Pit Formation Induced by Copper Contamination on Silicon Surface Immersed in Dilute Hydrofluoric Acid Solution

Formation of pitting at copper-contaminated sites on the silicon wafer surface during immersion in dilute hydrofluoric acid solution is elucidated by atomic force microscopy observations and electrochemical methods. It was discovered that the pit formation was promoted by the absence of light and hindered under illumination, irrespective of the conductivity type of silicon. From electrochemical measurement of voltammetry, the system was found to form a corrosion-type redox couple, composed of the anodic dissolution of silicon and the cathodic reduction of hydrogen ions, where the later reaction is enhanced by the presence of copper on the silicon surface. In addition, under illumination, either the cathodic or anodic reaction is enhanced, depending on the conductivity type of silicon due to a large increase in minority carrier concentration due to illumination. For creation of a localized pit, formation of the localized redox couple between copper and the nearby silicon surface is essential. This reaction is allowed under the darkened condition, but is obscured by the overwhelming amount of carriers generated under illumination.