Contour metrology using critical dimension atomic force microscopy

Abstract

The critical dimension atomic force microscopy (CD-AFM) has been proposed as an instrument for contour measurement and verification since its capabilities are complementary to the widely used scanning electron microscopy (SEM). Although data from CD-AFM are three dimensional (3-D) in structure, the planar two-dimensional data required for contour metrology are not easily extracted from CD-AFM data. This is largely due to the limitations of the CD-AFM method for controlling the tip position and scanning, in which the relevant sidewall data are only obtained in one lateral axis. To use CD-AFM for contour metrology, the extracted profiles must include actual sidewall data from both lateral axes. Using two images acquired from orthogonal scan directions, profile extraction, and a method to combine those profiles, a technique for obtaining contours with the CD-AFM is developed. The main sources of error for this technique are described. The contours derived from CD-AFM were compared with those obtained using the SEM. Our results show that CD-AFM has the potential to make important contributions to semiconductor contour metrology.