Aspect-Ratio-Dependent Etch effects in Titanium Deep Reactive Ion Etching
Résumé
Titanium-based microelectromechanical systems (MEMS) are attractive candidates for biomedical applications. For such devices, deep reactive ion etching (DRIE) is a key fabrication method that enables very high-aspect-ratio features to be performed into bulk titanium substrates. Most of the research work reported in the literature relies on a Cl 2 /Ar chemistry to deep etch titanium [1]-[3].
However, the DRIE technology on bulk titanium is not as mature as that on silicon and undesired effects such as the aspect ratio dependent etching (ARDE) have not been widely studied. The ARDE phenomenon, also known as “RIE lag”, consists in a strong correlation between the etching rate and the aspect ratio of the features (AR): the first decreases when the second increases [4].
To experimentally investigate process parameters leading to ARDE, a Cl2/SF6/O2 inductively coupled plasma (ICP) was used to etch deep trenches into bulk titanium substrates. The effects of ARDE are rather substantial in Cl2/SF6/O2 plasmas because the etching rate is very sensitive to the variation in the local atomic fluorine concentration as well as to the variation in the amount of passivating species. The pressure dependence of RIE lag has been studied and the influence of gas flow rates is investigated with respect to the etch rates.
References
[1] R. d’Agostino, F. Fracassi, and C. Pacifico, ‘Dry etching of Ti in chlorine containing feeds’, Journal of Applied Physics, vol. 72, no. 9, pp. 4351–4357, Nov. 1992, doi: 10.1063/1.352199.
[2] F. Fracassi and R. d’Agostino, ‘Chemistry of titanium dry etching in fluorinated and chlorinated gases’, Pure and Applied Chemistry, vol. 64, no. 5, pp. 703–707, Jan. 1992, doi: 10.1351/pac199264050703.
[3] E. R. Parker, B. J. Thibeault, M. F. Aimi, M. P. Rao, and N. C. MacDonald, ‘Inductively Coupled Plasma Etching of Bulk Titanium for MEMS Applications’, J. Electrochem. Soc., vol. 152, no. 10, pp. C675–C683, Jan. 2005, doi: 10.1149/1.2006647.
[4] R. A. Gottscho, ‘Microscopic uniformity in plasma etching’, J. Vac. Sci. Technol. B, vol. 10, no. 5, p. 2133, Sep. 1992, doi: 10.1116/1.586180.