Spectroscopic Ellipsometry and Raman Studies on Sputtered TiO2 Thin Films

Bojan Karunagaran ,  Kyunghae Kim ,  Suresh Kumar Dhungel ,  Jinsu Yoo ,  Devanesan Mangalaraj ,  Junsin Yi 

Sungkyunkwan University, School of Information and Communication Engineering, 300 Chunchun-dong, Jangan-gu, Suwon 440746, Korea, South

Abstract

Titanium dioxide films have been deposited using DC magnetron sputtering onto well-cleaned p-type silicon substrates at the ambient temperature at an oxygen partial pressure of 7x10-5 mbar and total sputtering pressure of 1x10-3 mbar. The compositions of the films were found to be stoichiometric (O/Ti=2.07) as analyzed by Auger Electron Spectroscopy (AES). The rms roughness of the film is evaluated as 4.8 nm using ex-situ atomic force microscopy.

Optical constants of the films have been determined by spectroscopic ellipsometry (SE) in the photon energy range 1.2 to 5.5 eV at room temperature. The measured dielectric-function spectra reveal that the distinct structures at energies of the E1 (3.53eV), E1+Δ1(3.97eV) and E2 (4.82eV) critical points are due to interband transitions. The dielectric related Optical constants, such as the refractive index, extinction coefficient, absorption coefficient and normal incidence of reflectivity are determined from the SE data and analyzed.

Films of thickness 140 nm are calcinated in air in a muffle oven for 1h at 673 and 773 K. After each calcination, the Raman spectrum was recorded. The frequencies of the Raman bands are identified as 637, 513, 396, 195.1 and 144.3cm-1. Using factor group analysis the 396 cm-1 peak is assigned to the B1g mode(ν4), 637cm-1 peak to the Eg mode (ν1), 513 cm-1 peak to the A1g + B1g modes (ν2 + ν3). It was observed from the factor plane analysis that the A1g (ν3) and B1g (ν2) modes both involve the Ti - O bond stretching normal to the film plane. The peaks at 195.1 and 144.3 cm-1are assigned to the Eg modes represented by ν5 and nu6. In the case of the annealed films, there is no significant change in the peak position and also the intensity of the peaks increases at the same time the FWHM decreases with the increase in the annealing temperature, which can be attributed to the improvement in the crystallanity,which is supported by XRD.

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Presentation: oral at E-MRS Fall Meeting 2004, Symposium G, by Bojan Karunagaran
See On-line Journal of E-MRS Fall Meeting 2004

Submitted: 2004-04-30 08:30
Revised:   2009-06-08 12:55
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