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The lattice strain in excimer laser crystallized polycrystalline Si (poly-Si) thin films reflects the grain growth induced by the laser irradiation. In this report, the measurement of the lattice strain is made by using the energy-dispersive grazingincidence X-ray diffraction with synchrotron radiation. The excimer laser crystallized poly-Si thin films show tensile lattice strain in the directions parallel to the substrate surface. The { 111 } strain increases from 2.2 x iO to 5.0 x iO when the grain size increases from 40 to 200 nm. The strain is anisotropic between the { 111 } strain and the {220} strain in the layer near the substrate interface when the grain size is small. Carrier mobility in a thin film transistor tends to increase when the strain increases and the anisotropy decreases.

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The fabrication of n+ and p+ silicon thin film by using a combination of ‘‘spin-on-glass’’ and XeCl excimer-laser doping is described. The doping can be achieved by rapid dopant atom diffusion into molten silicon from a spin-coated film containing the dopant. This technology offers the advantages of process simplicity, low processing temperature, and ultrashallow high-concentration doping. The obtained sheet resistances (2 kΩ/⧠ for n+ and 9 kΩ/⧠ for p+) are acceptable for thin-film transistors (TFTs). The energy required for doping into a thin film was less than half of that for a silicon wafer. This is mainly due to the absorption rate difference between noncrystalline and crystalline silicon. This process appears extremely promising for TFT fabrication.

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