DEPTH PROFILING OF THE GE CONCENTRATION IN SIGE ALLOYS USING INSITU ELLIPSOMETRY DURING REACTIVE-ION ETCHING

The complex refractive index of SiGe alloys at 632.8 nm has been measu red as a function of the Ge concentration using in situ ellipsometry w hile the material is slowly removed from a silicon substrate using rea ctive-ion etching (RIE). Homogeneous, strained epitaxial SiGe films on silicon substrates were used. The Ge concentration was obtained by Ru therford backscattering. If an unknown SiGe structure is etched with R IE, in situ ellipsometry yields combinations of the ellipsometric angl es PSI and DELTA with time. Starting at the Si substrate, these points are, on a point-to-point basis, converted into combinations of comple x refractive index and depth in a numerical procedure. For this invers ion of the ellipsometry equations, the known relation between the real and the imaginary part of the refractive index of SiGe is used. Final ly the refractive indices are converted into Ge concentrations. Thus t he depth profile of the Ge concentration in an unknown epitaxial SiGe structure can be inferred from an in situ ellipsometric measurement du ring RIE of the unknown structure. The obtained resolutions in depth a nd Ge concentration are 0.3 nm and 0.3%, respectively.