Copper diffusion into single-crystalline TiN studied by transmission electron microscopy and atom probe tomography

Mühlbacher, Marlene; Martín, Francisca Méndez; Sartory, Bernhard; Schalk, Nina; Keckes, Jozef; Lu, Jun; Hultman, Lars; Mitterer, Christian

doi:10.1016/j.tsf.2014.11.084

Cited by 16 publications

(18 citation statements)

References 31 publications

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“…Pole figure measurements and TEM investigations discussed in the appended Paper I confirm that the TiN/Cu bilayers exhibit a cube-on-cube epitaxial relationship with the substrate, i.e. {001}<010>TiN/Cu || {001}<010>MgO [9]. It has to be noted that neither the influence of the TiN stoichiometry nor of differential thermal expansion during the deposition process has been taken into account in the above discussion.…”

Section: Epitaxial Growth Of Single-crystalline Filmsmentioning

confidence: 94%

“…The IVAS software package can calculate unknown ion fractions based on information of nonoverlapping peaks and expected isotope abundances. In Paper I the result of such a calculation is compared to compositional information obtained by elastic recoil detection analysis and both are found to be in excellent agreement [9]. On the other hand, for material systems exhibiting significant major peak overlaps or thermal tails, a more advanced algorithm such as the blind peak deconvolution proposed by Johnson et al has to be employed, which also accounts for system inherent peak broadening [123].…”

Section: Data Processing and 3d Reconstructionmentioning

confidence: 96%

“…However, constraints in fabrication and processing, such as the lattice mismatch to the substrate and thermal budget limitations, have prohibited the successful industrial implementation of such barrier layers as yet [3]. Paper I emphasizes the excellent performance of single-crystalline TiN barriers, which are demonstrated to withstand annealing temperatures of 900 °C and show only limited Cu diffusion after annealing at 1000 °C [9]. On the other hand, polycrystalline TiN diffusion barrier layers are frequently applied in industry and widely studied in literature.…”

Section: Developments In Tin Diffusion Barrier Designmentioning

confidence: 99%

“…It is also possible to achieve atomic resolution in Z-contrast images [102][103][104]. An example of the suitability of Z-contrast imaging in diffusion barrier assessment is presented in Paper I, where a Cu diffusion zone is identified by contrast variation in a HAADF image [9].…”

Section: Z-contrastmentioning

confidence: 99%

“…Paper I focuses on the structural and elemental characterization of the Cu/bulk TiN interface and correlates experimental observations of Cu diffusion in single-crystal TiN with results of first-principles studies [9]. Paper II compares the diffusion of Cu in single-and polycrystalline TiN barrier layers.…”

Section: Introductionmentioning

confidence: 99%

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High-resolution characterization of TiN diffusion barrier layers

Mühlbacher¹

2015

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Titanium nitride (TiN) films are widely applied as diffusion barrier layers in microelectronic devices. The continued miniaturization of such devices not only poses new challenges to material systems design, but also puts high demands on characterization techniques. To gain understanding of diffusion processes that can eventually lead to failure of the barrier layer and thus of the whole device, it is essential to develop routines to chemically and structurally investigate these layers down to the atomic scale. In the present study, model TiN diffusion barriers with a Cu overlayer acting as the diffusion source were grown by reactive magnetron sputtering on MgO(001) and thermally oxidized Si(001) substrates. Cross-sectional transmission electron microscopy (XTEM) of the pristine samples revealed epitaxial, single-crystalline growth of TiN on MgO(001), while the polycrystalline TiN grown on Si(001) exhibited a [001]-oriented columnar microstructure. Various annealing treatments were carried out to induce diffusion of Cu into the TiN layer. Subsequently, XTEM images were recorded with a high-angle annular dark field detector, which provides strong elemental contrast, to illuminate the correlation between the structure and the barrier efficiency of the single- and polycrystalline TiN layers. Particular regions of interest were investigated more closely by energy dispersive X-ray (EDX) mapping. These investigations are completed by atom probe tomography (APT) studies, which provide a three-dimensional insight into the elemental distribution at the near-interface region with atomic chemical resolution and high sensitivity. In case of the single-crystalline barrier, a uniform Cu-enriched diffusion layer of 12 nm could be detected at the interface after an annealing treatment at 1000 °C for 12 h. This excellent barrier performance can be attributed to the lack of fast diffusion paths such as grain boundaries. Moreover, density-functional theory calculations predict a stoichiometry-dependent atomic diffusion mechanism of Cu in bulk TiN, with Cu diffusing on the N-sublattice for the experimental N/Ti ratio. In comparison, the polycrystalline TiN layers exhibited grain boundaries reaching from the Cu-TiN interface to the substrate, thus providing direct diffusion paths for Cu. However, the microstructure of these columnar layers was still dense without open porosity or voids, so that the onset of grain boundary diffusion could only be found after annealing at 900 °C for 1 h. The present study shows how to combine two high resolution state-of-the-art methods, TEM and APT, to characterize model TiN diffusion barriers. It is shown how to correlate the microstructure with the performance of the barrier layer by two-dimensional EDX mapping and three-dimensional APT. Highly effective Cu-diffusion barrier function is thus demonstrated for single-crystal TiN(001) (up to 1000 °C) and dense polycrystalline TiN (900 °C)

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Section: Epitaxial Growth Of Single-crystalline Filmsmentioning

confidence: 94%

Section: Data Processing and 3d Reconstructionmentioning

confidence: 96%