Kazumasa Ikuse

Sputtering yields of Au by low-energy noble gas ion bombardment

Sputtering yields of gold (Au) by noble gas (He, Ne, Ar, Kr or Xe) ions have been measured in the low injection energy range 25–200 eV. The yield data presented here were obtained from mass-selected ion beam sputtering experiments, in which the ion beam has a very narrow energy spread and contains no impurity ions. The newly obtained yield data set, together with the fitting functions for the yield dependence on the injection energy, provide an accurate and reliable database for the study of fundamental physical mechanisms of sputtering phenomena at low energies, where experimental data had been scarce.

Measurement of Magnesium Oxide Sputtering Yields by He and Ar Ions with a Low-Energy Mass-Selected Ion Beam System

Sputtering yields of magnesium oxide (MgO) by He and Ar ion bombardment were measured at relatively low incident energies with monochromatic ion beams generated by a low-energy mass-selected ion beam system. The measured sputtering yields and their ion incident energy dependence are found to be significantly different from those proposed by an earlier study based on numerical simulations [S. J. Yoon and I. Lee: J. Appl. Phys. 91 (2002) 2487], which seems to be the only source of MgO sputtering yield data widely available in the community for a relatively wide range of ion incident energies. Given the fact that MgO is extensively used as barrier coating of plasma display panel (PDP) cells and the amount of sputtered MgO in PDP cells can affect their discharge characteristics to a large extent, our results indicate that a fundamental revision is urgently needed for the study of MgO sputtering by noble gas ion bombardment.

Surface Modification of Poly(methyl methacrylate) by Hydrogen-Plasma Exposure and Its Sputtering Characteristics by Ultraviolet Light Irradiation

Surface modification of poly(methyl methacrylate) (PMMA) films by hydrogen-plasma exposure has been studied in the light of sputtering resistance of polymer-based materials in plasma etching processes. Surface measurements of PMMA were performed with X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and spectroscopic ellipsometry. It has been found that oxygen atoms are preferentially removed from the surface when a PMMA film is subjected to hydrogen-plasma exposure, with the depth of modification being about 40 nm in the case we examined. Hydrogen-plasma exposure is also found to reduce the sputtering yields of PMMA by ultraviolet light irradiation, as in the case of Ar+ ion irradiation [S. Yoshimura et al.: J. Vac. Soc. Jpn. 56 (2013) 129]. The results suggest that PMMA films become hardened and more sputtering resistant due to the formation of a thick (i.e., 40 nm in the case of this study) amorphous carbon layer by hydrogen-plasma exposure. Hydrogen-plasma exposure is thus an effective technique to increase etching resistance of polymer films.

Generation of Free Radicals in Liquid by Atmospheric-Pressure Plasmas and its Application to Biology and Medicine

The use of low-temperature, non-cauterizing plasmas has recently attracted much attention in the plasma research community as effective means for medical treatment and material processing for medical applications. For example, recent studies have shown that the application of a low-temperature atmospheric-pressure plasma (APPs) directly to living cells and tissues has some therapeutic effects such as blood coagulation, angiogenesis, prevention of organ adhesion, and wound healing. The cause of such effects is reactive oxygen species (ROS) /reactive nitrogen species (RNS) provided by the plasma. Under typical conditions, tissues and cells of living bodies are immersed in liquid (such as blood or lymph), so when an APP is applied to them, the reactive species generated by the plasma are dissolved into the liquid before interacting with living organisms. Reactive species and charged particles supplied to on the liquid surface, however, may be converted to different types of reactive species in the liquid phase. In this presentation, after a brief review on biological/medical application of APPs, numerical simulation of liquid-phase ROS/RNS reaction equations in pure water will be discussed. The simulation results are then compared with experimental data on cell proliferation affected by plasma exposure. It has been found that cell viability in the culture medium is strongly affected by long-time exposure of the cells to low-weight less reactive (and therefore relatively long-lived) molecules such as hydrogen peroxide H2O2 or hydroperoxyl radicals HOO rather than cell interactions with highly reactive species or large organic molecules modified by plasma-generated reactive species. APPC12 The 12th Asia Pacific Physics Conference

Sputtering yields of magnesium hydroxide [Mg(OH)2] by noble-gas ion bombardment

Magnesium oxide (MgO) is widely used for barrier coating of plasma display panel (PDP) cells and its resistance against ion sputtering is a critical issue for the prolongation of lifetime of PDPs. The top surface of an MgO barrier coat may be hydrated to form a thin layer of magnesium hydroxide [Mg(OH)2] due to moisture inadvertently contained in the gas of the PDP cell. In this study, sputtering yields of Mg(OH)2 by low-energy noble-gas ion bombardment have been evaluated experimentally with the use of a mass-selected ion beam system and compared with those of MgO. It has been found that the etched depths of Mg(OH)2 and MgO are nearly equal when they are subject to the same noble-gas ion bombardment conditions.

Measurement of sticking probability and sputtering yield of Au by low-energy mass selected ion beams with a quartz crystal microbalance

A measurement system of sticking probability and sputtering yield in the energy range of 0–500 eV has been established with a low-energy mass selected ion beam system. The small change in mass of the substrate material by injected ions can be evaluated with the quartz crystal microbalance (QCM). In this study, sticking probabilities and self-sputtering yields of Au were measured as functions of the injection energy of Au ions.

Effect of ultraviolet light irradiation on etching process of poly(methyl methacrylate) by ion beam injections

Effects of ultraviolet (UV) light irradiation on polymer dry etching processes have been investigated with the use of a low-energy mass-selected ion beam injection system. Etching yields of poly(methyl methacrylate) (PMMA) by Ar or CF3 ion beam injections were evaluated from the loss of PMMA film weight measured by a quartz crystal microbalance (QCM) during the ion beam injection process with or without simultaneous UV light irradiation. Significant enhancement of the etching yield of PMMA was observed during the simultaneous irradiation with CF3 ion beam and UV light over the sum of its sputtering yields obtained from separate ion-beam or UV-light injection processes. By contrast, no significant change of etching yields was observed when the UV light was superposed on the Ar ion beam.

Measurement of Au sputtering yields by Ar and He ions with a low-energy mass selected ion beam system

The Au sputtering yields by noble gas ions below 200 eV were measured with a low-energy mass selected ion beam system. Au sputtering yields by He and Ar ions were measured and found to incease monotonically with the ion injection energies. It was also found that the sputtering yields by He were much lower than those by Ar.

Effect of light irradiation from inductively coupled Ar plasma on etching yields of SiO2 film by CF3 ion beam injections

Effects of light irradiation on etching yields of SiO2 films by CF3 ion beams have been investigated with a low-energy mass selected ion beam system. An inductively coupled plasma (ICP) from Ar gas was used as the light source. The spectrum of light emitted from the Ar ICP was measured by vacuum ultraviolet and visible monochromators. Etching yields of SiO2 films by 470 eV CF3 ion beam injections were obtained from the ratio of the number of incident CF3 ions to that of removed SiO2 atoms during the ion beam injection process with or without simultaneous light irradiation from the Ar ICP. The incident ion number was evaluated from the integration of temporal evolution of ion beam current. The number of removed atoms can be obtained from the etched depth of SiO2 films measured by a laser interferometer. It is found that the obtained SiO2 etching yield by simultaneous irradiation of CF3 ions and photons from the light source was smaller than that by ion beam irradiation only.