Copper (Cu) is used as an interconnect material in many applications owing to its high thermal, electrical conductivity and excellent electromigration resistance. Though this material has many advantages, the main drawback is that it gets oxidized on exposure to air. Thermo-compression bonding is a wafer bonding technique that uses metal layers for heaping wafers, which aids in attaining outstanding electrical conductivity without weakening the mechanical properties. The adsorbed oxide layer hurdles the proper bonding to happen between the wafers. In order to enhance the diffusion between the metal layers, the copper oxide layer should be removed which necessitates the requirement of high temperature, pressure, long bonding time and the inert gas atmosphere throughout the Cu-Cu thermo compression wafer bonding process. Simultaneous application of high temperature and pressure for a long time leads to the deterioration of the underlying sensitive components. This paper aims to present several techniques such as surface treatment, chemical pretreatment, surface passivation, crystal orientation modification, stress gradient in the thin film and formic acid vapour treatment which are used in order to avoid the deterioration of underlying sensitive devices and to obtain a proper bonding between the wafers at low temperature and pressure.

中文翻译：

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用于微系统集成的铜铜热压晶片键合技术

铜 (Cu) 由于其高导热性、高导电性和优异的抗电迁移性，在许多应用中被用作互连材料。虽然这种材料有很多优点，但主要的缺点是它暴露在空气中会被氧化。热压键合是一种晶圆键合技术，它使用金属层来堆叠晶圆，这有助于在不削弱机械性能的情况下获得出色的导电性。吸附的氧化层阻碍了晶片之间发生适当的键合。为了增强金属层之间的扩散，需要去除氧化铜层，这需要在整个Cu-Cu热压晶片键合过程中需要高温、高压、长键合时间和惰性气体气氛。长时间高温高压同时应用，导致底层敏感元件劣化。本文旨在介绍几种技术，如表面处理、化学预处理、表面钝化、晶体取向改性、薄膜中的应力梯度和甲酸蒸汽处理，以避免底层敏感器件的劣化并获得晶圆之间在低温和压力下适当的键合。