70 cm radio frequency hollow cathode plasma source for modification of foils and membranes

For industrial use long linear plasma sources are needed. Basing on a radio frequency (13.56 MHz) hollow cathode discharge (HCD) concept proved for 30 cm long cathodes, an upscaled version of the plasma source with cathode length of 70 cm was developed. Additional hollow anode plasma chambers allow easier switching to an HCD discharge mode. Holes between anode and cathode plasmas cause a local increase in the ion concentration by a factor of 40 (up to 2 x 10(11) cm(-3)). Homogeneity of the cathode plasma was examined by use of a double Langmuir probe technique. It improves with increasing number of holes distributed along the cathode trench. To characterize the process uniformity, polypropylene foil and cellulose membrane were used. Typical process conditions are RF power of 600 W, argon flow 60 seem, pressure in the process chamber 0.1 Pa. The contact angle measured with water on the polypropylene surface decreases from 100 degrees to 50 degrees after 2 s of treatment in plasma with ion concentrations of more than 2 x 10(10) cm(-3). The distributions of the contact angle over the foil width show minima for places of maximum ion concentration and are almost identical on both foil sides. The intensity of the spectral line at 308.6 nm wavelength was measured as a function of time after discharge ignition for determination of the water outgasing from the cellulose. The amount of water in the discharge correlates with the ion concentration. The second emission intensity maximum after about 7 s of treatment occurs at the position with highest ion concentration. The warming up of the membrane is the most probable reason for this effect. (C) 1997 Elsevier Science S.A.