Asymmetric line profile measurement using angular scatterometry

Scatterometry is an optical measurement technology based on the analysis of light scattered, or diffracted, from a periodic array of features. It is not an optical imaging technique, but rather a model based metrology that determines measurement results by comparing measured light scatter against a model of theoretical scatter signatures. Angular scatterometers in particular function by scanning the features to be measured through a range of incident angles, and measuring the light scattered into the zeroth, or specular, diffraction order. Prior work in angular scatterometry used the technique for the measurement of line profiles in resist and etched materials. In this work applications of scatterometry for the measurement of asymmetric line profiles (unequal sidewall angles, for example) are presented. Beginning with simulated results form the theoretical model, the importance of measuring through complementary (positive and negative) angles of incidence will be demonstrated. Then, actual measurement data from three different sample sets will be presented. The results show that the method has good sensitivity for measuring line asymmetry, and can therefore be used for qualifying processes for which symmetric results might be desired, such as lithography and etch processing.