Effect of the deposition process on the composition and structure of sputtered lanthanum cuprate films

Abstract La-Cu-O thin films were deposited by two different methods. As a first process, the films were deposited by co-sputtering of metallic copper and lanthanum targets in various Ar-O 2 reactive mixtures. The oxygen flow rate introduced into the deposition chamber was optimised to fully oxidise the sputtered atoms. The atomic ratio La/Cu in the film was adjusted by the variation of the pulsed DC current applied to the copper target. Within this process, the experimental window range for successful synthesis of films with the expected La/Cu ratio was found to be very narrow. The second process, namely, reactive sputtering of a composite La-Cu target, showed easier control of the film composition. The La/Cu atomic ratio was strongly dependent on the composite target that evolved during the use of target. Whatever the deposition process, an annealing step in air was necessary to obtain the crystalline La 2 CuO 4 phase. To find the temperature of crystallisation, a sample was annealed successively from 100 to 600 °C by step of 100 °C, plus an annealing at 800 °C. The crystalline nature of the sample was ensured by X-ray diffraction measurement after each annealing.