COMPREHENSIVE INTERPRETATION OF THE PREFERRED ORIENTATION OF VAPOR-PHASE GROWN POLYCRYSTALLINE SILICON FILMS

A comprehensive interpretation of the preferred orientations (PO) of poly-Si films prepared from various vapor-phase methods is presented. Existing theories and models are examined by comparing a wide variety of experimental results of PO published so far. Preferential nucleation and the conventional concept of the surface free energy are found to apply only to a limited range of deposition parameters. On the other hand, a combination of two concepts, i.e., the microscopic geometry of growing surfaces and the surface kinetics, proves to be very important in interpreting the wide variation of PO. The concept of the microscopic geometry of the surface considers the minimum numbers of atoms and bonds required for nucleation, lateral growth, and etching that characterizes the growth ability of planes. In addition, interpretation of the deposition parameter dependencies of the PO requires the concept of surface kinetics including diffusion of precursors, hydrogen coverage, and the surface reaction time which depends on the substrate temperature and gas pressure. The combined concepts can account for most of the observed POs (mainly [100] and [110]) which depend on feed gases and the deposition parameters. Other specific growth modes such as facet growth or microtwins are considered for the [111] PO. The POs for n- and p-type doped films are different from those of undoped films, and their origin is also discussed in terms of their growth rates. (C) 1995 American Vacuum Society.