Linewidth measurement from a stitched AFM image

Image stitching is a technique that combines two or more images to form one composite image, which provides a field of view that the originals cannot. It has been widely used in photography, medical imaging, and computer vision and graphics. For such applications, the emphasis is on the appearance of the composite image from a rendering perspective and not on performing measurements using the composite image. The potential use of image stitching in dimensional metrology is a relatively less explored field. In our experiment, a linewidth structure with nearly vertical sidewalls is imaged by an atomic force microscope (AFM) using a multi-walled carbon nanotube tip. Since the nanotube is mounted at an angle with respect to the surface, the resulting image of such a structure exhibits significant probe-related distortion on one side but very little on the other. If the sample is rotated by 180 degrees, then both sidewalls can be accurately imaged. The two images can be stitched together to form a composite image in which both sidewalls are minimally distorted. Our paper describes AFM linewidth measurements using a composite image developed by manually stitching two individual images. The results are compared with measurements taken with critical-dimension AFM (CD-AFM), which is capable of measuring structures with near-vertical sidewalls. The challenge is to perform the stitching well enough that the composite image can be used for linewidth metrology. Our preliminary results on two different structures show agreement between image stitching and CD-AFM.