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

Abstract

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 CF 4 . The simulation takes into account the following charged particles: electrons, two kinds of positive ions (Ar ϩ , CF 3 ϩ ), and two kinds of negative ions (F Ϫ , CF 3 Ϫ ). The model considers electron-Ar collisions, electronϪCF 4 collisions, various kinds of collisions of CF 3 ϩ , F Ϫ , CF 3 Ϫ , or Ar ϩ with Ar or CF 4 , 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/CF 4 mixture, as well as for pure Ar and pure CF 4 discharges at a pressure of 200 mTorr. It is observed that at high CF 4 concentration the discharge behaves as a typical electronegative discharge and that CF 3 ϩ is the major positive ion. At low CF 4 concentration, keeping the other operating parameters the same, the double layer structure and the electron density maxima at the bulk-sheath interface, which are representative for an electronegative discharge, disappear and the Ar ϩ density exceeds the CF 3 ϩ density by more than 1 order of magnitude. The results show that the F Ϫ ions are the dominant negatively charged species for all Ar/CF 4 ratios investigated.

Ionization by Drift and Ambipolar Electric Fields in Electronegative Capacitive Radio Frequency Plasmas

“…It was demonstrated that this is a novel mode of discharge operation not related to the and modes [14]. Moreover, local extrema of the electric field at the sheath edges accelerating electrons towards the adjacent electrode were observed [16]. However, the mechanisms causing these fields and, thus, the operation mode have not been clarified yet.…”

Computer Simulations for Processing Plasmas

“…Plasma etching by cc rf discharges is well recognized for its anisotropy, which is a critical process parameter in integrated circuit manufacturing. To study the detailed dynamic behavior of ions and electrons in such kind of plasma, and to calculate the EEDFs and (especially) IEDFs, which are important quantities for etching applications, we have developed a PIC‐MC model for a cc rf reactor, in a mixture of CF 4 /Ar/N 2 24,25. This is a typical gas mixture used for plasma etching of silicon and SiO 2 in the semiconductor industry.…”

Modeling of the effect of radicals on plasmas used for etching in microelectronics

“…The most abundant radical in plasmas containing CF 4 is CF [15,16] and it can be found even at abundances of the order of several %. As CF have attachment at low energies with thresholds considerably smaller than that of the dissociative electron attachment for electrons in CF 4 the overall attachment rate is enhanced and extended to lower energies.…”