Maskless extreme ultraviolet lithography

Abstract

Masks have been identified as the high risk, high cost issue for extreme ultraviolet (EUV) lithography. Challenges in EUV mask technology such as providing a pellicle and correcting defects have prompted the search for a maskless technique. Here we describe two approaches in which the mask of a current EUV system is replaced by an array of micron-sized mirrors. Patterns are achieved by modulating individual mirrors to create selected bright and dark spots. In one approach, individual mirrors can be lowered by $\text{λ/4}$ to yield locally dark regions because of destructive interference. In another approach, each mirror is mounted on a cantilever. Selected cantilevers can be tilted such that incident light from those mirrors is out of the pupil of the imaging objective. The wafer is mechanically scanned and the object is electronically scrolled across the array of mirrors in order to build up the required pattern. We have simulated the mechanical properties of the micron-sized mirrors and some aerial images showing that sub-100 nm features appear feasible.