Leonidas Tsetseris 1 in collaboration with

1. Common origin for enhanced low-dose-rate sensitivity and bias-temperature instability under negative bias Leonidas Tsetseris1 in collaboration with R. D. Schrimpf1, D. M. Fleetwood1, R. L. Pease2, S. T. Pantelides1,3 1Vanderbilt University 2RLP Research Inc. 3Oak Ridge National Lab Work supported by AFOSR

2. Outline • Enhanced low-dose-rate sensitivity (ELDRS) • ELDRS under negative bias • Degradation under negative bias (NBTI) • Common origin for NBTI and ELDRS • Role of trapping, release, and reactions of hydrogen • Implications and conclusions

3. ELDRS Degradation of many bipolar technologies enhanced at low dose-rates Previous models for zero or positive gate bias: Space charge model (Fleetwood et al., IEEE TNS’96, Rashkeev et al., IEEE TNS’02) Bimolecular mechanism model (Hjalmarson et al., IEEE TNS’02) Migration-reaction of hydrogen on the oxide side of the Si-SiO2 interface

4. ELDRS observed under negative bias Vg ELDRS: a new regime Density of interface traps in a gated LPNP transistor after irradiation at high (H) and low (L) dose-rates under gate biases 0, -50, and -100 v.

5. Degradation under negative Vg: Negative Bias Temperature Instability (NBTI) Typical NBTI conditions: Oxide Electric field: 2-6 MV/cm Temperature T: 75-200 ºC Increase of interface traps-oxide trapped charge at stress time ts I: Reaction-limited phase; II: Diffusion-limited phase

6. ELDRS-NBTI Under negative bias protons in the oxide move away from the interface • Are there additional mechanisms for interface trap formation? • Is degradation at negative bias related to NBTI? • Why is there a dose-rate dependence for Vg < 0? • What are the effects of annealing, device history, polarity?

7. Reactions: A → B DE : Reaction Energy Ea: Reaction Barrier Barriers ↔ Activation Energy Ea B DE A METHODOLOGY • First-principles (density-functional) calculations • Pseudopotentials, plane-wave basis, supercells • Study plausible and competing mechanisms • Study of charged states (trapping of carriers)

8. = H = Si = O NBTI: A (mostly!) HYDROGEN STORY Interface traps: Si dangling bond (D) Hydrogen Passivates-Depassivates: Si-H + H ↔ D + H2 D + H ↔ Si-H

9. = H = Si = O REACTION (depassivation) DE ~ 0.5 eV Ea ~ 1 eV

10. B No holes B DE ≈ 0.6eV Ea≈ 1.2eV A A With holes B DE ≈ 0.2eV Ea≈ 0.35eV A SOURCE (of Hydrogen) Dissociation of P-H complexes Confirm experiments (Herring & Johnson, 1992, and others) 30%-40% PH complexes, Seager & Anderson, Sol. State Comm. ‘90

11. Release of H from dopants Minority carriers promote H release: D+H- + hole → D+ + H0 Reduced binding energy + reduced diffusion barrier → enhanced dissociation for H0 from dopants

12. H release rate, g dose rate Trapping of H Dose-rate dependence of degradation Role of “bimolecular” reaction (Hjalmarson et al., TNS’02): H0 + H0 → H2 Steady-state condition for H: kg – kHH C2 – rH C = 0 Depassivation: H+ + SiH → Pb + H2 Sublinear dependence of concentration of Pb on dose rate g (ti: irradiation time): HIGH DOSE-RATE EFFECT SUPPRESSED

13. Ring Charge 0 1.15 eV 0.9 eV Charge + Oxygen 0.2 eV Chain Silicon 0.46 eV Charge ++ L. Tsetseris, Sanwu Wang, and S. T. Pantelides, APL’06 Trapping site for hydrogen: oxygen clusters Thermal donor

14. Trapping site for hydrogen: oxygen clusters Oxygen Silicon Hydrogen Efficient trapping with a release barrier of ~ 1.8 eV L. Tsetseris, Sanwu Wang, and S. T. Pantelides, APL’06

15. CONCLUSIONS-IMPLICATIONS • ELDRS is possible for negative gate bias • H released in Si, creates interface traps • Common origin with NBTI • Degradation suppressed at high dose-rate • Interface roughness may play a role (MOSFET vs bipolar) • Dopant profile • Other trapping sites L. Tsetseris et al., IEEE TNS’06