Crystallization of polycrystalline silicon thin film by excimer laser annealing

Abstract

Enhancing the crystallization of silicon thin film is important for better performance of thin film transistor (TFT). In an attempt to achieve this goal,a fundamental study was carried out to enhance the crystallization of doped silicon thin film (STF) with various types of dopants. The dopants used in this research are copper, aluminium and germanium. Initially the amorphous silicon (a-Si) film was prepared by low pressure physical vapour deposition (PVD). The STF was annealed using a combination of two techniques. Firstly, the doped STF was annealed by conventional method using tube furnace. Secondly, annealing was done using argon fluoride (ArF) excimer laser. The microstructure of thin film was analyzed using metallurgical technique via field emission scanning electron microscope(FESEM) and atomic force microscope (AFM). In general the grain size of doped STF increased with the energy density of the excimer laser except for Si:Ge. However, the crystallization was found to decrease after exceeding the critical or super lateral growth (SLG) energy. The optimum grain size achieved by Si:Cu, Si:Al, and Si:Ge thin film were 143.2, 129.2 and 105.6 nm respectively at the corresponding SLG energy each of 345.00, 356.11, and 413.78 mJcm-2 respectively. Copper was found to be the best dopantbased on its largest grain size achievement. The enhancement of crystallization was also carried out using single heat treatment that are a conventional furnace heat treatment and directly using ELA separately. Apparently, the combination of the two techniquesoffers better performance in comparison to any single heat treatment.