Cu/SiO<inf>2</inf> hybrid bonding: Finite element modeling and experimental characterization

Abstract

Among the numerous ways to address 3D stacking of integrated circuits, a promising method is Cu/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> hybrid bonding, which is the simultaneous metallic bonding of the interconnection pads and direct bonding of the dielectric surfaces. Prior to bonding, a chemical-mechanical polishing step is necessary, resulting in copper pads being slightly overpolished compared to the surrounding oxide regions (dishing effect). This effect, if too important, can prevent bonding and thereby lead to electrical connection failure between top and bottom parts. In order to better understand the involved phenomena and to perform virtual prototyping, a 3D finite element model for the thermal annealing of Cu/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> hybrid bonded pads is presented, taking into account the dishing effect. In this work, the contributions to bonding of thermoelastic deformation and cohesive interactions are investigated, and the impact of pad shape on Cu-Cu interface closure during thermal annealing studied. In addition, a parametric study is conducted, in order to identify the most efficient design and process parameters to improve bonding quality.