Noise analysis for through-focus scanning optical microscopy

A systematic noise-analysis study for optimizing data collection and data processing parameters for through-focus scanning optical microscopy (TSOM) is presented. TSOM is a three-dimensional shape metrology method that can achieve sub-nanometer measurement sensitivity by analyzing sets of images acquired through focus using a conventional optical microscope. We show that the best balance between signal-to-noise performance and acquisition time can be achieved by judicious spatial averaging. Correct background-signal subtraction of the imaging system inhomogeneities is also critical, as well as careful alignment of the constituent images in the case of differential TSOM analysis.