Real time monitoring of the growth of transparent thin films by spectroscopic ellipsometry

Real time monitoring of the growth of plasma deposited transparent thin films by spectroscopic phase modulated ellipsometry is presented. Two on-line methods of determination of the refractive index n and the film thickness d are evaluated, before extension to feedback control. The first one is based on the inversion of the Fresnel equations. This method is very fast (0.2 s with a conventional PC 486 computer) but requires the simultaneous measurement of various photon energies to be extended on thick layers. A 5% relative precision is obtained on 5000-6000-Angstrom-thick films even when deposited at a high deposition rate (32 Angstrom s(-1)). On the other hand, better precision can be obtained using a slower least square fit procedure based on single photon energy measurement of the outermost layer. In particular, in the latter case, the product nd can be determined with a 1% precision, up to 5000-6000 Angstrom. (C) 1996 American Institute of Physics.