Modeling and experimental verification of illumination and diffraction effects on image quality in x-ray lithography

Abstract

Most analyses of the effects of diffraction and source coherence on image quality in proximity x-ray lithography have used Kirchhoff boundary conditions and scalar diffraction theory. In this article we treat the x-ray absorber as a lossy dielectric and employ the vector form of Maxwell’s equations to calculate image intensity as a function of position for lines, spaces, and gratings, at 100 nm linewidths and below. We show that vector and scalar theories give different results. Simulations are done for two point sources (CuL and an Fe-plasma) so that calculations could be compared with our experimental results. Agreement was excellent for 80 and 50 nm features at relatively large gaps. We define image contrast and show that, contrary to common intuition, it is enhanced (and spurious ringing is suppressed) as penumbral blurring is increased, reaching a maximum when the extent of blurring is somewhat larger than the minimum feature size.