The Influence of Target-Substrate Bias on Pulsed Laser Deposited Yba 2 Cu 3 0 7-6
- PDF / 294,825 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 107 Downloads / 184 Views
THE INFLUENCE OF TARGET-SUBSTRATE BIAS ON PULSED LASER DEPOSITED YBa 2 Cu 3074 D.B. Chrisey, J.S. Horwitz, K.S. Grabowski, M.E. Reeves, M.S. C.R. Gossett 20375-5000 Naval Research Laboratory, Washington, D.C.
Osofsky, and
ABSTRACT We have deposited YBa 2 CU307 _6 thin films onto SrTiO3 substrates at 700°C as a function of target-substrate bias (0 to 300 V) in order to make use of the positive ions in the laser produced plume to assist in the determine deposition. The films were extensively characterized to differences in film properties (composition, structure, and transport). The results suggest that film properties were optimized at or near a targetsubstrate bias of 100 V, although, the differences in film properties were within the margin of reproducibility.
Pulsed laser deposition (PLD) has quickly been recognized as the primary technique for in situ deposition of the high temperature superconductors, in part, because it offers many advantages not available through conventional physical vapor deposition (PVD) techniques (i.e., magnetron sputtering, e-beam coevaporation, etc.) [1,2]. These advantages include the rapid production of smooth films and stoichiometric deposition from a single target in a high background pressure (-100 mtorr) of oxygen. An additional benefit is the hyperthermal energy distribution of ejected species (-1-10 eV) which aids in lowering the substrate processing temperature [3,4]. Attempts have been made to lower the substrate processing temperature further by modifying the basic process, e.g., introduction of a biasing ring either for incorporating an oxygen plasma [5] or to expose the laser-produced plume to an electric field [6]. In this paper we characterize the dependence of film properties on the target-substrate bias between 0 V (no bias) and 300 V. The goal of this effort was utilization of the positive ions present in the laser-produced plume to assist in the deposition. The process of ion beam assisted deposition (IBAD is defined as the process whereby PVD deposited atoms are simultaneously struck by a flux of low energy ions) is known to result in better adhesion and cohesion of the film, modified residual stress, and increased density in addition to lowering the substrate processing temperature for various phases [7]. Therefore, the hope was that by applying a substrate bias, laser-produced positive ions would enhance the PLD film quality.
The apparatus used for PLD of YBa.Cu 30 7 6 thin films included a KrF
excimer laser (A-248 nm) operated at 4 Hz and focussed onto a rotating 2 YBa 2 Cu 3 0 7 _6 pellet to an energy density -2 J/cm . The target-substrate distance was -3 cm. The axis of rotation of the pellet holder was at an angle of 45* with respect to the beam direction. In order to deposit superconducting material uniformly over larger substrate areas the pellet was mounted at a 17° tilt angle with respect to the rotation axis. The laserproduced plume would thus wobble rather than just rotate, depositing material uniformly over larger areas. The SrTi0 3 substrates were
Data Loading...
