IMPROVED REGISTRATION ACCURACY IN E-BEAM DIRECT WRITING LITHOGRAPHY

This paper reports on techniques for improving registration accuracy in electron beam (EB) direct writing lithography for a 0.25 mum process. An analysis of registration accuracy for the EB writing system was performed with the goal of minimizing registration errors, since mark detection and stage positioning accuracies are not sufficient for a 0.25 mum process. To improve mark detection accuracy, a new technique based on the correlation parameter optimization method was developed, and the stage guide mechanism was reinforced to improve stage positioning accuracy. Using these two techniques, the calculated registration accuracy was improved to 0.070 mum (\xBAR\ +3sigma). EB direct writing incorporating the above was applied to the development of a 256 Mbit DRAM, having a minimum feature size of 0.25 mum. A sufficient registration accuracy of 0.075 mum(\xBAR\ +3sigma was obtained for the EB writing layer.