Subnanometer Accuracy of Surface Characterization by Reflected-Light Differential Interference Microscopy

TL;DR

This paper develops a quantitative reflected-light differential interference microscopy technique capable of measuring surface height variations with subnanometer precision, enabling real-time, large field-of-view surface characterization of micro/nano-electromechanical systems.

Contribution

The authors introduce a novel optical system that achieves subnanometer axial resolution for surface height measurement using reflected-light differential interference microscopy.

Findings

Achieved 0.13 nm axial precision in surface height measurement.

Demonstrated real-time characterization of nanometer-scale surface steps.

Validated the method with fabricated nanometer-size steps.

Abstract

We theorize the surface step characterization by reflected incoherent-light differential interference microscopy with consideration of the optical diffraction effect. With the integration of localization analysis, we develop a quantitative differential interference optical system, by which we demonstrate that the axial resolution of measuring surface height variation is sensitive to the shear distance between the two spatially differentiated beams. We fabricate three nanometer-size steps by photolithography, and successfully characterize their 1D height variations with 0.13 nm Hz^(-1/2) axial precision. Our result suggests that the optical differential interference microscopy can be used for real-time characterization of surface structure with a subnanometer accuracy and a large field of view, which is greatly beneficial to the surface characterization of micro/nano-electromechanical systems.