Research Fields

Development and Applications of Submicron Secondary Ion Mass Spectrometer

2.c Development of a Three-Dimensional Microanalysis Method Using Ion and Electron Dual Focused Beams

We are developing a novel three-dimensional microanalysis method using a focused ion beam (FIB) and a finely-focused electron beam (EB). Our method employs an FIB as a micro-crosssectioning tool and an EB as a probe for sanning Auger electron microscope (SAM). Targets of the 3D-analysis are individual microparticles and ICs.

Conventional 3D-analysis is performed with the combination of ion beam etching using raster scan mode and the lateral mapping of the crater bottom. In this case, it is very difficult to obtain the 3D-elemental map of single particulate sample because of the uneven erosion caused by the incident angle dependence of sputtering yields.

In our method, the lateral mapping is performed not on a crater bottom but a planar cross-section etched with a slowly-scanned FIB. As shown in the figure, a 3D-elemental map of a particle is obtained with the repetition of the cross-sectioning and the elemental mapping of the cross-section. We have previously shown that the topographic effect can be negligible in this slow scan mode, named Shave-off scan.

Another aim of the dual beam concept is a new electron post-ionization technique to improve the sensitivity and quantification of FIB-SIMS. In order to obtain high post-ionization yields, we plan to perform the simultaneous bombardment of the FIB and the EB on the same spot on a sample surface.

In order to realize these two analysis modes, we are developing an ion and electron dual focused beam apparatus.

Overview of the Dual Focused Beam Apparatus

• Beams and Analyzers : FIB (Ga liquid metal ion source), EB (LaB₆), QMS (Quadrupole Mass Spectrometer), CMA (Cylindrical Mirror Analyzer)
• Instrumental Features : The FIB and EB are perpendicularly directed to each other in order to analyze cross-sections from normal in Auger mapping. The sample potential is kept at ground level so as to perform various analysis modes (SIMS, AES, etc.) simultaneously using the combinations of the beams and the analyzers. This is an important point for obtaining information on a limited volume of a sample as much as possible. The dual beam and other controllers are specially designed and manufactured for the purpose.
• Present Stage : To date, the development of each control system, such as the dual beam controllers or signal processing unit, has been finished. At present, we are making a sequence control software for the 3D-analysis, and optimizing the Auger mapping function for microarea analysis.

Experimental Results

• FIB-induced Auger Electron Spectroscopy and Elemental Mapping : We first measured FIB-induced Auger spectra from pure solids. Furthermore, the elemental mapping of Al was performed by using an FIB-induced Al_LMM peak. We now estimate the applicability of IAE to surface analysis, and study the fundamentals of ion-induced Auger emission (IAE) particularly in relation to secondary ion emission.
• Sequential control program of the FIB and the EB for three-dimensional analysis : We made a soft ware for the 3D-analysis in which the FIB and the EB are scanned under adequate conditions for the cross-sectioning and the Auger mapping, respectively. Because the Auger mapping function has not been completed, in a test run the FIB was used for both cross-sectioning and imaging (absorbed current image).