Reactive ion etching for high aspect ratio silicon micromachining

Abstract

High aspect ratio technology is the key technology for advanced microelectro-mechanical systems (MEMS) fabrication. In order to realise more compact and low cost MEMS fabrication techniques the combination of lithography and reactive ion etching (RIE) techniques has been proposed. The development of costly high-density sources and operating with low substrate temperature is very promising technique to achieve the over 100 μm range depth with vertical sidewalls. Here we try to extend the available and existing etch technology for this purpose. The use of Cl containing technology was started about two decades ago and successfully applied to Si-trench etching and Al etching. The possibility to extend this technology for the fabrication of MEMS is presented. In order to evaluate the suitability of RIE, the change of lateral dimensions versus depth has been evaluated for deep structuring of silicon material with fluorine, chlorine and bromine plasma chemistries, respectively, as well as for various compounds based on these halogens. A conventional planar RIE reactor, in some cases with low substrate temperature, has been used. The use of RIE has the advantage that a large variety of materials, including Si and quartz may be processed with very high anisotropy, thus meeting advanced microelectronic and quite diverse MEMS requirements. The development of new etching technology to meet the new requirement of MEMS fabrication is the driving force behind this article.