AVS 51st International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Paper TF-ThM3
Substrate Temperature Dependence of the Roughness Evolution of Hot-wire Deposited a-Si:H Studied by Real-Time Spectroscopic Ellipsometry and Atomic Force Microscopy

Thursday, November 18, 2004, 9:00 am, Room 303C

Session: Modeling & Fundamentals in Thin Film Deposition
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
E. Langereis, Eindhoven University of Technology, The Netherlands
M.C.M. van de Sanden, Eindhoven University of Technology, The Netherlands
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The growth process of hydrogenated amorphous silicon (a-Si:H) by hot-wire CVD is studied by analyzing the surface roughness evolution during film growth for different substrate temperatures. This analysis gives information on aspects such as nucleation and initial film growth, surface roughening and smoothening, and surface diffusion mechanisms. Purely amorphous films have therefore been deposited at low deposition rates while monitoring the growth by real time spectroscopic ellipsometry for temperatures between 70 and 450 @degree@C. The thickness of the surface roughness is deduced from a two-layer optical model and analyzed as a function of the film thickness. Furthermore, the surface roughness of the as-deposited films has also been analyzed by atomic force microscopy (AFM) yielding information about the lateral scaling of the roughness. The initial film roughness is identical for all substrate temperatures indicating a similar nucleation behavior at the different temperatures. The position of the amorphous-to-amorphous roughening transition is observed within the film thickness range of 10-20 nm while an optimum is found for 250 @degree@C. The final surface roughness at a film thickness of 200 nm decreases up to substrate temperatures of 250 @degree@C after which the surface roughness remains fairly constant. The growth exponent @beta@ deduced from the roughness evolution as a function of deposition time, however, decreases for increasing temperature from ~0.20 at 70 @degree@C to ~0.05 at 450 @degree@C in agreement with the temperature dependence of the roughness exponent @alpha@ deduced from the AFM measurements. This suggests a thermally activated surface diffusion mechanism which will be discussed in detail and the relation between the surface roughness evolution and the a-Si:H film properties will be addressed.