Excimer laser crystallized silicon films have been studied as a function of
the number of laser shots, and the influence of the use of such
polycrystalline films in thin film transistors (TFTs) has also been
investigated. It is found that electron Mobility, one of the most important
of all TFT characteristics, increases monotonically with the number of
irradiations, with maximum mobility being obtained at about 20 shots. This
result is not due to grain size, since transmission electron microscopy
indicates that the number of laser shots does not affect grain size in
polycrystalline silicon films. Raman studies and TFT carrier transport
analysis, on the other hand, suggest that this increase in electron mobility
may be explained by the decrease in grain boundary defects and defects
inside grains.