Abstract
This chapter discusses porous silicon (PS) sacrificial layer technologies as a tool for forming three-dimensional (3D) structures within bulk silicon. PS formation is explained in a detailed way with the help of diagrams. Considering the energetic conditions that prevail at the solid–liquid interface, the electrochemical processes that lead to the formation of PS can be understood. With this knowledge, doping profiles can be designed which restrict the PS formation process to specified surface- and subsurface areas within the preprocessed wafers. 3D structures consisting of bulk Si can be formed by selectively forming the PS in the specified areas and by removing the PS from the anodized wafers afterward. The success of this technology is demonstrated by means of several device demonstrators, including airbag igniters and field effect gas sensors. The industrial maturity of the PS sacrificial layer technology is demonstrated by a manifold absolute pressure sensor with integrated CMOS electronics for automotive applications.
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