Effect of laser-induced dissociation of SiH₃ radicals in SiH₄ plasmas during atomic hydrogen measurements using laser-induced fluorescence by a two-photon excitation

We investigated the influence of laser-induced dissociation of SiH₃ radicals in SiH₄ plasma during measurements of atomic hydrogen densities in the plasma. The measurements were made using two-photon excitation of hydrogen atoms from the ground state to the n = 2 state at 243 nm and simultaneous excitation from the n = 2 state to the n = 3 state at 656 nm. We concluded that some hydrogen atoms were generated by laser-induced dissociation of SiH₃ radicals. The ratio of atomic hydrogen density thus generated to the total density observed by the method was 20 ±20% for the following discharge conditions: gas flow rate of 5 sccm, gas pressure of 11 Pa, and radio frequency (13.56 MHz) power of 2 W, for electrode diameters of 100 mm and the separation of 40 mm. Taking this into account, we determined the atomic hydrogen density in the plasma for the condition to be (5±2) × 10¹⁷ m^-3.