A Study of Helium Ion Induced Secondary Electron Production

The scanning electron microscope (SEM) is a popular instrument used for imaging because of its high resolution images it can generate. However the new scanning helium ion scanning microscope (SHIM) can produce higher resolution and better contrast images than the conventional SEM. In both the microscopes secondary electron (SE) signal is the most widely used imaging mode because of their high yield efficiency and their high spatial resolution. In order to be able to properly evaluate the relative strengths and weaknesses of electron induced SE (eSE) and ion induced SE (iSE) imaging a detailed model able to quantify them is required. Unlike in the case of eSE where there have been considerable amount of experimental and theoretical studies, there have been very few for iSE. A detailed Monte Carlo simulation of helium ion beam interaction with solids , IONiSE (Ion Induced SE) was developed. IONiSE is designed to provide data on questions such as the variation of the incident beam range, and the yield δ_iSE of iSE, as a function of the He+ ion energy and choice of sample, as well as the behavior of iSE yield with surface topography, spatial resolution of the iSE. This simulation employs a combination of „semi empirical‟ model for secondary electron production, and the SRIM routines that describe ion stopping power, scattering, and transport. This is a parametric model and hence requires that the material dependent parameters be determined by fitting to experimental yield data. This model shows predictable behavior for wide range of elements and it can be applied with equal ease to even complex compounds. The model can also be used for other applications like energy deposition profiles in ion beam lithography, critical dimension metrology using helium ions, ion beam deposition and etching studies and ion beam induced current in semiconductor devices.