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Article

The Effect of Co/TiN Interfaces on Co Interconnect Resistivity

by
Poyen Shen
,
Sanzida Rahman
,
Daniel M. Syracuse
and
Daniel Gall
*
Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, 110 8th St, Troy, NY 12180, USA
*
Author to whom correspondence should be addressed.
Surfaces 2025, 8(4), 89; https://doi.org/10.3390/surfaces8040089
Submission received: 17 October 2025 / Revised: 4 December 2025 / Accepted: 10 December 2025 / Published: 13 December 2025
(This article belongs to the Special Issue Surface Engineering of Thin Films)
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Abstract

Electron transport measurements on Co/TiN multilayers are employed to explore the effect of TiN layers on Co resistivity. For this, 50 nm thick multilayer stacks containing N = 1–10 individual Co layers that are separated by 1 nm thick TiN layers are sputter deposited on SiO2/Si(001) substrates at 400 °C. X-ray diffraction and reflectivity measurements indicate a tendency for a 0001 preferred orientation, an X-ray coherence length of 13 nm that is nearly independent of N, and an interfacial roughness that increases with N. The in-plane multilayer resistivity ρ increases with increasing N = 1–10, from ρ = 14.4 to 36.6 µΩ-cm at room temperature and from ρ = 11.2 to 19.4 µΩ-cm at 77 K. This increase is due to a combination of increased electron scattering at interfaces and grain boundaries, as quantified using a combined Fuchs–Sondheimer and Mayadas–Shatzkes model. The analysis indicates that a decreasing thickness of the individual Co layers dCo from 50 to 5 nm causes not only an increasing resistivity contribution from Co/TiN interface scattering (from 9 to 88% with respect to the room-temperature bulk resistivity) but also an increasing (39 to 154%) grain boundary scattering contribution, which exacerbates the resistivity penalty due to the TiN liner. These results are supported by Co/TiN bilayer and trilayer structures deposited on Al2O3 (0001) at 600 °C. Interfacial intermixing causes Co2Ti and Co3Ti alloy phase formation, an increase in the contact resistance, a degradation of the Co crystalline quality, and a 2.3× higher resistivity for Co deposited on TiN than Co directly deposited on Al2O3(0001). The overall results show that TiN liners cause a dramatic increase in Co interconnects due to diffuse surface scattering, interfacial intermixing/roughness, and Co grain renucleation at Co/TiN interfaces.

1. Introduction

A major challenge for the continued miniaturization of features in integrated circuits is the rise in signal delay and power consumption caused by an increasing interconnect resistance [1,2,3,4]. This resistance increase is due to diminishing conductor dimensions, resulting in a decreasing ratio of the cross-sectional area over the wire length. The decreasing conductor dimensions also cause the resistivity size effect [2,5,6,7,8,9,10], which refers to a resistivity increase at reduced dimensions due to electron scattering at surfaces [11,12,13,14,15], interfaces [16,17,18,19], and grain boundaries [20,21,22,23]. Extensive ongoing materials research focuses on quantifying the resistivity size effect for different conductors to evaluate their potential to provide a conductance benefit for highly scaled interconnects [24,25,26,27,28,29,30]. Interconnect research also includes the liner layer, which is designed to increase the adhesion between the conductor and the dielectric or diffusion barrier [31,32,33,34] and is important for interconnect reliability [35,36,37,38]. The liner affects the interconnect resistance in multiple ways: (i) It alters the electron scattering specularity p at the conductor–liner interface [39,40,41], which, in turn, affects the conductor resistivity as described by the classical Fuchs and Sondheimer (FS) model [42,43]. (ii) The liner occupies a considerable fraction of the cross-sectional area of the trench used for the interconnect line, resulting in a higher resistance and an exacerbated resistivity size effect, motivating the development of particularly thin liner solutions [1,44,45,46,47]. (iii) The interconnect stack includes contacts between vertical (via) and horizontal (line) interconnects, which typically are separated by a liner layer such that the current needs to flow across a high-resistance conductor–liner–conductor interface, motivating high-conductivity liners [48,49,50]. (iv) The liner acts as a nucleation layer for subsequent conductor deposition and, therefore, affects the conductor microstructure and, in particular, the grain size and orientation distribution, which contribute to the resistivity size effect [33,51,52]. Our present study explores the resistance effects for the Co (conductor) and TiN (liner) material system.
Cobalt (Co) is a potential Cu replacement metal [53,54,55,56,57,58] due to its relatively low predicted product of the bulk resistivity times the bulk electron mean free path, ρo × λ = 7.3/4.8 × 10−16 Ωm2 [59], which predicts a relatively low resistivity size effect. In addition, the high melting point and cohesive energy in comparison to Cu suggest higher reliability against electromigration and time-dependent dielectric breakdown [35,60] and facilitate integration with relatively thin TiN liner layers [61,62,63,64,65,66]. TiN is expected to result in diffuse (p = 0) electron scattering at the Co/TiN interfaces [16], but the relatively low TiN resistivity [67,68,69,70,71] is expected to provide a high Co-TiN-Co interface conductivity. In addition, TiN has been demonstrated as a wetting layer for the growth of Cu and Ag [16] and may similarly also aid Co deposition and increase the Co grain size, resulting in increased Co interconnect conductivity.
In this paper, we employ transport measurements on Co/TiN multilayer thin films to explore the effect of Co/TiN interfaces on the resistivity of Co. The multilayers consist of alternating Co and TiN layers, using a constant TiN thickness of 1 nm for all samples, representing a typical TiN liner thickness. The number of individual Co layers is varied in the range of N = 1–10, and the Co layer thickness is varied in the range of dCo = 50–5 nm, such that the total nominal Co thickness for all samples is kept constant at 50 nm. The resistivity of the superlattices parallel to the Co/TiN interfaces increases with increasing N, which is attributed to both increasing electron scattering at Co/TiN interfaces as well as a decreasing Co grain size caused by Co renucleation on each TiN interlayer.

2. Materials and Methods

Co/TiN multilayers were deposited on SiO2/Si(001) and Al2O3(0001) wafers in an ultra-high vacuum DC magnetron sputter deposition system with a base pressure of 10−9 Torr [72]. The 10 × 10 mm2 substrates consisted of (i) a 100 nm thick SiO2 layer that was deposited on Si(001) by plasma-enhanced chemical vapor deposition, which formed a smooth amorphous surface and electrically insulated the multilayers from the Si wafers, or (ii) single-crystal Al2O3(0001), which facilitated epitaxial growth of Co(0001) or TiN(111). The substrates were cleaned in subsequent ultrasonic baths of Hellmanex solution, acetone, isopropyl alcohol, and deionized water for 15 min each, attached to a molybdenum block with colloidal silver paint, inserted into the deposition system through a load lock, and degassed in vacuum at 800 °C for one hour using a radiative pyrolytic graphite heater. The substrate temperature was then reduced to 400 °C (or 600 °C for deposition on Al2O3(0001)), which was chosen to maximize multilayer crystalline quality and minimize Co-TiN intermixing, as quantified by X-ray diffraction and reflectivity. Depositions were performed using 5 cm diameter 99.99% pure Co and 99.995% pure Ti targets facing a continuously rotating substrate at a 12 cm distance and at −45° and 45° tilts. They were sputter cleaned prior to deposition for 10 min with closed shutters. Subsequently, the shutters in front of the Co and Ti targets were alternately opened and closed, and inlet valves for processing gas were simultaneously switched to obtain 10 mTorr 99.999% pure Ar or 7.5 mTorr 99.999% pure N2 for Co and TiN depositions, respectively, yielding the desired multilayers. Constant DC power of 200 and 50 W to the Co and Ti targets resulted in deposition rates of 0.083 and 0.087 nm/s for Co and TiN, respectively. The bottom layer for all multilayers was a 1 nm thick TiN layer, which facilitated Co wetting on SiO2 and also reduced the possibility for Co diffusion into or reaction with the substrate. Different multilayers with different individual Co layer thicknesses, dCo = 5–50 nm, were deposited by adjusting the Co deposition time from 60 to 600 s, while the TiN deposition time was kept constant at 11 s for all TiN layers, yielding a constant TiN thickness of 1.0 nm. The number of multilayer periods, N = 1–10, was varied in such a way that the total amount of Co for each multilayer was the same nominal 50 nm. For example, the N = 1 sample consisted of one 50 nm thick Co layer on top of one 1 nm thick TiN layer, while the N = 10 sample consisted of ten 5 nm thick Co layers, separated by 1 nm thick TiN layers. These samples are summarized in Table 1. In addition, 75 nm thick TiN/Co bilayers and trilayers were deposited on Al2O3(0001) at 600 °C such that the total amount of TiN (45 nm) and Co (30 nm) was kept constant. This included stacks with (i) 45 nm thick TiN on top of 30 nm thick Co, (ii) 30 nm thick Co on top of 45 nm thick TiN, and (iii) 22.5 nm thick TiN on top of 30 nm thick Co on top of 22.5 nm thick TiN. This second set of samples is summarized in Table 2.
X-ray diffraction (XRD) analyses were performed using a PANalytical X’pert PRO MPD system with a λKα = 1.5418 Å Cu source. Symmetric θ–2θ scans were acquired with a fixed 0.5° divergence slit and a PIXcel solid-state line detector operating in scanning mode with a 14 mm active length corresponding to 255 active channels. Grazing incidence X-ray diffraction (GIXRD) patterns were collected using a parabolic mirror yielding a parallel beam with a < 0.055° divergence, incident at a constant angle ω = 2°. The latter was chosen to maximize the thin film XRD peak intensity while ensuring that diffracted intensity is detected from the whole layer thickness. ω rocking curves of Co 0002 reflections were obtained using the same parabolic mirror, a fixed 2θ = 44.38°, and the line detector operating in receiving mode with a 0.165 mm active length. X-ray reflectivity (XRR) scans were acquired with the same parallel beam geometry, with the line detector operating in receiving mode with a 0.165 mm active length. The measured XRR data were fitted using the PANalytical X’Pert Reflectivity software 1.3a, which employs the Parratt formalism, following the procedure of our previous work on multilayers [17,18,72,73]. The model for data fitting included alternating TiN and Co layers on SiO2, with densities fixed at literature values of 5.4, 8.9, and 2.65 g/cm3, respectively. The free fitting parameters were the thickness of each layer within the multilayer stack and the roughness of each interface and top surface.
The multilayer sheet resistances were measured in air at 293 K with a linear four-point probe with spring-loaded tips and a 1.0 mm inter-probe spacing. Measurements at 77 K were taken with the same linear four-point probe with both sample and probe tips completely immersed in liquid nitrogen. The resistivity was determined from the measured sheet resistance using the measured thickness and the appropriate geometric correction factor [74].

3. Results and Discussion

Figure 1 shows typical X-ray reflectivity patterns from Co/TiN multilayer films consisting of N = 1, 2, 3, 4, 7, or 10 Co and TiN layers, as labeled. The measured intensity is plotted as solid lines in a logarithmic scale as a function of the scattering angle 2θ = 0.1–3° and offset by factors of 10 for clarity purposes. The plot includes, as a dotted line, the typical result from curve fitting for N = 2. The N = 1 sample consists of a single Co layer on top of a 1 nm thick TiN layer on SiO2/Si(001). Its pattern shows a critical angle 2θ = 0.51° ± 0.02°, close to the expected 0.48° for pure Co with a density of 8.9 ± 0.1 g/cm3. The pattern also shows thickness fringes near 2θ = 0.95° and 1.11°, indicating a Co thickness of 55.2 nm, in reasonable agreement with the nominal 50 nm. The N = 2 sample shows a qualitatively similar pattern. However, its critical angle 2θ = 0.47° ± 0.02° is moved to a slightly lower angle, and the fringes are less pronounced, which is attributed to a relatively high interface and surface roughness. More specifically, the data fitting for this sample (red dotted line) indicates a multilayer with two Co layers with a 4.1 nm interface roughness. The patterns from the multilayers with increasing N = 3, 4, 7, and 10 indicate a continued decrease in the critical angle to 2θ = 0.45°, 0.40°, 0.34°, and 0.32°. This is attributed to a decreasing effective overall multilayer density associated with an increasing volume fraction of the lower-density TiN within the multilayer in combination with the possible development of an underdense microstructure associated with Co renucleation at each TiN interface, leading to a decreasing grain size with increasing N, as discussed below. In addition, the fringes near 2θ = 1° become less pronounced for N = 3 and 4 and cannot be detected for N = 7 and 10. This indicates an increasing Co/TiN interface roughness with increasing N. The patterns from the N = 4, 7, and 10 multilayers exhibit broad (weak) features with maxima at 1.3° and 2.4°, which are attributed to superlattice fringes [17,72]. Data fitting cannot uniquely determine the associated superlattice periods (nominally, 13.5, 8.1, and 6.0 nm) from these fringes due to their low intensity above the background noise. We note that the TiN cannot be directly detected from these XRR patterns, but the continuous change, in particular the decrease in resolved fringes with increasing N, clearly demonstrates the increasing perturbation that the TiN depositions cause to the Co microstructure.
Figure 2 shows grazing incidence X-ray diffraction θ–2θ patterns from six 50 nm thick Co/TiN multilayer films containing N = 1, 2, 3, 4, 7, and 10 Co layers. The measured intensity is plotted on a linear scale, and the patterns are offset for clarity purposes. The N = 1 pattern shows a relatively strong peak at 2θ = 44.5° due to the Co 0002 reflection. Other possible peaks from Co 10 1 - 0 and Co 10 1 - 1 would be expected at 2θ = 41.6° and 47.4° for a random crystalline orientation. However, they have insufficient intensity to be distinguishable from the background noise. This suggests a tendency for a 0001 preferential crystalline orientation of the Co layer, since the expected 10 1 - 0 peak intensity from Co with randomly oriented grains is similar to the 0002 intensity, while the Co 10 1 - 1 reflection for randomly oriented grains is expected to be four times stronger than the Co 0002 (JCPDS Card No. 01-071-4239). We note that the 0001 out-of-plane crystalline alignment is relatively weak since GIXRD measures the 0001 planes with a 20° tilt with respect to the surface normal, and symmetric XRD θ–2θ scans could not detect any Co peaks due to low intensity, suggesting considerable grain misalignment in combination with a small grain size and/or low crystalline quality. Increasing the number of Co layers to N = 2, 3, 4, 7, and 10 results in qualitatively and quantitatively similar GIXRD patterns, indicating that the degree of crystalline alignment is independent of the number of Co/TiN interfaces, which is important for the interpretation of the transport results presented below. This is further illustrated in the inset of Figure 2, which shows higher resolution and higher signal-to-noise ratio GIXRD scans of the Co 0002 peak from the N = 1 and N = 10 samples. Their full-width at half-maximum (FWHM) peak widths of σ = 0.70° and 0.73° are nearly identical. This corresponds to X-ray coherence lengths ξ = λ/(σ cos θ) = 13.1 and 13.6 nm, respectively. These coherence lengths measured by GIXRD are for a direction perpendicular to the 0001 planes, that is, at a 20° tilt with respect to the surface normal. We note that ξ is larger than the dCo = 5 nm Co layer thickness for the N = 10 sample, indicating that crystalline grains are larger (approximately along the growth direction) than individual Co layers, suggesting that either the Co/TiN interfaces exhibit local epitaxy or the nominally 1 nm thick TiN layers are not continuous, allowing Co grains to extend across 2–3 layers. This suggests some Co-TiN interfacial intermixing, which is consistent with the interface roughness > 4 nm measured by XRR.
Figure 3 is a plot of the resistivity ρ of Co/TiN multilayers vs. the thickness dCo of individual Co layers within the multilayers. The blue triangle and red square data points are the resistivity measured at 77 and 293 K, respectively, and the lines through the data points are the result from curve fitting using a combined Fuchs–Sondheimer and Mayadas–Shatzkes model, as discussed below. The data is also presented in Table 1. The room-temperature resistivity decreases from ρ = 36.6 µΩ-cm for dCo = 5.1 nm to ρ = 30.9, 26.9, 25.5, 19.6, and 14.4 µΩ-cm for dCo = 7.3, 12.8, 17.0, 25.5, and 51.0 nm, corresponding to multilayer films with N = 10, 7, 4, 3, 2, and 1 Co layers, respectively. The resistivity at 77 K shows a similar decrease with increasing dCo, from 24.6 to 21.3, 17.0, 14.0, 11.4, and 6.9 µΩ-cm. These values are lower than at 293 K, which is due to the reduced electron–phonon scattering at low temperatures. The resistivity difference Δρ between the two plotted data sets in Figure 3 decreases from 12.0 to 7.5 µΩ-cm with increasing dCo, indicating that Matthiessen’s rule for additive resistivity contributions from electron–phonon and other scattering processes does not apply to our Co/TiN multilayers. The average measured Δρ = 9.8 μΩ-cm is 67% larger than the reported Δρ = 5.82 µΩ-cm for bulk Co, based on ρ = 6.37 µΩ-cm at 293 K and ρ = 0.55 µΩ-cm at 77 K. The larger Δρ for the multilayers is likely due to a reduction in the effective cross-sectional area of conducting Co caused by Co/TiN interfacial intermixing. More importantly, all multilayers have resistivities that are well above the reported bulk values. This is attributed to electron scattering at Co/TiN interfaces and at grain boundaries, as quantitatively discussed below.
We describe the measured ρ vs. dCo in our multilayers using a parallel conductor model, where each Co layer acts as an individual conductor such that the multilayer resistivity becomes identical to the resistivity of each individual Co layer. This approach neglects the electron transport in the TiN interlayers as well as their thickness, which is expected to be negligible as discussed before. The resistivity of an individual Co layer with thickness dCo is described by a combined Fuchs–Sondheimer (FS) [42,75] and Mayadas–Shatzkes (MS) [76] model for surface and grain boundary scattering, respectively, yielding the approximate expression:
ρ Co = ρ o + ρ o λ Co [ 3 4 d Co ( 1 − p ) ] + ρ o λ Co [ 3 R 2 D ( 1 − R ) ] .
This equation contains multiple correlated parameters that cannot all be independently determined by direct data fitting. More specifically, both the surface scattering contribution and the grain boundary scattering contribution to the resistivity, the second and third terms in Equation (1), respectively, are proportional to ρo × λCo. While the former is proportional to 1/dCo, the latter is proportional to 1/D, where D increases as dCo increases. As a consequence, the parameters cannot be independently determined. Thus, for the data analysis in this paper, we fix all parameters based on previously reported values with the exception of the grain size D, which is determined by the fitting procedure. More specifically, the bulk resistivity ρo is kept fixed at 0.55 and 10.34 µΩ-cm for 77 and 293 K, respectively, where the former is the reported bulk resistivity ρo,77K at 77 K [77] and the latter is the sum of ρo,77K plus our measured average Δρ = 9.79 μΩ-cm due to phonon scattering, as discussed above. The probability p for specular scattering at the Co/TiN interfaces is set to zero for all samples and at all temperatures, assuming completely diffuse interface scattering, based on the reported diffuse electron scattering at Co-TiN interfaces [78]. The product of bulk resistivity times electron mean free path, ρo × λCo, is fixed to the previously reported value of 12.2 × 10−16 Ωm2 [9], which is independent of temperature and corresponds to a Co bulk electron mean free path λCo = 11.7 nm at room temperature and λCo = 220 nm at 77 K. The average electron grain boundary reflection probability in Co is set to R = 0.3 for all samples and temperatures, based on previously reported studies [23,79,80,81]. The solid blue and red lines in Figure 3 are the result of curve fitting to the 77 and 293 K data. This is performed using Equation (1) with the above-discussed fixed parameters, while the grain size D is the only free fitting parameter. D is expected to increase with dCo, following a power law, D ∝ dCon, as is common for polycrystalline film growth [82]. Thus, our fitting procedure includes (i) estimation of D using Equation (1) for each sample and temperature, (ii) taking the average of the estimated D at 77 and 293 K for each given sample, and (iii) curve fitting of these average D values with the power law. This process yields a growth exponent n = 0.4, matching typical values for thin film deposition at relatively low homologous temperatures [82], as is the case for Co deposition at Ts = 400 °C with a melting point of Tm = 1495 °C, corresponding to a homologous temperature of 0.38. The resulting grain size increases (as expected) monotonously with increasing dCo from 4.9 nm for dCo = 5.1 nm to D = 19.7 nm for dCo = 51 nm. The blue and red curves in Figure 3 describe the measured data well, indicating that Equation (1), which accounts for both interface and grain boundary scattering, can simultaneously describe the low temperature and room-temperature resistivity. We note that additional microstructural features, such as interface roughness or interfacial intermixing, may also contribute to the resistivity but are not explicitly accounted for in Equation (1); that is, they are effectively accounted for by the surface and grain boundary scattering terms, which, in turn, become “effective” scattering contributions. More quantitatively, surface and grain boundary scattering contribute 9.1 and 15.9 µΩ-cm to the room-temperature resistivity of the dCo = 5.1 nm sample, corresponding to 88% and 154% of 10.34 µΩ-cm due to bulk scattering. In contrast, the corresponding values for the dCo = 51 nm sample are only 9% and 39%. These values demonstrate the large effect that TiN liners can have on Co resistivity and that this effect is not only due to diffuse surface scattering but also compounded by Co renucleation at the Co/TiN interfaces, resulting in a small Co grain size and a correspondingly large resistivity contribution from grain boundary scattering.
Figure 4 shows X-ray diffraction θ–2θ patterns from two bilayer and one trilayer stacks deposited on Al2O3(0001) at 600 °C. Each stack has a total thickness of 75 nm, and its layer sequence is illustrated in the schematics on the right. The measured intensity is plotted on a logarithmic scale, and the patterns are offset by factors of 10 for clarity purposes. All three patterns show a double-peak feature at 2θ = 41.70° and 41.80° due to the Al2O3 0006 substrate reflections of the CuKα1 and CuKα2 lines. The red pattern from the bilayer structure with 45 nm TiN on top of 30 nm Co shows a peak at 2θ = 44.38°, which is attributed to Co 0002 and corresponds to an out-of-plane lattice parameter of 0.4081 nm. The blue pattern from the Co/TiN/Al2O3(0001) sample shows peaks at 2θ = 36.85° and 44.31°, which are attributed to TiN 111 and Co 0002 reflections. The Co 0002 peak intensity is half as strong as that from the TiN/Co/Al2O3(0001) sample, indicating a degradation in the cobalt crystalline quality and/or 0001 crystalline alignment when Co is deposited on TiN 111 instead of directly on Al2O3(0001). The pink pattern from the trilayer stack, where 30 nm of Co is sandwiched between two 22.5 nm thick TiN layers, shows the same TiN 111 and Co 0002 peaks at 2θ = 36.92° and 44.31. The TiN 111 peak intensity is as strong as the TiN 111 reflection from the Co/TiN/Al2O3(0001) sample, but the Co 0002 intensity is 3 times weaker than for the Co/TiN/Al2O3(0001) sample, indicating a further Co crystal degradation after depositing a TiN layer on the top. Two additional peaks at 2θ = 37.31° and 43.59 are attributed to 022 and 111 reflections from the intermediate alloys Co2Ti and Co3Ti, respectively [83]. This suggests an increased level of Co-Ti intermixing, which is attributed to the presence of two Co/TiN interfaces in the trilayer structure. The inset in Figure 4 shows a Co 0002 ω-rocking curve from the TiN/Co/Al2O3(0001) bilayer, obtained using 2θ = 44.50° corresponding to the Co 0002 peak position. The peak has an FWHM of 0.05°, indicating strong Co [0001] crystal alignment along the growth direction, consistent with previous reports on the epitaxial growth of Co(0001)/Al2O3(0001) [84,85]. We note that comparable measurements on the other two samples do not yield a sufficient signal-to-noise ratio to determine the rocking curve width, consistent with the lower intensity of the Co 0002 peaks in the θ–2θ scans and the corresponding lower crystalline quality and crystalline alignment.
Table 2 shows the measured sheet resistances Rs from the three 75 nm bilayer and trilayer samples discussed above and also from a single 45 nm thick TiN/Al2O3(0001) and a single 30 nm thick Co(0001)/Al2O3 (0001) layer. Rs = 23.8 Ω/sq from the TiN layer yields a resistivity ρTiN = 107 μΩ-cm for a TiN layer directly deposited on Al2O3(0001). Correspondingly, Rs = 3.3 from the Co layer yields a resistivity ρCo = 9.8 μΩ-cm for a Co(0001) layer directly deposited on Al2O3(0001).
We use data in Table 2 to determine the amount of the intermixed alloy and the resistivity increment in the cobalt layer due to TiN templating, which results in crystalline quality degradation of the Co layer. For this purpose, a parallel conductor model is applied, where the total sheet conductance 1/Rs is the sum of the sheet conductance of the TiN layer, the Co layer, and the interfacial alloy layer:
1 R s = d TiN ρ TiN + d Co ρ Co + d a ρ a
Here, ρTiN, ρCo, and ρa are the resistivities of TiN, Co, and the interfacial alloy, while dTiN, dCo, and da are the corresponding layer thicknesses, respectively. We note that ρTiN and ρCo are functions of the microstructure and depend on the underlying layer. We assume that the interfacial intermixing causes an equal reduction in the thickness of adjacent TiN and Co layers. Thus, for bilayer structures dTiN = (45 − da/2) nm and dCo = (30 − da/2) nm, while the total thickness remains 75 nm. We first consider the bilayer sample TiN/Co/Al2O3(0001). The Co layer is directly deposited on the Al2O3(0001), such that we expect its resistivity to match that of the Co/Al2O3(0001), i.e., ρCo = 9.8 μΩ-cm. The resistivity of the interfacial alloy is fixed at ρa = 145 μΩ-cm, based on the previously reported studies [39], while the resistivity of TiN which is deposited on top of Co is expected to be larger than that of TiN/Al2O3(0001) and within the large range of previously published TiN resistivities [86,87], so ρTiN for this sample is between 107 and 300 μΩ-cm. Using an arbitrary “average” value of 200 μΩ-cm and solving Equation (2) for the interfacial alloy thickness yields da = 24.8 nm. We note that there is a relatively large uncertainty in both at ρa and ρTiN. However, because these resistivities are much larger than ρCo, the majority of the current is flowing through the Co layer, and the calculated da is relatively insensitive to the exact values for ρa and ρTiN. For example, changing the TiN resistivity by 50 μΩ-cm to ρTiN = 150 or 250 μΩ-cm results in da = 26.0 or 24.1 nm, respectively, with both values within 1.2 nm from the calculated da = 24.8 nm. We also note that the interdiffusion that results in the interfacial alloy is expected to lead to a continuously varying composition without sharp interfaces between Co, alloy, and TiN. Thus, da represents an effective thickness of the interfacial layer where diffusion has been sufficient to cause the postulated large resistivity. Since even 1% of impurities in metals causes substantial (~2x) resistivity changes, da represents the interfacial thickness where at least an estimated 1% of Co and TiN are intermixed.
We now consider the Co/TiN/Al2O3(0001) bilayer sample. Here, the TiN layer is directly deposited on Al2O3(0001) such that it has an expected resistivity ρTiN = 107 μΩ-cm. In contrast, ρCo is unknown because it is deposited on TiN, which causes a degradation of the Co crystalline quality, as presented in Figure 4. However, it is reasonable to assume the same level of TiN-Co interfacial intermixing for the Co/TiN/Al2O3(0001) and the TiN/Co/Al2O3(0001) samples. Thus, we know from above that da = 24.8 nm, and the only unknown in Equation (2) becomes ρCo. Solving for ρCo yields 22.7 μΩ-cm. This is 2.3 × larger than ρCo = 9.8 μΩ-cm from Co directly deposited on Al2O3(0001); that is, the degradation in the crystalline quality of Co deposited on TiN results in a doubling of Co resistivity, which is consistent with the steep resistivity increase with decreasing dCo shown in Figure 3.
Lastly, we consider the trilayer stack. Based on the analyses from the bilayers, we set ρCo = 22.7 μΩ-cm, ρa = 145 μΩ-cm, and ρTiN = 107 and 200 μΩ-cm for the bottom and top TiN layers, respectively. The intermixing at the two TiN-Co interfaces is assumed to be equal to that of the TiN-Co interfaces in the bilayer structures. Therefore, da = 24.8 nm, dTiN = (22.5 − da/2) nm = 10.1 nm for both bottom and top TiN layers, and dCo = (30− da) nm = 5.2 nm. We note that the relative uncertainty in these numbers is large. In particular, these numbers suggest a negligible Co thickness of 5.2 ± 2 nm, which is consistent with the weak XRD Co peak for this sample shown in Figure 4. Nevertheless, using these numbers and an expression similar to Equation (2) yields an expected sheet resistance for the trilayer structure of 14.0 Ω/sq. This agrees (within 23%) with the measured Rs = 18.1 Ω/sq, indicating that the quantitative resistance analyses are successful.

4. Conclusions

Co/TiN multilayers were deposited on SiO2/Si(001) at 400 °C by sputtering alternating Co and Ti sources with Ar and N2 processing gases. X-ray reflectivity measurements indicate an increasing Co/TiN interface roughness with an increasing number of multilayer periods. X-ray diffraction measurements suggest that Co grains penetrate discontinuous nominally 1 nm thick TiN layers. The multilayer resistivity increases with decreasing thickness of individual Co layers. This is caused by compounding effects from increasing interface and grain boundary scattering, resulting in a room-temperature resistivity that is 254% above that for bulk Co for dCo = 5.1 nm. Co/TiN bilayer and trilayer stacks deposited on Al2O3(0001) at 600 °C reveal Co/TiN interfacial intermixing and the formation of Co2Ti and Co3Ti alloy phases, which cause a considerable increase in the contact resistance. In addition, Co deposited on TiN has a lower crystalline quality and a 2.3× higher resistivity than Co directly deposited on Al2O3(0001), confirming the negative impact of TiN liners on the Co conductivity. The overall results show that TiN liners cause a dramatic resistivity increase in Co interconnects due to diffuse surface scattering, interfacial intermixing/roughness, and Co grain renucleation at Co/TiN interfaces.

Author Contributions

Conceptualization, P.S. and D.G.; methodology, P.S., S.R. and D.M.S.; validation, P.S., S.R. and D.M.S.; formal analysis, P.S.; investigation, P.S., S.R., D.M.S. and D.G.; resources, D.G.; data curation, P.S.; writing—original draft preparation, P.S.; writing—review and editing, P.S., S.R., D.M.S. and D.G.; visualization, P.S.; supervision, D.G.; project administration, D.G.; funding acquisition, D.G. All authors have read and agreed to the published version of the manuscript.

Funding

The authors acknowledge funding from the Semiconductor Research Corporation (SRC) under task 3085.001 and SRC/DARPA under JUMP 2.0 center tasks 3137.019 and 3137.021; the National Science Foundation (NSF) under grant No. 2328906 through the Future of Semiconductors program supported by NSF and industry partners; and the NY State Empire State Development’s Division of Science, Technology and Innovation (NYSTAR), through Focus Center-NY–RPI Contract C210117.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

References

  1. Kim, H. Recent Trends in Copper Metallization. Electronics 2022, 11, 2914. [Google Scholar] [CrossRef]
  2. Rossnagel, S.M.; Kuan, T.S. Alteration of Cu Conductivity in the Size Effect Regime. J. Vac. Sci. Technol. B 2004, 22, 240–247. [Google Scholar] [CrossRef]
  3. Ciofi, I.; Contino, A.; Roussel, P.J.; Baert, R.; Vega-Gonzalez, V.-H.; Croes, K.; Badaroglu, M.; Wilson, C.J.; Raghavan, P.; Mercha, A.; et al. Impact of Wire Geometry on Interconnect RC and Circuit Delay. IEEE Trans. Electron Devices 2016, 63, 2488–2496. [Google Scholar] [CrossRef]
  4. Huynh-Bao, T.; Ryckaert, J.; Tokei, Z.; Mercha, A.; Verkest, D.; Thean, A.V.Y.; Wambacq, P. Statistical Timing Analysis Considering Device and Interconnect Variability for BEOL Requirements in the 5-Nm Node and Beyond. IEEE Trans. Very Large Scale Integr. Syst. 2017, 25, 1669–1680. [Google Scholar] [CrossRef]
  5. Xu, W.H.; Wang, L.; Guo, Z.; Chen, X.; Liu, J.; Huang, X.J. Copper Nanowires as Nanoscale Interconnects: Their Stability, Electrical Transport, and Mechanical Properties. ACS Nano 2015, 9, 241–250. [Google Scholar] [CrossRef]
  6. Rogozhin, A.E.; Glaz, O.G. Materials for Interconnections of Integrated Circuits with Design Standards Less Than 5 Nm. Russ. Microelectron. 2024, 53, 91–103. [Google Scholar] [CrossRef]
  7. Lee, R.T.P.; Imakita, K.; Pattanaik, G.; Yonezawa, R.; Yu, K.-H.; Mayersky, J.; Suzuki, H.; Wajda, C. Interconnect Technology for the Angstrom Era and Beyond. In Proceedings of the 2025 22nd International Workshop on Junction Technology (IWJT), Kyoto, Japan, 4–6 June 2025; IEEE: New York, NY, USA, 2025; pp. 41–43. [Google Scholar]
  8. Ceyhan, A.; Naeemi, A. Overview of the Interconnect Problem. In Carbon Nanotubes for Interconnects; Springer International Publishing: Cham, Switzerland, 2017; pp. 3–36. [Google Scholar]
  9. Gall, D. The Search for the Most Conductive Metal for Narrow Interconnect Lines. J. Appl. Phys. 2020, 127, 050901. [Google Scholar] [CrossRef]
  10. Gall, D. Electron Mean Free Path in Elemental Metals. J. Appl. Phys. 2016, 119, 085101. [Google Scholar] [CrossRef]
  11. Reider, A.M.; Kronthaler, A.; Zappa, F.; Menzel, A.; Laimer, F.; Scheier, P. Comparison of Continuous and Pulsed Low-Power DC Sputtered Ti Thin Films Deposited at Room Temperature. Surfaces 2025, 8, 36. [Google Scholar] [CrossRef]
  12. Naeemi, A.; Pan, C.; Ceyhan, A.; Iraei, R.M.; Kumar, V.; Rakheja, S. BEOL Scaling Limits and next Generation Technology Prospects. In Proceedings of the 51st Annual Design Automation Conference, San Francisco, CA, USA, 1–5 June 2014; pp. 1–6. [Google Scholar]
  13. Barmak, K.; Coffey, K.R. Epitaxial Metals for Interconnects Beyond Cu: Resistivity, Reliability. In Proceedings of the 2020 International Symposium on VLSI Technology, Systems and Applications (VLSI-TSA), Hsinchu, Taiwan, 10–13 August 2020; IEEE: New York, NY, USA, 2020; pp. 115–116. [Google Scholar]
  14. Han, H.J.; Kumar, S.; Jin, G.; Ji, X.; Hart, J.L.; Hynek, D.J.; Sam, Q.P.; Hasse, V.; Felser, C.; Cahill, D.G.; et al. Topological Metal MoP Nanowire for Interconnect. Adv. Mater. 2023, 35, e2208965. [Google Scholar] [CrossRef]
  15. Jeng, C.; Wan, W.; Lin, H.; Liang, M.-S.; Tang, K.; Kao, I.; Lo, H.; Chi, K.; Huang, T.; Yao, C.; et al. BEOL Process Integration of 65nm Cu/Low k Interconnects. In Proceedings of the IEEE 2004 International Interconnect Technology Conference (IEEE Cat. No.04TH8729), Burlingame, CA, USA, 7–9 June 2004; IEEE: New York, NY, USA, 2004; pp. 199–201. [Google Scholar]
  16. Chawla, J.S.; Zhang, X.Y.; Gall, D. Epitaxial TiN(001) Wetting Layer for Growth of Thin Single-Crystal Cu(001). J. Appl. Phys. 2011, 110, 043714. [Google Scholar] [CrossRef]
  17. Shen, P.; Gall, D. Electron Scattering at Interfaces in Epitaxial W(001)-Mo(001) Multilayers. J. Appl. Phys. 2024, 136, 075305. [Google Scholar] [CrossRef]
  18. Shen, P.; Lavoie, C.; Gall, D. Electron Scattering at Interfaces in Ru(0001)/Co(0001) Multilayers. J. Appl. Phys. 2025, 137, 025303. [Google Scholar] [CrossRef]
  19. Lanzillo, N.A.; Restrepo, O.D.; Bhosale, P.S.; Cruz-Silva, E.; Yang, C.C.; Youp Kim, B.; Spooner, T.; Standaert, T.; Child, C.; Bonilla, G.; et al. Electron Scattering at Interfaces in Nano-Scale Vertical Interconnects: A Combined Experimental and Ab Initio Study. Appl. Phys. Lett. 2018, 112, 163107. [Google Scholar] [CrossRef]
  20. Lee, J.W.; Song, J.Y. Synethesis of Single-Crystal Cu Via for BEOL Interconnect. In Proceedings of the 2025 IEEE International Interconnect Technology Conference (IITC), Busan, Republic of Korea, 2–5 June 2025; IEEE: New York, NY, USA, 2025; pp. 1–3. [Google Scholar]
  21. Henriquez, R.; Flores, M.; Moraga, L.; Kremer, G.; González-Fuentes, C.; Munoz, R.C. Electron Scattering at Surfaces and Grain Boundaries in Thin Au Films. Appl. Surf. Sci. 2013, 273, 315–323. [Google Scholar] [CrossRef]
  22. Lee, H.-C.; Ok Park, O. Electron Scattering Mechanisms in Indium-Tin-Oxide Thin Films: Grain Boundary and Ionized Impurity Scattering. Vacuum 2004, 75, 275–282. [Google Scholar] [CrossRef]
  23. Zhu, Y.F.; Lang, X.Y.; Zheng, W.T.; Jiang, Q. Electron Scattering and Electrical Conductance in Polycrystalline Metallic Films and Wires: Impact of Grain Boundary Scattering Related to Melting Point. ACS Nano 2010, 4, 3781–3788. [Google Scholar] [CrossRef]
  24. Zhang, M.; Gall, D. Resistivity Scaling in Epitaxial CuAl2(001) Layers. IEEE Trans. Electron Devices 2022, 69, 5110–5115. [Google Scholar] [CrossRef]
  25. Choi, D.; Barmak, K. On the Potential of Tungsten as Next-Generation Semiconductor Interconnects. Electron. Mater. Lett. 2017, 13, 449–456. [Google Scholar] [CrossRef]
  26. Vyas, A.A.; Zhou, C.; Yang, C.Y. On-Chip Interconnect Conductor Materials for End-of-Roadmap Technology Nodes. IEEE Trans. Nanotechnol. 2018, 17, 4–10. [Google Scholar] [CrossRef]
  27. Chen, L.; Ando, D.; Sutou, Y.; Koike, J. CuAl2 Thin Films as a Low-Resistivity Interconnect Material for Advanced Semiconductor Devices. J. Vac. Sci. Technol. B Nanotechnol. Microelectron. Mater. Process. Meas. Phenom. 2019, 37, 031215. [Google Scholar] [CrossRef]
  28. Kumar, R.; Pathania, S.; Guglani, S.; Kumar, A.; Kumar, S.; Roy, S.; Kaushik, B.K.; Sharma, R. Role of Grain Size on the Effective Resistivity of Cu-Graphene Hybrid Interconnects. In Proceedings of the 2020 IEEE 70th Electronic Components and Technology Conference (ECTC), Online, 3–30 June 2020; IEEE: New York, NY, USA, 2020; pp. 1620–1625. [Google Scholar]
  29. Zhang, M.; Adelmann, C. Prospects and Challenges of Compound Conductors for Advanced Interconnect Applications. J. Appl. Phys. 2025, 138, 090902. [Google Scholar] [CrossRef]
  30. Zhang, M.; Scheerder, J.E.; Soulie, J.-P.; Wu, C.; Park, S.; Tőkei, Z.; Fleischmann, C.; Adelmann, C. Reduced Compositional Fluctuations in Epitaxial NiAl Thin Films. In Proceedings of the 2025 IEEE International Interconnect Technology Conference (IITC), Busan, Republic of Korea, 2–5 June 2025; IEEE: New York, NY, USA, 2025; pp. 1–3. [Google Scholar]
  31. Hu, C.K.; Gignac, L.; Rosenberg, R. Electromigration of Cu/Low Dielectric Constant Interconnects. Microelectron. Reliab. 2006, 46, 213–231. [Google Scholar] [CrossRef]
  32. Kaloyeros, A.E.; Eisenbraun, E. Ultrathin Diffusion Barriers/Liners for Gigascale Copper Metallization. Annu. Rev. Mater. Sci. 2000, 30, 363–385. [Google Scholar] [CrossRef]
  33. Zhang, X.; Cao, L.; Ryan, V.; Ho, P.S.; Taylor, B.; Witt, C.; Labelle, C. Co Liner Impact on Microstructure of Cu Interconnects. ECS J. Solid State Sci. Technol. 2015, 4, N3177–N3179. [Google Scholar] [CrossRef]
  34. Hayashi, R.; Ogawa, M.; Oshio, S.; Adachi, K.; Tanaka, T.; Tada, M. Low Resistive Ru Thin Film on Dielectrics without Adhesive Liner for Sub-2 nm Interconnects. In Proceedings of the 2025 IEEE International Interconnect Technology Conference (IITC), Busan, Republic of Korea, 2–5 June 2025; IEEE: New York, NY, USA, 2025; pp. 1–3. [Google Scholar]
  35. Wen, L.G.; Roussel, P.; Pedreira, O.V.; Briggs, B.; Groven, B.; Dutta, S.; Popovici, M.I.; Heylen, N.; Ciofi, I.; Vanstreels, K.; et al. Atomic Layer Deposition of Ruthenium with TiN Interface for Sub-10 Nm Advanced Interconnects beyond Copper. ACS Appl. Mater. Interfaces 2016, 8, 26119. [Google Scholar] [CrossRef]
  36. He, M.; Zhang, X.; Nogami, T.; Lin, X.; Kelly, J.; Kim, H.; Spooner, T.; Edelstein, D.; Zhao, L. Mechanism of Co Liner as Enhancement Layer for Cu Interconnect Gap-Fill. J. Electrochem. Soc. 2013, 160, D3040–D3044. [Google Scholar] [CrossRef]
  37. Edelstein, D.; Uzoh, C.; Cabral, C.; DeHaven, P.; Buchwalter, P.; Simon, A.; Cooney, E.; Malhotra, S.; Klaus, D.; Rathore, H.; et al. A High Performance Liner for Copper Damascene Interconnects. In Proceedings of the IEEE 2001 International Interconnect Technology Conference (Cat. No.01EX461), Burlingame, CA, USA, 6 June 2001; IEEE: New York, NY, USA, 2001; pp. 9–11. [Google Scholar]
  38. van der Veen, M.H.; Jourdan, N.; Gonzalez, V.V.; Wilson, C.J.; Heylen, N.; Pedreira, O.V.; Struyf, H.; Croes, K.; Bommels, J.; Tokei, Z. Barrier/Liner Stacks for Scaling the Cu Interconnect Metallization. In Proceedings of the 2016 IEEE International Interconnect Technology Conference/Advanced Metallization Conference (IITC/AMC), San Jose, CA, USA, 23–26 May 2016; IEEE: New York, NY, USA, 2016; pp. 28–30. [Google Scholar]
  39. Chen, G.S.; Lin, M.J.; Huang, C.W.; Cheng, Y.L.; Fang, J.S.; Lin, C.I. The Impact of Titanium Alloying on Altering Nanomechanical Properties and Grain Structures of Sputter-Deposited Cobalt for Electromigration Reliability Enhancement. J. Alloys Compd. 2024, 1003, 175564. [Google Scholar] [CrossRef]
  40. Josell, D.; Brongersma, S.H. Size-Dependent Resistivity in Nanoscale Interconnects. Annu. Rev. Mater. Res. 2009, 39, 231–256. [Google Scholar] [CrossRef]
  41. Konar, A.; Shinde, P.P.; Pandian, S.; Adiga, S.P.; Subramanya Mayya, K.; Cho, Y.; Shin, H.-J.; Park, S. Non-Specular Scattering of Carriers from Surface Defects in Thin Metal Interconnects. J. Appl. Phys. 2020, 128, 185103. [Google Scholar] [CrossRef]
  42. Sondheimer, E.H. The Mean Free Path of Electrons in Metals. Adv. Phys. 1952, 1, 1–42. [Google Scholar] [CrossRef]
  43. Lucas, M.S.P. Electrical Conductivity of Thin Metallic Films with Unlike Surfaces. J. Appl. Phys. 1965, 36, 1632–1635. [Google Scholar] [CrossRef]
  44. Nies, C.L.; Natarajan, S.K.; Nolan, M. Control of the Cu Morphology on Ru-Passivated and Ru-Doped TaN Surfaces-Promoting Growth of 2D Conducting Copper for CMOS Interconnects. Chem. Sci. 2022, 13, 713–725. [Google Scholar] [CrossRef] [PubMed]
  45. Nogami, T.; Gluschenkov, O.; Sulehria, Y.; Nguyen, S.; Huang, H.; Lanzillo, N.A.; DeSilva, A.; Mignot, Y.; Church, J.; Lee, J.; et al. Advanced BEOL Interconnects. In Proceedings of the 2020 IEEE International Interconnect Technology Conference (IITC), Online, 5–9 October 2020; IEEE: New York, NY, USA, 2020; pp. 1–3. [Google Scholar]
  46. Zeng, Z.; Yu, B.; Cao, Y.; Xue, X.; Xu, J.; Zhang, Y.; Wang, X.; Fang, J.; Zhang, Y. BEOL Cu Gap-Fill Performance Improvement for 14 nm Technology Node. In Proceedings of the 2020 China Semiconductor Technology International Conference (CSTIC), Online, 17–29 June 2020; IEEE: New York, NY, USA, 2020; pp. 1–5. [Google Scholar]
  47. Park, K.; Simka, H. Advanced Interconnect Challenges beyond 5 nm and Possible Solutions. In Proceedings of the 2021 IEEE International Interconnect Technology Conference (IITC), Online, 6–9 July 2021; IEEE: New York, NY, USA, 2021; pp. 1–3. [Google Scholar]
  48. Moon, J.H.; Jeong, E.; Kim, S.; Kim, T.; Oh, E.; Lee, K.; Han, H.; Kim, Y.K. Materials Quest for Advanced Interconnect Metallization in Integrated Circuits. Adv. Sci. 2023, 10, e2207321. [Google Scholar] [CrossRef]
  49. Tallapalli, S.K.; Vijayakumar, V.; Panigrahy, A.K.; Vignesh, N.A. Defect Analysis and Optimization of Nanomaterial-Based Liner Materials for 3D-IC Integration. Analog Integr. Circuits Signal Process. 2025, 124, 36. [Google Scholar] [CrossRef]
  50. Ren, X.; Wu, Y.; Su, H.; Sun, Y. Develop Self-Forming Conformal Multifunctional Interconnect Layer to Meet the Demands of Advanced Cu Interconnect. In Proceedings of the 2025 26th International Conference on Electronic Packaging Technology (ICEPT), Shanghai, China, 5–7 August 2025; IEEE: New York, NY, USA, 2025; pp. 1–3. [Google Scholar]
  51. Jog, A.; Gall, D. Electron Scattering at Surfaces and Grain Boundaries in Rh Layers. IEEE Trans. Electron Devices 2022, 69, 3854. [Google Scholar] [CrossRef]
  52. Kitada, H.; Suzuki, T.; Akiyama, S.; Nakamura, T. Influence of Titanium Liner on Resistivity of Copper Interconnects. Jpn. J. Appl. Phys. 2009, 48, 04C026. [Google Scholar] [CrossRef]
  53. Mont, F.W.; Zhang, X.; Wang, W.; Kelly, J.J.; Standaert, T.E.; Quon, R.; Ryan, E.T. Cobalt Interconnect on Same Copper Barrier Process Integration at the 7 nm Node. In Proceedings of the 2017 IEEE International Interconnect Technology Conference (IITC), Hsinchu, Taiwan, 16–18 May 2017; IEEE: New York, NY, USA, 2017; pp. 1–3. [Google Scholar]
  54. Bekiaris, N.; Wu, Z.; Ren, H.; Naik, M.; Park, J.H.; Lee, M.; Ha, T.H.; Hou, W.; Bakke, J.R.; Gage, M.; et al. Cobalt Fill for Advanced Interconnects. In Proceedings of the 2017 IEEE International Interconnect Technology Conference (IITC), Hsinchu, Taiwan, 16–18 May 2017; IEEE: New York, NY, USA, 2017; pp. 1–3. [Google Scholar]
  55. Nogami, T.; Patlolla, R.; Kelly, J.; Briggs, B.; Huang, H.; Demarest, J.; Li, J.; Hengstebeck, R.; Zhang, X.; Lian, G.; et al. Cobalt/Copper Composite Interconnects for Line Resistance Reduction in Both Fine and Wide Lines. In Proceedings of the 2017 IEEE International Interconnect Technology Conference (IITC), Hsinchu, Taiwan, 16–18 May 2017; IEEE: New York, NY, USA, 2017; pp. 1–3. [Google Scholar]
  56. Kelly, J.; Kamineni, V.; Lin, X.; Pacquette, A.; Hopstaken, M.; Liang, Y.; Amanapu, H.; Peethala, B.; Jiang, L.; Demarest, J.; et al. Annealing and Impurity Effects in Co Thin Films for MOL Contact and BEOL Metallization. J. Electrochem. Soc. 2019, 166, D3100–D3109. [Google Scholar] [CrossRef]
  57. Kelly, J.; Chen, J.H.-C.; Huang, H.; Hu, C.K.; Liniger, E.; Patlolla, R.; Peethala, B.; Adusumilli, P.; Shobha, H.; Nogami, T.; et al. Experimental Study of Nanoscale Co Damascene BEOL Interconnect Structures. In Proceedings of the 2016 IEEE International Interconnect Technology Conference/Advanced Metallization Conference (IITC/AMC), San Jose, CA, USA, 23–26 May 2016; IEEE: New York, NY, USA, 2016; pp. 40–42. [Google Scholar]
  58. van der Veen, M.H.; Vandersmissen, K.; Dictus, D.; Demuynck, S.; Liu, R.; Bin, X.; Nalla, P.; Lesniewska, A.; Hall, L.; Croes, K.; et al. Cobalt Bottom-Up Contact and via Prefill Enabling Advanced Logic and DRAM Technologies. In Proceedings of the 2015 IEEE International Interconnect Technology Conference and 2015 IEEE Materials for Advanced Metallization Conference (IITC/MAM), Grenoble, France, 18–21 May 2015; IEEE: New York, NY, USA, 2015; pp. 25–28. [Google Scholar]
  59. Thakral, A.; Jog, A.; Gall, D. Resistivity Size Effect in Epitaxial Face-Centered Cubic Co(001) Layers. Appl. Phys. Lett. 2024, 124, 121601. [Google Scholar] [CrossRef]
  60. Griggio, F.; Palmer, J.; Pan, F.; Toledo, N.; Schmitz, A.; Tsameret, I.; Kasim, R.; Leatherman, G.; Hicks, J.; Madhavan, A.; et al. Reliability of Dual-Damascene Local Interconnects Featuring Cobalt on 10 Nm Logic Technology. In Proceedings of the 2018 IEEE International Reliability Physics Symposium (IRPS), Burlingame, CA, USA, 11–15 March 2018; IEEE: New York, NY, USA, 2018; pp. 6E.3-1–6E.3-5. [Google Scholar]
  61. Yeoh, A.; Madhavan, A.; Kybert, N.; Anand, S.; Shin, J.; Asoro, M.; Samarajeewa, S.; Steigerwald, J.; Ganpule, C.; Buehler, M.; et al. Interconnect Stack Using Self-Aligned Quad and Double Patterning for 10 nm High Volume Manufacturing. In Proceedings of the IEEE International Interconnect Technology Conference (IITC), Santa Clara, CA, USA, 4–7 June 2018; IEEE: New York, NY, USA, 2018; p. 144. [Google Scholar]
  62. Hung, R.; Park, J.H.; Ha, T.H.; Lee, M.; Hou, W.; Lei, J.; Bakke, J.R.; Sharma, S.; Sharma, K.R.; Kim, N.S.; et al. Extreme Contact Scaling with Advanced Metallization of Cobalt. In Proceedings of the 2018 IEEE International Interconnect Technology Conference (IITC), Santa Clara, CA, USA, 4–7 June 2018; IEEE: New York, NY, USA, 2018; pp. 30–32. [Google Scholar]
  63. Vega-Gonzalez, V.; Montero, D.; Versluijs, J.; Pedreira, O.V.; Jourdan, N.; Puliyalil, H.; Chehab, B.; Peissker, T.; Haider, A.; Batuk, D.; et al. Process Integration of High Aspect Ratio Vias with a Comparison Between Co and Ru Metallizations. In Proceedings of the 2021 IEEE International Interconnect Technology Conference (IITC), Online, 6–9 July 2021; IEEE: New York, NY, USA, 2021; pp. 1–3. [Google Scholar]
  64. Hsu, C.P.S.; Chen, P.Y.T. Selective Ru or Co Etch for 3 nm Applications. Solid State Phenom. 2021, 314, 307–311. [Google Scholar] [CrossRef]
  65. Zhang, L.; Wang, S.; Wang, T.; Lu, X. Polishing Mechanisms of Various Surfactants in Chemical Mechanical Polishing Relevant to Cobalt Interconnects. Int. J. Adv. Manuf. Technol. 2023, 128, 5425–5436. [Google Scholar] [CrossRef]
  66. Naik, M. Interconnect Trend for Single Digit Nodes. In Proceedings of the 2018 IEEE International Electron Devices Meeting (IEDM), San Francisco, CA, USA, 1–5 December 2018; IEEE: New York, NY, USA, 2018; pp. 5.6.1–5.6.4. [Google Scholar]
  67. Cheng, Y.L.; Wei, B.J.; Shih, F.H.; Wang, Y.L. Stability and Reliability of Ti/TiN as a Thin Film Resistor. ECS J. Solid State Sci. Technol. 2013, 2, Q12–Q15. [Google Scholar] [CrossRef]
  68. Lee, D.; Park, J.; Park, S.; Woo, J.; Moon, K.; Cha, E.; Lee, S.; Song, J.; Koo, Y.; Hwang, H. BEOL Compatible (300 °C) TiN/TiOx/Ta/TiN 3D Nanoscale (~10 nm) IMT Selector. In Proceedings of the 2013 IEEE International Electron Devices Meeting, Washington, DC, USA, 9–11 December 2013; IEEE: New York, NY, USA, 2013; pp. 10.7.1–10.7.4. [Google Scholar]
  69. Lehninger, D.; Mertens, K.; Gerlich, L.; Lederer, M.; Ali, T.; Seidel, K. Room Temperature PVD TiN to Improve the Ferroelectric Properties of HZO Films in the BEoL. MRS Adv. 2021, 6, 535–539. [Google Scholar] [CrossRef]
  70. Lee, C.-C.; Shen, Y.-L.; Kang, Y. Prediction of Interfacial Adhesion Strength of Nanoscale Al/TiN Films Passed through Patterned BEOL Interconnects. Mater. Sci. Semicond. Process. 2015, 39, 1–5. [Google Scholar] [CrossRef]
  71. Sagi, K.V.; Amanapu, H.P.; Alety, S.R.; Babu, S.V. Potassium Permanganate-Based Slurry to Reduce the Galvanic Corrosion of the Cu/Ru/TiN Barrier Liner Stack During CMP in the BEOL Interconnects. ECS J. Solid State Sci. Technol. 2016, 5, 256. [Google Scholar] [CrossRef]
  72. Shen, P.; Gall, D. Electron Scattering at Ru–TiN–Ru Interface Stacks. IEEE Trans. Electron Devices 2024, 71, 6970–6975. [Google Scholar] [CrossRef]
  73. Shen, P.; Gall, D. Metal-Metal Contact Resistance Measurements. In Proceedings of the 2024 IEEE International Interconnect Technology Conference (IITC), San Jose, CA, USA, 3–6 June 2024; IEEE: New York, NY, USA, 2024; pp. 1–3. [Google Scholar]
  74. Smits, F.M. Measurement of Sheet Resistivities with the Four-Point Probe. Bell Syst. Tech. J. 1958, 37, 711–718. [Google Scholar] [CrossRef]
  75. Fuchs, K. The Conductivity of Thin Metallic Films According to the Electron Theory of Metals. Math. Proc. Cambridge Philos. Soc. 1938, 34, 100–108. [Google Scholar] [CrossRef]
  76. Mayadas, A.F.; Shatzkes, M. Electrical-Resistivity Model for Polycrystalline Films: The Case of Arbitrary Reflection at External Surfaces. Phys. Rev. B 1970, 1, 1382. [Google Scholar] [CrossRef]
  77. Milosevic, E.; Kerdsongpanya, S.; McGahay, M.E.; Zangiabadi, A.; Barmak, K.; Gall, D. Resistivity Scaling and Electron Surface Scattering in Epitaxial Co(0001) Layers. J. Appl. Phys. 2019, 125, 245105. [Google Scholar] [CrossRef]
  78. Milosevic, E.; Gall, D. Electron Scattering at Co(0001) Surfaces: Effects of Ti and TiN Capping Layers. AIP Adv. 2020, 10, 055213. [Google Scholar] [CrossRef]
  79. Milosevic, E.; Kerdsongpanya, S.; Gall, D. The Resistivity Size Effect in Epitaxial Ru(0001) and Co(0001) Layers. In Proceedings of the 2018 IEEE Nanotechnology Symposium (ANTS), Albany, NY, USA, 14–15 November 2018; IEEE: New York, NY, USA, 2018; pp. 1–5. [Google Scholar]
  80. Pal, A.K.; Chaudhuri, S.; Barua, A.K. The Electrical Resistivity and Temperature Coefficient of Resistivity of Cobalt Films. J. Phys. D. Appl. Phys. 1976, 9, 2261–2267. [Google Scholar] [CrossRef]
  81. Wislicenus, M.; Liske, R.; Gerlich, L.; Vasilev, B.; Preusse, A. Cobalt Advanced Barrier Metallization: A Resistivity Composition Analysis. Microelectron. Eng. 2015, 137, 11–15. [Google Scholar] [CrossRef]
  82. Dulmaa, A.; Cougnon, F.G.; Dedoncker, R.; Depla, D. On the Grain Size-Thickness Correlation for Thin Films. Acta Mater. 2021, 212, 116896. [Google Scholar] [CrossRef]
  83. Ali, A.; Park, K.R.; Haq, M.A.; Sung, J.M.; Jeong, D.W.; Song, Y.; Kim, B.S. In-Situ Nitriding of CoTi Powders for TiN Shell Formation via Diffusion-Controlled Mechanism. J. Alloys Compd. 2025, 1036, 181886. [Google Scholar] [CrossRef]
  84. Ago, H.; Ito, Y.; Mizuta, N.; Yoshida, K.; Hu, B.; Orofeo, C.M.; Tsuji, M.; Ikeda, K.; Mizuno, S. Epitaxial Chemical Vapor Deposition Growth of Single-Layer Graphene over Cobalt Film Crystallized on Sapphire. ACS Nano 2010, 4, 7407–7414. [Google Scholar] [CrossRef]
  85. Choi, J.W.; Ham, D.; Han, S.; Noh, D.Y.; Kang, H.C. Nanoscale Soft Wetting Observed in Co/Sapphire During Pulsed Laser Irradiation. Nanomaterials 2021, 11, 268. [Google Scholar] [CrossRef]
  86. Wongpiya, R.; Ouyang, J.; Chung, C.J.; Duong, D.T.; Deal, M.; Nishi, Y.; Clemens, B. Structural and Electrical Characterization of CoTiN Metal Gates. J. Appl. Phys. 2015, 117, 075304. [Google Scholar] [CrossRef]
  87. Hosseini, M.; Koike, J. Amorphous CoTix as a Liner/Diffusion Barrier Material for Advanced Copper Metallization. J. Alloys Compd. 2017, 721, 134–142. [Google Scholar] [CrossRef]
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Figure 1. X-ray reflectivity curves from 50 nm thick Co/TiN multilayer films containing N = 1–10 Co layers. The dotted line is the result of curve fitting for N = 2. The schematics on the right illustrate the multilayer stack for N = 1 and 3.
Figure 1. X-ray reflectivity curves from 50 nm thick Co/TiN multilayer films containing N = 1–10 Co layers. The dotted line is the result of curve fitting for N = 2. The schematics on the right illustrate the multilayer stack for N = 1 and 3.
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Figure 2. Grazing incident X-ray diffraction patterns from 50 nm thick Co/TiN multilayer films with N = 1–10 Co layers. The inset shows the 0002 peak widths of 0.70° and 0.73° from the N = 1 and N = 10 samples, respectively.
Figure 2. Grazing incident X-ray diffraction patterns from 50 nm thick Co/TiN multilayer films with N = 1–10 Co layers. The inset shows the 0002 peak widths of 0.70° and 0.73° from the N = 1 and N = 10 samples, respectively.
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Figure 3. Resistivity ρ vs. individual Co layer thickness dCo in 50 nm thick Co/TiN multilayer films measured at 77 and 293 K. The solid lines are results from curve fitting using Equation (1).
Figure 3. Resistivity ρ vs. individual Co layer thickness dCo in 50 nm thick Co/TiN multilayer films measured at 77 and 293 K. The solid lines are results from curve fitting using Equation (1).
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Figure 4. XRD θ–2θ patterns from 75 nm thick Co/TiN bilayer and trilayer stacks deposited on Al2O3(0001) at 600 °C. The inset shows the ω rocking of the Co 0002 peak for TiN/Co/Al2O3(0001).
Figure 4. XRD θ–2θ patterns from 75 nm thick Co/TiN bilayer and trilayer stacks deposited on Al2O3(0001) at 600 °C. The inset shows the ω rocking of the Co 0002 peak for TiN/Co/Al2O3(0001).
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Table 1. Resistivity ρ of Ti/Co multilayers containing N Co layers.
Table 1. Resistivity ρ of Ti/Co multilayers containing N Co layers.
N ρ (µΩ-cm)
1Co/TiN/SiO214.4
51 nm1 nm
2(Co/TiN) × 2/SiO219.6
25.5 nm1 nm
3(Co/TiN) × 3/SiO225.5
17.0 nm1 nm
4(Co/TiN) × 4/SiO226.9
12.8 nm1 nm
7(Co/TiN) × 7/SiO230.9
7.3 nm1 nm
10(Co/TiN) × 10/SiO236.6
5.1 nm1 nm
Table 2. Sheet resistance Rs from Ti/Co layers deposited on Al2O3(0001).
Table 2. Sheet resistance Rs from Ti/Co layers deposited on Al2O3(0001).
Rs (Ω/sq)
TiN/Co/Al2O3(0001)4.7
45 nm30 nm
Co/TiN/Al2O3(0001)8.0
30 nm45 nm
TiN/Co/TiN/Al2O3(0001)18.1
22.5 nm30 nm22.5 nm
TiN/Al2O3(0001)23.8
45 nm
Co/Al2O3(0001)3.3
30 nm
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Shen, P.; Rahman, S.; Syracuse, D.M.; Gall, D. The Effect of Co/TiN Interfaces on Co Interconnect Resistivity. Surfaces 2025, 8, 89. https://doi.org/10.3390/surfaces8040089

AMA Style

Shen P, Rahman S, Syracuse DM, Gall D. The Effect of Co/TiN Interfaces on Co Interconnect Resistivity. Surfaces. 2025; 8(4):89. https://doi.org/10.3390/surfaces8040089

Chicago/Turabian Style

Shen, Poyen, Sanzida Rahman, Daniel M. Syracuse, and Daniel Gall. 2025. "The Effect of Co/TiN Interfaces on Co Interconnect Resistivity" Surfaces 8, no. 4: 89. https://doi.org/10.3390/surfaces8040089

APA Style

Shen, P., Rahman, S., Syracuse, D. M., & Gall, D. (2025). The Effect of Co/TiN Interfaces on Co Interconnect Resistivity. Surfaces, 8(4), 89. https://doi.org/10.3390/surfaces8040089

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