Susumu Namba

Effective deep ultraviolet photoetching of polymethyl methacrylate by an excimer laser

Photoetching of polymethyl methacrylate (PMMA) for pulsed high power UV light is demonstrated. As a high power UV light source, a KrF excimer laser was used. Etching depth obtained by deep UV light irradiation has not only energy dependence, but also power dependence. It increased abruptly by increasing the exposed power density for the same exposed energy density.These experimental results show that high power excimer lasers are the effective light source for UV photoetching of PMMA.

Focused ion beam induced fine patterns of organogold films

It has been found that a relatively low‐dose focused ion beam irradiation makes an organogold film insoluble to its solvents (e.g., trichloroethylene), resulting in submicron pattern formation. Ion beam induced, low conductivity as with resistivities of (4–4000) MΩ/⧠ has been observed for more than 1×1015 ions/cm2 dose for a 0.65‐μm‐thick film. However, by heat treatment at 300 °C after low‐dose ion beam patterning, gold patterns with resistivity of 3×10−4 Ω cm, which is about 100 times the bulk gold value, are obtained.

Thin-film long-wire antenna for 10.6 μm CO_2 laser radiation

Thin-film warm carrier devices which had 100-, 400- and 450-µm-long thin-film antennas were fabricated, and antenna properties at CO2 laser frequency were investigated. It was found that the fabricated thin-film antenna works as a long-wire antenna with electrical loss for CO2 laser radiation.

In situ observation and correction of resist patterns in atomic force microscope lithography

In atomic force microscope lithography using negative-type resist, the increase of the resist thickness of the exposed part before development is observed in the dose range from 8×10−13 to 10−16 cm−2. The increase is about 1 nm with a dose of 8×10−13 cm−2, which is less than one-tenth of the threshold dose for polymerization of resist. The phenomena of the increase of resist thickness is used for in situ observation of the exposed pattern before development. With this in situ observation, precise correction of the lithography pattern can be made before development.

Numerical studies of quantum conduction through a junction of wide‐narrow geometry

The conductance of the wide‐narrow geometry in the ballistic transport regime has been calculated by numerical scattering matrix methods. The oscillations of the conductance as a function of the width of the wide region relative to that of the narrow region was found. The period of oscillation corresponds to twice the width, where a new subband is generated as the width of the wide region is increased. The amplitude of the oscillation decreases with an increase in the width of the wide region. The effects of contact potential at a junction are also discussed.

Self-Development Mechanism of Nitrocellulose Resist: Electron Beam Irradiation.

The decomposition mechanism of a nitrocellulose film induced by irradiation of an electron beam and He+ ion beam was investigated by monitoring the changes of the infrared spectra. With irradiation of the electron beam, it was found that the electronic stopping power caused the decomposition of the nitrocellulose resist by breaking the R-O-NO2 bond. In addition, it was found that oxidation due to oxygen supplied from NO2 enhanced the decomposition, and finally, a residue was formed. This is almost the same result as obtained by heat treatment. In the case of He+ ion irradiation, the electronic stopping power caused the same decomposition process as did irradiation of the electron beam. However, the residue formed was sputtered off due to the nuclear stopping power.

An annular electron beam for longitudinal electron beam pumped high power lasers

A new pumping scheme was designed for a laser oscillator of a longitudinal electron beam pumped high power laser. In this system, an annular electron beam was converged and guided along the optical axis by a carefully shaped magnetic field which enabled a total reflector of the optical cavity to be placed on the optical axis. For KrF laser oscillation, the output energy and efficiency were 5 J and 4%, respectively.

Effects of Heat Treatment on the Sensitivity of Warm Carrier Devices for CH3OH Laser Radiation

Warm carrier infrared laser detectors, which have 0.1 µm-diameter ohmic contact electrode, were fabricated using a focused ion beam, and the effects of heat treatment on the detection sensitivity of the devices were studied at the CH3OH laser frequency. It was found that the sensitivity of the device increased by 100 times with heat treatment at 450°C.

Transport Properties in Hexagonal Arrays of Antidots with Different Carrier Densities

Magnetotransport measurement has been performed in two-dimensional electron gas with a hexagonal array of antidots. Several magnetoresistance peaks are observed and are analyzed with an extended Drude model. The calculation is in good agreement with experimental results. The carrier concentration is varied by gradual illumination and the dependence of magnetoresistance on carrier concentration is measured and discussed.

Magnetotransport in One-Dimensional Lateral Surface Superlattice Fabricated by Low-Energy Argon Ion Irradiation

One-dimensional lateral surface superlattice has been fabricated into the high-mobility heterostructure by low-energy ion irradiation and the magnetotransport properties are investigated. At weak magnetic field, Weiss oscillations are observed and this indicates that weak modulation potential is introduced in two-dimensional electron gas by low-energy ion irradiation. Moreover, Hall resistance oscillations are observed as theoretically predicted. A positive magnetoresistance observed around zero magnetic field is investigated in detail and is compared quantitatively with the theory of magnetic breakdown. At a high magnetic field where the cyclotron radius is much smaller than the superlattice period, anisotropic magnetoresistance with respect to the direction of current flow is observed.