AVS 50th International Symposium
    High-k Gate Dielectrics and Devices Topical Conference Tuesday Sessions
       Session DI-TuA

Paper DI-TuA5
Enhanced Tunneling in Symmetric Stacked Gate Dielectrics with Ultra-thin HfO@sub 2@ Layers (0.5-10. nm) Sandwiched between Thicker SiO@sub 2@ Layers (1.5 nm)

Tuesday, November 4, 2003, 3:20 pm, Room 317

Session: High-k Dielectric Characterization
Presenter: C.L. Hinkle, North Carolina State University
Authors: C.L. Hinkle, North Carolina State University
C. Fulton, North Carolina State University
G. Lucovsky, North Carolina State University
R.J. Nemanich, North Carolina State University
Correspondent: Click to Email
A novel method for obtaining the tunneling mass, m@sub eff@, and conduction band offset energy with respect to Si, E@sub B@, for high-k gate dielectrics is presented. It is based on a quantum mechanical WKB-approximation that explains large bias dependent increases in tunneling in symmetric stacked devices with ultra-thin HfO@sub 2@ layers (~0.5 nm) sandwiched between thicker SiO@sub 2@ layers (~1.0-1.5 nm) as compared with reference devices with homogenous SiO@sub 2@ dielectrics. J-V traces for substrate injection indicate a marked departure from the approximately exponential bias dependence of homogenous dielectrics for V@sub ox@ = V@sub g@ - V@sub fb@ >1 V. This correlates with differences between the tunneling attenuation factors, @alpha@@sub i@t@sub i@ = 4@pi@t@sub i@(2m@sub effi@E@sub Bi@)@super 0.5@/h, in the constituent layers, i, where t@sub i@ is the i@super th@ layer thickness. For V@sub ox@ >1 eV, small decreases in @alpha@t(SiO@sub 2@) compared to larger decreases in @alpha@t(HfO@sub 2@) result in a marked increase in their ratio. For V@sub ox@ > 1.5 V, there is minimal attenuation in the HfO@sub 2@ layer, so that the tunneling current is determined predominantly by the SiO@sub 2@ layer. At V@sub ox@ = 3V, the relative current with respect to the reference Si device is >1000. By analyzing these data, and increasing the thickness of the HfO@sub 2@ layer beyond 2 nm to determine the thickness at which relative tunneling begins to decrease due to increased attenuation in that component of the stack, values of m@sub eff@ = 0.15±0.05 m@sub o@ and E@sub B@ = 1.4±0.2 eV are obtained for HfO@sub 2@.