Use of metal-organic precursor materials has permitted thermal CVD of many metal nitrides at remarkably low temperatures and without corrosive by-products. Metallic TiN, VN, Nb3N4 and Mo2N3; semiconducting GaN and Sn3N4; and insulating AIN, Zr3N4, Hf3N4 and Ta3N5 can be deposited at temperatures typically in the range 100 to 400 C. Deposits free of carbon are obtained by transamination reactions of metal dialkylamido precursors with a sufficiently large excess of ammonia. The resulting TiN films are good diffusion barriers, and provide low contact resistance between metals and silicon.
Transparent semiconducting oxide films, such as SnO2, ZnO and TiO2, are often made by MOCVD for use in solar cells, energy-efficient window coatings and electro-optical displays. These wide band-gap semiconductors can be doped to n-type conductivity by a variety of dopant elements. Fluorine is the dopant which produces materials with the highest electron mobility, conductivity and transparency, by substituting for oxygen. Certain organic fluorine compounds have been found to be very effective fluorine dopants for these CVD reactions, yielding films with very shallow donors having nearly 100 % electrical activity.
Precursors for the CVD of alkaline earth metal oxides, particularly barium, lack the volatility and stability needed for reproducible deposition of superconducting, ferroelectric or magnetic oxides. Use of ammonia or volatile amines as carrier gases greatly enhances the volatility and stability of betadiketonates of barium, strontium and calcium, providing high and stable transport rates for source temperatures below 100 C, even for non-fluorinated ligands.
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