Spectroscopic Studies on Electroless Deposition of Copper on Hydrogen-Terminated Si(111) Surface in NH4F Solution Containing Cu(II) Ions

Abstract

The electroless deposition of copper on the hydrogen-terminated Si(111) surface was investigated by means of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, scanning tunneling microscopy (STM), and energy-dispersive spectroscopy (EDS). The hydrogen-terminated Si(111) surface prepared was stable under air atmosphere for a day or more. It was found from ATR-FTIR that two bands centered at 2000 and 2260 <TEX>$cm^{-1}$</TEX> appeared after the H-Si(111) surface was immersed in 40% <TEX>$NH_4F$</TEX> solution containing 10 mM <TEX>$Cu^{2+}$</TEX>. On the other hand, STM image included the copper islands with a height of 5 nm and a diameter of 10-20 nm. The EDS data displayed the presence of copper, silicon and oxygen species. The results were rationalized in terms of the redox reaction of surface Si atoms and <TEX>$Cu^{2+}$</TEX> ions in solutions, which are changed into <TEX>$Si(OH)_x(F)_y$</TEX> containing <TEX>$SiF_6^{2-}$</TEX> ions and neutral copper islands.