Non-Uniform Faraday Shield for Uniform ICP Plasma Density
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Solution Overview
Problem
Inductively coupled plasma (ICP) systems face issues with peaked plasma density, capacitive coupling leading to increased electron temperature and ion energy, resulting in unwanted sputtering and degradation of RF windows in multi-aperture high current ion beam systems.
Innovation Solution
A Faraday shield with a non-uniform opacity structure is used around a linear RF antenna, varying opacity along the antenna axis to control capacitive coupling and maintain uniform plasma density and ion energy, reducing sputtering and enhancing RF window longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an RF antenna is immersed in plasma to excite gas by inductive coupling, then plasma generation is effective, but capacitive coupling increases electron temperature and ion energy, causing sputtering and degradation of RF windows
Solution Approach 1:
A dielectric enclosure acts as an intermediary between the RF antenna and the plasma, allowing inductive coupling to generate plasma while preventing direct capacitive coupling that causes harmful ion bombardment and sputtering of the RF window
Solution Approach 2:
The system separates the antenna from direct plasma contact by introducing a dielectric enclosure, dividing the plasma generation function from the window protection function to eliminate the harmful capacitive coupling effect
2Reliability
If a dielectric enclosure surrounds the antenna to protect it, then antenna protection is improved, but plasma density becomes peaked in the middle of the chamber, unsuitable for multi-aperture systems
Solution Approach 1:
The Faraday shield introduces non-uniform opacity distribution around the dielectric enclosure, creating different electromagnetic field penetration characteristics at different locations to achieve uniform plasma density across the chamber while maintaining antenna protection
3Stability of the object's composition
If uniform opacity Faraday shield is used around the antenna, then plasma density uniformity is improved, but non-uniform voltage distributions along the antenna still affect ion beam quality
Solution Approach 1:
The Faraday shield transitions from uniform to non-uniform opacity distribution, with varying transparency at different angular positions to compensate for non-uniform voltage distributions along the antenna and achieve uniform ion beam current extraction
Solution Approach 2:
The opacity parameter of the Faraday shield is varied non-uniformly around the antenna to match and compensate for the non-uniform voltage distribution pattern, optimizing ion beam current 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 non-uniform opacity Faraday shield achieves a more uniform plasma density and ion beam current, reducing material erosion and improving the stability of the ion source by compensating for non-uniform voltage distributions along the antenna.
Implementation Method 1
an RF antenna also couples capacitively with the plasma in practical implementations
Implementation Method 2
The electromagnetic energy generated by the antenna then passes through the dielectric window to excite feed gas disposed within the plasma chamber by inductive coupling
Implementation Method 3
The antenna is then excited using an RF power supply. The electromagnetic energy generated by the antenna then passes through the dielectric window
Implementation Method 4
A Faraday shield, disposed around the antenna, and arranged between the antenna and the dielectric enclosure. The Faraday shield may include a non-uniform opacity structure
Implementation Method 5
too much capacitive coupling is detrimental to the plasma source because a relatively higher degree of capacitive coupling from the antenna to plasma will decrease plasma density and increase the electron temperature of the plasma. This fact may lead to an increase of plasma potential in the plasma and consequently an increase of ion energy of ions crossing the plasma sheath (the thin layer separating the plasma from the wall) and impinging on surfaces such as an RF window or other shield, resulting in unwanted sputtering of material
Data Source
AI summary
An antenna assembly, comprising: an antenna; a dielectric enclosure surrounding the antenna; and a Faraday shield, disposed around the antenna, and arranged between the antenna and the dielectric enclosure, wherein the Faraday shield comprises a non-uniform opacity along an antenna axis of the antenna, wherein a first opacity of the Faraday shield at a first position along the antenna axis is greater than a second opacity of the Faraday shield at a second position along the antenna axis of the antenna.