Thin-film transistors (TFTs) were fabricated on polycrystalline silicon (poly-Si) films formed by position-controlled largegrain growth technology using an excimer laser. The field-effect mobility, on-off transition slope, and threshold voltage were 914 cm 2 V À1 s À1 , 93 mV/decade, and 0.58 V for the n-channel device, and 254 cm 2 V À1 s À1 , 122 mV/decade, and À0:43 V for the p-channel device, respectively. These values indicate that TFTs had an ultrahigh performance comparable to that of {100}-oriented crystal-silicon metal-oxide-semiconductor (MOS) transistors. Furthermore, their effective mobilities had the same effective field and temperature dependences as those of MOS transistors, indicating that electrons and holes were predominantly scattered not by random grain boundaries or defects in the Si film, but by phonons at the SiO 2 -Si interface, similarly to those of crystal-silicon MOS transistors. These attractive results were obtained as a result of the fact that the TFT channel region was made up of nearly {100}-oriented single grains.

The factors affecting the elongation of Si grains were investigated for the excimer-laser-induced lateral grain growth method. The length of Si grains was found to depend on the laser light intensity profile, the waveform of the laser light pulse, particularly at its tail region, and the sample structure. Grains as long as 25 mm were successfully grown at room temperature using a combination of a V-shaped light intensity profile, a light pulse waveform with a long tail, and a stacked sample structure with a cap layer. Grains of 11 mm in length were also grown in a capless sample.

We have developed a method of preselecting a lucky nucleus among many simultaneously born nuclei for the growth of position-controlled large single Si grains by excimer-laser-induced lateral crystallization. Using this method, arrays of large Si grain of almost 5 Â 5 mm 2 size were successfully grown with a single shot. The result of electron backscattering diffraction pattern (EBSP) analysis indicated that most of the large Si grains had no random boundaries inside, which means that each grain grew from only a preselected lucky nucleus. It was confirmed that the margins to the vertical mispositioning of the sample surface from the focal point and also to the fluctuation of average irradiation light intensity were sufficiently large. Therefore, our method seems to be very attractive for industrial applications.

A conventional phase modulator having only “holes” (or “bumps”) on a quartz plate has been found to have insufficient depth-of-focus (DOF) characteristics. This poor DOF can be attributed to the phase advancement (or retardation) of the zeroth-order diffracted light wave. This phase effect has been applied to developing two types of modulator: one with a sufficiently large DOF, and the other, a single-plate phase modulator capable of producing a two-dimensional light intensity profile suitable for growing arrays of large grains. It was confirmed experimentally that this single-plate modulator could grow arrays of large grains 5 µm in pitch.

We have developed an advanced sample structure for large-grain growth by excimer-laser crystallization of Si. More than 10μm long grains were grown laterally in a 50nm thick Si layer by phase-modulated excimer-laser annealing. A photosensitive SinormalOx capping layer prepared using a conventional plasma-enhanced chemical vapor deposition apparatus enables this longer lateral growth with lower irradiated intensity of laser light than those with the conventional SinormalO2 capping layer.