Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Patent
1997-10-14
1999-11-16
Anderson, Bruce C.
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
25049221, H01J 3730, H01J 3726
Patent
active
059862645
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The subject of this invention is an ion beam preparation device for processing electron microscopy specimens with a vacuum chamber and at least one ion source for specimen bombardment in a specimen holder by a noble gas ion beam, in particular with argon ions.
For electronmicroscopical observation of specimens the latter must be suitably prepared, e.g. by ion beam etching (D. G. Howit,, Ion Milling of Materials Science Specimens for Electron Microscopy: A Review, Journal of Electron Microscopy Technique 1: 405-414 (1984); A. Garulli, A. Armigliato, M. Vanzi, Preparation of Silicon Specimens for Transmission Electron Microscopy, J. Microsc. Spectrosc. Electron. Vol. 10, No. 2, 1985, 135-144).
Ion etching for preparing specimens used in scanning electron microscopy (SEM) and transmission electron microscopy (TEM) is a method that is principally used where conventional chemical and electrochemical processes fail or yield only inadequate preparation results. This applies in particular to TEM cross-sectional preparation of material and layer combinations with strongly selective etching behavior, and to chemically resistant materials. For these cases ion etching has developed into a routinely practiced method.
Whereas in the beginning cross-section specimens were usually examined with transmission electron microscopes with an acceleration voltage of 100 kV, preference is now given to medium voltage equipment with 300 kV and field emission sources. This equipment ensures uniform transmissibility of the cross-section specimens and is able to form beam probes in the nm range. This establishes the technical preconditions for structural examination and material analysis (EELS, EDX) in the finest details, that is, also on nanostructures.
The development of the nanotechnology, that is, the creation and utilization of structures and dimensions in the submicrometer and nanometer range (e.g. semiconductor component structures), imposes significantly more demanding requirements on the preparation technique. The necessary etching to the desired thickness of structures with extremely small dimensions requires a significantly better observation possibility of the specimen during the etching process so that the momentary stadium of the specimen preparation can be accurately determined.
The currently known, conventional ion beam etching systems such as the RES 010 from BAL-TEC, the PIPS model 691 and the Dual Ion Mill from Gatan, as well as the Ion Beam Thinning Unit from Technology LINDA, use light microscopy with a maximum magnification factor of 100 for observing the specimens. This is generally inadequate already in the cross-section preparation of simple multilayer systems because the moment at which the etching process is terminated cannot be accurately determined. In the case of specimen etching to the desired thickness of selected structures, in-situ evaluation of whether or not the structure of interest is located within the thinned down specimen area is entirely impossible. This applies already to structures (also samples with periodic structures) in the .mu.m range! As a consequence an elaborate "trial and error" process is needed in which the specimen must be repeatedly transferred between the etching system and the transmission electron microscope or the corresponding specimen holders. This often results in destruction of the specimen.
Another disadvantage of the known ion beam etching systems is the poor controllability of the final stage in the etching process. Neither the optical observability nor the automatic cut-outs known from the known ion beam etching systems allow determination of the exact etching process termination. The sensitivity of the optical and electronic cut-offs used in these equipments is inadequate for switching off the etching process on time. This applies in particular to the ion beam preparation of cross-section specimens. A certain improvement is achieved by the RES 010 from BAL-TEC which uses a special specimen holder with built-in Faraday cup for d
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Anderson Bruce C.
Bal-Tec A.G.
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