반응성 DC 스퍼터링에서 방전 전류 및 산소 분압 변화에 의한 TiOX 박막 성장과 물성 연구

Abstract

Titanium oxide (TiOX) have a various physical and chemical properties with a reactive nature, which is controlled by crystallinity and stoichiometry. The growth of TiOx thin films with various oxygen contents has mainly been accomplished by varying the ratio of argon to oxygen partial pressure during the sputtering process. However, the reactive gas, oxygen, in a DC sputtering process is known to poison the metal target surface by oxidation. The oxidation degree of the target also influences the plasma discharge mode and thus the oxygen content and crystal structure of the metal oxide thin films. Therefore, in order to grow with controllable stoichiometry and crystallinity of the titanium oxide thin films, it is necessary to understand the relationship between the oxidized condition of the target and the thin film growth condition. In this study, titanium oxide (TiOX) thin films were grown under the constant current mode in reactive DC sputtering methods. The reactive oxygen gas flow was adjusted along with the plasma discharge current in order to achieve wide range of the target impedance which is a good indicator of the target oxidation. The oxidized condition of titanium target was identified with the change in the plasma discharge parameter by monitoring the discharge voltage and target impedance. The crystal structural properties of the thin films were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The chemical bonding structure and oxygen content of the TiOX thin films measured by X-ray photoelectron spectroscopy (XPS). Furthermore, the electrical transport property was studied by Hall effect measurement. Thin films grown in metal mode or transition region with relatively lower target impedance form the cubic TiO crystal structures containing amorphous titanium oxides while those in the oxidation mode form the amorphous TiOX thin film. In addition, the crystal size and crystallinity of the thin film increases with a lower target impedance. The TiOx thin films grown in the metallic mode and transition region include a multiple mixed phases of metallic Ti, TiO, Ti2O3 and TiO2, and the thin film formed in the oxidation mode shows only TiO2 phase. Consequently, as the oxygen content of TiOx decreases and the discharge current increases, the target impendence is suppressed but metallic phases of Ti, TiO, and Ti2O3 is developed. Furthermore, the electrical properties of the TiOx thin films indicate a p-type characteristics with a various charge carrier concentration and sheet resistance depending on the oxygen contents.