer circuit, low-pass filters, and adjustment circuits to process signals, reducing noise and environmental influences by converting high-frequency signals to direct-current signals and adjusting amplitudes, thereby improving signal-to-noise ratio and measurement accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a resistance bridge circuit is used to adjust the zero point, then the zero point can be adjusted, but the circuit becomes highly susceptible to temperature changes and environmental interference

Engineering Contradiction:

Improvezero point adjustment accuracyVSAvoidstability against temperature and environmental changes

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent extracts and removes the resistance bridge circuit from the measurement system. Instead of using a resistance bridge circuit for zero point adjustment, the invention directly connects the detecting coil and dummy coil in series, eliminating the source of temperature susceptibility and environmental interference while maintaining zero point adjustability through other means.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the electrical resistance bridge circuit with a direct series connection of coils. This substitution eliminates the complex electrical components that are susceptible to temperature changes, creating a more stable measurement system that relies on the fundamental electromagnetic properties of the coils themselves.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If the output signal is processed using conventional methods, then the signal can be detected, but the signal-to-noise ratio is low and measurement accuracy deteriorates

Engineering Contradiction:

Improvefilm thickness measurement accuracyVSAvoidnoise interference

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a signal processing circuit as an intermediary between the eddy current sensor and the measurement system. This circuit includes components that selectively amplify the measurement signal while attenuating noise, effectively mediating the transfer of information from the sensor to the measurement device and improving the signal-to-noise ratio.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the electrical parameters of the measurement system by using a signal processing circuit that modifies signal amplitude and frequency characteristics. This allows the system to operate in an optimal parameter range where the signal-to-noise ratio is maximized, thereby improving measurement accuracy.

Inventive Principle:

Principle #35Parameter changes

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 configuration enhances the accuracy of film thickness measurements by reducing noise and environmental interference, allowing for precise detection of thin film thicknesses and improving the reliability of endpoint detection in semiconductor wafer polishing processes.

Implementation Method 1

a mixer circuit that accepts the output signal and a signal of a predetermined frequency as input, multiplies the two input signals, and outputs an output signal obtained by the multiplication

Methodology Applied

Scientific EffectFrequency mixing:

Implementation Method 2

a low-pass filter that accepts the output signal output by the mixer circuit as input, cuts a high-frequency signal included in the output signal received as input, and outputs at least a direct-current (DC) signal

Methodology Applied

Scientific EffectElectrical filtering: Filter (electronic)

Implementation Method 3

Eddy current, sensors are used for applications such as Mm thickness measurement and displacement measurement

Methodology Applied

Scientific EffectEddy current: Eddy Currents

Implementation Method 4

an eddy current sensor using three coils is used to detect a polishing endpoint

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS11852472B2Output signal processing circuit for eddy current sensor and output signal processing method for eddy current sensor

Publication Date: 2023.12.26 EBARA CORP

AI summary

An eddy current sensor assembly includes an eddy current sensor and an output signal processing circuit that processes an output signal from the eddy current sensor. The output signal processing circuit includes a mixer circuit that accepts the output signal and a signal of the predetermined frequency as input, multiplies the two signals received as input, and outputs an output signal obtained by the multiplication, and a low-pass filter that accepts the output signal output by the mixer circuit as input, cuts a high-frequency signal included in the output signal received as input, and outputs at least a direct-current (DC) signal.