Formation and high-temperature stability of CoSix films on an SiO2 substrate

Abstract

A thin α-Co layer with an amorphous Si underlayer has been sputter deposited onto a thermal SiO2 substrate, rapid thermal annealed in N2 at 700–1050 °C, and the phases formed examined using Auger electron spectroscopy, transmission electron microscopy, electron diffraction, and sheet resistance measurements. A CoSix film results where x is constant with depth and determined by the relative amounts of Co and Si deposited. With increasing x, phases identified are α- and β-Co containing dissolved Si, Co2Si, CoSi, and CoSi2. At high temperatures, the CoSi2 film agglomerates and thins the underlying oxide probably on account of excess Si in the silicide film. Furthermore, in an N2 atmosphere, the CoSi2 globules are converted into CoSi in accordance with the phase diagram.

Reaction mechanism of cobalt with silicon dioxide

“…This proposal is consistent with that of Morgan et al 8 who calculated a ternary phase diagram of Co-Si-O showing that cobalt should not react with SiO 2 but also mentioned that in the presence of small concentrations of oxygen, a reaction between cobalt and SiO 2 to produce an orthosilicate phase is possible.…”

“…The micrograph shows the coalescence of the cobalt layer, similar to results reported in literature. [3][4][5][6][7][8][9][10] Note the tread marks on the SiO 2 layer near the cobalt islands. It seems that in agglomeration, the cobalt islands sometimes left a mark on the SiO 2 surface.…”

“…7 Another study suggested that cobalt should not react with SiO 2 based on a calculated phase diagram while it proposed that cobalt reacts with SiO 2 by dissolving Si to form cobalt silicide while releasing oxygen. 8 These authors did suggest that cobalt silicate formation is possible with a trace level of oxygen, though they did not observe any evidence of orthosilicate formation. We have also presented evidence of reactions between cobalt and the SiO 2 substrate.…”

“…Elimination of oxygen contaminant through surface in situ cleaning or annealing in a forming gas ambient has resulted in a significant reduction of the interaction between cobalt and SiO 2 , consistent with the calculated phase diagram and thermodynamic calculation. 8 It is proposed that the majority of oxygen required for the reaction is present on the cobalt surface, possibly in the form of OH bonds. The product of the Co/SiO 2 /O 2 reaction is proposed to be the cubic cobalt silicate phase, Co 2 SiO 4 , based on transmission electron microscopy ͑TEM͒ diffraction patterns.…”

Highly chiral-selective growth of single-walled carbon nanotubes with a simple monometallic Co catalyst

“…While SiO 2 -Co reactions are thermodynamically unfavorable, 22,39 they can be triggered by the presence of impurities such as oxygen or surface water 40 leading to silicide 39 or silicate [40][41][42] formation.…”