Chemical Vapor Deposition

Chemical vapor deposition (CVD) is a method of forming thin solid film on a substrate by the reaction of vapor phase chemicals which contain the required constituents. The reactant gases are activated by various energy forms such as chemical, thermal, plasma or photon, and reacted on and/or above the temperature-controlled surface to form the thin film. The reactive species, energy, rate of chemical supply, substrate temperature and substrate itself largely determine the film properties. A wide variety of thin films are prepared by CVD for use in semiconductor device fabrication. The selection of materials such as polysilicon, silica glass, doped silica glass borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), silicon nitride, tungsten, tungsten silicide, titanium nitride, and other emerging dielectrics, conductors, semiconductors is typically based on meeting integration requirements and cost target. The silica based materials chosen in the early semiconductor development is simply due to its compatibility with silicon in nature. The demands for shrinking geometry size and more functionality on devices put down more requirements: diffusion barrier (for sodium), step coverage by reflow or as-deposited conformality, film stress and interface control (adhesion, wetting). The never ever ended drives from consumers for lower price force manufacturers to balance between the cost of fabrication and performance enhancement. For some materials such as silicon, silica glass, and silicon nitride, and other dielectrics, CVD is the simplest and the most cost effective way. But for conductor materials, physical vapor deposition (PVD) is a more traditional way to deposit; only the cases where PVD cannot or very difficult to achieve, CVD prevail. One outstanding requirement is step coverage.