Sensitivity factors of CAR electron beam resists

Abstract

Over the years for enhanced resolution, electron beam exposure tools have migrated to higher accelerating potentials. High kV exposure requires faster resist to offset the loss of absorbed radiation. In addition, in order to maintain throughput in mask writing tools, photoresist sensitivities of the order of 5 μC/cm2 at 50 kV are needed and likewise 5 μC/cm2 at 100 kV for projection exposure tools. To meet this sensitivity requirement there is an keen interest in using chemically amplified resists (CAR). The CAR resists offer additional benefits such as high contrast, improved resolution, larger process windows, and dry resistance. This study is focused on enhancing the sensitivity of a low activation ketal protected polyhydroxystyrene. One such resist, which has been reported previously, is insensitive to the post apply bake temperature and does not require a post exposure bake. To enhance the resolution, process latitudues, and chemical contrast, base quenchers are usually added to limit the diffusion of the acid after exposure. To improve the sensitivity of the formulation, the effect of the acid generator (AGX), type of base, base concentrations and ratios in Combination with the polymer protection level has been studied. Yields of acid formed were measured by titration and NMR. It was also found that both the AGX and base has an inhibition effect on dissolution. By increasing the amount of AGX and decreasing the polymer protection level, the sensitivity of the formulation was improved while maintaining the resist contrast, resolution, vacuum stability, and bake latitudes. In addition, the Sensitivity of the resist can be altered by quantity and type of added base. We have also investigated the effect of Pka of the base on the sensitivity, and process exposure latitude. The ionic onium acid generators or non ionic hydroxyimides provide adequate acid when coupled with adjusted concentrations of base to achieve 5 μC/cm2 at 100 kV.