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

Abstract

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 2000 mJ/m(2) after annealing at 100degreesC. 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. (C) 2004 American Institute of Physics