Comparison of Microstructure and Crystal Structure of Polycrystalline Silicon Exhibiting Varied Textures Fabricated by Microwave and Very High Frequency Plasma Enhanced Chemical Vapor Deposition and Their Transport Properties

Abstract

Micro- and crystal structures of polycrystalline silicon (poly-Si) films fabricated by low temperature (≤360°C) plasma enhanced chemical vapor deposition (PECVD) were examined. Crystal orientation could be controlled by varying the source gas ratio SiF4/H2. (220) oriented films were obtained at low gas flow rate ratios while (400) preferentially oriented films were obtained at higher SiF4/H2 ratios either by a remote-type microwave PECVD or a capacitive coupled parallel electrode very high frequency (VHF) PECVD. It was found that micro- and crystal structures were a strong function of orientation; that is, the crystal lattice in the (220) oriented film was under tensile strain and the crystalline grain had strong anisotropy of grain size. In contrast, the crystal lattice in the (400) oriented film was under compressive strain and evident anisotropy in the grain size could not be found. Furthermore, it was confirmed that the deposition of SiHn and/or SiHnFm and etching by fluorinated species and their competition played an important role in the selective growth. Fluorine-related species were also effective in growing large crystalline grains. Hall mobility of electron for (400) oriented films showed a monotonic increase with carrier density and achieved a large mobility of ∼10 cm2/Vs.