PhysicaC 175 (1991) 310-314 North-Holland Substrate bias effects during in situ growth of Y ,Ba2Cu307_-6 thin films by RF magnetron sputtering R. Pinto, J.I. Poothra, S.P. Pai, L.C. Gupta and R. Vijayaraghavan i’hta Institure qfFundamenral Research, Horni Bhahha Road, Bomhaj, 400 005, India Dhananjay Kumar and M. Sharon Chemu/r): Department, Indian Instlrute q/Technolog~.. Powal. Bornhay 400 076. India Received 26 November 1990 Revised manuscript received 14 February 199 I Superconducting Y,BazCu,O,_, thin films have been grown in situ by RF magnetron sputtering using a planar YBaCuO target with and without RF bias on the substrate. RF bias on the substrate has been found to have a significant effect on the composition of the sputtered film. While the Y and Ba contents in the film have been found to slightly decrease with increasing RF bias on the substrate, the Cu content has been found to increase significantly and approach that of the target at - 30 V substrate bias. The increase in Cu content of the film with increasing substrate bias has been attributed to a decrease in secondary electron bombard- ment of the film which increases the sticking coefficient of Cu atoms and does not affect that of Ba atoms at the applied substrate bias and temperature range. Nevertheless, low substrate power levels of 20 W have given films of improved thickness and com- positional uniformity. Films grown in situ at 65O’C on ( 100) MgO and at 680°C on ( 100) SrTiOl substrates have shown L, values of 80-82 K and a critical current density of 10’ A cm-* at 70 K. 1. Introduction One of the well known problems associated with the sputtering technique used for the growth of Y, BazCu@_,s ( 123 ) films is backsputtering caused by negative ions [ l-3 1. Since oxygen has a high ten- dency to form negative ions, the problem is very se- vere during in situ growth processes where high par- tial pressures of oxygen are used in the sputtering gas [ 4-61. The two most important solutions for elim- inating or minimizing the backsputtering problem are off-axis sputtering [ 7,8] and cylindrical hollow cathode sputtering [ 9, IO]. Both have significant dis- advantages: while the former involves complex sub- strate holders, especially for in situ growth, the latter requires a complex cathode. Therefore, planar ge- ometries with low target bias and use of magnetron mode at high sputtering pressures to thermalize the negative ions are attractive due to their simplicity [ 4,5 1. However, off-stoichiometric targets are gen- erally required. Therefore, use of RF bias on the sub- strate can have significant potential in controlling the composition and uniformity in planar geometries in- volving single composite targets. Drehman and Du- mais [ 1 1 ] have reported substrate bias effects in a planar RF diode configuration. The purpose of this paper is to report the effect of RF bias on the sub- strate during in situ growth of 123 films from a planar RF magnetron cathode. 2. Deposition process A 100 mm diameter planar target with a compo- sition Y,Ba3Cu50, was used. The required target composition was found empirically by estimating the loss of Ba and Cu in the film sputtered from a 123 target without substrate bias. The Y, Ba3Cu50, tar- get was prepared by compacting an appropriate mix- ture of 123 power, BaO and CuO into a flat disc and sintering it at 920°C for 12 h. A parallel plate RF magnetron sputtering system was used. The sputter- 092 l-4534/91 /$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)