Characterization of ultrathin Cr layers on PET by RBS and XRF

Abstract

AbstractWe studied the characterization of thin metallic layers vacuum‐deposited by magnetron sputtering onto commercial polyethylene terephthalate (PET) films in an industrial web coater. Because the technology of metal coating for technical films tends more and more towards nanotechnology, quantitative surface and interface analysis are required to optimize the metallization procedures. An important factor is the thickness of the thin coated layers. A powerful tool to characterize chemical composition and layer thickness of such nanofilms quantitatively is low‐energy Rutherford backscattering spectroscopy (LE‐RBS); it is, however, not suitable for production control. A standard industrial tool for these measurements at higher layer thickness is x‐ray fluorescence spectroscopy (XRF). This method is highly sensitive and reproducible but needs calibration standards.We show that the thickness of chromium layers in the subnanometre range can be determined by means of LE‐RBS without deterioration of the PET film. We further show that a set of layers of different thickness can be measured by LE‐RBS with sufficiently high accuracy to serve as calibration standards for XRF or optical density measurement. From the correlation of the results obtained by RBS and XRF, we learn about the uncertainties induced by the production process (lateral uniformity) and by the analytical techniques. Copyright © 2002 John Wiley & Sons, Ltd.