Effect of Cu Pad Geometry and Dishing in Cu/Sicn Hybrid Bonding Process: A Finite Element Analysis Study

Abstract

The Cu/dielectric hybrid bonding is a face-to-face wafer bonding technology that utilizes the thermal expansion of the Cu pad embedded in dielectrics. It is receiving significant attention due to the advantage of achieving high interconnect density through submicron-level fine-pitch bonding. The finite element method (FEM) is beneficial for hybrid bonding research because it provides insight on the bonding mechanism by simulating the expansion of the Cu pad with increasing temperature. The effects of pad shape and dishing by chemical-mechanical polishing (CMP) were studied by FEM for fixed dimensions of Cu pads, 4 or 10 μm in size and 0.5 μm in thickness [1] [2]. However, studies on the hybrid bonding process for Cu pads with finer dimensions and various geometries using FEM analysis are currently lacking.In this study, we simulated the Cu/SiCN hybrid bonding process using ANSYS to investigate the effects of Cu pad geometry and Cu dishing by CMP. The diameter and thickness of the circular Cu pad were ranging from 0.1 to 1.5 μm and 0.15 to 0.45 μm. The Cu dishing depth was varied between 2 to 5 nm. For bonding process, at first the dielectrics of the two wafers were in contact with each other at room temperature. Then, the temperature was raised to the annealing temperature to simulate the Cu-to-Cu bonding process. At different annealing temperature, the bonding area was estimated with varying diameter, thickness, and dishing depth of the Cu pad. The Cu-to-Cu bonding area was mapped according to the Cu pad geometry, and the geometry of the Cu pad suitable for hybrid bonding was proposed. The protrusion of the Cu pad caused by the thermal expansion was also investigated for a single wafer to discuss the effect of the Cu pad dimension on the bonding area. Acknowledgments This work was supported by SK hynix Inc.