| AVS 57th International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS1-ThA |
| Session: | Plasma Modeling |
| Presenter: | A. Agarwal, Applied Materials Inc. |
| Authors: | A. Agarwal, Applied Materials Inc. S. Rauf, Applied Materials Inc. K. Collins, Applied Materials Inc. |
| Correspondent: | Click to Email |
Plasma etching of high aspect ratio (HAR) features is extremely challenging as it places great emphasis on uniformity of just about every characteristic of the plasma: density, fluxes, fields, energy and angular distributions to mention a few. At large aspect ratios, even minor variations in the bulk plasma can translate into huge deviations on the feature scale. One important plasma characteristic that influences etch properties is the ion temperature. Small variations in ion temperature can lead to non-uniform or tapered etch profiles since even marginally cold ions when accelerated through the sheath (having large voltage drops for HAR process) can deviate significantly from the normal leading to offset of the bottom of the feature compared to the top.
In this work, a 2/3 dimensional plasma equipment model (CRTRS) [1] has been used to assess the consequences of ion and neutral temperature on etching processes. CRTRS previously only included continuity and momentum equations for charged species. The model has been improved to include solution of the energy equations for all heavy neutral and charged species to obtain the ion and neutral temperatures. The model results have been validated using experimental data from laser induced fluorescence measurements.[2] In this talk, results of this validation exercise will be discussed. We found that while ion temperatures peak in the sheath region near the electrodes under the influence of high electric fields, neutral radicals’ temperature peak predominantly in the bulk via collisions with ions (for example, charge exchange reactions). Consequently, inclusion of Franck-Condon heating sources is important for low fragmenting gas mixtures such as pure Ar compared to, for example, N2 to accurately predict neutral temperatures.
The validated model is then applied to a typical high-power HAR etch process. Modeling results are used to understand the impact of gas and ion temperatures on electron heating and power deposition mechanisms, ion energy and angular distributions, plasma uniformity and neutral radical composition. Plasma characteristics are investigated for etch-relevant feed gas mixtures over a wide range of pressures (20 – 100 mT).
1 A. Agarwal, P.J. Stout, S. Rauf and K. Collins, 56th AVS Symposium 2009.
2 G.A. Hebner and A.M. Paterson, Plasma Sources Sci. Technol. 19, 015020 (2010).