Naoya Kawamoto

Grain Enlargement of Polycrystalline Silicon by Multipulse Excimer Laser Annealing: Role of Hydrogen

The role of hydrogen introduced into melt-Si during excimer laser annealing (ELA) is examined from the viewpoint of grain enlargement. An amorphous silicon (a-Si)/SiN/quartz glass structure is successfully prepared by a catalytic chemical vapor deposition (Cat-CVD) method for a SiN film, in which the hydrogen concentration of the SiN film is controlled. The grain size increases as the hydrogen concentration decreases, and it partially exceeds 2 µm when the hydrogen concentration of the SiN film is fixed at 2.3 at. %. The relationship between defects at grain boundary and hydrogen is also considered.

Effect of Hydrogen and Thermal Conductivity on Nucleation of Polycrystalline Si by Excimer Laser Annealing

The influence of hydrogen on the nucleation of polycrystalline Si (poly-Si) during excimer laser annealing (ELA) of amorphous silicon (a-Si) films was investigated in detail. The results of Raman spectroscopy reveal that the internal stress and defect density in the poly-Si films strongly depend on substrate structures which are made of quartz, SiO2/SiN/glass and SiO2/glass. From the thermal-desorption spectrum and surface morphology characterization using scanning electron microscopy (SEM), it was clarified that the origin of the difference is due to both the hydrogen incorporated in the a-Si from the SiN film by diffusion via SiO2 and the thermal conductivity of the SiO2, SiN and quartz. We also discuss the nucleation process taking into account the hydrogen burst and the thermal conductivity of the substrates.

Effect of Hydrogen on Secondary Grain Growth of Polycrystalline Silicon Films by Excimer Laser Annealing in Low-Temperature Process

The effect of hydrogen on the crystallization of amorphous silicon (a-Si) by excimer laser annealing was investigated for a-Si films deposited on silicon nitride (SiNx) films. The effect of hydrogen atoms provided from SiNx films at various hydrogen concentrations was particularly studied. As hydrogen concentration increases, the grain size of polycrystalline silicon (poly-Si) films increases. It is found that high-quality poly-Si films are obtained at a low laser energy density by controlling the hydrogen concentration in the SiNx films and the laser energy density.

INFLUENCE OF MICROROUGHNESS OF SI AND NATIVE OXIDE ON ADSORPTION OF ORGANIC CARBON IN WATER

The relationship between adsorption of organic carbon present in water and Si surface roughness is examined. The mean roughnesses, Ra, of Si(100) surface after etching in HF solution is the same as that of Si(111) surface. There is no difference between the roughness of the native oxide formed during rinse in ultrapure water and that of the native oxide/Si interface for Si(111). The roughness shows a constant value over all rinse times. These studied observations indicate that the microroughness of the Si surface does not serve as the dominant adsorption site for organic carbon. It is also shown that the field-enhanced oxidation at the beginning of the growth of the native oxide film is important to discuss the dominant adsorption site.

Internal Stress in Polycrystalline Si Film Recrystallized by Excimer Laser Annealing

Internal stresses in polycrystalline-Si (poly-Si) films fabricated by excimer laser annealing on the SiO2/glass, SiO2/SiN/glass and quartz substrates are examined by the Raman transverse optical phonon peak shift. The full-width at half maximum of the peak and the grain morphology are also measured. The relaxation of the internal stress due to the formation of a secondary crystal grain in the poly-Si film on the SiO2/glass substrate is also discussed.

Initial stage of adsorption for organic carbons and native oxide growth on Si wafer

Abstract The adsorption of the organic carbon floating in the water on Si surface was examined by adding the polyethelpolyole into the ultrapure water wherein total organic carbon (TOC) is smaller than 5 ppb. AFM and XPS measurements strongly indicate that the adsorption of the organic carbon on the Si surface has a close relationship with the native oxide growth. The relationship between the C 1S integral intensity and the TOC agrees to that between the oxide thickness and the TOC for some types of wafers. The adsorption of organic carbons is affected by the electron concentration of the Si wafer. In other words, it is affected by the field-enhanced oxidation. The new model for the adsorption of the organic carbon, which assumes the field-enhancement due to the Coulombs force was discussed. The organic carbons which are floating near the Si surface easily adsorb to the Si surface, because the oxygen ions of the covalent bond in the organic carbons are pulled by the Coulombs force between the donor ions of the Si surface depleted layer and the oxygen negative ions.

Enhancement of Secondary Grain Growth of Low-Temperature Polycrystalline Silicon by Visible Laser Irradiation: Visible-Laser-Induced Lateral Crystallization

In this paper, we propose and investigate a new concept of visible-laser-induced lateral crystallization (VILC) for decreasing process temperature. Visible laser is irradiated onto a polycrystalline Si film before or after ultraviolet laser irradiation. Lateral growth is enhanced by laser heating at the grain boundary since the absorbance of the grain boundary is larger than that of the in-grain. The enhancement of secondary grain growth is discussed from the viewpoints of both the prolongation of the time of the thermal profile and the increase in temperature at the grain boundary.

Hydrogen Modulation-Doped Structures to Improve Crystalline Fraction of Polycrystalline Silicon Films Prepared by Excimer Laser Annealing at Low Energy Densities

An excimer laser annealing (ELA) of amorphous silicon (a-Si) with a hydrogen modulation-doped layer (ELHMD) was investigated using a-Si films with various H concentrations and H distributions for forming high-quality polycrystalline silicon (poly-Si) films at a low energy irradiation (100 mJ/cm2). Poly-Si films with a high crystalline fraction of 80% are obtained by controlling the H concentration distribution and shot number for ELA. In addition, the film exfoliation caused by a H2 burst can be suppressed, and secondary grain growth can be induced using HMD a-Si films. It is considered that the nucleation is enhanced by the recombination energy of the H atoms around the Si–H2 bond during Si melting and that H desorption affects grain growth and film exfoliation.

Role of hydrogen in polycrystallne Si by excimer laser annealing

The role of hydrogen in the Si film during excimer laser annealing (ELA) has been successfully studied by using a novel sample structure, which is stacked by a-Si film and SiN film. Hydrogen contents in the Si films during ELA are changed by preparing samples with hydrogen content of 2.3-8.2 at.% in the SiN films with a use of catalytic (Cat)-CVD method. For the low concentration of hydrogens in the Si film, the grain size increases by decreasing hydrogen concentration in the Si film, and the internal stress of the film decreases as increasing the shot number. For the high concentration of hydrogens in the Si film, hydrogen burst was observed at 500 mJ/cm 2 and the dependence of the internal stress on the shot number becomes weak even at 318 mJ/cm 2 . These phenomena can be understood basically using the secondary grain growth mechanism, which we have proposed.