Schottky Thermal Field Emitter Integrated Beam Splitter
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Solution Overview
Problem
Existing scanning electron microscopes (SEMs) using Schottky thermal field emitters face challenges with beam splitting, including energy spread and trajectory displacement due to space charge effects, resulting in low current and poor focusing of split electron beams when the beam splitter is located far from the emitter, and high vacuum maintenance costs when integrated within the FEG.
Innovation Solution
Integrating a beam splitter microhole array directly above and in close proximity to the Schottky thermal field emission (TFE) extractor faceplate using a standoff, allowing for immediate splitting of the electron beam near its origin, reducing space charge effects and maintaining high current in each split beam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the beam splitter is located far from the Schottky TFE emitter, then the device complexity is reduced and vacuum maintenance is simplified, but the pre-split beam current travels long distances causing space charge effects that broaden energy spread and displace trajectories, resulting in beamlet blur and de-focusing
Solution Approach 1:
The beam splitter is merged with the extractor assembly by integrating it onto the extractor faceplate, creating a unified structure that eliminates the need for separate remote positioning while maintaining precise beam control
Solution Approach 2:
The beam splitting action is performed preliminarily immediately after electron emission from the cathode, before the beam has a chance to diverge significantly or accumulate space charge effects that would degrade beam quality
2Device complexity
If the beam splitter is located far from the Schottky TFE emitter, then the device structure is simplified, but the total current of each split beam becomes very small due to strong beam divergence allowing only few electrons to pass through individual holes
Solution Approach 1:
The beam splitter is combined with the extractor faceplate into a single integrated assembly, positioning the splitter holes at the optimal location immediately where the beam emerges from the cathode
Solution Approach 2:
The beam is split preliminarily at the source region where the beam is still highly collimated and contains the maximum concentration of electrons, ensuring sufficient current in each beamlet before divergence occurs
3Manufacturing precision
If the beam splitter is integrated within the FEG, then the beam splitting is performed at the optimal location near the emitter, but high vacuum maintenance becomes difficult and manufacturing costs increase
Solution Approach 1:
The beam splitter is merged with the extractor assembly which is already part of the vacuum-tsealed FEG structure, utilizing existing vacuum infrastructure rather than requiring separate vacuum systems
Solution Approach 2:
The extractor faceplate serves multiple functions: it acts as both the electrical extractor electrode and the mechanical support structure for the beam splitter, eliminating the need for additional vacuum-compatible components
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 enhances the resolution, speed, and throughput of SEMs by maintaining high current and reducing energy spread and trajectory displacement in the split beams, improving focusing quality and SEM performance.
Implementation Method 1
A Schottky TFE source consists of a single-crystal tungsten wire with a very sharp tip equipped with a zirconium reservoir around the tungsten wire. The tip is mounted on a hairpin filament, which is used to maintain the tip at a temperature of 1750 K to 1850 K. Electrons are emitted from the tip due to both thermal excitation and the electrical field at the tip.
Implementation Method 2
The second electrode is an extractor having an aperture just above the tip of the wire. Electrons are emitted from the tip due to both thermal excitation and the electrical field at the tip. In a non-limiting example, the extractor voltage may be on the order of 2 kV to 7 kV.
Implementation Method 3
Integrating a beam splitter microhole array directly above and in close proximity to the Schottky thermal field emission (TFE) extractor faceplate using a standoff, allowing for immediate splitting of the electron beam near its origin
Implementation Method 4
a standoff integrated with the extractor faceplate, and a microhole array integrated with the standoff and being disposed opposite the extractor faceplate
Data Source
AI summary
A Schottky thermal field emitter (TFE) source integrated with a beam splitter by a standoff, which supports the beam splitter above the Schottky TFE extractor faceplate by a distance of 0.05 mm to 2 mm. The beam splitter includes a microhole array integrated with the standoff and being disposed opposite the extractor faceplate, the microhole array having a plurality of microholes that split the electron beam generated by the Schottky TFE into a plurality of beamlets. The support and extractor may be fabricated from the same material or from different materials. The support may be formed from a high temperature resistive material, which causes a potential difference between the extractor and the microhole array. This potential difference creates positively charged electrostatic lenses at the microholes, which increases current in the individual beamlets. Voltage on the microarray plate may be varied to achieve a high beamlet current.