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

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Abstract
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-Å-thick films even when deposited at a high deposition rate (32 Å 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 Å.