Continuous carbon deposition on a silicon (1 0 0) surface, a MD simulation study

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Abstract

The deposition of multiple carbon atoms on a crystalline silicon (Si) surface is modelled at 5 eV energy by using molecular dynamics simulations combined with a third generation force field that includes bond breaking and formation. Force field parameters are taken from a previous work. These simulations allow for atomic scale insights into the deposition mechanisms and an easier comparison with experimental observations. The results, including distributions of implantation depth, carbon concentrations, sticking coefficients, radial distribution function, and angular distributions are compared for different incidence angles. Due to the deposition of carbon atoms inside the silicon structure, silicon carbide starts to form. The crystalline structure has been investigated for different conditions to get a better understanding of the damaging and growth mechanisms. It is found that a lot of deformation is accumulated in the area of deposition near to the surface but underneath the surface the silicon has still a more crystalline structure. The variation of the silicon (carbide) structure slightly depends on the angle of incidence. For the conditions used for these simulations, the sticking probability is always high and varies between 95% and 100%, which can be attributed to the high affinity of carbon for silicon.

Introduction

Silicon Carbide (SiC) is a semiconductor material with a wide band gap which has interesting properties for many applications, including among other high-power and high-frequency electronic devices [1], nuclear technology, deep-space missions and in the semiconducting industry [2], [3]. At the same time, the performances of such devices significantly depend on the defects formed during crystal growth or ion implantation processes. In order to investigate the influence of the defects on the SiC properties, several theoretical and experimental studies have been carried out. Both, the electrical and physical properties of SiC, or devices made of SiC, change with the SiC crystalline structure [4]. As per example, the fabrication of light emitting diodes depends on the intrinsic defects in Silicon carbide [5]. In order to understand how the material properties depend on the growth conditions, a detailed insight into the deposition of carbon materials on silicon substrates is of key importance for thin film growth via plasma deposition techniques and sputter deposition.

Over the past couple of decades, computer simulation techniques have proven to be very powerful tools for the understanding of various chemical and physical processes at an atomic level. In particular, plasma–surface interactions [6], [7] as well as ion bombardment processes [8], [9], [10] have often been investigated by molecular dynamics (MD) methods as they provide a fully deterministic description of the system of interest over short periods of time. Besides, while high-energy sputtering processes are well described by binary collisions models [11], the low impact energies needed for matter deposition are better described by force field based MD methods [12], [13]. MD simulations indeed allow us to take into account all the interactions between the atom being deposited and the neighbouring atoms during the whole process, which is crucial when the projectile has a low enough velocity to experience the chemical interactions of other atoms.

In this paper, we present the beginning of SiC film formation by sending low-energy carbon atoms onto a silicon substrate using MD simulations. We use MD simulations coupled with the reactive force field developed by Kieffer and coworkers [14], [15], [16] and modified for surface and irradiation studies [10] to study the deformation of the silicon crystalline structure and the beginning of silicon carbide (SiC) formation by low-energy carbon deposition, i.e. conditions found in plasma deposition processes. The force field developed by Kieffer and coworkers has been selected for its ability to model the breaking and formation of bonds within the system and for its charge transfer routine allowing the atomic charges to adapt to the chemical environment of each atom. In addition, we have previously presented new force field parameters for the C–Si interactions [17]. In this paper we use them to investigate how continuous or multiple carbon deposition on the silicon surface may influence substrate amorphization, interface formation and thin film growth as compared to what was observed on crystalline and amorphous silicon surfaces [18]. In order to verify the structure of Si(C) during the deposition process for different incidence angles, carbon concentrations, radial distribution functions and angular distributions have been calculated for different slabs and compared.

Section snippets

Computational details

MD simulations are performed using the reactive force field developed by Kieffer and his co-workers [14], [15], [16]. The parameters for Si–Si and Si–C interactions are presented in [10] and [17]. For the continuous carbon deposition on the Si(1 0 0) surface, similar conditions have been used than in [18] for the deposition of single carbon atoms on a Si(1 0 0) surface. A 8 × 8 × 8 supercell containing 4096 Si atoms is used. The deposition of each carbon in a continuous fashion has to be divided into

Results and discussion

We will present and discuss how low energy deposition of multiple carbon atoms modifies the silicon structure. Previously, a channelling effect has been observed when a single carbon is deposited on the crystalline Si(1 0 0) surface [18] at an incidence angle of 45° relative to the normal of the surface, leading to the deepest implantation of the carbon. This channelling effect is attributed to the low-density channels that go through the crystalline silicon structure following the [1 1 0]

Conclusion

Using the third generation force field by Kieffer and coworkers, multiple carbon deposition on a crystalline silicon surface is modelled in order to get a better understanding of carbon deposition and implantation and Si lattice deformation during low-energy carbon atom interactions with a Si(1 0 0) surface. The deposition energy of 5 eV used here is typical for sputter deposition and plasma surface treatments. The radial distribution function reveals the deformation of the Si structure as a

Acknowledgement

The present project is supported by the National Research Fund, Luxembourg (C09/MS/15).

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