Location control of Si thin-film grain using Ni imprint and excimer laser annealing

A novel method of locating Si crystal grains by combining Ni imprint and excimer laser annealing (ELA) is demonstrated. Ni imprint is used for the purpose of creating Si crystal nuclei that act as the seed for the subsequent crystallization by ELA. Two Ni-imprint processes were investigated; (1) Ni imprint at the SiO₂ substrate surface followed by the deposition of amorphous Si (a-Si), and (2) a-Si deposition on the SiO₂ substrate followed by Ni imprint at the a-Si film surface. The annealing used to form nuclei at the imprinted sites was carried out at temperatures below 450 °C. XeCl-laser-based ELA of the sample thus prepared resulted in the formation of about 2 μm sized Si grains at the imprinted sites, whereas the grain consists of several sub-grains radially grown from the center of the grain. The application of Secco's etching to the location-controlled grains formed by Ni imprint at the SiO₂ substrate delineated a cavity at the middle of the grain, whereas no cavity was observed in the grains formed by Ni imprint at the a-Si surface. Thus, Ni imprint at the a-Si surface produces higher-quality Si grains than Ni imprint at the SiO₂ substrate surface. Details of the experimental conditions used to create the location-controlled grains are described.