Spectroscopic Study of Hafnium Silicate Alloys prepared by RPECVD: Comparisons between Conduction/Valence Band Offset Energies and Optical Band Gaps

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Title: Spectroscopic Study of Hafnium Silicate Alloys prepared by RPECVD: Comparisons between Conduction/Valence Band Offset Energies and Optical Band Gaps
Author: Hong, Joon Goo
Advisors: Gerald Lucovsky, Committee Chair
Carlton Osburn, Committee Member
Gerd Duscher, Committee Member
Klaus Bachmann, Committee Member
Abstract: Aggressive scaling of devices has continued to improve MOSFET transistor performance. As lateral device dimensions continue to decrease, gate oxide thickness must be scaled down. As one of the promising high k gate oxide material, HfO₂ and its silicates were investigated to understand their direct tunneling behavior by studying conduction and valence band offset energies with spectroscopy and electrical characterization. Local bonding change of remote plasma deposited (HfO₂)[subscript x](SiO[subscript 8322;)[subscript 1-x] alloys were characterized by Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) as a function of alloy composition, x. Two different precursors with Hf Nitrato and Hf-tert=butoxide were tested to have amorphous deposition. Film composition was determined off-line by Rutherford backscattering spectroscopy (RBS) and these results were calibrated with on-line AES. As deposited Hf-silicate alloys were characterized by off-line XPS and AES for their chemical shifts interpreting with a partial charge transfer model as well as coordination changes.Sigmoidal dependence of valence band offse energies was observed. Hf 5d state is fixed at the bottom of the conduction band and located at 1.3 ± 0.2 eV above the top of the Si conduction band as a conduction band offset by x-ray absorption spectroscopy (XAS). Optical band gap energy changes were observed with vacuum ultra violet spectroscopic ellipsometry (VUVSE) to verify compositional dependence of conduction and valence band offset energy changes. 1 nm EOT normalized tunneling current with Wentzel-Kramer-Brillouin (WKB) simulation based on the band offset study and Franz two band model showed the minimum at the intermediate composition matching with the experimental data. Non-linear trend in tunneling current was observed because the increases in physical thickness were mitigated by reduction in band offset energies and effective mass for tunneling. C-V curves were compared to each other, and more hysteresis was observed with increasing x. Localized Hf 5d state as a trap site was the reason for hysteresis and its reverse direction with temperature-dependent C-V curves. Temperature-dependent I-V study located Hf 5d state. For the integration issue, nitridation study was performed at the interface, surface and both. Interfacial nitridation gave more effective reduction in EOT.
Date: 2003-12-31
Degree: PhD
Discipline: Materials Science and Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/2978

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