Mask writing time explosion and its effect on CD control in e-beam lithography

Abstract

As semiconductor features shrink in size and pitch, the extreme control of CD uniformity and MTT is needed for mask fabrication with e-beam lithography. And because of huge shot density of data, the writing time of e-beam lithography for mask fabrication will be increased rapidly in future design node. The beam drift caused by charging of optic system and current density drift can affect the beam size, position and exposure dose stability. From the empirical data, those are the function of writing time. Although e-beam lithography tool has the correction function which can be applied during writing, there are remained errors after correction which result in CD uniformity error. According to the writing time increasing, the residual error of correction will be more important and give the limit of CD uniformity and MTT. In this study, we study the beam size and exposure dose error as a function of time. Those are mainly caused by charging and current density drift. And we present the predicted writing time of e-beam lithography below 32nm node and estimate its effect on CD control error. From the relation between writing time and CD control error, we achieve the limit of CD uniformity with e-beam mask writer. And we suggest the method to achieve required CD uniformity at 22nm node and beyond.