Mechanisms of Surface Evolution during the Growth of Undoped Nanosilicon Films

Abstract

The thickness dependence of the surface roughness and the grain size of nanosilicon films, produced by low-pressure chemical vapour deposition, has been found, by using atomic force microscopy. A correlation between the surface roughness, grain size, and transformation of a film structure from the equiaxial structure into a fibrous one is established. Possible mechanisms of surface evolution are analyzed. K e y w o r d s: nanosilicon films, surface roughness, grain growth, mechanism of grain growth, atomic force microscopy.

Ellipsometric studies of nanocrystalline silicon films with the thicknesses less than 100 nm

“…Nanocrystalline silicon films were prepared by chemical vapour deposition in a reduced-pressure reactor [10]. Film deposition occurred at the substrate temperature 630C on crystalline Si substrate covered by a SiO 2 layer with the average thickness 100 nm.…”

“…In Ref. [10] it has been assumed that the corresponding grains grow basing on crystal lattice rotation, and so the film growth is accompanied by formation of stress defects (e.g., cracks of the crystal lattice). Moreover, silicon oxide clusters are not formed due to a high temperature of the substrate [30].…”

“…It is known that the physical properties of silicon films strongly depend on the conditions of their growth and internal parameters. This has stipulated their comprehensive researches in the recent decades [5][6][7][8][9][10][11][12][13]. One of the most common methods for growing nanocrystalline silicon films is a chemical vapour deposition [5,14].…”

“…On the other hand, the grain size determines the electrical properties of the films, because the grain boundaries are potential barriers for carriers [1,3]. The recent AFM-studies [10] have demonstrated that the grain size depends on the thickness of deposited films: the films with the thicknesses less than 50 nm contain the grains with the average size 25-30 nm, while the films thicker than 50 nm contain the grains as large as 180-200 nm. This shows that, if the film thickness is less than 100 nm, some reconstruction of its internal structure occurs, thus leading to a sharp change in the nanosilicon grain size.…”

“…In addition, the spectroscopic ellipsometry allows for determining nanoscale heterogeneity in the transition layers and a surface roughness of the films [16]. According to the AFM [10] and TEM [16] studies, the surface structure depends notably on crystallinity of the film: the greater the latter, the more significant roughness is observed on its surface. Thus, the ellipsometry technique enables one to estimate the internal structure of the nanosilicon films, which is extremely important at the early stages of the film growth.…”