Void generation during the annealing process of very narrow copper wires

Abstract

We carried out experiments on stress-induced void formation in ultrathin Cu wires while varying heat-treatment temperature, wire dimensions, and overlayer thickness. We also did molecular dynamics simulations of void formation in a buried wire of nanometer scale and compared these results with experimental results to clarify details of the void formation mechanism. The experimental and simulation results showed good accordance in explaining the effects of wire width, overlayer thickness, and cooling rate on void formation. ͑1͒ The narrower the wire width, the easier the void formation. ͑2͒ The thicker the overlayer, the easier the void formation. ͑3͒ The larger the cooling rate, the greater the suppression of void formation. From the obtained results, we constructed a void formation model for a buried wire. The basic concept of the model describes how local strain at four trench corners is relaxed in the buried wire in the annealing process. There are two ways to relax the local strain: ͑1͒ structural relaxation to strengthen adhesion between the wire and substrate and ͑2͒ reduction of the surface area to minimize surface energy. The way preferred is dependent on how parameters such as system temperature and wire dimensions are combined. Based on the void formation model, we interpreted the effects of wire strain, wire dimensions, and overlayer thickness.

Hot ductility behavior of AD730™ nickel-base superalloy

“…They have been related to the growth (Fig 7 a and b) and coalescence of voids (Fig. 7 c and d), and cavities nucleated at grain boundaries which have been connected to the surface and assisted surface crack growth due to the reduction of the surface area resulting in the formation of a large number of microvoids that produce a dimpled crack surface [35,[40][41][42]. For the low heating rate, void coalescence could take place and the dimples appear larger, while for the fast heating rate very small dimples are observed at the fracture surface.…”