High-RI resist polymers for 193 nm immersion lithography

A critical aim within the field of 193 nm immersion lithography is the development of high refractive index immersion fluids and resists. Increases in the refractive index (RI) of the immersion fluid will result in increases in the numerical aperture and depth of focus. Increasing the RI of resist polymers will improve exposure latitude for the process. A challenge for increasing the RI of resist polymers is to do so without detrimentally affecting other properties of the polymer such as transparency, line edge roughness, adhesion and plasma etch resistance. It is well known in the literature that introducing sulfur, bromine or aromatic groups into a polymer structure will increase its RI. However, due to the relatively strong absorption of phenyl groups at 193 nm these groups have to be avoided. Furthermore, the use of bromine poses problems associated with contamination of the silicon wafer. Hence, in this study, a systematic approach has been used to increase the sulfur content of 193 nm type resist polymers, by synthesis of sulfur-containing monomers and by performing bulk modifications of the polymer. The effect of sulfur content on the RI at 193 nm was then investigated. A broad study of the relationship between molecular structure and RI dispersion from 250-180 nm has also been undertaken, and conclusions drawn using QSPR methodologies. Finally, the effect of sulfur content on other lithography parameters, such as transparency, adhesion and plasma etch resistance, was also evaluated

Synthesis of high-refractive index sulfur containing polymers for 193-nm immersion lithography: A progress report

To be able to extend the 193 nm immersion lithography technology platform, the development of high refractive index immersion fluids and resists is required. This paper reports our investigations into generating high refractive index polymers for use in photoresist formulations for 193 nm immersion lithograph. In this study a series of model compounds have been screened for refractive index and transparency at 589 nm and 193 nm. For the compounds studied this series of experiments demonstrated that sulfur-containing compounds have a positive effect on the refractive index of a molecule at 589 nm. However, the situation is complicated by the presence of absorption bands for some small molecules in the low waveleingth region. To demonstrate this, we examined the refractive index dispersion of a series of molecules based on ethyl acetate with varying degrees of sulfur substitution. These results indicated that an anomalous increase in refractive index could be expected 20 - 30 nm above the absorption maximum. The implications for design of high refractive index resists for 193 nm immersion lithography are discussed

Volatile products and new polymer structures formed on Co-60 gamma-radiolysis of poly(lactic acid) and poly(glycolic acid)

A gas product analysis has been conducted on gamma-irradiated samples of poly(lactic acid) (PLA) and poly(glycolic acid) (PGA) by means of gas chromatography. The major volatile products have been identified to be CO, CO2, CH4 and C2H6 for PLA, and CO and CO2 for PGA. In addition, the yield of evolved gases for PLA has been found to be 1.81 for CO2, 0.98 for CO, 0.026 for CH4 and 0.012 for C2H6; and that for PGA to be 1.70 for CO2 and 0.42 for CO. The new chain ends formed due to gamma-induced bond cleavage in PLA have been assigned to CH3-CH2-CO-O- and CH3-CH2-O-CO-, and the G values for formation of these chain ends were found to be 1.9 and 0.6, respectively. The G value for chain scission reported previously of 2.3 is comparable with that for the formation of the propanoic acid end group. (C) 1997 Elsevier Science Limited

Quantitative analysis of bismaleimide-diamine thermosets using near infrared spectroscopy

A method is reported for studying the polymerisation kinetics of a commonly used bismaleimide monomer, 1,1'-(methylenedi-4,1-phenylene)bismaleimide (MDP-BMI) with aromatic diamines such as 4,4'-diaminodiphenylmethane (DDM). Fourier-transform near infrared (FT-NIR) spectroscopy was used to obtain quantitative data using an in-situ technique. The NIR technique was used to measure the concentration of the various functional groups in the BMI/diamine resins with respect to time during isothermal cure. Quantitative data were obtained for all the functional groups in the resins studied, either from direct measurement or from the mass balances involved in the reactions. In order to obtain truly quantitative data, Fourier self-deconvolution of the spectra was used to enhance peak separations and the determination of peak areas. A substantial difference in reactivity between primary and secondary amine was observed in the systems studied. This has significant implications for the modelling of the polymerisation kinetics where the conversions of primary and secondary amines have not been separately measured. Differences in the reactivities of different resin formulations where observed when the diamine was changed from DDM to 4,4'-diaminodiphenylsulphone (DDS). There is a strong suggestion that one of the initial reaction products has a catalytic effect on the reaction, at least when using DDS as the diamine. The most likely identity of the species involved in this self-catalysis is the secondary amine formed by reaction of the maleimide double bond with a primary amine. (C) 2000 Elsevier Science Ltd. All rights reserved