Surface pretreated low-temperature aluminum–aluminum wafer bonding

Aluminum–aluminum wafer bonding is becoming increasingly important in the production of CMOS microelectromechanical systems. So far, successful bonding has required extreme processing temperatures of 450 °C or more, because the chemically highly stable oxide layer acts as a diffusion barrier between the two aluminum metallization layers. By using the ComBond ® system, in which a surface treatment and subsequent wafer bonding are both performed in a high vacuum cluster, for the first time successful Al–Al wafer bonding was possible at a temperature of 150 °C. The bonded interfaces were characterized using C-mode scanning acoustic microscopy and transmission electron microscopy, and featured areas of oxide-free, atomic contact.