Scanning Tunneling Microscopy of Cobalt on Silicon Surfaces: A study on formation and properties of metallic nano structures

Applied Science

Submonolayer growth of Co on H-passivated Si(100) surfaces and nanoscale metallization with Co on patterned H–Si(100)

Nucleation and growth of submonolayer Co coverage on H-passivated Si(100) surfaces was studied in situ by UHV-STM. Non-epitaxial Co islands are formed after room temperature deposition of Co on H–Si(100); the island number density grows with Co coverage in agreement with predictions of an isotropic two-dimensional random walker. Moreover, the fabrication of Co-silicide nanowires (width <10 nm) was explored by STM nanolithography on H–Si(100) and subsequent Co deposition. The room temperature wires appeared granular, while those annealed at 683 K showed a more compact structure.

The temperature evolution of ultra-thin films in solid-phase reaction of Co with Si (111) studied by scanning tunneling microscopy

The solid-phase reaction of 5 Å of Co with the Si (111) surface is investigated by scanning tunneling microscopy (STM) in the range from room temperature to 700 °C. Room-temperature deposition leads to a granular film surface. The small grains transform upon annealing between 200 and 300 °C into triangular surface terraces with step heights of 1.5 and 3.1 Å. Further annealing up to 500 °C leads to their growth and a decrease of the relative number of 1.5 Å steps. These observations are explained by the formation of a cobalt silicide with a CsCl-type lattice. Furthermore, apart from the known 2×2 reconstructions and the unreconstructed surface, various surface features like individual double-line-shaped defects and steps with a height of 0.4 Å are resolved. Finally, the formation of pinholes is observed after annealing at 500 °C. They lead upon further annealing to a complicated pinhole-induced CoSi2 network that breaks up into individual islands at ~700 °C

Diffusion, nucleation and annealing of Co on the H-passivated Si(100) surface

We investigate the diffusion, nucleation and annealing behaviour of Co on H-passivated Si(100) surfaces by scanning tunneling microscopy (STM). Due to the absence of nucleation sites for silicide formation, the nucleation and growth mode is dominated by the formation of non-epitaxial islands which merge by increasing Co coverage θ. The island number density N shows a power law dependence on coverage N∝θc (c=0.29±0.03) for room temperature deposition. Annealing at temperatures up to ~400°C results in small changes of the Co clusters, while deposition at elevated substrate temperatures (~400°C) results in the formation of fewer but coarser Co islands. Finally, at higher annealing temperatures (~490°C) where H desorption takes place, the formation of two-dimensional islands occurs which are surrounded by an irregular 2×n (n>1) reconstructed surface due to interstitial diffusion of Co into Si

Technology for nanoelectronic devices based on ultra-high vacuum scanning tunneling microscopy on the Si(100) surface

We describe two process steps in an STM-based fabrication technology for nanoelectronic devices. First, we have fabricated Co/Si metal lines on Si(100) surfaces by UHV-STM based nanolithography on a monohydride passivation layer. The STM tip was used to define depassivated lines

The temperature evolution of ultra-thin films in solid-phase reaction of Co with Si (111) studied by scanning tunneling microscopy

The solid-phase reaction of 5 Å of Co with the Si (111) surface is investigated by scanning tunneling microscopy (STM) in the range from room temperature to 700 °C. Room-temperature deposition leads to a granular film surface. The small grains transform upon annealing between 200 and 300 °C into triangular surface terraces with step heights of 1.5 and 3.1 Å. Further annealing up to 500 °C leads to their growth and a decrease of the relative number of 1.5 Å steps. These observations are explained by the formation of a cobalt silicide with a CsCl-type lattice. Furthermore, apart from the known 2×2 reconstructions and the unreconstructed surface, various surface features like individual double-line-shaped defects and steps with a height of 0.4 Å are resolved. Finally, the formation of pinholes is observed after annealing at 500 °C. They lead upon further annealing to a complicated pinhole-induced CoSi2 network that breaks up into individual islands at ~700 °C.

Diffusion, nucleation and annealing of Co on the H-passivated Si(100) surface

We investigate the diffusion, nucleation and annealing behaviour of Co on H-passivated Si(100) surfaces by scanning tunneling microscopy (STM). Due to the absence of nucleation sites for silicide formation, the nucleation and growth mode is dominated by the formation of non-epitaxial islands which merge by increasing Co coverage θ. The island number density N shows a power law dependence on coverage N∝θc (c=0.29±0.03) for room temperature deposition. Annealing at temperatures up to ~400°C results in small changes of the Co clusters, while deposition at elevated substrate temperatures (~400°C) results in the formation of fewer but coarser Co islands. Finally, at higher annealing temperatures (~490°C) where H desorption takes place, the formation of two-dimensional islands occurs which are surrounded by an irregular 2×n (n>1) reconstructed surface due to interstitial diffusion of Co into Si.

Contact and Alignment Marker Technology for Atomic Scale Device Fabrication

This article reports on the technology to link atomic scale structures to macroscopic contact pads. Dedicated processes for electrode pattern formation in several materials have been developed and characterised. For pattern formation in CoSi2 a thermal compromise between proper silicide formation and lateral dimension loss has been established. The thermal stability of Pt and W submicron patterns (or the silicides of these) has been investigated. First results, for W in particular, show that atomically clean and flat surfaces can be realized coexisting with useful metallization patterns.