CHARACTERIZATION OF INTERMETALLIC PHASES AND OXIDES FORMED IN ANNEALED NI AL MULTILAYER STRUCTURES/

Two different multilayer structures composed of ten alternating Ni and Al thin films were sputter deposited on Si (111) substrates. These mu ltilayers with individual Ni and Al thin film thicknesses of about 25 nm and 38 nm and of 25 nm and 13 nm, respectively, have the average co mpositions of Ni0.50Al0.50 and Ni0.75Al0.25. The samples were heat tre ated in a differential scanning calorimeter instrument with a constant heating rate of 40 degrees C min(-1) in Ar from room temperature to 5 50 degrees C. The compositions of as-deposited and heat-treated sample s were studied with high-resolution Anger electron spectroscopy (AES) rotational depth profiling, X-ray photoelectron spectroscopy (XPS) ana lyses show an excess of Ni in both annealed samples. X-ray diffraction measurements of annealed multilayers show the formation of Ni2Al3 and NiAl3 phases in the Ni0.50Al0.50 sample and the presence of Ni3Al and Ni Al-3 phases with some excess of Ni in the Ni0.75Al0.25 sample. AES and XPS investigations of the reacted layers after 15 min annealing i n air at 500 degrees C disclose considerably different surface oxide t hin films: on the Ni0.50Al0.50 layer the oxide thin film consists of A l2O3 with a small amount of NiO, whereas that on the top of the Ni(0.7 5)A(0.25) layer is thicker and consists of NiO on top and some Al2O3 b elow.