Sonoko Migitaka

Laser terahertz emission system to investigate hydrogen gas sensors

A laser terahertz emission system is proposed to investigate the catalytic metal/semiconductor interfaces of hydrogen sensors. Samples were fabricated by depositing a catalytic metal thin film on a semi-insulating silicon substrate. A femtosecond laser was used to radiate terahertz waves from the sample in a gas cell filled with a hydrogen and nitrogen gas mixture. The peak amplitude of the terahertz waves decreased with increasing hydrogen concentration. We also fabricated a metal-oxide-semiconductor field effect transistor hydrogen sensor, and compared its properties with the terahertz radiation properties. These results suggest that the laser terahertz emission system is a potential tool to investigate catalytic metal/semiconductor interfaces.

Negative electron-beam nanofabrication resist using acid-catalyzed protection of polyphenol provided by phenylcarbinol

A high-resolution negative electron-beam (EB) lithography resist based on an acid-catalyzed protection reaction of a polyphenol enabled by a phenylcarbinol has been developed for nanofabrication. Polyphenol-3, which is synthesized by condensation of α,α,α′-tris(4-hydroxyphenyl)1-ethyl-4-isopropylbenzene with m-cresol, was selected as the most suitable matrix resin for the resist. 1,3,5-tris[1-(1-hydroxyethyl)]benzene (Triol-2) was found to be the best protection reagent among the six phenylcarbinols evaluated. Line-and-space patterns of 80 nm with edge roughness of less than 10 nm were delineated by using a resist composed of Triol-2, diphenyliodonium triflate, and polyphenol-3 in conjunction with an EB writer (20 μC/cm2 at 50 kV). Spectroscopic studies clearly showed that the acid-catalyzed protection reaction of the polyphenol brought about by Triol-2 is responsible for the resist insolubilization.

On-chip base sequencing using a two-stage reaction-control scheme: 3.6-times-faster and 1/100-reduced-data-volume ISFET-based DNA sequencer

A novel two-stage reaction-control scheme with a background-cancelling circuit - for reducing data volume and analysis time of an ion-sensitive-FET (ISFET) - based DNA sequencer-is proposed. The scheme successfully reduces the background noise and renders time-consuming background analysis unnecessary. It also reduces sample-to-data time by 72% (3.6 times faster) and data volume by two orders of magnitude.

Negative resists for electron-beam lithography utilizing acid-catalyzed intramolecular dehydration of phenylcarbinol

Acid-catalyzed intramolecular dehydration of phenylcarbinol is used to design highly sensitive negative resists for electron beam lithography. Of the phenylcarbinol resists evaluated in this study, the resist composed of 1,3-bis(alpha-hydroxyisopropyl)benzene (Diol-1), m/p-cresol novolak resin, and diphenyliodonium triflate (DIT) shows the best lithographic performance in terms of sensitivity and resolution. Fine 0.25-micrometer line-and-space patterns were formed by using the resist containing Diol-1 with a dose of 3.6 (mu) C/cm2 in conjunction with a 50 kV electron beam exposure system.

Contrast-boosted resist using a polarity-change reaction during aqueous base development

A high-contrast resist, called a contrast boosted resist (CBR), using a water-repellent compound that changes into hydrophilic compounds during aqueous base development has been developed for electron-beam (EB) lithography. TBAB, 1,3,5-tris(bromoacetyl)benzene, was identified as the best water-repellent compound for the CBR. A CBR composed of novolak resin, hexamethoxymethylmelamine, 1,3,5-tris(trichloromethyl)triazine as an efficient acid generator, and TBAB enables the definition of 0.225-micrometer line-and-space patterns with an exposure dose of only 2 (mu) C/cm2 using an EB writing system (acceleration voltage: 50 kV). The polarity change caused by the reaction of the TBAB with the base as well as crosslinking of the novolak resin by the TBAB are assumed to enhance the contrast in the CBR.

Terahertz emission properties from palladium/silicon interface

Laser terahertz (THz) emission and detection system for investigating the catalytic metal/semiconductor interface of the hydrogen sensors was proposed and developed. THz radiation from palladium/silicon structures was successfully obtained. The properties of THz radiation under hydrogen and nitrogen gas mixture were investigated. The peak amplitude of THz radiation was decreased by increasing the volume concentration of hydrogen gas. This change in the amplitude can be explained by change in the local field near the surface of silicon. This result indicates that the system a potential tool for nondestructive and noncontact measurement of the hydrogen sensors.

Acid-breakable-resin-based chemical amplification positive resist for 0.1-μm-rule reticle fabrication: design and lithographic performance

We have designed a new chemical amplification (CA) positive resist for 0.1micrometers reticle fabrication. This positive resist consists of an acid-generator, an acid-diffusion controller, and an acid-breakable (AB) resin that can be converted to initial polyphenol units by an acid-catalyzed reaction. In the exposed region, main-chain scission of the AB resin matrix produces nearly mono-dispersed fragments (the polyphenol). This complete fragmentation results in an extremely high dissolution rate with an aqueous-base developer (tetramethylammonium hydroxide: 2.38 wt%). The AB resin-based resist enabled fabrication of scum free 0.15micrometers line-and-space patterns on a CrOx plate by using a 50-kV electron-beam reticle writer (HL series). The line- edge roughness of patterns delineated by this resist (<10 nm) was less than half that for previously developed novolak-resin-based CA resists (RE series:>30nm).

Effect of Basic Additives on Acid-Catalyzed Electron-Beam Negative Resist Using Intramolecular Dehydration of Phenylcarbinol

The effect of basic additives on a negative electron-beam resist utilizing acid-catalyzed intramolecular dehydration of 1,3,5-tris(2-(2-hydroxypropyl))benzene (Triol) was investigated. Quinoline was selected as the most effective additive to suppress acid-diffusion among investigated ones. Though the addition of quinoline decreased the Triol resist sensitivity, it enhanced the contrast and critical-dimension (CD) deviation stability to post-exposure-baking temperature variation. Optimized resist system achieved the CD deviation stability: 1.5 nm/°C and 100-nm line and space patterns with a dose of 6.2 µC/cm2 @ 50 kV. Influence of the additive on the Triol resist insolubilization mechanism was discussed.