Yoshitake Ohnishi

ULTRAHIGH RESOLUTION OF CALIXARENE NEGATIVE RESIST IN ELECTRON BEAM LITHOGRAPHY

A nonpolymer material, calixarene derivative (hexaacetate p‐methnylcalix[6]arene) was tested as a high‐resolution negative resist under an electron beam lithography process. It showed under 10‐mm resolution with little side roughness and high durability to halide plasma etching. A sub‐10‐nm Ge quantum wire was perfectly etched off without defects. Such a performance is suitable for nanoscale device processes.

Nanometer‐scale resolution of calixarene negative resist in electron beam lithography

New nonpolymer materials, calixarene derivatives were tested as high‐resolution negative resists for use in electron beam lithography. Arrays of 12‐nm‐diam dots with a 25 nm pitch were fabricated easily. The sensitivity of calixarene in terms of area dose ranged from 700 to 7000 μC/cm2, and the required dose for dot fabrication was about 105 electrons/dot. The standard area dose for calixarene is almost 20 times higher than that for polymethyl methacrylate (PMMA), but the electron spot dose for dot fabrication by calixarene is almost the same as that for PMMA and other highly sensitive resists such as SAL (chemically amplified negative resist for electron beam made by Shipley). The electron spot dose for such extremely small dots does not seem to depend on standard area dose, but any resist tends to require the same dose under exposure in a 50 keV electron beam writing system. We propose a qualitative exposure model that suggests a tradeoff of dose and dot size. The calixarene seems to be promising materi...

Calixarene Electron Beam Resist for Nano-Lithography

New electron beam (EB) resists made of calixarene resists are introduced. Typical sensitivities of calixarene resists range from 700 µ C/cm2 to 7 mC/cm2. High-density dot arrays with 15 nm diameter constructed using calixarene resist were easily delineated using a point EB lithography system. Our results suggest that the resolution limit of calixarene resists is dominated by a development process such as adhesion to a substrate rather than by the EB profile. Calixarene resists are resistant to etching by halide plasma. We also demonstrated nanoscale devices processed by using calixarene resists. Calixarene resists are promising materials for nanofabrication.

Heterogeneous distribution of interstitial oxygen in annealed Czochralski‐grown silicon crystals

It is shown that interstitial oxygen infrared (IR) absorption at 515 cm−1 decreases anomalously compared with the absorption at 1106 cm−1 in heat‐treated Czochralski‐grown silicon wafers. This phenomenon is described by the close correlation between the absorption coefficient ratio αr (α1106/α515), the half‐bandwidth of the 1106‐cm−1 peak, and the precipitated oxygen content during heat treatments. As a result, it is suggested that on the basis of IR absorption spectrum data interstitital oxygen atoms distribute heterogeneously in a silicon matrix as the forestage of Si‐0 complex precipitation.

Calixarenes—prospective materials for nanofabrications

Abstract A new group of electron resists, calixarene resists, are presented. These small, cluster-like molecules provide convenient means for making nanostructures. For example, hexaacetate of methylcalix[6]arene easily gives a 10 nm scale pattern in E-beam lithography with conventional resist processes. Synthesis, identification and characterization of these compounds are described with examples of nanofabrications.

A negative photoresist (TAS) for a bi‐layer resist system

A new negative photoresist TAS for a bilayer resist system has been developed. TAS is composed of poly(triallylphenylsilane), PTASi, and bisazide. PTASi is prepared by the cyclopolymerization of triallylphenylsilane with benzoylperoxide (BPO) in refluxing benzene. PTASi has a five‐membered ring and a six‐membered ring in a main chain with an allyl group as a side chain. The cyclized structure gives a high softening point, 127–130 °C (Mw is 47 000). The allyl group and bisazide are highly sensitive to UV irradiation forming mainly an aziridine ring. The sensitivity (Dig) for TAS (Mw of PTASi is 49 000) is 0.8 s in a nitrogen atmosphere, while a suitable exposure time for Shipley photoresist MP‐1300 is 7–10 s. TAS shows a high O2–RIE resistance. The thickness reduction of TAS under O2–RIE is only 1500 A compared to a 1.6 μm layer of Shipley photoresist MP‐1300. Thus, TAS is suitable for use as the top layer in a bilayer resist system. Submicron patterns with steep profile are obtained.

Properties of nematic liquid crystals doped with hydroquinone and p‐benzoquinone: Long‐term dynamic scattering under dc excitation

The effect of a charge‐transfer complex pair on dynamic scattering (DS) properties in nematic liquid crystals is reported. With the use of a hydroquinone‐quinone complex pair as dopant, more than one‐year continuous dc operation of DS has been achieved. Purification of materials and use of hermetically sealed cells are necessary. Since nematics doped with conventional organic electrolytes do not show long lives under dc operation, a reversible oxidation‐reduction process was found to play a fundamental role in achieving long dc operation lives of DS in the present nematics. The mechanism of the electrochemical process in DS is briefly discussed.

Oxygen ion-beam etch resistance of metal-free and organosilicon resist materials

Abstract Oxygen ion-beam etch resistance of metal-free and organosilicon resist materials has been studied, using an etching system with a Kaufman ion gun. The etch rate for metal-free resist materials is inversely proportional to the number of effective carbon atoms in a material. The effective term means subtracting the number of oxygen atoms from that of carbon atoms. This result suggests that the etch-rate determining step is the sputtering of carbon atoms which are not bonded to oxygen atoms. Carbon atoms bonded to oxygen atoms, for example >C=O or ⪰C-O-, may spontaneously desorb to form a volatile product CO under ion bombardment. The etch-rate ratio of an organosilicon resist material P(SiSt-CMS) to AZ1350J markedly increases with decreasing acceleration energy. This is because the rate determining step for an organosilicon resist material is mainly due to the sputtering of silicon atoms in the polymer. This is supported by the fact that the etch rate of an organosilicon resist material increases with increasing beam angle, while that of metal-free resist material monotonically decreases with increasing beam angle.

Resolution of calixarene resist under low energy electron irradiation

Abstract The resolution and sensitivity of calixarene resists in relation to incident electron energy were studied. While the sensitivity of the resists was varied in compliance with Bethe theory for the changes of the electron energy, resolution of the resists in terms of the minimum dot size, shows almost the same value of about 10 nm for each electron energy. A Monte Carlo simulation suggests the electron dose at the edge of the dot pattern was only one hundredth of that at the center of the electron beam. This means the major factor in limiting the resolution in calixarene resists was not the electron beam. This means the major factor in limiting the resolution in calixarene resists was not the electron beam profile, but other factors such as a limit due to development processes.

Nonpolymer new organic film for local insulation in laser-direct-writing circuit restructuring for large-scale integrated circuits

A new nonpolymer organic material, hexaacetate p‐methylcalix [6] arene (hereafter referred to as MC6AOAc), has been successfully applied to the localized insulator for large‐scale integration (LSI) circuit restructuring. A conductive line, necessary for the restructuring, was written on the MC6AOAc film by laser chemical vapor deposition with no damage to the film. The leakage current through the film was kept within the permissible limit. The unnecessary part of the film for LSI testing was easily removed by an ethanol rinse without damage to the interconnection, in a self‐aligned manner, with the written line as a mask. This technology extends the usability of the LSI circuit restructuring.