Capacitance Detection Circuit for Electrostatic Wafer Holding
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Solution Overview
Problem
Conventional detection circuits for electrostatic holding devices face challenges in accurately detecting capacitance changes, particularly for small capacitance values and varying materials, due to limited capture ranges and dependence on specific capacitance values, leading to false results and the need for complex adaptations.
Innovation Solution
A detection circuit with a phase control circuit, including a reference oscillator, phase comparator, and voltage-controlled oscillator, where the capacitance to be detected is connected directly to the VCO circuit, allowing for adjustable reference frequencies and reduced dependence on internal capacitance, enabling precise detection of capacitance changes across a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional detection circuits with fixed capture ranges are used, then detection is reliable within specific capacitance ranges, but the circuit cannot detect capacitance changes across different operating phases (e.g., wafer placement vs. clamping) without leaving the locked state
Solution Approach 1:
The patent implements a dynamic reference frequency adjustment mechanism where the reference oscillator's frequency is automatically adapted based on the detected capacitance range. The system transitions from a fixed capture range to a dynamic range adaptation approach, allowing the detection circuit to maintain locked state across different operating phases (wafer placement, clamping, declamping) by adjusting the reference frequency to match the current capacitance conditions.
Solution Approach 2:
The patent changes the electrical parameter (reference frequency) of the detection circuit dynamically. By adjusting the reference frequency parameter in response to detected capacitance variations, the system maintains optimal detection conditions across different operating phases without requiring hardware modifications or leaving the locked state, thus resolving the contradiction between reliability and adaptability.
2Power
If blocking condensers with high capacitance are used to couple clamp electrodes to the oscillator, then the circuit can operate at high voltage, but detection of small capacitance changes is hindered due to the large capacitance value
Solution Approach 1:
The patent extracts the high voltage coupling function from the signal detection path by using blocking condensers solely for DC isolation while connecting the capacitance-to-frequency conversion circuit directly to the clamp electrodes. This separation allows the detection of small capacitance changes without the interference of large blocking condenser capacitance, as the measurement path no longer includes these large capacitance values.
Solution Approach 2:
The patent introduces an intermediary capacitance-to-frequency conversion circuit that translates the capacitance changes of the clamp electrodes into frequency variations. This intermediary mechanism allows high voltage operation to be maintained while enabling precise detection of small capacitance changes, as the conversion circuit operates at low voltage and translates the physical quantity (capacitance) into a measurable signal (frequency) without being affected by the blocking condenser capacitance.
3Measurement precision
If additional measurement electrodes are mounted on the clamp carrier next to the clamp electrodes, then capacitance detection is enabled, but the function of the clamp carrier is restricted due to the special surface requirement
Solution Approach 1:
The patent makes the clamp electrodes serve dual functions: both electrostatic clamping and capacitance detection. By using the same clamp electrodes for both holding the wafer and detecting capacitance changes, the system eliminates the need for separate measurement electrodes, thus maintaining the full functionality of the clamp carrier surface while enabling precise capacitance detection.
Solution Approach 2:
The patent merges the clamping function and detection function into a single electrode system. The clamp electrodes are used both for generating electrostatic holding forces and for sensing capacitance changes. This consolidation eliminates the need for additional measurement electrodes and special surface treatments, reducing device complexity while maintaining 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 solution allows for reliable and precise detection of capacitance changes, including small variations, with reduced complexity in adapting to different application conditions, enhancing the reliability of component detection in various operating phases of the holding device.
Implementation Method 1
The phase comparator is configured for generate a control voltage input to the VCO circuit as a function of a deviation between a reference signal from the reference oscillator device and a VCO feedback signal from the VCO circuit
Implementation Method 2
The phase control circuit is configured to control the VCO circuit as a function of the capacitance to be detected and to output an output quantity characteristic of the capacitance, based on the control voltage of the VCO circuit
Implementation Method 3
The electrostatic holding forces are generated when the clamp electrodes are subjected to a high voltage and the clamp carrier is correspondingly electrically charged. The charged clamp carrier attracts the component so that this adheres to the free surface of the clamp carrier
Implementation Method 4
By means of capacitance measurement at the clamp electrodes, or additional measurement electrodes of the electrode device, it can be detected whether, and if so where, a component is located on the clamp carrier, and whether the component is in the clamped state
Data Source
AI summary
Detection circuit for detecting electrical capacitance of electrode device in electrostatic holding device with clamp carrier, particularly for detecting component held by holding device, includes phase control circuit couplable to electrode device and has reference oscillator device, phase comparator and VCO circuit (VCOC). Phase comparator is arranged to generate a control voltage of VCOC as a function of reference signal from reference oscillator device and of VCO feedback signal from VCOC, at least one phase control circuit is configured for controlling VCOC as a function of capacitance to be detected, and for outputting an output signal characteristic of capacitance based on control voltage of VCOC, phase control circuit is configured for connection to electrode device such that VCOC contains capacitance to be detected as frequency-determining component, and reference oscillator device is configured for generating reference signal with adjustable reference frequency. Electrostatic holding device includes at least one such detection circuit.