Investigation of Low-Pressure Sn-Passivated Cu-to-Cu Direct Bonding in 3D-Integration

Area of Science:

• Materials Science
• Electrical Engineering
• Nanotechnology

Background:

• Copper-to-copper direct bonding is crucial for 3D integrated circuits (3D ICs).
• Conventional bonding methods require high temperatures, high pressures, and precise height control, limiting their application.
• Developing low-cost, low-energy bonding techniques is essential for advanced semiconductor manufacturing.

Purpose of the Study:

• To investigate the feasibility of low-temperature, low-pressure copper-to-copper direct bonding using tin passivation.
• To determine the optimal tin thickness, bonding temperature, and pressure for successful bonding.
• To evaluate the bonding performance under various conditions, including post-planarization.

Main Methods:

• Electroplated copper surfaces were passivated with tin (Sn) of varying thicknesses (600 nm, 800 nm, 1 μm).
• Bonding experiments were conducted at low temperatures (220 °C, 250 °C) and low pressure (1 MPa).
• Transmission electron microscopy (TEM) was used to analyze the microstructure, adhesion, and intermetallic compounds (IMCs).

Main Results:

• Successful copper-to-copper bonding was achieved at low temperatures and pressures (1 MPa) without planarization by utilizing tin passivation.
• The minimum required tin thickness was determined to compensate for height differences.
• Optimized bonding parameters were identified for different temperatures, and bonding was successful even under more severe conditions post-planarization.

Conclusions:

• Tin passivation enables low-temperature, low-pressure copper direct bonding, offering a viable alternative to conventional methods for 3D ICs.
• This approach simplifies the bonding process by eliminating the need for high temperatures and planarization.
• The study provides valuable insights into optimizing tin-based bonding for advanced packaging technologies.