A new oxidation-resistant CoSi₂ process for self-aligned silicidation (salicide) technology

This paper presents a new oxidation-resistant and self-aligned CoSi₂ process using amorphous-Si (a-Si)/Co bilayer metallization. It is shown that, even in an environment without introducing any flowing inert gas, the detrimental reaction between Co metal and ambient impurities, e.g. O₂ and H₂O, can be completely impeded by a covered thin a-Si layer during the thermal silicidation cycle. Moreover, despite a capped a-Si layer over Co film, the satisfactory self-aligned silicidation properties can be retained if the initial silicidation temperature is kept below 500°C in N₂ ambient. Furthermore, the dependences of both oxidation-resistant and self-aligned silicidation properties on the thicknesses of a-Si and Co films are studied in detail. Based on experimental analysis, the allowed process window for the a-Si film thickness can be determined and is shown to increase with increasing the Co film thickness. An empirical process rule is experimentally obtained to determine the optimal thickness relation between a-Si and Co films for the a-Si/Co bilayer process. Thus, a simple and practical self-aligned CoSi₂ process with extremely high immunity to ambient impurities is proposed for SALICIDE applications.