A comparison between aluminum and copper interactions with high-temperature oxide and nitride diffusion barriers

Abstract

A comparative study between the high-temperature diffusion barriers against either Al or Cu has been made. Several conducting oxides (RuO2, Mo–O) and nitrides (W–N) were examined using cross-sectional transmission electron microscopy, Auger electron spectroscopy and x-ray diffraction. Copper was chosen as a less reactive metal than aluminum, and it is widely used in Al–Cu interconnections. Al was found to reduce both oxides to form a thin self-limiting layer of Al2O3, which hinders interdiffusion between Al and Si. In addition, a localized and nonuniform reaction occurs at the RuO2/SiO2 interface giving rise to the metal-rich silicide Ru2Si. Cu was fully oxidized by reduction of RuO2 to form Cu2O but did not reduce Mo–O. For Cu on W–N, no reactions occur. However, we observe a significant modification of the Al/W–N interface. A nonuniform reaction giving WAl12 and a continuous thin amorphous layer which appears to be N-rich aluminum are present. When the W–N is exposed to air before Al deposition, an aluminum oxide is formed at Al/W–N interface and prevents the formation of WAl12. These results indicate that the formation of interfacial Al2O3 is a key ingredient in the success of high-temperature diffusion barriers for Al on Si. However, it may increase the contact resistance.