Mitsuaki Harada

Low-damage surface processing by gas cluster ion beams

Abstract Low-damage surface processing by gas cluster ion beams has been studied at acceleration voltages below 20 kV. Surfaces of several kinds of targets were smoothed significantly by CO 2 cluster ion irradiation at normal incidence. Surfaces were smoothed most effectively if the minimum cluster sizes were in the range of 150–250. SiO 2 films with a thickness of about 5.5 nm were grown on Si substrates at room temperature by irradiation with CO 2 cluster ions with a dose of 2 × 10 15 ions/cm 2 . A thin transition layer of 2.5 nm thickness was formed underneath the SiO 2 films. in addition, Si surfaces were cleaned after CO 2 and Ar cluster ion irradiation at low doses of less than 2 × 10 15 ions/cm 2 . The removal rates of surface impurities with cluster ions were 40–100 times higher than with monomer ions.

Photochemical etching of GaAs using synchrotron radiation

The photochemical etching of gallium arsenide by chlorine was investigated using synchrotron radiation. At the substrate temperatures above 25°C, both the irradiated and nonirradiated regions were uniformly etched. In case of substrate temperatures below -25°C, highly selective etching was observed in the irradiated region. We considered that at low temperatures, etching reaction caused by gas-phase excitation is suppressed and photochemical surface reaction becomes dominant.

SiO2 film formation at room temperature by gas cluster ion beam oxidation

Abstract High quality SiO 2 film of thicknesses less than 11 nm were formed on Si substrate surfaces at room temperature by irradiation with O 2 and CO 2 cluster ions. The acceleration voltages were in the range of 5–10 kV. The minimum cluster size was 250 molecules, thus the maximum energy per molecule was less than 40 eV. These SiO 2 films which were formed had a stoichiometric composition, smooth interfaces with Si substrates and low carbon content. The results indicate a high chemical reactivity of gas cluster ions. Thus, the gas cluster ion beam technique has a potential for the formation of various kinds of films at low temperatures.

Low-Temperature Oxidation of Silicon by O2 Cluster Ion Beams.

High-quality SiO 2 films up to 11 nm thick were grown on Si substrate surfaces at room temperature by O 2 cluster ion irradiation. No damage was observed after N 2 annealing at 400°C for 30 min in the I-V characteristics of the thermally grown gate oxides irradiated with 5 keV Ar cluster ions. These results indicate that O 2 cluster ions strongly enhanced the oxidation with low irradiation damage.

IRRADIATION EFFECTS OF O2 CLUSTER IONS FOR LEAD OXIDE FILM FORMATION

Abstract O 2 cluster ions were directed onto Si substrates, covered with SiO 2 , during the evaporation of Pb. By increasing the acceleration voltage, the irradiation of O 2 cluster ions enhanced the oxidation, crystallization and surface smoothing of the polycrystalline lead oxide films. They were preferentially oriented in the (111) direction at acceleration voltages above 5 kV. A significant smoothing effect was observed even if the acceleration voltage was as low as 1 kV. A surface roughness of 9 A was obtained at 7 kV.

IrSiN films with superior oxygen-diffusion barrier effect for stacked ferroelectric capacitors

IrSiN films (including IrSi film) formed by the reactive co-sputtering of Ir and Si targets have been investigated with regard to their oxygen-diffusion barriers in an application to stacked ferroelectric capacitors. The film properties and barrier effect were examined with relation to the N2/(Ar+N2) deposition flow ratio. In IrSiN films formed with a N2/(Ar+N2) flow ratio of 0.06 or 0.12, a shallow oxygen penetration depth of less than 20 nm was attained even under annealing in O2 at 800 °C for 40 min, and no reaction was observed with polycrystalline silicon (poly-Si) films. These films also adhered well to both poly-Si and SiO2 films. Therefore, the barriers are likely to prove extremely useful for integrated ferroelectric capacitors.

Generation of O2 and metalorganic cluster ion beams and its application to low-temperature thin oxide film formation

High-current O 2 and N 2 cluster ion beams were formed through a Laval nozzle by the combination of He mixing and gas cooling. The cluster current of 320 nA was obtained from O 2 cluster ions whose mean cluster size was 7000. Consequently, the equivalent ion current was as high as 2.2 mA. The optimum He flow ratio to obtain the most intense cluster beams was lower than those reported. The high-current O 2 cluster ion beams were successfully applied to the low-temperature formation of high-quality SiO 2 and PbO films. Generation of Ti(i-OC 3 H 7 ) 4 cluster ion beams (1.7 nA) was also demonstrated with the He bubbling method for the first time.

Pattern replication accuracy in 1:1 synchrotron radiation lithography

Abstract The replicated pattern distortion for feature sizes down to 0.15 μm, characterized by pattern linearity, pattern density dependence, and corner rounding, is investigated in synchrotron radiation (SR) lithography. In the investigation, a highly accurate X-ray mask delineated by a focused ion beam, a chemically amplified resist, and a Fresnel diffraction model simulator are used. At a 15 μm mask-to-wafer gap, no pattern proximity effect is observed. The corner rounding radius due to Fresnel diffraction is approximately 0.04 μm.

Pattern replication accuracy in 1 : 1 SR lithography

Abstract The replicated pattern distortion for feature sizes down to 0.15 μm, characterized by pattern linearity, pattern density dependence, and corner rounding, is investigated in synchrotron radiation (SR) lithography, using a highly accurate x-ray mask delineated by a focused ion beam. At a 15 μm mask-to-wafer gap, no proximity effect is observed. The corner rounding due to Fresnel diffraction is approximately 0.04 μm.

Exposure and resist-process condition dependence of replicated-pattern accuracy in SR lithography

Replicated pattern accuracy was investigated in synchrotron radiation (SR) lithography, using a chemically amplified (CA) negative-type resist and a highly accurate x-ray mask delineated by focused ion beams (FIB). The size of the hole resist pattern which is arranged in a lattice is affected by the proximity gap and the pattern pitch, but that of the dot resist pattern is hardly dependent on these variables. The dot resist pattern, which was replicated with the 0.25- micrometers -square hole mask pattern, became circular with a proximity gap of over 20 micrometers . In order to obtain highly accurate pattern shape as well as pattern size, the proximity gap should be less than 20 micrometers . The resist pattern size and shape depend on the exposure dose. This was confirmed through the simulation of Fresnel diffraction. The resist pattern was influenced considerably by the post-exposure baking (PEB) conditions, temperature and time. The PEB condition dependence of a replicated pattern was investigated. It is effective to extend the PEB time to improve the sensitivity without deforming the pattern shape.