Crystal grain nucleation in amorphous silicon

Abstract

The solid phase crystallization of chemical vapor deposited amorphous silicon films onto oxidized silicon wafers, induced either by thermal annealing or by ion beam irradiation at high substrate temperatures, has been extensively developed and it is reviewed here. We report and discuss a large variety of processing conditions. The structural and thermodynamical properties of the starting phase are emphasized. The morphological evolution of the amorphous towards the polycrystalline phase is investigated by transmission electron microscopy and it is interpreted in terms of a physical model containing few free parameters related to the thermodynamical properties of amorphous silicon and to the kinetical mechanisms of crystal grain growth. A direct extension of this model explains also the data concerning the ion-assisted crystal grain nucleation.

Metal-Induced Crystallization

“…On increasing the annealing temperature to 400 and 500 °C, there is further increase in the crystallite size of Si while crystallite size of the Sn phase is invariant at zero. This behavior is very similar to that observed in the case of Al induced crystallization (AIC) of a-Si (McCaldin & Sanku, 1971;Zener,1949;Spinella et al,1998) with one very crucial difference. No peaks corresponding to crystalline Sn are observed on annealing the films unlike the AIC case.…”

“…At this point, the possibility of new nuclei formation decreases. This type of crystallization pattern, where isolated grains start to interfere at an early stage of the process, is different to solid-phase crystallization of amorphous silicon (Spinella et al, 1998).…”

From amorphous to crystalline silicon nanoclusters: structural effects on exciton properties

“…As deduced from the present XAS data, the Si-ncls at this stage remain essentially amorphous and their overall volume does not increase considerably. This is interesting, as the crystallization temperature of amorphous Si is known to be significantly lower (about 500 • C) [28]. High crystallization temperatures have been observed before in Si-ncls embedded in amorphous oxides [2,3] and it is tempting to attribute this effect to the influence of the surrounding amorphous oxide network.…”

“…It is interesting to note that at 1000 • C partial crystallization is observed by Raman [21] and detected also by XRD measurements [3]. In fact, it is known that during the crystallization of bulk amorphous Si Si-dbs annihilate [28]. There is no apparent reason to assume that db annihilation would not also occur upon crystallization of a-Si-ncls embedded in the Si oxide.…”

Aluminum induced in situ crystallization of amorphous SiC

“…16 The difference in the Gibbs free energy of a-Si and c-Si is assumed as the driving force. 17 Similar mechanism has been proposed to explain Al-induced crystallization of a-SiC using the layer change method, 9,10 in which Al atoms diffuse into a-SiC during the postannealing and crystallize it but this mechanism is not applicable to the in situ crystallization caused by the cosupply of Al-, Si-, and C-containing precursors during the LPCVD process. The most similar process was in the case of amorphous Ge ͑a-Ge͒, where crystallization of a-Ge was achieved by the cosupply of Al and Ge at a fixed deposition temperature by rf sputtering.…”