Scalloping removal on DRIE via using low concentrated alkaline solutions at low temperature

• Published in: Sensors and actuators. A. Physical. 2011-11, Vol.170 (1), p.114-120
• Main Authors: Defforge, Thomas, Song, Xi, Gautier, Gaël, Tillocher, Thomas, Dussart, Rémi, Kouassi, Sébastien, Tran-Van, François
• Format: Article
• Language: English
• Subjects: Actuators; Cryogenic etching; DRIE; Etching; Evolution; KOH; Physics; Plasma Physics; Reactive ion etching; Roughness; Scalloping; Silicon; Smoothing; STiGer process; TMAH
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2011.05.028

The scalloping removal on the silicon via sidewalls after a Deep Reactive Ion Etching (DRIE) by the so-called STiGer process has been achieved using a low concentrated alkaline solution at low temperature. Post-etching to reduce sidewall roughness was carried out in both KOH and TMAH-based solutions where the mass concentrations varied between 2% and 5%. The influence of IsoPropyl Alcohol (IPA) addition and the behavior of alkaline mixtures at two different temperatures (10 °C and 22 °C) were also investigated. The production of silicon surfaces free of micro-pyramids (also known as hillocks) has gone through the optimization of every etching parameter. SEM pictures have qualitatively evidenced the scalloping reduction and the shapes evolution in time, whereas AFM measurements performed on the silicon via sidewalls have allowed a quantification of the smoothing effect of the alkaline solutions. The Root Mean Square roughness ( R q) of the reference (sample with scalloped sidewalls without smoothing treatments) was thus compared with the one for wet alkaline treated samples. The results demonstrate that the etched via sidewalls are 60 times smoother. This value is, to our knowledge, the most important smoothing effect described in the literature.