Excitation frequency effects on rf magnetron sputtering of YBa2Cu3O7−δ thin films

Abstract

Effects of an excitation frequency on on-axis rf magnetron sputtering have been studied for fabrication of YBa2Cu3O7−δ thin films on MgO (100). The excitation frequencies examined are 13.56, 40.68, 67.80, and 94.92 MHz. Sputtering was performed in a pure argon gas in order to distinguish excitation frequency effects of oxygen emitted from a target from those of oxygen in a mixture atmosphere. Excitation frequencies higher than 40.68 MHz result in both a low self-bias voltage and a narrow distribution of the energy of sputtering ions, which reduce resputtering of a film surface caused by negatively charged oxygen from the target. Thin films of a-axis oriented YBa2Cu3O7−δ deposited at 94.92 MHz have shown better morphology and crystallinity than those at lower excitation frequencies under the same conditions. Furthermore, a-axis oriented superconductive YBa2Cu3O7−δ films have successfully sputtered in 200 mTorr atmosphere of argon and oxygen on SrTiO3 (100) by using an excitation frequency of 94.92 MHz, showing a full width at half maximum of 0.1° in the rocking curve through the (100) peak and a very smooth surface. The zero resistance temperature is, at most, 33 K.