VIRTUAL INTERFACE METHOD FOR IN-SITU ELLIPSOMETRY OF FILMS GROWN ON UNKNOWN SUBSTRATES

In situ ellipsometry may be used for real time measurements on growing films through windows in deposition systems. It is well known that the initial film growth may be in the form of islands and other structures which may ultimately develop into a nearly homogeneous, isotropic growing film. Consequently, measurements in early growth phases do not agree with simple homogeneous, isotropic models which greatly complicates data reduction. A method is developed in which the refractive index and thickness of the overlayer can be computed without the need to consider the interface layer and substrate. Once the growth has passed the interface layer, a ''virtual interface'' is defined by a measurement at a point in time. Four additional measurements are made at subsequent times for computation of the optical properties of the growing overlayer film, four thicknesses (of growth past the virtual interface), and the complex reflection coefficients of the virtual interface. Results for Ni and Si films grown on BK7 glass substrates confirm the method.