Relationship between interfacial native oxide thickness and bonding temperature in directly bonded silicon wafer pairs

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Abstract
High-resolution transmission electron microscopy was employed to observe the morphology of the interfacial native oxide layers in the bonding interfaces of Czochralski (CZ) and float-zone (FZ) silicon pairs that were bonded at different temperatures. It is shown that the thickness of the interfacial native oxide layers decreases with increasing bonding temperature in the temperature range of 200 °C to 600 °C, and remains fairly constant in the range of 600 °C to 1200 °C in both CZ and FZ silicon wafer pairs. Three factors are proposed to interpret this phenomenon: bonding interface phase transition, variation of native oxide chemical structure, and relaxation of stress in native oxide. A different factor dominates the change in thickness of the interfacial oxide layers in a different temperature range.