Reaction between AlN and Metal Thin Films during High Temperature Annealing

Abstract

High temperature reactions between AlN and metal thin films were studied. Thin films of Ti, Zr, Cr, Ta, and Ni were sputtered on AlN and annealed isothermally at temperatures between 700°C and 950°C. These films have been classified into the following three groups after 830°C-annealing. Thin films of Ti and Zr formed aluminides at the interface and showed a high adhesion strength over 4.4×107Pa. Thin films of Ta and Cr had high adhesion strength over 4.4×107Pa, observed no compound peak by XRD. Poor adhesion strength of 4.4×105Pa was obtained between AlN and Ni and no compound was found at the interface. Films of titanium formed TiAl3 aluminide in the temperature range of 700°C to 950°C. It was assumed that the following three steps occurred, (1) Ti reduced the surface of AlN to metallic Al and N, (2) Al and N diffused into the Ti film, and (3) an aluminide compound formed. The obtained high adhesion strength of Ti and Zr thin films on AlN is considered to have been resulted from the aluminide formation by reaction between AlN and metal thin films. These abilities depend on the electronegativity of metals. The degrees of reaction between AlN and metal thin films were estimated from the relationships of their electronegativity and standard heat of formation of aluminides. It is possible that aluminides are formed on AlN with elements having electronegativities under 1.34eV, such as Zr (1.22eV), Nb (1.23eV), Mg (1.23eV), Hf (1.23eV), Mo (1.30eV), and Ta (1.33eV).