Switchable Gas Conductance for ICP Ion Source
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Solution Overview
Problem
Focused ion beam systems with inductively-coupled plasma (ICP) ion sources face challenges in rapidly switching between different process gases due to low gas conductance through small openings, leading to long purging times and potential contamination during gas changes.
Innovation Solution
The implementation of a switchable gas conductance system with a moveable structure that opens an alternate gas path for rapid gas removal and sealing during normal operation, allowing for increased pumping speed to evacuate the plasma chamber quickly, using either a source electrode as a gas vent or a capillary assembly as a poppet valve.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small opening is used for gas inlet to maintain pressure in the plasma chamber, then gas conductance is low and plasma stability is improved, but gas switching time increases significantly
Solution Approach 1:
The gas path is segmented into two separate paths: a first gas path with a small opening (aperture in source electrode) for maintaining plasma stability during operation, and a second gas path with a large opening (in the source tube wall) for rapid gas evacuation and switching. The moveable structure selectively opens or seals the second gas path based on operational needs.
Solution Approach 2:
The system transitions from a static gas path configuration to a dynamic one by introducing a moveable structure that can change the state of the second gas path opening. This moveable structure is positioned to seal the second gas path during plasma operation and open it during gas switching, enabling adaptive control of gas conductance.
2Manufacturing precision
If a small aperture in the source electrode is used for gas conductance, then plasma chamber pressure control is improved, but pumping speed during gas purging decreases
Solution Approach 1:
The gas conductance path is divided into two segments: a first segment through the source electrode aperture with small opening area for precise pressure control during plasma generation, and a second segment through the source tube wall with large opening area for high-speed gas evacuation. The moveable structure controls which segment is active at any given time.
Solution Approach 2:
The system dynamically switches between two gas conductance modes by moving the moveable structure. In the first mode, the moveable structure seals the second gas path, allowing only small conductance through the source electrode aperture for precise pressure control. In the second mode, the moveable structure opens the second gas path, enabling large conductance for rapid gas purging.
3Productivity
If the gas inlet opening is made larger to increase pumping speed, then gas switching time is reduced, but plasma stability deteriorates due to pressure fluctuations
Solution Approach 1:
The gas path is segmented into a first path with a small opening (aperture in source electrode) that maintains plasma stability by providing restricted gas flow, and a second path with a large opening (in source tube wall) that enables rapid gas switching when opened by the moveable structure.
Solution Approach 2:
The moveable structure dynamically controls the opening state of the second gas path. During plasma operation, it seals the second path to maintain stable pressure through the small first opening. During gas switching, it opens the second path to enable rapid evacuation through the large opening, thus dynamically adapting gas conductance to operational requirements.
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
Enables rapid switching between process gases, reducing purging time from potentially 30 minutes to under 5 minutes, minimizing contamination and improving operational efficiency in FIB systems.
Implementation Method 1
Plasma ion sources ionize gas in a plasma chamber and extract ions to form a beam that is focused on a work piece
Implementation Method 2
Energy is fed into the plasma chamber 102 from RF power supply 113 by antenna coils 114
Implementation Method 3
Pump 122 connected to gas supply line 104 through valve 123 removes gas from plasma chamber 102 through capillary 108 and gas supply line 104
Implementation Method 4
capillary tube 108 with a flow restriction 110
Implementation Method 5
ions are extracted through a source electrode aperture 116 in a source electrode 118 by extractor electrode 120
Data Source
AI summary
An openable gas passage provides for rapid pumpout of process or bake out gases in an inductively coupled plasma source in a charged particle beam system. A valve, typically positioned in the source electrode or part of the gas inlet, increases the gas conductance when opened to pump out the plasma chamber and closes during operation of the plasma source.