Chromium in amorphous hydrogenated carbon based thin films prepared in a PACVD process Original Research Article

The deposition of Cr-containing amorphous hydrogenated carbon (a-C:H) thin films on Si and Cu substrates in a radio frequency (rf) and middle frequency (mf) plasma activated chemical vapour deposition (PACVD) process is described. Negative DC bias voltage at the substrate and the composition of the process gas are two significant parameters in the deposition process. By applying a higher bias voltage the growth rate is increased. The dependence on the ratio of CH4 to Ar shows a saturation effect in the region of high CH4 concentration. This shows the significant contribution of an ion current to the film growth and a rf/mf power limited ion current in the selected parameter range. A decrease of the Cr content in the a-C:H films by increasing the CH4 to Ar flow ratio is measured by XPS while a correlation of the density of the electronic states at the Fermi level with the metal content in the a-C:H matrix is observed by UPS. No significant change in the ratio of sp2 to disordered bonded carbon atoms in the films deposited with the two methods is observed by Raman spectroscopy. Ageing tests of the samples at 250°C in air showed the increase of the solar absorption as well as the reduction of the thermal emission after 80 h treatment. These results show a total suppression of the copper diffusion through the diffusion barrier in the multilayer system.