Unaxis DRIE is used to etch deep anisotropic trenches in silicon substrates using the patented Bosch process. The Bosch process, also known as pulsed or time-multiplexed etching and alternates repeatedly between two modes, a deposit mode and an etch mode. Each phase lasts for several seconds. The etch phase uses SF6 to etch the silicon while the deposit phase uses C4F8 to passivate the substrate.

An inductively coupled plasma (ICP) generates a dense plasma near the top of the electrode. A second RIE generator, which is capacitively coupled to the wafer chuck, is used to independently bias the substrate to improve the directionality of the etch.

The passivation layer protects the entire substrate from further chemical attack and prevents further etching. However, during the etching phase, the directional ions that bombard the substrate sputter the passivation layer at the bottom of the trenches, but not along the sides. The bottoms of the trenches are thereby exposed to the SF6etchant. The SF6 chemistry can only etch silicon or polysilicon.