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

An atomic force microscope with a high-resolution three-axis laser interferometer for real-time correction of distorted topographic images has been constructed and investigated. With this apparatus, standard samples for a scanning probe microscope can be directly calibrated on the basis of stabilized wavelength of He-Ne lasers. The scanner includes a three-sided mirror block as a mobile target mirror for the interferometer, which realizes a rectangular coordinate system. The position coordinates of the sample is independently and simultaneously acquired with high-resolution (0.04 nm) X/Y/Z interferometer units and fed back for XY servo scanning and height image construction. The probe is placed on the sample surface at the intersection of the three optical axes of the interferometer with good reproducibility, so that the Abbe error caused by the rotation of the scanner is minimized. Image distortion in the XY plane and vertical overshoot/undershoot due to nonlinear motion of piezo devices, hysteresis, and creep are eliminated. The optical properties of the interferometers, mechanical characteristics of the scanner, and system performances in dimensional measurements for calibration standards are demonstrated. (C) 1999 American Institute of Physics. [S0034-6748(99)02508-3].