March tutorial-REV 2

tutorialAccurately measuring surfaceroughness requires under-standing the capabilitiesand drawbacks of yourinstrument.RoughBy Theodore Vorburger and Joseph Fu,National Institute of Standards andTechnology, and Ndubuisi Orji, University ofNorth Carolina CharlotteS urface roughness affects the function of a wide variety ofengineering components, including airport runways, highways,ship hulls, and mechanical parts. Perhaps the most demandingapplications are in the optics and semiconductor industries.Surface roughness causes scattering and stray light in optical documentary standards and has often been represented by σ in1-3systems and degrades the contrast and sharpness of optical the optics literature.images, so in general, the smoother the surface, the better the Because surface profiles z(x) are closely approximated incomponent will function. nearly all modern instruments by a digitized set of points z , theiIn the optics industry, the terms “surface roughness” and above formula is replaced in practice by its digital equivalent:“surface finish” are synonymous. The rms roughness is perhapsthe most widely used parameter for specification of the rough-ness of optical surfaces. For high-performance optics, such asthose in lithographic steppers, space optics, and laser gyro sys-tems, the rms roughness is specified in the subnanometer range.If the measured surface topography is represented as a surface where N is the number of data points in a measured ...