Journal of Vacuum Science & Technology B, Vol.26, No.6, 2116-2120, 2008
Enhancement in hyper-numerical-aperture imaging through selective TM polarization
The degradation of projected images using TM polarization is not intrinsic because losses in image contrast can be recoverable. By controlling the photoresist/substrate interface reflectivity, high modulation for TM polarization can be maintained for angles approaching 90 degrees in a photoresist. Although there is calculated loss of image contrast with increasing polarization angle using suppressed reflection (i.e., with an antireflection coating), the loss is not nearly as large when imaging over a reflective substrate. These results can potentially impact the design of illumination, possibly away from most recent TE-only schemes for oblique imaging angles and high numerical apertures (NA). Several cases of TM illumination are presented combined with tuned substrate reflectivity for 0.93 NA, 1.20 NA, and 1.35 NA and compared to results using TE illumination. Additionally, a scheme for frequency doubling with a single TM polarized exposure is presented. Using a single exposure and selective TM polarization, the reflective component produced at the photoresist/substrate interface is utilized for a four-beam imaging scenario. In doing so, patterns deposited into a photoresist film with double density are made possible.