Optimizing deposition parameters for the growth of YBCO thin films via RF magnetron sputtering

Abstract

Thin films of YBCO were grown via radio frequency (RF) magnetron sputtering from a single oxide target. Targets of different stoichiometries (Y:Ba:Cu ratios of 1:2:3, 1:3:4, 1:3:5, 1:4:5, 1:4:6) were made through the conventional solid state method. Appropriate amounts of Y₂O₃, BaCO₃ and CuO were mixed and sintered; 1" diameter and 0.125" thick pellets were formed by pressing 6.20g of resulting powders under a pressure of 8 tons for 5 minutes. The films were sputtered onto a MgO substrate using 50W of forward power. 50% Ar-50% O₂ and 100% Ar were used as sputtering atmospheres. The as-grown films were black-brown with a glassy surface. X-ray diffractometery (XRD) revealed the films to be very thin and not of crystalline structure. The films were relatively smooth with few protruding grains as shown by SEM. Energy dispersive X-ray analysis (EDAX) revealed that most of the deposited films was composed of copper for all different targets used. It was found that the above conditions do not produce films of a 1:2:3 stoichiometry. The low forward power together with the electropositive property of yttrium and barium prevented sufficient deposition of these materials on the substrate.
A current study is being done, using a fixed target of 1:2:3 ratio, to sputter on SrTiO₃ at substrate temperature of 500°C and Ar ambient atmosphere. Forward power is being varied at 20 and 50 W, depositing for a longer time at the lower power. The rate of target degradation increased as the forward power was increased thus limiting the duration for sputtering.