Effects of Si film thickness and substrate temperature on melt duration observed in excimer laser-induced crystallization of amorphous Si thin films using in-situ transient reflectivity measurements

Abstract

The influences of Si film thickness and substrate temperature on the melt duration of molten Si during excimer laser crystallization (ELC) have been theoretically and experimentally investigated. The melt duration of molten Si significantly changed with the increase in Si film thickness, especially at higher substrate temperature. In-situ time-resolved (∼ 1 ns) optical reflectivity measurements revealed that the longest melt duration of 400-nm-thick amorphous silicon (a-Si) film at substrate temperature of 500 °C was 1714 ns which is 4.54 times longer than that of 90-nm-thick a-Si film. The resulting polycrystalline silicon (poly-Si) thin films were characterized using Raman spectroscopy, field-emission scanning electron microscope and atomic force microscopy. It is found that the longest melt duration of molten Si is proportional to the Si film thickness and substrate temperature for Si thin film smaller than 200 nm. On the other hand, in the thicker Si thin film (> 200 nm), the grain size of poly-Si is not proportionally affected by variation in Si film thickness and substrate temperature, which is probably related to the different recrystallization mechanisms of Si thin films of different thickness. Micro-Raman scattering measurements revealed that the crystallinity of poly-Si in the ELC region improved to reach an excellent level, very near that of the single-crystal Si by preheating the substrate during ELC.