Hybrid-contours: a strategy for improving CD-SEM metrology over complex 2D patterns

Abstract

In the semiconductor manufacturing process, performing metrology over 2D complex features is mandatory for advanced technology nodes. Top-down critical dimension scanning electron microscopes (CD-SEMs) are widely used for many applications and are key enablers for metrology and process control. Nevertheless, one of the limitations one may observe when using CD-SEMs is the contrast variation (or lack of contrast) in areas where the pattern edges are parallel to the CD-SEM acquisition scan direction, which may lead to accuracy and precision loss. Model-based contour extraction solutions are often able to address this reduction in contrast while maintaining the accuracy and precision required by the different usages. However, for particularly low contrast/low SNR images, this may lead to a reduction in accuracy of the metrology process. This work explores the concept of hybrid contours generation, combining contours – coming from different scan directions – with pattern fidelity metrics, in order to overcome the issues related to edge detection accuracy and precision, especially in 2D shapes. It brings the advantage of combining relevant information from each image, weighted based on their reliability, which is estimated by a combination of the scan direction and the fidelity of the edge profile observed on the patterns. This method of combining contours improve 2D measurements and is also the most reliable way of building contours for OPC modeling, among other uses.