Characterization of a controlled electroless deposition of copper thin film on germanium and silicon surfaces

Nanofilms of copper were deposited on silicon and, for the first time, on polycrystalline germanium substrates by electroless deposition. Germanium or silicon disks were immersed in a 10mM copper sulfate solution containing dilute hydrofluoric acid at room temperature. This simple one-step deposition does not require the use of laborious operations or expensive equipment, that the reaction medium be degassed, or that the film be annealed. The copper film grows in a few minutes, producing a film on both Ge and Si that covers a very large area of the substrate in contrast to other metals such as Au, Ag, Pt and Pd for which deposition on Ge and Si produces islands or dendrites. Atomic force microscopy, X-ray photoelectron spectroscopy (XPS) and powder X-ray diffraction (PXRD) were used to characterize the microstructure and confirmed the formation of elemental copper nanofilms. The AFM micrographs reveal a Stranski-Krastanov type of film growth (layers + islands) that varies with the length of time the Ge or Si substrate is immersed in the CuSO4 solution. Thicker films were observed on the Ge than on the Si substrate resulting in larger particles and rougher surface than on Si. XPS analysis shows that the elemental copper is deposited on both Ge and Si substrates and that the films oxidize over a period of weeks with air exposure at room temperature. Finally, PXRD data reveal two preferential orientations (1 1 1) and (2 0 0) for the copper crystallites grown on both Ge and Si. The same intensity of the (1 1 1)-texture was measured on both Ge and Si substrate which is an important result because it has been shown that the (1 1 1) texture reduces stress-induced voiding and increases resistance to electromigration in metal interconnects. (C) 2010 Elsevier B. V. All rights reserved.