Fabrication of high performance 512K static-random access memories in 0.25 μm complementary metal–oxide semiconductor technology using x-ray lithography

Abstract

Functional 512K static random access memory (SRAM) devices containing more than 3.6 million transistors have been successfully fabricated in a 0.25 μm complementary metal–oxide semiconductor technology using compact storage ring x-ray lithography. In this demonstration a comparison of critical dimension control was made between x-ray and optical (i-line and excimer laser) lithography by fabricating SRAM devices using both lithographic techniques. For the x-ray fabricated devices the channel length, a key device performance parameter, was controlled to within 0.036 μm (3σ), demonstrating the excellent process robustness, and dimensional control available from x-ray lithography. These SRAMs 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 μm minimum channel length, was fabricated with 100% bit yield using x-ray lithography. 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.