Atomic nitrogen source for reactive magnetron sputtering

A source of nitrogen atoms is developed in order to use them as reactive species in magnetron sputtering. For that a microwave discharge is used: an electromagnetic surface wave launched by a surfaguide (J. Phys. D: Appl. Phys. 24 (1991) 1025) in a quartz tube sustains a plasma. The surface wave is reflected at each end of the tube by silver reflectors. The length of the plasma column is therefore limited and the power density is raised when the injected power increases. The pressure range in the discharge tube is fixed by a diaphragm adjusted between the discharge and the post-discharge. A differentially pumped quadrupole mass spectrometer samples the gas composition in the post-discharge chamber. The dissociation rate is determined by following the lowering of the molecular nitrogen signal when the plasma is ignited. The molecular beam coming from the post-discharge is chopped before entering the ionisation source of the spectrometer and the signal detection is made by a lock-in amplifier. The following parameters were varied for different flows and compositions: (i) the discharge pressure: by changing the diameter of the diaphragm between the discharge and the post-discharge, it can be varied from approximately 666 to 4000 Pa; (ii) the length of the discharge tube: 300 and 600 mm. Optical emission spectrometry measurements on the post-discharge have been made to validate the mass spectrometry measurement method.