Phase-Locked Plasma Electrode Waveforms for Charge Neutralization
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Solution Overview
Problem
Conventional plasma processing systems face limitations in precise control over plasma parameters, leading to non-uniform processing, reduced yield, and increased production costs, particularly in anisotropic plasma etch processes where differential charging in high aspect ratio contact structures results in profile defects such as distortion and tilting.
Innovation Solution
A novel power coupling scheme for capacitively-coupled plasma chambers where both the top and bottom electrodes are powered by phase-locked rectangular waveforms, with the top electrode having zero potential when the bottom electrode is biased, reducing sputtering and enhancing neutralization of positive charges in high aspect ratio contact structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sinusoidal or pulse-width modulated sinusoidal waveforms are used to sustain plasma, then the plasma can be maintained with simple waveform generation, but precise control over plasma parameters such as ion energy distribution, electron temperature, and density uniformity is limited
Solution Approach 1:
The patent applies periodic pulsed DC waveforms to both electrodes in a capacitively coupled plasma reactor. By using phase-locked periodic pulses with specific duty cycles and phase relationships, the system achieves precise control over plasma parameters including ion energy distribution, electron temperature, and density uniformity. The periodic nature of the waveforms allows for controlled plasma generation and termination cycles, enabling fine-tuned parameter control while maintaining relatively simple waveform generation circuitry.
2Manufacturing precision
If non-sinusoidal waveforms such as square waves and other pulsed waveforms are used to achieve better control and performance, then precise control over plasma parameters is improved, but the process development is complicated with many additional degrees of freedom
Solution Approach 1:
The patent segments the plasma generation process by applying independent pulsed DC waveforms to the top and bottom electrodes with different duty cycles and phase relationships. This segmentation allows separate control of plasma generation at each electrode, enabling precise control over ion energy distribution and plasma density uniformity. By dividing the control into electrode-specific parameters (duty cycle, phase offset, pulse width), the system achieves manufacturing precision without overwhelming process development complexity, as each parameter has a clear physical meaning and control effect.
3Reliability
If continuous DC bias is applied to the top electrode to generate ballistic electrons for neutralizing positive charges in HARC features, then charge neutralization is improved, but sputtering of the top electrode and foreign material deposition on the wafer increase
Solution Approach 1:
The patent applies periodic pulsed DC waveforms to the top electrode instead of continuous DC bias. During the pulse on-state, ballistic electrons are generated to neutralize positive charges in HARC features. During the off-state, ion bombardment and sputtering are reduced or eliminated. This periodic action maintains charge neutralization effectiveness while significantly reducing top electrode sputtering and foreign material deposition on the wafer, as the electrode is not continuously biased at high voltage.
Solution Approach 2:
The patent uses phase-locked pulsed waveforms where the top electrode pulse is timed to precede or coincide with the bottom electrode pulse. This preliminary action generates ballistic electrons from the top electrode before significant ion bombardment occurs, ensuring charge neutralization in HARC features is established in advance. The phase offset between electrodes allows the top electrode to perform its neutralization function during specific phases while avoiding continuous exposure to conditions that cause sputtering and contamination.
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 significantly reduces sputtering of the top electrode and improves the neutralization of positive charges, resulting in more uniform processing and reduced material deposition, thereby enhancing the quality and efficiency of plasma etching.
Implementation Method 1
applying AC waveforms to a bottom electrode in a plasma chamber to generate a plasma
Implementation Method 2
the first pulse train being offset in phase relative to the second pulse train so that each first off-state overlaps with each second on-state
Data Source
AI summary
A plasma processing method includes applying AC waveforms to a bottom electrode in a plasma chamber to generate a plasma. The method further includes applying a first pulse train including a first plurality of DC pulses to a top electrode in the plasma chamber, where each DC pulse of the first plurality of DC pulses includes a first on-state and a first off-state. And the method further includes applying a second pulse train including a second plurality of DC pulses to the bottom electrode in the plasma chamber, and where each DC pulse of the second plurality of DC pulses includes a second on-state and a second off-state, the first pulse train being offset in phase relative to the second pulse train so that each first off-state overlaps with each second on-state.