Abstract
We report density functional electronic structure calculations to monitor the change in the surface characteristics of the Si (100)-2x1 surface after fluorination followed by interaction with water. Embedded finite silicon clusters are used to model an extended Si (100)-2x1 surface. Two high symmetry pathways and subsequent adsorption sites were examined: (i) adsorption of an fluorine atom directing onto a silicon dangling bond to form a monocoordinated fluorine atom (ii) adsorption of a fluorine atom directing on top of silicon dimer to form a bridging dicoordinated fluorine atom. However, in the later case we find that no barrier exists for the bridging fluorine atom to slide towards silicon dimer dangling bond to form more stable mono coordinated Si-F bond. We calculated activation barriers and equilibrium surface configuration as a function of fluorine coverage upto 2.0 ML. We compared the stability of the fluorinated surface. The results were compared with existing experimental and theoretical results. The reaction of water with HF treated Si surface is monitored. It produces, as a first step, the exchange of Si-F with water to form Si-OH groups reducing the concentration of the fluorine on the surface, followed by a rapture of Si-Si bonds and finally the Si-O-Si bridge formation in the lattice.
Highlights
Chemical etching of silicon by fluorine plasma is one of the most important materials tailoring techniques in the manufacture of semiconductor devices[1,2]
As we find that the direction of the dangling bond is outward from the Si dimer bond, it looks Si-F mono coordinated bond formation is more feasible
It forms a stable bridge bond (3.0 eV) with a Si dimer. This shows the greater stability of the dangling bond, which further indicates the feasibility of the fluorine approach towards the dangling bond direction
Summary
Chemical etching of silicon by fluorine plasma is one of the most important materials tailoring techniques in the manufacture of semiconductor devices[1,2]. The adsorption and reaction of both molecular and atomic fluorine with the Si (100) surface has been examined by Engstrom et al[10] under ultra high vacuum conditions with supersonic molecular beam techniques, X-ray photoelectron spectroscopy, quadrupole mass spectrometry and low-energy ion-scattering spectroscopy They observed that adsorption probability of F (g) exceeds that for F2 (g) by approximately two orders of magnitude. In another study with ab initio derived molecular dynamics[28], it was pointed out that many different paths of reaction are competing e.g., fluorination of dangling bonds, breaking of dimer bonds and attack of subsurface Si atoms This leads to the concurrent formation of adsorbed SiF, SiF2 and SiF3. We propose a plausible mechanism of the initial stage of fluorine etching to explicitly monitor the role of water in the etching phenomenon
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