Taming pattern and focus variation in VLSI design

Abstract

Tight ACLV control has become increasingly difficult due to the diminishing process constant. K1. Focus variation and pitch variation are two major systematic components of ACLV. In this paper, we demonstrate these systematic effects and propose a design flow which exploits the systematic effect. We demonstrate the systematic ACLV by showing a Bossung plot for a nominal 90nm technology node. The plot is generated by simulation with lithographic parameters closely resembling a production technology node. Traditionally, tight CD control is achieved by sophisticated RET such as OPC, SRAF, AltPSM and more recently the Dense Template Design.1 The CD variation is specified in the design manual and the circuit designs will ensure functionality by building in enough margin to account for the variability. Even though, the systematic components of CD variation are understood, they have always been considered together with other random components as being random. This approach has left design performance on the table. We propose a holistic design flow by integrating the technology development process, design process and the manufacturing process. This holistic approach is aiming to tame the systematic through-pitch and through-focus CD variation. We quantify the design timing benefit using this approach by circuit design experiments. Results of our experiments show that timing uncertainty can be reduced by up to 30%. We also discuss other possibilities which are infeasible to carry out in traditional approach with silos of technology development, design and manufacturing.