1 Introduction

Over the last 15 years wafer bonding has emerged from a tricky laboratory experiment to an industrial process. Silicon wafer bonding is today used for the manufacture of silicon-on-insulator (SOI) materials and sensors [COL 97, HOL 92]. The possibility of using wafer bonding as a general method in integrating materials to circumvent problems related to epitaxial growth of dissimilar materials is under intensive discussion. The publication of scientific reports on wafer bonding are steadily increasing. However, the pre-history of wafer bonding started long ago. Back in 1734, Desaguliers observed how "The friction of surfaces decreases with decreasing surface roughness up to a point where the surfaces are so well polished that they stick together resulting in dramatically increased friction" [DAW 79]. In 1936 Lord Rayleigh made the first systematic study of sticking properties of polished glass pieces. In his work "A study of glass surfaces in optical contact" [RAL 36] he established the first scientific basis of wafer bonding. The modern history of wafer bonding started in the late 60's, when Wallis and Pomerantz reported the possibility of using a combination of elevated temperature and an electric field to fuse glass pieces to silicon [WAL 69]. The method is known as anodic bonding. Later on in 1985/1986 Lasky and co-workers reported the use of wafer bonding without electrostatic fields for the formation of SOI materials [LAS...