Pulsed Laser Deposition of Epitaxial (110) TiN Films on (100) GaAs - Processing, Characterization and Modeling
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variation of the substrate temperature and the chamber pressure with time at the deposition temperature of 4500 C is presented in Figure 1.This variation with deposition time is observed at the other growth temperatures. The substrate temperature was increased during the first 5-7 minutes of the film growth at 400 - 450 C/min, followed by a slow ramp up at 100 - 140 C/min up to the stabillized temperature. The deposition was carried out for 40 minutes, followed by a slow cooling rate of 50- 80 C/min. It should be mentioned that after stabilization, the temperature increased by 400- 500 C due to a heat mirror effect [5], so that the substrate temperature increased to 5000 C at the end of deposition process.
400e
3 E"
Sta 300'3
2 E
0020 110
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60 Time (min)
8 s
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Figl. Variation of the deposition temperature (squares) and chamber pressure (circles) during (110) TiN film
growth on (001) GaAs by PLD technique.
The electrical resistivity of the TiN films on GaAs (100) was measured by four-probe technique. X-ray diffraction studies have been carried out on RIGAKU X-ray diffractometer using Cu-Ka radiation. Transmission electron microscopy studies have been carried out on TOPCON EM-002B, operated at 200 kV (spherical aberration coefficient - 0.5 mm, resolution - 0.18 nm). The Raman scattering spectra were obtained using Argon ion laser beam of 514.5 nm in the plane polarized mode and a SPEX 1704 spectrometer with a one-meter single monochromator giving a resolution of 0.5 A. The TiN films 300 - 400 A thick, were characterized for electric properties at room temperature by a four-point probe technique. The lowest room temperature resistivity - 49.7 gil-cm was measured in films grown at 4500 C, while the resistivity for the films grown at 3500 C was 136.1 RtQ-cm. A higher value of resistivity, 83.3 g.tl-cm, for the films deposited at 5500 C can be explained by the polycrystalline microstructure of the TiN film. The differences in the resistivity can be explained in terms of the grain size and stoichiometry at different deposition temperatures. The value of the resistivity was found to be very sensitive to changes in the process parameters. The microstructure and orientation of the TiN films have been characterized by X-ray diffraction as shown in Figure 2. At the three substrate temperatures, the (220) TiN peak is aligned with (hOO) peaks of GaAs, revealing that the predominant orientation is (110) TiN / (hOO) GaAs. In addition the very small (200) TiN peak present in the films deposited at 3500 C and 5500 C suggests texturing or polycrystalline nature of these films. The films deposited at 4500 C have not exhibited a (200) TiN peak and epitaxial growth with [1 10]TiN//[100]GaAs is achieved. Raman scattering has been performed to characterize stoichiometry of the TiN films. It is known that first order Raman scattering results from the phonon density due to defects (vacancies). In particular, the phonon density of states shifts to the higher frequencies when the nitrogen deficiency increases [6]. Th
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