System for measuring the thickness and index refraction of a film

摘要

Apparatus (10, 100) and a method for measuring the thickness of a film (15) having top and bottom surfaces provide a first coupler (16, 162) for generating a first probe light signal and a second probe light signal from a low coherence light sourceÄ12Ü. The first probe light signal is directed towards the top surface of the filmÄ15Ü at a first angle of incidence and the light leaving the top surface of the filmÄ15Ü is collected. Similarly, the second probe light signal is directed towards the top surface of the filmÄ15Ü at a second angle of incidence different from said first angle of incidence and the light leaving the top surface of the filmÄ15Ü is also collected. The collected light is combined to form a collected light signal which is input to a receiverÄ18Ü that determines the time delay between light reflected from the top and bottom surfaces of the filmÄ15Ü. In the preferred embodiment, the receiverÄ18Ü 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. <IMAGE>