Scanning Infrared Microscopy Study of Annealing Behavior of Interfacial Micro-Voids in Direct Bonded Silicon

The density of micro-voids with dimensions from several to a few tens ¿m at the interface of bonded silicon wafers formed during annealing at different temperatures was investigated by using a submicron resolution Scanning Infrared Microscope (SIRM). For low temperature heat treatment (400°C) the density and size (i.e. area) of micro-voids have been found to be much larger in the case of bonding with hydrophilic wafers than for the hydrophobic one. By increasing the amnealing temperature up to 1150°C, the density and size of micro-voids decreased in both cases, but more significantly for hydrophobic wafer bonding. The cause of the different annealing behaviour of micro-voids between hydrophilic and hydrophobic samples is believed to be the native oxide forming only on the surface of the hydrophilic wafers during storage and surface treatment.