Japanese Journal of Applied Physics

The application of deep UV phase shifted-single layer halftone reticles to 256 mbit dynamic random access memory cell patterns

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We have applied deep UV (DUV) halftone reticles, with a single layer absorptive shifter consisting of silicon nitride, to 256 Mbit dynamic random access memory (DRAM) critical levels, and have evaluated the resolution in those cell patterns. For the periodic line levels, halftone reticles were combined with off-axis illumination (OAI) techniques. Resolution capabilities were characterized not only with stepper exposures but also with direct aerial image measurement. For hole levels such the Storage Node and Bitline Contact, halftone reticles offered clear improvement with standard illumination as compared to conventional reticles. For line levels such the Isolation, Wordline and Bitline, dramatic improvement was obtained with the combination of halftone reticles and off-axis illumination. © 1994 IOP Publishing Ltd.