Ion beam induced enhanced diffusion from gold thin films in silicon

TL;DR

This study investigates how ion beam irradiation enhances gold atom diffusion into silicon substrates, revealing depth profiles, phase formation, and the effects of film thickness and fluence on diffusion behavior.

Contribution

It demonstrates the role of ion beam parameters and film thickness in controlling gold diffusion and silicide formation in silicon, highlighting the absence of confinement effects and the influence of amorphization.

Findings

Gold atoms diffuse up to 265 nm depth at high fluence in thick films.

Gold silicide formation occurs at fluences ≥ 1x10^14 ions/cm^2.

Amorphization of silicon correlates with large mass transport during irradiation.

Abstract

Enhanced diffusion of gold atoms into silicon substrate has been studied in Au thin films of various thicknesses (2.0, 5.3, 10.9 and 27.5 nm) deposited on Si(111) and followed by irradiation with 1.5 MeV Au2+ at a flux of 6.3x10^12 ions cm-2 s-1 and fluence up to 1x10^15 ions cm-2. The high resolution transmission electron microscopy measurements showed the presence of gold silicide formation for the above-mentioned systems at fluence greater than equal to 1x1014 ions cm-2. The maximum depth to which the gold atoms have been diffused at a fluence of 1x10^14 ions cm-2 for the cases of 2.0, 5.3, 10.9 and 27.5 nm thick films has been found to be 60, 95, 160 and 13 nm respectively. Interestingly, at higher fluence of 1x1015 ions cm-2 in case of 27.5 nm thick film, gold atoms from the film transported to a maximum depth of 265 nm in the substrate. The substrate silicon is found to be amorphous at the above fluence values where unusually large mass transport occurred. Enhanced diffusion has been explained on the basis of ion beam induced, flux dependent amorphous nature of the substrate, and transient beam induced temperature effects. This work confirms the absence of confinement effects that arise from spatially confined structures and existence of thermal and chemical reactions during ion irradiation.