For years, scatterometers have been providing full profile information on line/space arrays. These profiles are often compared to XSEM images in order to show how well they match. This is done by placing the profiles and images next to each other or by overlapping them. The comparisons, however, are typically qualitative; this makes it difficult to determine exactly how good the match is. Furthermore, this qualitative comparison makes it difficult to determine whether profiles from one scatterometry tool or model match corresponding XSEM images better than another tool's or model's profiles. This study circumvents this problem by making multiple measurements of critical dimension, sidewall angle, and height/depth from XSEM images, and then comparing them to scatterometry measurements previously collected from the same locations. The vehicle that is used for this study is a series of etched STI wafers that were subjected to a range of etch processes. Total Measurement Uncertainty (TMU) analysis is used to properly quantify the comparisons. Both scatterometry library and regression models are investigated; the results from both of these methods are compared to the XSEM measurements and to each other. A technique to estimate the accuracy of the XSEM measurements themselves is also used. Results show that, within statistical error, both scatterometry methods provide the same information about the samples. Furthermore, the data reveal that the scatterometer is in most cases about as accurate as the XSEM metrology in quantifying significant structural components of the samples. Finally, examples showing how the increased sampling of scatterometry can be used to improve etch process development is provided.