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| YPS Schottky type field emission (FE) sources can be used in many brands of focused electron beam systems including SEM, TEM, Auger and CD-SEM systems. These high quality FE sources are an excellent and cost effective drop-in alternative for FEI and Denka style FE sources. The YPS FE source is a thermal field emitter (TFE) cathode featuring a layer of zirconium oxide on a <100> oriented single crystal tungsten wire with a very sharp tip. The tip is
mounted on a hairpin filament that is used to maintain the tip at a temperature of around 1800K. |
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The tip just penetrates the aperture hole in a cylindrical suppressor electrode mounted around the assembly. Electrons are emitted from the tip due to both thermal excitation and an electrical field at the tip due the potential difference between it and an extractor electrode. The YPS Schottky tip radius is typically 0.3µm to ensure high brightness of the source. |
| Currently there are three types of FE sources available: The YPS-174, the YPS-184 and the YPS-M20 Mini Module. This product line is aimed to customers who are comfortable with changing field emission sources and know how to change, load and align the TFE cathodes in a clean environment. It is also an excellent product for developers building custom-designed electron beam columns using TFE sources. The operating vacuum for TFE sources is typically better than 1x10-9 mbar. This is higher than the operating vacuum for tungsten or LaB6
sources, but less stringent than for cold field emission sources. |
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YPS-174 Standard Schottky FE Module
The YPS-174 is the most common standard Schottky field emitter module which is equivalent in dimensions to both FEI – and Denka – standard Schottky field emission cathodes. The suppressor aperture has a diameter of 400µm. The emitter protrudes 250µm from the suppressor electrode. The YPS-174 is compatible with thermal field emission sources used on systems from Amray, Hitachi, JEOL, ZEISS/LEO, FEI (pre 2002), PHI and Riber. |
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YPS-184 Schottky FE Module
The YPS-184 Schottky Module is a drop-in alternative for the FEI SEM unit. The suppressor aperture has a diameter of 500µm and the emitter protrudes 250µm from the suppressor electrode. The YPS-184 module is also compatible with Tescan FESEMs. |
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YPS-M20 Mini Module TFE Source
The YPS-M20 Mini module TFE source is a complete pre-aligned assembly with a smaller style suppressor, ceramic insulator and extractor. The YPS-M20 Mini Module is a high grade alternative FE source for the Applied Materials/OPAL CD-SEMs. |
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| TFE Module | YPS-174 | YPS-184 | YPS-M20 |
| Amray | X | ||
| Applied / OPAL | X | ||
| FEI (pre 2002) | X | X | |
| Hitachi (TFE) | X | ||
| JEOL (TFE) | X | ||
| LEO (Gemini) | X | ||
| PHI | X | ||
| Riber | X | ||
| Tescan | X | ||
| ZEISS (Gemini) | X |
| Prod # | Description | Unit | Price | Order / Quote | |||
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| YPS-174 TFE source |
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| YPS-184 TFE source |
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| YPS-M20 Mini Module TFE Source |
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Each YPS Schottky FE Module comes with a data sheet which includes:
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| Emitter Type | Thermionic | Thermionic | Schottky FE | cold FE |
|---|---|---|---|---|
| Cathode material |
W |
LaB6 |
ZrO/W (100) |
W(310) |
| Operating temperature [K] |
2,800 |
1,900 |
1,800 |
300 |
| Cathode radius [nm] |
60,000 |
10,000 |
< 1,000 |
< 100 |
| Effective source radius [nm] |
15,000 |
5,000 |
15 (*) |
2.5(*) |
| Emission current density [A/cm2] | 3 | 30 | 5,300 | 17,000 |
| Total emission current [µA] | 200 | 80 | 200 | 5 |
| Normalized brightness [A/cm2.sr.kV] | 1 x 104 | 1 x 105 | 1 x 107 | 2 x 107 |
| Maximum probe current [nA] | 1000 | 1000 | 10 | 0.2 |
| Energy spread @ cathode [eV] | 0.59 | 0.40 | 0.31 | 0.26 |
| Energy spread @ gun exit [eV] | 1.5 - 2.5 | 1.3 - 2.5 | 0.35 - 0.7 | 0.3 - 0.7 |
| Beam noise [%] | 1 | 1 | 1 | 5 - 10 |
| Emission current drift [%/h] | 0.1 | 0.2 | < 0.5 | 5 |
| Operating vacuum hPa/mbar1 | < 1 x 10-5 | < 1 x 10-6 | < 1 x 10-9 | < 1 x 10-10 |
| Typical Cathode life [h] | 100 | > 1000 | > 5000 | > 2000 |
| Cathode regeneration | not required | not required | not required | every 6 to 8 hours |
| Sensitivity to external influence | minimal | minimal | low | high |
Frequently asked questions about field emission sources
Q. Are FE sources less reliable than thermionic sources?
A. No - they can be very reliable, working over many months continuously.Q. What are the advantages of Schottky field emission compared to cold field emitters e.g. W(310) or W(111)?
A. The major advantages are better beam current stability, less stringent vacuum requirements and the fact that there is no need for periodic emitter flashing to restore the emission current.Q. What are the vacuum requirements for operation of a Schottky field emission source?
A. Normally 10-9 mbar or better in the source region.Q. What are the brightnesses of Schottky sources as compared to thermionic sources?
A. Schottky emitters have brightnesses of about 108 Acm -2sr-1 whereas thermionic emitters have about 10 5 Acm-2sr-1.Q. Do Schottky emitters need replacing very frequently?
A. The lifetime of a Schottky emitter is determined by the life of the Zr reservoir in the tip structure. This is normally about 8000 hours.Q. Are there special steps to be taken in turning on a Schottky source?
A. Care is needed to avoid thermal shock to the emitter and to avoid electrical breakdown transients as the extraction voltage is applied. Further, the operating temperature should not exceed 1850 K.Q. How do I operate the YPS Schottky Field Emitter?
A. The same way as other TFE sources. The YPS source is supplied with a Schottky Emitter data sheet, unique to each emitter.Q. Can any thermionic source be replaced by a Schottky field emitter?
A. In principle yes. There may be a need for differential pumping of the source in order to maintain adequately low pressure.Q. What performance can be obtained if an LaB6 source is replaced by a Schottky field emission source on a PHI 600 series probe or its equivalent?
A. Upgraded PHI 660 systems with the YEO3/P660 product has improved the spatial resolution to close to that of the PHI 680.