With the application of a Co salicide process in deep submicrometer integrated circuits manufacturing, the potential benefit of its linewidth independent sheet resistance could be hindered due to the interaction of traces of gaseous impurities from different sources with silicide formation. In this work, we first analyze in situ the thermal desorption behavior of various dielectric and metal layers encountered in Co salicide process, by using the rapid thermal processing tool-atmospheric pressure ionization mass spectrometry. Based on these results as well as information from the literature, the detrimental impact of gaseous impurities (mainly O-2 and H2O) has been analyzed. The key facts are that Si has a stronger chemical affinity to O than Co, and the interaction of Co and Si oxide occurs only with great difficulty. We also argue that impurities from thermal desorption can have a stronger impact to the silicidation (edge thinning effect) compared to the impurities already in the processing ambient, due to its strong and direct interaction to the adjacent Co/Si interface. The fundamental principle of a technical solution is that the process should prevent O from coming into the Co/Si interface, and/or should be capable of removing the Si oxide already there. A few solutions reported in literature, including depositing Co at elevated temperatures, Co with reactive or nonreactive capping, and the use of Co(Ti) alloys, are analyzed.