MODIFICATION OF AL2O3-TIN INTERFACE CHEMISTRY TO IMPROVE ADHESION IN CVD COATINGS

Thin interlayers are often used to improve adhesion between functional CVD coatings. It is also possible to modify the surface chemistry of a CVD layer so that the subsequent CVD layer is better adhered. This h as been done in the case of Al2O3 and TiN by exposing the Al2O3 surfac e to a high concentration of NH3 at high temperature for a limited tim e. A thermodynamic analysis shows the possibility for substituting N f or O in the Al2O3 surface using this method. Scanning electron microsc opy and Rutherford backscattering spectrometry (RBS) were used to anal yze the interface chemistry. RBS was used to identify a depletion of o xygen in the near surface region of Al2O3 and the presence of TiN to a depth of 0.4 mu m in the Al2O3 layer. Scratch testing with a diamond stylus was used to affirm the improved adhesion. The method is attract ive because it simply involves exposing the surface to a controlled en vironment. CVD of a very thin uniform interlayer is more difficult.