FIRST-PRINCIPLES CALCULATIONS OF RADIATION-INDUCED PHENOMENA

1. FIRST-PRINCIPLES CALCULATIONS OF RADIATION-INDUCED PHENOMENA Sokrates T. Pantelides Department of Physics and Astronomy, Vanderbilt University, Nashville, TN and Oak Ridge National Laboratory, Oak Ridge, TN The theory team: Sasha Batyrev, Matt Beck, Matt Evans, Ryan Hatcher, Sergey Rashkeev, Leonidas Tsetseris, Sanwu Wang Plus Atomic-resolution microscopy/EELS by S.J. Pennycook AFOSR/MURI 2005

2. THEORY OBJECTIVES • DISPLACEMENT DAMAGE • Defects, charging • electrons • ALTERNATE DIELECTRICS • Interface structure, interface defects, NBTI,… • CARRIER MOBILITIES • LEAKAGE CURRENTS

3. THEORY OBJECTIVES • DISPLACEMENT DAMAGE • Defects, charging • electrons • ALTERNATE DIELECTRICS • Interface structure, interface defects, NBTI,… • CARRIER MOBILITIES • LEAKAGE CURRENTS

4. MODELING FOR RAD-HARD CIRCUITS ENERGY DEPOSITION  MATERIALS DEVICESCIRCUITS

5. mobilities

6. A Displacement Single Event How does energy translate to electrical activity?

7. APPROACH: DENSITY FUNCTIONAL THEORY • PSEUDOPOTENTIALS, SUPERCELLS • TOTAL ENERGY, FORCES ON ATOMS • EVOLUTION OF SYSTEM • (electrons in instantaneous ground state) • DEFECT CONFIGURATIONS • BULK – INTERFACE • CHARGING

8. APPROACH II: TIME-DEPENDENT DENSITY FUNCTIONAL THEORY • PSEUDOPOTENTIALS, SUPERCELLS • SIMULTANEOUS EVOLUTION OF ELECTRONS AND NUCLEI

9. Hatcher

10. Hatcher

11. Hatcher

12. THEORY OBJECTIVES • DISPLACEMENT DAMAGE • Defects, charging • electrons • ALTERNATE DIELECTRICS • Interface structure, interface defects, NBTI,… • CARRIER MOBILITIES • LEAKAGE CURRENTS

13. ALTERNATE (HIGH-K) DIELECTRICS • EPITAXIAL CRYSTALLINE OXIDES • SiO2 + OTHER OXIDE (HfO2, …) • SiO2 + SILICATE • SiO2 + SiON

14. 0.5 nm SiO2 Si HfO2 Van Benthem, Pennycook

15. 10 Number of Hf atoms 8 6 4 2 0 2 8 6 0 4 Distance from the Si-SiO2 interface (Å) Van Benthem, Pennycook

16. Hf atom near Si-SiO2 interface (DFT calculations) d = 2.3 Å from interface E= 0 eV d =1.5 Å from interfaceE=+2.6 eV DAMAGE IN Si SUBSTRATE! Rashkeev

17. Interstitial vs substitutional Hf atoms in SiO2 films LOCALIZED STATES IN THE Si GAP Rashkeev

18. Si Interface Hf Rashkeev

19. 625 K 300 K IT (HfO2) OT (HfO2) OT (SiO2) IT (SiO2) ENBTI ~ 0.3 eV NEGATIVE BIAS TEMPERATURE INSTABILITY Zhou et al. APL 2004

20. Ea=1 eV DFT CALCULATIONS DE=0.5 eV Q(H2)=0.45 eV Q(H+)=0.8 eV Diffusion-reaction theory Jepson & Svensson 1977 ENBTI = ½ DE + ¼ Q(H2)=0.35 eV Tsetseris et al. APL 2005 KEY MECHANISM FOR NBTI: DEPASSIVATION OF HYDROGENATED DEFECTS • H+ RELEASE • DEPASSIVATION Si-H + H+↔ D+ + H2 Tsetseris

21. THEORY OBJECTIVES • DISPLACEMENT DAMAGE • Defects, charging • electrons • ALTERNATE DIELECTRICS • Interface structure, interface defects, NBTI,… • CARRIER MOBILITIES • LEAKAGE CURRENTS

22. Universal mobility curve

23. MOBILITIES IN STRAINED Si MOSFETS Fischetti et al. 2002

24. MOBILITIES IN DOUBLE-GATE SOI MOSFETS Uchida et al., IEDM Tech. Dig. (2002)

25. V(z) • EFFECTIVE-MASS THEORY SiO2 Si • ENERGY BANDS • INFINITE POTENTIAL BARRIER ~100A ALL MOBILITY CALCULATIONS SUPPRESS ATOMIC-SCALE DETAIL • INTERFACE ROUGHNESS

26. energy (eV) 8 SiO2 Si 7 position (Å) 6 5 4 3 2 1 -4 -2 0 2 4 6 8 Band gap variation across the Si-SiO2 interface

28. Si SiO2 Si SiO2 OXYGEN PROTRUSION SUBOXIDE BOND

29. Oxygen Protrusion Scattering potentials Suboxide Bond Electron Density Evans

30. UMC Uchida et al. 2003 Evans

31. Evans, Caussamel

32. metal n-type Si oxide Fowler-Nordheim tunneling n-type Si metal oxide EC EC EF EV EV

33. DATA: Fukuda et al. JAP, 1998 Lu