Abstract

We are doing physical optics modeling of a soft x-ray projection lithography system. The system being modelled consists of projector and condenser optics. The object mask is imaged onto the photoresist with the projector, an off-axis f/5 Schwarzs-child reflective microscope. The condenser is an off-axis section of an elliptical mirror. It images the incoherent, 14-nm laser-plasma source into the entrance pupil of the Schwarzschild, as in Kohler illumination. It is widely understood that the f/5 Schwarzschild must have wave-front errors that are small relative to the 14 nm wavelength if 200 nm features are to be sharply imaged onto the chip. How about the condenser mirror? How good does it have to be? We generate specifications for the mirror, as well as alignment tolerances. In addition, we study the effects on the image of edge diffraction in the condenser system.

© 1992 Optical Society of America