Polycrystalline silicon, a molecular dynamics study: I. Deposition and growth modes

Abstract

Polycrystalline silicon (poly-Si) significantly expands the properties of the ICT miracle material, silicon (Si). Depending on the grain size and shape as well as the grain boundary structure, the properties of poly-Si exceed what single crystal (c-Si) and amorphous (a-Si) silicon can offer, especially for radio frequency (RF) applications in microelectronics. Due to its wide range of applications and, on the one hand, its theoretically and technologically challenging microstructure, poly-Si research is the most timely. In this report, we describe how we simulate and analyse the phenomena and mechanisms that control the effect of poly-Si deposition parameters on the structure of the deposited poly-Si films using classical molecular dynamics simulations. The grain shape and size, degree of crystallinity, grain boundary structure and the stress of poly-Si films are determined depending on the growth temperature, temperature distribution in the growing film, deposition flux, flux variation and the energy transferred to the film surface due to the deposition flux.

The main results include: (i) the dependence of the crystallinity profile of the deposited poly-Si films on the stress, temperature and the different parameters of the deposition flux, (ii) growth modes at the early stages of the deposition, (iii) interaction and stability of seed crystallites at the early stage of the deposition of poly-Si films and the transition from the isolated crystallite growth to the poly-Si growth, (iv) interplay of the temperature, crystallinity, crystal shape and heath conductivity of different Si phases, (v) four different stages of crystallite growth are described: nucleation, growth, disappearance and retardation.

Polycrystalline silicon, a molecular dynamics study: II. Grains, grain boundaries and their structure

“…The image is repeated twice in both directions for better visualisation of the side regions of the simulation cell. This crosssection of the initial growth stage can be compared to the SEM image of the surface of a thick poly-Si film shown in [8]. There is a clear difference between these two cross-sections.…”

“…The reduction of loss, crosstalk, and nonlinearity depends largely on the detailed atomic structure of the grain boundaries, which in turn depends on the poly-Si growth parameters and post-treatments [7]. The present study is the second part of a series of studies of poly-Si (Part I [8] deals with the deposition of poly-Si).…”

“…The poly-Si films analysed in the present work have been produced in our previous work [8] using the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) molecular dynamics simulator [17]. In these simulations, poly-Si was grown on top of amorphic silicon by depositing silicon atoms.…”

“…The methods used in the study are presented in section 2. In section 3 we analyse the grain and grain boundary structures of the poly-Si films produced by the molecular dynamics technique [8]. Then we study the grain orientation distribution, the distribution of the thickness of the grain boundaries, and the effects of deposition temperature and post-annealing on them.…”