Simultaneous measurement of optical properties and geometry of resist using multiple scatterometry gratings

Abstract

Optical properties (n&k) of the material films under measurement are commonly assumed invariant and fixed in scatterometry modeling. This assumption keeps the modeling simple by limiting the number of floating parameters in the model. Such scatterometry measurement has the potential to measure with high precision some of the profile parameters (CD, Sidewall angle). The question is: if the optical properties modeled as "fixed" are actually changing - would this modeling assumption impact the accuracy of reported geometrical parameters? Using the example of a resist profile measurement, we quantify the "bias" effect of un-modeled variation of optical properties on the accuracy of the reported geometry by utilizing a traditional fixed n&k model. With a second model we float an additional optical parameter and lower the bias of the reported values - at the expense of slightly increased "noise" of the measurement (more floating parameters - less precision). Finally, we extend our multi-stack approach (previously introduced as enabler to the product-driven materials characterization methodology) to augment the spectral information and increase both precision and accuracy through the simultaneous modeling of multiple targets. © 2010 Copyright SPIE - The International Society for Optical Engineering.