Electroless NiMo-P thin films for capping/barrier layer applications

Copper is implemented for ULSI interconnects fabrication using electrochemical (ECD) plating. However, this technology faces challenges such as metal corrosion, weak adhesion, and diffusion of copper in silicon. Forming barrier and capping layers successfully address these issues. One of the recent approaches are the formation of such layers by electroless deposition of thin polymetallic alloy films. In this presentation, electrolessly deposited nickel based alloys, e.g. NiMo-P were investigated for their use capping layers in IC technology. These ternary alloy films provide significantly lower resistivity than other barriers, and the electroless deposition process can achieve formation of ultra thin, selective deposits. Additionally, using these films as metal cap layers is believed to improve also the electromigration reliability of Cu ICs. The basic properties of various ternary alloys are presented. Our analysis focused primarily on the influence of experimental conditions on thin film composition, structure and resistivity. Resistivity values were in the range of 60 - 70 muOmegacm for NiMo-P, depending on the thickness. The polycrystalline structured thin films suggest resisting Cu diffusion up to 450degreesC for 1h and are therefore used as diffusion barriers. For the application of these films as metallic caps onto Cu inlaid structures, a. complete wet chemical process sequence consisting of cleaning, activation and electroless deposition has been investigated.