Thin film reaction kinetics of niobium/aluminum multilayers

Abstract

Phase formation kinetics in Nb/Al multilayered thin films having overall compositions of 25, 33, 50, and 75 at. % Al have been investigated using scanning calorimetry, x-ray diffraction, and cross-sectional transmission electron microscopy. The first phase to form upon annealing the Nb/Al layered structure of all samples is the NbAls intermetallic. Calorimetry clearly identifies the NbAls formation to be a two-stage process. The first stage is the formation of a planar layer by nucleation and growth to coalescence while the second stage is the thickening of the planar layer. The large amount of heat released (and hence large volume fraction of NbAls formed) during the first reaction stage is consistent with heterogeneous nucleation at well-isolated sites in the Nb/Al interface. This is surprising in light of the large thermodynamic driving force expected for nucleation and suggests that the local nonequilibrium nature of the Nb/Ai interface greatly reduces the driving force for nucleation. The next phase observed in samples of 25 and 33 at. % Al is the Al5 superconducting phase, Nb3Al. The NbsAl growth completes a first reaction stage similar to the NbAls, but the subsequent thickening reaction stage is not observed without simultaneous Nb2Al growth. The high interface velocities derived from the calorimetry for formation of both NbAls and the Al5 Nb7A1 indicate that atomic transport must be by grain boundary diffusion. 1341

Direct observation of NiSi lateral growth at the epitaxial θ-Ni2Si/Si(1 0 0) interface

“…These models are based on different approximations and different phenomena. However, all of the models consider the diffusion along the interfaces and they conclude that the product phase should reach a stationary thickness that depends on the kinetics parameters, in accordance with the experimental results [14][15][16][17]19]. The models also led to a relatively similar particle shape.…”

“…Several experimental studies [14][15][16][17][18][19] reported the presence of a discontinuous phase as the first results of the reaction between the two other phases. However, the entire particle shape has not been reported; thus, it is not possible to compare these experimental results with existing models [13,20,22,23].…”

“…Differential scanning calorimetry (DSC) showed that the formation of a single product phase occurs in a two-step growth process for silicides [13][14][15] and other compounds [16,17]. Apart from DSC measurements, Lucadamo et al [18] presented evidence for a two-stage reaction mechanism in Nb/Al multilayer thin-films by TEM and in situ X-ray diffraction (XRD) experiments using high-intensity synchrotron radiation.…”

Influence of layer microstructure on the double nucleation process in Cu∕Mg multilayers

“…They reported that the growth of the intermetallic CuMg 2 phase takes place in two well separated stages: nucleation and lateral growth of the intermetallic along the interface until coalescence is complete, followed by a diffusion limited vertical growth of the same intermetallic phase. A similar behavior has been observed in other multilayer systems such as Al/ Ni, 11,15 Al/ Nb, 9,16,17 Al/ Ag, 18 Al/ Co, 3 Ni/ Si, 7,16 V / Si, 19 or Cu/ Sn. 20 Coffey et al 16 developed a kinetic model that incorporates the two stage model and allowed the simulation of the corresponding calorimetric traces.…”

Atomic layer deposited ultrathin metal nitride barrier layers for ruthenium interconnect applications

“…No signature of preferential orientation of the RuSi phase was observed in the pole figures. This twostage silicide reaction phenomenon could be understood after Coffey et al 28 The first stage between 439 °C < T < 524 °C in fig. 2 could be interpreted as the nucleation and lateral growth of a very thin layer of the RuSi phase in the plane of the substrate.…”