Low-temperature direct bonding of diamond (100) substrate on Si wafer under atmospheric conditions

Direct bonding of a diamond (100) substrate and a Si wafer was achieved at 250°C under atmospheric conditions. Prior to the bonding process, the diamond substrate was treated with H₂SO₄/H₂O₂ and NH₃/H₂O₂ mixtures, whereas the Si wafer was irradiated using oxygen plasma. By applying the pressure during the annealing process, the substrates were entirely bonded, except for the contaminated areas. The bonded specimen was fractured when a shear force of 1.7 MPa was applied. The electron microscopic observation indicated that the diamond and Si substrates were atomically bonded through a 3-nm-thick SiO₂ layer without significant loss of diamond crystallinity. The integration of diamond (100) substrates on an Si wafer would contribute to the fabrication of future diamond devices.