Evolution of microstructure and phase in amorphous, protocrystalline, and microcrystalline silicon studied by real time spectroscopic ellipsometry

Authors

R. W. Collins, Pennsylvania State University
A. S. Ferlauto, Pennsylvania State University
G. M. Ferreira, Pennsylvania State University
Chi Chen, Pennsylvania State University
Joohyun Koh, Pennsylvania State University
R. J. Koval, Pennsylvania State University
Yeeheng Lee, Pennsylvania State University
J. M. Pearce, Pennsylvania State UniversityFollow
C. R. Wronski, Pennsylvania State University

Document Type

Article

Publication Date

7-1-2003

Volume

78

Issue

1-4

Journal

Solar Energy Materials and Solar Cells

First Page

143

URL with Digital Object Identifier

10.1016/S0927-0248(02)00436-1

Last Page

180

Abstract

Real time spectroscopic ellipsometry has been applied to develop deposition phase diagrams that can guide the fabrication of hydrogenated silicon (Si:H) thin films at low temperatures (< 300°C) for highest performance electronic devices such as solar cells. The simplest phase diagrams incorporate a single transition from the amorphous growth regime to the mixed-phase (amorphous + microcrystalline) growth regime versus accumulated film thickness [the a → (a + μc) transition]. These phase diagrams have shown that optimization of amorphous silicon (a-Si:H) intrinsic layers by RF plasma-enhanced chemical vapor deposition (PECVD) at low rates is achieved using the maximum possible flow ratio of H2 to SiH4 that can be sustained while avoiding the a → (a + μc) transition. More recent studies have suggested that a similar strategy is appropriate for optimization of p-type Si:H thin films. The simple phase diagrams can be extended to include in addition the thickness at which a roughening transition is detected in the amorphous film growth regime. It is proposed that optimization of a-Si:H in higher rate RF PECVD processes further requires the maximum possible thickness onset for this roughening transition. © 2002 Elsevier Science B.V. All rights reserved.