Duo-Plasmaline — a linearly extended homogeneous low pressure plasma source

Abstract

A linearly extended plasma source — the Duo-Plasmaline — was developed. It can be used in a large frequency and pressure range. The plasma is excited by microwaves of 2.45 GHz at a pressure <1000 Pa (10 mbar). In the Duo-Plasmaline device the microwaves are fed into the vacuum chamber from both sides of a waveguide, consisting of a copper rod as inner conductor and plasma produced outside of a quartz tube forming the outer conductor. The microwave propagates mainly in the space between the inner rod and the quartz tube filled with atmospheric pressure. This plasma source allows the production of an extended homogeneous plasma up to several meters, the length of the plasma column can easily be controlled by the microwave power. The plasma parameters were measured in dependence on the axial and the radial distances from the plasma source: electron density and electron temperature by a Langmuir probe, microwave intensity by a pick up probe. It is shown that an excellent homogeneity of the electron density can be achieved along the axis of the plasma source. In the radial distance the electron density decreases nearly exponentially. A further result is that the microwave field is radially shielded by the electron density of 2×10 11 cm −3 produced near by the surface of the quartz tube. The etch rate of polymethylmethacrylate (Plexiglas®) in an oxygen plasma and the deposition of quartz-like films produced in a plasma of hexamethyldisiloxane and oxygen as monomers show also an excellent axial homogeneity. This newly developed plasma source is well suited for large area plasma treatment, e.g. coating, etching, cleaning and surface modification. Two-dimensional plasma devices can be obtained by an array of individual plasma sources of the described type.