Cobalt Silicide Interconnection from a Si/W/Co Trilayer Structure

Abstract

A Si/W/Co trilayer structure which consists of a top insulating Si film, a middle buffering W film, and a bottom Co film is proposed to form cobalt silicide. Because the top Si layer can hinder the oxidants and contaminants from penetrating into the bottom layers, the silicidation process is insensitive to the annealing atmosphere. The middle W film can prevent the top Si layer from reacting with the bottom Co film to form an unwanted cobalt silicide film. It can also react with the bottom Co film to form a Co‐W alloy. Thus, the unsilicided Co film can be completely transformed into the Co‐W alloy which can be etched out with the same chemical etchant as that for the W film. By using the Si/W/Co (100 nm/50 nm/40 nm) trilayer structure on single‐crystal Si substrates and silicidation at 700°–800°C for 30 min in flowing , the obtainable sheet resistance is 1.7–2.0 Ω/□. This corresponds to a film resistivity of 20 μΩ · cm. Since Co is the dominant diffusion species in forming , and the Co‐W alloy formed upon the oxide layer has a higher silicidation temperature than the pure Co film, cobalt silicide cannot grow laterally on top of the oxide layer.