A simple method for the determination of slowly varying refractive index profiles from in situ spectrophotometric measurements

摘要

Reliable control of the deposition process of optical films and coatingsfrequently requires monitoring of the refractive index profile throughout thelayer. In the present work a simple in situ approach is proposed which uses aWKBJ matrix representation of the optical transfer function of a single thinfilm on a substrate. Mathematical expressions are developed which represent theminima and maxima envelopes of the curves transmittance-vs-time andreflectance-vs-time. The refractive index and extinction coefficient depthprofiles of different films are calculated from simulated spectra as well asfrom experimental data obtained during PECVD of silicon-compound films.Variation of the deposition rate with time is also evaluated from the positionof the spectra extrema as a function of time. The physical and mathematicallimitations of the method are discussed.