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

Abstract

The cementation or electroless deposition of copper on a hydrogen-terminated H-Si111 surface in concentrated ammonium fluoride (NH 4 F) and dilute hydrofluoric acid HF solutions containing copper ion (Cu 2 ) was investigated using attenuated total reflectance-Fourier transform infrared ATR-FTIR spectroscopy and X-ray photoelectron spectroscopy XPS. When the H-Si111 sample was immersed in a 40% NH 4 F solution containing 10 M Cu 2 , 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-Si111 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 Cu 2 -free NH 4 F solution, indicating that the Si oxide grew underneath the copper layer. When the H-Si111 sample was immersed in a 0.5% HF solution containing 10 M Cu 2 , 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 Si111 surface. The amount of copper deposited on the H-Si111 surface in the dilute HF solution containing Cu 2 was much less than that in the NH 4 F solution containing the same amount of Cu 2 . The oxide was not observed on the H-Si111 surface after being immersed in the dilute HF solution containing 10 M Cu 2 .