Towards Standardization of Hybrid Bonding Interface: In-depth Study of Dielectrics on Direct Bonding

Hybrid bonding has become the key technology to enabling high density interconnect interfaces for fine pitch integration through the direct bonding of dielectrics followed by the embedded copper pad diffusion in a post-bond anneal process. There have been a variety of dielectric materials studied for direct bonding among the field to achieve high bonding quality. However, the lack of standardization of bonding dielectrics prevents the enabling of the mixed-foundry capabilities, e.g. for 2.5D and 3D integration. In this work, we focus on the in-depth understanding of the fundamental bonding behaviors of various dielectric material pairs (SiCN, SiO
2
, SiN, SiON) by correlating the film compositions, dangling bonds, and porosity with CSAM and the bond energy of the bonded interface. It is the first time that we successfully demonstrate the quantification of the nanogap density at the bonded interface through positron annihilation spectroscopy (PAS) analysis and simulations. Beyond that, we systematically evaluate all the dielectric materials on the dielectric constants and their potential sensitivity to the integrated process flow for hybrid bonding. With all the characteristics taken into consideration, the bonding between non-hydrogenated SiN and hydrogenated SiO
2
, where the film deposition temperatures are below 300 °C for device compatibility, is first-time demonstrated that outstands among all the dielectric pairs investigated in this work with their highest bond energy (> 2.5 J/m
²
) and CSAM-void-free bonding interface after 250 °C of post-bond anneal. Thus, we propose an optimal dielectric pair option for the standardization of the direct bonding to extend the flexibility of the mixed-foundry chiplet ecosystem for advanced heterogeneous integration.