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Reliability of ZrO 2 films grown by atomic layer deposition

Reliability of ZrO 2 films grown by atomic layer deposition. D. Caputo , F. Irrera, S. Salerno Rome Univ. “La Sapienza”, Dept. Electronic Eng. via Eudossiana 18, 00184 Rome (Italy) S. Spiga, M. Fanciulli Laboratorio MDM-INFM, via C. Olivetti 2 20041 Agrate Brianza (Italy). Aim of the work.

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Reliability of ZrO 2 films grown by atomic layer deposition

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  1. Reliability of ZrO2 films grown by atomic layer deposition D. Caputo, F. Irrera, S. Salerno Rome Univ. “La Sapienza”, Dept. Electronic Eng. via Eudossiana 18, 00184 Rome (Italy) S. Spiga, M. Fanciulli Laboratorio MDM-INFM, via C. Olivetti 2 20041 Agrate Brianza (Italy)

  2. Aim of the work • To verify the reliability of ZrO2 films embedded in MOS structures as gate dielectric • Electrical characterization by means of I-V curves and C-V measurements in as grown conditions and after constant current stress (CCS) • Extraction of defect density

  3. Why high-k dielectrics? • SiO2 thickness below 2 nm is required in the 2005 technology node • Substitution of SiO2 with oxides with higher dielectric constant • Equivalent Oxide Thickness EOT = eSiO2/ehigh-k tox • Candidates: Al2O3, Gd2O3, ZrO2, HfO2,. . . . Requirements Good chemical stability, amorphous network, large energy gap and high band offset with siliconand of course … lower leakage current

  4. Devices under test Al ZrO2 SiO2 Silicon substrate Vgate Silicon substrate is 2-3 W cm 1.2 ±0.1nm thick native SiO2 layer 19.1±0.3 nm thick ALCVD ZrO2 layer

  5. About the leakage in ZrO2 films …..

  6. Fresh SamplesCurrent-voltage measurements Fowler-Nordheim Poole-Frenkel ?

  7. Fresh SamplesFOWLER-NORDHEIM regime If meff = 0.5 m0 then Al-ZrO2 barrier is 0.3 eV

  8. Fresh SamplesWeak accumulation condition (0<Vgate<1 V) t-1 Current (A/cm2) Transport dominated by charge trapping and de-trapping

  9. Stressed Samples: Current-voltage measurementsCumulative Constant Current Stress @ 1nA/cm2

  10. Stressed Samples:Time behavior of the defect density extracted from PF conduction Scattering Induced Degradation (SID) model

  11. Stressed Samples: Current-voltage measurementsCumulative Constant Current Stress @ 1nA/cm2

  12. Stressed Samples: Weak accumulation condition (0< Vgate < 1V) • I(t)= q.N.A.(2tb)-1 tunneling front model ** q electron charge N defect density A area b a constant • the same defect states are involved in the trapping-detrapping process, i.e the Fermi level remains almost constant with the applied voltage ** S. Manzini, A. Modelli, “Insulating films on semicond.”,Elsevier Science, 112, (1983) D.J. Dumin, J.R. Maddux, IEEE Trans. on Electron Dev., 40, 986, (1993).

  13. Weak accumulation condition (0< Vgate < 1V) t1/2 Defect density greater than 1019 cm-3 pins the Fermi level

  14. Stressed Samples: Current-voltage measurementsCumulative Constant Current Stress @ 1nA/cm2

  15. Strong accumulation condition (Vgate > 1V) Unlike in SiO2 the FN treshold voltage shifts

  16. Capacitance measurements: fresh samples er≈ 22 CFB = 168 nF/cm2 VFB = 450 mV Nbulk≈ 1019 cm-3

  17. Capacitance measurements: low level stress • Negative shift of VFB due to trapping of negative charge • A decrease of capacitance in the strong accumulation region due to variation of the interfacial SiOxZr layer thickness

  18. Capacitance measurements: high level stress • Positive shift of VFB due to trapping of positive charge • A tendency to saturation in the strong accumulation region

  19. Conclusions • Electrical characterization of fresh and stressed ZrO2 films deposited onto native SiO2 on Si by ALCVD • Densities of native bulk defects were estimated in the order of 1019 cm-3 • The density of bulk defects follows a square root time dependence (Scattering Induced Degradation model) • Leakage current of ZrO2 films is lower than that of thicker SiO2 films • Deposition technology needs to be improved

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