Paper VT-ThP8
Optimization of a Multitarget Sputtering System for the Production of Magnetic Tunneling Junctions and Multilayers

Thursday, October 18, 2007, 5:30 pm, Room 4C

Our work consists in a renovation project for an obsolete multitarget sputtering system, previously used for industrial purposes, in order to revert it to research objectives with a cost-effective operation, saving as many original components as possible. The system was equipped with a control rack, a large cylindrical vacuum chamber and a complete rotary / turbomolecular pump evacuation subsystem; substrates where inserted into a slit close to a vacuum oven by vertically lifting the whole chamber above the steel basement by means of an oleodynamic piston. The rotating oven slit was manually positioned above one of the three target sources allowing a rotation of 270°. Our newly realized system maintains the original control rack, the evacuation subsystem and the basement. A smaller cylindrical chamber has been designed in order to reduce both void spaces and evacuation time; all inner parts of the AISI 316L walls have been polished to minimize the outgassing rate while the opening is assisted by a vertical lift motor and performed only for scheduled maintenance, because a load-lock chamber is now connected to the operation chamber via a gate valve. This smaller buffer chamber has been designed either to insert and recover substrates or to serve as a second process chamber for the realization of tunneling barrier thin oxyde layers, where an oxygen line inlets the reactive gas and a sapphire window allows UV radiation to assist the critical step. Specimens are transferred to the carrying slit inside the process chamber via a magnetic manipulator; this slit is positioned above the desired sputtering source by means of an AC brushless motor operated by a remote control software. The rotating subsystem allows a full rotation (360°), the running cables being substituted by an ad hoc designed electrical rotating contact that ensures quite low electric field at contact point, no debris and appropriate friction during operation. A particular manual implementation allows one to choose between the simultaneous rotation of two coaxial axes and the movement of only one of them. The first axis is connected to the substrate slit and the other one to the shutter, which may interrupt the deposition process or interpose suitable masks to transfer geometries to the substrates. This solution ensures a higher vacuum level, with only one mechanical feedthrough, as well as much lower costs.