Electrical properties of Si-Si interfaces obtained by room temperature covalent wafer bonding

Abstract

We study covalent bonds between p-doped Si wafers (resistivity $10 X cm) fabricated on a recently developed 200 mm high-vacuum system. Oxide-and void free interfaces were obtained by argon (Ar) or neon (Ne) sputtering prior to wafer bonding at room temperature. The influence of the sputter induced amorphous Si layer at the bonding interface on the electrical behavior is accessed with temperature-dependent current-voltage measurements. In as-bonded structures, charge transport is impeded by a potential barrier of 0.7 V at the interface with thermionic emission being the dominant charge transport mechanism. Current-voltage characteristics are found to be asymmetric which can tentatively be attributed to electric dipole formation at the interface as a result of the time delay between the surface preparation of the two bonding partners. Electron beam induced current measurements confirm the corresponding asymmetric double Schottky barrier like band-alignment. Moreover, we demonstrate that defect annihilation at a low temperature of 400 C increases the electrical conductivity by up to three orders of magnitude despite the lack of recrystallization of the amorphous layer. This effect is found to be more pronounced for Ne sputtered surfaces which is attributed to the lighter atomic mass compared to Ar, inducing weaker lattice distortions during the sputtering.

Characterization of Wafer-Bonded Oxide-Free Silicon with Surfaces Treated with an Ion-Bombardment Procedure

“…Later studies by Takagi et al, (7) characterized the mechanical properties of the bonded interface for bonded Si wafers treated with the argon ion bombardment treatment and found the mechanical bond strength to be comparable to the mechanical strength of bulk Si. Work by Jung et al, (8) investigated the electrical properties of bonded Si wafers treated with argon ions with parameters similar to those used in our work presented here. Their electrical measurements and modeling determined that the damaged layer can be treated as a nearly square energy barrier that spans the thickness of the damaged region.…”

Effect of Combined Hydrophilic Activation on Interface Characteristics of Si/Si Wafer Direct Bonding

“…On the other hand, O 2 plasma activation will generate induced charges at the bonding interface; thus, the fixed oxide charges and the interface trap density increase. These oxide charges form a depletion region and generate additional energy states at the bonding interface, resulting in the increase of the barrier height [31] and further raise the resistance. Otherwise, the resistance increases with the increase of O 2 plasma activation time.…”

“…trap density increase. These oxide charges form a depletion region and generate additional energy states at the bonding interface, resulting in the increase of the barrier height [31] and further raise the resistance. Otherwise, the resistance increases with the increase of O2 plasma activation time.…”

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

“…There are many reports in the current literature of bonding a diverse roster of materials using this ion bombardment approach (4,5,6). However, fundamental understanding of bonded interfaces prepared using this ion bombardment surface treatment is still in its infancy; in particular, understanding the transport characteristics across the bonded interface.…”