Contactless measurement of surface shape of diffusely scattering objects e.g. semiconductor wafers - using interferometric arrangement for three=dimensional measurement with minimal coherence length and illumination aperture angle less than observation aperture angle

摘要

The interferometric arrangement consists of a light source and optical elements. An unfocussed image of the object is produced by an imaging system. The coherence length of the illumination is as short as possible but not less than the surface roughness depth. The illumination aperture angle is smaller than the observation aperture angle. A photoreceiver is pref. not larger than the average speckle size. The contrast of the interference in each speckle is pref. separately evaluated whilst the light path difference between the object and the reference beam is modulated. The object point distance or roughness depth is derive from the speckle contrast as a function of the light path difference. ADVANTAGE - Highly accurate measurement.