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Direct bonding describes a wafer bonding process without any additional intermediate layers. The bonding process is based on chemical bonds between two surfaces of any material possible meeting numerous requirements.〔 These requirements are specified for the wafer surface as sufficiently clean, flat and smooth. Otherwise unbonded areas so called voids, i.e. interface bubbles, can occur.〔 The procedural steps of the direct bonding process of wafers any surface is divided into # wafer preprocessing, # pre-bonding at room temperature and # annealing at elevated temperatures. Even though direct bonding as a wafer bonding technique is able to process nearly all materials, silicon is the most established material up to now. Therefore, the bonding process is also referred to as silicon direct bonding or silicon fusion bonding. The fields of application for silicon direct bonding are, e.g. manufacturing of Silicon on insulator (SOI) wafers, sensors and actuators.〔 == Overview == The silicon direct bonding is based on intermolecular interactions including van der Waals forces, hydrogen bonds and strong covalent bonds.〔 The initial procedure of direct bonding was characterized by a high process temperature. There is demand to lower the process temperature due to several factors, one is for instance the increasing number of utilized materials with different coefficients of thermal expansion. Hence, the aim is to achieve a stable and hermetic direct bond at a temperature below 450 °C. Therefore, processes for wafer surface activation i.e. plasma treatment or chemical-mechanical polishing (CMP), are being considered and are actively being researched.〔 The upper limit of 450 °C bases on the limitations of back-end CMOS processing and the beginning of interactions between the applied materials.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Direct bonding」の詳細全文を読む スポンサード リンク
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