Increase in electrical resistivity of copper and aluminum fine lines

The resistivities of thin films and fine lines of copper (Cu) and aluminum (Al) were measured by a resistance ratio method (referred to as "RR method" hereafter), which measures the ratio of room-temperature resistance to liquid-nitrogen-temperature resistance. This method can predict resistivity exactly without the need for precise and detailed line or film dimension measurements. Thinner films and finer lines have higher resistivities in the case of both Cu and Al, with Cu showing larger resistivity increases (films and lines) than Al. From the present data, we estimated the electron mean free path of Cu to be 55 nm, which is close to most of the previously reported values, and that of Al to be 22 nm. Line resistivities depend not only on the line width but also on line thickness. We propose a simple equation for expressing line resistivity in terms of line thickness and width.