Extending KrF Lithography to 0.13 um sub-8F2 DRAM Technology: The Importance of Lithography-Centric Design

Abstract

Conventional optical lithography using a KrF excimer laser (λ =248 nm) is routinely used to manufacture DRAM technologies at ground rules as small as 0.15 μm. Due to the relative immaturity of ArF (λ =193 nm) lithography, it is desirable to continue to use KrF lithography for ground rules in the 0.13 μm regime. Simultaneously, continued DRAM chip scaling has led to investigation of open bit line architectures, whose theoretical minimum cell size is 4F, where F is the minimum feature dimension. This has die size advantages over the 8F minimum cell area of a conventional folded bit line cell. This cell architecture, combined with aggressive ground rule scaling, presents a unique challenge for optical lithography. In this paper, we discuss the evolution of sub-8F cell designs relative to lithographic difficulty, and present examples of design sorting for best lithographic performance.