GaAs wafer bonding by atomic hydrogen surface cleaning

A method of large-area wafer bonding of GaAs is proposed. The bonding procedure was carried out in an ultrahigh vacuum. The wafer surfaces were cleaned at 400 and 500 °C by application of atomic hydrogen produced by thermal cracking. The wafers were brought into contact either immediately after the cleaning, or at temperatures as low as 150 °C, without application of a load, and successfully bonded over the whole area. High-resolution transmission electron microscopy revealed that the wafers could be directly bonded without any crystalline damage or intermediate layer. From a mechanical test, the fracture surface energy was estimated to be 0.7–1.0 J/m2, which is comparable to that of the bulk fracture. Furthermore, this bonding method needs no wet chemical treatment and has no limits to wafer diameter. Moreover, it is suitable for low temperature bonding.