Wafer-level vacuum sealing using AgAg thermocompression bonding after fly-cut planarization

This paper reports novel wafer-level vacuum sealing technology for the heterogeneous device integration for advanced micro-electronics, such as LSI integrated intelligent and autonomic sensors. Vacuum sealing was successfully achieved by thermocompression bonding using electroplated Ag bonding frames after single point diamond fly-cut planarization. At a bonding temperature of 350 °C, the average bonding shear strength of around 200 MPa was obtained, and the leak rate of the sealed cavities was lower than 3.6 × 10-14 Pa m3/s. Shear deformation by high speed mechanical cutting during planarization is demonstrated to induce fine Ag grains on the surface of the bonding frame, which promotes atomic diffusion through grain boundaries, relating to the obtained high shear strength at a relatively low temperature. Simultaneously TiN barrier layer sufficiently inhibits Ag atomic diffusion into a Si substrate during a heating process, which is confirmed by the secondary ion mass spectrometry (SIMS). The developed process is useful for the advanced wafer-bonding-based vacuum packaging for stepped micro structures and temperature-sensitive devices in terms of high reliability, simple pre-treatment and low cost.