Interdiffusion at the Al2O3/Ti interface studied in thin-film structures

Abstract

The early-stage interfacial reactions between amorphous Al 2 O 3 (a-Al 2 O 3 ) and crystalline α-Ti (c-Ti) thin films were studied in thin-film structures with two different thicknesses. Smooth silicon (111) substrates were covered firstly with a TiN thin-film diffusion barrier and then with a crystalline Ti layer. Finally, amorphous Al 2 O 3 was sputter deposited onto the crystalline Ti layer. The samples were heated in a differential scanning calorimeter with a linear heating rate of 40°C min -1 -from room temperature up to different final temperatures of 350-700°C in an argon atmosphere to activate reactions at the a-Al 2 O 3 /c-Ti interfaces-and then rapidly quenched. The interdiffusion at the a-Al 2 O 3 /c-Ti interface was studied using the rate of change of the reaction width obtained from Auger electron spectroscopy (AES) sputter depth profiles. The beginning of the reaction, which involves the diffusion of oxygen (followed by Al) into the c-Ti thin film, was observed at ∼425°C. The activation energy at the a-Al 2 O 3 /c-Ti interface was found to be 1.6 eV for the oxygen diffusion from the amorphous Al 2 O 3 into the c-Ti thin film between 425°C and 650°C, and 0.9 eV for the Al diffusion between 500°C and 625°C. The new crystalline reaction product is composed of α 2 -Ti 3 Al phase and a solid solution of oxygen in α-Ti. The influence of different sample structures on kinetic quantities is discussed. © 1998 John Wiley & Sons, Ltd.