Jean-Francois Veyan

Enhancing the Reactivity of Al/CuO Nanolaminates by Cu Incorporation at the Interfaces

In situ deposition of a thin (∼5 nm) layer of copper between Al and CuO layers is shown to increase the overall nanolaminate material reactivity. A combination of transmission electron microscopy imaging, in situ infrared spectroscopy, low energy ion scattering measurements, and first-principles calculations reveals that copper spontaneously diffuses into aluminum layers (substantially less in CuO layers). The formation of an interfacial Al:Cu alloy with melting temperature lower than pure Al metal is responsible for the enhanced reactivity, opening a route to controlling the stochiometry of the aluminum layer and increasing the reactivity of the nanoenergetic multilayer systems in general.

Comparative time-resolved study of the XeF2 etching of Mo and Si

In situ and time-resolved infrared absorption spectroscopic measurements reveal that, under typical processing conditions (∼300u2002K, approximately Torr pressures), XeF2 reacts efficiently but very differently with Mo and Si substrates. This kinetic study of the surface etching processes, based on the time evolution of both reactants and products, demonstrates that the mechanisms for Mo and Si etching are different. While XeF2 produces substantial roughening and a thick fluorosilyl layer on the crystalline Si surface (>200u2002nm), it only reacts with the surface atoms of amorphous Mo with substantially slower kinetics. The measured kinetics are quantified by simulation and the final profile experimentally obtained on etched Si surface is shown to be consistent with a recent theoretical study of the characteristic diffusion-controlled etching of silicon.

XeF2-induced removal of SiO2 near Si surfaces at 300 K: An unexpected proximity effect.

XeF2 interaction with SiO2/Si stacks has been investigated to understand the role of Si in proximity of SiO2 during XeF2 exposures of Si/SiO2 stacks. In situ Fourier transform infrared absorption spectroscopy, using a custom-made reaction cell compatible with high XeF2 pressures, reveals that, while pure SiO2 is not etched by XeF2, the oxide in SiO2/Si stacks is effectively removed when XeF2 has access to the silicon, i.e., when the Si in close proximity to the oxide is etched. Thick oxides (∼1–2u2002μm) are removed if sample edges are accessible, while thinner oxides (50–100 nm) are removed without requiring edge access. This unexpected SiO2 removal is found to be due to the formation of reactive fluorine species (XeF and F) evolved by the reaction of XeF2 with Si, which can, subsequently, etch SiO2. Calculations based on density functional theory provide critical insight into the underlying energetics and reaction pathways controlling XeF2 etching of both Si and SiO2.

Cobalt and iron segregation and nitride formation from nitrogen plasma treatment of CoFeB surfaces

Cobalt-iron-boron (CoFeB) thin films are the industry standard for ferromagnetic layers in magnetic tunnel junction devices and are closely related to the relevant surfaces of CoFe-based catalysts. Identifying and understanding the composition of their surfaces under relevant processing conditions is therefore critical. Here we report fundamental studies on the interaction of nitrogen plasma with CoFeB surfaces using infrared spectroscopy, x-ray photoemission spectroscopy, and low energy ion scattering. We find that, upon exposure to nitrogen plasma, clean CoFeB surfaces spontaneously reorganize to form an overlayer comprised of Fe2N3 and BN, with the Co atoms moved well below the surface through a chemically driven process. Subsequent annealing to 400u2009°C removes nitrogen, resulting in a Fe-rich termination of the surface region.

Colored porous silicon as support for plasmonic nanoparticles

Colored nanoporous silicon thin films were employed as dielectric spacing layers for the enhancement of localized surface plasmon (LSP) polaritons. Upon formation of Au nanoparticles (Au-NPs) on these layers, a visible color change is observed due to multiple LSP resonance excitations. Far-field effects were assessed by angle-resolved reflectometry. Resonance enhancements, particularly for s-polarized light, account for the observed color change and are discussed in terms of effective medium and Mie scattering theory. Enhancements of the electric field strengths in the near-field and of the absorption in the substrate were deduced from finite difference time domain calculations and exceed considerably those of the non-porous Au-NP/Si interface. First results of improved photoelectrocatalytic hydrogen evolution at these interfaces are discussed. Samples were prepared by varied procedures of metal assisted etching and dry etching with XeF2. Structural and chemical properties were investigated by scanning el...

Initial nitride formation during plasma-nitridation of cobalt surfaces

Nitridation of metal surfaces is of central importance in microelectronics and spintronics due to the excellent mechanical, thermal, and electrical properties of refractory nitrides. Here, we examine the chemical and structural modification of cobalt surfaces upon nitrogen plasma treatment, using in situ spectroscopic methods, as a method for synthesis of cobalt nitride thin films. We find that nitrogen is incorporated below the surface and forms an ultrathin film of CoN at temperatures as low as 50u2009°C. In addition, we observe the incorporation of oxygen and NO+ within the surface region. The nitrided cobalt surfaces are fully passivated by N, O, and NO+. These results provide a route for incorporation of cobalt nitride into a wide range applications.

Vapor Phase Cleaning and Corrosion Inhibition of Copper Films by Ethanol and Heterocyclic Amines

Cleaning and passivation of metal surfaces are necessary steps for selective film deposition processes that are attractive for some microelectronic applications (e.g., fully aligned vias or self-aligned contacts). For copper, there is limited knowledge about the mechanisms of the copper oxide reduction process and subsequent passivation layer formation reactions. We have investigated the in situ cleaning (i.e., oxidation and reduction by vapor-phase species) and passivation of chemical-mechanical polishing (CMP)-prepared Cu films in an effort to derive the mechanisms associated with selectively tailoring the surface chemistry. By monitoring the interaction of vapor-phase ethanol with the surface species generated after ozone cleaning at 300 °C, we find that the optimum procedure to remove these species and avoid byproduct redeposition is to use atomic layer deposition (ALD)-like binary cycles of ethanol and N2, with active pumping. We have further explored passivation of clean Cu using benzotriazole and 2,2-bipyridine in an ALD environment. Both molecules chemisorb on clean Cu in an upright orientation, with respect to the metal surface at temperatures higher than the melting point of the organic inhibitors (100 ≤ T < 300 °C). Both molecules desorb without decomposition from clean Cu above 300 °C but not from Cu2O. Previous studies related to the passivation of Cu surfaces using heterocyclic amines have focused on solution-based or ultrahigh vacuum applications of the passivation molecules onto single crystalline Cu samples. The present work explores more industrially relevant vapor-phase passivation of CMP-cleaned, electroplated Cu samples using ALD-like processing conditions and in situ vapor-phase cleaning.