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 A1 or Cu has been made. Several conducting oxides (RuQ2, 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 AI2O3, which hinders interdiffusion between Al and Si. In addition, a localized and nonuniform reaction occurs at the Ru02/Si02 interface giving rise to the metal-rich silicide Ru2Si. Cu was fully oxidized by reduction of Ru02 to form Cu20 but did not reduce Mo-C). For Cu on W-N, no reactions occur. However, we observe a significant modification of the Al/W-N interface. A nonuniform reaction giving WA112 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 WA112. These results indicate that the formation of interfacial Al203 is a key ingredient in the success of high-temperature diffusion barriers for Al on Si. However, it may increase the contact resistance. © 1989, American Vacuum Society. All rights reserved.