Tokio Takei

Silicon Wafer Bonding Mechanism for Silicon-on-Insulator Structures

X-ray diffraction topography and tensile testing are used to study the perfection of bonded interfaces in the sandwich structure where one of the two silicon wafers used had an SiO2 layer applied to it first. The tensile strength and the formation of unbonded areas (voids) were compared to the cases where two bare silicon wafers were used and where both wafers were coated with oxide. There are two mechanisms for wafer bonding: one is for a lower temperature and another is for a higher temperature range. It is concluded that a strong affinity between the two wafers at low temperatures is essential to obtaining tight bonding after a high-temperature anneal. A proper amount of H, OH and H2O on the wafers plays an important role in good chemical bonding below 800°C. Above 1000°C an interaction between adjacent atoms to create covalent bonding and deformation of the SiO2 layer are effective in establishing good bonding.