Gaseous hydrogen atoms H(g) produced in hydrogen plasma abstract hydrogen adatoms H(ad) to generate hydrogen molecular desorption from Si surfaces. Direct abstraction, H(g) + D(ad) → HD(g), as well as indirect abstraction, H(g) + D(ad) → D2(g), are found to show complex kinetics of desorption. The mechanisms of the direct and indirect abstraction paths are discussed in terms of both hot complex of H atoms bound to a HSi-SiH cell and thermodynamical instability of the dihydrides phase. Dynamics of the abstracted HD molecules is found to be much richer in translational energy in comparison with the case of thermal desorption. Based on the knowledge accumulated in the thermal desorption and abstraction experiments, hydrogen uptake as well as both the direct and indirect abstractions on Si(100) are simulated to reproduce the corresponding experimental data. Finally, the significance of hydrogen-surface chemistry in the plasma-enhanced Si CVD is discussed.
The growth kinetics of amorphous silicon (a-Si) and microcrystalline silicon (μc-Si) thin films fabricated by plasma-enhanced chemical vapor deposition (PECVD) is discussed for developing low-cost and high-efficiency solar cells. Surface reactions are reviewed associated with the a-Si growth and the nucleation of μc-Si. With respect to the film growth of μc-Si after the nucleation, roughness evolutions were evaluated using an atomic force microscope, and scaling analyses were carried out on fractal structures of growing surfaces, because scaling exponents give a great insight into the growth kinetics. On the basis of results of scaling analyses in conjunction with Monte Carlo simulations, the growth kinetics of microcrystalline silicon thin films, actually used for the high-efficiency solar cells, is discussed.
Plasma wall interaction in fusion reactors is very complicated phenomena, because plasma facing materials suffer heavy irradiation of plasma particles, neutrons, impurity deposition and high flux heat load synergistically. This article introduces fundamental process of hydrogen and helium irradiation effects which are very important to understand plasma wall interaction in materials and also introduces recent studies on nano-scale plasma-wall interaction in actual experimental plasma confinement devices.
We have proposed a novel plasma processing, i.e., radical-controlled processing using radical injection technique, and demonstrated the formation of carbon nanowalls (CNWs) using fluorocarbon plasma-enhanced chemical vapor deposition assisted by hydrogen atom injection. CNWs can be described as the two-dimensional graphite nanostructures with edges, which are composed of the stacks of plane graphene sheets standing almost vertically on the substrate, forming wall structure with high aspect ratio. Growth mechanism of CNWs was discussed on the basis of density measurements of important radicals in the plasma. Moreover, CNWs were formed by using the multi-beams of fluorocarbon radicals, hydrogen atoms and ions, and the effect of ion bombardment on the nucleation of CNWs was investigated.
A carbon-loss-damage in a low-dielectric-constant film (porous SiOCH) for the silicon LSI devices was qualitatively investigated. It was found that the damage induced by plasma processes was dependent not only on the kinds of incident reactive species in plasmas, but also on the carbon bonding structure in the porous SiOCH film. Ion species in Ar and He plasmas and oxygen atoms induced sever damage on the film. Nitrogen and hydrogen atoms induced the damage relatively near the surface region of the film. Metastable-state atoms of Ar and He also induced the damage only the surface of the film. As a result of the comparison between methyl groups and methylene bridges in the film, the bonding state of methylene-bridge had larger resistance to the plasma damage than that of methyl group.
Understanding and controlling of plasma-induced surface reactions are quite important for developing the future plasma processing including thin film deposition. We used “in-situ”, “real-time” infrared absorption spectroscopy in multiple internal reflection geometry (MIR-IRAS), to elucidate the mechanism of plasma-induced surface reactions during plasma enhanced chemical vapor deposition of amorphous carbon film. We examined the influence of substrate temperature on the surface reaction process, by analyzing infrared absorption spectra of Si surfaces during deposition of amorphous carbon film. We found that the deposition rate and the growth mode drastically change with varying the substrate temperature. We suggest that at low substrate temperature the film growth depends predominantly on the gas phase reaction, while at high temperature the film growth mode depends on the surface reaction as well as the gas phase reactions.
A “non-local” measurement scheme was introduced in order to clarify spin injection into multi-layer graphene at room temperature (RT) with reliability. The introduction of the “non-local” method can exclude spurious signals, such as anisotropic magnetoresistance effect, from the measurements, because an electric current pass is completely separated by a spin current pass (spin current is flow of pure spin) and an electrochemical potential of spin current is detected as proof of spin injection. Spin injection and spin current generation in MLG was succeeded at RT, which was the first success of observing spin current in molecules. Furthermore, a “local” magnetoresistance effect was recently observed at RT, and spin coherence was precisely and quantitatively estimated by using a Hanle-type spin precession method, where spin coherent length and spin coherent time were estimated to be 1.6 μm and 120 ps at RT, respectively.