Development of Copper Thermal Coefficient For Low Temperature Hybrid Bonding

We present a modeling framework to guide the development and optimization of the hybrid bonding process. The key challenge is to achieve fully-bonded Cu-Cu metal interfaces/pads at low thermal budget such as 200–250 °C to mitigate adverse thermal impact to the device structures. In this paper, we explore modification of the material coefficient of thermal expansion (CTE) and optimization with lower annealing temperature. To investigate new material solutions with a higher CTE, Classical Molecular Dynamics (CMD) simulation technique was implemented in the modelling framework. Two types of material modeling have been proposed for CTE improvement: i) Cu alloying; and ii) Cu capping. Simulation results show that copper alloying with selected metals can provide up to 40% improvement in CTE, and with capping, CTE can be improved up to 43% at optimal capping layer thickness. A continuum-scale thermo-mechanical model has been developed to study the Copper pad/pad interactions during the hybrid bonding process. Using this model, a parametric study is carried out on the effect of coefficient of thermal expansion (CTE) of different Copper alloys at low temperature regimes. The results show that CTE plays a significant role in bond quality and 40% improvement on CTE can facilitate the full Cu/Cu pad bonding at desired temperature regimes.