Optical Emission Spectroscopy of BaxSr1-xTiO3 Thin Films Deposition

Pulse modulated hollow cathode RF plasma jet system was used for deposition of BaxSr1-xTiO3 (BSTO) and SrTiO3 (STO) thin films on Si and on multi-layer Si/SiO2/TiO2/Pt substrates. Optical emission spectroscopy was used for control of concentration of particles sputtered from the hollow cathode. Relation between ratio of spectral intensity of Ba, Ba, Sr and Sr lines and ratio of Ba and Sr concentration in the deposited film was found. Deposited thin films were analyzed by X-ray diffraction, which confirmed presence of BSTO and STO perovskite phase in the films. All films with high enough Ba concentration (0.5 ≤ x ≤ 0.9) prepared by low pressure RF plasma jet sputtering system exhibited good shaped dielectric hysteresis loops typical for ferroelectric phase. Introduction STO and BSTO films have wide applications due to their dielectric properties. Many methods were used up to now for BSTO films deposition [e.g.,Pervez et al., 2004; Im et al., 2002; Abe, 2001]. BSTO thin films can be used for capacitors due to their high dielectrical constant and are also very promising for microwave components as for example microwave varactors, phase shifters, or tunable filters. BSTO thin films are usually prepared by CVD, MOCVD [Weiss et. al., 2000], sol-gel [Jin et. al., 2000], or magnetron sputtering [e.g.,Pervez et al., 2004; Im et al., 2002]. Usual methods use elevated substrate temperatures above 600–900 °C or thermal post-deposition treatment for proper crystallization and oxidation of BSTO films. In this work the development of RF hollow cathode plasma jet sputtering system for high quality STO and BSTO thin films fabrication and their characterization including first dielectrical and optical properties studies are presented. Among others some results of optical emission spectroscopy performed during deposition process are presented too. Ferroelectrical properties of BSTO films seem to be bound on concentration of Ba and Sr and their proportion nBa/nSr in the resulting film. By means of optical emission spectroscopy it is possible to control ratio of Ba and Sr in plasma jet and therefore in the film too. Experiment Figure 1 shows the plasma jet configuration used for STO and BSTO thin films deposition. The reactor chamber was continuously pumped by combination of Roots and rotary vane pump during the deposition. BSTO films were deposited on silicon substrate coated with Pt/TiO2/SiO2 and on bare Si substrates. For deposition of SrTiO3 thin films the nozzle was made of pure SrTiO3 ceramic. In order to deposit BaxSr1-xTiO3 thin films one part of the nozzle was made of SrTiO3 and one part from BaTiO3, as it can be seen in Fig 1. Since it was known that STO ceramics has lower sputtering rate than BaTiO3 (BTO) ceramics, the STO part was placed at the nozzle outlet, where the hollow cathode plasma has the highest density. The internal diameter of the nozzle was 3 mm. The length of the nozzle was 30 mm. The STO part was also made longer than the BTO part. The length of the STO part was 25 mm and the length of the BTO part was 5 mm. WDS'05 Proceedings of Contributed Papers, Part II, 402–407, 2005. ISBN 80-86732-59-2 © MATFYZPRESS