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Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide Leakage Currents

Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide Leakage Currents. P.M. Lenahan, J.J. Mele, A.Y. Kang, J. P. Campbell Penn State University, University Park, PA 16802 S.T. Liu Honeywell Corp. Plymouth, MN 55441 R.K. Lowry and D. Woodbury Intersil Corp.

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Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide Leakage Currents

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  1. Direct Experimental Evidence Linking Silicon Dangling Bond Defects to Oxide Leakage Currents P.M. Lenahan, J.J. Mele, A.Y. Kang, J. P. Campbell Penn State University, University Park, PA 16802 S.T. Liu Honeywell Corp. Plymouth, MN 55441 R.K. Lowry and D. Woodbury Intersil Corp. Melbourne, FL 32902 R. Weimer, Micron Technologies Boise, Idaho 83707-0006

  2. Ec Stress Induced Leakage (SILC) Trap CB Edge Inelastic tunneling of silicon conduction band electrons through oxide defects near the Si/SiO2 boundary. EF VB Edge CB Edge Ev SiO2 Si VB Edge S.Takagi, et al. Trans.Electron.Dev 46, 348 (1999) E.Rosenbaum and L.F.Register, IEEE Trans.Electron.Dev. 44, 317(1997)

  3. Literature suggests oxygen vacancy centers (E’ centers): • J.H.Suehle, et al. IRPS (1994) • J.H.McPherson and H.Mogul, J.Appl.Phys, 84, 1513 (1998) • B.Schlund, et al. IRPS (1996) • D.J.Dumin and J.Maddux, IEEE Trans.Electron.Dev., 40, 886 (1993) • S.Takagi, et al. IEEE Trans.Electron.Dev., 46, 348 (1999) • A.Yokozawa, et al. IEDM (1997)

  4. At least two independent studies indicate that E’ centers are generated when oxides are subjected to high electric fields. ** So, if we could link E’ center density to leakage current, we could establish an important role for the centers in oxide leakage phenomena. * W. L. Warren and P.M. Lenahan, JAP 62, 4305 (1987), IEEE Trans Nucl. Sci 34, 1355 (1987) * H. Hazama, et al. Proceedings of the Workshop on Ultra Thin Oxides Jap.Soc. Appl. Phys. Tokyo 1998. Cat. No. Ap 982204 pp201-212.

  5. Test E’ hypothesis with neutral E’ centers Ec Ec Ec Ec Ev Ev Ev Ev + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + SiO2 Si Si SiO2 (Any net space charge near the Si/SiO2 boundary will decrease the tunneling barrier and increase oxide current for any gate potential.)

  6. Approach: (a) Generate neutral E’ centers in a wide variety of oxides, annihilate the E’ centers by various means. (b) Compare generation and annihilation of the E’ centers with generation and annihilation of oxide leakage current. (Are they strongly correlated?) (c) Compare experimental results and “theoretical work on inelastic tunneling and SILC. (Are the defect densities “reasonable” in terms of the (very crude) theory available.)

  7. Oxides Utilized in the Study: 3.3nm (forming gas) 3.3nm (no forming gas) 45 nm (forming gas) (all thermally grown)

  8. 3.3nm Oxide (forming gas) Arbitrary Units As Processed Post VUV Post Anneal Pb0 E’ 3440 3445 3450 3455 3460 3465 3470 3475 3480 3485 Magnetic Field (Gauss)

  9. E’ and Leakage Current Generation 3.3nm oxide (forming gas)

  10. E’ and Leakage Current Anneal 3.3nm oxide (forming gas)

  11. 3.3nm Oxide (no forming gas) 90 MIN ANNEAL 90 MIN VUV Virgin ESR Amplitude (Arb. Units) Pb0 E’ 3440 3450 3460 3470 3480 Magnetic Field (G) 14

  12. I-V Characteristics of 3.3nm Oxide (no forming gas)

  13. E’ and Leakage Current Generation 3.3nm oxide (no forming gas)

  14. E’ and Leakage Current Anneal 3.3nm oxide (no forming gas)

  15. 45nm Oxides As Processed Post VUV Arbitrary Units Post VUV and Anneal Pbo (g=2.0058) E` [g(z.c.)=2.0005] 3440.5 3445.5 3450.5 3455.5 3460.5 3465.5 3470.5 3475.5 3480.5 Magnetic Field (G)

  16. E’ and Leakage Current Generation 3.3nm oxide (forming gas) 20

  17. E’ and Leakage Current Anneal 45nm oxide (forming gas)

  18. Conclusions In several quite different oxides we find that: (1) Generation of E’ centers is accompanied by generation of oxide leakage currents. (2) A brief 200oC anneal in air annihilates most of the E’ centers and most of the leakage current.

  19. Since (A) earlier work by two independent groups show that E’ centers are generated by high field stressing oxides, And (B) recent theoretical and experimental studies indicate that E’ centers are good candidates for leakage current defects, we conclude that E’ centers are important, probably dominating defects in SILC (and RILC) in a wide range of oxides on silicon.

  20. Many studies report generation of interface states in conjunction with the creation of stress induced leakage currents. Several studies also report a strong correlation between SILC and interface state generation. Why is this so?

  21. Before Stressing Oxide Si Si Si Si Si Si Si Si Si/SiO2 H H H H Si Si Si Si After Stressing Oxide Si Si Si Si H H H H Si/SiO2 Si Si Si Si

  22. Consider Statistical MechanicsThe system will approach the lowest Gibbs Free Energy: G = H-TS E’ E’H O O Si O Si O H Oxide O O Pb PbH H Si/SiO2 Si Si Si Si Si Si Si Si h 0 (The oxide and interface Si-H bond enthalpies will be about equal)

  23. Entropy: S = k ln (Ω) (Total of N sites) Suppose all E’ dbs are unpassivated … O O O Si O Si Si O O O O O S = k ln(1) Contribution to configurational entropy of N E’ sites: Suppose all Pb dbs are passivated (Total of M sites) … H H H H Si Si Si Si Contribution to configurational entropy of M PbH sites: S = k ln(1)

  24. Suppose we remove one H from the M PbH sites; the configurational entropy changes: ∆S = k ln (M) … H H H Si Si Si Si Suppose we add one H to the N E’ sites; the configurational entropy changes: ∆S = k ln (N) … O O O Si Si Si H O O O O O O The Gibbs free energy of the system will be lowered by the transfer of some hydrogen from Pb sites to E’ sites. (If kinetics allows it)

  25. The process will occur to some extent. To how great an extent? PbH + E’ + H2 Pb + E’H + H2 [Pb] [E’H] = exp ( - ∆G / kT) = K ~ 1 [PbH] [E’]

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