Val Krukonis

Immersion liquids for lithography in the deep ultraviolet

The requirements of liquids for use in immersion lithography are discussed. We present simple calculations of the transmission and index homogeneity requirements of the immersion liquid (T > 0.95 and δn < 5×10-7 respectively for sin θ = NA/n = 0.9 and a working distance of 1 mm) along with the temperature and pressure control requirements which follow from them. Water is the leading candidate immersion liquid for use at 193 nm, and we present data on its chemical compatibility with existing 193 nm resists through dissolution/swelling and surface energy studies. We find that it has a minimal impact on at least some current 193 nm resists. At 157 nm, suitably transparent immersion fluids remain to be identified. Perfluorinated polyethers (PFPE) are among the most transparent organics measured. The lowest PFPE absorbance at 157 nm can be further reduced by roughly a factor of two, from 6 to 3 cm-1 through removal of dis-solved oxygen. We also discuss our efforts to understand the origin of the remaining absorbance through supercritical CO2 fractionation.

Fractionation of high density polyethylene in propane by isothermal pressure profiling and isobaric temperature profiling

Abstract High density polyethylene was fractionated with respect to molecular weight and dissolution temperature in supercritical and near-critical propane. Isothermal pressure profiling in the liquid (polymer)-super-critical fluid regime resulted in 14 fractions with narrow polydispersity. The liquid-crystal phase separation technique of Pennings was extended from organic solvents to compressed propane for fractionation with respect to dissolution temperature and therefore crystallizability in the semicrystalline solid-supercritical fluid regime by isobaric temperature profiling above the second critical endpoint pressure. The influence of molecular weight, crystalline content, and mass transfer limitations is discussed. The authors believe this is the first time a crystal phase fractionation has been reported in supercritical fluids. The process is suggested as an alternative to temperature rising elution fractionation (TREF) developed to fractionate linear low density polyethylene on the basis of short chain branching.