Capacitance Shielding for Electrostatic Chuck Position Sensing
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Solution Overview
Problem
Existing capacitance monitoring systems face challenges in accurately determining the position of a workpiece on an electrostatic chuck due to background capacitance, which reduces resolution and makes it difficult to distinguish between the presence and clamping of the workpiece.
Innovation Solution
A method and apparatus that apply a time-varying voltage signal with a DC offset to a conductor, shielding it, and monitoring power-related parameters to sense the capacitance of a load, effectively neutralizing cable capacitance and enhancing resolution by applying the same signal to the shield, allowing for precise capacitance monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a larger capacitance range is used to accommodate background capacitance, then the measurement range is improved, but the resolution deteriorates
Solution Approach 1:
The patent applies the principle of converting harm into benefit by using the background capacitance (cable capacitance) as a reference value. The system measures the difference between the total capacitance (load + cable) and the reference capacitance (cable only), which converts the harmful background capacitance into a useful reference for eliminating its effect. This allows the system to maintain high resolution while accommodating varying background conditions.
2Adaptability or versatility
If cable length is increased to reach the load, then the adaptability is improved, but the background capacitance increases reducing resolution
Solution Approach 1:
The patent implements feedback by continuously measuring the capacitance of the cable (reference measurement) and using this information to compensate for its effect on the load measurement. The system performs separate measurements to characterize the cable capacitance and then subtracts this from the total capacitance measurement, effectively feedback-compensating for the cable's harmful capacitance effect.
Solution Approach 2:
The patent introduces an intermediary approach by separating the cable capacitance measurement from the load capacitance measurement. The cable is measured as a separate reference element, and this reference value is then used to eliminate the cable's capacitance effect from the load measurement, effectively mediating the interference between the cable and the load.
3Measurement precision
If shielding is added to the conductor, then the measurement precision is improved by reducing interference, but the device complexity increases
Solution Approach 1:
The patent applies universality by making the shield serve multiple functions: it provides electromagnetic shielding to reduce interference, serves as a reference electrode for capacitance measurement, and forms part of the measurement circuitry. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving improved measurement precision.
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 approach enables improved resolution in capacitance measurement, allowing for accurate detection of the workpiece's position and clamping status by effectively neutralizing background capacitance and enhancing the sensitivity of the monitoring system.
Implementation Method 1
applying the same signal to the shield, allowing for precise capacitance monitoring
Implementation Method 2
shielding at least a portion of the conductor with a shield
Data Source
AI summary
Systems, methods, and apparatuses for measuring capacitance of a load. The method includes applying, via a conductor, a time-varying voltage signal with a DC offset to the load. At least a portion of the conductor is shielded with a shield and the time-varying voltage signal is applied to the shield. The conductor is coupled to the load and one or more power-related parameters of the conductor are monitored to monitor the capacitance of the load.