Investigation of Cu whisker growth by molecular beam epitaxy

Abstract

There is a trend towards smaller and smaller structures (nanostructures/miniaturization) which is well known in microelectronic, energy and semiconductor applications. Nanoengineering is expected to lead to significant improvements in the intrinsic properties of structures, e. g., in energy storage for supercapacitors. In this context, a deeper understanding of the growth mechanisms of the thinnest crystal layers is of crucial importance for the controlled growing of nanowhiskers with outstanding properties. In the present study, we consider a simple whisker growth model based on the surface energy (i. e., wettability) of the components and investigate the effect of the carbon interlayer deposited on a Si (111) wafer using the magnetron sputtering technique on the whisker formation during the subsequent molecular beam epitaxy process in the Si-C-Cu system. In the present study, the topographic holes in the carbon layer which are the preferred nucleation areas of whiskers were identified by a series of scanning tunneling microscopy analyses, and the natural hole density was statistically determined. Using atomic force microscopy, the surface roughness of the carbon layer was characterized. The results of our investigations indicate that there is a correlation between the hole density in the carbon layer and the density of Cu nanowhiskers. This may validate the supposition that the holes in the carbon layer are the preferred nucleation sites for whiskers - an effect that could be relevant for future works on the growth of nanowhiskers at predefined positions.