AVS 47th International Symposium
    Dielectrics Wednesday Sessions
       Session DI+EL+MS-WeA

Paper DI+EL+MS-WeA10
Formation of Ultrathin Yttrium Silicate by Thermal Oxidation of Yttrium on Silicon

Wednesday, October 4, 2000, 5:00 pm, Room 312

Session: Alternate Gate Dielectrics
Presenter: M.J. Kelly, North Carolina State University
Authors: M.J. Kelly, North Carolina State University
J.J. Chambers, North Carolina State University
D. Niu, North Carolina State University
G.N. Parsons, North Carolina State University
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We show that direct thermal oxidation can be used to form thin (<50@Ao@) high-k metal silicate layers directly on crystalline silicon. Bulk thermodynamics indicates that several high-k metal oxides (including oxides of Hf, Zr, Al, Y, La, etc.) will be stable with respect to silicon dioxide formation when the oxide is in contact with silicon. However, most low temperature approaches (PVD, CVD, or MBE) for metal oxide deposition on silicon involve elementary reaction steps that include metal-silicon bond formation before oxidation, resulting in uncontrolled interface layers between the metal oxide and silicon. We can utilize this mechanism to form yttrium silicate films on silicon by first sputtering thin (<10@Ao@) metal films on silicon, vacuum annealing at 300-600°C to form a silicide, then oxidizing at 600-900°C. XPS, medium energy ion scattering, and IR indicate film composition is close to yttrium orthosilicate (Y2O3·SiO2) with some excess Y2O3, depending on anneal conditions. Oxidation kinetics (determined from thicknesses measured by TEM) indicate an initial fast oxidation rate (due to oxidation of metal silicide), followed by a slower process (due to oxidation of underlying silicon). CV analysis of 42@Ao@ films show oxide equivalent thickness ~12@Ao@, consistent with dielectric constant ~14. Leakage is <1A/cm2 at 1V in accumulation. IR and XPS indicate that films do not phase separate when annealed up to 900°C for 20 minutes. Thin (<10@Ao@) silicon oxide and nitride interface layers have been formed in-situ by remote plasma exposure before metal deposition and their effect on interface reaction kinetics have been analyzed by XPS and MEIS. Interfacial oxide is observed to have a negligible effect on interface reactions, but results suggest interface nitrogen tends to block silicide formation before oxidation. These results give important insight into controlling interface structure for implementing high-k materials into silicon devices.