Plasma Processing Apparatus Impedance Control
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Solution Overview
Problem
In pulse-modulated plasma processing, high frequency power control during the pulse-off period is challenging due to reflection waves, leading to instability and increased load on the power supply, especially when the modulation frequency is high, affecting the control of high/low pulse modulation methods.
Innovation Solution
A plasma processing apparatus that uses a weighted average of load impedance measurements during pulse-on and pulse-off periods to adjust the output impedance, reducing reflection waves and allowing for stable operation at higher load powers, thereby simplifying hardware and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulse modulation frequency is increased to improve processing speed and productivity, then productivity is improved, but reflection waves increase causing instability and increased load on power supply
Solution Approach 1:
The patent implements a feedback control mechanism where the control unit monitors the pulse modulation operation and adjusts the high frequency power supply parameters in real-time. When reflection waves are detected or anticipated at higher modulation frequencies, the system automatically adjusts impedance matching or power levels to maintain stability, thus resolving the contradiction between high productivity and power supply reliability.
Solution Approach 2:
The system dynamically adjusts operating parameters based on the pulse modulation frequency. At higher frequencies, the control unit modifies power supply settings, impedance matching network parameters, or pulse duty cycles to optimize performance while suppressing reflection waves, enabling the system to maintain stability across varying productivity requirements.
2Stability of the object's composition
If high frequency power is continuously supplied to maintain plasma generation, then plasma stability is improved, but power consumption and load on power supply increase
Solution Approach 1:
The patent employs periodic pulse modulation of the high frequency power supply, switching between on and off states at controlled frequencies. This periodic action maintains plasma generation stability during the on-period while reducing overall power consumption during off-periods, thus resolving the contradiction between plasma stability and power consumption.
Solution Approach 2:
The system dynamically changes power supply parameters including frequency, amplitude, and duty cycle of the pulse modulation to optimize the balance between plasma stability and power consumption. By adjusting these parameters based on process requirements, the system maintains adequate plasma stability while minimizing energy usage.
3Use of energy by moving object
If pulse-off period is extended to reduce power consumption and reflection waves, then power consumption is reduced, but plasma generation stability deteriorates
Solution Approach 1:
Instead of completely turning off the power during the pulse-off period, the system applies a reduced power level or maintains a minimal plasma generation state. This partial action reduces power consumption and reflection waves while preventing complete plasma extinction, thus maintaining plasma generation stability without excessive power usage.
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 efficient pulse modulation of high frequency power between high and low levels, improving process control and reducing the load on the high frequency power supply, while maintaining high process performance and stability.
Implementation Method 1
Electrons are accelerated in a high frequency electric field generated between the upper electrode and the lower electrode by applying the high frequency power, and plasma is generated as a result of ionization by collision between the electrons and a processing gas.
Implementation Method 2
a matching device provided on a transmission line for supplying the high frequency power for plasma generation measures a load impedance during a pulse-on period within each cycle, and controls a reactance of a variable reactance element provided in a matching circuit such that the load impedance measurement value may be equal to or approximate to a matching point
Data Source
AI summary
A plasma processing apparatus can efficiently perform a pulse modulation method of switching a high frequency power to be used in a plasma process between a high level and a low level alternately according to a duty ratio of a modulation pulse. In this plasma processing apparatus, when performing a high/low pulse modulation on the high frequency power for plasma generation, if a weighted variable K is set to be 0.5<K<1, a constant reflection wave power PRH is generated on a high frequency transmission line of a plasma generation system even during a pulse-on period Ton. Meanwhile, during a pulse-off period Toff, a reflection wave power PRL decreases. By adjusting the value of K, a balance between the reflection wave power PRH during the pulse-on period Ton and the reflection wave power PRL during the pulse-off period Toff can be controlled.