1. 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)

2. Aim of the work To verify the reliability of ZrO 2 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? SiO 2 thickness below 2 nm is required in the 2005 technology node Substitution of SiO 2 with oxides with higher dielectric constant Equivalent Oxide Thickness EOT =  SiO2 /  high-k t ox Candidates: Al 2 O 3, Gd 2 O 3, ZrO 2, HfO 2,.... Requirements Good chemical stability, amorphous network, large energy gap and high band offset with silicon and of course … lower leakage current

4. Silicon substrate SiO 2 V gate ZrO 2 Al Devices under test Silicon substrate is 2-3  cm 1.2 ±0.1 nm thick native SiO 2 layer 19.1±0.3 nm thick ALCVD ZrO 2 layer

5. About the leakage in ZrO 2 films …..

6. Fresh Samples Current-voltage measurements Poole-Frenkel Fowler-Nordheim ?

7. Fresh Samples FOWLER-NORDHEIM regime If m eff = 0.5 m 0 then Al-ZrO 2 barrier is 0.3 eV

8. Fresh Samples Weak accumulation condition (0<V gate <1 V) Transport dominated by charge trapping and de-trapping t -1 Current (A/cm 2 )

9. Stressed Samples: Current-voltage measurements Cumulative Constant Current Stress @ 1nA/cm 2

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

11. Stressed Samples: Current-voltage measurements Cumulative Constant Current Stress @ 1nA/cm 2

12. Stressed Samples: Weak accumulation condition (0< V gate < 1V) I(t)= q. N. A. (2t  ) -1 tunneling front model ** q electron charge N defect density A area  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< V gate < 1V) Defect density greater than 10 19 cm -3 pins the Fermi level t 1/2

14. Stressed Samples: Current-voltage measurements Cumulative Constant Current Stress @ 1nA/cm 2

15. Strong accumulation condition (V gate > 1V) Unlike in SiO 2 the FN treshold voltage shifts

16. Capacitance measurements: fresh samples C FB = 168 nF/cm 2 V FB = 450 mVN bulk ≈ 10 19 cm -3  r ≈ 22

17. Capacitance measurements: low level stress Negative shift of V FB due to trapping of negative charge A decrease of capacitance in the strong accumulation region due to variation of the interfacial SiO x Zr layer thickness

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

19. Conclusions Electrical characterization of fresh and stressed ZrO 2 films deposited onto native SiO 2 on Si by ALCVD Densities of native bulk defects were estimated in the order of 10 19 cm -3 The density of bulk defects follows a square root time dependence (Scattering Induced Degradation model) Leakage current of ZrO 2 films is lower than that of thicker SiO 2 films Deposition technology needs to be improved