Oxidation behavior of Pt–Ru bimetallic thin films as gate electrodes by atomic layer deposition

Investigating the oxidation behavior of a bimetallic thin film for a durable gate electrode in complementary metal–oxide semiconductor (CMOS) devices is challenging. Herein, Pt–Ru bimetallic thin films were synthesized using atomic layer deposition (ALD), followed by intentional oxidation at 600 °C. The as-deposited Pt–Ru thin films presented distorted lattices due to the solid solution, whereas the X-ray diffraction (XRD) peaks of the oxidized Pt–Ru thin films did not shift, except for the Pt-rich oxidized Pt–Ru thin films. Interestingly, due to the high resistance of Pt to oxidation, Ru atoms in the Pt-rich oxidized Pt–Ru thin films were not oxidized under an oxidation atmosphere. Upon increasing the Ru content, Ru atoms started to oxidize, followed by full oxidization into Ru oxide in the Ru-rich Pt–Ru thin films. Simultaneously, Ru atoms moved to the surface and were oxidized with surface oxygen, thereby separating the upper Ru oxide and Pt metal layer. The resistivity of the oxidized Pt–Ru thin films increased as the Ru content increased, whereas the as-deposited Pt–Ru thin films exhibited a volcano-shaped peak depending on the relative composition between Ru and Pt. The work functions of the oxidized Pt–Ru thin films were higher than those of the as-deposited films, due to the higher work function of RuO₂ than those of Ru metals; however, the Pt-dominant Pt–Ru thin films showed similar values both before and after oxidation, owing to the unoxidized Ru atoms.