RF Frequency Hopping for Periodic Load Impedance Variations
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Solution Overview
Problem
RF generator systems face challenges in efficiently delivering power to plasma chambers due to intermodulation distortion (IMD) caused by multiple RF frequency sources, leading to reduced power delivery and increased costs associated with higher power levels.
Innovation Solution
The implementation of a frequency hopping pattern in the RF generator system, where the frequency of the source RF generator is adjusted in synchronization with the bias RF generator, using an extremum seeking iterative learning control approach to mitigate IMD effects by determining optimal frequency offsets and adjustments based on perturbations, thereby minimizing reflected power and maximizing forward power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple RF frequency sources are used in the plasma chamber, then process versatility and plasma control capability are improved, but intermodulation distortion increases causing reduced power delivery efficiency
Solution Approach 1:
The patent implements periodic frequency hopping of the source RF generator in synchronization with the bias RF generator. The source frequency is periodically adjusted according to a predetermined pattern that correlates with the periodic impedance variations caused by the bias RF signal, thereby maintaining power delivery efficiency while allowing multiple RF sources to operate
Solution Approach 2:
The patent dynamically changes the operating frequency parameter of the source RF generator based on detected impedance variations. By adjusting the source frequency in response to impedance changes caused by the bias RF signal, the system maintains optimal power transfer while accommodating the presence of multiple RF sources for enhanced process control
2Power
If RF generator power levels are increased to compensate for IMD losses, then forward power delivery is maintained, but cost and energy consumption increase
Solution Approach 1:
Instead of increasing power levels to compensate for IMD losses, the patent changes the frequency parameter of the source RF generator. By tuning the frequency to match the periodic impedance variations, the system maintains efficient power transfer at lower power levels, avoiding the energy waste associated with over-powering the system
3Loss of energy
If frequency hopping pattern is applied to mitigate IMD, then power delivery efficiency is improved, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent employs a feedback mechanism where the controller detects impedance variations caused by the bias RF signal and automatically adjusts the source frequency accordingly. This closed-loop feedback system manages the complexity by automating the frequency adjustment process, reducing the need for manual intervention while maintaining high power delivery efficiency
Solution Approach 2:
The patent uses a predetermined frequency hopping pattern that is established in advance based on the known periodic nature of bias RF-induced impedance variations. By pre-programming the frequency adjustment pattern, the system reduces real-time computational complexity while still achieving effective IMD mitigation
Data Source
AI summary
A radio frequency (RF) power generation system includes a RF power source that generates a RF output signal delivered to a load. A RF power controller is configured to generate a control signal to vary the RF output signal. The controller adjusts a parameter associated with the RF output signal, and the parameter is controlled in accordance with a trigger signal. The parameter is adjusted in accordance with a cost function, and the cost function is determined by intruding a perturbation into an actuator that affects the cost function. The actuator may control an external RF output signal, and the trigger signal may vary in accordance with the external RF output signal.