Abstract: A transparent chuck is used to force a semiconductor wafer to take a prescribed shape. Any gap which is formed between the chuck and the wafer can be imaged through the transparent chuck. An interferometer is used to illuminate the gap with a narrow band illumination to create interference fringes in the gap. The fringes can be electronically imaged to create a digital input to a computer. Merit functions corresponding to the total volume of fringes in the gap or to the summation of nearest neighbor slopes of such fringes provide a measure of the thickness of such gap.

Abstract: An oblique incidence multispectral interferometric apparatus and the process of using it for measuring gross surface height errors of for measuring the total thickness of a substrate such as a semiconductor wafer or a photo mask. The instrumentation can be configured to either measure the air film between a reference flat and the substrate, or it can measure the air film on both sides of a substrate placed between reference flats. If the substrate is a flexible silicon wafer then it can be held against a known reference flat using a vacuum or other suitable means or the wafer surface can be measured from both sides in a free standing mode. In all cases the thickness map of the air space or spaces between the substrate surface or surfaces and a corresponding calibrated reference surface is measured using multispectral pattern matching.

Abstract: The thickness of the entire surface of a thick semiconductor (94) layer on an insulator is determined all at once by dividing the surface into a plurality of pixels, by varying the length of a variable length optical path (110) in a Michelson interferometer (66) having an infrared source (62), illuminating the entire surface of the layer with an image of the IR source during the length variation operation, and by detecting (64) the product of the intensity (I.sub.s (z)) from the Michelson interferometer and the reflectivity R(t) of the layer as the path length is varied, such being indicative of the thickness of the layer, and by determining, for each pixel, which one of a plurality of groups of stored reflectance values, for a corresponding plurality of thicknesses, best matches the detected values, thereby providing a thickness map of the semiconductor layer.