RF Generator Pulse Control for Impedance Matching
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Solution Overview
Problem
RF generators in plasma etching processes face challenges in precisely controlling power and frequency to maintain impedance matching across multiple discrete states, especially when load impedance changes occur at high frequencies, leading to limited tuning capabilities and potential mismatch in impedance for states other than the initial frequency-tuned state.
Innovation Solution
A pulse control circuit is implemented in the RF generator, which includes a pulse control module, power control module, frequency control module, and pulse generating module to manage discrete states by adjusting power levels and frequencies based on feedback signals, allowing for quick transitions and optimal impedance matching across all states through step-wise control of power and frequency setpoints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If continuous wave signal is applied to the load, then the RF signal output is stable and continuous, but the ability to respond quickly to load impedance changes is limited
Solution Approach 1:
The patent applies pulsed RF signal delivery instead of continuous wave signals. The system uses periodic pulsing with adjustable pulse widths and intervals to deliver RF power to the load. This periodic action allows the system to quickly adjust between pulses in response to impedance changes while maintaining stable power delivery during each pulse, thus resolving the contradiction between stability and response speed.
2Loss of energy
If impedance matching is optimized for one frequency state, then reflected power is minimized at that state, but other discrete states experience impedance mismatch
Solution Approach 1:
The patent implements dynamic impedance matching by independently controlling both amplitude and frequency for each discrete state. The system adjusts the RF signal frequency dynamically based on the required state, allowing optimal impedance matching at each frequency point. This dynamic adaptation enables the system to minimize reflected power at each state rather than being optimized for only one frequency, thus resolving the contradiction between energy loss and adaptability.
Solution Approach 2:
The system changes multiple parameters simultaneously - both amplitude and frequency - to achieve optimal performance at each discrete state. By independently adjusting frequency for each state in addition to amplitude control, the system can adapt to different load conditions and maintain impedance matching across multiple operating points, resolving the limitation of single-state optimization.
3Speed
If pulse width is reduced for faster response, then the response time to impedance changes decreases, but the delivered power per pulse is reduced
Solution Approach 1:
The patent employs dynamic adjustment of pulse parameters including pulse width, amplitude, and frequency. The system can adaptively select optimal pulse widths for each operating condition - using shorter pulses for rapid response when impedance changes occur and longer pulses when maximum power delivery is needed. This dynamic control allows the system to optimize the balance between response time and power delivery based on real-time process requirements.
Data Source
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AI summary
A radio frequency generator (30, 32) includes a power control module (74, 76), a frequency control module (78, 80) and a pulse generating module (86, 88). The power control module (74, 76) is configured to generate a power signal indicating power levels for target states of a power amplifier (40, 42). The frequency control module (78, 80) is configured to generate a frequency signal indicating frequencies for the target states of the power amplifier (40, 42). The pulse generating module (86, 88) is configured to (i) supply an output signal to the power amplifier (40, 42), (ii) recall at least one of a latest power level or a latest frequency for one of the target states of the power amplifier, and (iii) adjust a current power level and a current frequency of the output signal from a first state to a second state based on the power signal, the frequency signal, and at least one of the latest power level and the latest frequency of the power amplifier (40, 42).