Laser crystallization and structural characterization of hydrogenated amorphous silicon thin films

The influence of hydrogen and film thickness on the excimer laser-induced crystallization of plasma-enhanced chemical-vapor deposition-grown hydrogenated amorphous silicon thin films has been studied. Films with hydrogen concentrations varying from 1 to 10 at. % have been crystallized using short pulses from a XeCl excimer laser, at fluences sufficient to induce melting throughout the thickness of the films. Dehydrogenation prior to laser exposure was necessary only for films having initial hydrogen concentrations larger than 5 at. %. The structural properties of the laser-crystallized materials were studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The AFM measurements revealed that films requiring no dehydrogenation are smoother after laser crystallization than those requiring laser dehydrogenation, and that the roughness of these films increases as a function of film thickness, although it could be reduced by multiple laser exposure. Smoother films (root-mean-square roughness ∼4.1 nm) were obtained by melting only the near-surface region of the film after the initial full melt exposure. TEM revealed that the laser-crystallized films consist of grains with sizes that are comparable to the film thickness.