Optical absorption and emission spectroscopy studies of ammonia-containing plasmas

The chemistry of NH3/Ar/He plasmas was investigated, using a combination of ultraviolet (UV) optical absorption spectroscopy (OAS) and optical emission spectroscopy (OES). Absolute NH3 number densities in 1 Torr plasmas were measured by OAS as a function of inductively coupled plasma power and substrate heater temperature (T-h). OES and actinometry were used to determine semi-quantitative H-atom density. A 'self-actinometry' method was introduced to measure the absolute number density of N-2 that formed following the dissociation of NH3 and secondary reactions. In this approach, small amounts of N-2 are added to the NH3-containing plasma, leading to an increase in the N-2(C (3)Pi(u) -> B (3)Pi(g)) emission intensity. This provides an accurate calibration factor for converting relative N-2 emission intensities into absolute number densities. The number densities of NH3 were found to decrease with increasing power and T-h, reaching >90% dissociation at 400W and 900 K. N-2 densities increased with power and T-h. The majority of dissociated NH3 was converted to N-2 (i.e. the total nitrogen content was conserved in the sum of these two species). The major hydrogen-containing species appeared to be H-2; however, a substantial amount of H-atoms (comparable to H-2) was present at the highest powers.