STUDY OF CAF2 GROWTH ON SI, A-SIO2 BY IN-SITU SPECTROSCOPIC ELLIPSOMETRY

Ellipsometric measurements have been performed in situ on very thin Ca F2 films at fixed wavelength lambda during deposition or vs. wavelengt h at different deposition steps. In modelling tan PSI and cos DELTA sp ectra as a function of lambda at different stages of growth, the Brugg eman effective medium theory is used to describe the interfaces. The v alue of the index of refraction n depends strongly on the nature and t he temperature of the substrate, and on the thickness of CaF2 films. F or films deposited at 400-degrees-C on Si wafers covered with their na tive oxide, cross-sectional high resolution electron microscopy shows that, in spite of the presence of a SiO2 layer (2 nm thick), CaF2 grow s on Si through this layer. A model including interfacial layers, whic h takes into account this interaction with the Si substrate, is propos ed for reproducing ellipsometric data. For CaF2 films deposited on SiO 2, no evidence for chemical interaction has been found.