Anodization of Tantalum Films for the Enhancement of Monolayer Seeding and Electroless Copper Plating

Abstract

Ta is a common barrier component for Cu metallization because of their immiscibility resulting in lack of mutual chemical reactivity and solubility. Conventionally, Cu is pre-sputtered on Ta as a seed layer, followed by Cu electroplating. Electroless metallization of Cu on Ta through self-assembled monolayer (SAM) seeding is rarely studied. Herein, electrochemical anodization of Ta films in an ethanol-based solution is performed to achieve a functionalized surface for sequential silanization of (3-aminopropyl)trimethoxysilane (APTMS), seeding, and electroless Cu plating. The SAM grown on hydrously (1% H2O) anodized Ta films is fully oriented, acting as an effective seed anchoring agent and adhesion promoter to yield high densities of Ni seeds (>5 × 1015 m−2) and tight binding of a Cu film (25.6 MPa). However, the SAM grown on anhydrously anodized Ta films has a substantially deteriorated ordering, giving poor seeding (<8 × 1014 m−2) and Cu-film adhesion (8.8 MPa). Similar deteriorations are observable from the pristine Ta film. The enhancements of SAM silanization and Ni seeding are caused by the improvement of chemical structure of anodization-induced surface tantalum oxide. The role of water in the anodization solution in enhancing anodization efficiency and SAM orientation is fully discussed.