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The promotion of cell proliferation by non-equilibrium atmospheric-pressure plasma is a promising technology for regenerative medicine. The fibroblast suspension was irradiated with electrically neutral radicals. Radial irradiation was performed using an atmospheric-pressure radical generator with a working gas mixture of Ar, O2, and N2. Carboxy-PTIO (c-PTIO), a scavenger of nitric oxide radical (NO•), was dissolved in the fibroblast suspension. Selective irradiation with electrically neutral radicals promoted fibroblast proliferation by 36 % without c-PTIO in liquid. In contrast, proliferation-promoting effects were significantly reduced to 13 % with c-PTIO. Fluorescence probes for reactive oxygen and nitrogen species (RONS) and NO• showed that intracellular RONS and NO• levels were increased by radical irradiation and reduced with c-PTIO in the fibroblast suspension. NO• was detected in the radical-irradiated solutions using electron spin resonance. These results suggested that plasma-generated NO• promotes fibroblast proliferation in liquids.

Ethanol production by budding yeast was compared between direct and indirect plasma irradiation. We observed enhancement of ethanol production and cell growth not by indirect plasma irradiation but by direct plasma irradiation. Glucose consumption was increased in budding yeast by direct plasma irradiation. Extracellular flux analysis revealed that glycolytic activity in the budding yeast was elevated by direct plasma irradiation. These results suggest that direct plasma irradiation enhances ethanol production in budding yeast by elevating the glycolytic activity.

A brief history of the development of our plasma technology for the disinfection of agricultural harvests is presented in this review. We focused on the influence of reactive oxygen species (ROS), e.g. ground-state oxygen atoms [O(3P j )], excited-state oxygen molecules [O2(1Δg)], and ozone (O3), generated from atmospheric-pressure plasmas on the inactivation of fungal spores under dry conditions. For elucidating the inactivation mechanisms, it is essential to reveal the key ROS. Using some powerful tools, we revealed that the dose of O(3P j ) strongly correlates with the inactivation of fungal spores when compared to those of another ROS, such as O2(1Δg) and O3. The balance of antioxidants in the spores is possibly modulated by O(3P j ), leading to oxidation of organelles in spores. Herein, we introduce and discuss how O(3P j ) contributes to the inactivation of fungal spores associated with in situ diagnostics of plasma generated ROS and in situ intracellular observations of a few fungal spore species.

Single-walled carbon nanotubes (SWNTs) were synthesized with a high growth rate by an arc plasma method employing the electrodes made from a Ni–Y mixture catalyst. In a previous study, it was reported that the monitoring of high-crystallinity SWNT growth enabled the evaluation of the results of the optical emission spectroscopy (OES) of C2, Ni, and Y. Here, the impact of helium pressure of arc plasma on the high crystallinity of SWNTs was determined by considering the high intensity ratios of catalytic metals over C2 emissions at low helium pressures in the arc plasma.

Graphenes of nanometer-scale grain size (nanographenes) were synthesized using in-liquid plasmas with alcohols or hydrocarbons. This method of nanographene synthesis showed a trade-off relationship between crystallinity and synthesis rate. The high crystallinity of nanographenes synthesized with alcohols was evaluated from the small full width at half maxima (FWHM) of the G band in Raman scattering spectra. On the other hand, in the case of using hydrocarbons such as n-hexane and benzene, a significantly high synthesis rate was obtained but the crystallinity of nanographenes was low. It was found that hydroxyl groups and oxygen atoms of liquid sources play important roles in determining the crystallinity of synthesized nanographenes.

Etching characteristics of hexagonal and triangular cavities on a 1?1?1-oriented silicon wafer in the etchant of ethylene diamine, pyrocatechol and water (EDP/EPW) were investigated. The patterns are aligned to keep the sides perpendicular to 1?1?0 crystal orientations, in order that the sidewalls of cavities are parallel to {1?1?0} crystalline planes. RIE-ICP etching is used to define the depth of the triangular and hexagonal cavities, and EDP etching is followed for different etching times. The final self-etch-stop profiles of cavities are determined by the dimension of mask patterns and the depth of cavities in the wafer. The etching process of the hexagon and triangle cavities is modeled, based on the crystal structure and wet etching principle. The results of etched cavities confirm the condition to determine the final etching profiles.

We have developed a novel temperature measurement system for controlling the temperature of each layer of multilayered substrates, such as a silicon on insulator (SOI), and have evaluated the system using a three-layered substrate, whose top and bottom layers are silicon, each 360 µm in thickness, and whose interlayer is quartz, 1 mm in thickness. From these results, we have confirmed that the system has a resolution of less than 1°C in the top and bottom layers of the substrate.

Polytetrafluoroethylene (PTFE)-like films were formed by electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition (ECR-PECVD) employing the solid material evaporation technique where the PTFE was evaporated by a CO2 laser resulting in the production of fluorocarbon species. This system does not employ any perfluorocompound (PFC) feed gases which cause global warming. In this system, it was found that C2F4 and higher species such as CxFy (x≥2) were generated by CO2 laser evaporation. The films were analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared absorption spectroscopy (FT-IR). As a result, the chemical composition of films formed at microwave powers below 0.4 kW indicated a PTFE-like structure with an F/C ratio of 2.0 and a dielectric constant of 2.0. Densities of CFx (x=1–3) radicals and F atoms in the ECR plasma employing the solid material evaporation technique were measured to understand the behavior of these radicals by infrared diode laser absorption spectroscopy (IRLAS) and actinometric optical spectroscopy (AOES), respectively. From these measurements, higher species of C2F4 and CxFy were clarified to be the important precursors of PTFE-like fluorocarbon films.

We have applied a compact electron-bean-excited plasma (EBEP) source to the cleaning process for a glass disk. Since the EBEP enables us to control the ion sheath bias on the floating substrate by changing the electron-beam energy, the substrate ion bombardment energy to perform a reactive ion etching (RIE) can be determined without applying additional bias power supply such as RF. The source system has been modified in several ways so that it can be reliably used in the O2 plasma for a long time. In order to evaluate the cleaning capability of the source system, the etch performance of carbon film was investigated. It was found that the etching rate increased with electron-beam current and electron acceleration voltage. The etch rate of 4 nm/s was obtained at Va of 100 V and Ia of 2.5 A.

We have deposited hydrogenated amorphous carbon (a-C:H) films called diamond-like carbon (DLC) on an electrically floating disk using a compact electron-beam-excited plasma (EBEP) employing toluene and ethylene as feed gases. Since the EBEP source enables us to control the ion sheath bias on the floating substrate by changing the electron-beam energy, the substrate ion bombardment energy needed to form the DLC film can be determined without applying an additional bias power supply such as RF. The relationship among the DLC film properties, the deposition rate and the electron-beam acceleration voltage for both feed gases has been investigated. In order to achieve uniform deposition on a disk of 80 mm diameter, the optimization of the compact EBEP source has been examined as well. A high-quality DLC film with good film uniformity on the disk was synthesized at high acceleration voltage employing toluene gas.

We developed a new compact electron-beam-excited plasma (EBEP) source with a multihole grid. The source can be reliably operated under low-pressure conditions by controlling the electron-beam current and electron-beam energy independently. In this study, we applied the compact EBEP source to the generation of nitrogen plasma. The absolute nitrogen (N) atom densities in the plasma were evaluated using vacuum ultraviolet absorption spectroscopy (VUVAS) with a high-pressure microdischarge hollow cathode (MHCL) as a light source. The electron density and electron temperature were measured using a Langmuir probe. The behavior of N atom densities and electron densities in the plasma are discussed.

For polymer electrolyte fuel cell applications, carbon nanowalls (CNWs) were synthesized by radical-injection plasma-enhanced chemical vapor deposition, and a high density of Pt nanoparticles (>1012 cm−2) was supported on the CNWs using a supercritical fluid deposition system. The high potential cycle tests were applied and the electrochemical surface area of the Pt nanoparticle-supported CNWs did not change significantly, even after 20 000 high potential cycles. According to transmission electron microscopy observations, the mean diameter of Pt changed slightly after the cycle tests, while the crystallinity of the CNWs evaluated using Raman spectroscopy showed almost no change.

Bactericidal effects of phosphate buffered saline treated with electrically neutral oxygen radicals on Escherichia coli (E. coli) are studied using an atmospheric pressure radical source and colony counting method. To clarify the bactericidal mechanism, the chemistry in phosphate buffers treated with oxygen radicals with and without saline has been quantitatively investigated using the well-established chemical reporters N,N-diethyl-p-phenylenediamine reagent and Amplex Red for residual chlorine (HClO and ClO−) and hydrogen peroxide (H2O2), respectively. From the results, we have found that the presence of chlorine in the solutions treated with oxygen radicals is the most important factor in the further chemical reactions to generate hypochlorous acid in E. coli death, and H2O2 is also linked to the bactericidal effect via an indirect chemical pathway.

Single-walled carbon nanotubes (SWNTs) were synthesized with a high growth rate using an arc plasma employing carbon electrodes with a Ni–Y mixture catalyst. However, the mechanism of growth of highly crystalline SWNTs has not been clarified. Reactions between carbon and catalyst are considered to be one of the crucial factors in SWNT growth. Optical emission spectroscopy (OES) provides the information about the species in the plasma. C2, Ni, and Y emissions in the arc plasma at different currents were measured to investigate the relationship between active species in the arc plasma and the SWNT synthesis. On the basis of OES results, it was found that the balance between catalytic metal atoms and C2 radical emissions indicated the crystallinity ratio of SWNTs in thin graphitic or amorphous carbon layers. These results are useful for controlling the growth of SWNTs employing arc plasmas.

The effect of O2 additions below 0.2% to N2 was investigated for the cleaning of organic contaminants on an indium tin oxide film using a nonequilibrium atmospheric-pressure pulsed plasma. A remarkably high cleaning efficiency was obtained for plasma treatment with additions from 0.025 to 0.1% O2 to N2. The concentration of the ground state oxygen radical [O(3P)] was measured using vacuum UV laser absorption spectroscopy. It was found that the key factor for the surface cleaning was the scission of carbon bonds due to UV emissions, and subsequent oxidation due to O(3P) and ozone.

The behaviors of translational temperatures and absolute densities of Si atoms in very high frequency (VHF)-capacitively coupled SiH4 plasmas with dilution of Ar gas were measured by the ultraviolet absorption spectroscopy employing a ring dye laser and a hollow cathode lamp. We have found that the absolute densities of Si atoms are on the order of 109–1010 cm-3 with considerably high temperatures of 458–1258 K at a total pressure of 10.64 Pa, a SiH4 flow rate of 0–15 sccm, an Ar flow rate of 100 sccm, and a VHF power of 1500 W with an exciting frequency of 27 MHz or 60 MHz. The temperatures and densities increased with increasing SiH4 flow rate ratio. The temperatures at 27 MHz were larger than those at 60 MHz in the same SiH4/Ar flow rate ratio. The mechanism is discussed on the basis of the measured electron density, SiH4 molecule density, and the optical emission intensity of Ar.

The translational temperature and absolute density of Si atoms in capacitively coupled SiF4 plasmas driving with the very high frequency (VHF) of 27 MHz or 60 MHz were measured by ultraviolet absorption spectroscopy employing a ring dye laser and a hollow cathode lamp. High temperatures of Si atoms above 1000 K at 27 MHz were obtained at an electron density of 5.0×1010 cm-3, which is considerably larger than that at 60 MHz at the same electron density. The translational temperature and absolute density of SiF4 molecules were also evaluated using infrared diode laser absorption spectroscopy. From the results measured systematically, it is proposed that the hot Si atom is created due to the difference in the energy of Si atoms produced from the electron impact dissociation of SiFx (x = 1-3) radicals and SiF4 molecules. This result is very important from the viewpoint of diagnostics of atoms and plasma chemistries.

Actual Si wafer temperatures during plasma etching processes were temporally measured using a real-time wafer-temperature monitoring system with autocorrelation-type frequency-domain low-coherence interferometry. Indeed, the Si wafer temperature, which was 20 °C before the process, rapidly increased in 10 s. Then, the temperature rise gradually slowed, but continued to increase and reached 45 °C after 600 s. This can be due to the fact that there exists a heat source for the wafer other than the plasma. Reasonably, the Si wafer was found to be sensitive to the temperature of the disk covering the area around the wafer, i.e., the focus ring. Usually, the temperature of the focus ring is not controlled and causes the radial distribution of Si wafer temperature. Consequently, the Si wafer temperature should be controlled with the temperature increase of other heat sources, especially the focus ring.

We have quantitatively investigated the oxidative inactivation process of Penicillium digitatum spores including intracellular nanostructural changes through neutral oxygen species with a flux-defined atmospheric-pressure oxygen radical source, using fluorescent confocal-laser microscopy and transmission electron microscopy (TEM). The results suggest that neutral oxygen species, particularly ground-state atomic oxygen [O(3Pj)], which is an effective species for inactivating P. digitatum spores, inhibit the function of the cell membrane of spores without causing major superficial morphological changes at a low O(3Pj) dose of ~2.1 × 1019 cm−2 under an O(3Pj) flux of 2.3 × 1017 cm−2 s−1, following the oxidation of intracellular organelles up to an O(3Pj) dose of ~1.0 × 1020 cm−2. Finally, intracellular nanostructures are degraded by excess oxygen radicals over an O(3Pj) dose of ~1.0 × 1020 cm−2.

We have compared in detail the robust characteristics of an autocorrelation-type frequency-domain low-coherence interferometry (ACT-FD-LCI) system without a reference mirror with those of the conventional frequency-domain low-coherence interferometry (FD-LCI) system with a reference mirror. The standard deviation of temperature measurement was less than 0.04 °C at temperatures below 550 °C for a typical thickness of 480 µm, as determined from the measured optical path length. The robustness of performance against disturbances has been markedly improved, as compared with a precision of 0.28 °C in the conventional FD-LCI system with the reference mirror. In particular, we have confirmed that the ACT-FD-LCI system has a large tolerance to disturbances due to dispersion and changes in the polarization of the signal light owing to the removal of the reference mirror.

To investigate the inactivation process of Penicillium digitatum spores through neutral oxygen species, the spores were treated with an atmospheric-pressure oxygen radical source and observed in-situ using a fluorescent confocal-laser microscope. The treated spores were stained with two fluorescent dyes, 1,1′-dioctadecyl-3,3,Y,3′-tetramethylindocarbocyanine perchlorate (DiI) and diphenyl-1-pyrenylphosphine (DPPP). The intracellular organelles as well as the cell membranes in the spores treated with the oxygen radical source were stained with DiI without a major morphological change of the membranes. DPPP staining revealed that the organelles were oxidized by the oxygen radical treatment. These results suggest that neutral oxygen species, especially atomic oxygen, induce a minor structural change or functional inhibition of cell membranes, which leads to the oxidation of the intracellular organelles through the penetration of reactive oxygen species into the cell.

To investigate the inactivation process of Penicillium digitatum spores treated with a non-equilibrium atmospheric pressure plasma, the spores were observed using a fluorescent microscope and compared with those treated with ultraviolet (UV) light or moist heat. The treated spores were stained with two fluorescent dyes, 1,1'-dioctadecyl-3,3,Y,3'-tetramethylindocarbocyanine perchlorate (DiI) and diphenyl-1-pyrenylphosphine (DPPP). The intracellular organelles as well as cell membranes in the spores treated with the plasma were stained with DiI without a major morphological change of the membranes, while the organelles were never stained in the spores treated with UV light or moist heat. Moreover, DPPP staining revealed that organelles were oxidized by plasma treatment unlike UV light or moist heat treatments. These results suggest that only plasma treatment induces a minor structural change or functional inhibition of cell membranes, which leads to the oxidation of the intracellular organelles without a major deformation of the membranes through the penetration of reactive oxygen species generated by the plasma into the cell.

We proposed an optical-fiber-type broadband cavity ring-down spectroscopy system using wavelength-tunable ultrashort pulsed light. The absorbance of glucose in various concentrations in water was derived from the ring-down plots of intensities of the interference waveforms generated using a Mach–Zehnder interferometer with different optical delay path lengths, which were shifted by an automatic optical switching module. The absorption spectrum of glucose was obtained in the wavelength region from 1620 to 1690 nm by varying the wavelength using wavelength-tunable ultrashort pulsed light, which was generated from a femtosecond pulsed laser and polarization-maintaining fiber. The measurement error of concentration was improved using multiple linear regression analysis of absorption spectra. The results demonstrate that the optical-fiber-type cavity ring-down spectroscopy system has the potential to measure broadband absorption spectra with high sensitivity.

Indium–zinc-oxide (IZO) films were synthesized by radio frequency magnetron sputtering. In order to clarify the mechanisms of IZO film formation, the absolute densities of In and Zn atoms were measured simultaneously by absorption spectroscopy employing the multi-micro hollow cathode lamp. Their densities were measured to be 109 to 1011 cm-3 and increased with pressure from 1 to 10 Pa. The density ratios of In to Zn in the gas phase corresponded to the ratios of film composition, and the relative amount of Zn atom increased with decreasing pressure. Carrier density increased with decreasing density ratio of In to Zn owing to the increase in the number of oxygen vacancies, which was clarified from the O 1s spectra obtained by X-ray photoelectron spectroscopy. A low resistivity of 10-6 Ω m and an optical transmission of over 80% in the visible region were achieved at a pressure of 1 Pa.

The behaviors of Pb and metastable He atoms in the multi-micro hollow cathode lamp (multi-MHCL) at pressures of the order of kPa have been investigated by diode laser absorption spectroscopy. The pressure broadening effect for absorption line-profile was overlapped to Doppler profile and was estimated to be 0.26 MHz/Pa from line-profiles of metastable He atoms in the range from 5 to 10 kPa. The translational temperatures of metastable He atoms decreased from 830 to 410 K with increasing the pressure from 5 to 10 kPa. From line-profiles of Pb atoms, the temperatures and densities of Pb in the multi-MHCL were evaluated to decrease from 820 to 610 K and 9.0×1011 to 4.6×1011 cm-3 with increasing He pressure from 4.9 to 7.4 kPa, respectively. The Lorentz broadenings was larger than those of He atom and the pressure dependence were estimated to be 0.22 MHz/Pa. The behaviors of emission intensities corresponded with those of atomic densities due to enhancement of sputtering. From these results, the multi-MHCL with line-profile guaranteed has been realized for measuring multi-metallic atom densities precisely.

The optimum conditions for a plasma etching device are generally determined from the results of etching a sample while varying an external parameter (e.g., gas mass flow, gas mixing ratio, process chamber pressure, or plasma source power). However, to realize controlled plasma etching with few fluctuations on a subnanometer scale, it is essential to develop a system that is controlled in real-time based on internal plasma parameters (e.g., densities and energies of radicals and ions), which directly determine process characteristics, rather than external plasma parameters. We have developed an autonomously controlled plasma etching system that performs integrated monitoring of radicals in the gas phase and on the surface of films. The etching rate of organic materials could be autonomously controlled based on hydrogen and nitrogen radical densities obtained in real-time.

We have successfully performed real-time noncontact monitoring of substrate temperature and thin film thickness during plasma etching using optical-fiber-based low-coherence interferometry. The simultaneous measurement of the silicon (Si) substrate temperature and the etching depth of the silicon dioxide (SiO2) thin film on this substrate was performed in a dual-frequency capacitively coupled Ar/C4F8/O2 plasma. The SiO2 film thickness was deduced from the ratio of the interference intensity at the SiO2/Si interface to that at the Si/air interface. The measurement error in the SiO2 film thickness was less than 11 nm. The temperature variation of the Si wafer was derived from the temperature change of its optical path length. The temperature measurement error, caused by the shift in optical path length due to the change in SiO2 film thickness, was reduced from 7.5 to 0.6 °C by compensating for the shift using the SiO2 thickness data. This method enables precise control of etching performance and improves process reproducibility.

The precise etching of organic films with a low dielectric constant (low-k) in a dual-frequency capacitively coupled plasma etching reactor with a plasma generation of 100 MHz and an applied bias of 2 MHz employing a gas mixture of hydrogen and nitrogen was performed by real-time control of the densities of hydrogen (H) and nitrogen (N) radicals based on real-time measurement of the Si substrate temperature. H and N radical densities were monitored near the sidewall of the reactor by vacuum ultraviolet absorption spectroscopy, and temperature was monitored by an optical fiber-type low-coherence interferometer. On the basis of the results of surface analysis by X-ray photoelectron spectroscopy, etched profiles were effectively determined from the chemical component of protection layers on the sidewall of the etched pattern affected by the ratio of H/(H+N) and substrate temperature. As the etching feature evolves, the ratio of radical density should be controlled temporally to maintain vertical profiles according to the change in substrate temperature. As a result, we have successfully realized an organic film with a vertical feature. These results indicate the need for autonomous control of the etch process based on real-time information on the plasma process for the next-generation ultrafine etching.

Penicillium digitatum spores were inactivated using an oxygen-radical source that supplies only neutral oxygen radicals. Vacuum ultraviolet absorption spectroscopy was used to measure the ground-state atomic oxygen [O (3Pj)] densities and they were estimated to be in the range of 1014–1015 cm-3. The inactivation rate of P. digitatum spores was correlated with the O (3Pj) density. The result indicates that O (3Pj) is the dominant species in the inactivation. The inactivation rate constant of P. digitatum spores by O (3Pj) was estimated to be on the order of 10-17 cm3 s-1 from the measured O (3Pj) densities and inactivation rates.

We performed real-time non-contact monitoring of temperatures of a silicon wafer and chamber parts in plasma etching processes using optical fiber-based low-coherence interferometry. The measurements were performed in dual-frequency capacitively coupled Ar/C4F8/O2 plasma processes. The temperature of a 780-µm-thick Si wafer was measured with a deviation of 0.11 K. Comparison between in-situ measurement results of an on-wafer temperature sensor and an optical-fiber type fluorescence temperature sensor confirmed that the low-coherence interferometry had superior performance in monitoring the temperature of the Si wafer in real-time. This method will enable better control of etching performance with improved process reproducibility.

The absolute densities and translational temperatures of Si atoms in very high frequency capacitively coupled SiH4 plasmas diluted with Ar, N2, and H2 gases were investigated by ultraviolet absorption spectroscopy with a ring dye laser and a hollow cathode lamp. It was found that the absolute density of Si atoms was of the order of 109–1010 cm-3 and the translational temperature of Si atoms ranged from 620 to 1130 K at a total pressure of 11 Pa, a dilution gas flow rate of 100 sccm, and a SiH4 flow rate of 0–15 sccm. The absolute densities and temperatures of Si atoms in plasma at an excitation frequency of 27 MHz were larger than those at 60 MHz under the conditions at the same electron density. Si atom heating was due to the energy of Si atoms released from the electron impact dissociation of SiH x (x=1–4). The translational temperatures of Si atoms in SiH4/Ar, SiH4/N2, and SiH4/H2 plasmas were evaluated to be 970, 1030, and 1130 K, respectively, at a frequency of 27 MHz, a SiH4 flow rate of 10 sccm, and a VHF power of 1500 W. The effect of Si atoms and SiH3 radicals on film deposition was investigated for SiH4/N2 in 27 MHz and 60 MHz plasmas. From the measurement using Fourier transform infrared absorption spectroscopy, the peak of the Si–H bond decreased and that of the N–H bond increased with increasing excitation frequency. Therefore, the film deposited at 60 MHz indicated a nitride-rich composition in comparison with that at 27 MHz. The contribution ratio of Si atoms to SiH3 radicals for film deposition in 27 MHz plasma was larger than that in 60 MHz plasma. These results are very important from the viewpoint of understanding neutral radical chemistries in the plasma and their related processing.

The measurement method for determining absolute densities of SiF4 molecules in a reactive plasma has been established using infrared diode laser absorption spectroscopy (IRLAS). The spatial distribution of line averaged absolute densities of SiF4 molecules has been investigated in the electron cyclotron resonance (ECR) plasma reactor employing SiF4 gas using infrared diode laser absorption spectroscopy without a multiple reflection cell, namely, single-path IRLAS. Furthermore, the spatial distributions of SiF2 radical densities are measured using laser-induced fluorescence (LIF) technique. It was found that the line averaged absolute density of SiF4 molecules indicated the hollow-type distribution in the reactor, while SiF2 radical densities had the maximum value near the plasma boundary. On the basis of these measured results, the formation mechanism of spatial distribution of SiF4 and SiF2 densities in the plasma reactor are clarified.

A novel dry etching process for amorphous silicon (a-Si) and tungsten (W) for chemical vapor deposition (CVD) chamber cleaning has been performed by electron cyclotron resonance (ECR) O2 plasma employing a solid-material evaporation system where fluorocarbon species are produced from fluorinated ethylene propylene (FEP) by CO2 laser evaporation for preventing global warming. This process enables us to realize etching of materials without using any perfluorocompound (PFC) feed gases which have a high global warming potential (GWP). Etching characteristics together with diagnostics of the F atom density, CFx (x=1–3) radical densities, electron density and temperature have been investigated as functions of pressure. As a result, it was found that etching rates of a-Si and W films were determined based on the F atom density, ion flux and ion bombardment energy. Furthermore, etching rates of a-Si and W films increased by heating the fluorocarbon species before introducing them into the plasma reactor. Thus, high rates of etching of a-Si and W films were successfully achieved by this novel etching process compared with conventional etching using ECR plasma with CF4/O2 feed gases.

We have developed a measurement method for obtaining spatial distributions of absolute densities of CF and CF2 radicals in a plasma reactor by combining single-path infrared laser absorption spectroscopy (IRLAS) and laser-induced fluorescence (LIF) techniques. This novel method has been successfully applied to the spatial distribution measurement of absolute densities of CF and CF2 radicals in an electron cyclotron resonance (ECR) plasma reactor employing a tetrafluorocarbon gas (C4F8). It was found that CF radical densities were higher than CF2 ones in the plasma region but lower outside the plasma region.

Diamond was successfully synthesized by using H2-rich CH4/CO/H2 and H2-rich CH4/H2 inductively coupled plasmas at a pressure of 11 Pa. The ratio of particle size to deposition time, as a criterion of the diamond growth rate, in H2-rich CH4/CO/H2 mixture gas plasmas was higher than that in H2-rich CH4/H2 mixture gas plasmas. The deposits in H2-rich CH4/H2 and H2-rich CH4/CO/H2 mixture gas plasmas were found to contain nondiamond phases, as confirmed by Raman spectroscopy. In order to investigate the mechanism involved in diamond formation, C-atom densities in the plasmas were measured by vacuum ultraviolet absorption spectroscopy with a carbon hollow cathode lamp. In addition, CH, OH and H-atom emission intensities were measured by optical emission spectroscopy. As a result, it was found that the C-atom densities increased considerably with increasing mixture ratio of CO to CH4. On the basis of the correlation between the quality of deposits and the C-atom densities, C-atoms were determined to probably contribute to the formation of nondiamond phases in the deposits.

We measured Einstein's A coefficient of the transition line of the C atom at 296.7 nm (2s2p 3 5S2 - 2s 22p 2 3P2), which is useful for the absorption spectrocopic measurement of C atom density in processing plasmas. Einstein's A coefficient was evaluated from the emission decay rate of the 296.7 nm line in an electron cyclotron plasma employing CO gas. The obtained value of 3.9×104 s-1 is almost 2000 times as large as the reported theoretical A coefficient [G. H. Garstang: The Observatory 82 (1962) 50].

Carbon atom densities in an inductively coupled radio frequency (13.56 MHz) CO and CO and H2 mixed plasmas were successfully measured for the first time using ultra-violet absorption spectroscopy (UVAS) with a carbon hollow cathode lamp. This method, developed for monitoring carbon atoms in-situ in the plasmas, is very useful for the investigation of etching and chemical vapor deposition (CVD) processes containing carbon atoms and the sputtering system employing a carbon target.

For plasma-assisted processing of future semiconductor devices, a new compact microwave plasma source has been specifically designed. The source is versatile in that plasma production is possible over a wide pressure range. Measured plasma parameters include electron densities in excess of 1011 cm-3 and low plasma potential (2 gas was employed to correlate the oxygen atom density with the plasma operating conditions. At a microwave power of 300 W and a O2 partial pressure of 16.6 Pa oxygen atom densities in excess of 1.9×1015 cm-3 have been measured, which gives dissociation rates of O2 of approximately 20%. Effects of wall materials on the oxygen atom density were also investigated. Using a Teflon liner at high pressures provides a 37% increase in oxygen atom density due the lower recombination coefficient of Teflon compared to stainless steel.

The behavior of Si atoms and SiH x + (x=0–3) ions in electron cyclotron resonance (ECR) SiH4/Ar and SiH4/H2 plasmas was investigated by ultraviolet absorption spectroscopy and quadrupole mass spectrometry as a function of microwave power, pressure and SiH4 flow rate ratio. The behavior of ions in SiH4/H2 plasmas is different from that in SiH4/Ar plasmas. This behavior is discussed from the generation and loss of each species. Moreover, the effects of Si atoms and ions on film formation are discussed based on these results.