Kosuke Takenaka

Characterization of Inductively-Coupled RF Plasma Sources with Multiple Low-Inductance Antenna Units

We have developed a cylindrical RF plasma source by the inductive coupling of multiple low-inductance antenna (LIA) units and analyzed the plasma density profile of this source using fluid simulation. Experiments using four LIA units showed a stable source operation even at 2000 W RF power, attaining plasma densities as high as 10^{11}–10^{12} cm^3 in an argon pressure range of 0.67 –2.6 Pa. The amplitude of antenna RF voltage was measured to be less than 600 V, which is considerably smaller than those obtained using conventional ICP antennas. The radial distribution of plasma density sustained using four LIA units showed excellent agreement with profiles numerically predicted using a fluid-simulation code.

Effects of Antenna Size and Configurations in Large-Area RF Plasma Production with Internal Low-Inductance Antenna Units

Recent trends of liquid crystal display (LCD) fabrication toward a significant enlargement of glass substrates require large-area plasma sources with a scale length exceeding 1 m. To meet this requirement, large-area plasma sources with internal low-inductance antenna (LIA) units have been developed for uniform processes, in which design principles for selecting antenna size and configurations in the multiple installation of the LIA units are established. In this study, the effects of antenna size were examined in terms of plasma production characteristics indicating small increase in plasma density with a decrease in antenna size (or antenna impedance). Furthermore, plasma density distributions with the LIA units were investigated to understand the nature of plasma diffusion, which can be utilized for designing plasma profiles with multiple LIA units. First, it was shown that the plasma density distributions followed exponential decay as a function of distance from the antenna. Secondly, the measured plasma density profiles with multiple LIA units were shown to agree well with those obtained by superposing those described by exponential functions, which can be utilized for prediction.

Characterization of Ion Energy Distribution in Inductively Coupled Argon Plasmas Sustained with Multiple Internal-Antenna Units

We have characterized the ion energy distribution in argon plasmas sustained by multiple internal antenna units as a function of Ar pressure. The distribution has been measured using an ion energy analyzer with a mass separator. The peak of ion energy distribution depended more strongly on pressure and corresponded to the magnitude of plasma potential. The full width at half maximum of the distributions decreased with decreasing antenna RF voltage caused by a decrease in Ar pressure.

Development of Large Area Plasma Reactor Using Multiple Low-Inductance Antenna Modules for Flat Panel Display Processing

This article reports characteristics of plasmas sustained with LIA modules and profile control capabilities. Experiments with a meter-scale reactor demonstrated uniform plasma production to attain densities as high as 5x1011 cm-3 at an argon pressure of 1.3 Pa and an RF power of 4 kW. Design issues for large-area plasma sources with a scale-size of 3 m were also presented to exhibit the feasibility of novel large-area plasma sources to meet the requirements of the next-generation meters-scale processing.

H-assisted plasma CVD of Cu films for interconnects in ultra-large-scale integration

Abstract H-assisted plasma CVD (HAPCVD), in which Cu(hfac)2 is supplied as the source material, realizes control of qualities of Cu films, since H irradiation is effective in purifying the Cu films, increasing the grain size, and reducing the surface roughness. Conformal deposition in fine trenches can be realized by decreasing dissociation degree of Cu(hfac)2 using the HAPCVD. Cu(hfac) is identified as the radical mainly contributing to the deposition. Based on the results, we proposed a model in which Cu(hfac) and H react on surfaces to deposit Cu films. We also demonstrated conformal deposition of smooth Cu films of 30 nm thickness and 1.9 mV cm resistivity and almost complete Cu filling in trenches 0.35mm wide and 1.6 mm deep using the HAPCVD.

Effects of discharge voltage waveform on the discharge characteristics in a helium atmospheric plasma jet

We present here an analysis of the discharge characteristics of a He plasma jet operating under three different types of applied voltage waveform: (a) a μs-pulse voltage waveform with a slow voltage rise time, (b) ns-pulse, and (c) rectangular voltage waveforms with fast voltage rise time. Optical emission measurements show that the application of a voltage with a fast voltage rise time induces rapid discharge growth and, consequently, produces an abundance of energetic electrons, which in turn leads to high optical emission from the O atoms. We also estimate the optical emission efficiency of the O atom (ηo), which corresponds roughly to the production efficiency of the reactive O species. ηo increases with increasing applied voltage, and the highest value of ηo is obtained in the shortest pulse discharge, which was ignited by a ns-pulse voltage waveform with a fast voltage rise time and short pulse width.

Anisotropic deposition of Cu in trenches by H-assisted plasma chemical vapor deposition

We have realized anisotropic deposition of Cu, for which Cu is filled preferentially from the bottom of trenches without being deposited on their sidewall, using H-assisted plasma chemical vapor deposition. The anisotropic deposition has two interesting features. One is the fact that the narrower the width of trench, the faster the deposition rate on its bottom becomes. The other is the self-limiting characteristic, that is the deposition in the trench stops automatically just after filling it completely. Such a type of deposition has a potential to overcome common problems associated with conformal filling: namely, small crystal grain size below half of the trench width, and formation of a seam with residual impurities of relatively high concentration.

Effects of gas flow on oxidation reaction in liquid induced by He/O2 plasma-jet irradiation

We present here analysis of oxidation reaction in liquid by a plasma-jet irradiation under various gas flow patterns such as laminar and turbulence flows. To estimate the total amount of oxidation reaction induced by reactive oxygen species (ROS) in liquid, we employ a KI-starch solution system, where the absorbance of the KI-starch solution near 600 nm behaves linear to the total amount of oxidation reaction in liquid. The laminar flow with higher gas velocity induces an increase in the ROS distribution area on the liquid surface, which results in a large amount of oxidation reaction in liquid. However, a much faster gas flow conversely results in a reduction in the total amount of oxidation reaction in liquid under the following two conditions: first condition is that the turbulence flow is triggered in a gas flow channel at a high Reynolds number of gas flow, which leads to a marked change of the spatial distribution of the ROS concentration in gas phase. Second condition is that the dimpled liquid surface is formed by strong gas flow, which prevents the ROS from being transported in radial direction along the liquid surface.

Influence of He Gas Flow Rate on Optical Emission Characteristics in Atmospheric Dielectric-Barrier-Discharge Plasma Jet

We present here the analysis of the characteristics of a dielectric-barrier-discharge (DBD) plasma jet in open air using the optical emission spectroscopy (OES). The OES on oxygen emission is useful to estimate the presence of reactive excited O atoms. The O emission intensity is much higher near the quartz-tube outlet and abruptly decreases with distance from the quartz tube. Our experiments also show that the DBD plasma jet is quite sensitive to He gas flow rate (RHe-gas flow): increasing RHe-gas flow induces weak pulse discharge, resulting in decreasing O emission intensity.

Control of deposition profile of Cu for large-scale integration (LSI) interconnects by plasma chemical vapor deposition

H-assisted plasma chemical vapor deposition (HAPCVD) realizes control of deposition profile of Cu in trenches. The key to the control is ion irradiation to surfaces. With increasing the flux and energy of ions, the profile changes from conformal to subconformal and then to an anisotropic one, for which Cu material is filled from the bottom of the trench without deposition on the sidewall. H3+ and ArH+ are identified as the major ionic species which contribute to the control, and hence the deposition profile also depends on a ratio R = H2/(Ar + H2).