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Dislocation-pipe diffusion in nitride superlattices observed in direct atomic resolution

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ABSTRACT

Device failure from diffusion short circuits in microelectronic components occurs via thermally induced migration of atoms along high-diffusivity paths: dislocations, grain boundaries, and free surfaces. Even well-annealed single-grain metallic films contain dislocation densities of about 1014 m−2; hence dislocation-pipe diffusion (DPD) becomes a major contribution at working temperatures. While its theoretical concept was established already in the 1950s and its contribution is commonly measured using indirect tracer, spectroscopy, or electrical methods, no direct observation of DPD at the atomic level has been reported. We present atomically-resolved electron microscopy images of the onset and progression of diffusion along threading dislocations in sequentially annealed nitride metal/semiconductor superlattices, and show that this type of diffusion can be independent of concentration gradients in the system but governed by the reduction of strain fields in the lattice.

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The operation of dislocation-pipe diffusion by strain fields around a threading dislocation line.High-resolution STEM micrographs, corresponding EDS- and strain mapping of the same area of a HfN/ScN superlattice sample as-deposited (a), and after annealing for 24 h and 48 h, respectively, at 950 °C (b) and (c). The onset of Hf diffusion along the dislocation line after deposition is already visible in (a). From the change in the shape of the Hf diffusion front after annealing in (b), the diffusion length can be directly measured and an average value calculated. The (contrast enhanced) enlarged region in the inset in (b) shows pairs of edge dislocations at the cores of the vertical dislocation line, in the center along which the diffusion occurs. Strain mapping reveals high strain fields around the dislocation line of the as-deposited sample (a), that become significantly reduced by the diffusion of Hf after 24 h of annealing (b), and relaxes the lattice almost entirely once the pipe formation is completed (c). Shown is the y-component of the strain tensor εyy, i.e. parallel to the direction of diffusion. Strain is measured with reference to a lattice region outside the field of view, about 15–20 nm away from the dislocation core. Strain shown in (1/100) %.
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f3: The operation of dislocation-pipe diffusion by strain fields around a threading dislocation line.High-resolution STEM micrographs, corresponding EDS- and strain mapping of the same area of a HfN/ScN superlattice sample as-deposited (a), and after annealing for 24 h and 48 h, respectively, at 950 °C (b) and (c). The onset of Hf diffusion along the dislocation line after deposition is already visible in (a). From the change in the shape of the Hf diffusion front after annealing in (b), the diffusion length can be directly measured and an average value calculated. The (contrast enhanced) enlarged region in the inset in (b) shows pairs of edge dislocations at the cores of the vertical dislocation line, in the center along which the diffusion occurs. Strain mapping reveals high strain fields around the dislocation line of the as-deposited sample (a), that become significantly reduced by the diffusion of Hf after 24 h of annealing (b), and relaxes the lattice almost entirely once the pipe formation is completed (c). Shown is the y-component of the strain tensor εyy, i.e. parallel to the direction of diffusion. Strain is measured with reference to a lattice region outside the field of view, about 15–20 nm away from the dislocation core. Strain shown in (1/100) %.

Mentions: In order to quantify the findings above, a sequential annealing series was performed. Figure 3 shows atomically resolved STEM micrographs and corresponding elemental EDS maps together with strain mapping employing geometric phase analysis (shown is the εyy component of the strain tensor, parallel to the direction of diffusion, see Supplementary Materials online for detailed information) of the threading dislocation line region of the same sample area as-deposited (3a), after 24 h annealing at 950 °C (3b), and after a total of 48 h annealing at 950 °C (3c). The same sample region could be repeatedly identified for the sequential imaging due to a characteristic shape of the sample surface in the area of interest (cf. Supplementary Figure 2). Along the dislocation line in (3a), an onset of diffusion has already taken place during the magnetron-sputter deposition of the layers at elevated temperatures (see methods for growth details). Noticeably, the layers curve towards the substrate while the coherency of the lattice is continuously maintained, unlike as in e.g., low-angle tilt boundaries. After 24 h of annealing, Hf has diffused massively into the ScN along the dislocation line towards the direction of the substrate, however, has not yet reached the respective next neighbouring HfN layers below. Along the path of diffusion, pairs of edge dislocations (enlarged in the contrast enhanced inset in (3b)) become apparent.


Dislocation-pipe diffusion in nitride superlattices observed in direct atomic resolution
The operation of dislocation-pipe diffusion by strain fields around a threading dislocation line.High-resolution STEM micrographs, corresponding EDS- and strain mapping of the same area of a HfN/ScN superlattice sample as-deposited (a), and after annealing for 24 h and 48 h, respectively, at 950 °C (b) and (c). The onset of Hf diffusion along the dislocation line after deposition is already visible in (a). From the change in the shape of the Hf diffusion front after annealing in (b), the diffusion length can be directly measured and an average value calculated. The (contrast enhanced) enlarged region in the inset in (b) shows pairs of edge dislocations at the cores of the vertical dislocation line, in the center along which the diffusion occurs. Strain mapping reveals high strain fields around the dislocation line of the as-deposited sample (a), that become significantly reduced by the diffusion of Hf after 24 h of annealing (b), and relaxes the lattice almost entirely once the pipe formation is completed (c). Shown is the y-component of the strain tensor εyy, i.e. parallel to the direction of diffusion. Strain is measured with reference to a lattice region outside the field of view, about 15–20 nm away from the dislocation core. Strain shown in (1/100) %.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5382674&req=5

f3: The operation of dislocation-pipe diffusion by strain fields around a threading dislocation line.High-resolution STEM micrographs, corresponding EDS- and strain mapping of the same area of a HfN/ScN superlattice sample as-deposited (a), and after annealing for 24 h and 48 h, respectively, at 950 °C (b) and (c). The onset of Hf diffusion along the dislocation line after deposition is already visible in (a). From the change in the shape of the Hf diffusion front after annealing in (b), the diffusion length can be directly measured and an average value calculated. The (contrast enhanced) enlarged region in the inset in (b) shows pairs of edge dislocations at the cores of the vertical dislocation line, in the center along which the diffusion occurs. Strain mapping reveals high strain fields around the dislocation line of the as-deposited sample (a), that become significantly reduced by the diffusion of Hf after 24 h of annealing (b), and relaxes the lattice almost entirely once the pipe formation is completed (c). Shown is the y-component of the strain tensor εyy, i.e. parallel to the direction of diffusion. Strain is measured with reference to a lattice region outside the field of view, about 15–20 nm away from the dislocation core. Strain shown in (1/100) %.
Mentions: In order to quantify the findings above, a sequential annealing series was performed. Figure 3 shows atomically resolved STEM micrographs and corresponding elemental EDS maps together with strain mapping employing geometric phase analysis (shown is the εyy component of the strain tensor, parallel to the direction of diffusion, see Supplementary Materials online for detailed information) of the threading dislocation line region of the same sample area as-deposited (3a), after 24 h annealing at 950 °C (3b), and after a total of 48 h annealing at 950 °C (3c). The same sample region could be repeatedly identified for the sequential imaging due to a characteristic shape of the sample surface in the area of interest (cf. Supplementary Figure 2). Along the dislocation line in (3a), an onset of diffusion has already taken place during the magnetron-sputter deposition of the layers at elevated temperatures (see methods for growth details). Noticeably, the layers curve towards the substrate while the coherency of the lattice is continuously maintained, unlike as in e.g., low-angle tilt boundaries. After 24 h of annealing, Hf has diffused massively into the ScN along the dislocation line towards the direction of the substrate, however, has not yet reached the respective next neighbouring HfN layers below. Along the path of diffusion, pairs of edge dislocations (enlarged in the contrast enhanced inset in (3b)) become apparent.

View Article: PubMed Central - PubMed

ABSTRACT

Device failure from diffusion short circuits in microelectronic components occurs via thermally induced migration of atoms along high-diffusivity paths: dislocations, grain boundaries, and free surfaces. Even well-annealed single-grain metallic films contain dislocation densities of about 1014 m−2; hence dislocation-pipe diffusion (DPD) becomes a major contribution at working temperatures. While its theoretical concept was established already in the 1950s and its contribution is commonly measured using indirect tracer, spectroscopy, or electrical methods, no direct observation of DPD at the atomic level has been reported. We present atomically-resolved electron microscopy images of the onset and progression of diffusion along threading dislocations in sequentially annealed nitride metal/semiconductor superlattices, and show that this type of diffusion can be independent of concentration gradients in the system but governed by the reduction of strain fields in the lattice.

No MeSH data available.


Related in: MedlinePlus