Masakazu Baba

DNA size separation using artificially nanostructured matrix

We have demonstrated two types of size separation of biomolecules using a nanostructured matrix artificially fabricated using electron-beam lithography: sieve-type separation using a regular pillar array structure and size exclusion chromatography (SEC) type separation using a structure with narrow and wide gaps. With these devices, samples of double-stranded DNA molecules (2, 5, and 10 k base pairs) were clearly separated into bands; smaller molecules eluted earlier in the sieve type while they eluted later in the SEC type. The nanostructured matrix enables various types of molecular separation by changing the design of the nanostructure. Moreover, it should be easy to integrate the matrix with other biomolecular fluidic devices because it does not require a filling medium.

Chlorine-Based Smooth Reactive Ion Beam Etching of Indium-Containing III-V Compound Semiconductor

Very smooth and vertical etching of InP by Cl2 reactive ion beam etching has been achieved under high temperature (≈200°C), high ion energy (≈1 keV) and low Cl2 pressure (~10-5 Torr). The roughness is estimated to be a few nm by scanning tunneling microscopy and no contamination except for Cl was observed by in situ Auger electron spectroscopy. Under these etching conditions, the etched depth is precisely controlled (σ=22 nm) by simply monitoring the electrode curtent of the ion accelerating grid. Other III-V compound semiconductors, such as GaAs, InGaAs, AlGaInP and InAlAs have also been etched smoothly and vertically. Multilayers of these materials, such as InP/InGaAsP, AlGaInP/GaInP, and InAlAs/InGaAs/InP have been etched without steps between the layers on the sidewalls.

ATOMIC DESORPTION OF CHLORINE ADSORBED ON SI(111) WITH A SCANNING TUNNELING MICROSCOPE

This letter reports the selective atomic desorption of Cl atoms adsorbed on an Si(111)7×7 surface by field evaporation using a scanning tunneling microscope (STM). After using STM to study the reaction of the Cl on the surface, the STM tip is placed on the adsorbed Cl and pulse voltage is applied. This results in selective atomic desorption of Cl. Although both desorption and readsorption are observed at a low pulse voltage of +4–+6 V, only desorption occurs at a high pulse voltage over +6 V.

Electron beam induced selective etching and deposition technology

Abstract W deposition, using a WF 6 source by electron beam induced surface reaction, has been studied by Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The initial growth process has been observed in situ by AES and TEM. As a result, it became clear that a growth rate for W is 1.5 A/min at 3.5×10 −7 Torr and β-W clusters are formed by electron beam irradiation of the WF 6 adlayer. Moreover, it has been observed that W layers are formed by coalescing the W clusters by electron beam irradiation at 5×10 −7 Torr WF 6 gas pressure. Furthermore, a nanostructure involving a W rod with 15 nm diameter has been demonstrated by using electron beam induced surface reaction. Direct writing into Si and GaAs has been demonstrated by electron beam induced surface reaction using XeF 2 and Cl 2 sources. A scanning tunneling microscope(STM) has been used to directly write deposition patterns of metal and carbon, and etching patterns of Si. These features have been obtained down to 50nm. A 0.6 μm resist pattern has been precisely transfered into a Si substrate by showered-electron beam assist-etching at 1×10 −4 Torr Cl 2 gas pressure. A side-wall roughness of replica grating patterns has been successfully measured by using a new STM tip made by electron beam deposition.

Atomic modification of an Si(111)7×7 surface with adsorbed chlorine atoms using a scanning tunneling microscope

A scanning tunneling microscope is used to modify a Si(111)7×7 surface structure with adsorbed chlorine atoms. One Si adatom at the center site is extracted from the surface by field evaporation and the other atom is moved by field‐induced diffusion. This modification is caused by the coordinated breaking of bonds and the moving of adatoms to their adjacent areas as the result of Cl chemical reactivity.

Measurement of Sidewall Roughness by Scanning Tunneling Microscope

A scanning tunneling microscope (STM) is a highly effective tool for observing a microfabricated pattern. However, it is difficult to measure sidewall roughness using a conventional STM because of the restriction of the tip shape and one-dimensional servo system. The main objective of this study is to develop a sidewall roughness characterization tool. The electron-beam deposition method is applied to preparing a novel STM tip shape. A two-dimensional servo system, with a subnano-vibration mode to provide vibrations below 1 nm for x- and z-directions to a tip during scanning, has been developed for sidewall roughness measurement.

Nanolithography Developed Through Electron-Beam-Induced Surface Reaction

Nanolithography has been studied by using electron beam-induced selective etching and deposition (EBISED) technology. Ten-nm linewidth polymethylmethacrylate (PMMA) resist patterns and 14 nm diameter carbon dot patterns have been demonstrated by 50 kV scanning electron microscope (SEM)-EBISED. A tungsten rod pattern with 15 nm diameter and carbon dot patterns with 10 nm diameters have been fabricated by scanning transmission microscope (STEM)-EBISED and scanning tunneling microscope (STM)-EBISED technologies, respectively. Atomic layer etching for GaAs has been also achieved by STM-EBISED using a Cl2 adlayer. Moreover, low damage dry etching has been demonstrated by Masked-EBISED using showered electron beam.

Atomic layer etching and sidewall roughness measurement using the scanning tunneling microscope

Nanostructure technology has been studied by electron beam induced surface reaction using scanning tunneling microscopy (STM). Atomic layer etching for GaAs has been achieved by STM-assisted etching using a Cl2 adlayer. Moreover the side-wall roughness of GaAs patterns etched by reactive ion beam etching has been successfully measured using a new STM tip made by electron beam deposition.

Planar Ultra-Filtration Chip for Rapid Plasma Separation by Diffusion

Plasma can be extracted in two seconds with a planar ultra-filtration chip without using centrirugation. The planar structure of the chip makes it suitable for mass production by indenting on plastic, and, the chip requires no extra equipment for separation. The chip is thus applicable to disposable devices for ‘point-of-care’ blood testing.

Nanostructure Technology Developed Through Electron-Beam-Induced Surface Reaction

Nanostructure technology has been studied by using electron beam-induced surface reactions. Ten-nm linewidth polymethylmethacrylate (PMMA) resist patterns and 14-nm diameter carbon dot patterns have been demonstrated by 50 kV electron beam with a gas introduction line. It has been confirmed that damage induced by electron beam assisted dry etching is less than that induced by reactive ion beam etching. Atomic layer etching for GaAs has been achieved by scanning tunneling microscope (STM) assisted etching using a C12 adlayer. A side-wall roughness of GaAs patterns etched by reactive ion beam etching has been successfully measured by using a new STM tip made by electron beam deposition.