Polymer etching and deposition of amorphous silicon using a VHF coaxial helix plasma source

Coaxial helical resonators are used in the field of high-frequency engineer ing. Their favorable geometric construction suggests their utilization asa plasma source for etching and deposition The plasma source consists of a cy lindrical outer conductor, closed on one side, and a rotationally symmetric al inner conductor of spiral form (helix) measuring one-quarter of the wave length of the r.f. Using the electric and outer magnetic fields of the heli cal resonator, the plasma is generated within the resonator and above its o pen end. Copper-laminated polyimide foils were patterned (6-12 Pa pressure, O-2/CF4 atmosphere: 20% CF4 in O-2, 100 seem gas flow, r.f.: 40.68 MHz 200 W, r.f. bias: 13.56 MHz 300 W). The distance between the plasma source and the polymer varied from 50 to 150 mm. The polymer thickness was 50 mu m, a nd this was masked by a 5-mu m copper layer. Etch rates of up to 1.65 mu m min(-1) were obtained. Deposition experiments of amorphous silicon (25-400 seem silane flow, 1000 seem helium flow for dilution, 6-20 W r.f., 20-40 Pa pressure,no r.f bias, 350 degrees C substrate temperature) resulted in dep osition rates of 3.6-10 mu m h(-1). The maximum thickness uniformity error was 5%. (C) 1999 Elsevier Science S.A. All rights reserved.