RF Tuning Circuit for Plasma Uniformity in Processing Chambers
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Solution Overview
Problem
Plasma-assisted etching processes in semiconductor manufacturing face challenges due to non-uniformities in plasma density and plasma sheath shape, caused by harmonic frequency waves, leading to variations in etched feature profiles and reduced device yield.
Innovation Solution
A plasma processing system with a substrate support assembly and tuning circuits that adjust the fundamental RF frequency and harmonics, using capacitive and inductive elements to control plasma uniformity across the substrate surface, ensuring consistent ion flux and energy distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If RF power is used to generate plasma, then plasma density is maintained, but harmonic frequency waves cause non-uniformities in plasma density and sheath shape
Solution Approach 1:
A matching network is introduced as an intermediary component between the RF power source and the electrode. This matching network includes harmonic filtering capabilities that allow the fundamental RF frequency to pass through while blocking harmonic frequency waves, thereby maintaining plasma density while reducing non-uniformities caused by harmonics
Solution Approach 2:
The impedance of the matching network is adjusted to optimize the transmission of fundamental RF frequency while attenuating harmonic frequencies. By changing electrical parameters (impedance, frequency filtering characteristics) of the matching network, the system maintains adequate plasma density while reducing the adverse effects of harmonic waves on plasma uniformity
2Reliability
If harmonics are generated during plasma formation, then plasma is maintained, but etch rate and profile non-uniformity occur
Solution Approach 1:
The matching network serves as a mediator that separates the fundamental RF frequency from harmonic frequencies. It allows the fundamental frequency necessary for plasma maintenance to pass through while filtering out harmonics that cause etch non-uniformity, thus maintaining both plasma reliability and etch precision
Solution Approach 2:
The harmful harmonic frequency waves are extracted or removed from the RF power transmission path using the matching network's filtering capability. This extraction of harmonics while retaining the fundamental frequency resolves the contradiction between maintaining plasma and achieving uniform etching
3Quantity of substance
If standing waves are created by short wavelength harmonics, then plasma is formed, but non-uniform plasma distribution from center to edge occurs
Solution Approach 1:
The matching network acts as an intermediary that prevents harmonic frequency waves with short wavelengths from reaching the electrode and creating standing waves. By filtering these harmonics before they interact with the plasma, the system maintains plasma formation while achieving more uniform plasma distribution across the substrate
Solution Approach 2:
The matching network converts the potentially harmful effect of harmonic generation into a beneficial filtering action. The harmonics that would normally create standing waves and non-uniform plasma distribution are instead used to identify the need for impedance matching and frequency filtering, which ultimately improves plasma uniformity
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 system achieves improved plasma processing uniformity and reduced defectivity by managing harmonic frequency waves, resulting in consistent etch rates and feature profiles across the substrate.
Implementation Method 1
A radio frequency (RF) generator is electrically coupled to an RF electrode, wherein the RF generator is configured to generate a plasma within the processing volume by delivering an RF signal to the RF electrode
Implementation Method 2
A first filter assembly is electrically coupled between the first electrode and the first voltage generator, wherein the first filter assembly includes one or more capacitive and inductive elements that are configured to substantially block the fundamental RF frequency and harmonics of the fundamental RF frequency received at the first electrode from flowing to the first voltage generator
Implementation Method 3
A first tuning circuit electrically coupled between the first electrode and the first filter assembly, wherein the first tuning circuit includes a plurality of impedance generating elements that include at least one or more variable impedance element. The plurality of impedance generating elements of the first tuning circuit are configured to adjust one or more characteristics of the fundamental RF frequency and/or one of the harmonics of the fundamental RF frequency established at the first electrode
Data Source
AI summary
Embodiments of the disclosure include an apparatus and a method for controlling plasma uniformity by controlling plasma density in the bulk plasma over the center region and circumferential edge region of the substrate. Plasma uniformity can be controlled by use of an RF tuning circuit coupled to one of a plurality of electrodes positioned relative to a substrate during plasma processing. By adjusting the electrical characteristics of at least one of the RF tuning circuits, the effect that the generated RF fundamental frequency and related RF harmonic frequencies have on the plasma processing results can be controlled. Beneficially, the use of one or more of the tuning circuits and methods of using the same may be used to provide individual tuning knobs for controlling reactive neutral species concentration, ion energy and angular distribution, ion directionality and directionality uniformity, and separately controlling ion flux and reactive neutral species uniformity across the surface of the substrate.