Spontaneous direct bonding of thick silicon nitride

Wafers with 1 mu m LPCVD silicon-rich nitride layers have been successfully direct bonded to silicon-rich nitride and boron-doped silicon surfaces. A chemical-mechanical polishing treatment was necessary to reduce the surface roughness of the nitride before bonding. The measured surface energies of the room-temperature bond were comparable to values found for Si-Si hydrophilic bonding. A mechanism similar to this bonding is suggested for silicon nitride bonding.