Hybrid bonding is a major enabler for devices requiring 3D stacking with high interconnection density. An in-depth reliability study is performed for the specific Cu/SiO2 integration to identify the potential failure mechanisms. A high robustness is evidenced down to bonding pitch 0.81 μm for the standard reliability tests such as Thermal Cycling (TC) tests, High Temperature Storage (HTS) test, Stress induced Voiding (SiV), Time Dependent Dielectric Breakdown (TDDB) or electromigration. The hybrid bonding interface is stable under thermal stress with no atomic or ionic Cu diffusion observed through the hybrid bonding interface. The role of the thin self-formed cuprous oxide at the Cu/SiO2 interface in the case of misaligned bonding pads is believed to play a major role in the high robustness to reliability tests.