FABRICATION OF HIGH-PERFORMANCE 512K STATIC-RANDOM ACCESS MEMORIES IN0.25 MU-M COMPLEMENTARY METAL-OXIDE-SEMICONDUCTOR TECHNOLOGY USING X-RAY-LITHOGRAPHY

Functional 512K static random access memory (SRAM) devices containing more than 3.6 million transistors have been successfully fabricated in a 0.25 mum complementary metal-oxide semiconductor technology using c ompact storage ring x-ray lithography. In this demonstration a compari son of critical dimension control was made between x-ray and optical ( i-line and excimer laser) lithography by fabricating SRAM devices usin g both lithographic techniques. For the x-ray fabricated devices the c hannel length, a key device performance parameter, was controlled to w ithin 0.036 mum (3sigma), demonstrating the excellent process robustne ss, and dimensional control available from x-ray lithography. These SR AMs had excellent electrical characteristics, including cycle times of 1.8 ns and access times of 3.7 ns. The ability of the existing x-ray lithography infrastructure to produce a fully functional (''perfect'') chip has been demonstrated in a companion device fabrication program. A 512K SRAM chip of a slightly different design, with 0.35 mum minimu m channel length, was fabricated with 100% bit yield using x-ray litho graphy. This article describes these device demonstrations, including the observed advantages of x-ray lithography, as well as the status of IBM's x-ray lithography program and associated infrastructure.