Scanning Interference Microscopy for Surface Characterization

Recent work has introduced the concept of scanning interference microscopy which has 3-D resolution comparable to a confocal microscope (1). This is obtained by performing interference microscopy with spatially incoherent and broadband illumination. By scanning along the optical axis, one can measure the coherence function at each point in the image. This coherence function can be processed to obtain various pieces of information. The maximum of the envelope of the coherence function corresponds to the surface height. By Fourier processing of the fringes at each point, the spectral reflectivity can be measured for that point, determining both the magnitude and the phase of the reflection as a function of wavelength. Thus a tremendous amount of information is available, but at the cost of a high processing overhead. A PC based system which provides a low cost solution with good performance will be discussed, with trade-offs between range resolution, number of points processed, and precision versus the processing time and hardware requirements analyzed. Traditionally, interferometric techniques have not been applicable to optically rough surfaces or heterogenous surfaces. This talk will discuss how scanning interference microscopy can be applied to such surfaces.