Measurement of the adhesion strength of metal oxide and metal nitride thin films sputtered onto glass by the direct pull-off method

We have measured the adhesion strengths of metal oxide and metal nitride thin films reactively sputtered onto glass substrates using a specially devised direct pull-off test. For double-layer coatings such as metal nitride (CrN_x, TiN_x)/metal oxide (Al₂O₃, SnO₂, Ta₂O₅, TiO₂, ZnO, ZrO₂)/glass, separation usually took place at the nitride/oxide interface. The adhesion strength at the interface was found to depend on the strength of chemical bonding in the films concerned: for the same nitride top layer, the adhesion strength increased as the strength of the metal-oxygen (M-O) bond in the oxide underlayer decreased. X-ray photoelectron spectroscopy (XPS) measurements showed that a mixed layer was created at the nitride/oxide interface and that the adhesion strength at the interface increased with increasing thickness of the mixed layer. For single-layer coatings such as metal nitride (CrN_x, TaN_x, TiN_x, ZrN_x)/glass, the adhesion strength of the film to the glass substrate was found to increase with increasing strength of the M-O bond between the metal atom (M) in the nitride film and an oxygen atom (O). These adhesion behaviors could be explained by adhesion models based on chemical bonds at the interfaces.