In Situ Doped Polysilicon (ISDP) Hydrophilic Direct Wafer Bonding for MEMS Applications

Abstract

In this paper, Chemical Mechanical Polishing is used to reduce RMS roughness of as-deposited ISDP from 3.2 nm down to 0.18 nm. This surface preparation allows ISDP thin films to be direct bonded to polycrystalline and monocrystalline Si, as well as thermal SiO2. Mechanically strong bondings are obtained showing surface energies higher than the Si fracture energy of 2250 mJ.m−2 and adherence energy up to more than 6000 mJ.m−2 after annealing at 1100 °C. Infrared images and Scanning Acoustic Microscopy confirm that ISDP can be used to fabricate void-free assemblies after annealing. The hermeticity analysis of cavities sealed by ISDP direct bonding showed maximum leak rate lower than 10−11 Pa.m3s−1 after 18 weeks.

Room Temperature Seal-Ring Au-to-Au Bonding Hermeticity and Reliability Testing

“…The membrane needs to be flexible enough in order to obtain measurable deflection values. By measuring shift of the membrane deflection over time, the hermeticity can be estimated using the elasticity equations [4].…”

“…Leakage overtime can result in lowering the sensitivity of the device and thus degradation of its functionalities. Today's robust and hermetic wafer-level bonding technologies, including thermocompression bonding [3], direct bonding [4], anodic bonding [5] and eutectic bonding [6], enable excellent encapsulation hermeticity even for prolonged lifetime of over 20 years [3]. Compared to components-level packaging, wafer-level bonding has a cost saving benefit since it enables batch processing [7], [8].…”