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A suggested mechanism for silicon direct bonding from studying hydrophilic and hydrophobic surfaces

Silicon direct bonding (SDB) between both hydrophilic and hydrophobic surfaces was studied by measuring the surface energies. Without annealing, roughly the same energies were measured for both types of surfaces. The strongest bonds were achieved for hydrophobic surfaces, annealed at 600 degrees C and above. The established mechanism for SDB, where OH groups are held responsible for the initial attraction force, cannot explain bonding between hydrophobic surfaces where almost no OH groups are present. By calculating the surface energy/mole, and comparing this to data for hydrogen bonds and van der Waals forces, a novel mechanism for SDB is proposed where the initial attraction is due to van der Waals forces.