A dry plasma etch method commonly used to “micromachine” silicon structures is Deep Reactive Ion Etching (DRIE). Deep trenches with vertical sidewalls and excellent uniformity can be achieved using the Bosch process. This technique, developed by Robert Bosch GmbH, uses sulfur hexafluoride (SF6) for a high silicon etch rate, followed by a gas such as octafluorocyclo-butane (C4F8) to form a teflon-like protective barrier on the etched sidewalls. The latter favors etching in the vertical direction only. The alternating SF6 and C4F8 steps are typically repeated several hundred times to achieve the desired trench depth.
Point of exhaust scrubbing is required for MEMS Etch, since the waste fluoride byproducts are both highly toxic and corrosive. Additionally, the perfluorinated compounds SF6 and C4F8 are greenhouse gases with high global warming potential.
|MEMS Etching||Typical Gases Used|
|Bosch process||SF6, C4F8|