TRANSPARENT AND CONDUCTING ZNO(AL) FILMS DEPOSITED BY SIMULTANEOUS RF-EXCITATION AND DC-EXCITATION OF A MAGNETRON

RF magnetron sputtering of zinc oxide films (ZnO:Al and ZnO) is mostly used for the deposition of the window and contact layer for heterojun ction thin film solar cells. A drawback of this sputtering technique i s the small deposition rate. This is caused by the low DC voltage that develops at the target, since the sputtering rate in the energy range below 1 keV depends linearly on the acceleration voltage in the catho de fall. In order to increase the target voltage, a simultaneous excit ation by RF (13.56 MHz) and DC has been used. Excitation by DC increas es the deposition rate up to a factor of 1.5. On the other hand, RE-ex citation decreases the specific resistance significantly. The reason f or the better electrical properties of RF-sputtered films is the highe r energy of the ions (up to a factor of 2.5) that bombard the substrat e during the deposition. (C) 1998 Elsevier Science S.A.