AVS 50th International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS1-ThM

Paper PS1-ThM7
Temperature Dependence of the SiH@sub 3@ Surface Reactivity During Plasma Deposition of a-Si:H Studied by Time-resolved CRDS

Thursday, November 6, 2003, 10:20 am, Room 314

Session: Plasma-Surface Interactions: Deposition
Presenter: J.P.M. Hoefnagels, Eindhoven University of Technology, The Netherlands
Authors: J.P.M. Hoefnagels, Eindhoven University of Technology, The Netherlands
Y. Barrell, Eindhoven University of Technology, The Netherlands
M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands
W.M.M. Kessels, Eindhoven University of Technology, The Netherlands
Correspondent: Click to Email
The surface reactivity of SiH@sub 3@ - the dominant radical during deposition of hydrogenated amorphous silicon (a-Si:H) from SiH@sub 4@ plasmas - has been investigated to obtain information on the elemental surface reactions during a-Si:H film growth. To do so, we have measured the surface reaction probability @beta@ of SiH@sub 3@ for substrate temperatures in the range of 50-450 °C by means of the novel time-resolved cavity ringdown spectroscopy (@tau@-CRDS) method. In this method, the highly-sensitive CRDS absorption technique is used to map the temporal decay of the SiH@sub 3@ radical density (probed at the Ã@super 2@A@sub 1@'<-@td X@@super 2@A@sub 1@ transition) after a minor periodic modulation of the density during regular plasma operation. From measurements of the SiH@sub 3@ loss time versus the SiH@sub 4@ partial pressure, it has been verified that SiH@sub 3@ is not lost by gas phase reactions, as is, e.g., the case for the Si radical. The surface reaction probability of SiH@sub 3@ has been deduced for different substrate temperatures from the pressure dependence of the SiH@sub 3@ loss time using information on the gas temperature and the diffusion of SiH@sub 3@ towards the surface. The gas temperature - determined from Doppler broadening of Si absorption lines - is ~1500 K and is unaffected by the substrate temperature. This procedure has revealed that the surface reaction probability of SiH@sub 3@ is independent of the substrate temperature with a value of @beta@=0.30±0.03. For comparison, the surface reaction probability of Si has been determined for 200 °C and is very close to unity (0.95<@beta@@<=@1). These observations will be discussed in terms of the contribution of different plasma radicals to film growth and the possible SiH@sub 3@ surface reactions taking place. The results suggest a two-reaction step growth mechanism for a-Si:H with a temperature-independent abstraction reaction of H from the surface as the rate-limiting step.