GROWTH AND PROPERTIES OF DIAMOND FILMS PREPARED BY MICROWAVE PLASMA CHEMICAL VAPOR-DEPOSITION USING DIFFERENT OXYGEN-CONTAINING SOURCE GASES

The formation of polycrystalline diamond films using activated chemical vapor deposition (CVD) processes is known to be improved by addition of oxygen species to the gas phase leading to an enhanced growth rate and a better phase purity of the deposited diamond films. In order to optimize process conditions and to get an insight into the underlying mechanisms, microwave plasma-activated chemical vapor deposition (MPCVD) of diamond on Si(100) and cemented carbide substrates was performed using carbon monoxide, carbon dioxide and dimethyl ether as oxygen sources in addition to the commonly used CH4/H-2 gas mixture. Admixture of the oxygen source gases allow diamond deposition with enhanced growth rates and better quality compared to the pure CH4/H-2 atmosphere. Significant differences concerning the amount of carbon in the gas phase, for which diamond deposition can be achieved, are established. Diamond films produced with CO2 have the lowest nucleation densities and no deposition of diamond without addition of CH4 was observed. In contrast to CO2, CH4 addition is not necessary to grow diamond from CO/H-2 but small amounts of methane result in considerably increased growth rates. The influence of the source gases on physical film properties like adhesion, strain, and IR transmission of free standing membranes is reported. The results of this study are discussed with regard to film applications and growth mechanisms.