Subpixel image stitching for linewidth measurement based on digital image correlation

The inevitable tilt angle resulting from attaching a carbon nanotube to an atomic force microscope (AFM) probe causes probe-related distortion on one sidewall of the linewidth sample during an AFM scan. In order to obtain accurate images at both sidewalls, an image stitching method was proposed in our previous research. An improved digital image correlation technique is outlined here to register two scanned images and detect the relative lateral distortion between them. Then image correction is performed pixel by pixel on both images prior to the stitching. A composite image is formed by stitching these two corrected images, and the linewidth is calculated based on this composite image. Since this method removes a significant portion of in-plane distortion between two images due to the nonlinearity of the AFM piezoelectric tube scanner, uncertainty in the calculation of linewidth due to the image stitching component is estimated to be reduced to the subpixel level from its former estimation of approximately three pixels. The procedure is tested with two standard linewidth features.