Comparison between Bosch and STiGer Processes for Deep Silicon Etching.

Thomas Tillocher,Philippe Lefaucheux,Rémi Dussart,Gaëlle Antoun,Mohamed Boufnichel,Jack Nos

doi:10.3390/mi12101143

Abstract

The cryogenic process is well known to etch high aspect ratio features in silicon with smooth sidewalls. A time-multiplexed cryogenic process, called STiGer, was developed in 2006 and patented. Like the Bosch process, it consists in repeating cycles composed of an isotropic etching step followed by a passivation step. If the etching step is similar for both processes, the passivation step is a SiF4/O2 plasma that efficiently deposits a SiOxFy layer on the sidewalls only if the substrate is cooled at cryogenic temperature. In this paper, it is shown that the STiGer process can achieve profiles and performances equivalent to the Bosch process. However, since sidewall passivation is achieved with polymer free plasma chemistry, less frequent chamber cleaning is necessary, which contributes to increase the throughput.

Highlights

Deep silicon etching, called silicon DRIE (Deep Reactive Ion Etching), has become an essential process step in micromachining, where high aspect ratio structures are often required
The two main DRIE processes, the Bosch process and the cryogenic process, which have been used for about 3 decades, exploit this technique in different ways
The Bosch process is time-multiplexed, which consists in repeating cycles comprising an etch step and a passivation step [1,2,3,4,5,6,7]

Summary

Introduction

Called silicon DRIE (Deep Reactive Ion Etching), has become an essential process step in micromachining, where high aspect ratio structures are often required. Ions break though the passivation layer at the etch front and, from one cycle to the other, an isotropic cavity is etched underneath the previous one. This eventually leads to anisotropic profiles with a characteristic roughness at the sidewalls known as “scalloping”. The amplitude of these ripples is usually kept to a minimum value by reducing the etch step time. Such a roughness can be an issue where smooth sidewalls are required. The polymer layer is deposited on the chamber walls and, periodic cleaning procedures are necessary to keep

Methods

Results

Conclusion