Hirokazu Kaki

Large-Area and High-Speed Deposition of Microcrystalline Silicon Film by Inductive Coupled Plasma using Internal Low-Inductance Antenna

A novel inductively-coupled RF plasma source with internal low-inductance antenna (LIA) units was developed to synthesize microcrystalline silicon (µc-Si) film on a large glass substrate. A film thickness profile on a 600×720 mm2 glass substrate was achieved with high plasma uniformity and a variation of less than ±5% without a standing-wave effect. Raman and transmission electron microscope (TEM) analysis revealed that highly crystallized µc-Si films, which were directly deposited on a glass substrate, were synthesized without an amorphous-phase incubation layer at the substrate interface. A bottom-gate thin-film transistor (BG-TFT) was fabricated employing an optimized µc-Si layer and exhibited a field-effect mobility of 3 cm2/(Vs), which is one order higher than that of a typical amorphous silicon TFT.

Periodic grain-boundary formation in a poly-Si thin film crystallized by linearly polarized Nd:YAG pulse laser with an oblique incident angle

We investigated the periodic grain-boundary formation in the polycrystalline silicon film crystallized by a linearly polarized Nd:YAG (where YAG is yttrium aluminum garnet) pulse laser with an oblique incident angle θi=25°, compared with the normal incident angle θi=0. The alignment of the grain boundary was uncontrollable and fluctuated in the case of the oblique incident and large irradiation pulse number while that in the case of the normal incident was performed stably. It was found that the main cause for its low controllability was the nonphase matching between the periodic surface corrugation of the crystallized silicon film and the periodic temperature profile induced by the laser irradiation. Also, it was found that, in the case of θi=25°, the dominant periodic width of the grain boundary depended on the pulse number N. That is, it was around λ∕(1+sinθi) for small N≈10 and λ∕(1−sinθi) for large N≈100 at the laser wavelength of λ=532nm. In order to explain this dependence, we proposed a model to t...

Influence of the Beam Irradiation Conditions on an Si Film Melting-Crystallized by a Nd:YAG Pulse Laser Beam with Linear Polarization

We investigated the influence of the irradiation conditions of the coherent length and the polarization of the laser beam, the incident angle θi, the pulse number, the fluence, the substrate temperature and the a-Si film thickness on the melting-crystallization of an a-Si film and the controllability of the periodic grain boundary location by using a linearly polarized laser beam. For formation of periodic grain boundary in the crystallized Si film, the linear polarization is key factor rather than the coherent length. Also, the a-Si film thickness should be around 60 nm for large optical absorption, and the high substrate temperature and the large pulse number are preferable. By using a p-polarized beam, the grain boundary width can be expanded proportional to 1/(1-sin θi) roughly. In order to suppress the ablation of the film and to increase the productivity, the fluence should be adjusted precisely.

Surface modification of an amorphous Si thin film crystallized by a linearly polarized Nd:YAG pulse laser beam

Amorphous Si films of 60 and 10nm thick on glass substrates were irradiated by a linearly polarized Nd:YAG pulse laser with the wavelength λ=532nm at the incident angle θi=0. The surface of the irradiated 60-nm-thick film had both periodic ridges perpendicular to the electric field vector E and aperiodic ridges roughly parallel to E, where the spatial period of the periodic ridges was almost λ. From the continuous 10-nm-thick film, the separate rectangular Si islands were formed with a periodic distance of λ, with the edges parallel or perpendicular to E. When θi was increased from normal incidence of the s-polarized beam for a 60-nm-thick film, the aperiodic ridges were reduced while the periodic ridges were still formed. For a 10-nm-thick film, the Si stripes were formed perpendicular to E, using the s-polarized beam at θi=12°. In order to investigate the mechanisms of the surface modifications of, in particular, aperiodic ridges, islands, and stripes, we improved the previous theoretical model of the p...

Multireflection Effect on Formation of Periodic Surface Structure on an Si Film Melting-Crystallized by a Linearly Polarized Nd:YAG Pulse Laser Beam

We investigated the multireflection effect on the formation of a periodic surface structure produced by a linearly polarized Nd:YAG laser beam of 532 nm on an Si film deposited on a glass substrate, as well as on heating rate in the film, compared with an excimer laser beam. From the theoretical calculation results, it was found that the formation of the periodic surface structure and heating rate strongly depended on film thickness or that they were influenced by the multireflection effect. The thickness most effective for forming the periodic surface structure and heating rate was about 60 nm. Furthermore, we attempted to verify the calculation results by carrying out an experiment in which we checked whether the periodic structure was formed on the surface of the melting-crystallized Si films. As a result, the thickness range for producing the periodic surface structure was found to be from 50 to 70 nm, which were larger than the theoretical values of 40 to 60 nm.

Influence of the beam irradiation condition with oblique incidence on crystallization of an Si film by a linearly polarized pulse laser

We investigated influence of the beam irradiation conditions with oblique incidence on crystallization of an Si film by a linearly polarized pulse laser in order to enlarge the periodic width of grain boundary. The irradiation conditions are fluence, pulse number and film thickness. We can obtain the periodic width of about 900 nm by increasing the incident angle to 25°. The experimental results suggest that the pulse number and the film thickness should be controlled properly as well as fluence in order to produce large grain stably for the oblique incidence. The detail of these conditions was discussed.

Numerical Analysis for Lateral Grain Growth of Poly-Si Thin Films Controlled by Laser-Induced Periodic Thermal Distribution

In order to obtain a large Si grain and to control the location of grain boundary in a Si film thermally melting-crystallized by pulse laser, we have proposed to use a periodic thermal distribution spontaneously induced by a linearly polarized laser beam. The lateral grain growth of polycrystalline Si thin films, which is controlled by the laser-induced periodic thermal distribution, was analyzed numerically by two-dimensional finite element computer simulations. From this analysis, it can be conclude that the laser irradiation should be performed to melt not all but most of Si film or melt it partially, making the large difference between the maximal and minimal temperature in the thermal distribution. It was also found that the temperature difference was increased with the optical absorption in the Si film and the fluence.