Dual Cathode Ion Source Beam Uniformity Control
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Solution Overview
Problem
Existing ion sources struggle to maintain uniformity of the ribbon ion beam without compromising beam current and parallelism, as downstream components used to compensate for non-uniformity often reduce overall beam current and introduce non-parallelism.
Innovation Solution
A dual cathode ion source with independently biased cathodes and filaments, controlled by a controller using a beam profiler to adjust bias voltages and filament currents, allowing for precise tuning of the ribbon ion beam uniformity without sacrificing beam current or parallelism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If downstream components are used to compensate for non-uniformity in the ribbon ion beam, then beam uniformity is improved, but beam current is reduced and parallelism is lost
Solution Approach 1:
The ion source is divided into two separate cathodes (first cathode and second cathode), each capable of independent operation. This segmentation allows independent control of electron emission from each cathode, enabling precise tuning of the ion beam profile at the source rather than requiring downstream compensation that would reduce beam current
Solution Approach 2:
Each cathode is equipped with independent bias power supplies and filament control, allowing local adjustment of electron emission characteristics. This enables different regions of the ion beam to be optimized independently for uniformity while maintaining overall beam current and parallelism
2Manufacturing precision
If downstream components are used to compensate for non-uniformity in the ribbon ion beam, then beam uniformity is improved, but beam parallelism is reduced
Solution Approach 1:
The ion beam is pre-tuned for uniformity and parallelism at the source by independently controlling the two cathodes before the beam enters the downstream transport region. This preliminary adjustment eliminates the need for downstream components that would disrupt beam parallelism while achieving the desired uniformity
3Device complexity
If a single cathode is used in the ion source, then device complexity is reduced, but control over beam profile is insufficient
Solution Approach 1:
The single cathode is segmented into two independent cathodes, each with its own filament and bias power supply. This segmentation provides the additional control degrees of freedom needed to independently tune the ion beam profile while maintaining a relatively simple overall device structure
Solution Approach 2:
The independent bias power supplies allow dynamic adjustment of each cathode's electron emission characteristics. This enables real-time control and tuning of the ion beam profile to match specific process requirements, providing adaptability without significant complexity increase
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 solution enables improved control over the ribbon ion beam uniformity, maintaining high beam current and parallelism, reducing the need for compensatory adjustments in downstream components and shortening tuning processes.
Implementation Method 1
A filament is disposed behind the cathode and energized to emit thermionic electrons. These electrons then strike the back surface of the cathode, causing the cathode to increase in temperature and emit electrons into the ion source chamber.
Implementation Method 2
These energized electrons collide with a feed gas in the ion source chamber to create ions, which can be extracted through an extraction aperture in the ion source.
Data Source
AI summary
An ion source having dual indirectly heated cathodes is disclosed. Each of the cathodes may be independently biased relative to its respective filament so as to vary the profile of the beam current that is extracted from the ion source. In certain embodiments, the ion source is used in conjunction with an ion implanter. The ion implanter comprises a beam profiler to measure the current of the ribbon ion beam as a function of beam position. A controller uses this information to independently control the bias voltages of the two indirectly heated cathodes so as to vary the uniformity of the ribbon ion beam. In certain embodiments, the current passing through each filament may also be independently controlled by the controller.