Eddy Current Sensor Calibration for Polishing Film Thickness
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Solution Overview
Problem
Eddy current sensors used in polishing apparatuses for monitoring conductive film thickness experience signal drift due to environmental changes and operational conditions, leading to errors in detecting polishing end points and film thickness, necessitating frequent calibration that reduces apparatus availability.
Innovation Solution
A method and apparatus that calibrate the eddy current sensor during processes like pad dressing or replacement, using correction signal values to adjust output signals, allowing continuous accurate monitoring of film thickness without stopping the polishing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the eddy current sensor is calibrated frequently to maintain measurement accuracy, then the measurement precision is improved, but the productivity deteriorates due to apparatus downtime
Solution Approach 1:
The system performs preliminary calibration actions during pad dressing or replacement operations that would occur anyway in the polishing process. By capturing sensor output signals during these predetermined timing points and using them to create correction values, the system prepares calibration data in advance without requiring separate calibration downtime, thus maintaining both measurement accuracy and productivity
2Device complexity
If the eddy current sensor output signal is used directly for monitoring, then the device complexity is reduced, but the measurement precision deteriorates due to signal drift from environmental changes
Solution Approach 1:
The system establishes a feedback mechanism where sensor output signals are continuously monitored during pad dressing or replacement, correction values are calculated based on these signals, and the correction values are applied to subsequent film thickness measurements. This closed-loop feedback approach compensates for signal drift caused by environmental changes while maintaining a relatively simple device structure
Solution Approach 2:
The system changes the operational parameters of the eddy current sensor by utilizing it during different process states (pad dressing or replacement versus normal polishing). By capturing sensor signals during these distinct states and deriving correction values, the system adapts to environmental parameter changes without increasing device complexity
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
Enables continuous and accurate monitoring of film thickness without lowering the availability of the polishing apparatus, as calibration is performed during necessary processes, effectively mitigating signal drift issues.
Implementation Method 1
This eddy current sensor is configured to supply a high-frequency alternating current to a coil so as to induce an eddy current in the conductive film to thereby detect the thickness of the conductive film from a change in impedance caused by a magnetic field of the eddy current induced
Implementation Method 2
When an AC power supply sends a high-frequency alternating current I1 to a coil 1, magnetic lines of force, induced in the coil 1, pass through the conductive film. As a result, mutual inductance occurs between a sensor-side circuit and a conductive-film-side circuit, and an eddy current I2 flows through the conductive film
Data Source
AI summary
A method monitors a change in film thickness during polishing using an eddy current sensor. This method includes acquiring an output signal of the eddy current sensor as a correction signal value during water-polishing of a substrate, during dressing of the polishing pad, or during replacement of the polishing pad, calculating a correcting amount from a difference between the correction signal value and a predetermined correction reference value, calculating an actual measurement signal value by subtracting the correction amount from the output signal of the eddy current sensor when polishing a substrate having a conductive film, and monitoring a change in thickness of the conductive film during polishing by monitoring a change in the actual measurement signal value.