Surface Interactions of NH2 Radicals in NH3 Plasmas

Using the imaging of radicals interacting with surfaces (IRIS) technique, the scattering of NH 2 on a variety of substrates has been measured during NH 3, NH 3 /H 2, and NH 3 /SiH 4 plasma processing. In most cases, NH 2 surface scattering was greater than unity for 300 K substrates, suggesting that NH 2 is produced through surface reactions. Removal of the charged species from the plasma molecular beam results in a significant decrease in scattered NH 2 signal. We have also measured velocity distributions and translational temperatures for NH 2 radicals scattering from 300 K substrates. Monte Carlo simulation methods were used to model spatially and temporally resolved profiles of scattered molecules. The model assumes an initial Gaussian distribution for radicals across the laser beam and calculates time-dependent changes in the profiles using Maxwell−Boltzmann distributions. For NH 2 radicals scattering from a 300 K Si substrate, the translational temperature, ϑ Tsc, is 400 ± 30 K, significantly higher than the substrate temperature. Removal of the charged species from the plasma molecular beam results in a decrease in translational temperature for scattered NH 2 molecules, ϑ Tsc = 300 ± 30 K. This suggests ions are important in surface production of NH 2 and in the translational temperature of the scattered radicals.