SILICON CONTAMINATION OF SUBSTRATES IN FLUOROCARBON PLASMAS PRODUCED PRODUCED IN GLASS REACTORS

Extensive research has been carried out in recent years using fluorocarbon plasmas for modification and depositions on polymer substrates. In some cases anomalous results have been obtained that are not explainable based on conventional fluorine chemistry. In this investigation pure polypropylene films were exposed to carbon tetrafluoride plasmas in a Pyrex glass reactor. At short reaction times (less than 1 min) significant amount of silicon was detected by ESCA on the surface of the films. Analysis of liquid nitrogen trapped fluorocarbon plasma gases and molecular fragments indicated high concentrations of silicon and carbon containing species, the former indicative of ablation and etching reactions of the glass reactor walls. The production of a relatively high quantity of fluorosilicon derivatives was explained by the greater affinity of silicon for fluorine than for carbon, with the tendency to readily form SiF4. These fluorosilicon radical and ionic species generated under cold plasma conditions can easily react with polymeric substrates causing unexpected surface modifications. In addition Si-F bonds could be readily hydrolyzed to SiOH islands on the surface of the substrate to impart anomalous characteristics. (C) 1994 John Wiley & Sons, Inc.