Tungsten/carbon masks in x-ray projection lithography

A theoretical investigation is presented of electron scattering effects in tungsten/carbon mask fabrication process for x-ray projection lithography. A Monte Carlo simulation is carried out and results are utilised to evaluate proximity effects. Electron-beam energy (20 to 100 keV) and mask substrate material (silicon and diamond) are process variables considered. The results demonstrate that, in the presence of a bulk substrate, higher-contrast patterns can be obtained, at intermediate energies, by using diamond rather than silicon. Finally, in order to fully benefit from the more favourable diamond scattering properties, a diamond membrane is proposed as mask-supporting layer, allowing to further improve lithographic resolution at higher e-beam energies.