Optimization of RET flow using test layout

Abstract

At advanced technology nodes with extremely low k1 lithography, it is very hard to achieve image fidelity requirements and process window for some layout configurations. Quite often these layouts are within simple design rule constraints for a given technology node. It is important to have these layouts included during early RET flow development. Most of RET developments are based on shrunk layout from the previous technology node, which is possibly not good enough. A better methodology in creating test layout is required for optical proximity correction (OPC) recipe and assists feature development. In this paper we demonstrate the application of programmable test layouts in RET development. Layout pattern libraries are developed and embedded in a layout tool (ICWB). Assessment gauges are generated together with patterns for quick correction accuracy assessment. Several groups of test pattern libraries have been developed based on learning from product patterns and a layout DOE approach. The interaction between layout patterns and OPC recipe has been studied. Correction of a contact layer is quite challenge because of poor convergence and low process window. We developed test pattern library with many different contact configurations. Different OPC schemes are studied on these test layouts. The worst process window patterns are pinpointed for a given illumination condition. Assist features (AF) are frequently placed according to pre-determined rules to improve lithography process window. These rules are usually derived from lithographic models and experiments. Direct validation of AF rules is required at development phase. We use the test layout approach to determine rules in order to eliminate AF printability problem.