Influence of contamination in scanning electron microscopes on the profile of relief elements in monocrystalline silicon
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INFLUENCE OF CONTAMINATION IN SCANNING ELECTRON MICROSCOPES ON THE PROFILE OF RELIEF ELEMENTS IN MONOCRYSTALLINE SILICON
V. P. Gavrilenko, A. Yu. Kuzin, V. B. Mityukhlyaev, A. V. Rakov, P. A. Todua, M. N. Filippov, and V. A. Sharonov
UDC 621.382
Results from studies of the influence of contamination in S-4800 scanning electron microscopes on the profile of relief elements in monocrystalline silicon are presented. It is shown that the form of the profile of relief elements varies as a result of irradiation by electrons with energy 20 keV. The dependences of the dimensional parameters of the relief elements on the electron irradiation dose for different irradiation regimes are also considered. Keywords: contamination, scanning electron microscope, relief elements, measure of width and period, electron irradiation dose.
Measurements of the parameters of objects in a scanning electron microscope are accompanied by the formation of a contamination film on the surface of the test object [1]. The effect of contamination is caused by polymerization of hydrocarbon molecules that have been adsorbed by the surface under the effect of electron irradiation. It is believed that this effect may be reduced though it cannot be completely eliminated [2]. The formation of a contamination film on the relief elements of a surface is capable of altering the dimensional parameters of the elements, a result which must be taken into account when measuring objects of nanometric dimensions. The problem becomes especially important in the case of standard nanorelief samples of a surface intended for the calibration [3] and inspection [4] of scanning electron microscopes, since hydrocarbon pollution of the surface of a standard sample may alter its metrological characteristics. For example, in [5] the problem of contamination-induced degradation of a standard NIST sample created in the form of a step structure of silicon is studied and a technique is proposed for estimating the permissible number of measurements with the use of a given standard sample. The present study is concerned with the determination of the variation in the dimensions of the relief elements of a surface as a result of contamination in a scanning electron microscope using as an example the MShPS-2.0K width and period measure, performed by means of methods of secondary electron emission and x-ray micro-analysis in a scanning electron microscope [6]. Experimental Conditions. The MShPS-2.0K width and period measure was fabricated on a substrate of monocrystalline silicon oriented along the plane (100) by means of photolithography with subsequent etching. The measure consists of five identical modules each of which comprises three step structures of the same type, denoted I– I, II–II, and III–III. In turn, each of the structures has a nominal value of the step of 2 μm and consists of ten ridges separated by grooves. Ridges of trapezoidal form were created in the substrate by the method of anisotropic etching. The lateral sides of the ridges coincide with the planes {111}.
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