Sputter pumps

Fig. 5. Plots of pump-down performance for pumps operating on 0.1-m-dia x 0.43-m-long stainless-steel tubing. Curves 1—4 are sputter-ion pumps of different makes curve 5 is Orbitron type and curve 6, LN-trapped oil DP. Pressure is measured using Bayard-Alpert gauge (BAG) (26). To convert Pa to...

Alternatively the gas is passed over CuO pellets at 300° to remove hydrogen and hydrocarbons, over Ca chips at 600° to remove oxygen and, finally, over titanium chips at 700° to remove nitrogen. Also purified by freeze-pump-thaw cycles and by passage over sputtered sodium [Arnold and Smith J Chem Soc, Faraday Trans 2 77 861 1981]. 

A versatile Laser-SNMS instrument consists of a versatile microfocus ion gun, a sputtering ion gun, a liquid metal ion gun, a pulsed flood electron gun, a resonant laser system consisting of a pulsed Nd YAG laser pumping two dye lasers, a non-resonant laser system consisting of a high-power excimer or Nd YAG laser, a computer-controlled high-resolution sample manipulator on which samples can be cooled or heated, a video and electron imaging system, a vacuum lock for sample introduction, and a TOF mass spectrometer. 

For IBSCA analysis, standard HV or, better, UHV-equipment with turbomolecular pump and a residual gas pressure of less than 10 Pa is necessary. As is apparent from Fig. 4.46, the optical detection system, which consists of transfer optics, a spectrometer, and a lateral-sensitive detector, is often combined with a quadrupole mass spectrometer for analysis of secondary sputtered particles (ions or post-ionized neutrals). 

Such vessels can also be baked at a temperature of several hundred degrees, to drive off any gas adsorbed on metal surfaces. The pumping function of an ion gauge was developed into efficient ionic pumps and turbomolecular pumps , supplemented by low-temperature traps and cryopumps. Finally, sputter-ion pumps, which rely on sorption processes initiated by ionised gas, were introduced. A vacuum of 10 "-10 Torr, true UHV, became routinely accessible in the late 1950s, and surface science could be launched. 

CVD does not usually require the low pressures which are necessary with sputtering, MBE, and other PVD processes. Consequently the vacuum system is simpler and less costly. Mechanical pumps are adequate for many operations. Vane pumps, built with corrosion resistant material, are preferred. If properly maintained, these pumps will operate for long periods of time. 

The drawback of GALDI is the possible contamination of the ion source with graphite powder that can cause short circuits. The authors have found that the application of thin graphite films and low laser powers minimise the amount of sputtering in the ion source. However, modern commercial spectrometers have compact ion sources that can be easily contaminated, and care should be taken in the use of this methodology. The same is true for turbomolecular pumps if they are located directly below the ion source. 

The pumping speed of sputter-ion pumps depends on the pressure and the type of gas. It is measured according to the methods stated in DIN 28 429 and PNEUROP 5615. The pumping speed curve S(p) has a maximum. The nominal pumping speed is given by the maximum of the pumping speed curve for air whereby the corresponding pressure must be stated. 

For air, nitrogen, carbon dioxide and water vapor, the pumping speed is practically the same. Compared with the pumping speed for air, the pumping speeds of sputter-ion pumps for other gases amount to approximately ... 

Sputter-ion pumps of the triode type excel in contrast to the diode-type pumps in high-noble gas stability. Argon is pumped stably even at an inlet pressure of 1 10 mbar. The pumps can be started w/ithout difficulties at pressures higher than 1 10 mbar and can operate continuously at an air inlet producing a constant air pressure of 5 10 mbar. A new kind of design for the electrodes extends the service life of the cathodes by 50 %. 

Influence on processes in the vacuum chamber by magnetic stray fields and stray ions from the sputter-ion pump. 

Fig. 2.64 Stray magnetic feid of a sputter-ion pump in two piaces paraiiei to the iniet Hange (inserts) cun/es show tines of constant magnetic induction B in Gauss. 1 Gauss = 1 10 > Testa...

Three differing capacities of a pump for the gases which can be pumped result from the size of the three surfaces (baffle, condensation surface at the outside of the second stage and sorption surface at the inside of the second stage). In the design of a cryopump, a mean gas composition (air) is assumed which naturally does not apply to all vacuum processes (sputtering processes, for example. See 2.1.9.6 Partial Regeneration ). 

For the production of pressures in the ultrahigh vacuum region, sputter-ion, and sublimation pumps, as well as turbomolecular pumps and cryopumps, are used in combination with suitable forepumps. The pump best suited to a particular UHV process depends on various conditions (for further details, see Section 2.5). 

Instead of rotary pumps, large water jet, steam ejector, or water ring pumps can be used. For batch evacuation, and the production of hydrocarbon-free fore vacuum for sputter-ion pumps, adsorption pumps (see Section 2.1.8.1) are suitable. If the use of oil-sealed rotary vane pumps cannot be avoided, basically two-stage rotary vane pumps should be used. The small amount of oil vapor that backstreams out of the Inlet ports of these pumps can be almost completely removed by a sorption trap (see Section 2.1.4) Inserted In the pumping line. 

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