Surface roughness reduction for AlCu-based metallization: implications from an integrative point of view

Abstract

For an AlCu-based metallization utilized in a state-of-the-art production environment we demonstrate that, beyond the more traditional electromigration properties, also surface roughness needs to be considered carefully in order to achieve optimal yields. Through experiments carried out on blanket wafers, mechanisms are proposed which account for a reduced surface roughness of aluminum grown on titanium rather than on a sandwich of titanium and titanium nitride. The evolution of aluminum grain growth and thus roughness is studied for the two different metal stacks. The practical implications of a reduced surface roughness for integration purposes is subsequently shown by considering etch behavior, short yield as well as signals depending on the metal’s reflectivity.