Scanning Differential Phase Contrast Optical Microscope Application to Surface Studies and Micro Metrology

Abstract

The characteristics and theory of operation of a new scanning differential phase contrast optical microscope are described, and a number of results are presented.

High contrast micrographs of a polished steel sample are included, showing clearly the grain boundaries, as well as some fine structure within the grains. Micrographs are also presented of natural diamonds, both in polished and unpolished forms. In the former, many polishing lines are visible and in the latter, one clearly sees a large number of stacking faults.

Results on the study of monolayers of Langmuir — Blodgett films are also presented. The micrographs clearly show the boundaries, as well as non-uniformities within the films. The ability of the System to image objects showing refractive index variation is demonstrated by producing micrographs of an exposed but undeveloped photoresist film, and a partially doped silicon sample. In each case, a qualitative comparison is made with the differential interference (Nomarski) micrograph of the same field of view.

Since the measured phase gradients can be related directely to the laser wavelength, the technique can be made quantitative. By integrating the detected signal with respect to time, it is possible to obtain a phase profile of the sample surface being scanned, to an accuracy of the order of 10^-8 radians.