Three-dimensional image visualization using the real-time confocal scanning optical microscope

The development of the real-time confocal scanning optical microscope (RSOM) has made it easy for those familiar with standard optical microscopes to use the excellent range definition and cross-sectioning ability afforded by the RSOM to inspect integrated circuits. The ability of the RSOM to optically section a sample allows us to construct three-dimensional (3D) image projections of the sample surface. The depth response function, |V(z)|², of the microscope can be used to relate the relative height of a particular point on the sample to the received intensity allowing the surface to be reconstructed from the microscope image. Surface reconstructions based upon this method are shown to have comparable resolution to information from each optical section to determine the 'coarse' height at each pixel location. Height variations within each section can be calculated using the received intensity at each pixel location in conjunction with the depth response function of the microscope. The intra-layer height variations are added to the coarse height at each pixel location to produce a map of the integrated circuit surface. The surface reconstruction can be shaded according to the strength of the received signal or with a lighting model to emphasize different properties of the surface. The surface reconstruction calculated using the depth response function of the microscope can be correlated to the surface roughness of the material. The surface roughness of a metal film is measured using the RSOM and compared to values obtained with a stylus profilometer. The effect of focal position on 3D image construction and defect detection is considered by examining several overlay structures.