Use of Si KLL Auger shifts and the Auger parameter in XPS to distinguish Ti silicides from a Ti/Si mixture in thin films

Abstract

A particular wafer processing step involves deposition of a Ti thin film (˜6 nm to ˜13 nm) on Si, under processing conditions intended to form a silicide with specific electrical properties. It is difficult, however, to distinguish silicide formation from mere elemental inter-diffusion. Routine laboratory XPS, using an Al X-Ray source(1486.6ev), does have an appropriate probing depth for the film stack involved, but the chemical shifts in Ti (2p) and Si(2p) are too small (<0.3ev), particularly if small charging artifacts might be present. The Si KLL Auger transition, accessed using a Zr X-Ray source (2042.4ev), has much larger shifts. We demonstrate its use to reliably and non-destructively distinguish Ti silicide formation from simple inter-diffusion, even when the layer of interest may lie below a TiN capping layer and some ambient surface oxidation. We also report Auger Parameters and discuss the advantages and disadvantages of their use.