Defined crystallization of amorphous-silicon films using contact printing

Patterned Ni layers are printed on amorphous-silicon $\mathrm{(a-}\mathrm{Si})$ films and, during this printing, the metal patterns induce lateral crystallization of the precursor $\mathrm{a-}\mathrm{Si}$ layer. The printing process consists of simultaneously pressing the Ni printing plate to an $\mathrm{a-}\mathrm{Si}$ layer and annealing at 550 °C. Printing times of 1 and 3 h are explored. The growth rate of the Ni-induced lateral crystallization is about 8 μm/h in this process. After this printing, Raman spectra show that the resulting polycrystalline-silicon (poly-Si) regions have the characteristic transverse-optical 519 cm⁻¹ phonon peak typical of crystalline silicon. The nonprinted, noncrystallized $\mathrm{a-}\mathrm{Si}$ areas have the Raman signature of $\mathrm{a-}\mathrm{Si};$ i.e., they do not have any peak. The resulting laterally crystallized Si area shows a morphological texture (i.e., a strip-like morphology) originating from the printed Ni area and growing in one direction in transmission electron microscope imaging. In terms of the selective area diffraction pattern (i.e., diffraction spot position and crystal structure), the signature of the area directly contacted by the Ni cannot be distinguished from that of the surrounding laterally crystallized silicon film. This printing approach can be used for channel crystallization/device isolation resulting in a saving of device fabrication steps.