Electrostatic Wafer Clamping with Filter-Tolerant Capacitance Sensing
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Solution Overview
Problem
The presence of filters, such as RF filters, in electrostatic chuck systems significantly attenuates capacitance sensing signals, making it difficult to monitor the position of workpieces accurately.
Innovation Solution
A system using a pulsed or square wave signal before the filter and a voltage sensing circuit after the filter to measure the rate of change in voltage, allowing capacitance sensing despite the presence of filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a filter (e.g., RF filter) is added to protect the power supply, then power supply protection is improved, but capacitance sensing sensitivity deteriorates significantly
Solution Approach 1:
The patent divides the sensing signal path into two separate paths: one path includes the filter for power supply protection, while the other path provides an alternative sensing route that bypasses the filter. This segmentation allows the system to maintain both power supply protection and sensing sensitivity by using different paths for different functions.
Solution Approach 2:
The patent introduces an intermediary sensing circuit that measures capacitance through a different mechanism that does not rely on the high-frequency signal path blocked by the filter. This intermediary approach allows capacitance sensing to function independently of the filter's signal blocking characteristics.
2Reliability
If a filter is placed in the signal path, then power supply protection is improved, but signal attenuation increases
Solution Approach 1:
The patent segments the signal path so that the filter is placed only in the power supply protection path, while the capacitance sensing path remains separate and unfiltered. This allows the filter to protect the power supply without attenuating the sensing signals.
Solution Approach 2:
The patent uses an intermediary sensing circuit that measures capacitance through a path that does not include the filter, thereby eliminating signal attenuation caused by the filter while maintaining power supply protection.
3Reliability
If high-impedance filtering is used to protect the power supply, then power supply reliability is improved, but capacitance sensing capability deteriorates
Solution Approach 1:
The patent divides the circuit into separate functional segments: the power supply protection segment with high-impedance filtering, and the capacitance sensing segment with low-impedance direct coupling. This segmentation allows each segment to optimize its function without interfering with the other.
Solution Approach 2:
The patent introduces an intermediary sensing circuit that acts as a mediator between the power supply and the capacitance measurement, providing a separate measurement path that does not suffer from the high-impedance filtering effects.
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 accurate monitoring of workpiece position and clamping state by overcoming signal attenuation, ensuring reliable electrostatic clamping and reducing errors in processing systems.
Implementation Method 1
These chucks utilize electrostatic force to hold the workpiece in place. The electrostatic chuck includes electrodes that are energized with a clamping voltage, which electrostatically clamps the workpiece to the surface of the electrostatic chuck.
Implementation Method 2
The position of the workpiece can be detected by monitoring the capacitance of a combination of the workpiece and the electrostatic chuck. When the workpiece is properly positioned on the electrostatic chuck, the sensed capacitance may be higher than when the workpiece is not properly positioned.
Implementation Method 3
the presence of a filter (e.g., an RF filter such as a high-impedance resistor) to protect the power supply is sometimes desired and can render inoperable known capacitive sensing systems for wafer clamping as these filters largely block the high frequency and low amplitude sensing signals
Data Source
AI summary
A capacitance sensing system including an output, a power source configured to provide a voltage to the output, a pulsed source configured to provide a time-varying pulse train to the output, a filter arranged between the pulsed source and the output, and a sensing circuit arranged between the filter and the output. The sensing circuit can be configured to measure a voltage between the filter and the output, and based on the voltage, determine an unknown capacitance that the output is coupled to, such as that of an electrostatic chuck. This capacitance is proportional to the substrate position and indicates a quality of chucking.