Violeta Georgieva

Numerical study of Ar/CF4/N2 discharges in single- and dual-frequency capacitively coupled plasma reactors

A one-dimensional particle-in-cell/Monte Carlo model is developed to study capacitively coupled (cc) radio-frequency discharges in a gas mixture of Ar, CF4, and N2. The charged species, which are followed in the model, are: Electrons and Ar+, CF3+, N2+, F−, and CF3− ions. The simulation considers electron – neutral (Ar, CF4, and N2) collisions, various kinds of collisions of ions with neutrals, positive–negative ion recombination, and electron–ion recombination. The model yields results for electron and ion densities, fluxes and energy distributions, collision rates and electric field, and potential distributions. The simulations are performed for a 0.8/0.1/0.1 ratio of Ar/CF4/N2 mixture at a pressure of 30 mTorr in single (13.56 MHz) and dual frequency (2+27 MHz) cc reactors and a comparison between the two frequency regimes is made. Results show that the structure of the discharges is electronegative in both cases. F− and CF3− ions are the main negative charge carriers in the single and dual frequency r...

Numerical simulation of dual frequency etching reactors: Influence of the external process parameters on the plasma characteristics

A one-dimensional particle-in-cell/Monte Carlo model is used to investigate Ar∕CF4∕N2 discharges sustained in capacitively coupled dual frequency reactors, with special emphasis on the influence of the reactor parameters such as applied voltage amplitudes and frequencies of the two voltage sources. The presented calculation results include plasma density, ion current, average sheath potential and width, electron and ion average energies and energy distributions, and ionization rates. The simulations were carried out for high frequencies (HFs) of 27, 40, 60, and 100MHz and a low frequency (LF) of 1 or 2MHz, varying the LF voltage and keeping the HF voltage constant and vice versa. It is observed that the decoupling of the two sources is possible by increasing the applied HF to very high values (above 60MHz) and it is not defined by the frequency ratio. Both voltage sources have influence on the plasma characteristics at a HF of 27MHz and to some extent at 40MHz. At HFs of 60 and 100MHz, the plasma density ...

Sputter-deposited Mg-Al-O thin films: linking molecular dynamics simulations to experiments

Using a molecular dynamics model the crystallinity of MgxAlyOz thin films with a variation in the stoichiometry of the thin film is studied at operating conditions similar to the experimental operating conditions of a dual magnetron sputter deposition system. The films are deposited on a crystalline or amorphous substrate. The Mg metal content in the film ranged from 100% (i.e. MgO film) to 0% (i.e. Al2O3 film). The radial distribution function and density of the films are calculated. The results are compared with x-ray diffraction and transmission electron microscopy analyses of experimentally deposited thin films by the dual magnetron reactive sputtering process. Both simulation and experimental results show that the structure of the Mg‐Al‐O film varies from crystalline to amorphous when the Mg concentration decreases. It seems that the crystalline Mg‐Al‐O films have a MgO structure with Al atoms in between. (Some figures in this article are in colour only in the electronic version)

Particle-in-cell/Monte Carlo simulation of a capacitively coupled radio frequency Ar/CF4 discharge: Effect of gas composition

A one-dimensional particle-in-cell/Monte Carlo model is developed to study a capacitively coupled radio frequency discharge in a gas mixture of argon and CF4. The simulation takes into account the following charged particles: electrons, two kinds of positive ions (Ar+, CF3+), and two kinds of negative ions (F−, CF3−). The model considers electron–Ar collisions, electron−CF4 collisions, various kinds of collisions of CF3+, F−, CF3−, or Ar+ with Ar or CF4, and positive–negative ion recombination. The probability for the positive–negative ion recombination is determined from a recombination rate constant. The ion–neutral elastic and reactive collisions are simulated by an ion–molecule collision model for endothermic reactions. The typical results of this model are electron and ion densities, fluxes and energy distributions, collision rates, and electric field and potential distributions. The simulation is performed for 0.1/0.9, 0.5/0.5, and 0.9/0.1 ratios of a Ar/CF4 mixture, as well as for pure Ar and pure ...

Compositional effects on the growth of Mg(M)O films

The influence of the composition on the crystallographic properties of deposited Mg(M)O (with M=Al, Cr, Ti, Y, and Zr) films is studied. For a flexible control of the composition, dual reactive magnetron sputtering was used as deposition technique. Two different approaches to predict the composition are discussed. The first is an experimental way based on the simple relationship between the deposition rate and the target-substrate distance. The second is a route using a Monte Carlo based particle trajectory code. Both methods require a minimal experimental input and enable the user to quickly predict the composition of complex thin films. Good control and flexibility allow us to study the compositional effects on the growth of Mg(M)O films. Pure MgO thin films were grown with a (111) preferential out-of-plane orientation. When adding M to MgO, two trends were noticed. The first trend is a change in the MgO lattice parameters compared to pure MgO. The second tendency is a decrease in the crystallinity of the MgO phase. The experimentally determined crystallographic properties are shown to be in correspondence with the predicted properties from molecular dynamics simulations.

Modeling of the plasma chemistry and plasma–surface interactions in reactive plasmas

In this paper, an overview is given of modeling activities going on in our research group, for describing the plasma chemistry and plasma–surface interactions in reactive plasmas. The plasma chemistry is calculated by a fluid approach or by hybrid Monte Carlo (MC)–fluid modeling. An example of both is illustrated in the first part of the paper. The example of fluid modeling is given for a dielectric barrier discharge (DBD) in CH4/O2, to describe the partial oxidation of CH4 into value-added chemicals. The example of hybrid MC–fluid modeling concerns an inductively coupled plasma (ICP) etch reactor in Ar/Cl2/O2, including also the description of the etch process. The second part of the paper deals with the treatment of plasma–surface interactions on the atomic level, with molecular dynamics (MD) simulations or a combination of MD and MC simulations.