Interdiffusion reliability and resistivity scaling of intermetallic compounds as advanced interconnect materials

Abstract

Intermetallic compounds have been proposed as potential interconnect materials for advanced semiconductor devices. This study reports the interdiffusion reliability and resistivity scaling of three low-resistivity intermetallic compounds (Cu2Mg, CuAl2, and NiAl) formed on thermally grown SiO2. Experimental observations and thermodynamic calculations indicated good interdiffusion reliability with CuAl2 and NiAl but not with Cu2Mg. This was due to slow reaction between Al and SiO2 in conjunction with strong chemical bonds of Cu–Al and Ni–Al. As for resistivity scaling, all three intermetallic compounds showed better resistivity scalability than Cu. Resistivity of the thin films was measured and characteristic parameters were obtained by curve fitting using a classical scattering model. First-principles calculations were carried out to determine the electron mean free path and bulk resistivity in order to explain the resistivity scaling. The results showed the importance of having optimum microstructure features, i.e., low-defect-density surface, interface, and grain boundaries in addition to optimum material properties, i.e., a short mean free path and low bulk resistivity. CuAl2 and NiAl appeared to satisfy the interdiffusion and resistivity conditions and be promising candidates to replace Cu interconnections for future devices.

Anisotropic Resistivity Size Effect in Epitaxial Mo(001) and Mo(011) Layers

“…The corresponding effective mean free paths at 77 K, = 143 ± 7 nm and = 86 ± 3 nm, are nearly an order of magnitude larger than at 295 K. This is due to the reduced electron–phonon scattering at low temperatures which reduces the resistivity but increases the mean free path, leading to an expected constant ρ o λ product. Our measurements yield ρ o λ * = (7.7 ± 0.2) and (6.2 ± 0.2) × 10 −16 Ωm 2 for Mo(001) and Mo(011) layers at room temperature and ρ o λ * = (6.7 ± 0.3) and (4.0 ± 0.1) × 10 −16 Ωm 2 at 77 K; that is, the measured ρ o λ product is nearly temperature-independent, with 13% and 35% smaller values at 77 K than at 295 K. These deviations are small in comparison to the order-of-magnitude changes in ρ o and λ and may be attributed to (a) a thickness-dependent electron–phonon coupling factor [ 63 ], (b) a wave vector-dependent electron–phonon scattering cross-section [ 64 , 65 ], and/or (c) the breakdown of the FS model in the limit of small thickness and low temperature [ 66 ]. We reiterate that this analysis does not explicitly account for electron scattering at small-angle grain boundaries, which is justified by the measured rocking curve widths ranging from 0.1 to 2.6° for Mo(001) and 0.03 to 0.14° for Mo(011), as shown in Figures S3 and S4 .…”

Materials Quest for Advanced Interconnect Metallization in Integrated Circuits

“…This article provides a multifaceted and comprehensive review and summary of the challenges that BEOL Reproduced with permission. [284] Copyright 2021, American Institute of Physics publishing. b) Abnormal resistivity drop in Ag-Cu alloys of specific composition.…”

“…However, the difference in the oxide growth rates, caused by the diffusivity difference between cations and anions inside the two materials, leads to the formation of a thinner Al 2 O 3 , which has a slower oxide growth rate. [284] NiAl and CuAl 2 have been studied beyond 3-nm node metallization materials. [298] The strong chemical bonding (or enormous cohesive energy) between Cu-Al or Ni-Al leads to a slow reaction between SiO 2 and Al.…”

“…Figure 16. a) Calculated Fermi surfaces of the intermetallic compounds and Cu. The surface colors represent the anisotropic k-dependent EMFP.Reproduced with permission [284]. Copyright 2021, American Institute of Physics publishing.…”

First principles-based screening method for resistivity scaling of anisotropic metals

“…As more exotic metal materials and compounds with complicated band structures are being considered for nanoscale interconnect applications [14,15,[27][28][29][30][31][32], their resistivity (scaling) can be expected to depend strongly on temperature and, for polycrystalline textured or single crystal interconnects, the orientation of the interconnect line with respect to the lattice orientation. Therefore, the usefulness of the ρλ product as a figure-of-merit can be questioned, as it does not capture the anisotropy of the charge carriers in the conduction band(s).…”