Pulsed laser annealing of silicon thin films in application to thin film transistors

The formation and growth mechanism of poly silicon (poly-Si) grains in thin films via laser annealing of amorphous silicon (a-Si) thin films are studied and a novel process is developed that produces location-controlled and laterally grown p-Si grains. To understand the recrystallization mechanism, the temperature history and liquid-solid interface motion during excimer laser annealing of 50 nm-thick amorphous and polysilicon films on fused quartz substrates are intensively investigated by in-situ time-resolved thermal emission measurements, optical reflectance and transmittance measurements at visible and near-IR wavelengths, combined with electrical conductance measurement. Based on the knowledge revealed via the diagnostics, a new double laser beam crystallization method is devised, which uses a temporally modulated Ar + laser for the purpose of preheating the a-Si film and controlling the cooling prior to the excimer laser pulse. This new method is able to produce poly-Si grains grown upto 30 μm at the desired position.; It is found that the temperature response, melt propagation and evolution of the recrystallization process are fundamentally different in the partial melting and the complete melting regimes.; Evidence of spontaneous nucleation occurring in the l-Si for laser fluences that are high enough to melt a-Si films completely is revealed through the comparison of optical models to the experimental results. Two optical models are built for melting and solidification.; The thermal conductivity of a-Si thin films is determined by non-intrusive, in-situ optical transmission measurement. The temperature dependence of the film complex refractive index is measured by spectroscopic ellipsometry. The acquired transmission signal is fitted with predictions obtained by coupling conductive heat transfer with multilayer thin film optics. The results are in excellent agreement with the 3ω method.; A new double laser recrystallization technique is developed using a temporally modulated continuous wave (CW) Ar+ laser in conjunction with a superposed nanosecond laser pulse to produce ultra-large lateral grain growth at the irradiated spot. This innovative method readily produces poly-Si grains grown up to 30 μm at the desired position without dependence on the laser fluence of the nanosecond pulsed laser. To clarify the grain growth mechanism, numerical calculation is carried out. The lateral temperature isotherms established across the molten pool in the preheated a-Si films promote large lateral growth. (Abstract shortened by UMI.)...