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P: Plasmaphysik
P 11: Plasma Wall Interaction
P 11.2: Talk
Wednesday, March 19, 2003, 11:50–12:10, FO1
Time-resolved cavity ringdown spectroscopic study of the surface reactivity of SiH3 versus substrate temperature for plasma deposition of a-Si:H — •Johan Hoefnagels, Yolanda Barrell, Alquin Stevens, Erwin Kessels, and Richard van de Sanden — Center for Plasma Physics and Radiation Technology, Department of Applied Physics, Eindhoven University of Technology, The Netherlands
Essential for the understanding of the growth mechanism during plasma deposition, is a detailed understanding of the surface processes during film growth. In case of plasma deposition of amorphous silicon (a-Si:H) from SiH4 plasmas it is found that the growth is dominated by SiH3 radicals and that the surface composition changes drastically with increasing substrate temperature Tsub. Therefore, to gain insight in the growth mechanism the SiH3 surface reaction probability β SiH3 has been determined as a function of Tsub by means of the novel time-resolved cavity ringdown spectroscopy (τ-CRDS). In this technique, the highly sensitive CRDS method is used to map the temporal decay of an increased radical density produced by a minor periodic modulation to the applied plasma power during regular a-Si:H deposition. The temporal decay depends on the loss due to diffusion to and reaction at the a-Si:H surface, thus yielding β SiH3.
Remarkably, the surface reaction probability of SiH3 is independent of Tsub (β SiH3=0.30±0.03). Moreover, combination with Si growth flux measurements yields that the SiH3 sticking probability is also independent of Tsub. These results in addition to literature findings have led to a 2-reaction step growth mechanism, which will be discussed.