Laser crystallization and structural characterization of hydrogenated amorphous silicon thin films

The influence of hydrogen and film thickness on the excimer laser-induced c rystallization of plasma-enhanced chemical-vapor deposition-grown hydrogena ted amorphous silicon thin films has been studied. Films with hydrogen conc entrations varying from 1 to 10 at. % have been crystallized using short pu lses from a XeCl excimer laser, at fluences sufficient to induce melting th roughout the thickness of the films. Dehydrogenation prior to laser exposur e was necessary only for films having initial hydrogen concentrations large r than 5 at. %. The structural properties of the laser-crystallized materia ls were studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The AFM measurements revealed that films requiring no deh ydrogenation 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 similar to 4.1 nm) we re obtained by melting only the near-surface region of the film after the i nitial full melt exposure. TEM revealed that the laser-crystallized films c onsist of grains with sizes that are comparable to the film thickness. (C) 1999 American Institute of Physics. [S0021-8979(99)07811-1].