Nobuyuki Matsuzawa

Plasma‐polymerized C60/C70 mixture films: Electric conductivity and structure

Polymerization of a mixture of C60/C70 in rf plasma is reported. The electric dark‐current conductivity of the plasma‐polymerized mixture of C60/C70, which is approximately 10−7 S/cm in the atmosphere, does not depend on the applied voltage at least in the range of −25 to 25 V. A semiconductor‐type temperature dependence of the conductivity in the higher‐temperature domain was observed, and the band‐gap energy was estimated to be 2.1 eV. The conductivity increased with increasing temperature from 25 to 230 °C in vacuum, whereas in the atmosphere the conductivity increased upon decreasing the temperature below 80 °C. It is supposed that in this temperature domain the electric conductivity is enhanced by the existence of water molecules on the film, the surface of which is characterized by a high hydrophilicity. The surface morphology of the polymerized film was characterized by the presence of aggregates with diameters of about 300 A and the surface was highly hydrophilic, polar, and heterogeneous. The sur...

Theoretical Calculation of Photoabsorption of Various Polymers in an Extreme Ultraviolet Region

We have calculated the linear absorption coefficients of various resist polymers using the mass absorption coefficients at 13 nm and the density obtained from the graph-theoretical treatment derived by Bicerano. The values indicate that the transmittance at 13 nm of conventional resists used in 193-nm, 248-nm and 365-nm lithography is about 30% when the thickness is 3000 A and 60–70% when it is 1000 A. This shows that conventional resists are suitable for an EUVL (extreme ultraviolet lithography) thin-layer resist (TLR) process using a hard-mask layer, but their large photoabsorption makes them unsuitable for a single-layer resist (SLR) process. To design polymers that are suitable for an SLR process, we further calculated the absorption of about 150 polymers. The results suggest that the introduction of aromatic groups into a polymer not only reduces the absorption at 13 nm but also increases the etching resistance.

Reduction of line edge roughness in the top surface imaging process

This article presents a novel top surface imaging (TSI) process that is highly sensitive and reduces line edge roughness (LER). We found that LER and residue decreased when we used a chemically amplified (CA) resist, consisting of a base polymer with a high molecular weight and a photo-acid generator producing an acid with a high molecular weight. The top thin silylated layer of the exposed region on the CA resist causes the LER. A breakthrough step in the dry-development process improves the silylation contrast between the exposed and unexposed regions. We then apply a novel step in the dry-development process which involves a predry development bake at a temperature above the glass transition temperature of the silylated polymer. This step is effective in rolling and smoothing the edge of silylated layer by thermal flow. By applying the predry-development bake step above the glass transition temperature, we were able to reduce the LER to less than 6 nm. We have demonstrated a novel TSI process for achie...

Macrocyclic functional dyes: Applications to optical disk media, photochemical hole burning and non-linear optics

Our recent research activities on macrocyclic functional dyes such as phthalocyanines and porphyrins are reviewed. For optical data storage, we have established tetrabenzoporphme derivatives are suitable for shorter wavelength recording. we have proposed new photon-mode superresolution. The playback of double density EFM signals was achieved using a naphthalocyanine derivative. For future ultrahigh density optical recording, tetraphenylporphine derivatives are found to be a promising class of photochemical hole burning materials. The potential recording density is expected to be enhanced by two or three orders of magnitude compared to conventional optical-data storage. Fundamental computational research is going on to develop new materials with high nonlinear optical properties. We have predicted the hyperpolarizabilities of a series of metallo-porphyrins. These theoretical calculations enabled us to quantitatively design materials.

Changes of chemical nature of photoresists induced by various plasma treatments and their impact on LWR

Changes in chemical nature of an ArF photoresist caused by various plasmas were analyzed, and it was found that the HBr plasma treatment induces a selective detachment of a heterocyclic unit of the photoresist, and the detached unit remains in the photoresist film. Thermomechanical analyses were performed, which showed that the softening temperature of the photoresist decreases by the HBr treatment, indicating that the detached heterocyclic unit acts as a plasticizer in the photoresist film. These results showed that the HBr treatment can be regarded as a softening process of the photoresist. This HBr treatment was applied to the fabrication of line patterns and it was shown that the treatment remarkably improves LWR (line width roughness) after etching. This improvement was more pronounced for the case of an isolated pattern than the case of a dense pattern. Further investigations on the HBr treatment were performed by changing the copolymerization ratio of a monomer containing the heterocyclic unit. It was shown that the reduction of LWR by the HBr treatment becomes more enhanced when the copolymerization ratio increases. However, an intensive HBr treatment was found to deteriorate LWR, showing that there is an optimum condition of the HBr treatment in terms of improving LWR.

Theoretical estimation of absorption coefficients of various polymers at 13 nm

The linear absorption coefficients at 13 nm were calculated for more than 150 polymers. The results indicate that an aromatic substitution lowers the absorption coefficient. This is because oxygen has a larger atomic absorption than carbon or hydrogen and the substitution reduces the relative oxygen content. Furthermore, the Ohnishi parameters for the polymers were calculated in order to investigate the relationship between the absorption at 13 nm and the etching resistance. This showed that polymers with aromatic groups tend to exhibit a lower absorption and a higher etching resistance than those without aromatic groups. This suggests that, regarding resist processes for EUV (extreme ultraviolet) lithography, a single-layer resist process employing no hard-mask layer is another promising candidate in addition to one that uses both an unltrathin resist layer (~100 nm thick) and a hard-mask layer

Theoretical calculations of photoabsorption of molecules in the vacuum ultraviolet region

The theoretical design of transparent materials for use as photoresist materials for F2 lithography (157 nm) requires molecular orbital calculations of the photoabsorption of molecules in the vacuum ultraviolet (VUV) region. To predict photoabsorption, this study employed ab initio molecular orbital calculations at the level of single-excitation configuration interaction (CIS) combined with an empirical correction to the calculated peak position. This method was used to calculate the photoabsorption spectra of various functional groups, such as alcohol, ether, ketone, carboxylic acid and ester groups, as well as several polymers and alicyclic groups. On the basis of the calculation results, the applicability of these functional groups to photoresists for F2 lithography is discussed.

Light stability of a β-cyclodextrin inclusion complex of a cyanine dye

The stability to light of 1,3,3,1′,3′,3′-hexamethyl-2,2′-indotricarbocyanine iodide (HITC) included in β-cyclodextrin (β-CyDx) has been examined. The quantum yield of the photodegradation of HITC was found to decrease with increasing formation of the inclusion complex, showing that the photostability of the dye can be improved by the formation of the complex. Emission from singlet oxygen (1Δg→3Σ–g, 1268 nm and 1580 nm) for systems of HITC with or without β-CyDx in aqueous solution was also measured. It was found that the amount of singlet oxygen generated by flash irradiation is reduced by the inclusion complex formation, and that the lifetime of singlet oxygen increased with increasing concentration of β-CyDx, suggesting that the photodegradation of HITC for the system of HITC/β-CyDx is reduced by two factors; first, the inhibited formation of singlet oxygen, and secondly, the inhibited attack of singlet oxygen on the dye.

Pattern collapse in the top surface imaging process after dry development

In this article the pattern collapse in a 193 nm top surface imaging process after dry development is described. We dry developed the resist with O2 and SO2 plasmas at low temperature in order to replicate a fine pattern profile. Pattern collapse occurred because of stress from neighboring patterns when SO2 was added at low substrate temperatures and the line/space binary pattern was below 0.15 μm. We found, using Auger electron spectroscopy analysis, that a sulfuric compound covered the side walls of the pattern when SO2 was used. We propose a pattern collapsing mechanism caused by the reaction of H2O with the evaporation of water adsorbed by the sulfuric compound on the resist pattern. It is therefore effective to decrease the sulfuric compound on the patterns before the wafer is removed from the etching chamber. Finally, we successfully replicated a sub-0.10 μm line and space pattern without pattern collapse.

Bond energies in organofluorine systems: applications to Teflon® and fullerenes

Abstract Computational chemistry methods have been used to calculate bond energies in organofluorine compounds. The bond strengths in models of Teflon® have been calculated by using ab initio molecular orbital theory. The CF bond strengths fall in the expected ranges. The CC bond strengths are much higher than those in the corresponding hydrocarbon model. The CF bond strengths in the C60F, C60F2 and C70F were calculated at the non-local density functional theory level. These bond strengths are much weaker than those in saturated organofluorine compounds.