Advanced etching of silicon based on deep reactive ion etching for silicon high aspect ratio microstructures and three-dimensional micro- and nanostructures

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Abstract

Different processes involving an inductively coupled plasma reactor are presented either for deep reactive ion etching or for isotropic etching of silicon. On one hand, high aspect ratio microstructures with aspect ratio up to 107 were obtained on sub-micron trenches. Application to photonic MEMS is presented. Isotropic etching is also used either alone or in combination with anisotropic etching to realize various 3D shapes.

Introduction

Less than 10 years ago, inductively coupled plasma (ICP) reactors have been introduced for silicon reactive ion etching (RIE) process leading to the deep reactive ion etching (DRIE) technique. The main novelties on these rather new ICP-RIE systems are the following:

  • Separation of the main plasma from the wafer

  • A higher plasma density

  • Improved Radio Frequency RF-power supply

  • Improved performance for pumping and mass-flow systems

  • Pulsed Low Frequency LF substrate biasing

  • New chemistry and new process (Bosch and cryogenic)

These hardware and process novelties led to improved performances, for instance:

  • Higher selectivity for deep etching (DRIE)

  • Higher aspect ratio (AR)

  • Higher etching rate, either for anisotropic or isotropic etching

  • Reduction of parasitic effects: notching, aspect ratio dependent Etching (ARDE), etc

The microfabrication of high aspect ratio microstructures (HARMS) is the main benefit of these technologies with numerous applications in the field of MEMS. There are two main ways of achieving HARMS by DRIE. The most popular way is the ‘Bosch process’, a patented process developed by Robert Bosch GmbH [1], which is based on alternating multiple steps of etching and sidewall passivation. The main alternative is the ‘cryogenic process’, relying on cooling the stage and silicon to cryogenic temperatures using liquid nitrogen [2], [3]. In this work, both processes are studied, sometimes in isotropic conditions, in order to obtain unusual shapes or unusual feature sizes.

Section snippets

Ultra-high aspect-ratio (AR) on sub-micron-wide trenches

Motivated by the need of fabricating silicon HARMS for nanophotonic applications [4], [6], we developed a technological process for manufacturing deep trenches and holes as well as silicon walls and pillars having sub-micron feature sizes.

All our DRIE experiments were performed on an ALCATEL 601E System. Fig. 1 shows our latest results related to deep etching of sub-micron trenches. One can see 0.374 μm—wide, 40.1 μm—deep trenches, corresponding to an aspect ratio of 107. To our knowledge, this

Using ICP reactor in isotropic conditions for 3D micromachining

In almost all cases, the main goal of using DRIE is the realization of vertical and deep HARMS. We also used the ALCATEL ICP reactor in isotropic conditions (using SF6 chemistry) in order to test the MEMSNAS process, which was proposed as a new 3D micromachining technique [7]. MEMSNAS is an acronym for Micro-loading Effect for Micromachining 3D Structures of Nearly All Shapes. Nearly all shapes are indeed obtainable by this process by taking advantage of the microloading effect: an array of

Acknowledgements

Part of this work was performed in the frame of the Sakura project, a joint French–Japanese project with a support from the French Ministry of Foreign Affairs and the Japanese Society for Promotion of Science (JSPS).

The authors would like to thank the staff of ADIXEN (Alcatel Vacuum Technology), in particular MM. Michel Puech, Nicolas Launay, Emmanuel Beaujon and Gilles Richier for their valuable help.

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