Chapter 7 - Thick-film silicon-on-insulator wafers preparation and properties

Abstract

This chapter reviews the methods of manufacturing bonded thick-film silicon-on-insulator (SOI) wafers used in microelectromechanical systems (MEMS) applications and typical properties of wafers are also summarized, focusing on data from large-series production of wafers. It details the approach that relies on mechanical back-grinding and optical precision polishing for final thinning of the SOI film. A comprehensive discussion of semiconductor wafer bonding technology and applications can be found in the references. SOI is a semiconductor structure consisting of a layer of single crystalline silicon separated from the bulk substrate by a thin layer of insulator. The SOI structure was created for the first time using silicon-on-sapphire. A review of SOI technologies with an emphasis on MEMS applications is also given. Bonded SOI wafers are composed of two silicon wafers bonded face-to-face with a buried oxide layer. One can choose the SOI parameters quite freely as the manufacturing process allows a wide range of independent wafer parameter values. Direct wafer bonding associated with mechanical thinning of the SOI layer is a generic technology that enables the fabrication of thick-film SOI wafers. It is perfectly adapted to the range of SOI layer thicknesses that are commonly used in MEMS applications. The selection of wafer type is based strongly on the performance versus overall cost per die and should include all aspects for consideration, a short description of the most important thin-film SOI manufacturing technologies are also given in this chapter.