Molecular-Dynamics Simulation of Silicon Irradiation with Low-Energy Noble Gas Ions
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lar-Dynamics Simulation of Silicon Irradiation with Low-Energy Noble Gas Ions A. A. Sychevaa, * and E. N. Voroninaa, b aSkobeltsyn
Institute of Nuclear Physics, Moscow State University, Moscow, 119234 Russia of Physics, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected]
bFaculty
Received January 11, 2020; revised February 25, 2020; accepted February 28, 2020
Abstract—Simulation of the irradiation of crystalline silicon with low-energy (50—500 eV) noble-gas ions (He, Ne, Ar, Kr, Xe) is performed using the molecular-dynamics method with damage accumulation. The analysis of structural changes in the near-surface layers of the material demonstrates significant differences between the mechanisms of silicon damage by light and heavy particles. It is shown that, under material irradiation with Xe ions and especially with He ions, the largest clusters are formed by atoms implanted in the material. Keywords: sputtering, surface segregation, simulation, molecular dynamics DOI: 10.1134/S1027451020040345
INTRODUCTION Physical sputtering, during which atoms are emitted from the surface layers of a target under irradiation with a beam of incident particles, is used in modern technological processes, including the plasma treatment of materials. One of the key problems of microelectronics and nanoelectronics is implementation of the technique of atomic-layer etching, which makes it possible during the plasma treatment to remove the material layer by layer with atomic precision and high selectivity. The distinctive feature of the used processes is the low energy of incident ions, which usually ranges from several tens to hundreds of electronvolts. Silicon is one of the materials that are most widely used in the modern microelectronics of materials. A large scope of experimental information on the physical sputtering of Si at energies that are higher than 1 keV [1—3] has been accumulated to date; this information agrees well with the Sigmund sputtering theory based on the linear cascade model [4]. However, for energies near the threshold value, existing experimental data are very uncoordinated and contradictory in some cases [5–7]. Theoretical description of the effect of low-energy ions on silicon is also difficult, because the approximations used in the linear cascade model are invalid [8, 9]. Within the framework of the Sigmund theory, it was assumed that, as a result of the effect of ions, the number of sputtered target atoms is proportional to the energy Edep released in a small surface region of the material near the impact point. The authors of [8, 9] showed that, for low-energy ions, the dependence of the sputtering yield on Edep is nonlin-
ear, and the form of the spatial region in which the ion energy is released predominantly depends on the type, the energy, and the incidence angle of the incident particle and also on the density of the target material. For example, at normal incidence of 250-eV Xe ions on the surface of crystalline Si, the indicated surface is an ellipsoid, whose major axi
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