Resolution enhancement with high transmission attenuating phase shift masks

Experiments to print 140nm lines and 140nm contact holes were optimized through simulation on an 18% transmitting phase shift mask for KrF lithography. A transmittance of 18% is to improve aerial image log slope through focus for the lines and contacts. The 140nm lines for all three pitches have a maximum depth of focus of at least 0.90 mu m. The exposure latitude of the 140nm lines is over 7.5% for all pitches to maintain 0.6 mu m depth of focus. Experiments show that the 140nm and 160nm contact holes resolve without side lobe printing through focus and through exposure. Reticle SEMs verify that a ternary contact hole mask is capable of manufacture. By adding both opaque and clear sub-resolution assist features, the experiments show contacts as small as 140nm resolve with 0.50 mu m focus latitude with 10% exposure latitude through pitch. Cross sectional SEMs verify that 140mm contact holes are open through pitch. Simulations to quantify the MEF show that the MEF for attenuating PSM decreases as the transmittance of the attenuating material increases. The MEF for a 30% transmitting attenuating material is 1.90 for a 150nm feature and the MEF for an alternating PSM is 1.42 for the same 150nm feature. Trends in aerial image CD variation due to aberrations were simulated for focal plane deviation, x coma, astigmatism, and spherical aberrations. The simulations of alternating PSM imaged with sigma of 0.35 suggest that alternating PSA? have the least CD variation due to focal plane deviation, astigmatism, and coma for dense pitches. The CD variation due to coma is comparable to 33% transmittance attenuating PSM for isolated lines. Furthermore alternating PSM is more susceptible to CD placement error due to coma compared to attenuating PSM. The 33% transmittance attenuating PSM has the least CD variation due to spherical aberration in comparison to BIM and alternating PSM.