Chemical etching of vicinal Si(111): Dependence of the surface structure and the hydrogen termination on the pH of the etching solutions

Abstract

Homogeneous hydrogenterminated Si(111) surface formed using aqueous HF solution and waterInfrared spectroscopy is used to study the etching process of stepped Si ( 111 ) 9° surfaces as a function of the pH of the etching HF solutions. This process results in complete H termination of the silicon surface, including terraces, steps, and defects; the surface structure can therefore be well studied using infrared (lR) spectroscopy. Polarized IR absorption spectra of the Si-H stretching vibrations (i.e., in the region 2060-2150 cm -\) vary dramatically as the pH of the etching solutions increases from 2.0 to 7.8. In general, higher pH solutions yield sharper bands and more easily assigned spectra, making it possible to identify the step and terrace species and thus to infer the surface structure and step morphology (i.e., to investigate the etching process). The data are explained by a model involving different etching rates for each individual surface species: The highest rate of removal is for isolated adatom defects located on (Ill) planes and the lowest is for the ideally H-terminated (111) planes themselves. For proper conditions of pH and etching time, atomically straight steps are formed due to faster removal of kinks than etching of the straight step themselves. The influence of steric hindrance is invoked to account for such preferential etching.

<i>In Situ</i> ATR-FTIR Observation about Surfactant/Hydrogen-TerminatedSi(111) Interface in Solution

“…The broadness would cause the wide vibration energy by H 2 O adsorption on the Si surface in flowing pure water [10]- [12]. Di-2-ethylhexyl sulfosuccinate sodium salt (aerosol OT) as surfactant is C 8 Figure 4. The spectra showed CH x stretching vibration, and the peak intensity was increased with the flowing time.…”

Structure of singly terminated polar DyScO3(110) surfaces

“…It appeared that selective Dy etching by strong alkaline solutions occurs mainly at the step edges, which is comparable to wet etching of SrTiO 3 (001) and Si (111) surfaces. 17,18 As a result, the etching rate severely depended on the surface morphology, which varied from substrate to substrate, independent of the miscut angle. Therefore a surface roughening step was introduced to increase the number of step edges.…”

Preparation of Atomically Flat Si(111)-H Surfaces in Aqueous Ammonium Fluoride Solutions Investigated by Using Electrochemical, In Situ EC-STM and ATR-FTIR Spectroscopic Methods

“…6 Pietsch et al reported on the ex situ STM results of Si/SiO 2 interface obtained in concentrated HF solution, which composed of small islands and pits with atomic roughness. 7 More detailed results of the preparation of atomically flat Si(111)-H surface can be seen in Behm's work in which the appearance of Si(111) surface investigated by ex situ STM was drastically changed with immersion time in 40% NH 4 F solution.…”