Ion-beam mixed ultra-thin cobalt suicide (CoSi₂) films by cobalt sputtering and rapid thermal annealing

Abstract

The influence of ion-beam mixing on ultra-thin cobalt silicide (CoSi₂) formation was investigated by characterizing the ion-beam mixed and unmixed CoSi₂ films. A Ge⁺ ion-implantation through the Co film prior to silicidation causes an interface mixing of the cobalt film with the silicon substrate and results in improved silicide-to-silicon interface roughness. Rapid thermal annealing was used to form Ge⁺ ion mixed and unmixed thin CoSi₂ layer from 10 nm sputter deposited Co film. The silicide films were characterized by secondary neutral mass spectroscopy, x-ray diffraction, tunneling electron microscopy (TEM), Rutherford backscattering, and sheet resistance measurements. The experi-mental results indicate that the final rapid thermal annealing temperature should not exceed 800°C for thin (<50 nm) CoSi₂ preparation. A comparison of the plan-view and cross-section TEM micrographs of the ion-beam mixed and unmixed CoSi₂ films reveals that Ge⁺ ion mixing (45 keV, 1 × 10¹⁵ cm⁻²) produces homogeneous silicide with smooth silicide-to-silicon interface.