Interface growth mechanism in ion beam sputtering-deposited Mo/Si multilayers

Abstract

Despite the technological importance of metal/Si multilayer structures in microelectronics, the interface reactions occurring during their preparation are not yet fully understood. In this work, the interface intermixing in Mo/Si multilayer coatings has been studied with respect to their preparation conditions. Various samples, prepared at room temperature with different Mo deposition rates (0.06–0.43 Å s⁻¹) and a constant Si rate, have been investigated by detailed TEM observations. Contrary to the Si-on-Mo interface where no evidence of chemical intermixing could be found, the Mo-on-Si interface presents a noticeable interface zone whose thickness was found to noticeably decrease (from 4.1 to 3.2 nm) when increasing the Mo deposition rate. Such intermixing phenomena correspond to diffusion mechanisms having coefficients ranging from 0.25 × 10⁻¹⁵ to 1.2 × 10⁻¹⁵ cm² s⁻¹ at room temperature. By assuming a diffusion mechanism mainly driven by Mo–Si atomic exchanges to minimize the surface energy, the diffusion dependence with Mo deposition rate has been successfully simulated using a cellular automaton. A refined simulation including Mo cluster formation is also proposed to explain the scenario leading to the full crystallization of Mo layers.

Acknowledgments

We would like to thank Dr Fiqiri Hodaj for his fruitful contribution. We would like to thank V. Muffato for her valuable technical support regarding the coating deposition and D. Muyard for the grazing X-ray characterizations. This work was performed under the auspices of the MEFI (French Ministry of Economy, Finance and Industry) and, partially, in the framework of the EXTUMASK MEDEA + project.