Raman Spectroscopy of Tin Films Deposited on Silicon (001) Substrate by Laser Physical Vapor Deposition
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193 Mat. Res. Soc. Symp. Proc. Vol. 317. ©1994 Materials Research Society
Table I. Raman scattering peaks in bulk polycrystalline titanium nitride Peak position (cm 1 )
Origin
Variation of peak ratio and position with nitrogen deficiency
200 300
Transverse acoustic(TA) Longitudinal acoustic(LA)
400
Second order transverse
500 520 to 580
acoustic (2TA) TA+LA Transverse optical (TO)
600
Second order longitudinal
800 1100
acoustic (2LA) LA+TO Second order transverse
Decrease Decrease
optical (2TO)
Decrease
Increase and shift to higher wavenumber Increase and shift to higher wavenumber Decrease Increase Decrease and shift to higher wavenumber
peaks observed in the stoichiometric and off stoichiometric TiN samples and the effect of nitrogen deficiency. The first order transverse acoustic peak TA(200 cm- 1 ) and longitudinal acoustic peak LA(300 cm- 1) arise because of the nitrogen deficiency (vacancies) so that the Ti atom vibrations contribute to a larger intensity of these peaks. These defect induced first order peaks have also been found to shift to a larger frequency with increasing nitrogen deficiency. The multiphonon peaks 2TA(400 cm- 1), LA+TA(500 cm- 1) and 2LA(600 cm1) are present only in the stoichiometric TiN. The defect induced first order transverse optical phonon peak TO(520-580 cm-1) arises because of the nitrogen ion vibrations near the titanium vacancies. The intensity of this TO peak decreases with higher nitrogen deficiency, although Ti vacancies may be present. In particular, this peak becomes smaller with increasing nitrogen deficiency and oxygen introduction. The multiphonon peaks, LA+TO (800 cm- 1 ) and 2TO (1100 cm- 1 ) are also found only with the stoichiometric samples. The scattering intensity of all these peaks decreases but the relative intensity of the acoustic to optical peaks increases with increasing nitrogen deficiency [4].
EXPERIMENTAL RESULTS Laser physical vapor deposition of TiN films on Si(001) substrate is carried out by ablation from a titanium nitride target using KrF excimer laser (wave length 248 nm, pulse duration 25 ns). The compacted and sintered very fine grain size target composition was close to 99.95 of the stoichiometric titanium nitride. A processing chamber with 10-7 torr base vacuum is used. The laser pulse energy density was chosen at 6 to 8 J/cm 2 to avoid particulate emission in the laser ablated plume. The thin films were deposited on a clean and hydrogen terminated Si(001) substrate kept 3-5 cm away from the target and the vacuum levels reached 10-6 torr during deposition. A pulse repition rate of 5 Hz was used to
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deposit thin films 50 to 100 nm in thickness. Deposition is carried out with the Si (001) substrate kept at different temperatures ranging from room temperature to 6000C. The films were characterized by scanning and transmission electron microscopy for crystalline quality, grain size and epitaxial growth, Auger spectroscopy for oxygen, nitrogen and titanium analysis, Raman spectroscopy for the first order defect induced scat
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