Toshihiko Kanayama

Nanolithography Using Fullerene Films as an Electron Beam Resist

Electron beam (e-beam) irradiation has been found to reduce the dissolution rate of evaporated C60 films in organic solvents such as monochlorobenzene, which shows that this material acts as a negative e-beam resist with a sensitivity of 1×10-2 C/cm2. It has higher dry-etch durability than conventional novolac resists. Its applicability to nanofabrication has been demonstrated by fabricating Si pillars of 20–30 nm diameter using electron cyclotron resonance microwave plasma etching and dot patterns defined in the C60 film as etching masks.

A Fullerene derivative as an electron beam resist for nanolithography

We have explored the application of chemical derivatives of C60 as high-resolution electron beam resists. Facile spin coating was used to produce ∼100-nm-thick films of a C60 tris adduct (three functional groups) on Si surfaces. We find that these films function as high-resolution negative resists for electron beam lithography using monochlorobenzene as a developer. The film has a sensitivity of ∼1 mC/cm2 for 20 keV electrons, an order of magnitude higher than that of C60 itself, and the dry-etch durability is much better than that of conventional novolac based electron beam resists. Features with widths of 20 nm were produced.

Topology and energetics of metal-encapsulating Si fullerenelike cage clusters

On the basis of a topological discussion as well as an ab initio calculation, we show that it is possible to construct a fullerenelike Si cage by doping a transition metal atom in the cage center. The cage is a simple 3-polytope which maximizes the number of its inner diagonals close to the metal atom. Our topological argument also reveals how closely the structure of the fullerenelike Si cages studied is related to that of fullerenes themselves.

A VISIBLE-NEAR INFRARED RANGE PHOTONIC CRYSTAL MADE UP OF SI NANOPILLARS

We studied a two-dimensional square lattice of Si nanopillars (SQLN) perspective for applications in waveguides. Reflection spectra of SQLN with the period of 270 nm were studied for different surrounding media, namely air and water. SQLN is shown to display photonic band gap (PBG) behavior in the visible–infrared spectral range. The energy positions and widths of the experimentally observed reflection bands are found to be in agreement with calculated PBG.

Maskless etching of a nanometer structure by focused ion beams

Microfocused heavy ion beams obtained from liquid metal ion sources of gallium, indium, and tin are bombarded onto silicon and gallium arsenide substrates, and the amorphous regions created are selectively dissolved in suitable etchants (ion bombardment enhanced etching). The area exposure doses required to etch to the depth of the calculated projected range of the incident ions are in the region of 5×10−6∼1×10−5 C/cm2 at accelerating voltages of 30∼50 kV,and the dose dependencies of the etched depths show rapid increases in specified dose regions. Widths of etched depths obtained in line delineations depend on a line exposure dose, and the minimum linewidth clearly obtained is 20∼40 nm for all the ion beams. From measurements of the dose dependencies of linewidth, the beam diameters are evaluated for various conditions of the source operation and of a lens acceptance half‐angle. The virtual crossover diameters that are independent of the half‐angle, are found to be 40∼50 nm for the gallium source and 67 ...

Subwavelength-Resolution Raman Microscopy of Si Structures Using Metal-Particle-Topped AFM Probe

Using depolarization of the 364 nm light scattered by a small particle on the (100)Si surface, one can obtain allowed 520 cm-1 Raman signal from the localized area of Si around the particle, while the ordinary Raman signal is forbidden by the polarization selection rules. We have realized this scheme using Ag-particle-topped quartz atomic force microscope (AFM) probe immersed into glycerol droplet on Si surface and applied to local stress measurement. Lateral resolution in the range of 100 nm was demonstrated, and stress variation in a strained Si film was investigated.

Silver-coated silicon pillar photonic crystals: Enhancement of a photonic band gap

For a two-dimensional lattice of Si pillars it is shown both experimentally and theoretically that a photonic band gap for the light polarized perpendicular to pillars can be strongly enhanced by means of a silver coating of the pillars. A sizable omnidirectional photonic band gap is demonstrated for both square and triangular lattice of silver-coated Si pillars in the near-infrared and visible spectral range.

Measurement of virtual crossover in liquid gallium ion source

Gallium ion probes of 50 keV obtained from a liquid metal ion source are recorded on silicon and gallium arsenide substrates by using the method of ion bombardment enhanced etching. The minimum linewidth obtained in line exposures is about 20 nm for both substrates which corresponds to the lateral spread of the implanted ions. For a specified value of the lens acceptance half‐angle, the line dose varies as a square function of the linewidth, which means that the distribution of the current density in the focused beam is Gaussian. From the theoretical evaluation of the full widths at half‐maximum of these distributions, the virtual crossover diameter of the source is estimated to be 40–45 nm independently of the emission current ranging from 4 to 12 μA, and of the value of the needle apex radius of the source in the range 1–3 μm.

10 nm scale electron beam lithography using a triphenylene derivative as a negative/positive tone resist

We show that the liquid crystal triphenylene derivative 2,3,6,7,10,11-hexapentyl-oxytriphenylene acts as a high-resolution electron beam resist. Using pentanol as a developer, positive behaviour was observed for electron doses greater than ~300µC cm-2 at 20 keV. At higher doses (>2.5 mC cm-2), the resist rapidly assumes negative tone behaviour. With the developer monochlorobenzene, only negative behaviour was observed, with a sensitivity of ~2.5 mC cm-2 at 20 keV. The resist allows relatively facile definition of 14 nm patterns (negative tone) with a 30 keV electron beam and without the need for any complex pre-irradiation preparation or post-irradiation processing of the resist.

Niobium silicide formation induced by Ar-ion bombardment

The effect of Ar‐ion bombardment on evaporated–Nb‐on‐Si systems has been investigated with He backscattering and x‐ray‐diffraction measurements. High‐dose bombardment with energetic Ar ions was found to induce intermixing between Nb and Si in the form of NbSi2. This effect has strong dependence on temperature during bombardment, although it cannot be explained as enhanced diffusion due to radiation damage or ion‐beam heating.