Extracting active dopant profile information from carrier illumination power curves

Abstract

The carrier illumination (CI) method is an optical nondestructive technique primarily used today for the in-line monitoring of ultrashallow doping profiles in advanced complementary metal oxide semiconductor devices. A CI measurement is basically a differential probe laser reflectivity measurement providing (indirect) information on the underlying active dopant structure. As the signal depends on the doping density as well as the junction depth, no unique answer can be extracted from a single measurement. When analyzing power curves (i.e., the CI signal as a function of the power of the pump laser), it is shown that the shape of the power curves is (simultaneously) extremely sensitive to many different physical parameters, such as junction depth (angstrom), carrier peak density (10%), profile steepness (few nm∕decade), etc. In this work, we present a detailed interpretation and deconvolution method enabling the independent extraction of the peak carrier density and the junction depth for (unknown) chemical vapor deposition-grown box-like profiles (with 1–2nm∕decade steepness). The method is based on the exploitation of two characteristics of the power curve, namely its signal value at a particular (arbitrary) power and the power at which an inflection point (second derivative zero) occurs. The physical interpretation on this approach will be presented and is supported by extensive three-dimensional axisymmetric numerical simulations.