Optical absorption and emission spectroscopy studies of ammonia-containing plasmas

The chemistry of NH 3 /Ar/He plasmas was investigated, using a combination of ultraviolet (UV) optical absorption spectroscopy (OAS) and optical emission spectroscopy (OES). Absolute NH 3 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 NH 3 and secondary reactions. In this approach, small amounts of N 2 are added to the NH 3 -containing plasma, leading to an increase in the N 2 ( C 3 Π u → B 3 Π g ) emission intensity. This provides an accurate calibration factor for converting relative N 2 emission intensities into absolute number densities. The number densities of NH 3 were found to decrease with increasing power and T h , reaching >90% dissociation at 400 W and 900 K. N 2 densities increased with power and T h . The majority of dissociated NH 3 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.