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Fabrication of high-density SRAM chips using mix-and-match x-ray lithography

As part of the Defense Advanced Lithography Program (DALP), IBM has fabricated 0.35 micrometers high-density static random access memory (SRAM) chips with all critical levels being exposed using synchrotron X-ray lithography. X-ray exposures for the four critical levels (isolation, gate, contact holes, and metal 1) were performed at the Advanced Lithography Facility (ALF) at the IBM East Fishkill, New York site. Nonlithographic processing and noncritical level optical exposures were performed in the Very Large Scale Integration (VLSI) pilot line at the IBM Manassas, Virginia site. Extensive alignment and process latitude studies were conducted to determine the best operating points in preparation for the full product SRAM runs. Overlay error, dose and gap latitude, etch bias control, and electrical test results will be presented and compared to results obtained with optical lithography.