Interdiffusion in the formation of thin niobium films on singlecrystal silicon under vacuum annealing conditions

Abstract

For the design of technological process for creating device structures based on niobium and single-crystal silicon with thedesired properties, empirical and theoretical knowledge about the solid-phase interaction process in the system of a thin niobium film is required. The purpose of the research was a comprehensive study of the redistribution of components during the formation of thin niobium films on single-crystal silicon obtained by magnetron-assisted sputtering followed by vacuum annealing. The structure and phase composition were studied by X-ray phase analysis, scanning electron microscopy, and atomic force microscopy. Distribution of components along the depth was determined using the Rutherford backscattering spectrometry. The traditional experimental method for studying the process of interdiffusion of components in binary macroscopic systems is the placing of inert marks. However, the use of this method in systems containing thin films is hindered by the comparable thicknesses of the films and marks. This circumstance makes the mathematical modelling the most convenient method for the analysis of the interdiffusion process in thin-film systems. The interdiffusion model during the formation of polycrystalline niobium film – single-crystal silicon systems, developing the Darken’s theory for the limited solubility components was proposed. Grain boundary diffusion of silicon in the intergrain space of a polycrystalline niobium film was proposed. Numerical analysis of the experimental distribution of concentrations within the model established that silicon is the dominant diffusant in the studied system. The temperature dependence of the individual diffusion coefficient of silicon DSi = 3.0 10-12exp(-0.216 eV/(kT)) cm2/s in the temperature range 423–773 K was determined. The model is applicable to the description of the redistribution of components in the thin niobium film – single-crystal silicon system prior to synthesis conditions providing the chemical interaction of the metal with silicon and the formation of silicides. It illustrates the mechanism of the possible formation of silicide phases not by layer-by-layer growth at the Nb/Si grain boundary, but in its vicinity due to deep mutual diffusion of the components

Keywords

• reactive interdiffusion
• limited solubility
• thin films
• niobium
• single-crystal silicon
• magnetron-assisted sputtering
• vacuum annealing
• rutherford backscattering spectrometry
• simulation method
• darken’s theory