Direct Wafer Bonding Surface Conditioning
The aim of this chapter is to describe the diverse surface conditioning processes that, alone or combined, allow direct bonding. For more than 20 years, direct bonding of Si and SiO2 have been evaluated and applied for microelectronics, micro-technologies, and optoelectronic applications. More recently, direct bonding has been successfully performed on materials as diverse as Ge, SiGe, III-V, SiC, glass, quartz, diamond, sapphire, perovskite, and metals. The surface conditioning processes must take into account the nature of each material, the state of its surface (i.e. surface bonds, micro-roughness, topography) and its structure (i.e. amorphous, single crystalline, polycrystalline). Cleaning processes and surface preparation must be customized for each single or composite material to insure high quality direct bonding. For most applications, direct bonding involves hydrophilic surfaces which are well suited to spontaneous adhesion at room temperature. Surface preparations that result in hydrophilic surfaces will be discussed, and a short overview will also be given on direct bonding of hydrophobic surfaces. The importance of customizing surface conditioning ...