Asymmetric Low Temperature Bonding Structure with Thin Solder Layers Using Ultra-Thin Buffer Layer.

Area of Science:

• Materials Science
• Electrical Engineering
• Nanotechnology

Background:

• Intermetallic compound (IMC) formation is a critical challenge in low-temperature bonding processes.
• Achieving reliable electrical isolation and solderability simultaneously is difficult in conventional bonding structures.
• High-density three-dimensional (3D) integration requires advanced interconnect technologies that minimize thermal budget.

Purpose of the Study:

• To investigate an asymmetric Cu to In/Sn bonding structure with a nickel ultrathin buffer layer (UBL) on the Cu side.
• To explore the effect of the Ni UBL on mitigating intermetallic compound (IMC) formation during bonding.
• To demonstrate the feasibility of low-temperature hybrid bonding for 3D integration using the proposed asymmetric structure.

Main Methods:

• Fabrication of an asymmetric bonding structure with a Ni UBL on the Cu interface.
• Optimization of bonding parameters, including temperature and time, for achieving robust interconnects.
• Characterization of the bonding interface to analyze IMC formation and bond quality.

Main Results:

• The Ni UBL effectively suppressed the formation of intermetallic compounds (IMCs) during the bonding process.
• An asymmetric structure successfully separated electrical isolation and solder processes, preventing IMCs during polymer curing.
• A well-bonded asymmetric structure was achieved using submicron solder at 150 °C for 15 minutes.

Conclusions:

• The asymmetric Cu to In/Sn bonding structure with a Ni UBL is a promising approach for low-temperature interconnects.
• This technology effectively prevents detrimental IMC formation, crucial for reliable 3D integration.
• The developed structure holds significant potential for advancing high-density 3D integration through low-temperature hybrid bonding.