Bias Signal Frequency Control for Plasma Ignition Impedance Matching
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Solution Overview
Problem
Existing plasma processing methods face challenges with impedance mismatch during plasma ignition, leading to increased reflected wave power, which can damage RF power sources and prolong plasma stabilization time, especially when high-frequency pulsed plasma is used.
Innovation Solution
Optimizing the supply of RF power by adjusting the bias signal frequency based on impedance matching conditions using a frequency adjustment method that reduces reflected wave power and shortens plasma ignition time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-frequency pulsed plasma is used for plasma processing, then processing speed and productivity are improved, but impedance mismatch occurs during plasma ignition causing increased reflected wave power that can damage RF power sources
Solution Approach 1:
The patent applies preliminary action by adjusting the bias signal frequency before plasma ignition occurs. The frequency adjustment is performed in advance during the ignition phase to prevent impedance mismatch, rather than correcting it after the problem arises. This proactive frequency tuning ensures that when high-frequency pulsed plasma is initiated for high-speed processing, the RF power source is already operating at optimal impedance conditions, preventing reflected wave damage while maintaining productivity.
Solution Approach 2:
The patent implements dynamics by making the bias signal frequency adjustable and variable rather than fixed. The frequency is dynamically tuned based on the plasma ignition state and impedance conditions. This dynamic adjustment allows the system to adapt to changing plasma conditions during ignition and steady-state operation, maintaining both high processing speed and RF power source safety across different operating phases.
2Productivity
If high-frequency pulsed plasma is used, then plasma processing efficiency is improved, but plasma stabilization time is prolonged due to impedance mismatch during ignition
Solution Approach 1:
The patent applies preliminary action by performing frequency adjustment of the bias signal before plasma ignition. This pre-adjustment ensures that the RF power source is operating at the optimal frequency for the specific plasma conditions, eliminating impedance mismatch issues that would otherwise delay plasma stabilization. By preparing the frequency in advance, the system achieves faster transition from ignition to stable high-frequency pulsed plasma operation.
Solution Approach 2:
The patent implements parameter changes by varying the bias signal frequency to optimize plasma ignition and stabilization. The frequency parameter is specifically adjusted based on impedance matching requirements during different plasma phases. This parameter optimization enables the system to achieve both high processing efficiency and reduced stabilization time by ensuring optimal coupling between the RF power source and plasma load throughout the ignition and steady-state periods.
3Device complexity
If conventional plasma excitation methods are used, then system complexity is kept simple, but reflected wave power increases causing potential damage to RF power sources
Solution Approach 1:
The patent applies feedback by implementing a control mechanism that monitors impedance conditions during plasma operation and adjusts the bias signal frequency accordingly. The system measures the actual plasma state and RF power source conditions, then uses this feedback information to dynamically tune the frequency for optimal impedance matching. This feedback control protects the RF power source from reflected wave damage while maintaining relatively simple system architecture.
Solution Approach 2:
The patent implements parameter changes by adjusting the bias signal frequency based on real-time impedance conditions. Rather than adding complex protective equipment, the solution modifies the operational parameters (frequency) of existing components to achieve impedance matching. This parameter-based approach maintains system simplicity while effectively preventing reflected wave damage to the RF power source.
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
The method effectively reduces reflected wave power and accelerates plasma ignition, improving power efficiency and reducing load on RF power sources by optimizing impedance matching during plasma ignition.
Implementation Method 1
a frequency fB(n) of a bias signal to be supplied to the lower electrode is determined
Implementation Method 2
an RF power source 31 configured to supply at least one RF signal (RF power) to at least one lower electrode and/or at least one upper electrode
Data Source
AI summary
A plasma processing method for performing plasma processing on a substrate, the method including: acquiring, for each control period of a bias signal, a parameter relating to an impedance matching state when supplying the bias signal to an electrode provided at a substrate support; and determining a frequency f(n) of the bias signal in an n-th control period according to Equation (1) below, f(n)=f(n−1)−Δf/ΔP×Pr(n−1)×F . . . (1).