Package structure and method for forming the same

A package structure, comprising:

• a first interconnect structure formed over a first substrate, wherein the first interconnect structure comprises a first dielectric layer;
• a second interconnect structure formed below a second substrate;
• and
• a bonding structure between the first interconnect structure and the second interconnect structure, wherein the bonding structure is embedded in the first dielectric layer, the bonding structure comprises a first intermetallic compound (IMC) and a second intermetallic compound (IMC), and a grain boundary is present between the first IMC and the second IMC.

A method for forming a package structure, comprising:

• forming a first interconnect structure over a first substrate;
• forming a first IMC over the first interconnect structure;
• forming a second interconnect structure over a second substrate;
• forming a solder layer over the second interconnect structure;
• and
• bonding the first substrate and the second substrate by bonding the first IMC to the solder layer to form a second intermetallic compound (IMC), wherein a grain boundary is present between the first IMC and the second IMC.