Impedance Dependent RF Power Control for Plasma Processing
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Solution Overview
Problem
In plasma processing systems, dependent RF generators struggle to quickly adapt to changing plasma impedance caused by independently pulsing RF signals due to the fast pulsing frequency, leading to inefficient power delivery as they require impractically high frequencies for self-tuning, which cannot keep up with the rapid impedance changes.
Innovation Solution
The dependent RF generators undergo a learning process to determine optimal tuned RF frequencies and threshold values during a learning period, allowing them to quickly switch between these frequencies during production time based on measured plasma parameters, eliminating the need for continuous frequency self-tuning and optimizing power delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If dependent RF generators perform continuous frequency self-tuning to adapt to changing plasma impedance, then power delivery efficiency is improved, but the tuning process cannot keep up with the fast pulsing frequency of independently pulsing RF signals
Solution Approach 1:
The patent applies preliminary action by pre-determining multiple optimal RF frequencies corresponding to different plasma impedance states (high power and low power states of the independently pulsing signal). Instead of continuously tuning during operation, the system proactively selects from pre-identified optimal frequencies based on the current power state, enabling rapid adaptation without time-consuming continuous self-tuning.
2Measurement precision
If multiple samples are taken during frequency self-tuning to determine optimal RF frequency, then measurement precision is improved, but the time required for tuning increases making it impractical for fast pulsing applications
Solution Approach 1:
The system performs frequency measurements and identifies optimal frequencies in advance during setup or less critical periods. Multiple samples are taken to establish accurate frequency-power state relationships, but this time-consuming measurement process occurs beforehand rather than during fast pulsing operation. During production, the system quickly switches between pre-determined optimal frequencies without repeating the full measurement sequence.
Solution Approach 2:
The patent implements a dynamic frequency selection mechanism that adapts to the pulsing power state. The system monitors the current power state (high or low) of the independently pulsing RF signal and dynamically selects the corresponding pre-determined optimal frequency from a set of calibrated frequencies, enabling rapid adaptation to changing plasma impedance conditions without continuous measurement.
3Adaptability or versatility
If dependent RF generators tune frequency in response to plasma impedance changes, then power delivery is optimized, but the response time is too slow for modern fast pulsing frequencies (10 KHz or faster)
Solution Approach 1:
The system pre-identifies optimal RF frequencies for different plasma impedance conditions (corresponding to high and low power states). This preliminary calibration establishes a lookup table of optimal frequencies that can be instantly accessed during fast pulsing operation, eliminating the need for slow continuous tuning while maintaining adaptability to impedance changes.
Solution Approach 2:
The system implements feedback by monitoring the power state of the independently pulsing RF signal and using this information to select the appropriate pre-determined optimal frequency. The feedback loop is simplified to monitor only the power state transitions rather than continuously analyzing plasma impedance, enabling rapid response at 10 KHz and faster pulsing frequencies.
Data Source
AI summary
Methods for processing a substrate in a plasma processing chamber employing a plurality of RF power supplies. The method includes pulsing at a first pulsing frequency a first RF power supply to deliver a first RF signal between a high power state and a low power state. The method further includes switching the RF frequency of a second RF signal output by a second RF power supply between a first predefined RF frequency and a second RF frequency responsive to values of a measurable chamber parameter. The first RF frequency and the second RF frequencies and the thresholds for switching were learned in advance during a learning phase while the first RF signal pulses between the high power state and low power state at a second RF frequency lower than the first RF frequency and while the second RF power supply operates in different modes.