Experimental Determination Of Thin Film Thickness By Polarized Light Scattering

Abstract

Determination of thin film thickness is ultimate important in many technology area, particularly those of optics and microelectronics. There are numerous ways to measure thin film thickness, many of them need after measurement numerical calculations, namely, some physical constants of the film: refractive index, absorption coefficient, or electrical conductivity, etc., need to be known beforehand in order to- carry out the calculation which. relates a certain measured physical quantity of the film: transmission spectrum, electrical resistance etc., to these constants and film thickness. The accuracy of these constants is crucial to the accuracy of the film thickness deduced from the calculation. Unfortunately, physical constants of thin films are always different significantly from those of bulk materials. The use of bulk value in the calculation inavoidably lead to inaccurate film thickness determination. There are some methods which directly measure the film thickness without numerical process and knowledge of other physical constants of the film. Among those methods, surface profile determination by stylus mechanically or by interferometry optically are frequently used. A film edge has to be created, the edge height measured directly by stylus profile or interference pattern is equal to the film thickness. There are some disadvantages for these methods, stylus may scratches the film and substrate which are soft, the range of film thickness which can be determined is limited by the optical wavelength in the interference method.