Michiaki Hashimoto

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.

Cis-Trans Photoisomerization of Perinaphthothioindigo for Use as a Photo-Imaging Sensor Using Fluorescence under He-Ne Laser Excitation

An imaging sensor based on the cis/trans isomerization of thioindigoid dyes is proposed. A photo-image (~500 nm) is stored as a density distribution of the trans-form in the cis-form material, and read out as fluorescence (~700 nm) from the trans-form by scanning with He-Ne laser (633 nm) excitation. As the fluorescence decay time of perinaphthothioindigo is 1.8 ns, the sensor permits rapid read-out. For light exposure L from 10-4 to 10-1 J/cm2 at 500 nm, the fluorescence intensity under laser excitation varies as L0.8.

Improvement of post-exposure delay stability of chemically amplified positive resist

We have been developing a novolak-based chemically amplified positive resist for next generation photomask (below 0.18 micrometer) fabrication. This resist prevents footing profile by use of a hydrophilic polyphenol compound. We succeeded in improving PED and PCD stability by addition of an ion- dissociative compound. We obtained vertical resist profiles on a chromium-oxide (CrOx) substrate. With the resist, we could make a well defined 0.25 micrometer line-and-space patterns on a CrOx substrate at a dose of 4.0 uC/cm2. Under the ambient air (amines concentration: 4 ppb, humidity: 45%), the line width change was less than 10 nm when the delay time between EB exposure and post-exposure-baking was from 0 to 8 hours. Under the same condition, the line width change was less than 20 nm even when the post-coating delay (PCD) time was 7 days.

Magnetically coupled MO double layer suitable for field modulation overwriting

Exchange coupled MO films like (PtCo/TbFeCo) and TbFeCo/TbFeCo) enable a very small external field of only 50 Oe for erase and write. Those are suitable media for a field modulation overwriting. In plane magnetized PtCo or low perpendicular anisotropy TbFeCo acts as the external field enhancing layer through exchange coupling with the TbFeCo recording layer.

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.

Negative resists for i-line lithography utilizing acid-catalyzed intramolecular dehydration reaction

Chemical amplification negative resist system composed of a novolak resin, a carbinol and an acid generator is investigated for i-line phase-shift lithography. The reaction in this resist is based on an acid-catalyzed intramolecular dehydration reaction. The dehydration products act as aqueous-base dissolution inhibitors, and carbinol compounds in unexposed areas work as dissolution promoters. The resist composed of a novolak resin, 1,4-bis((alpha) -hydroxyisopropyl) benzene (DIOL-1) and 2- naphthoylmethyltetramethylenesulfonium triflate (PAG-2) gives the best lithographic performance in terms of sensitivity and resolution. Line-and-space patterns of 0.275 micrometers are obtained using an i-line stepper (NA:0.45) in conjunction with a phase shifting mask.

Effects of light absorption in the resist layer in optical lithography

Effects of light absorption in the resist layer at i‐line exposure (wavelength 365 nm) are investigated using a newly developed clear resist. Exposure independent absorption (‘‘B parameter’’ proposed by Dill) at i line of the new resist is ∼ (1)/(3) (0.083 μm−1) that of a conventional g‐line‐use resist used for comparison. Both resists have nearly equal exposure dependent absorption (‘‘A parameter’’) at i line and development characteristics. The only difference between the two resists from the viewpoint of resolution is the B parameter. Thus, it is clarified that a decrease in the B parameter by a factor of (1)/(3) made a 20% improvement in resolution capability and produced a nearly square shaped resist‐pattern profile.

Novel Chemical Amplification System in Azide/Phenolic Resin-Based Negative Resist

A novel chemical amplification system based on an azide/phenolic resin-based negative resist is described. The new resist, which consists of an azide, a phenolic resin matrix, and a carboxylic acid, can be developed in aqueous alkaline solutions. Electron-beam exposure of this resist results in the production of a primary amine. In a subsequent post-exposure baking step, the primary amine catalyzes decarboxylation of the carboxylic acid. Additionally, the decarboxylation product acts as an aqueous alkaline dissolution inhibitor in the exposed areas. On the other hand, the carboxylic acid remaining in the unexposed areas promotes the dissolution rate of those areas. The new resist shows non-swelling pattern-formation by using the aqueous alkaline developer, and the sensitivity to electron beams is about three times higher than that of MRS.

Photobleachable Diazonium Salt-Phenolic Resin Two-Layer Resist System

This article describes a new negative two-layer photoresist system formed by a simple, successive spin-coating method. An aqueous acetic acid solution of diazonium salt and poly(N-vinylpyrrolidone) is deposited so as to contact a phenolic resin film spin-coated on a silicon wafer. The diazonium salt diffuses into the phenolic resin layer after standing for several minutes. The residual solution on the phenolic resin film doped with diazonium salt is spun to form the diazonium salt-poly(N-vinylpyrrolidone) top layer. This forms a uniform two-layer resist without phase separation or striation. Upon UV exposure, the diazonium salt in the top layer bleaches to act as a CEL dye, while the diazonium salt in the bottom layer decomposes to cause insolubilization. Half μm line-and-space patterns are obtained with an i-line stepper using 4-diazo-N,N-dimethylaniline chloride zinc chloride double salt as the diazonium salt and a cresol novolac resin for the bottom polymer layer. The resist formation processes, insolubilization mechanism, and the resolution capability of the new two-layer resist are discussed.