Quantification of SiGe layer composition using MCs + and MCs 2+ secondary ions in ToF-SIMS and magnetic SIMS

Abstract

The interest in using semiconducting layers of SiGe in microelectronics means it is important to be able to characterise the composition of such layers as a function of depth. SIMS is an essential technique for characterising such layers but quantification of the Ge concentration in SIMS depth profiles of SiGe requires knowledge of the secondary ion generation efficiency as a function of Ge concentration. We have studied the secondary ion emission of MCs + and MCs 2 + ions for SiGe layers with Ge concentrations ranging from 0 to 85 at.% Ge. A CAMECA IMS-5F and an ION-TOF ToF-SIMS V both with a 2 keV Cs primary beam were used. We find a good linear correlation between the ratio of SIMS secondary ion intensities I(GeCs n +)/ I(SiCs n +) (where n = 1 and 2) and the composition ratio [Ge]/[Si]. The same linear correlation is observed for results obtained using the ToF-SIMS, but the RSF deviates slightly from a linear relationship with the Ge concentration. If a sample with several known Ge concentrations is used as a standard to determine the factor of proportionality between the ratio of secondary ion intensities and the composition ratio then the Ge concentration in an unknown sample can be determined from the point by point GeCs n +/SiCs n + ratio, where n = 1 and 2.