From surface activation to microfluidic heat pipes: An innovative in-situ wafer level heterogenous bonding method

There has been considerable interest in low-temperature in-situ integration techniques for the fabrication of hetero-structured substrates and micro/nanosystems. This study presents a novel bonding approach that uses a water vapor-assisted surface activation strategy with neutral oxygen species (NOS). This method enables of highly efficient in-situ bonding process that utilizes the controllable and flexible environment to meet specific integration needs without exposure to the unstable ambient air. The NOS and water vapor increases hydroxyl groups, leading to smoother and more hydrophilic surfaces. The combined effects of NOS and the water vapor result in a larger bonded area ratio and significantly higher bonding energy compared to those activated by NOS alone. Meanwhile, the silicon oxide and quartz glass surfaces avoid being heavily electrically charged. This process thus achieved flawless silicon/quartz glass wafer bonding at 150 °C with a high bonding energy (∼4 J/m²) and Si/Si bonding pairs without any subsequent annealing voids. Then, the bonding pairs have been verified to have high reliability in extreme environments from −65 °C to 200 °C with no thermal-shocked cracks. The high-quality heterointerfaces could also withstand subsequent mechanical grinding and polishing for silicon-on-quartz glass (SOQ) fabrication. Moreover, a SOQ structured microfluidic heat pipe device was successfully fabricated based on the low-temperature in-situ heterogenous bonding. The robust heterointerfaces ensured non-leakage working during the heat dissipation. This facile and cost-effective bonding method is suitable for damage-free heterogeneous integration of active devices, micro/nanofluidic chips, and M/NEMS packaging. It has of great potential in fields such as biochemical analysis, quantum computing, and thermal sensing.