Point defects generated by direct-wafer bonding of silicon

High-purity float zone (FZ) silicon p- and n-type wafers were directly bonded hydrophobically at 700degreesC and 1050degreesC. Electrical I-V and capacitance-voltage (C-V) characterization was performed on p-n junctions of 2-mm square chips cut out from properly bonded areas of the wafers. The point defects were investigated by Deep Level Transient Spectroscopy (DLTS). As expected, annealing at 700degreesC resulted in high void density, while at 1050degreesC void-free bonded structures were formed. The I-V characteristics were dominated by recombination at the bonded interface and by the resistance of the n-type wafer. The point defects identified by DLTS are divacancy, vacancy-phosphor, and vacancy-oxygen complexes. These defects explain qualitatively the observed characteristics of the samples.