One aspect of the present disclosure pertains to an IC packaging structure that includes a bottom circuit structure having first semiconductor devices on a first substrate, a first interconnect structure over the first semiconductor devices, and a first bonding structure over the first interconnect structure; and a top circuit structure having second semiconductor devices on a second substrate, a second interconnect structure underlying the second semiconductor devices, and a second bonding structure underlying the second interconnect structure. The first bonding structure includes a first metal feature having a first crystalline bulk layer of a metal and a first amorphous surface layer of the metal. The second bonding structure includes a second metal feature having a second crystalline bulk layer of the metal and a second amorphous surface layer of the metal. The top circuit structure is bonded to the bottom circuit structure through the first and second amorphous surface layers.