Masato Hiramatsu

Optimum Light Intensity Distribution for Growing Large Si Grains by Phase-Modulated Excimer-Laser Annealing

Characteristics have been investigated for both KrF excimer-laser light and KrF excimer-laser crystallization of Si thin films. The results were applied to design an optical system for growing densely packed and large grains. A high-resolution beam profiler confirmed that the laser light intensity distribution on the sample surface had a nearly ideal triangular form with a maximum-to-minimum intensity ratio of approximately 2, as designed. This distribution could grow 5-µm-long grains with a packing efficiency close to 100% by a single laser light pulse.

An Advanced Sample Structure for Large-Grain Growth by Excimer Laser Crystallization

We have developed an advanced sample structure for large-grain growth by excimer-laser crystallization of Si. More than 10 μm long grains were grown laterally in a 50 nm thick Si layer by phase-modulated excimer-laser annealing. A photosensitive SiO x 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 SiO 2 capping layer.

Selective Deposition of Silicon by Mercury Sensitized Photochemical Vapor Deposition

The authors have developed a low-temperature process for selective deposition of silicon by mercury sensitized photochemical vapor deposition (Photo-CVD) without using ultraclean technology. It was found that hydrogen radical pretreatment was required to obtain selective deposition. There was an incubation period for not only SiO2 surface but also Si surface. It was confirmed that mercury sensitized Photo-CVD is a promising method for selective deposition process at low temperature using large-area glass substrate.

Influence of nitrogen incorporation in hydrogenated amorphous silicon films prepared by photochemical vapor deposition

The influence of nitrogen incorporation in a-Si:H films by mercury-photosensitized decomposition of a silaneammonia gas mixture was investigated. It was found that there are two different film structures of a-Si:H films. In a high nitrogen concentration, nitrogen is one of the elements of the a-SiNx alloy. On the other hand, in a low nitrogen concentration, nitrogen plays the role of a dopant in a-Si:H, and nitrogen-induced localized states are created at around 0.5 eV above the valence band edge.

Importance of pure Si films in pulsed-laser-induced lateral growth

We have investigated the effects of impurities in starting silicon films on excimer-laser-induced lateral growth characteristics. The films should have a low concentration of impurities to achieve long lateral growth, since impurities, such as carbon, nitrogen, oxygen, and fluorine, in the films were found to affect the lateral growth characteristics severely. A stacked structure with a capping layer is also considered essential for maintaining pure molten Si during lateral growth.

P‐50: Distinguished Poster Paper: Arrays of Large Si Grains Grown at Room Temperature for x‐Si TFTS

Arrays of large Si grains have been grown by phase-modulated excimer-laser annealing at room temperature. Home-plate- and square-shaped grains could be grown over the whole irradiated substrate area. These results indicate that the fabrication of x-Si TFTs on glass is a realistic development target.

The Selective Deposition of a Silicon Film on Hydrogenated Amorphous Silicon by Mercury Sensitized Photochemical Vapor Deposition

The authors have developed a low-temperature process for the first time for the selective deposition of a silicon film on hydrogenated amorphous silicon (a-Si:H) and on silicon nitride (SiNx) surfaces by mercury sensitized photochemical vapor deposition (Photo-CVD). The selective deposition of Si films was able to be achieved by hydrogen radical cleaning for 1 minute prior to the deposition. There were two different incubation periods for the a-Si:H and SiNx surfaces. Selective deposition was obtained by using this difference in the incubation periods between the deposition on an a-Si:H surface and on a SiNx surface. The field effect mobility and the off leakage current for thin film transistor (TFT) of the fabrication by using this selective deposition technique were of the 0.6 cm2 V-1 s-1 and 10-11 A order, respectively. It has been confirmed that photo-CVD is a promising method for the selective deposition process at a low temperature using a large-area glass substrate.

Deposition of Pure Hydrogenated Amorphous Silicon by Plasma-Enhanced Chemical Vapor Deposition for Polycrystalline Silicon Thin Film Transistors

A high-purity hydrogenated amorphous silicon film has been successfully deposited using an advanced plasma-enhanced chemical vapor deposition system that is available for mass-production use. Oxygen and carbon concentrations in the film were as low as 1.3×1017 and 2.6×1016 atoms/cm3, respectively, i.e., about hundredth part of the typical values achieved using a recent large-area deposition system and as low as those in CZ-Si wafers. The film was characterized as a function of SiH4 gas flow rate and outgas rate from the reaction chamber, and the results suggest that oxygen and carbon in the film comes predominantly from H2O and CO2 out-gassing from the chamber wall, respectively.

Preparation of Phosphorus-Doped Microcrystalline Silicon by Mercury-Sensitized Photochemical Vapor Deposition Process

Phosphorus-doped microcrystalline silicon (µc-Si) films were prepared on intrinsic hydrogenated amorphous silicon (a-Si:H) by mercury photosensitized decomposition of silane-phosphine-hydrogen gas mixture. We have obtained a high deposition rate of 15 nm/min and a high dark conductivity of 1.2 (Ωcm)-1 at the substrate temperature of 240° C. The photothermal deflection spectroscopy (PDS) measurement of n-type µc-Si film on a-Si:H showed that the µc-Si/a-Si:H interface state density made by photo-CVD was small compared with that of the same structure made by the conventional plasma enhanced CVD (PECVD) method.

Mercury-sensitized hydrogen radical photoetching of hydrogenated amorphous silicon

A study of the etching of hydrogenated amorphous silicon films has been carried out by using hydrogen radical produced by mercury-photosensitization of hydrogen gas. There was found it be an incubation period before etching began, and the incubation period depended on surface pretreatment conditions. It can be explained that the variation in incubation period strongly depend on unevenness of the a-Si:H surface. It has also been found that the actual etching rate of undoped a-Si:H increases with decreasing the substrate temperature. The authors consider that surface reaction, that is, adsorption of hydrogen radical, is dominant in this etching process.