AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM2
Surface Interaction of SiH@sub 3@ Radicals with Amorphous Silicon: Temperature Dependence of the SiH@sub 3@ Surface Reactivity and the Surface Hydride Composition

Wednesday, November 5, 2003, 8:40 am, Room 328

Session: Adsorption on Semiconductor Surfaces
Presenter: W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
Authors: W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
J.P.M. Hoefnagels, Eindhoven University of Technology, The Netherlands
P.J. Van den Oever, Eindhoven University of Technology, The Netherlands
Y. Barrell, Eindhoven University of Technology, The Netherlands
A.H.M. Smets, Eindhoven University of Technology, The Netherlands
M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
The growth of hydrogenated amorphous silicon (a-Si:H) thin films from SiH@sub 4@ plasmas is expected to be dominated by SiH@sub 3@ radicals created in the plasma. To obtain insight into the surface reactions of SiH@sub 3@ on the a-Si:H surface, the surface reaction probability of SiH@sub 3@ has been determined by time-resolved cavity ringdown spectroscopy. The experiments have been carried out under nearly pure SiH@sub 3@ conditions for substrate temperatures between 50-450 °C. It has been found that the surface reaction probability of SiH@sub 3@ is 0.30±0.03 independent of the substrate temperature. Information about the chemical state of the a-Si:H surface in terms of surface silicon hydrides has been determined by in situ attenuated total reflection infrared spectroscopy combined with Ar-ion induced desorption experiments. These experiments - carried out in the same temperature range - have revealed that the a-Si:H surface composition changes drastically with increasing substrate temperature from a -SiH@sub 3@ covered surface at low temperatures to a -SiH@sub 2@ and a -SiH covered surface at higher temperatures. From the combination of the experimental results and ab initio calculations and molecular dynamics simulations in the literature, it is concluded that a-Si:H film growth takes place by a two-step reaction mechanism of SiH@sub 3@ in which H abstraction from the surface by SiH@sub 3@ in an Eley-Rideal reaction is the rate-limiting step. This abstraction reaction, which requires nearly zero activation energy, is unaffected by the changing surface silicon-hydride composition and leads to temperature independent growth site creation. SiH@sub 3@ radicals can subsequently stick on the dangling bonds created. Furthermore, some preliminary ideas on an (associated) surface diffusion mechanism will be discussed on the basis of the surface roughness evolution of a-Si:H at different temperatures.