Silicon direct bonding: Via low-temperature wet chemical surface activation

Commercial silicon substrates were bonded via low-temperature wet chemical surface activation in a standard laboratory without ultrahigh vacuum or a clean room. A smooth direct bond with no voids or microcracks was obtained, and the best bonding strength reached up to 4.15 MPa at 250 °C with the 25 MPa pressure-assisted process. The p-n junction prepared using this method exhibited excellent I-V characteristics. An updated model for the silicon direct bonding mechanism was proposed and proved. Raman scattering analysis indicated an increase in the Si-OH density on the silicon surface after the activation treatment. Cross-sectional HRTEM and EELS analysis crossing the interface indicated that the Si-O-Si linkage on the bonding interface that formed after low-temperature annealing was of a lower density than that of the native oxide. The thickness of the bonding interface decreased and the silicate linkage underwent further densification when high-temperature annealing was executed.