Conducting atomic force microscopy studies of nanoscale cobalt silicide Schottky barriers on Si(111) and Si(100)

J. L. Tedesco, J. E. Rowe, Robert Nemanich

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

Cobalt silicide (CoSi2) islands have been formed by the deposition of thin films (∼0.1-0.3 nm) of cobalt on clean Si(111) and Si(100) substrates in ultrahigh vacuum (UHV) followed by annealing to ∼880 °C. Conducting atomic force microscopy has been performed on these islands to characterize and measure their current-voltage (I-V) characteristics. Current-voltage curves were analyzed using standard thermionic emission theory to obtain the Schottky barrier heights and ideality factors between the silicide islands and the silicon substrates. Current-voltage measurements were performed ex situ for one set of samples (termed "passivated surfaces") where the silicon surface surrounding the islands was passivated with a native oxide. Other samples (termed "clean surfaces") remained in UHV, while I-V curves were recorded. By comparing the barrier heights and ideality factors for islands on passivated surfaces and clean surfaces, the effects of the nonpassivated surfaces on conduction have been studied. The barrier heights measured from CoSi2 islands on clean surfaces are found to be ∼0.2-0.3 eV below barrier heights measured from similar islands on passivated surfaces. The main cause of the reduced Schottky barrier in the clean surface samples is attributed to Fermi level pinning by nonpassivated surface states of the clean silicon surface. However, the measured barrier heights of the islands are equivalent on both clean Si(111) and Si(100) surfaces, suggesting that the nonpassivated surface is influenced by cobalt impurities. Furthermore, the barrier heights of islands on the clean surfaces are lower than what can be explained by Fermi level pinning alone, suggesting the presence of additional reductions in the Schottky barrier heights. These variations are greater than what can be attributed to experimental error, and the additional barrier height lowering is primarily attributed to spreading resistance effects. Schottky barrier inhomogeneity is also identified as a possible cause of the additional barrier height lowering and nonideality in the Schottky contacts. Current-voltage measurements of the clean surface samples were also obtained at several temperatures. The barrier heights were found to decrease, and the ideality factors were found to increase with decreasing temperature. The dependence of the barrier height is attributed to the temperature variation of the Fermi level.

Original languageEnglish (US)
Article number083721
JournalJournal of Applied Physics
Volume105
Issue number8
DOIs
StatePublished - 2009

Fingerprint

cobalt
atomic force microscopy
conduction
electrical measurement
ultrahigh vacuum
silicon
causes
thermionic emission
electric potential
curves
temperature
electric contacts
inhomogeneity
impurities
annealing

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Conducting atomic force microscopy studies of nanoscale cobalt silicide Schottky barriers on Si(111) and Si(100). / Tedesco, J. L.; Rowe, J. E.; Nemanich, Robert.

In: Journal of Applied Physics, Vol. 105, No. 8, 083721, 2009.

Research output: Contribution to journalArticle

@article{f3859e1851da408ca827dbe99d49eeaa,
title = "Conducting atomic force microscopy studies of nanoscale cobalt silicide Schottky barriers on Si(111) and Si(100)",
abstract = "Cobalt silicide (CoSi2) islands have been formed by the deposition of thin films (∼0.1-0.3 nm) of cobalt on clean Si(111) and Si(100) substrates in ultrahigh vacuum (UHV) followed by annealing to ∼880 °C. Conducting atomic force microscopy has been performed on these islands to characterize and measure their current-voltage (I-V) characteristics. Current-voltage curves were analyzed using standard thermionic emission theory to obtain the Schottky barrier heights and ideality factors between the silicide islands and the silicon substrates. Current-voltage measurements were performed ex situ for one set of samples (termed {"}passivated surfaces{"}) where the silicon surface surrounding the islands was passivated with a native oxide. Other samples (termed {"}clean surfaces{"}) remained in UHV, while I-V curves were recorded. By comparing the barrier heights and ideality factors for islands on passivated surfaces and clean surfaces, the effects of the nonpassivated surfaces on conduction have been studied. The barrier heights measured from CoSi2 islands on clean surfaces are found to be ∼0.2-0.3 eV below barrier heights measured from similar islands on passivated surfaces. The main cause of the reduced Schottky barrier in the clean surface samples is attributed to Fermi level pinning by nonpassivated surface states of the clean silicon surface. However, the measured barrier heights of the islands are equivalent on both clean Si(111) and Si(100) surfaces, suggesting that the nonpassivated surface is influenced by cobalt impurities. Furthermore, the barrier heights of islands on the clean surfaces are lower than what can be explained by Fermi level pinning alone, suggesting the presence of additional reductions in the Schottky barrier heights. These variations are greater than what can be attributed to experimental error, and the additional barrier height lowering is primarily attributed to spreading resistance effects. Schottky barrier inhomogeneity is also identified as a possible cause of the additional barrier height lowering and nonideality in the Schottky contacts. Current-voltage measurements of the clean surface samples were also obtained at several temperatures. The barrier heights were found to decrease, and the ideality factors were found to increase with decreasing temperature. The dependence of the barrier height is attributed to the temperature variation of the Fermi level.",
author = "Tedesco, {J. L.} and Rowe, {J. E.} and Robert Nemanich",
year = "2009",
doi = "10.1063/1.3100212",
language = "English (US)",
volume = "105",
journal = "Journal of Applied Physics",
issn = "0021-8979",
publisher = "American Institute of Physics Publising LLC",
number = "8",

}

TY - JOUR

T1 - Conducting atomic force microscopy studies of nanoscale cobalt silicide Schottky barriers on Si(111) and Si(100)

AU - Tedesco, J. L.

AU - Rowe, J. E.

AU - Nemanich, Robert

PY - 2009

Y1 - 2009

N2 - Cobalt silicide (CoSi2) islands have been formed by the deposition of thin films (∼0.1-0.3 nm) of cobalt on clean Si(111) and Si(100) substrates in ultrahigh vacuum (UHV) followed by annealing to ∼880 °C. Conducting atomic force microscopy has been performed on these islands to characterize and measure their current-voltage (I-V) characteristics. Current-voltage curves were analyzed using standard thermionic emission theory to obtain the Schottky barrier heights and ideality factors between the silicide islands and the silicon substrates. Current-voltage measurements were performed ex situ for one set of samples (termed "passivated surfaces") where the silicon surface surrounding the islands was passivated with a native oxide. Other samples (termed "clean surfaces") remained in UHV, while I-V curves were recorded. By comparing the barrier heights and ideality factors for islands on passivated surfaces and clean surfaces, the effects of the nonpassivated surfaces on conduction have been studied. The barrier heights measured from CoSi2 islands on clean surfaces are found to be ∼0.2-0.3 eV below barrier heights measured from similar islands on passivated surfaces. The main cause of the reduced Schottky barrier in the clean surface samples is attributed to Fermi level pinning by nonpassivated surface states of the clean silicon surface. However, the measured barrier heights of the islands are equivalent on both clean Si(111) and Si(100) surfaces, suggesting that the nonpassivated surface is influenced by cobalt impurities. Furthermore, the barrier heights of islands on the clean surfaces are lower than what can be explained by Fermi level pinning alone, suggesting the presence of additional reductions in the Schottky barrier heights. These variations are greater than what can be attributed to experimental error, and the additional barrier height lowering is primarily attributed to spreading resistance effects. Schottky barrier inhomogeneity is also identified as a possible cause of the additional barrier height lowering and nonideality in the Schottky contacts. Current-voltage measurements of the clean surface samples were also obtained at several temperatures. The barrier heights were found to decrease, and the ideality factors were found to increase with decreasing temperature. The dependence of the barrier height is attributed to the temperature variation of the Fermi level.

AB - Cobalt silicide (CoSi2) islands have been formed by the deposition of thin films (∼0.1-0.3 nm) of cobalt on clean Si(111) and Si(100) substrates in ultrahigh vacuum (UHV) followed by annealing to ∼880 °C. Conducting atomic force microscopy has been performed on these islands to characterize and measure their current-voltage (I-V) characteristics. Current-voltage curves were analyzed using standard thermionic emission theory to obtain the Schottky barrier heights and ideality factors between the silicide islands and the silicon substrates. Current-voltage measurements were performed ex situ for one set of samples (termed "passivated surfaces") where the silicon surface surrounding the islands was passivated with a native oxide. Other samples (termed "clean surfaces") remained in UHV, while I-V curves were recorded. By comparing the barrier heights and ideality factors for islands on passivated surfaces and clean surfaces, the effects of the nonpassivated surfaces on conduction have been studied. The barrier heights measured from CoSi2 islands on clean surfaces are found to be ∼0.2-0.3 eV below barrier heights measured from similar islands on passivated surfaces. The main cause of the reduced Schottky barrier in the clean surface samples is attributed to Fermi level pinning by nonpassivated surface states of the clean silicon surface. However, the measured barrier heights of the islands are equivalent on both clean Si(111) and Si(100) surfaces, suggesting that the nonpassivated surface is influenced by cobalt impurities. Furthermore, the barrier heights of islands on the clean surfaces are lower than what can be explained by Fermi level pinning alone, suggesting the presence of additional reductions in the Schottky barrier heights. These variations are greater than what can be attributed to experimental error, and the additional barrier height lowering is primarily attributed to spreading resistance effects. Schottky barrier inhomogeneity is also identified as a possible cause of the additional barrier height lowering and nonideality in the Schottky contacts. Current-voltage measurements of the clean surface samples were also obtained at several temperatures. The barrier heights were found to decrease, and the ideality factors were found to increase with decreasing temperature. The dependence of the barrier height is attributed to the temperature variation of the Fermi level.

UR - http://www.scopus.com/inward/record.url?scp=65449120637&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=65449120637&partnerID=8YFLogxK

U2 - 10.1063/1.3100212

DO - 10.1063/1.3100212

M3 - Article

AN - SCOPUS:65449120637

VL - 105

JO - Journal of Applied Physics

JF - Journal of Applied Physics

SN - 0021-8979

IS - 8

M1 - 083721

ER -