Enhancement of downstream plasma density by a stepped-diameter radiofrequency plasma source under a static magnetic field for a compact sputtering reactor

A stepped-diameter insulator source cavity is employed to a radiofrequency (RF) plasma source for development of a sputtering reactor, where an inner diameter near the open source exit is enlarged compared with the upstream diameter and convergent-divergent magnetic field is applied near the source exit to inhibit the plasma loss to the wall by separating the plasma from the wall. Furthermore argon gas is introduced at the interface between the different diameter regions; a high plasma density of ∼5 × 10 ¹⁷ m ⁻³ can be obtained at ∼50 mm downstream of the source exit for an RF power of about 100 W. To enhance the sputtering performance, a permanent magnet is installed behind the target located downstream of the source and a target current can be increased. The results on the plasma density and a deposition rate of Cu film on a substrate are compared for different source cavities and gas injection locations, which confirm the validity of the stepped-diameter source cavity on the performance improvement of the sputtering reactor.