Aids for driving lithography hard: Wafer level process control features

Abstract

This paper investigates the design of targets for in-line lithography process control. The need for wafer-level understanding and control of defocus has driven the development of several of methods for detecting focus shifts. The methods are typically based on measurements of line-end shortening and use optical methods. This work starts a dual-tone pair of arrays, one built from resist lines and the other from resist troughs. These process control targets area also known as schnitzls. The influence of the shape of the individual lines, the line pitch and separation of arrays are investigated using both simulations and wafer resist CDSEM measurements. A theoretical model was applied to all data to enable objective comparison of different designs. A guide to dose and defocus target design for process window monitoring is provided as part of the summary.