Reliability Of Advanced Dielectrics In Gate Oxide And Device Level Packaging In MEMS
Rahman, Mohammad Shahriar
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The focus of this work is to study the feasibility, reliability and applicability of advanced dielectrics in both Metal Oxide Semiconductor Field Effect Transistor (MOSFET) gate oxide and device level packaging for Microelectromechanical Systems (MEMS). The scaling of silicon based MOSFET is approaching physical limits imposed by atomic structure. This continuous scaling trend of complementary MOSFET technologies introduces new challenges relating to power, heat and device behavior. To overcome the power dissipation and heating problems arising from gate leakage, high dielectric constant (high-k) materials are proposed. Hafnium based high-k dielectric layers and metal gate electrodes have been extensively investigated as alternative gate materials. Successful incorporation of these materials into the MOSFET gate stack with minimum feature size of 45nm has recently been reported. Here, the low frequency noise characteristics of MOSFETs with differently nitrided HfSiO gate dielectric materials are studied. To evaluate the high-k MOSFET performance using low frequency noise as a characterization tool, the devices were also subjected to different stress induced degradation. Device performance of differently nitrided samples is also compared with the control, pure HfSiO MOSFET sample. This work reports, for the first time, the low frequency noise performance of 2nm high-k gate dielectric material for the sub 45nm technology node. The advantages of the MEMS packaging approach described here compared to other MEMS packaging techniques are that it is a CMOS compatible low temperature method. Different MEMS devices can be used for vacuum encapsulation using this method. It does not require a high temperature deposition and etching of sacrificial materials and is stiction-free. Removal of the sacrificial layer is performed through openings, called trench cuts, and later the openings are sealed for encapsulation. For the MEMS packaging application, Al₂O₃ (alumina) is chosen as a resonator beam and sealing material. The primary reasons for choosing this material is due to the hard and stiff material property with high Young's modulus. Alumina can also be used in high temperature and under harsh environment. On top of that, packages with optical transparent window can be made with this material. For the first time this work was reported the use of alumina as a packaging material in MEMS.Extensive RF and reliability measurements were performed on the packaged resonators including evaluation of the package permeability, stress and cavity pressure. Long term and accelerated life testing on the packaged resonators indicated the robustness of the package.