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We have designed and developed a variety of hexafluoroalcohol (HFA) pendant methacrylate monomers and the corresponding imaging polymers for ArF lithography. It was found that HFA side chains are critical for "swelling free" dissolution properties for the polymers and resists. Through the incorporation of HFA functionalities, ArF resists can obtain linear dissolution properties commonly seen in 248nm ESCAP resists. These improved dissolution properties in turn significantly reduce PEB sensitivity of higher activation protecting group (e.g., methyladamantanyl) based ArF resists. We have also showed that the fluorine impact on etch rates can be modulated through the insertion of cyclic and aliphatic spacers between the main chain and the HFA functionalities. The key application space for HFA-methacrylate resists appears to be trench level lithography. It was also demonstrated that these HFA materials are compatible with immersion lithography and result in dramatically improved process windows for iso trench features, in addition to other lines/space features.

Using terpolymers of Poly(norbornene-alt-malefic anhydride-co-acrylic acid) [P(NB/MA/AA)], the dissolution inhibition mechanism for two types of common additives in 193nm resist formulations, tert-butylcarboxylate (e.g. tert-butyl cholate) dissolution inhibitors (DI) and onium salt photoacid generators (PAC's) were examined. For simple cholate ester derivatives, increasing interactions with maleic anhydride repeating units paralleled the dissolution inhibition (tert-butyllithocholate>tert-butyldeoxycholate>tert-butylcholate). For a wider range of cholate derivatives, increasing hydrophobicity as measured by logPoct or the cloud point formation in water/acetone mixtures, is a good predictor of increased dissolution inhibition. Increases in dissolution promotion appeared to track with the number of carboxylic acid moieties and the hydrophobicity of carboxylic acid moieties released upon acidolytic cleavage of carboxylate esters. Finally, for onium salt PAC's, increasing the size of fluorinated anions decreased dissolution inhibition. This may be because these anions offer more steric hindrance, which disfavors interactions with the terpolymer matrix. The nature of this interaction may be that of a PAG with carboxylic acid as judged from modeling studies with acetic acid in which increasing strength of the interaction correlated with increased dissolution inhibition (triflate>nonaflate> perflurooctanesulfonate)

The performance of a 193nm single layer resist based on a norbornene-malefic anhydride matrix resin has been optimized through a series of statistical design experiments. The SDE demonstrated the importance of setting the PEB temperature above the SB temperature with optimum performance being observed at a SB of 150°C and a PEB of 160°C. The lithographic performance of the resist was also strongly influenced by polymer composition, specifically acrylate loading and blocking level. Optimizing the composition of the polymer, gave resists with high etch resistance, square profiles and 0.130 micron dense line ultimate resolution in 0.5 micron thick films. The resist formulations are compatible with industry standard 0.262N TMAH. During exposure the resist does not suffer from the outgassing of volatile species (less than 1e12 molecules/cm2 x sec). A new thermally curable undercoat for bi-layer application has also been developed whose optical properties have been optimized to reduce reflectivity at the desired wavelength. The reflectivity has been reduced by a factor of eight over an earlier UV-cured version.

In this paper we report the results of a feasibility study of manufacturability of processes using plasma polymerized methylsilane (PPMS) as both a single-layer and a bilayer resist in both negative and positive tone development modes. PPMS has shown great promise as the basis for an all dry lithographic process. The photosensitive polymer is deposited in a low power plasma of methylsilane gas and is comprised of a Si-Si bonded network. PPMS undergoes efficient photo-oxidative crosslinking upon exposure to 248 or 193nm light in air to form an oxide-like material (PPMSO). We have identified several structural differences of films deposited at different temperatures and have correlated those differences to the air stability and the photosensitivity of PPMS films. We have also examined the effect of laser pulse power and repetition rate on the efficiency of exposure and conclude that the rate of oxygen diffusion into the film limits the effectiveness of high laser power for increasing the throughput of an exposure tool. We have concluded that positive tone PPMS processing is not practical because of the slow diffusion of oxygen through the film, required for effective photo-oxidation of PPMS to occur.

An optical pumping technique was used to enhance and localize nuclear magnetic resonance (NMR) signals from an n-doped GaAs/Al0.1Ga0.9As multiple quantum well structure, permitting direct radio-frequency measurements of gallium-71 NMR spectra and nuclear spin-lattice relaxation rates (1/T1) as functions of temperature (1.6 K < T < 4.2 K) and the Landau level filling factor (0.66 < v < 1.76). The measurements reveal effects of electron-electron interactions on the energy levels and spin states of the two-dimensional electron system confined in the GaAs wells. Minima in 1/T1 at v approximately 1 and v approximately 2/3 indicate energy gaps for electronic excitations in both integer and fractional quantum Hall states. Rapid, temperature-independent relaxation at intermediate v values indicates a manifold of low-lying electronic states with mixed spin polarizations.

Crystals of C60 or C70 cocrystallized with n-pentane grow as elongated, ten-sided columns. X-ray diffraction shows ordering of C60 or C70 molecules along the column and a remarkable tenfold symmetry normal to the column. The ratio of the x-ray-diffraction vectors of the two lowest-order diffraction spots is nearly equal to the “golden ratio,” τ. Despite these similarities with decagonal, quasicrystalline order, the diffraction indicates crystalline order with a twinned unit cell.

The intramolecularly H-bonded cis enolic form of malondialdehyde in chloroform is converted to an intermolecularly H-bonded trans enol by methoxy compounds such as methanol and 3,3-dimethoxypropanal. «Polar impurities» such as acetone and dioxane do not induce this effect

The fullerene C(60) can be converted into two different structures by high pressure and temperature. They are metastable and revert to pristine C(60) on reheating to 300 degrees C at ambient pressure. For synthesis temperatures between 300 degrees and 400 degrees C and pressures of 5 gigapascals, a nominal face-centered-cubic structure is produced with a lattice parameter a(o) = 13.6 angstroms. When treated at 500 degrees to 800 degrees C at the same pressure, C(60) transforms into a rhombohedral structure with hexagonal lattice parameters of a(o) = 9.22 angstroms and c(o) = 24.6 angstroms. The intermolecular distance is small enough that a chemical bond can form, in accord with the reduced solubility of the pressure-induced phases. Infrared, Raman, and nuclear magnetic resonance studies show a drastic reduction of icosahedral symmetry, as might occur if the C(60) molecules are linked.

ALKALI metal fuller ides exhibit superconductivity1–4 at temperatures surpassed only by the copper-oxide-based ceramics. Three types of stoichiometry and structure have been identified: A3C60 (ref. 5) (where A is K or Rb) with A+ cations intercalated in the face-centred cubic (f.c.c.) C60 structure, and A6C60 (ref. 6) or A4C60 (ref. 7) (where A is K, Rb or Cs) with body-centred arrays of C60 molecules. All A3C60 compounds reported so far are superconductors with transition temperatures that increase with unit cell size8,9. No successful preparation of bulk NaxC60 has been reported, although measurements of electrical conductivity10 and Raman11, ESR11 and photoemission12 spectra of thin films have given clear indications of NaxC60 formation. Here we report the synthesis and initial characterization of bulk NaxC60 (2≤x≤6) and mixed alkali phases Na2AC60 (where A is K, Rb, or Cs). All of these phases have intercalated f.c.c. structures. The Na6C60 structure has a Na4 cluster centred on the octahedral site. The Na2AC60 compounds superconduct for the larger A cations, but a crossover to nonsuperconducting behaviour occurs with decreasing cation size and correlates with a minimum in the unit cell volume.

SUPERCONDUCTING K3C60 (ref. 1) has been shown2 to have an intercalated face-centred cubic (f.c.c.) structure, and other A3C60 compounds (where A is K, Rb or mixtures of K, Rb and/or Cs) form an isostructural series with superconducting transition temperatures up to 31.3 K (ref. 3). Recently we reported413C NMR studies of KxC60 for x

THE recent syntheses1,2 of macroscopic quantities of C60 have suggested possible applications in host–guest and organic chemistry, tribology, electrochemistry and semiconductor tech-nology. Here we report the preparation of alkali-metal-doped films of C60 and C70 which have electrical conductivities at room temperature that are comparable to those attained by n-type doped polyacetylene. The highest conductivities observed in the doped films are: 4Scm−1 (Cs/C60), 100 (Rb/C60), 500 (K/C60), 20 (Na/C60), 10 (Li/C60), 2 (K/C70). The doping process is reversed on exposure of the films to the atmosphere. At high doping levels, the films become more resistive. We attribute the conductivity induced in these films to the formation of energy bands from the π orbitals of C60 or C70, which become partially filled with carriers on doping. The smaller alkali metal ions should be able to fit into the interstices in the lattice without disrupting the network of contacts between the carbon spheroids. In the case of C60, this would allow the development of an isotropic band structure, and we therefore propose that these materials may constitute the first three-dimensional 'organic' conductors.

The results of (13)C nuclear magnetic resonance (NMR) measurements on alkali fullerides KxC(60) are reported. The NMR spectra demonstrate that material with 0x3 is in fact a two-phase system at equilibrium, with x = 0 and x = 3. NMR lineshapes indicate that C(3-)(60) ions rotate rapidly in the K(3)C(60) phase at 300 K, while C(6)-(60) ions in the insulating K(6)C(60) phase are static on the time scale of the lineshape measurement. The temperature dependence of the (13)C spin-lattice relaxation rate in the normal state of K(3)C(60) is found to be characteristic of a metal, indicating the important role of the C(3-)(60) ions in the conductivity. From the relaxation measurements, an estimate of the density of electronic states at the Fermi level is derived.

We have grown crystals of the carbon structure C60 by sublimation. In contrast to solution-grown crystals, the sublimed crystals have long range order with no evidence of solvent inclusions. Sublimed C60 forms three dimensional, faceted crystals with a close-packed, face-centered cubic unit cell. We have refined a crystal structure using the “soccer ball” model of the C60 molecule. The results indicate that the C60 molecule has the expected spherical shape, however the data are not sufficiently accurate to unambiguously determine atomic positions.

THE magnetic susceptibility of C60 and the possibility of magnetic-field-induced π-electron ring currents in this carbon spheroid have been of interest since the initial experiments on carbon clusters1. If the molecule is regarded as a sphere with a radius of 3.5 A, on which 60 electrons are free to move, the Pauling ring-current model predicts a ring-current diamagnetic susceptibility 41 times the π-electron ring-current magnetic susceptibility of benzene with the field normal to the plane of the six-membered ring2,3. London theory predicts, however, that the π-electron ring currents in C60 should be weakly paramagnetic or diamagnetic, depending on the relative bond strengths used in the calculation2,3. With the availability of macroscopic quantities of C60 (ref. 4), it is now possible to study experimentally the magnetic properties of the molecule. Here we report on such measurements. We find that the diamagnetism of C60 is small, a result that we attribute to excited-state paramagnetic contributions to the π-electron ring-current magnetic susceptibility. Thus C60 seems to be an aromatic molecule with a vanishingly small π-electron ring-current magnetic susceptibility. We have performed similar measurements on C70, which indicate an appreciable π-electron diamagnetism, consistent with theoretical calculations. We attribute the differences in magnetic properties of these two molecules to their different fractions of five-membered ring structures. The fullerenes may thus constitute a class of compounds of 'ambiguous' aromatic character, traditional measures of which will not provide an adequate classification.

Nature 352, 701-703 (1991). THE positions of the alkali atoms, originally reported as (0,0.5, z) with z = 0.28, should read (x,0.5,0) with x = 0.22. These are the positions used in the calculations for Table 1 and the positions illustrated in Fig. 2.