Treatment of organic polymer surfaces by CF4 plasmas: Etching by fluorine atoms and influence of vacuum ultraviolet radiation

Previous works have shown that atomic fluorine is the main etching agent of organic polymer surfaces subjected to fluorinated plasma treatments. In th is work the etching probability per F atom impinging on a polymer-like mate rial (hexatriacontane C36H74, a model molecule for high density polyethylen e) has been estimated from direct measurements of the etching rate using a quartz crystal microbalance and from the absolute F atom concentration usin g threshold mass spectrometry. This etching probability has roughly the sam e value as the sticking probability of F atoms on this surface, which is in the range of 1%-3%. It has been pointed out that the reactivity of the sur face with respect to F atoms is enhanced when the polymer surface is seen b y the plasma. This could be due to either ions or vacuum ultraviolet (VUV) radiation. To more fully understand this point, we have built an external i ndependent VUV source to irradiate the sample and we have used threshold io nization mass spectrometry to monitor the F atoms kinetics. The simultaneou s irradiation of the substrate by VUV increases by a factor of 2 the reacti vity of the substrate with respect to F atoms. (C) 2001 American Institute of Physics.