Understanding systematic and random CD variations using predictive modeling techniques

Abstract

This work analyzes the contributions to CD variation by building 3 predictive models that describe linewidth variation. The first model uses an exposure and focus budget analysis to create distributions that are used as input into a Monte Carlo analysis, where the output is a distribution of linewidth. The second model explores the effects of systematic intra-field effects by assuming that lens properties such as aberration will only cause global changes to the CD function, i.e. the function only shifts in focus and exposure. In combination with measurements such as focal pane, illumination uniformity and flare, a description of AFLV is constructed that reveals CD maps of the image field as a function of system focus and exposure. The third model combines the previous two techniques by incorporating random and systematic errors to create an across-wafer linewidth variation simulation. An example is shown using a scanner system and 0.18 micrometers structures. Systematic contributors to AFLV such as aberrations and reticle errors are included, as well as addition of random distributions of tilt eros and full wafer processing errors.