Role of Potassium Permanganate-Based Solutions in Controlling the Galvanic Corrosion at Al-Co Interface

Al-Co metal gate has been recently proposed both for 25 and 11 nm devices as an alternative for Al-Ti used for 45 nm structures. The polishing dispersions used for Al-Ti gates when tested on Al-Co showed severe pitting and static etch rates upto ∼10 nm/min. The present work describes the development of the required chemistry to reduce the corrosion potential (E corr ) gap between Al and Co and minimize galvanic corrosion. The effect of pH, several oxidizers and additives on the open circuit potentials (E oc ) of Al and Co was investigated and it was discovered that solutions of KMnO 4 and saccharides help reduce the E corr gap in between Al and Co to ∼10 mV. A preliminary corrosion protection mechanism involving the formation of a protective manganese oxide coating on the surface of Al/Co is proposed.