Lithographic evaluation of deep-UV photoresists for 0.25- and 0.18-μm technology design rules

The t-BOC photoresists represent a well established reference in Deep UV lithography, but more and more `new generation' 248 nm products are proposed by all the major photoresist manufacturers. The purpose of this paper is to evaluate the compare the performances of the 2 t-BOC photoresists, with those of 4 other `new products', from the ESCAP and acetal families; these products (from 5 different manufacturers), are evaluated for 0.25 micrometers and 0.18 micrometers technologies design rules. The photoresists are compared with quantitative and qualitative criterias. The quantitative approach consists in the determination of the energy-focus latitudes, for isolated and dense patterns (0.2 and 0.25 micrometers nominal). The proximity effects are also evaluated in each case, for different pitches. The qualitative approach consists in the photoresist patterns profiles study (slope, standing waves, footing, undercut, ...). The stepper used for the evaluation is an ASML PAS 5500/90, with a numerical aperture and a partial coherence of respectively 0.5 and 0.63. The substrates consist of bare silicon, to get rid of possible photoresist-substrate incompatibilities. The conclusion of the study for 0.25 micrometers design rules is that the t-BOC materials still perform the best; for 0.2 micrometers design rules, the trend is the same, even if the conclusion must be taken with caution, due to the limitations of the 0.5 NA of the ASML PAS 5500/90 stepper.