Artifacts in EFTEM images
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In some cases, measurements and analyses of EFTEM images are still valuable, even though some artifacts are not avoidable, as far as the artifacts can be distinguished. Here, we will show an example. The valence state of Co can be indirectly determined by mapping the Si ELNES characteristics for the cases of CoSix (x = 1 or 2). Figure 3387a shows the as-measured and background-subtracted Si L2,3 EELS spectra of CoSi and CoSi2. The spectra for both silicides have Si L2,3 edge onsets located at 100.6 eV, while the Si ELNESs are slightly different. The CoSi2 ELNES has one broad peak with a characteristic pre-edge peak, while the CoSi ELNES does not show this pre-edge peak. Based on those characteristics, the parameters for three-window EFTEM method in Table 3387 are used. Here, in order to distinguish between CoSi and CoSi2, the pre-edge peak of CoSi2 was used, while the third peak of CoSi at 145 eV was used for the post-edge window. Using those settings, the Si ELNES maps of CoSi and CoSi2 were obtained together with TEM image as shown in Figure 3387b. Note that the Ti, Co, and Si elements have overlapped layers as indicated in Figure 3387b (a). Although the Ti film also gave some unavoidable artifacts in the maps, it is very important that the grains consisting of CoSi and CoSi2 were still distinguished and the images revealed that a CoSi2 layer was formed between CoSi and Si substrate.

as-measured (a), and background-subtracted (b) Si L2,3 EELS spectra of CoSi and CoSi2

Figure 3387a. The as-measured (a), and background-subtracted (b) Si L2,3 EELS spectra of CoSi and CoSi2. Adapted from [1]

Table 3387. Three-windows imaging filter settings for Si L2,3 ELNES for CoSi and CoSi2. [1]

Compound Pre-edge window 1 (eV) Pre-edge window 2 (eV) Post-edge window (eV) Slit width (eV)

TEM image (a), as-measured (b), and background-subtracted (c) Si L2,3 ELNES maps of Ti/CoSi/CoSi2 layer stack

Figure 3387b. The TEM image (a), CoSi map (b), and CoSi2 map (c) of Ti/CoSi/CoSi2 layer stack. Adapted from [1].






[1] M. Worch, H.J. Engelmann, W. Blum, E. Zschech, Cross-sectional thin film characterization of Si compounds in semiconductor device structures using both elemental and ELNES mapping by EFTEM, Thin Solid Films 405 (2002) 198–204.




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