High-temperature Chemical Vapour Deposition Process

6 High-temperature Chemical Vapour Deposition Process 

One of the key technical issues is to select suitable material as the substrate. Graphite and silicate glass are widely used because graphite is easily oxidised in air at 700°C and silicate glass can be etched away by HF acid. Sometimes Mo, Ta, W, SiC and Si3N4 are also employed due to their superior stiffness at elevated temperatures and inertness to reactant gases. 

Material deposited Precursor gases and flow rate (1-min- l) T emperature (°C) Pressure (T orr) Deposition rate (pm-min-1) 

Material Density fe-cm5) Thermal conductivity (W-m -KT1) Coefficient of thermal expansion(xl0-6 KT1) Elastic modulus (GPa) Polishabil ty (ARMS) 

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The halogenation of metals provides opportunities to study scaling reactions in which the reaction product is a pure ionic conductor, which can also be highly volatile. These systems can be studied at relatively low temperature they are important in their own right in terms of the mechanisms of extraction and chemical-vapour-deposition processes that employ gaseous halides as intermediate compounds. 

Physical vapour deposition (PVD) is a variety of vacuum deposition and is a general term used to describe any of a variety of methods to deposit thin fdms by the condensation of a vapourized form of the desired film material on to various workpiece surfaces (e.g., on to semiconductor wafers). The coating method involves purely physical processes such as high temperature vacuum evaporation with subsequent condensation, or plasma sputter bombardment rather than involving a chemical reaction at the surface to be coated as in chemical vapour deposition. 

There are several definitions of CVD in the published literature. A practical and common definition of CVD is that it is a complex process of depositing solid materials at a high temperature as a result of a chemical reaction. This deposition forms a special type of material commonly known as ordered crystal grown from vapour. 

Whilst the above definition introduces the basic high level understanding and observations of the process, a more concise and scientific definition for CVD is a process whereby a thin solid film is deposited onto a substrate through chemical reactions of the gaseous species. For structural component applications, the deposition typically takes place at a temperature of around 1000°C. It is the reactive processes that distinguish CVD process from physical vapour deposition (PVD) processes, such as physical evaporation process, sputtering and sublimation processes [1],... 

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