| Lasers are effective tools in material processing which benefits from highly concentrated photon energy/power. Laser annealing of Si structures for crystallization and dopant activation is the focus of this thesis.; Ultra-large-grained (up to 10 mum in lateral dimension) polycrystalline silicon films have been formed from 50-nm-thick amorphous silicon films by the double laser crystallization (DoubleLC) method. In-situ images were captured to monitor transient melting and solidification in order to understand the process induced by steep laser intensity gradients. Pre-patterned silicon films were also crystallized by DoubleLC and showed effects of local temperature profile modification by the shape of the island. Films as thin as 20 nm can be crystallized by DoubleLC, although higher laser fluence was required. AFM (atomic force microscope) images showed RMS surface roughness less than 3 nm. The highly localized crystal growth and well-defined crystal orientation allowed precise placement of TFT channels within large grains.; Design and fabrication processes of thin film transistors on 50nm poly-Si films were then described. Amorphous silicon films were crystallized by three different crystallization methods, i.e., double laser crystallization, excimer laser crystallization and solid phase crystallization. Thin film transistors (TFTs) were then built on crystallized Si films and the micro-fabrication processes were described in detail. The contact resistance problem in the first trial of TFT fabrication was discussed and solution has been found. The performance of TFTs on poly-Si films by DoubleLC and ELC has been compared and it was shown that TFTs by DoubleLC had much better performance than those by ELC. For the DoubleLC TFTs (at Vds = 1V), VT = 0.2 V, Ion/Ioff = 108 and mueff = 124 cm2/V·sec. For the ELC TFTs, VT = 7.9 V, Ion/Ioff = 10 4 and mueff = 43cm2/ V·sec.; Non-melt laser annealing (NMLA) of boron-implanted SOI wafers at 16keV with the dose of 1015 cm-2 was also studied. It was shown that the heavily doped top silicon layer of SOI wafer was effectively activated by multiple laser pulses at low fluence level. The measured sheet resistance is only 124 O/square (for thickness of 50 nm Si), which is comparable to the results by Rapid Thermal Annealing (RTA) method. No diffusion of boron profile was observed in SIMS results, and no evidence of melting was detected. Numerical simulation and thermal analysis indicated the temperature evolution and distribution in SOI wafer during and after the laser annealing pulse. (Abstract shortened by UMI.)... |
