Mechanisms and energy transfer for surface generation of NH2 during NH3 plasma processing of metal and polymer substrates

The interactions of NH2 radicals with different substrate materials during NH3 plasma processing were investigated using the imaging of radicals interacting with surfaces (IRIS) technique. NH2 scatter coefficients, S, were obtained as a function of applied rf power for polyimide, poly(tetrafluoroethylene) (PTFE), platinum, copper, and silicon substrates. For most experimental conditions, S greater than or equal to 1, indicating that NH2 surface generation occurs at the plasma-substrate interface. Information on energy transfer between NH2 and the different substrates during processing was gleaned from measurements of the translational temperature for scattered NH2 molecules, Theta (Tsc), as a function of applied rf powers. NH2 radicals scattered from Pt, Cu, and Si substrates have very little dependence of Theta (Tsc) on rf power, whereas the two polymeric materials demonstrate a nearly linear increase in Theta (Tsc) With applied rf power. The change was most dramatic for polyimide substrates, where Theta (Tsc), increased by similar to 120 K between 50 and 150 W. Scattering coefficients and Theta (Tsc) values measured using a molecular beam without ions indicate that charged species serve to increase both the kinetic energy and the amount of scattered NH2 radicals. Mechanistic implications for NH3 plasma processing are drawn from both the scatter coefficient results and the energy transfer data.