Low-temperature bonding of silicon-oxide-covered wafers using diluted HF etching

For bonded pairs of silicon-oxide-covered wafers, the bonding energy at low temperatures is significantly enhanced by very slight etching of the silicon oxide surfaces in diluted (0.05%–0.2%) HF aqueous solutions prior to room temperature contacting. The bonding energy is a factor of 10 higher than standard bonded pairs to about 2000mJ∕m2 after annealing at 100°C. The improved surface cleaning and activation with desired surface termination have been achieved by the HF dip. A fluorine concentration peak at the bonding interface measured by secondary ion mass spectroscopy suggests that the number of Si–O–Si covalent bonds at the bonding interface appears to be increased appreciably by the formation of fluorinated silicon oxide that absorbs water effectively.