<title>Thick porous silicon sacrificial layer formation using implanted mask technology</title>

Abstract

Surface micromachining is an established micro technology. The process is only limited by sacrificial layer thickness and sometimes a disturbing surface topology. This paper describes an innovative surface micromachining technology. Standard surface micromachining allows layer thickness of a few micrometer. Using porous silicon as sacrificial layer, it is possible to create any layer thickness up to 100 micrometers . Thick porous silicon sacrificial layers are used to combine the advantages of standard surface micromachining with the advantages of bulk micromachining. The problems resulting form surface topology are eliminated by using ion implanted masks. Based on different porous silicon formation mechanism for - and p-type silicon, it is possible to use n- implanted layers as masking material during the anodization of p-type silicon, resulting in a planar surface. For this masking technology, no additional masking layers are required. For free standing membrane generation it is possible to deposit e.g. a PECVD-layer on top of the porous silicon layer. If required, e.g. to protect free standing structures during following process steps from mechanical failures, it is possible to remove sacrificial layers with diluted alkaline solution in a final process step after dicing. A complete process flow has been developed for thick porous silicon layers up to 100 micrometers . The use of this sacrificial layer technology for thermally isolate gas sensor membrane fabrication and the detailed process parameters will be presented.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.