Single-step deep reactive ion etching of ultra-deep Silicon cavities with smooth sidewalls
Résumé
tA process based on deep reactive ion etching (DRIE) has been developed and optimized for the fabricationof millimeter deep silicon cavities with smooth sidewalls. The process combines two approaches whichinvolve an optimized etching process based on the classical Bosch process (Alcatel A601E equipment)followed by the use of an aqueous etchant solution of potassium hydroxide (KOH) to smooth the surfaceand remove the fluorocarbon contaminants remaining after the DRIE process. As DRIE highly dependson the opening size of the patterned etch mask, different opening sizes have been tested to completelyetch through a 1.4 mm thick silicon wafer. Additionally, the effect of different etch-stop materials ontothe sidewalls quality has also been characterized. Sidewall quality of etched-through cavities was char-acterized by scanning electron microscopy (SEM) and contact surface profilometry. This single-step DRIEetching followed by short exposure to KOH solution permits to smooth sidewalls and achieve a surfaceroughness as low as 50 nm, which is the roughness typically obtained with the Bosch process on standarddepths.