Influence of polarization on absorbance modulated subwavelength grating structures

The feasibility of using absorbance modulated structures as subwavelength optical transmission gratings was studied using both analytical techniques and finite element method simulations. Particular note was taken of the relevance of this work to absorbance modulation optical lithography (AMOL) and the understanding of the authors of how to control and improve the transmission of light through the photochromic layer. It was found that absorbance gratings share many characteristics with similar-sized metal gratings, in particular, transmitting transverse magnetic (TM) polarized light better than transverse electric polarized light. For both polarizations the transmission through an absorbance grating produces lower contrast intensity profiles compared to both metal and dielectric gratings; however, there was reasonable contrast to a depth of approximately 40 nm beneath the grating in the TM case for gratings with half-pitch as small as 20 nm. Full vector-field AMOL simulations demonstrate similar trends in which there was improved propagation and confinement of TM polarized light at the short resist-exposing wavelength.