Ultrathin Diffusion Barriers/Liners for Gigascale Copper Metallization

The transition to copper-based interconnects for sub-quarter-micron device technologies has generated significant challenges in the identification and development of the robust material and process technologies required to form reliable multilevel metallization interconnects. In particular, a critical need exists for the identification and development of diffusion barrier/adhesion promoter liner materials that provide excellent performance in preventing the diffusion and intermixing of copper with the adjacent dielectric and semiconductor regions of the computer chip. This review summarizes key technology trends in interconnect metallization, with emphasis on ultrathin liner materials, predominant diffusion mechanisms in liner materials, and most promising candidate liners for copper metallization. Key results are presented from the development of physical vapor deposition and chemical vapor deposition processes for binary refractory metal nitrides, such as tantalum nitride and tungsten nitride, and amorphous ternary liners, including the titanium-silicon-nitrogen, tantalum-silicon-nitrogen, and tungsten-silicon-nitrogen systems. The applicability of these materials as diffusion barriers in copper-based interconnects is reviewed and assessed, particularly in terms of driving failure mechanisms and performance metrics.