AVS 57th International Symposium & Exhibition
    Plasma Science and Technology Tuesday Sessions
       Session PS2-TuA

Paper PS2-TuA7
Modeling of a Transformer-type Toroidal Plasma Source

Tuesday, October 19, 2010, 4:00 pm, Room Galisteo

Session: Plasma Sources
Presenter: S. Rauf, Applied Materials Inc.
Authors: S. Rauf, Applied Materials Inc.
Z. Chen, Applied Materials Inc.
K. Collins, Applied Materials Inc.
Correspondent: Click to Email
Many semiconductor processing applications including thin film deposition and chamber clean use reactive radicals, which can be efficiently generated using a remote plasma source. One popular remote plasma source design contains a toroidal plasma cavity with a few ferrite rings wrapped around the toroid. A radio-frequency (RF) magnetic field is induced in the ferrites using current loops around the ferrites, and this magnetic field generates a toroidal RF electric field within the plasma. The operation of this plasma source is not unlike a traditional transformer with a high permeability core. High density plasma can be generated over a large volume in these sources at moderate pressures (a few Torr), where traditional inductively coupled plasmas would have been localized in the vicinity of the inductive coils. Such a source design has also been used to generate high density plasmas for dielectric etching and plasma ion implantation. Despite the popularity of this plasma source design, it has not been modeled in detail to the best of our knowledge. This paper describes a 2-dimensional model for a magnetically-coupled transformer-type toroidal plasma source. The plasma model consists of the Poisson equation, the continuity equations for all species, and the electron energy equation. The drift-diffusion approximation has been used for the charged species. Induced electromagnetic fields and the resulting power deposition have been determined by solving the relevant Maxwell equations with an equivalent magnetic current source. The model also considers gas flow through the plasma source. The 2-dimensional model is applied to the simulation of Ar/NH3 and Ar/O2 plasmas in a toroidal plasma source driven at 400 kHz. A ring-shaped plasma is generated in the vacuum chamber by the electromagnetic fields. This plasma is fairly uniform, except near the gas inlet where the species composition is different due to rapid dissociation of the incoming reactive gases. Plasma characteristics are investigated over 0.5 – 3.0 Torr pressure and 500 – 3000 W power ranges. Electron densities in the 1017 – 5×1018 m-3 range are observed for the conditions investigated and the incoming reactive gases almost completely dissociate in the plasma. Detailed plasma characteristics, structure of the electromagnetic fields, and composition of the resulting neutral species is discussed in the paper.