Gas Ion Source Electron Beam Brightness Control
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Solution Overview
Problem
Current particle-optical apparatus with gas ion sources face limitations in achieving high brightness and low energy spread, leading to geometrical and chromatic aberrations in ion spots, due to interference from optics and electric fields, and plasma and space charge effects.
Innovation Solution
The electron-emitting surface is positioned at the gas side of the diaphragm wall, with a high-brightness electron source placed close to the ionization volume to achieve a high electron current density, and a small ionization volume is maintained by using a combination of focusing optics and a second wall to control the acceleration and extraction fields, ensuring minimal interference and low energy spread.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a small ionization volume is used to achieve high brightness, then brightness is improved, but the electron current density requirement becomes more difficult to meet
Solution Approach 1:
The patent applies local quality by creating a highly localized region of high electron current density within the small ionization volume. The electron beam is focused to concentrate electrons precisely where needed (in the ionization volume near the exit diaphragm), while the rest of the electron source can have lower current density. This localized concentration achieves high brightness without requiring the entire electron source to operate at extreme current densities.
2Manufacturing precision
If imaging optics with small aberrations are used to focus electrons, then manufacturing precision is improved, but the focal length cannot be chosen arbitrarily small due to interference with ion extraction
Solution Approach 1:
The patent resolves the focal length constraint by moving the electron source to the gas side of the diaphragm wall, effectively using the third dimension (spatial arrangement relative to the diaphragm wall) to solve the problem. This repositioning allows the electron source to be close to the ionization volume without the optics interfering with ion extraction, as the ions are extracted through the diaphragm wall while electrons are supplied from the gas side.
3Illumination intensity
If the electron source is placed close to the ionization volume to achieve high electron current density, then brightness is improved, but the electron source may interfere with ion extraction
Solution Approach 1:
The patent applies segmentation by dividing the system into distinct spatial zones: the electron source and ionization region are on the gas side of the diaphragm wall, while ion extraction occurs through the diaphragm wall into the vacuum side. This spatial segmentation allows high electron current density near the ionization volume without interfering with ion extraction, as the two processes occur in separated but adjacent regions.
4Illumination intensity
If a small exit diaphragm is used to limit ionization volume, then brightness is improved, but the gas flow and pressure control become more difficult
Solution Approach 1:
The patent applies parameter changes by optimizing the relationship between exit diaphragm size, gas pressure, and electron beam parameters. Rather than simply reducing the diaphragm size, the system adjusts multiple parameters including gas pressure in the ionization volume, electron beam current and focus, to achieve high brightness while maintaining controllable gas flow through the small diaphragm opening.
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 configuration allows for a higher brightness and lower energy spread, enabling the formation of a small ion spot with reduced aberrations, improving the processing efficiency in semiconductor applications.
Implementation Method 1
Electrons generated by an electron source at the vacuum side of the diaphragm wall are accelerated by a first electric field, the acceleration field
Implementation Method 2
As a result of collisions between the electrons in the electron focus and the emerging gas atoms, gas ions are now formed in an ionization volume
Implementation Method 3
The ions are extracted from the ionization volume with the aid of a second electric field, the extraction field
Data Source
AI summary
The invention relates to an electron impact gas ion with high brightness and low energy spread. This high brightness is achieved by injecting electrons in a small ionization volume (from less than 1 μm to several tens of micrometers in size) from one side and extracting ions from the other. The electrons injected are produced by a high brightness electron source, such as a field emitter or a Schottky emitter.In one embodiment of the invention the required high electron density in the ionization volume is realized by placing a field emitter close to the ionization volume (e.g. 30 μm), without optics between source and ionization volume.In another embodiment of the invention the source is imaged onto a MEMS structure. Two small diaphragms of e.g. 50 nm are spaced e.g. 1 μm apart. The electrons enter through one of these diaphragms, while the ions leave the ionization volume through the other one. The two diaphragms are manufactured by e.g. drilling with an ion beam, resulting in two small and well aligned diaphragms.