Rf Hollow Cathode Plasma Jet Depopsition of Ba x SR 1-X TI0 3 Films
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RF HOLLOW CATHODE PLASMA JET DEPOPSITION OF BAXSR1-XTI03 FILMS N.J. IANNO1, R.J. SOUKUP1, Z. Hubička2, J. Olejníček2, and H. Šíchová2 1
Department of Electrical Engineering, 209N WSEC, University of Nebraska-Lincoln, NE 68588, USA; and 2 Institute of Physics ASCR, Na Slovance 2 182 21 Prague 8 Czech Republic Abstract An initial study of the RF hollow cathode plasma jet deposition of BaxSr1-xTiO3 has been performed. Deposition occurred from a single composite nozzle consisting of BaTiO3 and SrTiO3 at substrate temperatures on the 500-550 C range. It has been shown that film composition can be easily controlled by the nozzle composition as well as other deposition parameters. The as-deposited films exhibit clear BSTO peaks with grain size on the order of 30nm. Introduction Ferroelectric thin films have attracted considerable attention since they have application in dynamic random access memories (DRAM), non volatile memories, electro-optic switches, and most recently tunable phase shifters.1-4 Barium strontium titanate (BST) combines the merits of the high permitivity of BaTiO3 with the structural stability of SrTiO3 and therefore is an excellent choice for the above applications.5 We have developed a new technique for the deposition of high quality semiconductor material, and in this work we apply it to the deposition of BST.6-8 This technique is a hollow cathode plasma jet deposition. It has been used by others to deposit TiN, Ge3N4, LiCoOx and most recently we have improved the method to yield device quality a-Si:H, and a-SiGe:H. 6-12 We have deposited BST via this technique on bare silicon and Pt coated silicon wafers. We will report on the film composition as a function of the deposition conditions and post deposition processing. Experimental Appartus The low pressure plasma jet configuration for BST thin film deposition can be seen in Fig 1. The reactor chamber was continuously pumped. A cylindrical composite nozzle consisting of SrTiO3 and BaTiO3 is mounted inside a water cooled copper block. This copper block is also the electrical contact to an RF source operating at 13.56MHz. The working gas is Ar+O2 which flows through the nozzle and is controlled by electronic mass flow controllers. When driven by the RF source an intense hollow cathode discharge was generated inside the nozzle which reactively sputters the nozzle material.13 The flowing working gas forces the plasma and sputtered material out into the chamber where deposition occurs on the substrate. The internal diameter of the nozzle was 3 mm and the total length was 30 mm. In order to deposit BaxSr1-xTiO3 thin films the nozzle was composed from two parts as can be seen in Fig 1. Since it was known that STO has a lower sputtering rate than BTO, the STO portion was placed at the nozzle outlet where the hollow cathode plasma has the highest density. Previous work has shown the composition of the deposited material is a strong function of the length ratios.14
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Based on those results the length of the STO portion was set at 25 mm while the
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