Crystallization of Amorphous Titanium Oxide Thin Films by Pulsed UV-Laser Irradiation
- PDF / 1,011,153 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 16 Downloads / 219 Views
1kV 20rnA (Ar gas;2-3SCCM) 15cm 2 15cm Ti-metal (75mm in diameter) 1 X 10-4torr room temperature 0.5nm/min 447
Mat. Res. Soc. Symp. Proc. Vol. 397 01996 Materials Research Society
The UV light irradiation was conducted with a KrF excimer laser with a wavelength of 248nm. The laser light was pulsed to 20nsec (FWHM), and irradiated on the surface of the Ti-O films at 10Hz typically. The laser energy density was 20-6OmJ/cm 2 at the film surface. The optical properties were investigated between 200-800nm in wavelength. Crystal structure of the films was identified by X-ray diffraction (XRD) analysis. The microstructural changes induced by the irradiation were investigated using transmission electron microscopy (TEM). The binding condition of Ti-O in the films was investigated by X-ray photoelectron spectroscopy (XPS) and by analyzing the extended X-ray absorption fine structure (EXAFS) obtained in the synchrotron facility of the KEK in Tsukuba, Japan. Effects of the irradiation on the electrical properties were investigated by depositing the Ti-O films on a SAW filter, which is very sensitive to the conditions of the substrate surface [5-7]. The deposited of thin films induce a frequency shift depending on a thickness, the Young modulus, the Poisson's ratio and the residual stress of the films [8, 9]. In this study, Ti-O films were deposited on a 315MHz-SAW filter. The SAW filter is composed of an ST-cut quartz as a substrate and several hundred Al electrode fingers for oscillating and detecting the surface acoustic waves. An oscillator circuit was constructed with a filter and an amplifier. The frequency of the microwave resonating in the circuit was measured by a frequency counter and a spectrum analyzer. The frequency was defined as the "center frequency" of the SAW filter. The measurement was carried as the laser pulses were irradiated on the film deposited on the SAW filter. EXPERIMENTAL RESULTS AND DISCUSSION The XRD analysis revealed that the crystal structure of the as-deposited films is in amorphous state. Figure 2 shows transmission spectra of as grown Ti-O films on fused glass substrates. It was observed that these films have an optical band gap around 300nm in wavelength, though the gap is not well defined. In general, a single crystal of TiO 2 with the "rutile type structure" has a clear gap at 420nm. At 248nm, which is the wavelength of the laser light, the absorption coefficient was about 5.6x 105 cm-1. UV-laser pulses were irradiated on the as grown films. However, there was little change in the optical transmission shown in Fig. I and in the results obtained by XRD analyses before and after the irradiation.
100 lOO
U
.
' '0 0 ...
.
I..
.
. .
0
402
3
4
300
400
0 0 20
0200
500
Wavelength
600
700
800
(nm)
FIG.1. Transmittance of as-grown Ti-O films on fused glass. Film thickness ;(a)10mn. (b)20nm and (c)50nm.
448
In order to investigate the microstructure of the films, TEM analysis was carried out for the specimens composed of the Ti-O film on ST-cut quartz substrates. Figures
Data Loading...
