Comparison of instruments for measuring step heights and surface profiles

Abstract

Data for step heights and surface profiles obtained using two commercially available instruments are compared. It is shown that step height data obtained with the Dektak IIA are good to better than 1% for an 8900-Å step but that it is not possible to obtain accurate profiles of optical surfaces smoother than ~100 Å rms. The Talystep gives repeatable profiles of optical surfaces down to features smaller than 25 Å and repeatable measurements of step heights of sizes from the angstrom to micrometer range to better than 1%. Step height measurements with the Talystep appear to be limited by the digitization of the ±1-V dc output signal rather than by an intrinsic property of the instrument.