A Study of the Effect of the Hydrogen Gas Flow on the Quality of Thin CVD Diamond Films Deposited on Silicon Substrates in CH4/H2 Gas Mixture

Hydrogen contents in CVD diamond films play a major role in both the electrical and structural properties of the films. There have been reports on the effect hydrogen plays in the morphological formation of the CVD crystals. The morphological changes are attributed to the gas residence time, which has been shown to be inversely proportional to the total gas flow rate. The higher the gas residence time the slower the growth process, which is a characteristic of the formation of {100} crystals. It is as well known that the presence of high concentration of hydrogen in diamond films increases the films dc and ac electrical conductivities. This paper investigates the quantifiable effects of the hydrogen gas flow on the output variables of a microwave cavity plasma reactor (MCPR) for various percent of methane-hydrogen concentrations. The reactor output variables include film morphology, structural quality as measured by Raman spectra and scanning electron microscopy (SEM) techniques, linear growth rate, and carbon conversion efficiency. The study reveals the dependence of these variables on the total hydrogen gas flow rate. This detailed study resulted from over 250 experiments which represents over 2000 hours of reactor experimental operation.