Analysis of alignment modeling for Nikon steppers

The alignment system, as one of key component for stepper, developed rapidly in the last few years because of huge requirement on advanced exposing tools for VLSI and MEMS. Alignment accuracy is mainly affected by errors coming from mark deformations and optical system. In this paper, we combined mathematical model of Nikon stepper alignment optical system and analyzed alignment errors of Nikon stepper caused by mark deformation in different processes. The model was verified by different experiments. Finally some improvement process is put forward to enhance alignment accuracy.