Room-Temperature High-Performance InP/Si Surface-Activated Wafer Bonding for Electronic-Photonic System Integration Applications

Indium phosphide (InP)–silicon wafer bonding, which offers both high performance and fabrication efficiency at reduced cost, is widely regarded as a key enabler for next-generation electronic–photonic integrated circuits (EPICs). Among the available approaches, surface-activated bonding (SAB) has emerged as a particularly promising technique. Nevertheless, the bonding interface still faces significant challenges, as its mechanical strength, electrical conductivity, and thermal performance fall short of the desired standards. In this work, we introduce a proprietary in situ surface cleaning and activation process in conjunction with an ultrahigh-vacuum wafer bonding system to achieve robust InP/Si bonding at room temperature. A tensile strength of 3 MPa was obtained, sufficient to withstand mechanical stresses produced during subsequent front-end device fabrication processes. Following a brief low-temperature thermal treatment at 300 °C, readily available with many standard IC fabrication processes, the bonding strength exceeded 7 MPa, reaching the strongest InP bonding achieved with plasma-activated bonding (PAB). High-resolution TEM revealed a void-free, ordered interfacial layer less than 3 nm thick. X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS) were employed to evaluate crystallinity, stress uniformity, and oxygen/phosphorus distribution in the thinner and more vulnerable InP wafers. We discovered that Ar plasma cleaning and surface activation promote InP oxidation, degrading material properties. To mitigate this, alternative approaches such as employing larger ions (e.g., Xe) and reducing plasma energy are proposed. For the first time, current conduction mechanisms across the bonded interface are reported and suggested as a characterization tool for probing electrical and defect properties of the cross-wafer pn junction. These findings provide effective strategies for process optimization, enhancing both mechanical integrity and electrical reliability of bonded InP wafers, and underscore the potential of the proposed bonding approach to advance heterogeneous integration in future EPIC technologies.