<i>In situ</i> topography measurement in the SEM

Abstract

Abstract An automatic technique for measuring heights in situ in the SEM based on a combination of stereo‐metric and focusing methods has been developed. A pair of images of a surface element on the specimen is obtained by tilting the beam electrically in a manner such that the plane containing the tilt axis is coincident with the focal plane of the final lens. Cross‐correlation is used to determine the parallax between the image pair which is then used to iteratively correct the height of the tilt axis by changing the lens focus. As a result, the lens focus tracks the specimen topography. With an appropriate specimen surface containing high resolution features for image correlation, the technique is capable of maintaining both its lateral and vertical resolutions over several decades of height displacement up to 100 μm. In an experimental system based on a commercial electron‐optical column, spot, line profile, and three‐dimensional measurements have been demonstrated.