High numerical aperture lithographic imagery at the Brewster angle

Abstract

Recent advances have enabled exposure tool manufacturers to ship tools with numerical aperture (NA)=0.8, and to envision optics with even larger NA. Thus the lithography community must grapple with images formed by oblique waves close to the Brewster angle. (For a typical chemically amplified resist with index of refraction n=1.7, the Brewster angle is 59°, corresponding to NA=0.86.) In this paper we will consider some of the surprising phenomena that occur at such high NA. Both vector diffraction simulation results and experimental results from the IBM interferometric lithography apparatus will be discussed. One of the most interesting modeling predictions is that, near the Brewster angle, the swing curve for transverse magnetic (TM) polarization is much smaller than normal, while the swing curve for transverse electric (TE) polarization is much larger than normal, and experimental measurements verify this prediction. Special image cross sections using the Plagello decoration method will also demonstrate the loss of TM image contrast due to vector imaging effects. © 2002 society of Photo-optical Instrumentation Engineers.