Gaseous impurities in Co silicidation - Impact and solutions

With the application of a Co salicide process in deep submicrometer integra ted circuits manufacturing, the potential benefit of its linewidth independ ent 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 d ielectric and metal layers encountered in Co salicide process, by using the rapid thermal processing tool-atmospheric pressure ionization mass spectro metry. Based on these results as well as information from the literature, t he detrimental impact of gaseous impurities (mainly O-2 and H2O) has been a nalyzed. The key facts are that Si has a stronger chemical affinity to O th an Co, and the interaction of Co and Si oxide occurs only with great diffic ulty. We also argue that impurities from thermal desorption can have a stro nger impact to the silicidation (edge thinning effect) compared to the impu rities already in the processing ambient, due to its strong and direct inte raction to the adjacent Co/Si interface. The fundamental principle of a tec hnical solution is that the process should prevent O from coming into the C o/Si interface, and/or should be capable of removing the Si oxide already t here. A few solutions reported in literature, including depositing Co at el evated temperatures, Co with reactive or nonreactive capping, and the use o f Co(Ti) alloys, are analyzed. (C) 2001 The Electrochemical Society.