One goal of CD metrology is to monitor lithographic process control and how it relates to post-etch results. At present, in-fab process control for this purpose is achieved through top-down CD measurements. To acquire profile information requires destructive cross-section SEM measurements or time-consuming atomic force microscope (AFM) measurements. To find height and profile information about a resist or etched structure directly on a CD-SEM, new techniques using the combination of in-column beam tilt and stereographic imaging have been developed and implemented on the Applied Materials VeraSEM-3D(TM). The column of the VeraSEM-3D(TM) is designed to be able to electronically tilt the incident beam at small angles as it approaches the sample, through bending the beam within the column. Two images can be captured of the sidewall of the feature target, one at a smaller tilt angle and one at a larger tilt angle. Through image processing of these two images, a reconstructed profile can be mathematically generated. A feature height and sidewall angle can be calculated, and general shape information such as top-rounding, footing and undercutting can also be displayed. To benchmark the effectiveness of this new technique, an experiment has been conducted to quantify the repeatability and reproducibility of height and sidewall angle measurements of lines of resist-on-poly and the resulting etched poly lines, and correlate these to measurements of the these same profiles using cross-sectional SEM (XSEM) to determine the accuracy of the technique. This study will span a reasonable lithographic process window. We hope to demonstrate the necessary precision and accuracy capability to non-destructively replace some cross-section work. In applying these techniques to a common etch bias problem, we also hope to demonstrate a strong correlation which can be used to directly predict post-etch behavior and serve as a model for other etch processes, work with which XSEM cross-sections have typically been used until now.
