Adaptive Frequency Impedance Matching for Plasma Processing
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Solution Overview
Problem
Capacitively coupled plasma processing apparatuses face challenges in rapidly adjusting impedance matching due to mechanical limitations of variable reactance elements, leading to increased reflection waves during pulse-modulated high frequency power supply, which limits the suppression of electron temperature and charging damage in semiconductor manufacturing.
Innovation Solution
A method that involves starting a modulated high frequency power output with adjustable frequency based on moving average values of load impedance, allowing for adaptive and rapid frequency adjustments to maintain impedance matching, thereby reducing reflection waves and ensuring sufficient power delivery to the plasma.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a mechanical device such as a motor is used to adjust the variable reactance element of the matching device, then the impedance matching can be performed, but the adjustment speed is slow and cannot keep up with the pulse modulation cycle
Solution Approach 1:
The patent replaces the mechanical motor-driven variable reactance element with an electronically controllable impedance matching mechanism. The impedance matching is achieved through electronic signal processing and control circuits that can rapidly adjust the matching parameters without mechanical movement, thereby eliminating the speed limitation of mechanical devices while maintaining the impedance matching function.
Solution Approach 2:
The patent implements a dynamic impedance matching system that continuously adapts to changing plasma impedance conditions. The system uses real-time monitoring of reflection waves and dynamically adjusts the matching network parameters through electronic control, enabling the impedance matching to track the rapidly varying plasma impedance during pulse modulation cycles.
2Adaptability or versatility
If the frequency of high frequency power is fixed, then the system is simple to control, but the reflection wave cannot be sufficiently suppressed when impedance varies
Solution Approach 1:
The patent implements a feedback control mechanism that monitors the reflection wave amplitude and plasma impedance conditions in real-time. Based on the feedback signal, the system automatically adjusts the frequency of the high frequency power supply to maintain optimal impedance matching. This closed-loop control enables the system to adapt to impedance variations while keeping the frequency adjustment logic relatively simple.
Solution Approach 2:
The patent changes the frequency parameter of the high frequency power dynamically to match the varying plasma impedance. By adjusting the frequency rather than other complex parameters, the system achieves adaptability with minimal complexity. The frequency is modified within a controlled range to maintain resonance and minimize reflection waves.
3Object-affected harmful factors
If modulated high frequency power is used to suppress electron temperature and charging damage, then the processing quality improves, but reflection waves increase due to impedance mismatch
Solution Approach 1:
The patent applies preliminary anti-action by pre-adjusting the impedance matching parameters before the modulated high frequency power is applied to the plasma. The system predicts the impedance changes that will occur during modulation and proactively adjusts the matching network to compensate for these changes, thereby preventing reflection waves from increasing while maintaining the benefits of modulated power for suppressing electron temperature and charging damage.
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 adjusts the frequency of high frequency power adaptively and rapidly, reducing reflection waves and ensuring sufficient power delivery to the plasma, thereby improving the plasma processing efficiency and reducing electron temperature and charging damage.
Implementation Method 1
a gas supplied into the processing vessel is dissociated by a high frequency electric field which is generated between the upper electrode and the lower electrode
Implementation Method 2
a variable reactance element of the first matching device is adjusted to match an output impedance of the first high frequency power supply and an impedance at a load side thereof
Data Source
AI summary
An output of a modulated high frequency power is started from a high frequency power supply of a plasma processing apparatus. Here, a first period and a second period are repeated alternately. A moving average value of a load impedance of the high frequency power supply in a first sub-period in the past first period and a moving average value of a load impedance of the high frequency power supply in a second sub-period in the past first period are acquired. A frequency of the modulated high frequency power in the first sub-period and a frequency of the modulated high frequency power in the second sub-period are set according to the moving average values such that the load impedance of the high frequency power supply in the first sub-period and the load impedance of the high frequency power supply in the second sub-period approximate to a matching point.