MEASUREMENT OF ATOMIC-HYDROGEN IN A HOT-FILAMENT REACTOR BY 2-PHOTON LASER-INDUCED FLUORESCENCE

It is now well known that hydrogen atom supersaturation is a Prerequis ite for diamond film growth. However, the exact role played by atomic hydrogen remains unclear. Thus determination of the H concentration un der various experimental conditions is of great interest in understand ing the role of hydrogen in diamond deposition processes. It has been demonstrated previously that two-photon laser induced fluorescence (LI F) can be used to determine quantitative H-atom concentrations. We mea sured the spatial profile of the concentration and translational tempe rature of atomic hydrogen in a hot filament reactor during diamond dep osition process by two-photon LIF. Hydrogen atoms were excited to the n = 3 state by two photons at 205 nm wavelength and the emission of th e H(alpha) transition at 656 nm (n = 3 --> n = 2) was observed. UV lig ht at 205 nm was produced by an excimer pumped dye laser using rhodami ne B at 615 nm. This light was frequency doubled to produce 307.5 nm w hich was then mixed with 615 nm to give 205 nm. The energy obtained wa s typically 50 muJ for a pulse duration of about 30 ns and a laser ban dwidth of 2 pm. This work is complementary to measurements of atomic h ydrogen performed by intracavity laser absorption in CH4-H-2 mixtures.