AVS 50th International Symposium
    Thin Films Thursday Sessions
       Session TF-ThM

Invited Paper TF-ThM5
Understanding Radical-Surface Interactions in the Plasma-Assisted Deposition of Amorphous Hydrogenated Silicon

Thursday, November 6, 2003, 9:40 am, Room 329

Session: Modeling & Fundamentals in Thin Film Deposition
Presenter: S. Agarwal, Univ. of California, Santa Barbara
Authors: S. Agarwal, Univ. of California, Santa Barbara
S. Sriraman, Univ. of California, Santa Barbara
A. Takano, Fuji Electric Corp. R&D, Ltd., Japan
M.C.M. van de Sanden, Eindhoven Univ. of Tech., The Netherlands
D. Maroudas, Univ. of Massachusetts - Amherst
E.S. Aydil, Univ. of California, Santa Barbara
Correspondent: Click to Email
Hydrogenated amorphous silicon (a-Si:H) thin films grown by plasma-assisted deposition from silane-containing discharges are widely used in photovoltaic, imaging, and display devices. During plasma-assisted deposition, reactive radicals present in the discharge such as SiH@sub x@ (x = 1,2,3) and H impinge onto the substrate surface leading to film growth and H incorporation. The properties of the deposited films depend on the various reactions of radicals present in the discharge with the growth surface and, therefore, a fundamental understanding of such interactions is required for improving a-Si:H deposition techniques. We have studied radical-surface interactions in the deposition of a-Si:H thin-films through synergic use of experimental diagnostics such as in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and molecular-dynamics (MD) simulations based on the Tersoff's potential for Si. We have identified the various reactions of H and SiH@sub 3@ with a-Si:H films and determined their mechanisms and energetics. Surface H is removed by abstraction through the Eley-Rideal mechanism. Silicon is incorporated into the growing film through radical attachment to surface dangling bonds, as well as radical insertion into Si-Si surface bonds including dissociative adsorption reactions. In addition, reactions that involve radical migration on the surface are identified and analyzed. Finally, the H-induced crystallization of a-Si:H films during their post-deposition treatment by an H@sub 2@ plasma is addressed. The MD simulations show that H atoms diffuse into the a-Si:H film and insert into strained Si-Si bonds to form intermediate bridging and bond-centered H (Si-H-Si) configurations mediating the structural relaxation of the amorphous Si matrix leading to the disorder-to-order transition. The existence of bond-centered H(D) in a-Si:H films exposed to H(D) atoms was verified experimentally through IR spectroscopy.