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Sodium-hydride-graphite intercalation compounds have an ionic Na+-H--Na+ triple atomic layer intercalate structure with stoichiometric composition Na/H=1. The analysis of the thermoelectric power shows that the charge transfer from the NaH-intercalate to graphitic sheets is considerably smaller than that in isostructural KH-GICs. This suggest that the ionic NaH intercalate with Na/H=1 makes a complete charge transfer within the intercalate layers, resulting in the presence of small concentration of graphitic π-electron carriers.

The nature of smectic A liquid crystals and the phase transitions from smectic A to nematic phases are studied in the homologous series of 4-(4''-octyloxy-benzoyloxy)benzylidene-4'-substituted anilines, in which the substituents are H, F, Cl, Br, I, NO2 and CN. Measurements have been performed for the dipole moment of the molecule, the smectic A lattice period, the temperatures and the entropies of phase transitions, and the temperature dependence of the orientational order parameter, all of which provide information on the intermolecular pair potentials. It is shown that the introduction of a terminal polar substituent brings about counteracting contributions to the stability of the smectic A state. It is suggested that the reentrant nematic phase transition can appear in the strongly polar mesogens if the extent of antiparallel association of the molecules increases on lowering the temperature.

ZrSixOyis a candidate material for fabricating attenuated phase-shift masks used in ArF excimer laser lithography. To investigate the durability mechanism of ZrSixOyfilms following irradiation with an ArF excimer laser, we analyzed the films chemically and physically. The phase shift and the transmittance of a transmissive film with a high oxygen concentration increases and decreases, respectively, with irradiation. This is because of an increase of Si-O-Zr bond structures. The phase shift and the transmittance of an absorptive film with a low oxygen concentration decreases and increases, respectively, with irradiation because of photooxidation at the surface. The oxidation leads to the formation of Si-O-Zr and Si-O-Si bond structures in the films. Both films are stabilized by irradiation with a large irradiation energy. We interpret that both films are stabilized by the formation of Si-O-Zr bond structures, such as zircon, with saturation of oxygen concentrations at the surface.

We have developed a method of enhancing the resist contrast governed by the hydrogen-ion concentration in chemically amplified resist films. We consider the distribution of permittivity and the equilibrium constants of acids generated by photoirradiation. The hydrogen-ion concentration in a resist film containing a weak acid increases with increasing permittivity. If the permittivity of exposed areas is higher than that of unexposed areas, the resist contrast is greater than that of resist films whose permittivity is the same in both exposed and unexposed areas. Accordingly, the resolution capability is enhanced and the depth of focus is increased. Calculations based on a model in which an additive whose polarizability is increased by photoirradiation is mixed within the resist, indicated that (1) the resist contrast depends on the amount of polarizability change and the concentration of the additive, (2) the resist contrast takes a maximum value at an optimum exposure dose, and (3) an appropriate combination of available additives and available exposure doses can result in a resist contrast higher than that obtained when strong acids are generated and also higher than the optical contrast.

We have investigated the durability under ArF excimer laser light of bi-layer zirconium silicon oxide (ZrSixOy) films used as the shifter of an attenuated phase-shifting mask (Att-PSM). We have achieved excellent stability by using the structure of the transparent film (TF) on the absorptive film (AF) rather than the structure of AF on TF. We can estimate a sufficient lifetime of more than three years in mass production for TF/AF/quartz structure. By XPS analysis, it has been clarified that the surface of TF is stable to ArF irradiation and the surface of AF is easily oxidized by the irradiation. TF/AF/quartz is the optimum structure for the prevention of surface oxidation. 0.13 µm line patterns have been achieved with a sufficient process margin by using optimized bi-layer ZrSixOyfilms as an Att-PSM and off-axis illumination in ArF lithography.

We analyze the mechanism of microbridge formation on chemically amplified negative resist patterns through direct observation of progressive development in alkali-developers. The microbridge formation was attributed to contact occurring between adjacent resist patterns due to swelling of the resist. These swollen resist patterns contracted upon immersion in deionized water; however, bridge structures remained as microbridges between these patterns. The swelling of the resist films occurred more easily at defocus positions than at a focus center, and the microbridges localized near the top of the pattern at defocus positions and delocalized at a focus center. An optical simulation suggested that both the crosslinking density and its distribution determine the number and position of the microbridges. A scaling law governing microbridge formation is observed as a function of focus position and exposure dose.

We discuss the possibility of using optical lithography when the design size is below 130 nm. Our optical simulations at the laser wavelengths of KrF (248 nm), ArF (193 nm), F2(157 nm), Kr2(146 nm), ArKr (134 nm), Ar2(121 nm), and the extreme ultraviolet (EUV) (13 nm) indicate that the ArF excimer laser can be used up to the 100 nm generation and that the lithographic tool most suitable for the 70 nm generation is an ArKr laser system with a numerical aperture larger than 0.65. They also indicate that EUV sources will be needed for the 50 nm generation and that high-contrast resists will be needed for the 70 nm generation and beyond.

We demonstrate applications of alternating phase shift mask (Alt-PSM) techniques to ArF excimer laser lithography with a numerical aperture of 0.6 and a coherence factor of 0.3. A 0.10 µm line-&-space (L/S) pattern was fabricated using a single-layer resist and a 0.09 µm L/S pattern was fabricated using a silylation resist. However, the process window was smaller for the silylation resist than for the single-layer resist over the 0.10-0.13 µm L/S range. The maximum depth of focus (DOF) values were approximately 0.3, 0.5, and 0.9 µm for 0.10, 0.11, and 0.13 µm L/S patterns, respectively, for the single-layer resist. From exposure dose-DOF-tree analysis, we estimated the inclusive process margin including the critical dimension difference, the DOF, the dose margin, and the phase error. Assuming that the usable DOF is larger than 0.5 and 0.6 µm for 0.11 and 0.13 µm L/S patterns, respectively, the inclusive process margin for the single-layer resist is poor in comparison with future predictions.

This paper presents the formation results of 0.13-µ m device patterns using argon fluoride (ArF) excimer laser lithography that does not incorporate strong resolution enhancement techniques such as levenson type phase-shifting mask or quadrupole illumination. Device patterns of 0.13-µ m can be fabricated by ArF excimer laser lithography when a high performance single-layer photoresist, an anti-reflective layer, an attenuated phase-shifting mask with an off-axis illumination are used. A 0.5-µ m depth-of-focus with a 10.8% exposure latitude can be obtained. Furthermore, 0.12-µ m-rule gate patterns of memory and logic devices can be fabricated. A 1.0-µ m depth-of-focus for a 0.13-µ m pattern will be achieved.