The demand for smaller and faster microelectronic devices necessitates thinner diffusion barrier layers between the silicon semiconductor and copper conductor layers to prevent them from diffusing into each other and increasing resistivity along conducting pathways. To avoid the blurred silicon/copper interface, transition metals are being studied as ultrathin conductive barrier layers. Transition metal oxides usually have high dielectric constants and can be deposited in ultrathin films on silicon without diffusing into it as copper does, making it an ideal candidate for this application.
In our study, the ultra-thin film (5 nm) of cobalt metal with high purity (96.5% at cobalt) is successfully deposited by photo-assisted atomic layer deposition with remote plasma system. A 60 nm thick cobalt metal film grown after annealing at 250 °C were analyzed by X-ray diffraction and XPS. Reflections confirmed crystalline cobalt metal, with an average crystallite size of 33.5 ± 4.0 nm from the scherer equation. And continued sputtering resulted in ionizations that a film composition consisting of 96.5% cobalt metal after 5 min. The remainder of the film was oxygen, with carbon and nitrogen levels below the detection limits (< 1.0%). The top-down AFM images show as-deposited Co film at 200 °C with RMS of 1.1 nm and Co film at 180 °C with RMS of 0.6nm. And A 50± 5nm thick cobalt metal film was grown at 200 °C with 1.0E-5 μΩ.cm which are close to that of bulk cobalt (6.24 μΩ.cm at 20 °C).