Each new technology node tests the limits of optical Lithography. As exposure wavelength is reduced, new imaging techniques are needed to maximize resolution capabilities. The phase-shift mask (PSM) is one such technique that is utilized to push the limits of optical lithography. Altering the optical phase of the light that transmits through a photomask can increase the resolution of a lithographic image significantly. However, intensity imbalances between the etched and non-etched regions due to sidewall scattering can cause resolution, phase and placement errors on the wafer. One method to balance the transmission is to undercut the chrome or retract the quartz underneath the chrome in the etched regions. An alternating aperture phase-shift mask with undercut was successfully fabricated and showed improved intensity balance.
Cangemi, Marc J.
"Investigation of Undercut on Alternating Aperture Phase Shift Mask,"
Journal of the Microelectronic Engineering Conference: Vol. 13
, Article 11.
Available at: http://scholarworks.rit.edu/ritamec/vol13/iss1/11