Some observations on the amorphous to crystalline transformation in silicon

Abstract

An atomistic model for the transformation of amorphous (α) to crystalline silicon films while in contact with a crystalline substrate is presented. The atomic structure of the {100}, {110}, and {111} surfaces is examined and related to the observed interface migration rates. The assumption that for an atom to attach successfully to the crystal it must complete at least two undistorted bonds, leads to the prediction that the {100} amorphous/crystalline interface should advance fastest and the {111} slowest. The origin of crystal defects is discussed in terms of the atomistic recrystallization mechanism. Microtwins are found to be a logical consequence of crystallization on the {111} surfaces but are not expected to form on any other interface. Once microtwins are formed they can increase the recrystallization rate of a {111} surface. This phenomenon is both described in the model and experimentally observed.

Molecular dynamics simulation of the regrowth of nanometric multigate Si devices

“…Now both crystallization fronts are {100} planes. Growth along the h100i direction is fastest 32 and it shows few defects in the stacking sequence because the basic crystallization event involves only one atom that forms two bonds with the underlying crystal phase (see Fig. 5(c)), so no rotation or mismatch is possible in this case.…”

“…It is well known that regrowth along the h111i direction is slower that in h100i and shows frequent defects in the stacking sequence. 31,32 This is due to the fact that atoms in the {111} a/c interface have only one bond with the crystalline phase (see Fig. 5(a)).…”

“…Recrystallization along the h110i direction is faster that in h111i and does not show defects in the stacking sequence as frequently. 31,32 Nevertheless, although the bottom a/c interface has advanced 6 nms with respect to its original position, some defective structures do form beyond that distance. This is because, in order to advance the a/c interface along the diagonal h110i direction, two atoms in the amorphous phase have to bond together and with two atoms in the crystal phase as indicated in Fig.…”

Atomistic modeling of Ge damage accumulation, amorphization and solid phase epitaxial regrowth

“…The available possible positions are calculated and stored in a table where each of them will have a different rate to recrystallize. It is easy to appreciate that, following Drosd and Washburn (1982): a) {100} sites need only one atom to incorporate to the c-phase in order to grow; b) the {110} family needs two atoms per event; c) and d) {111} sites need three new crystalline atoms to fulfill the next growing step.…”

“…The very next amorphous Ge layer to the α/c interface is progressively crystallized when the number of atoms with two undistorted bonds, Drosd and Washburn (1982) is the one needed by the planar orientation. These numbers are 1, 2 and 3 for {100}, {011}, and {111} orientations, respectively.…”