Reduced Etch Lag and High Aspect Ratios by Deep Reactive Ion Etching (DRIE)

• Published in: Micromachines (Basel) Vol. 12; no. 5; p. 542
• Main Authors: Gerlt, Michael S., Läubli, Nino F., Manser, Michel, Nelson, Bradley J., Dual, Jürg
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 10.05.2021; MDPI
• Subjects: deep reactive ion etching; Etching; fabrication; High aspect ratio; Microfluidics; Miniaturization; process optimization; Reactive ion etching; reduced etch lag; Silicon wafers; small structures; United Kingdom > UK; Germany
• ISSN: 2072-666X; 2072-666X
• DOI: 10.3390/mi12050542

Deep reactive ion etching (DRIE) with the Bosch process is one of the key procedures used to manufacture micron-sized structures for MEMS and microfluidic applications in silicon and, hence, of increasing importance for miniaturisation in biomedical research. While guaranteeing high aspect ratio structures and providing high design flexibility, the etching procedure suffers from reactive ion etching lag and often relies on complex oxide masks to enable deep etching. The reactive ion etching lag, leading to reduced etch depths for features exceeding an aspect ratio of 1:1, typically causes a height difference of above 10% for structures with aspect ratios ranging from 2.5:1 to 10:1, and, therefore, can significantly influence subsequent device functionality. In this work, we introduce an optimised two-step Bosch process that reduces the etch lag to below 1.5%. Furthermore, we demonstrate an improved three-step Bosch process, allowing the fabrication of structures with 6 μm width at depths up to 180 μm while maintaining their stability.