Abstract text (incl. figure legends and references)

It is known that the atomic diffusivity of (111)- orientation surface is 3 to 5 order of magnitude higher than (110) and (100) surfaces, leading to the decrease of Cu to Cu bonding temperature to 150℃. In the present study, an 8-inch Si wafer has been evaporated firstly with Ag nanotwinned thin film with a thickness about 4 μm using the assistance of ion beam bombardment. FIB cross-sectional image reveals many columnar grains with an average width about 0.5 μm containing numerous parallelly aligned Ag nanotwins. XRD spectrum showed a strong Ag (111) peak without any other crystal orientations both in the central and edge regions, indicated the (111)- preferred orientation of the Ag nanotwinned films. The results are consistent with the top-view EBSD inverse pole figure analysis showing that a very high density of (111) orientation of 85.2% on the surface of the Si wafer. Furthermore, TEM analyses indicated that the twin characteristics of the grain structure in the Ag thin film can be evidenced from the symmetry relationship between the ( )M/( )M and ( )T/( )T diffraction patterns through the inset selected area electron diffraction (SAED) analysis taken from the [011] zone axis. The twin spacing can also be measured from the HR-TEM micrograph, which are ranged from 2 to 15 nm with an average value about 6 nm. It can also be observed from the HR-TEM analyses that the Ag (111) twin boundaries revealed a very fine atomic spacing about 0.2 nm. Finally, the direct wafer bonding at quite low temperatures ranging from 250 to 100℃ has been performed.

Fig.1 XRD and FIB analyses of the Ag nanotwins on Si wafer.

Fig.2 EBSD and TEM analyses of the Ag nanotwins on Si wafer and low temperature direct bonding of the wafers.