Pressure Modifications in CVD

In general, most reactions involving hazardous or toxic vapor phase precursors are operated at reduced pressure from a safety perspective. Additionally, the enhancement of kinetic steps often occurs by operating at reduced pressure. As indicated in the individual chapters of this book, many reaction schemes involve operation at low pressure, and, therefore, care must be taken with the vacuum system, its maintenance, and the exhaust of a reaction co-product stream. For specific applications of low pressure operation, the reader should consult the appropriate chapter on the material of interest. 

Whenever possible, more rapid turnaround time, the absence of load locks, the reduced maintenance cost associated with the avoidance of vacuum systems, and the ease of incorporation into continuous processing systems, all combine to make atmospheric pressure chemical vapor deposition an attractive technique. In general, removal of reaction co-products is accomplished by utilization of a large excess of carrier gas (typically argon or nitrogen). Additionally, it may be noted that the thermal oxidation 

Spray pyrolysis, as differentiated from chemical vapor deposition, involves the direct application of either a flame to a vapor phase stream, or the entrainment and transport of particulates or vapors in some direction non-perpendicular to a substrate surface. 

Although sometimes differentiated from spray pyrolysis, aerosol assisted CVD is essentially the same motif. It is, however, typically not conducted in a flame type regime. Nevertheless, frequently, materials are not transported perpendicular to a substrate surface, thereby bypassing one of the crucial elements of chemical vapor deposition - the ability to secure extraordinary step coverage in high aspect ratio materials, due to the non-line-of-sight technique. 

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