Scatterometry is anew optical technique for profile measurement, capable of providing 2 or 3 dimensional profile information. The scatterometry optical system can be made small and economic enough to enable integration into each production tool and is therefore ideally suited for integrated process control. In addition, the range of applications for which this method applicable is wide: lithography photoresist profiles, etch structures, and even measurements of transparent layer thickness above arrays after CVD or CMP steps. Scatterometry is base don the measurement of the optical diffraction characteristics of aperiodic structure. Interpretation is done by evaluating the expected spectrum for a given profile, comparing the result to the measurement, and continuously fitting the profile parameters until a best fit is achieved. The leading physical model used in scatterometry is the Rigorous Coupled-Wave Analysis (RCWA). It is based on dissecting the profile into several layers and treating each as a waveguide with a fixed cross-section. The accuracy of the model is determined by the resolution of the dissection, and the number of Fourier modes retained in the calculation. RCWA gives very accurate results provided sufficient number of modes and layers are used. As calculation time scales linearly with number of layers and roughly cubic with number of modes, this usually leads to long calculation time, thus inhibiting real time interpretation which is especially required for integrated metrology. One possible solution is to consider alternative physical models to replace RCWA, such as Green's Function Integral Formulation. The selection between calculation methods should be determined by the calculation time per given spectrum accuracy. The latter should be determined for each application, considering the required parameters to be measured. In this paper we examine the use of two different models for several applications, which will be briefly described. It will be shown that is some important applications use of GFI may be preferable for real time calculations relative to RCWA.