Real-time, interferometrically measuring atomic force microscope for direct calibration of standards

An atomic force microscope with a high-resolution three-axis laser interfer ometer for real-time correction of distorted topographic images has been co nstructed and investigated. With this apparatus, standard samples for a sca nning probe microscope can be directly calibrated on the basis of stabilize d wavelength of He-Ne lasers. The scanner includes a three-sided mirror blo ck as a mobile target mirror for the interferometer, which realizes a recta ngular coordinate system. The position coordinates of the sample is indepen dently and simultaneously acquired with high-resolution (0.04 nm) X/Y/Z int erferometer units and fed back for XY servo scanning and height image const ruction. The probe is placed on the sample surface at the intersection of t he three optical axes of the interferometer with good reproducibility, so t hat the Abbe error caused by the rotation of the scanner is minimized. Imag e distortion in the XY plane and vertical overshoot/undershoot due to nonli near motion of piezo devices, hysteresis, and creep are eliminated. The opt ical properties of the interferometers, mechanical characteristics of the s canner, and system performances in dimensional measurements for calibration standards are demonstrated. (C) 1999 American Institute of Physics. [S0034 -6748(99)02508-3].