Monitoring silicide formation via in situ resistance measurements

Silicide formation as a result of the reaction of metals with silicon is a widely studied topic in semiconductor industry since silicides form an essential part of modern day Integrated Circuits (ICs). In most situations the fundamental kinetics of silicide formation are analyzed using elaborate techniques such as X-ray Diffraction (XRD) and Rutherford Backscattering (RBS). From those data the resulting silicide thickness is then derived. We propose a simple and elegant alternative in the form of in situ four point probe resistance measurements. Subsequently, we calculate the resulting silicide thickness using a simple 3-layer (metal – metal silicide – silicon) resistive model. The devices under test consisted of Pd sputtered onto bare Si wafers. Pd was chosen as it is well described in literature and reacts already at low (< 150° C) temperatures. We looked at two different temperature regimes to validate our model: the high temperature (150 – 225° C) and the low temperature (50 – 150° C) regime. The results obtained via this simple measurement technique showed that silicide formation of Pd contacts on Si occurs already at 57° C. Furthermore, below approximately 100° C our results indicated that apart from Pd2Si formation also mixed layers of Pd in Si and vice versa exist whereas at higher temperatures these mixed layers are absent or not significantly present. For the high temperature data we found a good agreement between our results and literature. We therefore consider this measurement technique as an elegant, universally applicable method for monitoring silicide formation of metal-silicon contacts.