SOI Wafers

SOI (silicon-on-insulator) is a semiconductor technology which enables a full isolation of each electronic component on an integrated circuit by using a buried oxide layer. The heart of a SOI wafer is an ultra-thin, monocrystalline, conductive layer on a silicon wafer. All electronic operations take place, on this isolated layer, enabling higher switching frequencies and lower power consumption all the while avoiding unwanted heat production. SOI chips have been used recently in consumer goods and applications, such as computing, gaming, automotive, networking and imaging, as well as generally in devices requiring ultra low power consumption.

An accurate wafer bonding process is the key factor in obtaining high quality, single crystalline silicon films on insulating substrates. For SOI wafer manufacturing, a thermally oxidized silicon wafer will typically be bonded together with another silicon wafer that has a native oxide layer. This technique is called oxide-oxide bonding. Molecular, fusion or direct wafer bonding are other synonyms for this bonding method. Wet bench cleaning needs to be done prior to subsequent processes.

Ultra clean handling of wafers in class 1 environments throughout the whole process assures high-yield and void-free bonds. All essential steps from cleaning and alignment to pre-bonding and IR-inspection have to be combined in one high volume production system.

Cleaning - as controlled cleanliness is a must to guarantee proper surface conditioning - and plasma activation are important steps prior bonding. A mechanical flat-to-flat or notch-to-notch alignment is done on the same process station directly before bonding, followed by a controlled initiation of the bond front which is essential for void- and stress-free bonding. The bonding itself can take place under ambient atmosphere or vacuum. After the bonding is finished, a first quality investigation takes place using IR inspection.

Please see our related product EVG®850 for detailed information.


SOI wafers produced using Smart Cut® technology. Courtesy of SOITEC.

Power PC Chip manufactured on an SOI wafer. Courtesy of IBM.