Grain sizes have been observed quantitatively at the surface of thin electroplated copper layers by employing a grain boundary etching technique. In conventional copper layers deposited on TaN barrier layers, the typical grain size in the as-deposited layer is 360 nm at a thickness of 1000 nm. This size decreases rapidly with decreasing thickness and reaches 65 nm for 100 nm thick annealed layers, i.e., grain size is close to the thickness in such a layer. When lower stress layer is electroplated, however, the grain size in the annealed layer increases from 670 to 1150 nm for thick (1000 nm thick) and from 65 to 210 nm in 100 nm thick layers, respectively. Deposition of larger grain size copper layers is required in the electroplating of low-resistivity thin copper layers. (c) 2006 The Electrochemical Society.