1, Catcus Materials Inc., Tempe, Arizona, United States
3, Arizona State University, Tempe, Arizona, United States
Nano-Bonding™  consists of direct molecular cross-bonding between two surfaces at the nanoscale over a wafer area. This can occur if surfaces are planarized to make full contact at the macro-, micro-, and nano-scale. Wafer warping, typically a 25-60 microns of vertical displacement across the wafer focal plane has to be eliminated. At the micro-scale, surfaces need to be planar over micron lengths. At the nano-scale, atomic terraces need to extend over tens of nm so atomic steps are spread far apart.
With planarization, direct cross-bonding occur with direct exchange of electrons between the two surfaces without an adhesive or bonding phase. Nano-Bonding™ between heterogeneous semiconductor surfaces can create more efficient solar cells and integrate, optical and electronic devices into monolithic devices.
Nano-Bonding™ of GaAs(100) to Si(100) is conducted at near atmospheric pressure in air without the use of plasma activation or ultra high vacuum conditions.
Three Liquid Contact Angle Analysis (3LCAA) measures the surface energies of the GaAs(100) and the Si(100) surfaces to bond. Initial native oxides GaAs(100) are hydrophobic with an surface energy of 37.7 ± 1.7 mJ/m2. GaAs(100) is prepared into a hydrophilic surface with an energy of 65.4 ± 1.4 mJ/m2. Si(100) is processed to undergo an opposite transition Si(100) native oxides initially exhibit a hydrophilic surface with an energy of 52.7 ± 1.4 mJ/m2. Si(100) is then made hydrophobic with a surface energy of 48.2 ± 1.0 mJ/m2.
Ion Beam Analysis (IBA) evaluates the effect of surface preparation of GaAs(100) and Si(100). Oxygen Nuclear Resonance combined with MeV Ion Channeling allows for detection of oxygen and displaced GaAs and Si atoms in oxides before and after surface preparation. GaAs(100) hydrophobic native oxides contain about 30% Arsenic oxide and 60% Gallium oxide. After surface preparation, IBA detects an Arsenic-terminated surface with a layer of Gallium beneath.
In a set of identical experiments using seven pairs of 4” wafers, following native oxide removal and surface preparation, hydrophilic GaAs(100)/hydrophobic Si(100) pairs are Nano-Bonded™ at near atmosphere at temperatures of T < 200°C with a 57% success rate, measured via Confocal Scanning Acoustic Microscopy (C-SAM) imaging. An improved coverage of bonded area is anticipated once modification to equipment is performed. Bonded regions near atmosphere correspond to regions of compression during the Nano-Bonding™ process but can extend beyond. Finally, Transmission Electron Microscopy (TEM) imaging is used to examine the quality of GaAs/Si Nano-Bonded™ interface.
 Herbots et al. US Patent 9,018,077 (2015); 9,589,801 (2017).
 Herbots et al. US Patents Pending (2017)