Ultrathin polymer films for microlithography

Abstract

Ultrathin (14–22 nm) poly(methylmethacrylate) (PMMA) films prepared by both spin casting and Langmuir–Blodgett (LB) techniques and novolac films prepared by spin casting have been explored as high-resolution electron beam resists. One-eighth micron lines-and-spaces patterns (equal to the smallest beam diameter available) have been achieved by using a Perkin Elmer MEBES I pattern generation system as the exposure tool, and the definition of 45-nm features has recently been achieved by using a high-resolution electron beam lithography system. [J. H. Newman, K. E. Williams, and R. F. W. Pease, J. Vac. Sci. Technol. B 5, 88 (1987)]. The etch resistance of such films is sufficiently good to allow patterning of a chromium film suitable for photomask fabrication. The most surprising result has been that the pinhole densities in 14.3-nm LB PMMA film and 22-nm spin-cast novolac film are only a few per cm2, considerably lower than the density in spin-cast PMMA films of comparable thicknesses.