Accurate topographic images using a measuring atomic force microscope

A real-time measuring atomic force microscope (AFM) equipped with a high-resolution three-axis laser interferometer has been constructed. A three-sided mirror as a sample holder is placed on a three-dimensional (3D) scanner which was designed for axis-independent scanning. The mirror is scanned so that the cantilever traces the surface form. The traces of the mirror are monitored along the X/Y/Z-axis independently and simultaneously by the laser interferometers and fed back to the X-Y servo-scan and Z-height control. Each interferometer unit has a four-pass optical arrangement and homodyne detection system. After the digital signal processing of the four-phase output (phase-shifted by 90 degrees) from the detectors, the signal is introduced into a fringe counter, which has an electrical phase resolution of 2048. A final system resolution of 0.04 nm (lambda/16 384) has been realized. Topographic images of a standard sample of a precisely etched grid pattern (pitch and height) were taken with an without interferometric calibration. Piezo distortions along the X-Y plane caused by hysteresis or creep were almost eliminated. (C) 1999 Elsevier Science B.V. All rights reserved.