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

Michael S Gerlt,Jürg Dual,Bradley J Nelson,Michel Manser,Nino F Läubli

doi:10.3390/mi12050542

Michael S Gerlt, Jürg Dual + Show 3 more

Open Access

https://doi.org/10.3390/mi12050542

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Journal: Micromachines	Publication Date: May 10, 2021
Citations: 26	License type: CC BY 4.0

Affiliation: Institute for Biomedical Engineering

Abstract

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 width at depths up to while maintaining their stability.

Highlights

The Bosch process is one of the most common deep reactive ion etching (DRIE) processes as it consists of only two steps while not relying on fast response times that would only be attainable with high-end equipment, making it accessible for a broader audience and a large variety of research fields
We tackled two fundamental challenges of DRIE etching, namely the reactive ion etching (RIE) lag and high aspect ratio etching of small structures, and described the optimised processes in detail
Through an improved two-step Bosch process, we were able to etch trenches of various widths within a difference in etch depth of less than 1.5% while keeping the simplicity of the Bosch process to ensure the broad and well-established applicability of this procedure

Summary

Introduction

The standard fabrication steps used for the production of these microstructures consist of photolithography, etching, and post-processing such as bonding, dicing, and packaging. One of the most common processes for microstructure fabrication is deep reactive ion etching (DRIE), where physical and chemical etching are successfully combined [4]. The full potential of DRIE was revealed with the invention of a time-multiplexed alternating process of passivation and etching by Laemer and Schilp in 1996 [5]. Named after their employer, the Bosch process is nowadays one of the key processes in the silicon industry [6]. The characteristic scallops that result from the Bosch process are unavoidable

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