Increasing more bonding energy in nitrogen plasma-activated wafer bonding by HF-Dip

Nitrogen plasma-activated wafer bonding provides high-strength Si/Si wafer bonding. We found that a hydrofluoric (HF) pre-dip treatment can increase more bonding energy. By reducing drastically the annealing temperature to as low as 75°C, HF-dip and subsequent nitrogen-plasma activation can result in an bonding energy of the Si/Si pair comparable to the silicon fracture strength (2500 mJ/m²). In Si₃N₄/Si₃N ₄ wafer bonding, the room-temperature bonding results in interface energy as high as 537 mJ/m² and then reaches the silicon fracture strength through annealing at 200°C for 24 hours. We suggest that the high-strength bonding mechanism is the formation of Si-NH-Si bonds during annealing.