The goal of this study is to characterize the process latitude of an attenuated phase sgift mask on contact hole printing.The parameters chosen to examine the effect on process windows are numerical aperture (NA) and partial coherence (sigma). 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 is 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.

The goal of this study is to assess the capability of a negative DUV resist with application to metal layer lithography.The major issues encountered in metal layer lithography are CD non-.uniformity resulting from step height variation from memory cell to periphery and resist's bridging in the area of bank to bank connection within the cell of 64M DRAM. We have compared both positive-tone and negative-tone DUV resists with SiON as the bottom anti-reflection coating (BARC).The results indicate that the negative DUV resist shows no resist bridging problem and has better CD uniformity across step height variation region. The CD uniformity across banks of cells has improves by 10% in comparison with positive-tone resist. Process windows are enhanced in both exposure latitude and DOF. The etching resistance to metal is also improved by 20%.