3D Nanometrology Based on SEM Stereophotogrammetry
Vipin N. Tondare, John S. Villarrubia, Andras Vladar
Three-dimensional (3D) reconstruction of a sample surface from scanning electron microscope (SEM) images taken at two perspectives has been known for decades. However, this method has not been widely used in the semiconductor industry for 3D measurements of non-planar structures and integrated circuits. Nowadays, there exist several commercially available stereophotogrammetry software packages. For testing these software packages, in this study we used Monte Carlo simulated SEM images of virtual samples. A virtual sample is a model in a computer, and its true dimensions are known exactly, which is impossible for real SEM samples due to measurement uncertainty. The simulated SEM images can be used for algorithm testing, development, and validation. We tested two stereophotogrammetry software packages and compared their reconstructed 3D models with the known geometry of the virtual samples used to create the simulated SEM images. Both packages performed relatively well with simulated SEM images of a sample with a rough surface. However, in a sample containing zones with mostly uniform contrast, the height reconstruction error was ≈ 46 %. The present stereophotogrammetry software packages need further improvement before they can be used reliably with SEM images with uniform zones of contrast.