Techniques of cryogenic reactive ion etching in silicon for fabrication of sensors

Cryogenic etching of silicon, using an inductively coupled plasma reactive ion etcher ICP-RIE , has extraordinary properties which can lead to unique structures difficult to achieve using other etching methods. In this work, the authors demonstrate the application of ICP-RIE techniques which capitalize on the cryogenic properties to create different sensors geometries: optical, electrical, magnetic, and mechanical. The three techniques demonstrated are 1 single step deep etches with controllable sidewall profiles. Demonstrating this, silicon pillars with over 70 m depth and less than 250 nm sidewall roughness were etched using only 1.6 m of photoresist for use as solar cells. 2 Using the cryogenic etch for thick metallization and liftoff with a thin photoresist mask. Demonstrating this second technique, a magnetic shim was created by deposition of 6.5 m of iron into 20 m deep etched trenches, using the remaining 1.5 m photoresist etch mask as the liftoff mask. Using the same technique, 15 m of copper was lifted off leaving a 20 m deep plasma enhanced chemical vapor deposition silicon oxide coated, silicon channel with copper. 3 Use of a two step cryogenic etch for deep etching with reduced sidewall undercutting. This was demonstrated by fabrication of deep and anisotropic microelectromechanical systems structures; a mechanical resonator was etched 183 m deep into silicon with less than 3 m of undercutting. This work also describes the etch parameters and etch controls for each of these sensors. © 2009 American Vacuum Society. DOI: 10.1116/1.3196790