Microstructural control of amorphous silicon films crystallized using an excimer laser

The results of experiments using two techniques for microstructural control of laser-annealed silicon thin films on SiO₂ substrates are given. In the first set, photolithographically fabricated single-crystal silicon seed wafers in intimate contact with the silicon films are used to show that it is possible to control nucleation location during laser annealing. Laser energy density was varied from 250-450 mJ/cm² and the resultant microstructure was characterized using transmission electron microscopy (TEM). It was found to consist of four distinct regions. Areas adjacent to the seed consisted of grains with dimensions approximately 0.5 μm. The surrounding region consisted of larger (approximately 1 μm) rectangular grains. A third region was observed sporadically and consisted of large (approximately 1.5 μm) rectangular grains adjacent to the latter region. The fourth region occurred several microns away from the contact and consisted of a fine-grained microstructure. In the second set, fine mesh (19 μm) masks were used to selectively crystallize regions in laser-annealed films. The resultant microstructure was characterized using TEM and was found to consist of large (approximately 1.5 μm) edge grains with smaller (approximately 0.8 μm) grains just inside of the edge grains. A theoretical discussion is presented to explain the observed phenomena in both experiment sets.