Analysis of wavelength influence on a-Si crystallization processes with nanosecond laser sources

Abstract

In this work we present a detailed study of the wavelength influence in pulsed laser annealing of amorphous silicon thin films, comparing the results for material modification at different fluence regimes in the three fundamental harmonics of standard DPSS (diode pumped solid state) nanosecond laser sources, UV (355 nm), visible (532 nm) and IR (1064 nm). The crystalline fraction (% crystalline silicon) profiles resulted from irradiation of amorphous silicon thin film samples are characterized with MicroRaman techniques. A finite element numerical model (FEM) is developed in COMSOL to simulate the process. The crystalline fraction results and the local temperature evolution in the irradiated area are presented and analyzed in order to establish relevant correlation between theoretical and experimental results. For UV (355 nm) and visible (532 nm) wavelengths, the results of the numerical model are presented together with the experimental results, proving that the process can be easily predicted with an essentially physical model based on heat transport at different wavelengths and fluence regimes. The numerical model helps to establish the optimal operation fluence regime for the annealing process.