Eddy-Current Sensor Signal Processing Stabilizes Film Thickness Measurement
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Solution Overview
Problem
Eddy-current sensors used in film thickness measurement for semiconductor wafer polishing are prone to precision issues due to environmental changes and mechanical variations, causing shifts in the zero point and reducing measurement accuracy.
Innovation Solution
An output signal processing device for eddy-current sensors that includes an AC signal generator producing signals with varying amplitudes and phases, a data generator for adjusting these signals to match reference data, and a difference circuitry to calculate film thickness amplitude, minimizing the impact of environmental changes and mechanical variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional bridge circuit with variable resistance is used for zero-point adjustment, then the device complexity is reduced, but the measurement precision deteriorates due to temperature changes and mechanical variations causing zero-point shifts
Solution Approach 1:
The patent replaces the mechanical variable resistance adjustment mechanism with an AC signal generator that electronically generates reference signals. This substitution eliminates the mechanical components prone to drift and temperature effects, thereby maintaining device simplicity while significantly improving measurement precision and stability.
Solution Approach 2:
The patent changes the approach from adjusting resistance values in a DC bridge circuit to generating AC reference signals with specific amplitudes and phases. By using AC signals and comparing them with the detection coil output, the system achieves stable zero-point reference without being affected by temperature-induced resistance changes or mechanical variations.
2Measurement precision
If the bridge circuit parameters are adjusted for zero-point calibration, then the initial measurement accuracy is improved, but the reliability deteriorates over time due to parameter drift from temperature changes and mechanical variations
Solution Approach 1:
The AC signal generator automatically generates reference signals that self-adjust to match the detection coil's output characteristics. The system continuously maintains accurate zero-point reference without requiring external recalibration, as the generated reference signals adapt to environmental conditions, thereby improving both initial accuracy and long-term reliability.
Solution Approach 2:
The patent implements a feedback mechanism where the output from the detection coil is compared with the generated AC reference signal. The difference circuitry continuously monitors the discrepancy and the system adjusts the reference signal generation to maintain optimal alignment, ensuring stable and reliable measurements over time without parameter drift.
3Ease of operation
If the variable resistance is used for balance adjustment, then the ease of operation is improved during calibration, but the manufacturing precision deteriorates due to the susceptibility of the resistance to environmental changes
Solution Approach 1:
The patent replaces the manual variable resistance adjustment with an electronic AC signal generation system. The zero-point calibration is achieved by electronically generating and adjusting reference signals rather than mechanically adjusting resistance values, eliminating the susceptibility to environmental changes while maintaining ease of operation through electronic control.
Solution Approach 2:
The system changes from adjusting resistance parameters to generating and adjusting AC signal parameters (amplitude, phase, frequency). This parameter transformation allows for precise digital control of the reference signal characteristics, improving manufacturing precision and measurement consistency while remaining easy to operate through electronic interfaces.
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 solution enhances the precision of film thickness measurement by stabilizing the output signal processing, reducing the influence of environmental and mechanical factors, and improving the accuracy of detecting the optimal polishing endpoint.
Implementation Method 1
an exciting coil 72 capable of forming eddy current in a conductor mf
Implementation Method 2
a detection coil 73 that detects the eddy current that can be formed in the conductor
Data Source
AI summary
A retainer holds reference data for identifying a first AC generated signal corresponding to an output signal output in a reference state from a detection coil. When a film thickness of a conductor is to be measured, an AC signal generator generates the first AC generated signal based on the reference data and outputs it as a reference signal. When a film thickness of a conductor is to be measured, a difference circuitry receives input of an output signal and a reference signal output from the AC signal generator and acquires and outputs a film thickness amplitude that is a difference between the amplitude of the film thickness signal and the amplitude of the reference signal. The data generator in the reference state measures an amplitude of the output signal and generates the reference data.