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r Dependences of Silicon Sputtering by Gallium Focused Ion Beam V. I. Bachurina, *, I. V. Zhuravleva, D. E. Pukhova, A. S. Rudya, S. G. Simakina, M. A. Smirnovaa, and A. B. Churilova aValiev

Institute of Physics and Technology, Yaroslavl Branch, Russian Academy of Sciences, Yaroslavl, 150007 Russia *e-mail: [email protected] Received January 11, 2020; revised February 14, 2020; accepted February 17, 2020

Abstract—Angular dependences of the surface layer composition and the sputtering yield of silicon upon irradiation of the surface with a focused beam of gallium ions with an energy of 30 keV are obtained. The surface composition is analyzed by scanning Auger electron spectroscopy (SAES) and secondary ion mass spectrometry (SIMS). The sputtering yields are determined by measuring the volume of sputtering craters and irradiation doses. It is found that the content of gallium in the surface layer is about 30 at % with incidence angles close to the normal. With incidence angles greater than 30°, the concentration of gallium decreases quite sharply. The angular dependence of the sputtering yield of silicon does not correlate with the content of gallium in the surface layer and is rather well described by the cascade sputtering mechanism proposed by P. Sigmund. Keyword: sputtering, surface layers, focused ion beam, secondary ion mass spectrometry, scanning Auger electron spectroscopy DOI: 10.1134/S1027451020040229

INTRODUCTION Surface sputtering by focused ion beams (FIB), which was previously used in the preparation of samples for transmission electron microscopy (TEM) and in the analysis of integrated circuit failures, is now widely used for the formation of nanostructures on the surface of semiconductors [1, 2]. The sputtering of solids by ion bombardment has been studied for a long time, and a large amount of experimental and theoretical results have been obtained [3, 4]. It has become evident, however, that the bombardment of samples by focused beams (from 10 nm in diameter) and exposure to high radiation doses have a substantial effect on the development of surface topography in samples and on the formation of a layer of deposited sputtered material (which includes both the sample material and implanted ions from the primary beam) on the bottom and walls of the etch crater [5, 6]. In the case of the sputtering of silicon by a beam of gallium ions, the deposited layer contains Si and Ga. The sputtering yield of this layer can significantly differ from that of silicon, since the binding energy of gallium atoms on the surface is almost twice lower than that of silicon. Therefore, sputtering of the deposited layer will be largely determined by both the concentration of Ga and its chemical state (the presence of individual precipitates or the formation of chemical compounds with Si).

The creation of nanostructures with a high ratio of the height to linear planar dimensions by means of FIBs is usually accompanied by preliminary simulation of the process [7–9], which requires accurate data on the sputtering yields and