STRATEGIES TO IMPROVE LINEWIDTH CONTROL FOR 0.25[mu]m AND 0.18[mu]m DEVICES

Linewidth control in the 0.25μm-0.18μm range will be one of the biggest challenges for future optical lithography. Various parameters contribute to CD variations: stepper parameters, lens errors, mask imperfections, resist processing, wafer topography, proximity effects and operator errors. The goal of this paper is to elaborate on the most important contributors to CD variations. Linewidth control is studied directly, characterised by the 3σ variation of the CD spread. Our investigations are based on simulations and on experimental work. CD control for 0.25μm applications is compared for four resist strategies: negative tone resist with TAR, negative tone resist on BARC, positive tone resist on BARC and top surface imaging (TSI) in combination with dry development. Proximity correction is taken into account. Best results are obtained with the negative tone process on BARC and with TSI. Concerning CD-control for 0.18μm devices, a feasibility study is carried out, based on simulations. NA and σ optimisation will be required for sufficient CD control, as well as proximity correction on the mask. This feasibility study is illustrated with various experimental results obtained using TSI (Desire process).