Creep Characteristics of Electrolytic Copper Thin Films

Abstract

This paper describes the creep characteristics of three kinds of electrolytic copper thin films. Tensile creep and creep rupture tests were performed using three kinds of electrolytic copper thin films with 30mm gage length, 5mm width and 12μm thickness at 353K, 373K, 398K and 423K. The electrolytic copper plating thin films were direct current thin films (DC), periodic reverse pulse thin films (PL) and via fill thin films (VF). The DC and VF showed the same creep rupture lifetimes which were longer than those of the PL. Clear transient and steady creep stages were found in these kinds of the thin films but no acceleration creep stage was found. The minimum creep strain rates of the PL were faster than those of the DC and VF, which corresponded well with the creep rupture lifetimes. The thin film that yielded the faster creep strain rate had the shorter creep rupture lifetime. The relationship between the minimum creep strain rates and rupture lifetimes was well expressed by the Monkman-Grant equation. This implies that the creep rupture lifetime was mainly controlled by the creep deformation rate so that the thin film that has slower creep strain rate is preferable to use in electric devices because it has a stronger creep resistance. The creep rupture lifetimes at different temperatures were well correlated with the Larson-Miller parameter for each film. The correlation indicates that the temperature acceleration testing is performable to obtain the longer creep rupture lifetimes from the relatively shorter creep testing.