Methyl concentration measurements during microwave plasma-assisted diamonddeposition

Absolute line-of-sight averaged measurements of methyl radical concentratio ns in a microwave plasma-assisted diamond deposition reactor ave presented. The measurements are based on the use of broadband ultraviolet absorption spectroscopy to characterize the distinguishing absorption feature of methy l at 216nm associated with the X((2)A"(2)) --> B((2)A'(1)) electronic trans ition. The dependence of the line-of-sight methyl concentration and mole fr actions with the percentage of methane in the feed-gas, plasma power densit y, and position of substrate relative to the optical probe volume is studie d The measurements suggest that the near-substrate methyl mole fraction is only weakly sensitive to changes in substrate temperature and are largely i nfluenced by the gas phase temperature. A comparison is made between the me asured mole actions and recent predictions based on a one-dimensional model of this process. The measured mole fractions are consistently greater than those predicted by about a factor of ten. This discrepancy is explained in part by the line-of-sight limitations in experimental facility.