One problem interferometric profilers have in common, is that the phase change of the light which is reflected at the probe, depends on the complex refractive index of the probe's material and influences the profilers results. This article describes the principle of an optical profilometer which is a combination between an interferometric profiler and a micro-ellipsometer. This combination allows us to determine the geometrical height of a surface profile, with an accuracy of a few nanometers, even when the material of the probe varies laterally. The interferometric profiler uses an acousto-optical deflector in such a way, that it produces two first orders of diffraction, beside the zero order. Due to the principle of the acousto-optical deflector, these two first orders wave slightly different frequencies. This makes it possible to apply the principle of heterodyne detection to measure the difference in phase of these two beams. From this, the phase profile of the scanned surface can be calculated. With the help of the micro-ellipsometer the material dependency the phase of the reflected light can be determined with a high lateral resolution. Therefore the probe beam is focused on the probe with a microscope objective to reach a lateral resolution which is the same as that for the profilometer. Due to the principle of this micro-ellipsometer the probe is analyzed for several angles of incidence simultaneously. With the data of the micro-ellipsometer it is possible to compensate the errors of the profiler's data caused by varying materials.

Date Published: 14 June 1999
PDF: 8 pages
Proc. SPIE 3677, Metrology, Inspection, and Process Control for Microlithography XIII, (14 June 1999); doi: 10.1117/12.350789

Published in SPIE Proceedings Vol. 3677:
Metrology, Inspection, and Process Control for Microlithography XIII
Bhanwar Singh, Editor(s)