Three-dimensional beam tracking for optical lever detection in atomic force microscopy

Abstract

For the requirement to move a probe with respect to a large specimen like a silicon wafer, a three-dimensional beam tracking for optical lever force detection in atomic force microscopy has been developed. This beam tracking is not an approximate solution but an ideal solution in three-dimensional scanning. A set of tracking mirrors that are attached at the middle of a tube scanner steers a laser beam to a probe and to a detector during scanning. Tracking errors achieved were 2 and 7 nm in horizontal and vertical direction scans over 50 μm scanning. A simple theoretical error estimate revealed that less than 2 nm error is obtainable with moderate mirror mounting accuracy. To reduce the thickness of the scanner for coaxial optical microscope observation, the tube scanner was arranged sideways, resulting in 12 mm scanner thickness. A twist probe, pointed in the vertical direction to enter its tip into a narrow trench, was used for the probe. This system could obtain a semiconductor trench image successfully.