Resistance contributions to copper interconnects

Experimental decomposition of contributions of electron scattering events in deeply scaled interconnects has been complicated by the fact that grain size and line dimensions are generally not varied independently. In this paper, we describe a combination of experiments to examine scattering mechanism independently. The cross section of was changed by recessing individual copper interconnects from the top using wet chemical etching, which was combined with repeated cryogenic resistance measurements. A fit for the grain boundary reflectivity was then obtained. In addition, it was found that the average grain size increase from the bottom to the top of the interconnect. This was confirmed by TEM based grain size measurements. Further, in order to assess surface scattering, magnetoresistance was employed for the first time for interconnects. It is observed to be sensitive to the geometry of the line. The method also allows for independent assessment of sidewall vs. bottom/top surface scattering. Results indicate that sidewall scattering is more severe than top/bottom surface scattering.