This paper evaluates the resistivity, crystal grain structure and grain size distribution in 50 nm wide and 150 nm deep Cu interconnects electroplated using less leveler-containing high purity electrolyte. Resistivity of these sized Cu interconnects electroplated using 60 mu L leveler-containing electrolyte is found to be 25% lower than that of Cu interconnect electroplated using the 600 mu L (standard) leveler-containing electrolyte. The reduction of leveler content in electrolyte suppresses the Cl and Fe atom incorporation into the Cu interconnects and the formation of ClO and Fe(ClO) clusters at the grain boundary which reduces the grain growth in narrow Cu interconnects due to their pinning effect. The reduction of leveler content in electrolyte can also promote the formation of the as-electroplated Cu interconnects with very fine grain structure. When annealing these Cu interconnects electroplated using less leveler-containing electrolyte, the crystal grains can be considered to coarsen significantly due to the fewer numbers of ClO and Fe(ClO) clusters at the grain boundary and their large grain boundary energy. As a consequence of the significant grain coarsening, the numbers of crystal grains with less than 40 nm diameter are considered to diminish, resulting in low resistivity Cu interconnects. (C) 2017 The Electrochemical Society. All rights reserved.