Surface Roughness Measurement Using Scanning Electron Microscope with Digital Processing

Surface roughness measurement by scanning electron microscope (SEM) is investigated. The investigation was made by a digital processing technique, which follows a study by the analog method. The intensity of the backscattered electron signal is in proportion to the inclination of the surface profile, so that the surface profile can be obtained by integrating the backscattered electron signal along the scanning. The digital method made it possible to address the scannings and to designate the starting points for the processing on the respective scannings. The integral was carried out by a minicomputer that was connected through optical fibers which made the system free from transmission noise. The indicated positions can be monitored on a CRT display by overlapping these on the backscattered electron image. A simple and reliable calibration method is proposed by putting a standard test piece of the surface roughness close to the specimen. This confirmed that the order of 1/1,000 μm was obtained as the resolution of this method, as far as the inclination can be detected. The two dimensional roughness obtained for the scanning can be illustrated by isometric view (or by the equicontour map); this was impossible using the analog method. The noise effect by low- and high-frequency components could be eliminated by subtraction or by averaging, so a more accurate profile could be obtained.