Influence from the electronic shell structure on the range distribution during channeling of 40–300 keV ions in 4H-SiC

M K Linnarsson,A Hallén,L Vines

doi:10.1063/5.0054188

M K Linnarsson, A Hallén + Show 1 more

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https://doi.org/10.1063/5.0054188

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Abstract

Ion implantation is performed in 4H-SiC with 11B, 27Al, 31P, 51V, 71Ga, and 75As ions using energies between 40 and 300 keV at various fluences along the [000-1] or the ⟨11-2-3⟩ axes. Secondary ion mass spectrometry is utilized to determine the depth distribution of the implanted elements. A Monte Carlo binary collision approximation (MC-BCA) code for crystalline targets is then applied to explain the influence of the electronic shell structure on electronic stopping and the obtained channeled ion depth distributions. The results show that, as the atomic number increases in a row of the periodic table, i.e., as the ionic radius decreases and the electron clouds densify, the interaction with the target electrons increases and the range is reduced. The decreased range is particularly pronounced going from 27Al to 31P. The reduction in channeling depth is discussed in terms of electronic shells and can be related to the ionic radii, as defined by Kohn–Sham. It is shown that these shell effects in channeled implantations can easily be included in MC-BCA simulations simply by modifying the screening length used in the local treatment of electronic stopping in channels. However, it is also shown that, for vanadium ions with an unfilled d-shell, this simple model is insufficient to predict the electronic stopping in the channels.

Highlights

Ion implantations are regularly used in the semiconductor industry for material modification of mainly electrical properties
The results show that, as the atomic number increases in a row of the periodic table, i.e., as the ionic radius decreases and the electron clouds densify, the interaction with the target electrons increases and the range is reduced
It is shown that these shell effects in channeled implantations can be included in Monte Carlo binary collision approximation (MC-BCA) simulations by modifying the screening length used in the local treatment of electronic stopping in channels

Summary

INTRODUCTION

Ion implantations are regularly used in the semiconductor industry for material modification of mainly electrical properties. In parallel and independent terms, Firsov developed a theory for ion–solid interaction to predict ion ranges.[8] For a long time, Lindhard’s and Firsov’s theories have dominated the field of low-energy ion–solid interaction, and an introduction to the basic concepts of the two theories is given in Ref. 9 These two channeling theories do not include the effects of the atomic shell structure, which is needed, for instance, to describe the well-known Z1 oscillations, a periodic variation of electronic stopping with the atomic number of the ion (Z1).[15–17]. The channeling phenomena is not well described in SiC by commercial device process simulators, for example, Athena[43] and Sentaurus.[44] Most likely, this shortcoming to predict the maximum implantation depth is caused by electronic shell effects, strongly affecting the electronic stopping. The results explain well the deviations caused by the shell structure and show a simple way to modify the electronic stopping in the MC-BCA models in order to improve the predictions of channeled implantation in 4H-SiC

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SUMMARY