Skip to content

Hydrogen dissociation and diffusion near the Si(111)/a-SiO2 interface: Understanding degradation in MOSFETs

Evidence and attribution

Authority of statements

Prose below summarizes the publication identified by doi, title, and pdf_path.

Summary

ReaxFF molecular dynamics in LAMMPS (reax/c) studies hydrogen trapping and transport at a model Si(111)/amorphous SiO\(_2\) gate stack, motivated by NBTI/HCI-like depassivation of Si–H at the interface. The work reports dissociation probability vs incident H kinetic energy, diffusion activation energies near the interface vs bulk-like regions, and path analysis showing higher-barrier routes involving O and Si vacancies near the interface, rationalizing a larger effective activation energy (~0.8 eV near the interface vs ~0.2–0.4 eV in bulk silica cited from prior work).

Methods

  • Code & potential: LAMMPS (June 2014 release noted), ReaxFF parameterization from the cited reference for Si/O/H chemistry; integration schemes and ensembles include NVE, NVT, NPT with Nosé–Hoover thermostat/barostat as stated for different stages.
  • Interface construction: Amorphous SiO\(_2\) generated by melt–quench (7000 K melt, 1 ps, cool to 300 K in NVT, 0.1 fs timestep) with Si slab fixed/thermalized per protocol; further NPT relaxation (10 ps example segments in text) to obtain an interface consistent with prior references; Si(111) slab thermalized at 300 K.
  • Impulsive dissociation studies: Simulation box split so the impact region uses NVE while outer regions maintain NVT to avoid unphysical heating of the reservoir during energy injection; statistics over many velocity-scaled H impacts on Si–H sites.
  • Diffusion: MSD vs time after thermalization sweeps (300–600 K range in NVT, 300 ps segments noted); Arrhenius analysis for activation energies; pathway visualization distinguishing interstitial vs vacancy-mediated mechanisms.

Stages (consolidated). Si(111) slab on a-SiO\(_2\) in a three-dimensional periodic supercell; melt–quench of silica (7000 K, 1 ps, NVT, 0.1 fs), NPT relaxation (10 ps segments cited, Nosé–Hoover thermostat/barostat), Si thermalized at 300 K; impulsive Si–H studies use NVE in the impact zone with NVT reservoirs; NVT diffusion windows (300–600 K, 300 ps). Pressure target in NPT: N/A — cite PDF if not duplicated here. Electric field: N/A — not used. Enhanced sampling: N/A — umbrella / metadynamics / replica exchange not used.

Findings

  • Dissociation: Probability of Si–H bond breaking increases with initial kinetic energy of the hydrogen, supporting a picture analogous to hot-carrier-driven depassivation.
  • Diffusion barriers: Extracted activation energies for H/proton transport are consistent with cited literature for bulk silica in the low end, but larger (~0.8 eV) near the interface in the modeled system.
  • Mechanistic insight: Near-interface diffusion involves oxygen/silicon vacancy pathways with higher barriers than bulk-like interstitial diffusion, explaining the elevated effective activation energy at the interface compared to bulk a-SiO\(_2\).

Limitations

Interface preparation and ReaxFF accuracy constrain quantitative barrier values; statistics depend on the number of impact/diffusion samples collected in the study.

Reader notes (navigation)

These sections summarize what the checked-in extraction and abstracts support; they are not a substitute for the full PDF. For theme-level retrieval, see paper-index-by-domain and hubs linked from canonical_tags in the front matter above. Operators updating chunks should reconcile numbers with normalized/extracts/ and the version-of-record PDF when available.