Glancing-incidence and glancing-takeoff x-ray fluorescence analysis of Ni-GaAs interface reactions

Abstract

A thermally stable Ni-based ohmic contact is one of the most attractive contact materials for developing superior GaAs devices. To understand the interface reaction between an Ni thin film and a GaAs wafer, a combined grazing-incidence and grazing-takeoff x-ray fluorescence (GIT-XRF) method was applied. Ni thin films (∼10 nm in thickness) were deposited on GaAs wafers, then annealed at 373 and 473 K. When the conventional grazing-incidence XRF and grazing-exit XRF methods were separately applied to a sample annealed at 373 K, it was not possible to recognize interface reactions between Ni and GaAs. However, the small compositional change at the interface could be detected by the non-destructive GIT-XRF method. The diffusion of Ni atoms into the GaAs substrate, which was induced by heating at 473 K for 3 min, was clearly found by measuring the takeoff angle dependences of characteristic x-ray intensities at a grazing incidence angle of 2.5 mrad. Finally, the mixed Ni–GaAs layer was evaluated to be Ni5GaAs with a thickness of 15 nm by fitting calculated curves to experimental plots. Copyright © 2000 John Wiley & Sons, Ltd.