The Examination of Topographic Images in Resist Surfaces

Abstract

The high resolution examination of the microstructure of biological materials using soft x-rays has become possible because of the recent advances in long wavelength x-ray optics and in very large scale integrated circuit fabrication technology. As all microscopists are interested in the limits of their technique, the question of resolution is a topic of central interest. A comparison of the different methods of imaging with soft x-rays reveals that the contact method, called in the earlier literature microradiography, has the highest claimed resolution (5nm) (Spiller et al, 1979; Feder et al, 1977; Panessa-Warren, 1984). However, this is at variance with Flanders’ experiments in attempting to use carbon K α radiation to replicate lithographically tungsten lines using a mask which consisted of 30nm thick evaporated tungsten lines on a thin carbon support film (Flanders, 1980). The lines and spaces of the mask were examined in an electron microscope and were as small as 2nm in lateral width. Flanders found that the minimum linewidth possible to replicate with soft x-rays was 15nm. The height of this exposed and developed PMMA line was 60nm. At linewidths narrower than this, the lines on the PMMA appeared to disintegrate. There are similar resolution limitations in fabricating small lines and spaces in PMMA using electron beam writing, for which Mackie and Beaumont report that it is possible to produce 10nm wide lines by lift-off (Mackie and Beaument, 1985).