Evaluation of partial coherent imaging using the transfer function in immersion lithography

Abstract

The desired minimum feature size is decreasing for the future technology nodes. Immersion lithography has been actively pursued as a method of extending the resolution of optical lithography beyond 65 nm mode. Immersion lithography and hyper NA impact the selection and optimization of the various resolution enhancement techniques (RET). These can be selected as appropriate for each mask pattern. As the line width on target is narrower, the fine-line structure will no longer be discernible. Then this is the resolution limit of the system. Until recent times, the traditional means of determining the quality of an optical element or system of elements was to evaluate its limit of resolution. A useful parameter in evaluating the performance of a system is the modulation transfer function and this is analyzed for the hyper NA immersion lithography.