Abstract It has been found that a process-design interaction involving very large capacitor arrays is capable of causing voiding in well-formed copper trenches. This voiding is believed to be caused by the electrochemical dissolution of copper driven by the photovoltaic effect realized at p-n junctions. A series of experiments was performed to reproduce this voiding in a laboratory environment using water and exposure to light or dark. The experiments were performed on two different size capacitor arrays. In addition, similar experiments were performed on a large capacitor array that uses the opposite dopant isolation scheme. Conversely, copper dendrite growth was observed at the features of interest instead of dissolution, even under flowing de-ionized water (DI) conditions. The results are discussed in the context of known copper-water electrochemical equilibria and design implications are discussed.