Low-Temperature In Situ Bonding with Ion-Free Neutral Species and Ammonia-Enhanced Activation for Microfluidic Chip Architecture

With the advent of the AI era, silicon-based semiconductor material bonding has emerged as an important means to achieve optoelectronic integration and miniaturization. It is indispensable in areas such as micro/nanoelectromechanical systems (M/NEMS), Lab-on-Chip, silicon-on-insulator (SOI) substrates, and advanced hybrid bonding. However, existing bonding methods have several limitations, such as various types of plasma-induced damage and low in situ bonding strength. Plasma activation methods rely on physical damage sublayers caused by accelerated particle bombardment to enhance interfacial diffusion. Neutral species (NS) activation is an ion-free radical process, which has the advantage of being mild and causing low damage but inevitably makes the bonding strength suboptimal. In this study, we propose an ammonia vapor-assisted NS surface activation method that retains the advantages of NS activation while overcoming the bottleneck of low bonding strength. The rich modification of surface functional groups and the construction of softened subsurfaces were achieved. Then, bonding strengths of up to 3.1 J/m²were obtained at 300 °C. The obtained bonding interface is almost perfect, which is very different from the damaged layer obtained by conventional plasma activation. Thanks to the mild activation and high bonding strength, the Si/Si bonding interfacial defects were significantly suppressed after high-temperature annealing, and the microfluidic micro heat pipe could be operated without leakage. This in situ bonding method has excellent reproducibility, low charging performance, and low-induced damage properties, paving the way for bottom-up micro/nanodevice fabrication and cutting-edge optoelectronic integration applications. Four inch SiO₂/SiO₂, SiN/SiO₂, and glass/glass bonding are also demonstrated, suggesting that the technique may be universally applicable.