Kanji Shibagaki

Spatial distribution of the velocity distribution function of Fe atoms in a magnetron sputtering plasma source

We examined the spatial distribution of the velocity distribution function of Fe atoms in a conventional dc magnetron sputtering source by laser-induced fluorescence (LIF) imaging spectroscopy. By measuring the Doppler broadening of the excitation spectrum of LIF, we evaluated the velocity distribution function of Fe at many positions in the discharge space. By calculating the first- and second-order moments of the velocity distribution function, we obtained two-dimensional maps of the average velocity and the effective temperature in the r-z plane of the cylindrically symmetric magnetron discharge. The map of the average velocity clearly indicates that Fe atoms have fast velocity in the region adjacent to the target at a low discharge pressure such as 3 mTorr, while at a high gas pressure such as 20 mTorr, the average velocity of Fe atoms is almost zero in the entire discharge space. On the other hand, it has been found from the map of the effective temperature that the velocity distribution function obs...

Two-dimensional distributions of Ti and Ti+ densities in high-pressure magnetron sputtering discharges

We measured two-dimensional distributions of Ti and Ti+ densities in magnetron sputtering plasmas by laser-induced fluorescence (LIF) imaging spectroscopy. It has been found that the production of Ti+ is enhanced by a high gas pressure. The peak of the Ti+ density is located at a distance of 4–5 cm from the target surface, indicating the gas-phase production of Ti+ in the downstream plasma. Since the plasma density and the electron temperature measured using a Langmuir probe are low in the downstream plasma, this result suggests that the dominant production process of Ti+ is not electron impact ionization of Ti (Ti+e→Ti+e+e). Although another candidate for the gas-phase production of Ti+ is Penning ionization (Ti+ArM→Ti++Ar+e), experimental results on ArM is negative about the contribution of Penning ionization to the gas-phase production of Ti+.

Formation of Positive and Negative Carbon Cluster Ions in the Initial Phase of Laser Ablation in Vacuum

In this paper, the formation of Cn+ and Cn- cluster ions has been investigated. The carbon cluster ions were produced by the laser ablation of a rotating graphite target in vacuum. The study has been carried out using time-of-flight mass spectrometry. Mass spectra of positive and negative cluster ions were observed as a function of delay time between the irradiation of the laser pulse and the acceleration of ions. The mass distribution of clusters changed significantly in the initial phase (≤10 µs) after the irradiation of the laser pulse. The sizes of both positive and negative cluster ions grow with the increase in the delay time. These results indicate that clustering reactions progress even in vacuum without ambient gas. The mechanism of clustering is considered to be reactions among various carbon ions and neutral species in the laser ablation plume.

Chemical bonds of fluorocarbon films which can be a source of CFx radicals

Some experiments reported previously [e.g., K. Sasaki et al., J. Appl. Phys. 88, 5585 (2000)] show that fluorocarbon films can be a source of CFx radicals in fluorocarbon plasmas. In the present article, we examined the relationship between the degree of surface production and the chemical bonds of fluorocarbon films synthesized by various fluorocarbon plasmas with the addition of H2. The degree of surface production was evaluated from the absolute flux of CFx (x=1,2) radicals desorbed from fluorocarbon films. The composition of the chemical bonds was analyzed by x-ray photoelectron spectroscopy. As a result, significant surface production (>3×1015 cm−2 s−1) was observed when fluorocarbon film had the dominant –CF2 bond. The change in the dominant bond from –CF2 to –C–C resulted in the decrease in the degree of surface production.

Production of carbon clusters by laser ablation of polymers in vacuum

Time-of-flight mass spectrometry was used for analyzing ionic species produced by Nd:YAG laser ablation of polymers [polypropylene (PP), polyethylene (PE), and polytetrafluoroethylene] in vacuum. The temporal variation of the mass distribution after the laser irradiation was investigated. The target polymers were decomposed to almost atomic species by the laser irradiation. After the laser irradiation, significant temporal evolution of carbon cluster ions (CnHm+, CnHm−, and CnFm−) was observed. This result indicates that the cluster ions are produced from atomic species via gas-phase reactions in the ablation plume with no ambient gases. The mass spectra of Cn− and CnHm− obtained from the PP and PE targets suggest that even carbon clusters (C2k) are hydrogenated more efficiently than odd ones (C2k+1) to produce C2kHm.

Synthetic characteristics of large carbon cluster ions by laser ablation of polymers in vacuum

The synthetic characteristics of large carbon cluster ions by laser ablation of polymers in vacuum were investigated. Time-of-flight mass spectrometry was used for analyzing the masses of ionic species produced by laser ablation. We found that large carbon cluster ions Cn+ with n up to 400 were synthesized in vacuum when copolymer of ethylene and tetrafluoroethylene, polyvinyliden fluoride, and chlorotrifluoroethylene were employed as the target material. Since the synthesis of large cluster ions in vacuum is a surprising phenomenon, we examined the synthesis efficiency in various experimental conditions. By comparing mass spectra obtained from various polymers containing hydrogen and/or halogen atoms, the existence of both hydrogen and halogen atoms in polymers do not directly contribute to enhance the synthesis efficiency of large carbon clusters. In addition, microscopic observations of surface morphologies of laser-ablated polymers revealed that the clustering reactions in eroded craters had little co...

Synthesis of Heavy Carbon Clusters by Laser Ablation in Vacuum

It has been found that heavy carbon clusters can be produced by laser ablation in vacuum with no ambient gases. The synthesis of heavy clusters is obtained when a copolymer of ethylene and tetrafluoroethylene is employed as the target material for laser ablation. Time-of-flight mass spectrometry was used for analyzing ionic species produced by laser ablation. The significant temporal evolution of carbon cluster ions was observed even though no ambient gases were injected into the vacuum chamber. At ~ 10 µs after the irradiation of the laser pulse, we detected a large amount of carbon cluster ions Cn+ with n up to 400.

Laser desorption time-of-flight mass spectrometry of fluorocarbon films synthesized by C4F8/H2 plasmas

Molecular structures of fluorocarbon films synthesized by C4F8/H2 plasmas were analyzed by laser desorption time-of-flight mass spectrometry (LD-TOFMS). Mass peaks of positive and negative ions with m/z up to 250 were observed in the mass spectra. Most of these ions were assigned as atomic hydrogen, atomic fluorine, carbon clusters, hydrocarbon clusters, fluorocarbon clusters, and hydrofluorocarbon clusters. The mass spectra changed sensitively with the partial pressure of H2. The LD-TOFMS analysis showed that the films changed from a polytetrafluoroethylene-like film into crosslinked carbon- and hydrogen-rich one by the addition of H2. The change in the chemical composition of the mass spectrum was consistent with the analyses by conventional x-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. It is emphasized that LD-TOFMS can be used for the analysis of the degree of polymerization, which is an advantage of LD-TOFMS over the conventional analysis methods.

Synthesis efficiency of heavy carbon clusters from ETFE ablated by different numbers of laser pulse in vacuum

Abstract We have carried out mass spectral analysis of positive ions produced by laser ablation of a copolymer of ethylene and tetrafluoroethylene (ETFE: [CH 2 CH 2 CF 2 CF 2 ] n ) in vacuum using time-of-flight mass spectrometry (TOF-MS). The surfaces of the ETFE targets irradiated by different numbers of laser pulse were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Heavy carbon cluster ions C n + with n ≥30 were observed in the mass spectra. The fractional abundance of heavy clusters in the mass spectrum decreased with the number of laser pulse. On the other hand, carbon became rich in the atomic composition of the laser-irradiated surface, and the eroded area on the surface increased with the number of laser pulse. From these results, it is suggested that the carbon-rich material surface results in the less efficient production of heavy carbon clusters. In addition, it is also suggested that clustering reactions in eroded craters do not contribute to the synthesis of heavy clusters.

Estimation of Carbon Fluxes Interchanging between Chamber Wall and Gas Phase in Fluorocarbon Plasmas

We have evaluated carbon flux that contributes to the deposition of fluorocarbon film on the chamber wall in C4F8 and C4F8–H2 plasmas. The deposition flux was estimated from the deposition rate, carbon concentration, and weight density of the fluorocarbon film. In addition, the deposition carbon flux was compared with the carbon flux desorbed from the fluorocarbon film, which was roughly estimated by the inward diffusion fluxes of CF and CF2 having hollow-shaped density distributions. This is because the source of the inward diffusion fluxes is the production of CF and CF2 from the fluorocarbon film. In the case of pure C4F8 plasmas, the deposition carbon flux was on the order of <1014 cm-2s-1, which was much smaller than the desorption carbon flux on the order of 1015–1016 cm-2s-1. Accordingly, it is revealed that the carbon flux adsorbing to the chamber wall contributes negligibly to the growth of the fluorocarbon film, and mostly goes back to the gas phase. On the other hand, in C4F8–H2 plasmas, the deposition flux was on a comparable order to the desorption flux.