Katsuhiko Mutoh

Nanometer‐sized silicon crystallites prepared by excimer laser ablation in constant pressure inert gas

We report nanometer‐sized silicon (Si) crystallites prepared by excimer laser ablation in constant pressure inert gas ambient. Size distribution of the Si ultrafine particles depends on the pressure of inert gas ambients. The relation between the average size and the ambient pressure can be explained by an inertia fluid model. It is verified that the size of the Si ultrafine particles is ∼3 nm and greater in diameter. Furthermore, crystallinity of the nanoscale ultrafine particles is crystalline similar to that of bulk Si.

Reactive Ion-Beam Etching of InP with Cl2

Reactive ion-beam etching (RIBE) of InP with Cl2 at room temperature has been studied by varying the ion extraction voltage and the gas pressure. The sputtering yield is found to increase linearly with the ion extraction voltage above a threshold voltage. RIBE with a higher Cl2 gas pressure is dominated by the chemically reactive etching, and offers a higher etch rate and a smoother surface. Smooth surfaces with low concentrations of residual Cl atoms are obtained under the ion extraction voltage of 400 V and Cl2 gas pressure of 2.5×10-3 Torr.

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.

Soft‐x‐ray multilayer mirrors with laterally varying film thicknesses fabricated using laser‐beam‐scanning chemical vapor deposition

The authors have developed a control method of spatial film thickness distribution of multilayer mirrors for soft‐x‐ray focusing systems using an argon–fluoride (ArF) excimer laser‐induced chemical vapor deposition (LCVD). A line‐shaped laser beam is unidirectionally scanned over an area of 100×100 mm2. The scanning speed is controlled in response to a film thickness distribution which is required to be obtained. A tungsten–silicon (W/Si) multilayer with laterally varying film thickness is successfully fabricated on the design rule, and soft‐x‐ray (λ=12.8 nm; not polarized) reflectivities from 37% to 20% are obtained at the grazing angles from 18° to 22° in response to the film thickness distribution. Furthermore, the amount of the soft x rays reflected by the multilayer within 100 mm of the substrate is estimated at about 90% of that in the case of the designed distribution, and the feasibility of LCVD for fabricating multilayer mirrors for high performance soft‐x‐ray focusing systems has been demonstrated.

Simultaneous fabrication of vertical and 45° mirrors of InP for surface-emitting lasers using inclined Cl ion beams

Reactive ion beam etching (RIBE) of InP using inclined Cl ion beams has been studied. Straight-sloping side walls of InP grooves are fabricated using those of SiO2 as etching masks. By controlling the wall inclination of the SiO2 mask and the etch rate ratio of InP to SiO2, an InP groove with side-wall inclinations of 90° and 45° is obtained using one RIBE process. Furthermore, the walls of the groove are used for fabrication of the InGaAsP/InP surface-emitting laser with a Fabry-Perot resonator and a 45° mirror. A threshold current of 40 mA is obtained for the laser under continuous-wave operation at room temperature.

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

InGaAsP/InP horizontal cavity surface‐emitting lasers radiating in two opposite directions

A 1.3 μm InGaAsP/InP surface‐emitting laser of a new design is demonstrated. It consists of internal and external 45° micromirrors and emits beams from both the front and rear surfaces. The device has a buried crescent laser structure with reflection mirrors etched at vertical and 45° to the plane of the active layer. The mirror facets are fabricated using one reactive ion‐beam etching process. A threshold current of 80 mA, and each output power above 0.2 mW are achieved at room temperature.

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.