Patterned Cu Nanoparticle Film for All-Cu Interconnection Without Chemical Mechanical Polishing Pretreatment

Abstract

All-Cu interconnects with fine pitch scalability and excellent electrical performance are highly considered as the next interconnection node for the coming era of chiplet integration. However, current all-Cu interconnection through Cu-Cu direct bonding relies much on expensive chemical mechanical polishing (CMP) process to reduce surface roughness to several nanometers. Herein, Cu nanoparticle film prepared by pulsed laser deposition (PLD) was successfully patterned into micro bumps of 120 μm pitch and sintered at 160~250 °C to form all-Cu interconnects without using CMP pretreatment. The fabricated bumps had a low Young’s modulus of only 1GPa and could produce vertical collapse of several microns in bonding process, providing compliance with surfaces having high roughness and poor coplanarity. The bonded interconnects also exhibited excellent mechanical quality with shear strength >20 MPa at 160 °C, 15 MPa and >90 MPa at 250 °C, 20 MPa, which was superior to most reported Cu-Cu bonding using patterned nanomaterials. Patterning mechanism in PLD process involving incident characteristic of Cu nanoparticle flux, evolution of bump morphology was investigated and bump morphology’s influence on bonding properties was analyzed in detail. The strategy illustrated here could lead to develop a low-temperature, low-pressure assembly technique with less reliance on CMP for all-Cu interconnection.