The use of ultra-sensitive white light absorption spectroscopy in diamond CVD

We have carried out extensive investigations of the gas phase composition during diamond CVD in a conventional hydrogen rich environment. Absolute densities of CH/sub 3/, CH, and the hydrogen dissociation ratio have been measured in hydrocarbon-based plasma-enhanced CVD (PECVD) and hot filament CVD (HFCVD) environments. Additional species, C/sub 2/H/sub 2/ and C/sub 6/H/sub 6/ have been studied in hot filament activated diamond growth. High sensitivity white light absorption spectroscopy has been able to provide a quantitative description of the densities of all the single carbon hydrocarbon species in hydrogen-rich diamond growth. The most extensively studied species is the CH/sub 3/ radical. This radical is the key to the diamond growth mechanism in hydrogen-rich diamond CVD. As with many other polyatomic species, the excited electronic levels of CH/sub 3/ all dissociate. Consequently, laser-induced fluorescence measurements are not possible with this species. Prior to the work with high sensitivity white light absorption spectroscopy, the CH/sub 3/ radical had been detected using resonantly-enhanced multiphoton ionization (REMPI), infrared diode laser absorption and near threshold ionization mass spectrometry. Compared with these techniques, high sensitivity white light absorption spectroscopy is considerably simpler and more sensitive, even deep in the ultraviolet.