0.15-MU-M ELECTRON-BEAM DIRECT WRITING FOR GBIT DYNAMIC RANDOM-ACCESSMEMORY FABRICATION

This paper describes 0.15 mu m electron beam (EB) direct writing techn iques for Gbit dynamic random access memory (DRAM) fabrication. In ord er to use EB direct writing for reliable fine pattern fabrication on t he 0.15 mu m level, an EB direct writing system technique, a resist pr ocess technique, a cell projection (CP) mask preparation technique, wh ich is indispensable for improving the writing throughput, and a data preparation technique with proximity effect correction must be improve d respectively and combined successfully. The proximity effect correct ion for all fine patterns in a full-scale DRAM chip is especially impo rtant for achieving a CD accuracy of less than 0.02 mu m, which is req uired for device fabrication and margin. For obtaining the reliable sh ot stitching accuracy between CP and variably shaped (VS) EB writings, we adopted the cross-correlation method, which was used to decide the size and center position of the CP shot. A single-layer resist system without an over-coated conducting layer was used for reliable device fabrication. In addition, for improving the CD accuracy for all 0.15 m u m designed patterns in a full-scale chip, we developed a data partit ion process suitable for CP mask pattern data and an improved 1-dimens hinal(1-D) calculation method for proximity effect correction. Utilizi ng these techniques, the full-scale 4Gbit DRAM, which was designed wit h 0.15 mu m minimum feature size, was fabricated successfully with 0.0 5 mu m (\mean\ + 3 sigma) overlay accuracy, 0.02 mu m (\mean + 3 sigma ) stitching accuracy, and less than 0.02 mu m (3 sigma) CD accuracy, a ll of which were sufficient for the required device fabrication.