Mirror-based pattern generation for maskless lithography

摘要

In this paper, we consider the composition of integrated circuit patterns using dense arrays of mirrors. Typically the mirrors are 10-100 wavelengths in size and are demagnified some to form slightly sub-resolution spots or pixels at the wafer. The mirrors are actuated to modulate the light intensity. We consider both pure phase mirrors, moved in piston-like fashion, and tilting mirrors, which provide a mix of amplitude and phase modulation. We compare the image quality and useful process window for DUV or EUV imaging of typical features. The performance of both mirror types is similar when operated in gray-scale analog mode to provide arbitrary image placement and feature sizing, but for a given feature one mirror type will have slightly superior performance. Simple piston mirrors have a disadvantage with respect to image shift with defocus for certain features. A new type of mirror arrangement, termed the double-piston mirror, can equal or better the performance of tilt mirrors in all situations examined.