High-Vacuum Process Systems

Independent of the type of PVD method used to deposit a film or a film system, the deposition process is carried out in a sealed chamber which is first exhausted to a pressure of the order of 10 5 mbar or even lower values. The glass chambers used formerly have been replaced, with the exception of glass recipients for special purposes, such as apparatus for electron microscopic preparation techniques, by those of metal. Cylindrical and cubic chambers made of stainless steel provided with various flanges and windows are used today. The walls of the chambers can be heated and cooled by water running through double-wall constructions or in brazed-on half-round pipes fitted on the outside. The vacuum chambers are evacuated by different pumping systems. The simplest consists of a diffusion pump with or without a liq- 

Another pumping system may consist of a turbo-molecular pump, a Root s blower and a twin-stage rotary vane backing pump. 

It is interesting to note that pumping systems equipped with diffusion pumps are the cheapest but that the cryopumping systems are only slightly more expensive. 

Costs of acquisition of various types of high vacuum pumps as function of the size of the plants to be evacuated. 

Annual operating costs of various high vacuum Pumps (220 days with 9 hours electrical Power, water and liquid nitrogen) in arbitrary units as function of the intake aperture of the plant. BALZERS plants are specially considered. 

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Atomic layer deposition is a high vacuum process where small amounts of the precursors are leaked into the system sequentially with intermittent evacuations. The ALD enables the conformal deposition of atomically thin layers with precise thickness control at low temperatures without the typical aggregate formation in the gas-phase. 

The vacuum system must be able to attain the required pressures reliably despite these high gas loads. In the example shown, the system is evacuated with a combination of a backing and Roots pump. A diffusion pump along with a cold surface forms the high vacuum pump system. The cold surfaces pump a large portion of the vapor and volatile substances emitted by the plastic parts while the diffusion pump basically removes the non-condensable gases as well as the noble gas required for the sputter process. 

There are several types of interfaces that are of great practical importance and that will be discussed in turn. These general classifications include, solid-vacuum, liquid-vacuum, solid-gas, liquid-gas, solid-liquid, liquid-liquid, and solid-solid. From a practical standpoint, solid- and liquid-vacuum interfaces are of little concern. They are most often encountered in the context of theoretical derivations, since the absence of a second phase simplifies matters greatly, or in studies of high-vacuum processes such as deposition, and sputtering. The true two-phase systems (assuming that a vacuum is not considered to be a true phase ) are the ones which are of most importance in practical applications and that are addressed in most detail here. A list of commonly encountered examples of these interfaces is given in Table 2.1. 

Metallization occurs in high vacuum deposition systems using electron beam, flash, and resistive heating systems to evaporate the metal onto the substrate. Sputtering systems perform the same function under partial vacuum. Etching, either dry (plasma) or wet etching, processes remove... 

Aluminum is an attractive metal to use as a vacuum material because of its ease of fabrication, light weight, and high thermal conduchvity. However, the natural oxide that forms on aluminum and thickens with time is rather porous and can give appreciable outgassing. Mill-rolled aluminum has an outgassing rate -100 hmes that of mill-rolled stainless steel. Aluminum is not normally used for vacuum processing systems because it is soft and easily corroded. 

For materials of moderate to low porosity, a good starting vacuum level is 0.6 to 0.7 bar (18 to 21 in Hg), as the capacity of most vacuum pumps starts to fall off rapidly at vacuum levels higher than 0.67 bar (20 in Hg). Unless there is a critical moisture content which requires the use of higher vacuums, or unless the deposited cake is so impervious that the air rate is extremely low, process economics will favor operation at vacuums below this level. When test work is carried out at an elevation above sea level different than that of the plant, the elevation at the plant should be taken into account when determining the vacuum system capacity for high vacuum levels (>0.5 bar). 

Figure 3-45. High altitude process vacuum system, NPSH requirements.

Abstract A review is provided on the contribution of modern surface-science studies to the understanding of the kinetics of DeNOx catalytic processes. A brief overview of the knowledge available on the adsorption of the nitrogen oxide reactants, with specific emphasis on NO, is provided first. A presentation of the measurements of NO, reduction kinetics carried out on well-characterized model system and on their implications on practical catalytic processes follows. Focus is placed on isothermal measurements using either molecular beams or atmospheric pressure environments. That discussion is then complemented with a review of the published research on the identification of the key reaction intermediates and on the determination of the nature of the active sites under realistic conditions. The link between surface-science studies and molecular computational modeling such as DFT calculations, and, more generally, the relevance of the studies performed under ultra-high vacuum to more realistic conditions, is also discussed. 

All filtering and extraction systems must be checked for compatibility with the analyte of interest. Some or all of the analytes may be absorbed or otherwise lost during the extraction process, and this must be known beforehand. Carbon may be lost by high vacuum differentials between sampler and soil water. Long extraction times may lead to distortions in the results of the sample analysis [5],... 

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