Reaction processes on silicon surfaces studied using Fourier transform infrared spectroscopy

As integrated circuits have become smaller and more complex, there has been an increased focus on the understanding of the chemical mechanisms invoked in device processing steps. Fourier transform infrared spectroscopy has been employed to study silicon surface chemistry relevant to semiconductor processing techniques. Experiments were performed in-situ in an ultra-high vacuum chamber on high surface area porous silicon samples. For example, ammonia (NH{dollar}sb3{dollar}) is employed to grow silicon nitride layers for dielectric insulation. FTIR transmission spectroscopy was used to monitor the decomposition of NH{dollar}sb3{dollar} and ND{dollar}sb3{dollar} on porous silicon surfaces. The need for greater control over epitaxial growth processes has motivated the development of atomic layer epitaxy (ALE) techniques. In addition, the deposition of silicon and germanium on silicon surfaces is of increased importance due to the use of Si/Si{dollar}sb{lcub}rm 1-x{rcub}{dollar}Ge{dollar}sb{lcub}rm x{rcub}{dollar}Si heterostructures in electronic devices. FTIR spectroscopy has been employed to evaluate promising molecular precursors for silicon and germanium ALE including: disilane (Sb{dollar}sb2{dollar}H{dollar}sb6{dollar}), diethylsilane ((CH{dollar}sb3{dollar}CH{dollar}sb2)sb2{dollar}SiH{dollar}sb2{dollar}), ethylsilane (CH{dollar}sb3{dollar}CH{dollar}sb2{dollar}SiH{dollar}sb3{dollar}), diethylgermane ((CH{dollar}sb3{dollar}CH{dollar}sb2)sb2{dollar}GeH{dollar}sb2{dollar}), trichlorosilane (SiHCl{dollar}sb3{dollar}), and trichlorogermane (GeHCl{dollar}sb3{dollar}). The stable surface species were determined upon 200 K adsorption of these various molecular precursors. The thermal stabilities of the surface species were studied with annealing experiments. Finally, hydrogen passivation plays an increasingly important role in silicon surface cleaning and preparation. To measure the effectiveness of hydrogen passivation towards silicon surface contamination, FTIR transmission spectroscopy was used to monitor the oxidation of silicon surfaces versus hydrogen coverage. These studies revealed that oxidation rates and apparent oxygen saturation levels on porous silicon decrease as a function of initial surface hydrogen coverage.