Stitching accuracy measurement system for EB direct writing and electron-beam projection lithography (EPL)

We have developed a stitching accuracy measurement system for electron beam (EB) direct writing and electron beam projection lithography (EPL). This system calculates the amount of a stitching error between two EB shots from SEM images. It extracts a representative edge line of each pattern from the graphical format files (BMP, JPEG etc.) of SEM images and calculates a distance between each edge line as a stitching error. For obtaining a higher stitching accuracy of EB direct writing or EPL machines, it can analyze the relation of amounts and direction of a stitching error with a field size or a field position of these machines. We could successfully measure about 2.0 nm as a stitching error value in 0.1 micrometers L/S resist patterns on a bare-Si substrate and obtain 1.2 nm (3(sigma) ) as the measurement repeatability. It took 2.5 sec. for this system to measure one stitching region.