Effect of Native Oxide upon Formation of Amorphous SiO x Layer at the Interface of Directly Bonded Silicon Wafers

We have investigated the interface of directly bonded Czochralski silicon wafers with various thicknesses of initially grown native oxide film using high-resolution transmission electron microscopy (HR-TEM). It was found that the volume of the amorphous SiO x layer formed at the bonded interface decreased as the native oxide film thickness decreased. The estimated total number of oxygen atoms in the amorphous layer from HR-TEM observation was in fairly good agreement with the total number of oxygen atoms in the native oxide film. It is concluded, therefore, that the initial stage of the formation of the amorphous SiO x layer is mainly governed by the initially grown native oxide.