In this paper the preferred orientation of ZnO thin films grown on Si (100) substrates by radio frequency(RF) magnetron sputtering has been studied. At first, ZnO thin films were deposited at various temperature(200℃ - 300℃) and RF-input power(100 W - 200 W). At second, ZnO thin films were deposited for various time duration(15 seconds - 20 minutes) at 200 W - 300℃ which was the optimum condition for c-axis orientation according to the former results. And the dependence of c-axis orientation on film thickness and growth behavior has been investigated by X-ray diffraction(XRD) and transmission electron microscopy(TEM).
The orientation of ZnO films deposited at 200℃ was mixture of $(10\overline{10})$, (0002), and $(10\overline{11})$, but the films deposited at 300℃ had only (0002) orientation. The c-axis orientation of ZnO thin films grew better as increasing substrate temperature and RF-input power, but the property was more dependent on substrate temperature rather than on RF-input power. Highly c-axis oriented (0002) ZnO thin films of which the standard deviation of X-ray rocking curve was less than 3˚ were deposited at 200 W - 300℃.
The films deposited at 200 W - 300℃ for more than 2 minutes were c-axis oriented according to the X-ray diffraction analyses, but we could'nt know the properties of the films deposited for less than 1 minute by X-ray diffraction. Transmission electron microscopy study indicated that the films deposited for 15 seconds and 30 seconds were polycrystalline state with random orientation and the films deposited for 1 minute were c-axis oriented. According to the cross sectional transmission electron microscopy micrographs, the films deposited for 30 seconds had about 3 nm thickness. The films had random orientation, but high-resolution transmission electron microscopy micrograph showed that they had partially c-axis oriented grains. The films deposited for 1 minute had about 9 nm thickness and c-axis oriented ZnO was grown on the surface region of amorphous $SiO_2$. We considered that these results were caused by re-arrangement which was due to high substrate temperature promoted annealing effects.
We observed from the films deposited at 200 W - 300℃ for more than 20 minutes that c-axis orientation of polycrystalline ZnO thin films was determined at initial state of growth, and highly c-axis oriented columnar grains of which the surface flatness were less than 20 nm grew continuously from the region of initial layer to about 240 nm thickness.
