Optimization of attenuated phase-shift mask for contact hole printing

Abstract

The goal of this study is to characterize the process latitude of an attenuated phase gift mask on contact hole printing. The parameters chosen to examine the effect on process windows are numerical aperture (NA) and partial coherence. In addition to these, another important element we would like to determine from this test is the appropriate mask to wafer CD bias. The range of numerical aperture is from 0.5 to 0.63 and the range of partial coherence ins from 0.32 to 0.67. Within the ranges of study, it is found that the DOF increases with decreasing partial coherence for iso contacts, but decreases with decreasing partial coherence for dense ones. DOF increases with decreasing numerical aperture for both iso and dense contact holes as expected. The best DOF of 2.1 micron was obtained with 0.5 NA and 0.4 partial coherence. In general, the required energy to open contact holes increases with decreasing numerical aperture, while the impact of partial coherence on best dosage is not as predominant as NA does. The effect of pre-treatment delays the side lobe formation for iso contact holes while seems to have no effect on dense ones.