Bulk micromachining of silicon

TLDR

Bulk silicon etching remains the dominant fabrication method for micromachined sensors, actuators, and structures, with wet, vapor, and plasma approaches still widely used and unlikely to be displaced by newer surface‑micromachining techniques. The study reviews and compares bulk silicon etching processes across wet, vapor, and plasma categories, evaluating etch results, cost, complexity, and process compatibility. The authors present comparative analyses of each etching category and illustrate the techniques with several example micromachined structures.

Abstract

Bulk silicon etching techniques, used to selectively remove silicon from substrates, have been broadly applied in the fabrication of micromachined sensors, actuators, and structures. Despite the more recent emergence of higher resolution, surface-micromachining approaches, the majority of currently shipping silicon sensors are made using bulk etching. Particularly in light of newly introduced dry etching methods compatible with complementary metal-oxide-semiconductors, it is unlikely that bulk micromachining will decrease in popularity in the near future. The available etching methods fall into three categories in terms of the state of the etchant: wet, vapor, and plasma. For each category, the available processes are reviewed and compared in terms of etch results, cost, complexity, process compatibility, and a number of other factors. In addition, several example micromachined structures are presented.