Manufacturing implementation of deep-UV lithography for 500-nm devices

Lithographers have steadily reduced exposure wavelength and increased numerical aperture (NA) to maintain process window and simplicity. The G-line systems of the 1970s gave way to the I-line systems of the late 80s, and then to the deep ultraviolet (DUV) systems of today. This paper describes our characterization of a DUV lithography system for the manufacture of 16-Mb DRAM chips at 500-nm ground rules. The process consists of a positive-tone, aqueous-base developable photoresist with an overcoat for sensitivity control, and an anti- reflective coating (ARC) on selected levels. The exposure tools used are step-and-scan systems with a 0.36 NA and expose bandpass of 240 - 255 nm. Apply and develop processes are clustered with the expose tool to minimize defects, reduce cycle time, and eliminate process variables.