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Comparison of Phase Diagrams for vhf and rf Plasma-Enhanced Chemical Vapor Deposition of Si:H Films

Published online by Cambridge University Press:  21 March 2011

G.M. Ferreira ,
A.S. Ferlauto ,
J.M. Pearce ,
C.R. Wronski ,
C. Ross  and
R.W. Collins
G.M. Ferreira
Affiliation:
Center for Thin Film Devices, Penn State University, University Park, PA 16802, USA;
A.S. Ferlauto
Affiliation:
Center for Thin Film Devices, Penn State University, University Park, PA 16802, USA;
J.M. Pearce
Affiliation:
Center for Thin Film Devices, Penn State University, University Park, PA 16802, USA;
C.R. Wronski
Affiliation:
Center for Thin Film Devices, Penn State University, University Park, PA 16802, USA;
C. Ross
Affiliation:
2 Institut für Photovoltaik, Forschungszentrum Jülich, 52425 Jülich, Germany;
R.W. Collins
Affiliation:
Department of Physics and Astronomy, The University of Toledo, Toledo, OH 43606, USA.
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Abstract

Deposition phase diagrams are convenient for categorizing the evolution of the surface microstructure and phase with accumulated thickness for hydrogenated silicon (Si:H) films during plasma-enhanced chemical vapor deposition (PECVD). They can also be used to assess the electronic quality and device suitability of Si:H, based on previous correlations. In this study, phase diagrams have been applied in a comparison of Si:H PECVD using two different plasma excitation frequencies (rf: 13.56 MHz; and vhf: 60 MHz). Smooth crystalline Si (c-Si) wafer substrates have been used to obtain the surface roughness evolution with maximum sensitivity in the amorphous silicon (a-Si:H) growth regime. This study has shown that under all explored conditions of plasma power, frequency, and gas pressure, yielding deposition rates of 0.5-20 Å/s, a-Si:H exhibits improved microstructural characteristics with increasing H2-to-SiH4 flow ratio R right up to the amorphous-to-(mixed-phase microcrystalline) [a→(a+μc)] boundary of the phase diagram. For depositions at R values much lower than the a→(a+μc) transition for a thick film, vhf PECVD can provide a significant improvement in microstructural evolution over rf PECVD, for a given deposition rate. For optimum R just below the a→(a+μc) transition, however, vhf and rf a-Si:H films exhibit remarkably similar structural evolution for a given rate.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 808: Symposium A – Amorphous and Nanocrystaline Silicon Science and Technology-2004 , 2004 , A5.2
Copyright
Copyright © Materials Research Society 2004

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References

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