Grain alignment in thin silicon films by impurity controlled grain growth

The high potential of the out-of-plane grain alignment, especially for the improvement of the device characteristics that are connected to the quality of the Si-SiO2 interface, has been investigated since the 1980's.
The growth of aligned grains during the crystallization of amorphous silicon thin films strongly influences the electrical properties of thin film silicon based devices.
We investigated the influence of the phosphorus concentration on the surface energy driven {111} grain growth during low-temperature crystallization of 100 nm thick silicon films.
Amorphous silicon thin films were deposited by electron beam evaporation on an oxidized silicon wafer. Afterwards the films were implanted either by beam-line implantation or plasma immersion ion implantation (PIII). Finally the films were crystallized by furnace annealing at 600 °C in N2 atmosphere.
The samples were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Cross-sectional and plan-view TEM investigations demonstrate that the lateral grain size increases continuously with the impurity concentration. XRD investigations identified an optimal impurity concentration of ~10^20 ions/cm^3, i.e. a maximum of the integrated intensity and a minimum FWHM of the rocking curve of the (111) reflection.
Contrary to the seed selection through ion channeling technique, our method provides a grain alignment independent to the presence of pre-aligned seeds in the as-implanted film.