Surface Profiling With Optical and Mechanical Instruments

Abstract

Two types of interferometers and a mechanical stylus-type instrument have been used to make surface profile measurements on the same samples. All had comparable height sensitivities, of the order of 1 Å rms, but different lateral resolutions. The Optel profilometer1 is based on the principle of the Nomarski differential interference contrast microscope in which two beams of light separated by 0.3 μm are measured by two detectors. Values of the surface slope are calculated from the detector signals; integration yields a surface profile. The Wyko heterodyne profilometer2 is based on the Mireau interferometer. One light beam is reflected from the sample while a second beam is diverted by a beam splitter to a reference mirror located between the microscope objective lens and the sample. A 1024 element linear diode array measures the phase of the interference fringe pattern which is then transformed into a surface profile. In the Talystep instrument3 a 1 μm radius diamond stylus contacts the surface with a 1-2 mg loading that is light enough not to damage the surface. The vertical motion of the stylus as it moves across the surface is converted into a digitized electrical signal that directly gives the surface profile. Results of measurements made on different types of surfaces using the three instruments will be compared to show repeatability, height sensitivity, and lateral resolution. Special features of each instrument will also be discussed.