| AVS 57th International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS1-ThA |
| Session: | Plasma Modeling |
| Presenter: | J.A. Kenney, Applied Materials Inc. |
| Authors: | J.A. Kenney, Applied Materials Inc. S. Rauf, Applied Materials Inc. K. Collins, Applied Materials Inc. |
| Correspondent: | Click to Email |
As high aspect ratio (HAR) etch requirements have grown more stringent, the strategies used to deliver an appropriate combination of species to the wafer have evolved considerably. One common approach is to use a capacitively coupled plasma (CCP) reactor with a combination of generator frequencies and complex feed gas mixtures. The use of multiple frequencies allows for generation of a large plasma density using a high frequency source while biasing the wafer substrate at low frequency to control the flux and energy of impinging ions. Complex feed gases provide etch precursors from which to make volatile products as well as passivating species to protect certain features (e.g. sidewalls). Such a large parameter space of frequencies, powers, pressures, and feed gases to employ, however, has made modeling an increasingly attractive option to gain insight and understanding, both during engineering design and process development. Here, we use a plasma model to investigate the impact of frequency mixture in low pressure capacitively coupled discharges.
In our 2/3-dimensional fluid plasma model, charged species densities are computed by solving continuity equations for all species coupled with the full momentum equation (ions) or the drift-diffusion approximation (electrons). These equations, combined with the Poisson equation, which governs the electrostatic fields, are solved implicitly in time. The electron temperature is determined by solving the electron energy equation. The model also includes the full set of Maxwell equations in their potential formulation, Kirchhoff equations for the external circuit, and continuity equations for neutral species, along with non-uniform mesh generation to better resolve regions of interest. Ion energy and angular distributions are computed using a Monte Carlo-based particle simulation, which uses the spatially and temporally-resolved species densities, species fluxes, and electric fields from the plasma model as inputs.
In this work, we look at the impact of multiple frequencies on plasma density, uniformity, fluxes of neutrals and ions, and ion energy distributions. We consider frequencies in the range of 1 to 150 MHz in single-, dual-, and three-frequency configurations in CCP systems using a simple etch-relevant feed gas mixture (Ar/CF4) at 20 mT. Radio-frequency (RF) bias powers in the 1.0 – 7.0 kW range are employed.