Resist reflow modeling including surface tension and bulk effect

Abstract

Resist reflow is a simple and cost-effective technique of fabricating a sub-100 nm contact hole (CH) pattern. The predominant factors affecting resist reflow include baking temperature and time, the volume surrounding the CH, the pattern layout, and the resist material properties. Thus, to optimize the layout design and process parameters, we developed a simple resist flow model that could predict the resist reflow tendency as functions of the reflow temperature, CH size, and the initial shape, the pitch and irregularity of CH array. The basic fluid equation was used to express the flow of the resist, and the variations of viscosity and density as functions of reflow temperature and time were considered. We also included the surface tension and bulk effect in our reflow model, so that we could see the difference in CH surface roundness with different surface tensions. We could also see the difference in CH size among the irregular CHs and those with different duty ratios by including the bulk effect. Moreover, we simply attempted to correct the critical dimension difference with pitch as imposing a bias on each after-development contact hole.