Linearly extended plasma source for large-scale applications

A linearly extended plasma source - the Duo-Plasmaline - is characterised. The plasma is excited by microwaves of 2.45 GHz in a pressure range between 5 and 500 Pa. The device is similar to a coaxial wave guide. A quartz tube conveys through a vacuum chamber. A copper rod centered in the quartz tube is the inner conductor, and the plasma produced in the low-pressure regime outside the quartz tube represents the outer conductor. The microwaves are fed from both ends of the quartz tube into the wave guide and propagate mainly along the inner rod and the tube, filled with air at atmospheric pressure. The device generates a linearly extended plasma up to several meters, mainly controlled by the pressure and microwave power. The plasma source used here is expanded by a second parallel quartz tube both mounted and supplied parallel as a double line system. A sample stage movable perpendicular to the plasma source was mounted. The plasma was characterised for different plasma conditions by measurements of the electron density in relation to the axial and radial distances from the plasma source. The excellent axial homogeneity of the electron density is reflected in the homogeneous axial distribution of the etch rate of polymethylmetacrylate in an oxygen plasma. Also, the axial homogeneity of the deposition rate of quartz-like films polymerised in a plasma from hexamethyldisiloxane (HMDSO) and oxygen, is demonstrated. The newly designed linear plasma source is well suited for large-area plasma treatment and coating. (C) 1999 Elsevier Science S.A. All rights reserved.