Comparison of excimer laser recrystallized prepatterned and unpatterned silicon films on SiO2

The laser recrystallization of unpatterned and prepatterned silicon films on SiO2 is compared. For the prepatterned films, multiple-pulse laser irradiation at certain energy densities produces three well defined zones containing different microstructure. Two of these zones appear as bands along the edges of the prepatterned islands. The first zone, or “chill zone,’’ is found at the outer edge of the island, and consists of an ∼250-nm-wide band of heterogeneously nucleated fine grains. The second zone, or “columnar zone,’’ is found next to the chill zone, and is made up of large elongated grains, measuring about 1.5×0.5 μm, with their boundaries running perpendicular to the island edges. Finally, the third zone, or “equiaxed zone,’’ includes the remainder of the prepatterned island, and has a grain microstructure identical to the recrystallized unpatterned films. The creation and identification of these three zones for laser irradiated prepatterned Si films is presented. The laser conditions that create these zones, and the recrystallization mechanisms and resulting microstructure of each zone are presented in detail.