Design, operation mode, and stress control capability of S-Gun magnetron for ac reactive sputtering

In this paper, the design features, operation modes, and application capabilities of a new generation of the dual cathode S-Gun magnetron for ac (40 kHz) reactive sputtering are discussed. Due to its dual target arrangement and magnetic array configuration, the ac powered S-Gun is uniquely able to realize reactive sputtering processes free of parasitic arcing and disappearing anode effects thus enabling the formation of high quality dielectric films. The L-shaped magnetic array provokes the formation of a wide erosion zone covering the majority of the conical surface of the target. This prevents a build-up of thick dielectric films near the erosion zone allowing reliable arc-less operation of the S-Gun in a poison mode on a back branch of the hysteresis loop. The study has revealed that an effective approach to the process stability control can be based on the simultaneous use of discharge voltage, current, and applied ac power as a combined parameter for stabilization of the process work point. Using the internal shields as subsidiary passive anodes allows redistribution of the discharge current between the targets and the internal shields of the magnetron. A simplified model explaining how the current redistribution influences the substrate temperature and film stress by a controllable suppression of the flux of charged particles to the substrate is discussed. The effectiveness of this technique in stress control is demonstrated in conjunction with deposition of highly textured aluminum nitride films.