Phase shift mask ( PSM ) is a useful technique to higher the resolution and focus margin in the lithography process with sub-half micron range, which is limited by currently used process tools. PSM with i-line stepper is one of the leading candidates for mass production of 64M Bit Dram. In this study, in order to obtain the information about the basic trend and process limitation of PSM, we evaluated the PSM technique by simulation and lithographic experiment. However several difficulties were encountered when attempting to use the PSM in real process. These difficulties were mainly due to the process margin and variation in munufacturing a real device.
We simulated PSM by changing numerical aperture, patial coherence, focus, and pattern size for g-line and i-line. Intensity profiles of patterns were monitored for both conventional and phase shift mask ( alternating t>ye ). With those simulation results, we first analyzed the aerial image and studied the trend and limitation of PSM technology. Then we compared these results with experimental results of g-line and i-line process. Although the simulation and the experimental results showed that definable resolution limit and the resolution with depth of focus ( DOF ) margin were significantly increased by PSM technology, it was hard to control the process due to the errors occuring in manufacturing PSM. The study for resolution limit with marginal depth of focus led us to optimize the method how to approach the PSM from simulation. In addition, the process limitation and lithographic trend of PSM were investigated as well.