THE APPLICATION OF DEEP UV PHASE SHIFTED-SINGLE LAYER HALF-TONE RETICLES TO 256 MBIT DYNAMIC RANDOM-ACCESS MEMORY CELL PATTERNS

We have applied deep UV (DUV) halftone reticles, with a single layer a bsorptive shifter consisting of silicon nitride, to 256 Mbit dynamic r andom access memory (DRAM) critical levels, and have evaluated the res olution in those cell patterns. For the periodic line levels, halftone reticles were combined with off-axis illumination (OAI) techniques. R esolution capabilities were characterized not only with stepper exposu res but also with direct aerial image measurement. For hole levels suc h the Storage Node and Bitline Contact, halftone reticles offered clea r improvement with standard illumination as compared to conventional r eticles. For line levels such the Isolation, Wordline and Bitline, dra matic improvement was obtained with the combination of halftone reticl es and off-axis illumination.