Polishing effect of the plasma on the growth of YBa2Cu3O7−δ films by radio frequency sputtering

Abstract

The surface morphology of YBa2Cu3O7−δ (YBCO) films is crucial for applications such as multilayering and optical detection. In this article, we showed that the resputtering effect due to the rf plasma can planarize the surface morphology of YBCO films under specific conditions. By setting the relative position and angle of the heater to the gun, the plasma density over the substrate can be altered from an asymmetric to a symmetric distribution. When the substrate was near the plasma, the negative oxygen ions resputtered part of the mobile atoms from the surface of the film back into the plasma, which caused compositional distortion, delaying the merge of grains and leaving uncovered holes. With a longer distance, the resputtering effect was suppressed, and precipitates appeared on the surface of films, resulting in a rougher surface. At an optimum heater-to-gun configuration, the function of the resputtering effect produced a polishing effect on the surface of films, which made a smooth and precipitate-free YBCO film possible. We also found that this film with smooth and precipitate-free morphology exhibited suppressed superconductivity, Tc0 and Ton.