Currently, CD-SEMs are the tool of choice for inline gate length measurements for most semiconductor manufacturers. This is mainly due to their flexibility, throughput, and ability to correlate well to physical measurements (e.g., XSEM). Scatterometry, however, is still being used by an increasing number of manufacturers to monitor and control gate lengths. But can a scatterometer measure such small critical dimensions well enough? In this article, we explore this question by analyzing data taken from wafers processed using 90 nm node technology. We also show how total measurement uncertainty (TMU) analysis is used to improve the scatterometry model and understand the relative contributions from obstacles that hinder even better correlations.