Superior Electrical Characteristics of Au-Sn Intermetallic Compound with Ultra-Thin Buffer Layer Structure in Eutectic Bonding Technology for 3D Integrated Circuits Applications

This study explores the application of a nickel ultra-thin buffer layer (Ni UBL) for Au-Sn intermetallic compound (IMC) in the eutectic bonding technique for three-dimensional integrated circuits (3D ICs). The Ni UBL effectively decelerates the interdiffusion rate between Au and Sn layers, minimizing void formation, stabilizing the bonding structure, and thereby enhancing the bonding quality. Bonding experiments were conducted at the eutectic point of Au-Sn IMC (280°C) on both blanket wafers and patterned chips with Kelvin structures. The results showed significant improvements in bonding strength from 8.78 to 13.19 MPa, and in specific contact resistance, decreasing from 1.13×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> to 7.20×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> ohm-cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, with and without UBL, respectively. This study highlights the potential of Ni UBL structure for achieving reliable, high-performance, and low-thermal-budget bonding in advanced packaging and heterogeneous integration platforms.