This study involves the design and testing of off axis illumination apertures for an ASML 5500/90 248nm DUV stepper. X and V slot pole apertures based on dipole theory were designed, fabricated out of aluminum, and inserted into the optical column of the stepper. Test patterns consisting of vertically oriented features were printed with and without dipole illumination, exposed, and compared to determine their effectiveness. As expected, features which were to small to print under standard illumination imaged exceptionally well using the x slot pole aperture. The y slot pole aperture delivered the same results as standard illumination which was also expected. 0.24μm features were printed clearly and consistently under the off axis illumination scheme on a system specified to print a minimum feature size of 0.35μm with a numerical aperture of 0.5.
Malloy, Matthew E.
"Design and Testing of Off Axis Illumination Filters for a 248nm DUV Exposure System,"
Journal of the Microelectronic Engineering Conference: Vol. 13:
1, Article 8.
Available at: https://repository.rit.edu/ritamec/vol13/iss1/8