INTERFEROMETRIC MEASUREMENT OF THICKNESS OF ISOLATED TRANSPARENT FILMS

n interferometric method for determination of thickness of transparent isolated films (i.e. films without substrate) is proposed. In the present scheme the sample is inserted in one of the arms of laser Michelson interferometer (with a diverging input beam) and is rotated about the vertical axis resulting in an intensity modulation at the centre of the circular fringe pattern resulting in a rotation-angle vs. intensity plot. The location of the first minima (or maxima) from the normal incidence point is indicative of the film thickness. Some of the salient features of this method are (i) measurement is possible in the presence of local undulations of the uniform thickness sample, (ii) the normal incidence position of the sample need not be previously known since this is easily detectable from the generated plot, (iii) the accuracy of measurement increases with diminishing thickness and (iv) the measurement range is from hundreds of microns to about 0.2 micron.