Detection of hydrogen atoms in silane plasmas using laser-induced fluorescence by Lyman-alpha two-photon and simultaneous Balmer-alpha excitations

Measurements of atomic hydrogen densities in silane plasmas were accomplished using a two-photon excitation from the ground state (principal quantum number n=1) to the n=2 state at 243 nm, a simultaneous excitation from the n=2 state to the n=3 state at 656 nm, and an observation of fluorescence at 656 nm. First, the influence of the laser-induced dissociation of molecules and radicals in silane plasmas on measurements of hydrogen atoms during the application of this excitation scheme was investigated. Then, we determined the absolute density of hydrogen atoms to be (5±2) × 10¹⁷ m^-3 in a silane plasma at a flow rate of 5 sccm, a pressure of 11 Pa and a rf power of 2 W.