Copper was directly electrodeposited onto TiN diffusion barrier surface without employing a copper seed layer. Depending on the chemical condition of an electrolyte, especially pH, copper deposits on TiN had different nucleation and growth modes. pH of electrolyte was controlled by adding H2SO4 and NH4OH to the base solution of pH 3.56, which contained copper-citrate (Cu-Cit) complexes. Chelating ability of citrate was substantially influenced by pH and it strongly affected the nucleation of copper. Below pH 3.56, progressive nucleation of copper on TiN was mainly found, and irregular growth and low density of 3-5x10(7) cm(-2) of copper nuclei came out. Above pH 3.56, instantaneous nucleation of copper on TiN, which is desirable for filling of damascene structure, was mainly obtained, and hemispherical copper nuclei were uniformly distributed. Copper nuclei density increased from 5x10(8) to 1.5x10(10) cm(-2) as pH varies from 3.56 to 7.4. It closely approached a value of 2x10(10) cm(-2), which is theoretically needed for seedless copper filling in the sub-70 nm damascene structure for ultralarge-scale integration interconnects. (c) 2006 The Electrochemical Society.