AdvantagesThe use of an electron beam enables not only observation of the submicron world (TEM’s SEM’s and X-ray microanalysers) but also processing with submicron precision (electron beam lithography systems). The optimum cathode material for use in these instruments would possess the following properties: Low potential barrier (work function) High melting point and stability at high temperatures Low vapor pressure so as to reduce evaporation loss Chemical stability The relative drawbacks of tungsten cathodes are a work function of 4.7eV, insufficient beam current, and a short service life. LaB6 has a work function of 2.66eV – thus more easily emitting electrons – and is a relatively stable material, so it has been increasingly used as a material for cathodes instead of tungsten. Using LaB6 cathodes with TEMs and SEMs, even with the electron beam narrowed down, it is possible to obtain enough beam current to achieve better resolution and clear micrographs with less noise. The principle advantage, however, is that LaB6 can be used in a stable condition for a much longer time. Denka manufactures the purest, highest quality LaB6 crystals for use in their cathode tips.Applications are: SEM TEM X-ray Beam Analysis (EPMA) Electron Beam Lithography Benefits High Brightness: A LaB6 beam is 10 times brighter than tungsten, has superior resolution, and features a wide range of acceleration voltages. It provides sharp, clear pictures, down to the smallest detail. The initial brightness of a Denka Model 3 cathode (1 x 106A/cm2.Str) is substantially better than that of competing, mini-vogel type cathodes (typically 5 x 105A/cm2.Str). Long Life: Heat and vacuum are the final determinants of any cathode tip’s life, but at 1550°C and a vacuum of 10-7 Torr, a service life of about 500 hours can be expected. Stability: Thanks to its simple and durable construction, every Denka Model 3 LaB6 Cathode offers a stability of better than 3% per hour at 1550°C. Interchangeability: Denka Model 3 LaB6 cathodes are designed as direct replacements for tungsten filaments when a vacuum in the 10-7 range is provided. Comparison of Tip Configurations Available with Denka M-3 LaB6 AEI style Cathodes Flat Tip Standard (Round) Tip Sharp Tip 90° or 60° cone angle20/40/60/100µm flat tip radius 90° cone angle15µm tip radius 60° cone angle5µm and 10µm tip radius Brightness About 5 times that of tungsten2-5 x 105 A/cm2 • Str About 10 times that of Tungsten1 x 106 A/cm2 • Str Twice as bright as standard tips2 x 106 A/cm2 • Str Saturation Mono spot at about 1,400°C Mono spot at about 1,500°C Almost the same as standard tips Crossover Large (11-13µm) Small (7-10µm) Small (7-10µm) Angular Distribution Broad3.3-4.2 x 10-2rad Sharp1.6 x 10-2rad Sharp1.6 x 10-2rad Used Temperature Low Temperature High Temperature High Temperature Lifetime Long life (usable at low temperatures, and crystallizedend changes slowly) Long life; shorter than flat tips Short Operation Easy (thanks to its large spot size and broad adjusting range) Not so difficult Difficult (the point adjustment needed) Stability High (invulnerable to thermal expansion or vibration) High Middle (vulnerable to thermal expansion or vibration, adjustment is sometimes necessary) Technology Needed Ordinary High Very High Dimensions for EM Filament Bases (for Tungsten/Lab6) Filaments Base Type Diameter of Ceramic Disc(mm) Diameter of Pins(mm) Center Distance of Pins(mm) AEI 12.0 1.0 6.45 FEI/PHILIPS 26.0 1.0 5.0 JEOL K-type 28.0 1.2 8.0 HITACHI S-type 9.8 1.2 2.7 ZEISS (DSM & TEM), LEO (1450 & TEM), TESCAN 19.8 1.0 5.0 AMRAY (except 1200) 26.1 1.0 5.0 ISI/ABT/TOPCON2 pins 23.3 1.2 11.9 ISI/ABT/TOPCON 23.4 1.2 12.0 Electron Source Performance Comparison 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] 1.104 1.105 1.107 2.107 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/mbar < 1.10-5 < 1.10-6 < 1.10-8 < 1.10-10 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 1450 Denka M-3 LaB6 Cathode for JEOL Instruments(compatible with K-type filament base) 1451 Denka M-3 LaB6 Cathode for FEI, Philips Instruments (Except XL-30) 1452 Denka M-3 LaB6 Cathode for AMRAY Instruments(except 1200 Series) 1453 Denka M-3 LaB6 Cathode AEI base for Cambridge (except S2A and S4-10), Camscan, Electroscan, Leica, LEO and Zeiss (EVO®) Instruments 1454 Denka M-3 LaB6 Cathode for Hitachi Instruments 1449 Denka M-3 LaB6 Cathode for ZEISS/LEO TEM, Zeiss DSM SEMs, or TESCAN SEMs
