RF Impedance Matching Network Using Electronic Variable Capacitors
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Solution Overview
Problem
RF matching networks in semiconductor fabrication processes face challenges due to the mechanical failures of Vacuum Variable Capacitors (VVCs), which lead to downtime and inefficiencies in impedance matching, particularly as semiconductor devices become more complex and processing times shorten.
Innovation Solution
The implementation of an RF impedance matching network using electronically variable capacitors (EVCs) to rapidly determine and adjust capacitance values, reducing the time to create an impedance match between the plasma chamber and the RF generator, with an elapsed time of less than 150 μsec.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Vacuum Variable Capacitors (VVCs) are used in RF matching networks, then impedance matching capability is provided, but mechanical failures occur frequently leading to downtime
Solution Approach 1:
The patent replaces the mechanical VVC system with an electronically controlled capacitor system. The electronic capacitor is controlled by a microprocessor that adjusts capacitance values digitally, eliminating mechanical moving parts and their associated failures. This substitution directly resolves the contradiction by maintaining impedance matching capability while eliminating mechanical failure modes.
Solution Approach 2:
The patent changes the control parameter from mechanical position adjustment to electronic capacitance value adjustment. The microprocessor controls the capacitance of the electronic capacitor by changing electrical parameters rather than mechanical ones, enabling reliable and rapid impedance matching without mechanical wear or failure.
2Loss of time
If VVCs are used for impedance matching, then matching function is achieved, but matching time is excessive (1-2 seconds)
Solution Approach 1:
The replacement of mechanical VVC with electronic capacitor controlled by microprocessor enables much faster capacitance adjustment. Electronic switching and control occur in microseconds rather than the 1-2 seconds required for mechanical adjustment, directly reducing matching time and improving productivity.
Solution Approach 2:
The microprocessor pre-calculates the optimal capacitance values needed for impedance matching based on measured plasma impedance. This preliminary calculation allows the system to quickly switch to the correct capacitance setting without iterative mechanical adjustment, significantly reducing matching time.
3Adaptability or versatility
If frequent impedance adjustments are made using VVCs, then plasma impedance changes are tracked, but mechanical failures increase
Solution Approach 1:
The electronic capacitor system allows frequent capacitance adjustments without mechanical wear. The microprocessor can rapidly change capacitance values in response to plasma impedance changes without the mechanical components that would fail from repeated adjustments, maintaining adaptability while improving reliability.
Solution Approach 2:
The system continuously monitors plasma impedance and automatically adjusts capacitance values through the microprocessor-controlled electronic capacitor. This self-adjusting capability provides adaptability to plasma changes without requiring manual intervention or causing mechanical stress from frequent manual adjustments.
Data Source
AI summary
In one embodiment, an RF impedance matching network includes an RF input configured to operably couple to an RF source; an RF output configured to operably couple to a plasma chamber; a first electronically variable capacitor having a first variable capacitance; a second electronically variable capacitor having a second variable capacitance; and a control circuit operably coupled to the first and second electronically variable capacitors. The control circuit is configured to determine the variable impedance of the plasma chamber, determine a first capacitance value for the first variable capacitance and a second capacitance value for the second variable capacitance, and generate a control signal to alter the first and/or second variable capacitance. An elapsed time between determining the variable impedance of the plasma chamber to when RF power reflected back to the RF source decreases is less than about 150 μsec.