Characterization by RBS of hyper-thin SiO2 layers on various polymers

In order to investigate the growth mode of plasma-enhanced chemical vapor deposited (PECVD) SiO2 gas barrier layers on various polymers (namely polyimide. PI; polyethyleneterephthalate. PET; polycarbonate. PC) we use Rutherford backscattering spectroscopy (RBS) in two different ion beam modification (IBM) geometries. with 1 and 1.5 MeV alpha particles (He2+ ions). In the case of Kapton((R)) PI, a polymer which is damaged very little by the incident ion beam, we have followed the evolution of the surface concentration of silicon atoms versus PECVD growth duration: the relationship was found to be perfectly linear over a film thickness range 5 less than or equal to d less than or equal to 500 Angstrom. Using grazing incidence. we found a 7 nm thick "interphase" region between the SiO2 coating and the substrate. However, for the case of the two other polymers (PET and PC), major artifacts were noted during RBS measurements. even under very mild beam conditions (1 nA, 8.0 x 10(12) ions/cm(2)), because of the creation of abundant volatile molecular fragments by the incident particles below the surface of the organic substrate. Scanning electron micrographs confirm the damage caused by these volatile species, as they escape through the sample surface: this greatly limits the use of the RBS technique for most polymers, including PET and PC. (C) 2002 Elsevier Science B.V. All rights reserved.