Direct bonding between spacer and field emitter array using an electron-beam evaporated interlayer

This work reports a direct bonding method between silicon wafers using an interlayer. Thermal oxide, sputtered silicon nitride, molybdenum film and electron-beam evaporated silicon oxide were used as an interlayer. Silicon wafers were hydrophilized by one of the hot nitric acid, the sulfuric acid based solution and the ammonium hydroxide based solution, mated at class 100 hemisphere and heat treated. After hydrophilization of silicon wafers, the changes of the surface roughness' were studied by the atomic force microscopy(AFM) and the voids and the non-bonded areas were inspected by the infra-red(IR) transmission microscope. The bonding interfaces of the bonded pairs were inspected by a high resolution scanning electron microscope(SEM). Surface energies and tensile strengths of the bonded pairs were also tested by the crack propagation method and the push-pull meter, respectively. Surface energy of the Si-Si wafer pair annealed at 150 °C for 48 hours was about 7200 [erg/cm²] and its tensile strength was more than 18 MPa. This tensile strength is comparable with the bulk strength of the used silicon wafer.