Hisao Nagai

Behavior of atomic radicals and their effects on organic low dielectric constant film etching in high density N2/H2 and N2/NH3 plasmas

An organic film, FLARE™, is one of the most prospective candidates for interlayer insulating films with low dielectric constants (low k). This organic low k film was etched in inductively coupled high-density plasmas employing N2/H2 and N2/NH3 gases. By changing the mixing ratio of these gases, the anisotropic etching profile was obtained. The etching plasmas were evaluated by quadruple mass spectroscopy and the vacuum ultraviolet absorption spectroscopy employing microplasma as a light source. N and H radical densities were estimated on the order of 1011–1012 cm−3 and 1012–1013 cm−3, respectively. The behavior of etch rate corresponded well to that of H radical density. H radicals were found to be important species for organic low k film etching, while N radicals could not etch without ion bombardments. On the other hand, N radicals were found to be effective for the formation of protection layer on the sidewall against the etching by the H radicals. The ratio of H and N radical densities would be import...

Measurement of oxygen atom density employing vacuum ultraviolet absorption spectroscopy with microdischarge hollow cathode lamp

W and an O2 pressure ranging from 1.3 to 26.7 Pa. The behavior of O atom density measured using VUVAS technique was consistent with that obtained by actinometry technique using O emission intensities of 844.6 nm and 777.4 nm lines. Moreover, the lifetime of O atom in the afterglow plasma has been measured. The decay curves of the O atom density were fitted with exponential functions. The extinction process of O atom in the inductively coupled O2 plasma has been discussed.

Etching organic low dielectric film in ultrahigh frequency plasma using N2/H2 and N2/NH3 gases

The behavior of species in the gas phase and their effects on the etching characteristics of organic film with the lower dielectric constant (low-k) were investigated in 500 MHz ultrahigh frequency (UHF) plasma using N2/H2 and N2/NH3 gases. The absolute H and N radical densities and NH3 molecule density in etching plasmas were evaluated by the vacuum ultraviolet absorption spectroscopy and the infrared diode laser absorption spectroscopy technique, respectively. The effects of frequency that excited the plasma in the production of H and N radicals were clarified by comparing the behavior of radicals in the UHF plasma with that in the inductively coupled plasma (ICP) exciting at the frequency of 13.56 MHz reported in the previous study. H radicals were produced more efficiently from NH3 gas and N radicals more efficiently from N2 gas in the UHF plasma than in the ICP. H radicals were generated not only through the dissociation of the H2 molecule but also from NH3 molecules produced in the N2/H2 plasma. On ...

Fabrication of Multilayered SiOCH Films with Low Dielectric Constant Employing Layer-by-Layer Process of Plasma Enhanced Chemical Vapor Deposition and Oxidation

A multilayered SiOCH film was proposed as an interlayer insulating film with low dielectric constant (low k) for multilevel interconnection of next-generation ultralarge scale integrated circuits (ULSIs). Multilayered films were fabricated employing a layer-by-layer process of plasma-enhanced chemical vapor deposition (PECVD) using a hexamethyldisiloxane (HMDSO) monomer source and O2 plasma oxidation. The methyl-siloxane film consisting of siloxane (Si–O–Si) and Si–methyl (Si–CH3) bonds, was formed using PECVD with HMDSO and O2. In order to improve the dielectric properties of the film, the surface of the methyl-siloxane film was transformed into the low-density SiOCH layer through plasma oxidation. The multilayered structure composed of alternating methyl-siloxane and low-density SiOCH layers was fabricated. As a result of optimization of layer-by-layer process conditions, the multilayered thin film with low dielectric constant of 2.4 was successfully obtained.

On the mechanism of polytetrafluoroethylene ablation using a synchrotron radiation-induced photochemical process

Abstract To clarify the ablation mechanism of polytetrafluoroethylene (PTFE) by synchrotron radiation (SR), the effect of the photon energy distribution of an SR beam on the ablation rate was examined. Carbon (C) and a carbon/magnesium fluoride/carbon (C/MgF x /C) membranes were used as filters to modify the photon energy distribution of incident SR beam. The fragments resulting from the decomposition of PTFE by SR irradiation were measured with in situ quadruple mass spectroscopy (QMS). The ablation mechanism of PTFE is due to absorption of the SR by fluorine. In addition, SR ablation was applied to form patterns in metal fluoride films for the first time.

Nitriding of a tool steel with an electron-beam-excited plasma

Nitriding of a tool steel was carried out with an electron-beam-excited plasma (EBEP). EBEP is sustained with energetic electron beams over the pressure range of 10−3–101Pa by electron-impact ionization. Samples whose temperatures were controlled by electric radiant heater were exposed to EBEP. A nitrided layer of 100μm and a surface hardness of 1000HV(0.1) were achieved for tool steel SKD61 (JIS) at 800K and a treatment time of 3h. In order to measure the density of nitrogen atoms in EBEP, a vacuum ultraviolet absorption spectroscopy system was used. It was found that the density of nitrogen atoms increased from 1011to1012cm−3 linearly with an increase of electron beam current from 2to20A.

Plasma Induced Subsurface Reactions for Anisotropic Etching of Organic Low Dielectric Film Employing N2 and H2 Gas Chemistry

Subsurface reactions of organic low dielectric (low k) film exposed to plasmas with low ion bombardment energy were investigated by a real time analysis of Fourier transform infrared attenuated total reflection (FT-IR ATR). The exposure of N2 plasma resulted in the formation of a CN layer composed of C(sp2)=N and C(sp3)–N bonds. After the N2 plasma exposure, the surface was exposed to H2 plasma. C(sp1)≡N and C(sp2)=N bonds were removed by the H radicals, while the C(sp3)–N bond remained. It was found that the C(sp3)–N bond was the key chemical bond against H2 plasma exposure. Based on the analyses, a reaction model for anisotropic profile in organic low k film etching employing N–H plasmas is proposed.

Synthesis of diamond using a low pressure, radio frequency, inductively coupled plasma

Diamond was successfully synthesized using a low pressure, radio frequency (rf), inductively coupled plasma. A source mixture of methanol (CH3OH), hydrogen (H2), and water vapor (H2O) was introduced into a reaction chamber through a quartz tube of 12 mm inner diameter. A seven-turn rf coil was mounted on the quartz tube to produce high-density plasma. The Si substrate was located in a downstream region. Diamond formation was carried out with varying mixture ratio of source gases at total pressures of 70–140 mTorr. Diamond crystals exhibiting a well-defined 1332 cm−1 diamond Raman peak can be formed using CH3OH/H2/H2O mixtures at total pressures below 140 mTorr.

Effects of Oxygen and Nitrogen Atoms on SiOCH Film Etching in Ultrahigh-Frequency Plasma

Behaviors of absolute densities of O and N atoms and their effects on the etching characteristics of SiOCH film were investigated in ultrahigh-frequency (UHF) plasma. O2 or N2 are added into the plasma employing C4F8 diluted with Ar. The absolute densities of O and N atoms were evaluated by vacuum ultraviolet absorption spectroscopy (VUVAS), and CFx radical densities by infrared diode laser absorption spectroscopy (IR-LAS) technique. These radical densities were of the order of 1011–1012 cm-3 under typical etching conditions. It was found that the effect of the contribution of O atoms in SiOCH film etching was larger by one order of magnitude than that of N atoms.

Silicon–oxide etching process employing an electron-beam-excited plasma

Silicon–oxide (SiO2) etching employing an electron-beam-excited plasma has been investigated. SiO2 films were etched using self-bias induced by the electron beam for the generating plasma. As a source gas, the CF4 diluted by Ar (CF4/Ar) was employed. The etch rate of 117 nm/min has been obtained at a total pressure of 0.18 Pa and a total flow rate of 43 sccm with a CF4/Ar flow rate ratio of 13%. The etching was carried out at an electron-beam current of 9.5 A and an electron-acceleration voltage of 100 V without any additional bias power supply. The CF4/Ar plasma diagnostics was carried out by using a Langmuir probe and optical-emission spectroscopy. It has been found that the higher electron-beam current for generating plasmas improves the plasma density and sheath potential, resulting in a higher etch rate of SiO2. The results indicate that the electron-beam-excited plasma has a potential for application to micromachining processes.