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

Paper TF-ThM1
Evolution of Surface Morphology during Thin Film Growth by Hot-Wire CVD: Short-Range Smoothening and Long-Range Roughening

Thursday, November 18, 2004, 8:20 am, Room 303C

Session: Modeling & Fundamentals in Thin Film Deposition
Presenter: B.A. Sperling, University of Illinois at Urbana-Champaign
Authors: B.A. Sperling, University of Illinois at Urbana-Champaign
J.R. Abelson, University of Illinois at Urbana-Champaign
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During thin film growth by low-pressure chemical vapor deposition, the surface morphology evolves due to a kinetic competition between roughening, driven by self-shadowing or stochastic processes, and smoothening due to surface diffusion. When a very smooth substrate is used, the surface roughness increases only very slowly. A more powerful way to study the surface dynamics is to prepare a substrate with an intentional roughness of ~ 5 nm, then deposit film under "high quality" conditions that favor smoothness, and measure the rapid decrease in surface roughness with increasing film thickness. We use this procedure to study the growth of hydrogenated amorphous silicon by hot-wire chemical vapor deposition. Using in situ spectroscopic ellipsometry, we observe that the surface roughness of the film decreases as it grows. However, post-deposition atomic force microscopy reveals a linear increase in the roughness. We resolve this apparent discrepancy by analyzing the power spectrum densities of the atomic force images, which indicate that the growth surface is experiencing both short-range smoothening and long-range (global) roughening. The ellipsometry data agree semi-quantitatively with the short-range atomic force microscopy data, but due to light scattering they exclude information about the long-range components of roughness. The slope of the power spectrum density (short-range scaling) indicates that surface diffusion is the dominant smoothening mechanism, while the linear increase in roughness is consistent with columnar growth caused by self-shadowing. We also discuss possible means to interpret the rate of smoothening data in terms of the adspecies surface diffusivity during hot-wire chemical vapor deposition.