Electrochemical Processes for ULSI Interconnects

Abstract

Copper is widely used as interconnecting material in ultra-large-scale integration (ULSI) circuits (Fig. 13.1). Fabrication of copper interconnection has been achieved by “Damascene process” [1], which is an electrodeposition process combined with chemical–mechanical polishing (CMP) (Fig. 13.1) [2]. Damascene process led to a remarkable change in the industry. Most manufacturers have now converted to this electrodeposited copper interconnect technology. Before the introduction of copper to interconnects, aluminum and aluminum–copper alloy were used as the interconnecting materials for many years. Aluminum interconnect layers are easily fabricated by subtractive etching process. In process, the interconnect layers are deposited by physical vapor deposition, followed by reactive ion etching (RIE). Aluminum is preferable as interconnects because this material does not diffuse into SiO2 substrate and the layers adhere well to the substrate. However, resistivity of aluminum is relatively high (2.65 μΩ cm), and the layers suffer from the disadvantage of its poor electromigration resistance.