High-k gate dielectrics for silicon CMOS applications

This thesis focuses on the understanding of many fundamental properties of high-k gate dielectrics for Si CMOS gate applications, and on the development of ultra-thin ZrO₂/Zr silicate, titanium aluminates, and TiO ₂/SiN gate dielectrics.; The results demonstrate that the ultra-thin ZrO₂/Zr silicate films deposited by the JVD process can have EOTs down to 1 nm, and possess high thermal stability, among other good electrical properties. The presence of a thermally stable Zr silicate interfacial layer may prevent the formation of interfacial silicon oxide during anneal.; Our results also reveal that either incorporating Al into TiO₂, or using a high-quality ultra-thin JVD SiN layer can improve the properties of the gate stack after high temperature annealing. The nano-crystallization of titanium aluminates results in considerable degradation of transconductance and reliability.; The barrier heights over Si conduction band edge and conduction mechanisms of several scientifically and technically important high-k materials have been studied. Our results reveal that (1) Though Ta₂O ₅ possesses a larger bandgap than that of TiO₂, due to its adverse band alignment to Si band, Ta₂O₅ only has a barrier height of 0.28 eV over Si conduction band edge, which is much smaller than that of TiO₂. Therefore, Schottky emission or thermionic emission becomes the dominant conduction mechanism in over the Ta₂O ₅ barrier; (2) The high barrier height of 3.0 eV for ALD Al ₂O₃ over Si conduction band edge makes it attractive to block thermionic current at elevated temperatures; The barrier height of 2.1 eV for JVD ZrO₂/Silicate over the Si conduction band edge is sufficient to block thermionic current; (3) Incorporating Al into TiO₂ increases the barrier height of TiO₂ over the Si conduction band edge; (4) The work function of 4.7 eV for Tungsten makes its Fermi-level at the mid-gap of Si band.; Through the course of this dissertation study, we have found that (1) it is possible to make MOSFETs with high-k gate dielectrics with mobilities that fit closely to the universal mobility curve, (2) a major portion of the reduced transconductance or conductance can be attributed to trapping, (3) among MOSFET's with Hf silicate, HfO₂, and Hf aluminate, the device with Hf silicate shows the highest transconductance and lowest trap densities.