Digital Phase Controller for Plasma Reactor RF Waveforms
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Solution Overview
Problem
Existing plasma reactors face limitations in achieving fast and accurate phase correction between RF power waveforms applied to electrodes, leading to non-uniform plasma ion distribution and processing rates due to instability in analog phase controllers.
Innovation Solution
A digital phase controller system utilizing a feedback controller, clock generator, and direct digital synthesizer to adjust the phase difference between RF power amplifiers, ensuring precise and rapid phase correction by synchronizing clock signals and using read-only memories to generate waveform outputs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If analog techniques are employed in implementing the phase controller, then the device complexity is reduced, but the speed and accuracy of phase correction deteriorates due to instabilities
Solution Approach 1:
The patent replaces the analog phase controller with a digital phase controller that uses digital signal processing techniques. The digital controller employs a phase detector to measure phase difference, a microprocessor to calculate correction amounts, and digital signal generators to apply corrections. This substitution of analog electronics with digital systems eliminates the instabilities inherent in analog techniques while achieving faster and more accurate phase correction, directly resolving the contradiction between device complexity and measurement precision.
2Device complexity
If analog techniques are employed in implementing the phase controller, then the device complexity is reduced, but the speed of phase correction deteriorates
Solution Approach 1:
The digital phase controller uses a microprocessor-based system that can rapidly calculate phase differences and correction amounts at high speeds. The digital signal generators can apply corrections immediately without the bandwidth limitations of analog circuits. This digital implementation achieves faster phase correction speeds compared to analog techniques while maintaining manageable device complexity through integrated digital circuitry and software control.
3Productivity
If the reactor chamber size is increased to process larger workpieces, then the productivity is improved, but the manufacturing precision deteriorates due to non-uniform plasma distribution
Solution Approach 1:
The patent applies independent phase control to different regions of the reactor chamber by using multiple RF power sources with independently controllable phases. The top and bottom electrodes can have different phase angles applied to them, allowing local adjustment of plasma distribution characteristics. This enables optimization of plasma uniformity across large workpiece areas, resolving the contradiction between processing capacity and manufacturing precision.
Solution Approach 2:
The patent changes the phase angle parameter of RF power applied to different electrodes to control plasma distribution. By adjusting the phase difference between top and bottom electrode RF powers, the plasma ion density distribution can be optimized for uniformity across large workpieces. This parameter control mechanism enables large-chamber reactors to maintain high manufacturing precision while processing large-area workpieces, resolving the contradiction between productivity and manufacturing precision.
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 solution enables faster and more accurate phase correction, resulting in improved uniformity of plasma ion distribution and processing rates across the workpiece surface, enhancing the control over etch or deposition processes.
Implementation Method 1
a voltage controlled oscillator responsive to a control signal corresponding to a phase difference between the voltage controlled oscillator and a reference clock
Implementation Method 2
a digital synthesizer including an address generator having a pair of address outputs incremented in synchronism with the output clock. The address outputs are separated by an address difference that is a function of the phase correction signal output
Data Source
AI summary
Phase angle between opposing electrodes in a plasma reactor is controlled in accordance with a user selected phase angle. Direct digital synthesis of RF waveforms of different phases for the different electrodes is employed. The synthesis is synchronized with a reference clock. The address generator employed for direct digital synthesis is synchronized with an output clock signal that is generated in phase with the reference clock using a phase lock loop. The phase lock loop operates only during a limited initialization period.