Height Measurement Using High-Precision Atomic Force Microscope Scanner Combined with Laser Interferometers

摘要

We have developed a high-precision atomic force microscope (AFM) for measuring fine pattern structures for semiconductor process evaluation. Three-axis ultrahigh-resolution displacement sensors using modularized laser interferometers were built into an AFM scanner combined with piezoactuators, elastic parallel-plate structures and an on-axis optical microscope. A newly designed symmetrical layout of the optical path of homodyne interferometers and a digital signal processor (DSP) enabled highly stable measurements of the mechanical displacements of the tip of an AFM scanner. As a result of their ultrafine positioning capabilities, a resolution of the displacement sensors of 0.05 nm was achieved. The periodic error of laser waves was compensated by employing DSP-based processing. Thus, a wide linearity range from 0.1 to 1000 nm was demonstrated and a one-sigma repeatability of 0.25 nm was obtained by measuring reference samples of 50 and 1000 nm step heights. Finally, micro-roughness with a 0.1 nm height, a GaAs atomic step with a 0.3 nm height, patterns with high aspect ratios, and resist patterns were clearly observed using an interferometer displacement signal.