Surface Metrology

Surface Metrology

REO maintains 14 Fizeau interferometers for accurate measurement of surface figure, utilizing several different configurations for both in-process and final product measurement of surface figure of flat and spherical surfaces. REO has interferometers at 633nm and 1064nm. These instruments normally have an absolute accuracy of approximately l/100. REO maintains interferometers with apertures of up to 150mm diameter, with lateral resolution of up to 100um.

For aspheric surfaces, REO utilizes stylus profilometry to provide an accurate measure of the surface form. Stylus profilometry is a contact measurement in which a stylus (typically diamond or a hard metal) is brought into very light contact with the surface and then moved laterally across the surface while its vertical position is measured accurately, often interferometrically. Though it provides only a line profile of the surface form, the measurement can be repeated at multiple angles to produce an approximation of the surface form of rotationally asymmetric surfaces.  REO’s stylus profilometry is accurate to approximately 1nm rms, and suitable for diameters of up to 200mm.

REO also uses optical profilometry to measure surface roughness. This tool provides an interferometer which is contained within the objective of a microscope, providing much higher lateral resolution than a typical Fizeau configuration. Over a lateral length scale from approximately 1um to 150um, these instruments have a height measurement resolution of approximately 0.1A rms.

REO also utilizes today’s most advanced optical microscope technology to characterize surface defects and texture, with a number of camera-equipped high power compound microscopes. These tools have a range of illumination and contrast options, including Bright Field, Dark Field, Nomarski (DIC) and Circular DIC. Objective magnification of up to 50x allows resolution and quantitative measurement of features of approximately 2um diameter, and detection of defects of only a few hundred nanometers in size.

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