Orientation-controlled crystallization of amorphous silicon using rolled and annealed nickel tapes

Abstract

Polycrystalline silicon (poly-Si) have been gaining the importance for thin-film transistor (TFT) applications since it has a higher carrier mobility and current carrying capacity than hydrogenated amorphous silicon (a-Si:H). Among the many different methods for producing poly-Si films, silicide mediated crystallization (SMC) of amorphous silicon offers the advantage of producing large-grained poly-Si films at temperatures low enough for glass substrates while maintaining a high throughput without the need for expensive machinery. For further applications of poly-Si, the location and orientation of grains need to be controlled as well as the grain size. These issues become more critical as grains become larger, since there are fewer grains within a channel. Control of the grain orientation in poly-Si is difficult because nucleation is a stochastic process. However, if an external template for crystallization is provided, both the orientation and location of crystal grains can be controlled. In this study, we report on the results of using cold-rolled and annealed Ni tapes as a template for crystallization of a-Si:H thin films. We find that crystallization is mediated by $NiSi_2$ formation, and that all Si grains have their ＜110＞ axis oriented the same direction within just few degrees. Furthermore, nearly all of them had the same rotation about the ＜110＞ except for the presence of twins and/or type A-B formations. Despite the use of the nickel substrate, the Ni concentration within the Si film was below the detection limit of energy-dispersive x-ray spectroscopy ($10^{19} cm^{-3}$). This low-Ni contamination level is attributed to the presence of an oxide layer between the Ni substrate and the Si film. Amorphous silicon (a-Si) films deposited on oxidized silicon wafers were crystallized to a highly textured form using contact printing of rolled and annealed nickel tapes. Crystallization was achieved by first annealing the a-Si film in contact with Ni tape at...