Takashi Iwabuchi

Study of Hydrogen Vacuum-Ultraviolet Light Sources for Submicron Lithography

The output properties of hydrogen light sources and the resist parameters, such as spectral sensitivity and absorption coefficient, in the vacuum-ultraviolet (VUV) region were investigated. A very low exposure energy of about 1 mJ/cm2 was obtained by employing a very thin polymethyl methacrylate film and the VUV light of hydrogen microwave discharge. Contact photolithography using a Si/MgF2 mask and a trilayer resist system showed that submicron patterns as small as 0.2 ?m had been replicated at an exposure time of under 30 s.

Nanometer Pattern Transfer by VUV Lithography with a D2 Lamp

Vacuum-ultraviolet lithography of a trilayer resist system which consists of polymethyl methacrylate (PMMA), Si and polyimide has been studied using a deuterium lamp. The exposure dose needed for a 0.1-µm-thick PMMA film is less than 1 mJ/cm2, and a high etch rate ratio of 40 for polyimide to Si is obtained with the reactive ion beam etching (RIBE) technique. Using a simple contact exposure system and RIBE, photomask patterns are accurately transferred in the polyimide down to a linewidth of 0.2 µm, and 50-nm line patterns of polyimide are obtained.

Tungsten-carbon multilayers for x-ray optics prepared by ArF excimer-laser-induced chemical vapor deposition

The authors have studied the characteristics of tungsten (W) and carbon (C) thin films, and W/C multilayers prepared by ArF excimer‐laser‐induced chemical vapor deposition using tungsten hexafluoride and benzene gases. Amorphous W and C films with very smooth surfaces were obtained at substrate temperatures of 100–200 °C and 100–300 °C, respectively. In small‐angle x‐ray scattering measurements for the multilayers deposited at 200 °C, a first order of multilayer reflections were clearly observed. Furthermore, Auger electron spectroscopy showed that W and C layers in the multilayers were periodically deposited.

Fabrication of Tungsten-Carbon Multilayers for Soft X-Ray Optics Using Excimer-Laser-Induced Chemical Vapor Deposition Technique

The authors describe a new excimer-laser-induced chemical vapor deposition (LCVD) technique using laser-beam-scanning and ultrahigh-vacuum chamber systems. Film thickness distribution is controlled by scanning the laser beam on the substrate. Film thicknesses in LCVD with film depositions on the laser-beam transmitting window are also controlled by changing the deposition time. Tungsten-carbon multilayers of uniform thickness are successfully deposited on 2-inch-diameter substrates without being restricted by the beam size. A soft X-ray reflectivity of 25% is obtained at a grazing angle of 6°, and reflection peaks up to the third order are clearly observed for the first time in LCVD

Laser-Beam-Scanning Chemical Vapor Deposition Technique for Controlling the Spatial Thickness Distribution of Thin Films

We have developed a laser-beam-scanning chemical vapor deposition (CVD) system using a galvanometer scanner. The basic idea for controlling the spatial thickness distribution of films using the CVD system is discussed. Carbon films with uniform and concave thickness distributions are deposited and the distributions correspond directly to the laser-beam-scanning modes.

Thickness Control of Multilayer Films in Laser-Induced Chemical Vapor Deposition

The authors propose a sequence-control method for layer thicknesses by changing deposition time in the chemical vapor deposition with nonconstant deposition rates due to films deposited onto the laser-beam transmitting window. The method is applied to tungsten-carbon multilayer depositions using an ArF excimer laser.

Absorption Coefficient and Sensitivity of Positive and Negative Resists in the Vacuum Ultraviolet Region

Absorption coefficients for the resist materials (polymethyl methacrylate (PMMA) and partially chloromethylated polystyrene (CMS-DU)) were obtained in the vacuum ultraviolet (VUV) region. Negative and positive resist characteristics were investigated using a coherent VUV radiation source (λ=110-150 nm) generated by two-photon resonant four-wave mixing in Cd vapor. A very low exposure energy of approximately 1 mJ/cm2 was realized by employing a very thin resist film and using VUV light from the high-absorption region of the resist materials.

Characterization of tungsten-silicon multilayer mirrors fabricated using an ArF excimer laser

Tungsten-silicon (W/Si) multilayers for soft x-ray mirrors fabricated using argon-fluoride (ArF) excimer laser-induced decomposition of tungsten hexafluoride (WF 6 ) and disilane (Si 2 H 6 ) gases have been studied. The multi-layers are characterized using Auger electron spectroscopy, transmission electron microscopy and soft x-ray reflectivity measurement. The optical constants of W and Si films are determined, and then the interface roughness estimated at 1.5 nm rms is concluded to be a main cause to reduce the reflectivity.

Magnetron sputter-deposited Al2O3/SiO2 multilayer coatings for kilowatt excimer lasers with high repetition rates

The authors describe the multilayer coatings deposited using a magnetron sputtering method and their characteristics. In Al2O3/SiO2 multilayer mirrors fabricated on Si and SiC substrates, reflectivities of more than 99% are obtained both in XeCl and KrF excimer-laser wavelength regions. For antireflective windows, a reflectivity of 1% is obtained in SiO2/Al2O3/SiO2 trilayer systems coated on both sides of a CaF2 substrate in the two wavelength regions. In XeCl laser-beam irradiation tests, the fabricated multilayers show higher optical damage thresholds than do typical commercial mirrors. Furthermore, the multilayers show no reflection spectral change, even when heated to 800°C.