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Title: Photoemission Spectroscopic Studies of Metal-Gated MOS structures based on ultra-thin High-k Dielectrics
Authors: Choung, Jiyoung
Advisors: Robert M. Kolbas, Committee Member
Veena Misra, Committee Member
John F. Muth, Committee Chair
Jack E. Rowe, Committee Member
Robert J. Nemanich, Committee Co-Chair
Keywords: UPS
work function
metal gate
Issue Date: 5-Mar-2009
Degree: PhD
Discipline: Electrical Engineering
Abstract: The band structure and interface properties of high-κ MOS gate stack structures have been studied using a combination of x-ray and ultraviolet photoemission spectroscopy to comprehend the effective work function (EWF) variation during thermal processing. The possibility of controlling the effective work function of a metal by inserting an intentional dipole layer or additional charges is investigated using high-k gate stacks. The band bending of a Si interface and the electric field across the buffer oxide is explored using the band structure analysis of MOS capacitors. Prior to the band structure analysis of MOS capacitors, a high-κ/buffer oxide (SiO2) on p- and n-Si substrates is explored to observe the Si band bending and the electric field across the buffer oxide, which demonstrates the possibility for control of the effective work function of a metal by inserting an intentional dipole layer or additional charges. The Fermi level alignment of TiN/HfO2/p- and n-type Si is investigated, where three main conclusions are presented: 1) the Fermi level difference between TiN/high-κ/p- and n-type Si substrates has been identified with photoemission spectroscopy (XPS, UPS) and the results used to determine the band structure; 2) a systematic study of the core level spectra shifts of the Si 2p and Hf 4f display the Fermi level alignment; 3) the results indicate that the interfacial dipole at high-κ/buffer oxide contributes to the EWF of TiN in the structure. To observe the effects depending on different dielectrics on the EWF, TiN on SiO2, HfO2, and Al2O3 is investigated, and the results are found to be similar to the results obtained by Capacitance Voltage measurements. Finally, the process and temperature dependence of a PMOS capacitor (Ru/HfSiOx/n-Si) is studied. The process dependence showed that there is a large gap between the VWF and the EWF of Ru after annealing, and the interface at the high-κ/buffer oxide needs to be considered to tune the EWF. The temperature dependence revealed the thermal instability of Ru with HfSiOx over 700°C. This study suggests that the EWF is affected by the dipole layer not only at a metal/high-κ interface but also at a high-κ / SiO2 interface.
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