DETERMINATION OF ACCURATE METAL SILICIDE LAYER THICKNESS BY RBS

Rutherford Backscattering Spectrometry (RES) is a proven useful analyt ical tool for determining compositional information of a wide variety of materials. One of the most widely utilized applications of RES is t he study of the composition of metal silicides (MSi(x)), also referred to as polycides. A key quantity obtained from an analysis of a metal silicide is the ratio of silicon to metal (Si/M). Although composition al information is very reliable in these applications, determination o f metal silicide layer thickness by RES techniques can differ from tru e layer thicknesses by more than 40%. The cause of these differences l ies in how the densities utilized in the RES analysis are calculated. The standard RES analysis software packages calculate layer densities by assuming each element's bulk densities weighted by the fractional a tomic presence. This calculation causes large thickness discrepancies in metal silicide thicknesses because most films form into crystal str uctures with distinct densities. Assuming a constant layer density for a full spectrum of Si/M values for metal silicide samples improves la yer thickness determination but ignores the underlying physics of the films. We will present results of RES determination of the thickness v arious metal silicide films with a range of Si/M values using a physic ally accurate model for the calculation of layer densities. The thickn esses are compared to scanning electron microscopy (SEM) cross-section micrographs. We have also developed supporting software that incorpor ates these calculations into routine analyses.