Maskless extreme ultraviolet lithography

Masks have been identified as the high risk, high cost issue for extreme ul traviolet (EUV) lithography. Challenges in EUV mask technology such as prov iding a pellicle and correcting defects have prompted the search for a mask less technique. Here we describe two approaches in which the mask of a curr ent EUV system is replaced by an array of micron-sized mirrors. Patterns ar e achieved by modulating individual mirrors to create selected bright and d ark spots. In one approach, individual mirrors can be lowered by lambda/4 t o yield locally dark regions because of destructive interference. In anothe r approach, each mirror is mounted on a cantilever. Selected cantilevers ca n 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 u p the required pattern. We have simulated the mechanical properties of the micron-sized mirrors and some aerial images showing that sub-100 nm feature s appear feasible. (C) 1999 American Vacuum Society. [S0734-211X(99)17306-2 ].