Structure estimation of diamond-like carbon films by synchrotron X-ray reflectivity measurement

Using an X-ray reflectivity method we estimated the density of several Diamond-Like carbon (DLC) films. Those films were about 100-nm-thick and formed on Si substrates by Gas-Cluster Ion Beam assisted (GCIB), RF-plasma-CVD (RF), ECR-plasma-CVD (ECR), ion plating (IP) and filtered-cathodic-vacuum-arc (FCVA) deposition methods. The X-ray reflectivity measurement using a conventional X-ray source revealed that the average density values of the GCIB and FCVA DLC films were larger than 2.7 g/cm3, while those of other samples were less than 2.1 g/cm3. We also performed the X-ray reflectivity measurement using a highly parallel X-ray microbeam, formed from synchrotron X-rays, of 2.0 μm x 2.5 μm in size which is about two orders of magnitude smaller than the conventional X-ray probe. The X-ray microbeam enables us to evaluate a local fluctuation of the film density and the thickness with a spatial resolution of the probe size. It is revealed that the density of some DLC films varies abruptly near the interface on a Si substrate