Ion Species Dependence on the Interfacial Properties of Silicon Homojunctions Bonded Using an Ion Bombardment Treatment

Abstract

Direct wafer bonded p-type (001) silicon homojunction structures were prepared with an ion bombardment surface treatment using either Ar or Kr ions prior to bonding in a high-vacuum direct wafer bonding system. The ion energies used spanned from a factor of 0.5 to 5 times of a baseline energy E0 for Ar and 0.5 to 2.5 times for Kr. The ion bombardment surface treatment induces a thin ~nm amorphous region at the Si|Si bonded interface. X-ray reflectivity measurements were performed on ion-bombarded single unbonded wafers. It was found that the Ar treated wafers showed a weak surface mass density dependence with ion energy, while wafers treated with Kr showed a strong ion energy dependence. While the Ar treatment reduces the surface density to ~80% of bulk Si density, the Kr treatment reduces the surface density to as low as ~70% of bulk Si density using an ion energy of 2.5⋅E0. Current-voltage measurements were also used to probe the electrical resistance across the amorphous interfacial region of the bonded structures prepared with Ar ions.

Surface Activated Si-Si Wafer Bonding Using Different Ion Species

“…The accumulation of ion beam damage as a result of ion-solid interactions constitutes an amorphous layer. The presence of such layer reduces the conductivity across the bonding interface [1]. As this is an undesired effect for most electronic applications, it is essential to minimize the amorphous layer thickness (ALT).…”