RF Matching Network Tuning for Pulsed Plasma Impedance Control
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Solution Overview
Problem
Existing methods for processing substrates in vacuum chambers using RF power sources face challenges in tuning the RF matching network due to sideband reflections, which complicates the evaluation of match tuning, especially with pulse voltage generator (PVT) systems, as they need to account for both on and off impedances.
Innovation Solution
The implementation of a matching network with first and second sensors to measure impedance during RF generator pulse on time, coupled with at least one variable capacitor, allows for real-time tuning by a controller based on impedance values from pulse on or off states of a pulse voltage waveform generator, optimizing plasma impedance and minimizing total reflected power across all states during multilevel pulsing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the RF matching network tunes to a time averaging impedance, then the RF matching network tunes to a combination of PVT on and off impedances, but reflected power measurement becomes unreliable for evaluating match tuning
Solution Approach 1:
The patent segments the impedance measurement process by measuring impedance separately during pulse on-state and pulse off-state conditions rather than using a time-averaged measurement. This allows independent optimization for each state and eliminates the ambiguity of reflected power measurements that occur during transitions between states.
Solution Approach 2:
The system performs preliminary impedance measurements during both pulse on and off states before the actual processing operation. These pre-measured impedance values are then used to calculate optimal matching network settings, ensuring accurate tuning before the plasma processing begins, rather than relying on real-time reflected power measurements during pulsing.
2Adaptability or versatility
If the RF power source is switched between multiple states in multi-level pulsing, then process flexibility is improved, but the complexity of tuning the RF matching network increases
Solution Approach 1:
The patent divides the multi-level pulsing operation into discrete measurement phases, measuring impedance at each relevant state (on-state, off-state, and intermediate states). Each state is measured and optimized independently, then combined to determine the overall matching network settings, simplifying the tuning process despite multiple pulsing states.
Solution Approach 2:
The system implements feedback by continuously monitoring impedance during different pulse states and using this information to adjust matching network parameters. The controller uses measured impedance values from both on and off states to automatically optimize the matching network settings for multi-level pulsing operations, reducing manual tuning complexity.
3Productivity
If impedance measurements are taken during RF generator pulse on time, then real-time tuning is enabled, but measurement timing synchronization becomes more difficult
Solution Approach 1:
The patent uses feedback from the pulse voltage waveform generator to synchronize impedance measurements with the RF generator pulse timing. The system detects the pulse state transitions and automatically triggers measurements at the appropriate moments, enabling real-time tuning without manual synchronization complexity.
Solution Approach 2:
The measurement system is designed to self-synchronize with the pulsing operation by detecting pulse edges or transitions automatically. The impedance measurement circuitry activates itself at the correct timing based on the pulse waveform characteristics, eliminating the need for external synchronization signals or complex timing coordination.
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 approach enables optimized plasma impedance tuning, faster etch rates, improved spatial power distribution and uniformity, and flexibility in defining tuning targets based on varying process and pulsing conditions.
Implementation Method 1
The first sensor and the second sensor can be configured to measure impedance during an RF generator pulse on time
Implementation Method 2
At least one variable capacitor can be connected to the first sensor and the second sensor
Implementation Method 3
an RF generator operable at a first frequency connected to the chamber lid and configured to create a plasma from gases disposed in a processing region of the chamber body
Data Source
AI summary
Methods and apparatus for processing a substrate are provided herein. For example, a matching network comprises a first sensor operably connected to an input of the matching network and an RF generator operable at a first frequency and a second sensor operably connected to an output of the matching network and the plasma processing chamber. The first sensor and the second sensor are configured to measure impedance during an RF generator pulse on time. A variable capacitor is connected to the first sensor and the second sensor, and a controller is configured to tune the at least one variable capacitor of the matching network during the RF generator pulse on time based on impedance values measured during at least one of pulse on states or pulse off states of a pulse voltage waveform generator connected to the matching network or an RF signal of another RF generator operable at a second frequency different from the first frequency.