Spectroscopic Studies on Electroless Deposition of Copper on a Hydrogen-Terminated Si(111) Surface in Fluoride Solutions

The cementation or electroless deposition of copper on a hydrogen-terminated (H-)Si(111) surface in concentrated ammonium fluoride (NH4F) and dilute hydrofluoric acid (HF) solutions containing copper ion (Cu2+) was investigated using attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). When the H-Si(111) sample was immersed in a 40% NH4F solution containing 10 muM Cu2+, the ATR-FTIR showed a decrease in the monohydride (SiH), and XPS revealed the copper deposition and Si oxide formation as well as the existence of a small amount of fluorinated Si species on the H-Si(111) surface. After the surface was rinsed with ultrapure water, the amounts of SiH and Si oxide decreased and increased, respectively, while the fluorinated Si species disappeared. Copper and Si oxide were observed on the Si surface even after being etched in a Cu2+-free NH4F solution, indicating that the Si oxide grew underneath the copper layer. When the H-Si(111) sample was immersed in a 0.5% HF solution containing 10 muM Cu2+, the amounts of SiH decreased while those of the dihydride and trihydride significantly increased, reflecting the increase in the densities of the steps and kinks on the Si(111) surface. The amount of copper deposited on the H-Si(111) surface in the dilute HF solution containing Cu2+ was much less than that in the NH4F solution containing the same amount of Cu2+. The oxide was not observed on the H-Si(111) surface after being immersed in the dilute HF solution containing 10 muM Cu2+. (C) 2001 The Electrochemical Society.