Shou-ichi Uchino

A Novel Optical Lithography Technique Using the Phase-Shifter Fringe

A new optical lithography technique called outline pattern transfer imaging (OPTIMA) is described. OPTIMA utilizes an optical phase change at a clear phase-shifter pattern edge. Very narrow closed patterns can be delineated along the fringe of the phase-shifter pattern by this method. The resolution limitation of OPTIMA is presented using a newly developed high-resolution i-line negative resist. The resist is transparent (90% at 0.5 µm thickness) and has a high γ value (4.5). Results show that 0.13 µm-wide groove patterns can be delineated with an i-line stepper having 0.42 numerical aperture. Practical focus latitude and exposure latitude are obtained for 0.2 µm patterns. In OPTIMA, linewidth control is also possible by adding notch patterns at the shifter edge.

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.

Accurate critical dimension control by using an azide/novolak resist process for electron-beam lithography

Nanofabrication with accurate critical dimension control was investigated with a nonchemically amplified resist. The resist consists of 3,3′-dimethoxy-4,4′-diazidobiphenyl and cresol novolak (novolak). By using novolak with a small weight-average molecular weight (Mw), small resist surface roughness (nano edge roughness) was significantly suppressed down to 3 nm. Nanofabrications of 20-nm lines and spaces (L and S) and 20-nm dot patterns had been demonstrated with the resist. The pattern line-width linearity, the minimum size that the fabricated patterns width were equal to the designed ones, was also preserved down to 30-nm L and S. We investigated use of electron-beam/optical lithography to enhance throughput in nanofabrication. Fine gate structure of 70 nm with a large pad was demonstrated with the hybrid exposure.

Azide–novolak resin negative photoresist for i‐line phase‐shifting lithography

A negative photoresist consisting of 4,4’‐diazido‐3,3’‐dimethoxybiphenyl and a novolak resin, called micro resist for i‐line (MRI), has been prepared and evaluated for i‐line phase‐shifting lithography. MRI has a high transmittance (80%/μm) and a high resist contrast (γ) at i line (365 nm). Line‐and‐space patterns of 0.30 μm were achieved using MRI in conjunction with an i‐line phase‐shifting lithography. The insolubilization mechanism of MRI is attributed to a secondary amine formed by the reaction of nitrene with novolak resin.

Novel antireflection method with gradient photoabsorption for optical lithography

A new concept using the bottom antireflection layer with graded photoabsorption named GALA (gradient absorption layer) is described to resolve the problems with conventional antireflection methods, such as insufficient antireflection, substrate material, and structure dependence. The antireflection layer with high photoabsorption at the bottom eliminates the light reflected from the substrate and the graded photoabsorption suppresses the surface reflection of the layer. This new method can achieve extremely low reflection (less than 3 percent) for all substrates.

Negative resist systems using acid-catalyzed pinacol rearrangement reaction in a phenolic resin matrix

Acid-catalyzed dehydration of pinacols known as pinacol rearrangement has been utilized in the design of alkali developable, negative working resist systems. The resist systems are composed of a pinacol compound used as a dissolution inhibitor precursor, diphenyliodonium triflate and a novolak resin. The resist system using hydrobenzoin (HB) shows better lithographic performance than the resist systems using other pinacol compounds such as 1,1,2,2-tetramethylethylene glycol (TMEG), benzopinacole (BP), DL-(alpha) ,(beta) -di-(4-pyridyl) glycol (DPG), and 2,3-di-2-pyridyl-2,3-butanediol (DPB). In the unexposed region, HB acts as a dissolution promoter of novolak resin due to its hydrophilic property. HB reacts with acid to produce hydrophobic materials such as diphenyl-acetaldehyde. Therefore, the solubility of the HB resist film in alkaline developers decrease upon exposure to deep UV radiation and subsequent heating. The resist system has high contrast and high resolution capability. Line-and-space patterns of 0.3 micrometers are obtained using a KrF excimer laser stepper with a 5 mJ/cm2 dose.

Nanofabrication with a novel EB system with a large and stable beam current

We describe nanofabrication using a novel electron beam (EB) system that has a large and stable beam current, combined with high resolution resists. This system has a low aberration objective lens and a Zr/O/W cathode that provides a probe current of 1.2 nA. By detecting Si-groove marks, the system achieves high overlay accuracy of within 10 nm (mean + 3σ) over large areas. We have realized resist nanofabrication down to 10 nm with small nano edge roughness. By introducing a hard mask consisting of a thin (25 nm) SiO 2 layer, we have also obtained a poly-Si gate structure of 30 nm on a thin (4 nm) gate oxide.

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.