Quantum Mechanical Investigation of the Influence of the Local Environment on the Vibrational Properties of Si(111)-H

M. F. JUAREZ; E. M. PATRITO; P. PAREDES OLIVERA

Niza

Congreso; 61st annual meeting of the international society of electrochemistry: electrochemistry form biology to physics; 2010

International Society of Electrochemistry

Vibrational spectroscopy is among the most powerful probes of fundamental processes in microelectronics. In particular, infrared (IR) absorption spectroscopy provides insight into critical aspects of silicon surface structure and reactivity through analysis of the vibrational frequencies, band intensities, and line shapes. Changes in the surface infrared spectrum upon reactive exposure can be used to extract information concerning the chemical identity, surface coverage, and dynamic properties of the surface layer. The Si-H stretching vibration of the Si(111)-H surface gives one of the narrowest lines observed up to now in vibrational surface spectroscopy and reflects the high quality of this surface [1]. The close spacing of surface adsorbates has a pronounced effect on the vibrational spectrum because the motion of an individual oscillating dipole is influenced by the electric dipole field generated by the motion of its neighbors [2]. Also, subsurface oxidation produces changes in the Si-H stretching vibration, observed as broad bands at higher energies [3]. The effect of the different adsorbates on the polarization of the electron density of the SiH group and on the electronic structure of the surface was investigated by means of density functional theory calculations. The Si-H stretching frequency increases with the surface coverage of -CCH and -Cl species, and it decreases with the increase in the surface coverage of -CH3. Positive (negative) frequency shifts correlate with the increase (decrease) of electron density along the Si-H bond [4]. The Si-H stretching frequency varies linearly with the Si-H bond length for all the systems investigated. The Si-C, C-H, and Si-Cl stretching frequencies increase linearly with the surface coverage of the -CH3, -CCH, and -Cl groups. The back-bond oxidation of a SiH group produces an increase in its stretching frequency and a decrease of the stretching frequency of the surrounding unoxidized SiH groups. All the calculated frequencies show very good agreement with the experimental values.