Reactions of High-k Gate Dielectrics: Studies in Hafnium, Zirconium, Yttrium, and Lanthanum-based Dielectrics and in-situ Infrared Results for Hafnium Dioxide Atomic Layer Deposition

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Title: Reactions of High-k Gate Dielectrics: Studies in Hafnium, Zirconium, Yttrium, and Lanthanum-based Dielectrics and in-situ Infrared Results for Hafnium Dioxide Atomic Layer Deposition
Author: Kelly, Michael Jason
Advisors: David F. Ollis, Committee Member
Gregory N. Parsons, Committee Chair
H. Henry Lamb, Committee Member
Veena Misra, Committee Member
Abstract: According to the International Technology Roadmap for Semiconductors (2004) integrating a high dielectric constant (high-k) material into the gate stack will be necessary within the next two years (i.e., by 2007) to maintain the rate of scaling that has come to characterize the microelectronics industry. This work presents results for Y-, Zr-, Hf-, and La-based high-k gate dielectrics prepared by ex-situ oxidation of sputtered thin metal films and for HfO2 prepared by atomic layer deposition (ALD). The kinetics of substrate consumption during formation of yttrium silicate thin films were studied. We find results consistent with high-k dielectric formation by a two-step process in which yttrium metal reacts with the silicon substrate to form a metal silicide which is then oxidized to form the yttrium silicate dielectric. In other experiments, we show flatband voltage shifts of -0.2 and 0.95V in devices containing Zr-based dielectrics formed by oxidation of 8Å of Zr metal on Si at 600°C in N2O for 15 and 300s, respectively. Silicon oxidized in the same environment does not show this shift. The fixed charge scales with EOT for these films and is consistent with charge generation due to disruption of the SiO2 network by metal ions. Zr-based dielectrics exhibit this effect more strongly than Hf-based dielectrics. We show that La-based dielectrics absorb atmospheric H2O and CO2, and that reactions between these materials and deposited silicon electrodes are accelerated when H2O or other OH species are present at the interface. We show that the electrical properties of gate stacks having Ru and RuO2 electrodes in contact with PVD Y-silicate are more stable during thermal anneal than similar gate stacks having PVD ZrO2 or CVD Al2O3 dielectrics. For this work, we configured a Fourier transform infrared spectrometer for in-situ attenuated total reflection measurements and investigated ALD deposition of HfO2. We report the direct reaction of tetrakis(diethylamino) hafnium (TDEAHf) with SiH groups on HF-last Si. Island growth of HfO2 occurs, and SiH features are still present and shrinking after 200 cycles. To the best of our knowledge, these are the first in-situ FTIR results presented for atomic layer deposition using TDEAHf/H2O chemistry.
Date: 2006-05-08
Degree: PhD
Discipline: Chemical Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/3988


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