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Experimental and numerical study of the plasma in coaxial capacitive coupled radio frequency discharge

A coaxial configuration of discharge is proposed for plasma surface treatment and possibly other applications. The reactor is based on a cylindrical structure, with the inner cylinder radio frequency powered (RF, 13.56 MHz) and the outer cylinder grounded, playing the role of a guard ring. The charged species can escape from the inner cavity through two longitudinal slits made in both cylinders, aligned to each other, and producing a linear slab of plasma. Hence, it is possible to project the plasma directly onto a surface placed under the slits, called external plate. The operation of this device is uniform and stable in argon for a large pressure range (0.8–50 mbar). Furthermore, simulations using the Plasimo™ software package were performed to evaluate the plasma parameters and to explain the experimental results. The ion flux on the surface exposed to this plasma increases when RF power increases, and the pressure or gap distance to the plate decreases. This cylindrical capacitive coupled plasma configuration can be very effective for surface treatment of different materials (conductors or insulators) on large area (when the plate or the system is moving perpendicular to the slits) due to energetic ions and active species released from the plasma.