Optical characterization of doping profiles in silicon

A new method for doping profile reconstruction, starting from infrared spectroscopic measurements, is presented and numerically analyzed. We have developed, relying on the scattering integral equations, a new formulation allowing to directly relate the optical reflected intensity to the free carriers concentration. This formulation has been used to develop an iterative algorithm for dopant profiling. The main advantage of our approach is that the unknown dopant profile is modeled by a finite series of basic functions. As the series expansion allows to describe a wide class of profiles, it is not necessary to choose ``a priori'' the functional form of the doping profile (e.g. exponential function, gaussian function, error function etc.). This allows to reconstruct the actual profile, regardless of its similarity with the expected one.