Paper PS1-MoM9
Prediction of Feature Profile Evolution of Deep Si Etching under Effect of Plasma Molding in 2f-CCP in SF₆/O₂

Monday, October 15, 2007, 10:40 am, Room 606

Deep-RIE is widely used in MEMS fabrication. In large-scale etching, plasma molding is one of the important issues.¹ In our previous study, the influence of the ion transport under the distorted electric field, i.e., plasma molding, on the anisotropic Si etching was numerically investigated without considering the neutral reaction.² In this study, we numerically investigate the feature profile evolution of deep Si etching on the MEMS scale in a 2f-CCP in SF₆/O₂ under competition between Si etching by ions and F radicals and passivation layer formation by O radicals, including the effect of plasma molding. In SF₆(83%)/O₂ at 300 mTorr, for only physical SF₅⁺ ion etching of Si, the etching is enhanced at the bottom corner due to the distorted ion incidence on the wafer under the plasma molding. In the case of RIE caused by both SF₅⁺ ions and F radicals without passivation layer formation, the influence of the plasma molding on the feature profile is not observed because of a much higher etching rate of Si by F radicals than that by SF₅⁺. However, the bowed and undercut profiles appear significantly at the sidewall and near the silicon-mask interface. Finally, we estimate the feature profile evolution of Si by RIE with the passivation layer formed by O radicals. Under the presence of the plasma molding, the removal of the passivation layer by energetic ions at the bottom corner is strengthened by the effect of excess ion flux with distorted angular distribution. On the other hand, an insufficient amount of ions leads to less efficient removing the passivation layer at the center of the bottom. The chemical etching rate of Si layer for F radicals is much higher than that of passivation layer. Thus, when the passivation layer is removed by SF₅⁺ion impact, the etching of Si is enhanced by addition of F radicals. As a result, this indicates that anisotropy of the etching profile is not achieved especially at the bottom in SF₆(83%)/O₂ at 300 mTorr.³ Further investigation will be given for influence of the percentage of Oxygen on anisotropic feature profile on the MEMS scale in the 2f-CCP system.

¹D. Kim and D. J. Economou, IEEE. Trans. Plasma Sci., vol. 30, no. 5, pp. 2048-2058, 2002.
²F. Hamaoka, T. Yagisawa, and T. Makabe, Jpn. J. Appl. Phys., vol. 46, no. 5A, pp. 3059-3065, 2007.
³ -, IEEE Trans. Plasma Sci., (accepted for publication), Oct 2007.