Nanotwinned copper electroplating with halide engineered grain morphologies

Nanotwinned copper enables superior performances in material mechanics, electricity, and weld reliability, which attracts widespread fundamental research interests and meanwhile shows great application potential as the next-generation electronic interconnect materials in integrated circuits manufacturing and packaging. Halides are indispensably added in nt-Cu electroplating baths. Whereas, effects of halides on plating chemistry and microstructure manipulation are yet to be clearly understood. In this study, the type and concentration of halide are found interdependent with plating current and play significant roles in manipulating the growth and density coherent twin boundaries. Columnar-grained nanotwinned copper of high-density coherent twin lamellar can be electroplated in a wide range of chloride concentration and plating current. While equiaxial-grained nanotwinned copper of mild-density coherent twin lamellar is electroplated with intermediate bromide concentration and small plating current, showing prominent detwinned grain morphologies with further increase of current density or bromide concentration. The mechanism of halide-based microstructures engineering is revealed to be in close relation to differences in inhibiting ability of [gelatin-Cu⁺-halide] intermediate complex and desorption behaviors of the gelatin molecules anchored.

I. Introduction

Electroplated copper is the interconnect material for build-up of micro-nano scaled electronic circuits in integrated circuits manufacturing and packaging [1], [2]. Generally, copper electroplating demand for controllable growth morphology and minimal impurity defects. As advances of miniaturized interconnect structures and increased package density, it further demand for superior microstructural thermostability, mechanical strengthening-toughening, electromigration resistance, etc., which are closely related to the lattice orientation, grain size, and grain boundary characters of electroplated copper [3].