Unbiased roughness measurements: Subtracting out SEM effects

Most scanning electron microscope (SEM) measurements of pattern roughness today produce biased results, combining the true feature roughness with noise from the SEM. Further, the bias caused by SEM noise changes with measurement conditions and with the features being measured. The goal of unbiased roughness measurement is to both provide a better estimate of the true feature roughness and to provide measurements that are independent of measurement conditions. Using an inverse linescan model for edge detection, the noise in SEM edge and width measurements can be measured and removed statistically from roughness measurements. This approach was tested using different pixel sizes, magnifications, and frames of averaging on several different post-lithography and post-etch patterns. Over a useful range of metrology conditions, the unbiased roughness measurements were effectively independent of these metrology parameters. (C) 2018 Elsevier B.V. All rights reserved.