Dual Indirectly Heated Cathode Ion Source for Wear Balancing
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Solution Overview
Problem
The lifetime of ion sources in ion implantation systems is limited by the failure of cathodes, particularly when forming multi-charged arsenic ion beams, leading to unwanted maintenance and downtime.
Innovation Solution
The implementation of an ion source with multiple indirectly-heated cathodes, where a filament power supply is selectively electrically coupled to each cathode in alternating cycles based on predetermined criteria, such as duration and thickness, to evenly distribute wear and extend the ion source's operational life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single indirectly-heated cathode is used, then the ion source structure is simple, but the cathode lifetime is limited due to sputtering wear
Solution Approach 1:
The single cathode is divided into multiple cathodes (first cathode and second cathode). Each cathode can be independently operated and switched, allowing the system to alternate between them to distribute wear and extend overall lifetime.
Solution Approach 2:
The system changes the operational state parameter by switching between different cathodes based on predetermined criteria (duration and thickness). This allows even distribution of wear across multiple cathodes, extending the ion source lifetime up to four times compared to conventional single-cathode systems.
2Reliability
If the cathode thickness is increased to withstand sputtering, then the cathode lifetime is extended, but the heating efficiency decreases
Solution Approach 1:
Instead of using one thick cathode with poor heating efficiency, the system segments the cathode function across multiple thinner cathodes. Each cathode maintains good heating efficiency while the system alternates between them to achieve extended overall lifetime.
Solution Approach 2:
The system implements periodic switching between cathodes based on predetermined duration and thickness criteria. This periodic action allows each cathode to operate at optimal thickness for heating efficiency while the alternation distributes cumulative wear to extend overall system lifetime.
3Productivity
If the filament operates continuously, then the ion source productivity is maintained, but the cathode wear accelerates
Solution Approach 1:
The system implements periodic switching between multiple cathodes while maintaining continuous ion source operation. The filament power supply is selectively coupled to different cathodes in alternating cycles, ensuring uninterrupted productivity while distributing wear to extend cathode lifetime.
Solution Approach 2:
The system effectively 'discards' one cathode after it reaches wear limits and 'recovers' by switching to another cathode that has been wearing less. This allows continuous operation while managing cathode wear resources efficiently.
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 increases the lifetime of the ion source up to four times compared to conventional systems by evenly distributing wear across multiple cathodes, reducing downtime and enhancing overall productivity.
Implementation Method 1
a filament disposed within the first cathode body... the filament heats the cap
Implementation Method 2
emits electrons that heat the endcap through electron bombardment, thereby thermionically emitting ionizing electrons
Implementation Method 3
Ion sources (commonly referred to as arc discharge ion sources) generate ion beams used in implanters
Implementation Method 4
an extraction system, typically a set of electrodes, which energizes and directs the flow of ions from the source, forming an ion beam
Data Source
AI summary
An ion source has an arc chamber with a first end and a second end. A first cathode at the first end of the arc chamber has a first cathode body and a first filament disposed within the first cathode body. A second cathode at the second end of the arc chamber has a second cathode body and a second filament disposed within the second cathode body. A filament switch selectively electrically couples a filament power supply to each of the first filament and the second filament, respectively, based on a position of the filament switch. A controller controls the position of the filament switch to alternate the electrical coupling of the filament power supply between the first filament and the second filament for a plurality of switching cycles based on predetermined criteria. The predetermined criteria can be a duration of operation of the first filament and second filament.