A New Cleaning Technique for Corrosion Protection in Aluminum Metallization
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A NEW CLEANING TECHNIQUE FOR CORROSION PROTECTION IN ALUMINUM METALLIZATION Masako Kodera1,3, Shin-ichiro Uekusa3, Yoshitaka Matsui1, Naoto Miyashita1,3, Atsushi Shigeta1, Shinya Takahashi1, Murato Kawai1, Hiroshi Kawamoto1, and Manabu Tsujimura2 1 Toshiba Corporation, Yokohama, Japan 2 Ebara Corporation, Fujisawa, Japan 3 Meiji University, Kawasaki, Japan
ABSTRACT A new cleaning technique using gas dissolved water has been found to be effective in protecting against corrosion in aluminum metallization, which is also useful in post-cleaning of Cu CMP as already reported. Corrosion can be a significant concern in aluminum as well as in copper metallization. In Al CMP process, corrosion often occurs in contact with DIW because of the big potential difference between Al and the barrier metal. In this study, it has been confirmed that gas dissolved water is able to change the potential of various metal films, and that following Al CMP, post-cleaning using gas dissolved water instead of DIW can successfully protect against corrosion. Furthermore this technique is also effective in the post-cleaning process of Al wiring formed by RIE, which contains a slight amount of Cu. Because segregation of copper at the side-wall of wiring often occurs during RIE and the following processes, Al-Cu wiring is easily corroded during the DIW rinsing step in wet cleaning, which may cause killer defects. Gas dissolved water can remarkably decrease the potential difference between Al-Cu alloy and segregated Cu, as well as Al-Cu alloy and the Ti/TiN used as a barrier metal. Moreover, because it seems that a reaction occurs between cathode water and Ti/TiN, where electrons may be supplied there to corrosive sites, corrosion can be prevented. INTRODUCTION Aluminum metallization as well as copper metallization face the technology node of 70nm or finer pitch, where corrosion can be a fatal issue in forming wiring. In the case of copper, corrosion is easily induced by CMP slurry(1), cleaning solution, residual impurities, and environmental contamination during storage(2). Inhibitors such as BTA(3) are usually added to the slurry to prevent corrosion through CMP. Moreover, gas dissolved water is effective in preventing corrosion during post-CMP cleaning and storage, because of its ability to remove impurities such as sulfur, oxidation of copper surface, and decrease the potential difference between Cu and the barrier(2). On the other hand, aluminum wiring is also quite easily corroded during CMP(4,5), especially during the rinsing step with DIW(6) in post-CMP cleaning. Aluminum has remarkably low potential in DIW, which is –700mV vs Ag/AgCl, while that of the barrier metal is much higher, for example, around 0mV vs Ag/AgCl in the case of TiN. Because of this great potential difference between Al and the barrier metal, galvanic corrosion instantly occurs on the aluminum surface in contact with DIW. Furthermore, in the case of post-ash cleaning of Al-Cu wiring, galvanic corrosion is also easily caused by the potential difference between Al-
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