Asymmetric Bias Waveform Control for Plasma Etch IEDF
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Solution Overview
Problem
Existing bias supplies in plasma processing systems struggle to accurately control the sheath voltage (Vsheath) to achieve a desired ion energy distribution function (IEDF), which is crucial for controlling directionality, feature profile, and selectivity in plasma etching processes.
Innovation Solution
A bias supply system that applies an asymmetric periodic voltage waveform with specific sections and transitions, including a first section starting with a negative voltage, transitioning to a peak voltage, and then to a second negative voltage, and a second section with a voltage ramp between the second and a third negative voltage, allowing for adjustment of the transition slopes to control the ion energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a non-varying voltage is applied to a dielectric substrate, then the voltage application is simple, but the voltage cannot be placed across the surface of the substrate
Solution Approach 1:
The patent applies an alternating current (AC) voltage waveform instead of a non-varying voltage to the dielectric substrate. The periodic nature of the AC waveform enables the voltage to be effectively placed across the substrate surface during specific portions of the cycle, while maintaining operational simplicity through standardized waveform generation.
2Manufacturing precision
If an AC voltage is applied to control ion energy distribution, then the ion energy distribution can be controlled, but high-frequency harmonics are generated
Solution Approach 1:
The patent employs an asymmetric AC voltage waveform where the negative portion duration is longer than the positive portion. This asymmetry allows precise control of ion energy distribution during the negative cycle while reducing the generation of high-frequency harmonics compared to symmetric waveforms, as the extended negative portion provides smoother ion acceleration.
Solution Approach 2:
The patent dynamically adjusts the waveform parameters including duty cycle, frequency, and voltage amplitude to optimize ion energy distribution control. By making the waveform characteristics adjustable rather than fixed, the system can minimize harmful harmonics while maintaining precise control over ion bombardment energy.
3Manufacturing precision
If the waveform is changed to control directionality and selectivity, then the etching performance is improved, but the waveform complexity increases
Solution Approach 1:
The patent segments the AC waveform into distinct portions with different characteristics: a positive voltage portion and a longer negative voltage portion with specific duration ratios. This segmentation allows independent optimization of each portion for different etching requirements (directionality during positive cycle, selectivity during negative cycle) while maintaining overall waveform manageability through defined structural boundaries.
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 precise control of the ion energy distribution, improving the directionality, feature profile, and selectivity in plasma etching processes, while reducing high-frequency harmonics and plasma density, thus enhancing the overall efficiency and accuracy of the plasma processing.
Implementation Method 1
an alternating current (AC) voltage (e.g., high frequency AC or time varying periodic voltage waveform may be applied by a bias supply to the conductive plate (or chuck) so that the AC field induces a voltage on the surface of the substrate
Implementation Method 2
the surface of the substrate will be charged negatively, which causes ions to be attracted toward the negatively-charged surface during the negative portion of the periodic cycle
Data Source
AI summary
A bias supply comprising power circuitry configured to apply an asymmetric periodic voltage waveform at the output node wherein the asymmetric periodic voltage waveform comprises a first section that begins with a first negative voltage and changes during a first transition to a peak voltage before changing during a second transition to a second negative voltage and a second section that begins with the second negative voltage and comprises a voltage ramp between the second negative voltage and a third negative voltage. Transition circuitry is configured to adjust a slope of one, or both, of the first and second transitions.