Scanning multishot irradiations on a large-area glass substrate for Xe-Arc flash lamp crystallization of amorphous silicon thin-film

Abstract

Applying an in-line Xe-arc flash lamp annealing (FLA) process for the fabrication of low-temperature polycrystalline silicon (LTPS) on a large-scale glass substrate, this study investigates the effects of scanning multishot irradiations on the thermo-mechanical deformation of the substrate and the microscopic phase-change of the amorphous silicon (a-Si) thin-film. A glass substrate with thin-film structures was preheated at 650 °C, exposed to sequential multiple flashes, and thus heated rapidly far beyond the glass softening temperature to achieve crystallization of a-Si. Temperature variations in the substrate were predicted by one-dimensional heat conduction model with radiation absorption, and the structural deformations were simulated through a FEM code and compared to the experimental observations. The maximum temperatures arisen in the substrate during the second or subsequent flash irradiations were substantially lower than that during the first irradiation owing to reduced absorptions of flash energies. These absorption reductions were resulted from phase-changes of silicon from amorphous to polycrystalline. Those temperatures, however, were still sufficiently high to cause a significant thermal warpage, resulting in the bathtub shape of the substrate. The critical mechanisms for the warpage were the structural shrinkage and the gravitational sagging. In addition, the microscopic structural characteristics of the LTPS fabricated by the scanning multishot FLA process were explored through optical and Raman spectroscopies, and transmission electron microscopy.