The Efficiency of in-situ Cleaning Methods for Minimizing Electron Beam Induced Contamination Hamed Parvaneh, Hendrix Demers, and Eric Lifshin College of Nanoscale Science and Engineering, University at Albany – SUNY, 255 Fuller Road, Albany, New York 12203 As the features of interest in state-of-the-art integrated circuits (ICs) are getting smaller the ability of scanning electron microscopes (SEMs) to see things in detail in semiconductor metrology is worsening. One important reason is the formation of an electron beam induced contamination layer that seriously deteriorates image contrast and resolution. It can even be found in SEMs with so-called clean vacuum systems (no oil pumps). Different sources of the environmental contamination, including the sample itself have been discussed elsewhere [1]. This contamination layer is commonly attributed to the polymerization of low molecular weight hydrocarbon (HC) molecules on the surface of the sample following interaction with the electron beam. One way of removing them from the system is to promote their removal by oxidation processes [2]. In the current study we have evaluated the efficacy of this approach based on the use of an Evactron ® de-contaminator (XEI, Evactron ® 25 D-C) installed on a Dual beam FIB/SEM chamber (FEI, Nova NanoLab 600) equipped with an Energy Dispersive X-ray Spectrometer (Princeton Gamma-Tech, Si(Li)). The dual beam FIB/SEM was selected because of its usefulness in examining the grain structure of sub-100nm copper interconnects. One drawback in observing grain structure is the flatness of the finished surfaces prepared by FIB, which significantly reduces the variation in the secondary electron (SE) yield associated with any topography on the surface. Unlike the transmission electron microscopes where the diffraction contrast is usually the dominant mechanism for grain contrast, in SEMs the contrast is a result of point to point variation in the SE yield. This can be due to surface topography, chemical composition or crystallographic effects. Since in the case of FIB-prepared copper interconnects, the surface is flat and there is no chemical variation from grain to grain, the contrast will depend primarily on variations in crystallographic effects which are generally small compared to the other two and thus maybe difficult to observe. While our ultimate goal is to improve contrast in cross sectional images of microelectronic interconnects, our initial experiments involve measuring contamination rate buildup on a bare silicon substrate. The carbon buildup in a square raster 2.5 μm on a side was measured as a function of time both before and after the use of the Evactron ® de-contaminator. To avoid the possible effect of different currents in the before and after data, a graphite standard sample was used and the ratio of carbon peak intensity from HC layer to graphite standard is presented (k-ratio). The results shown in Figure 1, clearly indicates that there is little to no carbon buildup after using the de-contaminator. As an additional observation, the carbon intensity on the square produced in the first experiment, was re- measured after cleaning with Evactron ® . Since almost the same k-ratio was obtained, it is assumed that no polymerized carbon was removed by the Evactron ® for the conditions used in this experiment. Figure 2 also shows the oxygen and silicon signals as a function of time both before and after the cleaning. Since it was verified that there was no variation in probe current before and after cleaning, Microsc Microanal 15(Suppl 2), 2009 Copyright 2009 Microscopy Society of America 818 doi: 10.1017/S143192760909758X https://doi.org/10.1017/S143192760909758X Downloaded from https://www.cambridge.org/core. IP address: 18.206.13.133, on 05 Jun 2020 at 22:20:53, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.