Synergy of mercaptosilane monolayer embedding and extremely dilute cobalt alloying for metallization of copper without a conventional metallic barrier

Abstract

TaN/Ta bilayer is the standard barrier for the metallization of copper interconnects of current integrated circuit devices. However, thickness reduction of the barrier becomes a major bottleneck for the successful metallization of the downsizing copper interconnects in sub-7-nm technology nodes. Hence, the feasibility of a mercaptosilane self-assembled monolayer (SAM) as a barrier, as well as a seed adsorber for electroless copper metallization, is investigated. The mercaptosilane SAM after proper functionalization in a RCA-1 aqueous solution has the capacity to adsorb 3-nm-sized nickel particles, subsequently catalyzing the plating of extremely dilute Cu(Co) films with only 0.13 at.% of Co. Using the adhesion strength (13.1 MPa) and threshold temperature for thermal failure (450 °C) of pristine Cu/SiO2 as a control, Cu/SAM/SiO2 (pristine state) yields markedly enhanced adhesion strength and threshold temperature of 39.4 MPa and 500 °C, respectively. Cu(Co)/SAM/Cu exhibits even a much higher adhesion of 53.8 MPa (pristine state) and 74.6 MPa (annealed state). Seeding of the nickel particles by the functionalized mercaptosilane monolayer is clarified from the viewpoints of solution chemistry and proton exchange mechanism, and why only a tiny amount of cobalt is incorporated onto copper matrix is explained. The synergetic effect of the mercaptosilane monolayer embedding and extreme dilution of cobalt alloying on enhancing the adhesion and thermal stability of copper films is discussed considering the context of previous studies.