Effects of X-ray radiation on the surface chemical composition of plasma deposited thin fluorocarbon films M. Himmerlich a , V. Yanev b , A. Opitz c , A. Keppler a , J.A. Schaefer a , S. Krischok a, * a Institut fu ¨r Physik and Institut fu ¨r Mikro- und Nanotechnologien, Technische Universita ¨t Ilmenau, P.O. Box 100565, 98684 Ilmenau, Germany b Fraunhofer Institut fu ¨r Integrierte Systeme und Bauelementetechnologie, Schottkystraße 10, 91058 Erlangen, Germany c Institut fu ¨r Physik, Universita ¨t Augsburg, 86153 Augsburg, Germany Received 3 August 2007; received in revised form 7 December 2007; accepted 12 December 2007 Available online 23 December 2007 Abstract Different thin fluorocarbon (FC) films were deposited on Si(111) using plasma polymerisation and then exposed to X-ray radiation. Changes in the chemical composition of the deposited fluorocarbon films as a function of irradiation time were investigated in situ using X-ray photo- electron spectroscopy. The evaluation of the C1s and F1s core level induced emission as a function of exposure to X-ray radiation (Mg Ka, hn ¼ 1253.6 eV) reveals changes in the surface chemical composition of the FC polymer structure. The presented results indicate a high defluori- nation under X-ray irradiation. Additionally, binding energy shifts of the F1s and C1s peaks during the exposure associated with surface charging effects were observed. With ongoing exposure the surface charging decreases continuously and the FC surfaces become more conductive due to changes in the polymer structure. Different models have been used to describe the decomposition kinetics and surface composition. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Fluorocarbon films; Plasma polymerisation; X-ray irradiation; X-ray photoelectron spectroscopy; Fluorocarbon degradation 1. Introduction The plasma polymerisation of thin films from fluorinated monomers (such as tetrafluoroethylene C 2 F 4 , tetrafluorome- thane CF 4 , hexafluoroethane C 2 F 6 , trifluoromethane CHF 3 etc.) has been investigated recently with great interest [1e8]. These polymers are PTFE-like (PolyTetraFluoroEthylene- like) and are used as passivation and protection films [3,9], anti-wetting and anti-sticking layers [9,10], and biofunctional coatings [2,3,11]. In the field of electronics, these films are particularly interesting as passivating and electrical insulating layers in electronic devices [12], interlayer dielectrics for the next generation of multilevel integrated circuits [13,14] and optical coatings for integrated optical devices [15,16]. For possible applications, e.g. as aerospace sensors and detectors, X-ray sensors in computer tomography, detectors in nuclear radiology and nuclear reactors, these materials have to sustain X-ray radiation and maintain their unique properties. E-beams, UV and X-ray radiations are used for the modification and treatment of masks, circuit boards and insulator materials. It is known that many polymer materials are degraded by elec- tromagnetic radiation, particularly by ultraviolet and X-ray ra- diation, as well as by electrons and protons [17e24]. In the case of Teflon Ò PTFE and Teflon Ò FEP this may result in me- chanical degradation [21,22] and changes in wettability [23]. Changes in the surface chemical composition of various fluoropolymers during X-ray irradiation have been previously studied with X-ray photoelectron spectroscopy (XPS) [25e 29]. Wheeler and Pepper investigated in detail the changes in the surface composition of bulk PTFE under X-ray exposure [27] and under 3 keV electron irradiation [28] using XPS and mass spectroscopy. Upon irradiation a significant decrease in the main CF 2 peak intensity and formation of new peaks as- signed to CF 3 , CF, and CeC groups were observed. Similar * Corresponding author. Tel.: þ49 3677 69 3405; fax: þ49 3677 69 3365. E-mail address: stefan.krischok@tu-ilmenau.de (S. Krischok). 0141-3910/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2007.12.004 Available online at www.sciencedirect.com Polymer Degradation and Stability 93 (2008) 700e706 www.elsevier.com/locate/polydegstab