Method and apparatus for determining the thickness and index of refraction of a film using low coherence reflectometry and a reference surface

摘要

An apparatus and method for measuring the thickness of a film having top and bottom surfaces. The apparatus includes low coherence light source that generates a probe light signal. The film is positioned between first and second reference reflectors, the first reference reflector being partially reflecting. The probe light signal is applied to the film after passing through the first reference reflector. Part of the portion of the probe light signal leaving the film is reflected back toward the first reference reflector by the second reference reflector. The light exiting through the first reference reflector is collected to form the input to a receiver that determines the time delay between light reflected from the top and bottom surfaces of the film as well as the change in optical path length between said first and second reflectors resulting from the introduction of said film between said first and second reflectors. In the preferred embodiment of the present invention, the receiver is constructed from an optical autocorrelator or an optical spectrum analyzer that includes circuitry for providing the Fourier transform of the frequency domain spectrum measured from the combined light signal. Embodiments in which only one of the reference reflectors is utilized provide a means for simplifying the output spectrum from the receiver when multi-layer films are utilized.