Energetic Cs+ ion interaction with common microelectronic materials—An investigation of a future FIB candidate source

Abstract

In this paper, the authors studied the interaction of 14.5 keV accelerated Cs+ ion interaction with commonly used materials in the microelectronic industry. The motivation of this work was to examine the suitability of cesium as a future ion candidate for focused ion beam (FIB) nanomachining applications, from the beam–surface interaction aspect. Since nanometer scale Cs FIBs are uncommon, the authors have used a relatively broad Cs+ beam for this work. Two irradiation configurations were used: 60° and normal incidence with respect to the sample surface. Two sample types were irradiated, a pristine Si wafer piece and layered sample of tungsten over SiO2 on top of a Si substrate. Post Cs+ irradiation, the samples were capped and carefully prepared for transmission electron microscopy (TEM) and scanning transmission electron microscopy/energy dispersive spectroscopy inspection. TEM studies of the subsurface damage to the Si shows a regular amorphization process, without odd microstructural changes even for high applied dose. The amorphization depth in Si was found to be smaller than 25 nm and the Cs staining level to be about 10% by atomic densities. A very small amount of Cs was measured within the tungsten and the SiO2 layers, attributed to high diffusion rate of Cs in these materials. The authors believe that a Cs+ ion based source may be used for future nanomachining applications from the beam–surface interaction aspect. However, the high diffusion rates of Cs in the materials tested presents a concern regarding gate oxide contamination and subsequent complementary metal–oxide–semiconductor device degradation.