Variable Matching Unit for Plasma Ignition at Low Pressure
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Solution Overview
Problem
Conventional plasma processing apparatuses face difficulties in igniting plasma at low gas pressures, particularly in parallel plate type systems, and require cumbersome initial pressure settings to ensure plasma ignition, which can affect process stability.
Innovation Solution
A plasma processing method and apparatus that initiates radio frequency power application at an impedance where the peak radio frequency voltage is maximum, facilitating plasma ignition, and subsequently adjusts the matching unit to match the load impedance to the radio frequency power source, ensuring stable plasma generation and process reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gas pressure is lowered to the required level for plasma processing, then the plasma process can be performed, but the plasma becomes difficult to ignite
Solution Approach 1:
The patent applies preliminary action by setting the initial impedance of the matching unit to a specific value before plasma ignition occurs. This preliminary impedance setting ensures that the radio frequency voltage reaches its peak value, facilitating reliable plasma ignition at low pressures without requiring pressure adjustment during the process
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the impedance of the matching unit based on the plasma state. The system changes the impedance parameter from an initial optimized value for ignition to a matched value for stable plasma processing, resolving the contradiction between low pressure operation and reliable ignition
2Reliability
If the initial pressure is set much higher than the required level to ensure plasma ignition, then the plasma can be ignited reliably, but the pressure transition after ignition affects the process stability
Solution Approach 1:
The patent applies preliminary action by pre-setting the matching unit impedance to an optimized value before plasma ignition. This ensures reliable ignition at the target pressure without needing to start at a higher pressure, thereby maintaining process stability throughout the operation
Solution Approach 2:
The patent implements feedback by monitoring the plasma state and automatically adjusting the matching unit impedance to maintain optimal conditions. This feedback mechanism ensures both reliable ignition and stable process conditions without manual pressure adjustments
3Measurement precision
If the matching unit impedance is set to the matching point 50Ω before plasma ignition, then the impedance matching is optimized, but the plasma ignition becomes difficult at low pressures
Solution Approach 1:
The patent applies preliminary action by setting the matching unit impedance to a specific preliminary value optimized for ignition before plasma occurs, rather than setting it to the standard 50Ω matching point. This preliminary impedance setting ensures maximum radio frequency voltage and reliable plasma ignition
Solution Approach 2:
The patent applies dynamics by making the matching unit impedance adjustable and dynamic rather than fixed. The system transitions from a preliminary impedance value optimized for ignition to a matched impedance value for stable operation, adapting to different plasma states
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 improves plasma ignition reliability without requiring specific process condition changes and maintains stable plasma processes even at low pressures, ensuring high precision auto-matching and efficient plasma generation.
Implementation Method 1
a radio frequency power supply unit applies a radio frequency power to a radio frequency electrode disposed inside or outside a processing vessel or chamber
Implementation Method 2
to generate a plasma in the chamber
Implementation Method 3
a matching unit for matching an impedance at the side of a load (electrode, plasma and chamber) with an impedance at the side of the radio frequency power source
Data Source
AI summary
A plasma processing apparatus includes an upper matching unit 44 which is a variable matching unit whose impedance can be varied, and a main controller 100. The upper matching unit 44 includes a controller 104 for variably controlling the impedance positions of a variable reactance element of a matching circuit 102, a RF sensor for measuring a load impedance including the matching circuit 102, and a VPP measuring circuit 112 for measuring a peak value (peak-to-peak value) of a radio frequency voltage in a waveguide line at the output side of the upper matching unit 44. The main controller 100 executes and controls an autorunning of the matching units 44, 88 for optimizing an off preset of the impedance positions thereof. The plasma can be readily get ignited without requiring to set or change special processing conditions while influencing none of the processes.