Non-Contact, Sub-Surface Detection of Alloy Segregation in Back-End of Line Copper Dual-Damascene Structures
Alloy seedlayers for copper back-end of line interconnects have become common at technology groundrules of 45 nm and below, due to reliability requirements. The key requirement of the minority alloy component (e.g., Al or manganese, also referred to as the 'dopant') is that it segregates to the copper (Cu)/dielectric cap layer interface in order to promote adhesion between the Cu in the line and the dielectric capping layer. The segregation beneath the dielectric cap has a complex dependence on many process parameters and needs to be monitored across the wafer. In this paper, we present a contactless, in-line, fast, and reliable Kelvin probe technique for the sub-surface detection of alloy segregation in Cu interconnects for sub-22 nm technologies.