Definition of CVD

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], 

Mass transport of reactant gaseous species to vicinity of substrate  

Gaseous reactant species Absorbed intermediates Deposited solid species Gaseous byproduct species 

Diffusion of reactant species through the boundary layer to the substrate surface or homogeneous chemical reactions to form intermediates  

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These new systems are not accurately encompassed by the true definition of CVD, but will be considered here as they are an important step in the evolution of thin-fllm deposition techniques. Using these new delivery methods the stability of the precursor, and its reproducible behavior with respect to the method of delivery, is fundamentally more important than its volatility. Moreover, the clean deposition of the precursor and the subsequent low levels of impurities and defects within the final material can now be considered of greater importance than volatility when choosing or designing a precursor compound. 

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