An official website of the United States government
The effect of atomic-scale surface roughness on electron transport is investigated using 6.5 nm-thick epitaxial Ru(0001) films, a promising metal for next-generation interconnects. Sputter deposition at 350 °C followed by stepwise vacuum annealing to 950 °C yields atomically smooth Ru(0001)/Al2O3(0001) films which are subsequently roughened by depositing ΘRu = 0.5, 1.0, and 2.0 monolayers (MLs) of additional Ru at room temperature. In situ four-point probe measurements show a resistivity ρ = 9.08–9.44 μΩ cm for 6.5 nm-thick films and a 4%–6% increase in sheet resistance upon roughening, attributed to electron scattering at atomic-height surface steps. The measured resistivity penalty Δρr = 0.41 μΩ cm caused by a ΘRu = 0.5 ML coverage suggests formation of 2D islands with an average step-edge separation ls = 2.7 nm, as quantified by a step-edge scattering model. This is in good agreement with ls = 3.6 ± 0.3 nm estimated from atomic force micrographs. Increasing ΘRu further to 1.0 ML causes a slight decrease in roughness and Δρr, indicating coalescence of 2D islands which increases ls to 3.0 nm. However, a ΘRu = 2.0 ML coverage causes 3D mound formation, an increased resistivity penalty Δρr = 0.49 μΩ cm, and a reduced ls = 2.3 nm, consistent with a significant damping of Kiessig fringes measured by x-ray reflectivity. These results demonstrate that atomic-scale topographical variations impose significant resistivity penalties for deeply scaled metallic interconnects.
more »
« less
This content will become publicly available on March 1, 2027
Sputter deposition of epitaxial manganese boride Mn2B(100) films
Mn2B thin film deposition is explored because of the predicted promise of Mn2B as directional conductor for interconnects in integrated circuits. MnxB thin films, 40–80 nm thick, are deposited on Al2O3(0001), Al2O3(112¯0), and Al2O3(11¯02) substrates by combined d.c. and r.f. cosputtering from Mn and B targets, respectively. Energy dispersive spectroscopy analyses indicate that the Mn content decreases with increasing deposition temperature Ts = 600–800 °C, which is attributed to Mn evaporation from the substrate and growing film. Raising Ts from 600–700 °C also results in an increase in crystalline quality and surface roughness, while a further increase to Ts = 800 °C causes dewetting that results in discontinuous films. MnxB films on Al2O3(0001) and Al2O3(112¯0) form polycrystalline microstructures with random grain orientations, while Al2O3(11¯02) substrates facilitate epitaxial Mn2B(100) growth with Mn2B(100) || Al2O3(11¯02) and Mn2B[010] || Al2O3[1¯101], as determined by x-ray diffraction methods. However, the epitaxial Mn2B(100) matrix contains MnB or Mn impurity phase grains for films with B-rich or Mn-rich compositions, respectively. The room temperature resistivity ρ of polycrystalline MnxB films decreases from 153 to 70 μΩ cm with increasing x = 1.3–5.6 and is further reduced for epitaxial Mn2B(100)/Al2O3(11¯02) films with measured ρ = 44 and 107 μΩ cm for x = 2.9 and 1.7, respectively. These values are affected by electron scattering at residual impurity grains such that the Mn2B bulk resistivity along the high-conductivity [001]-direction is likely considerably smaller and may be competitive for the envisioned interconnect application.
more »
« less
- Award ID(s):
- 2328906
- PAR ID:
- 10698656
- Publisher / Repository:
- AVS
- Date Published:
- Journal Name:
- Journal of Vacuum Science & Technology A
- Volume:
- 44
- Issue:
- 2
- ISSN:
- 0734-2101
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
In this work, we demonstrate the growth and phase stabilization of ultrawide bandgap polycrystalline rutile germanium dioxide (GeO2) thin films. GeO2 thin films were deposited using RF magnetron sputtering on r-plane sapphire (Al2O3) substrates. As-deposited films were x-ray amorphous. Postdeposition annealing was performed at temperatures between 650 and 950 °C in an oxygen or nitrogen ambient. Annealing at temperatures from 750 to 950 °C resulted in mixed-phase polycrystalline films containing tetragonal (rutile) GeO2, hexagonal (α-quartz) GeO2, and/or cubic (diamond) germanium (Ge). When nitrogen was used as the anneal ambient, mixed GeO2 phases were observed. In contrast, annealing in oxygen promoted stabilization of the r-GeO2 phase. Grazing angle x-ray diffraction showed a preferred orientation of (220) r-GeO2 for all crystallized films. The combination of O2 annealing and O2 flux during growth resulted in r-GeO2 films with highly preferential alignment. Using electron microscopy, we observed an interfacial layer of hexagonal-oriented GeO2 with epitaxial alignment to the (11¯02) Al2O3 substrate, which may help stabilize the top polycrystalline r-GeO2 film.more » « less
-
GeSn films were simultaneously deposited on Si (100), Si (111), c-plane sapphire (Al2O3), and fused silica substrates to investigate the impact of the substrate on the resulting GeSn film. The electronic, structural, and optical properties of these films were characterized by temperature-dependent Hall-effect measurements, x-ray diffractometry, secondary ion mass spectrometry, and variable angle spectroscopic ellipsometry. All films were polycrystalline with varying degrees of texturing. The film on Si (100) contained only GeSn (100) grains, 40.4 nm in diameter. The film deposited on Si (111) contained primarily GeSn (111) grains, 36.4 nm in diameter. Both films deposited on silicon substrates were fully relaxed. The layer deposited on Al2O3 contained primarily GeSn (111) grains, 41.3 nm in diameter. The film deposited on fused silica was not textured, and the average grain size was 35.0 nm. All films contained ∼5.6 at. % Sn throughout the layer, except for the film deposited on Al2O3, which contained 7.5% Sn. The films deposited on Si (111), Al2O3, and fused silica exhibit p-type conduction over the entire temperature range, 10–325 K, while the layer deposited on the Si (100) substrate shows a mixed conduction transition from p-type at low temperature to n-type above 220 K. From ∼175 to 260 K, both holes and electrons contribute to conduction. Texturing of the GeSn film on Si (100) was the only characteristic that set this film apart from the other three films, suggesting that something related to GeSn (100) crystal orientation causes this transition from p- to n-type conduction.more » « less
-
Electron transport measurements on 60-nm-thick multilayers containing N = 2–58 individual Ru and Co layers are employed to quantify the specific resistance of Ru/Co interfaces. Sputter deposition on Al2O3(0001) at Ts = 400 °C leads to a 0001 preferred orientation with x-ray diffraction (XRD) Ru and Co 0002 peaks that shift closer to each other with increasing N, suggesting interfacial intermixing. The intermixing is quantified by x-ray reflectivity (XRR) and confirmed by an XRD Ru/Co alloy peak that develops during in situ synchrotron annealing as well as for deposition at a higher Ts = 600 °C. The room-temperature resistivity increases from 15.0 to 47.5 μΩ cm with decreasing superlattice period Λ = 60–2 nm. This is attributed to increasing electron scattering at the intermixed metal interfaces. The transport data are well described by a parallel conductor model that treats metal layers and the intermixed alloy as parallel resistors, where the resistivity of the intermixed alloy of 60.4 μΩ cm is determined from a co-deposited Ru/Co sample. Data fitting provides values for the effective thickness of the intermixed interface of 16.8 nm, in good agreement with the XRR value, yielding a Ru/Co contact resistance of 8.5 × 10−15 Ω m2 for interfaces deposited at 400 °C. The overall results show that the Ru/Co contact resistance is dominated by a high-resistivity interfacial alloy and, therefore, is a strong function of the deposition process, particularly the processing temperature.more » « less
-
Ru(0001) and Co(0001) films with thickness d ranging from 5 to 300 nm are sputter deposited onto Al2O3(0001) substrates in order to quantify and compare the resistivity size effect. Both metals form epitaxial single crystal layers with their basal planes parallel to the substrate surface and exhibit a root-mean-square roughness < 0.4 nm for Ru and < 0.9 nm for Co. Transport measurements on these layers have negligible resistance contributions from roughness and grain boundary scattering which allows direct quantification of electron surface scattering. The measured resistivity ρ vs d is well described by the classical Fuchs-Sondheimer model, indicating a mean free path for transport within the basal plane of λ = 6.7 ± 0.3 nm for Ru and λ = 19.5 ± 1.0 nm for Co. Bulk Ru is 36% more resistive than Co; in contrast, Ru(0001) layers with d ≤ 25 nm are more conductive than Co(0001) layers, which is attributed to the shorter λ for Ru. The determined λ-values are utilized in combination with the Fuchs-Sondheimer and Mayadas-Shatzkes models to predict and compare the resistance of polycrystalline interconnect lines, assuming a grain boundary reflection coefficient R = 0.4 and accounting for the thinner barrier/adhesion layers available to Ru and Co metallizations. This results in predicted 10 nm half-pitch line resistances for Ru, Co, and Cu of 1.0, 2.2, and 2.1 kΩ/µm, respectively.more » « less
