arXiv subjects

Kiroubanand Sankaran

Publications and source records attributed to Kiroubanand Sankaran.

8 recordsLinked to original sources

arXiv2025

Exploring binary intermetallics for advanced interconnect applications using ab initio simulations

The challenge of increasing copper (Cu) resistivity with diminishing Cu interconnect dimensions in complementary metal-oxide-semiconductor (CMOS) transistors, along with the imperative for efficient electron transport paths to fulfill scaling requirements in interconnects is significant. First-principles electronic structures calculations based on density functional theory have been performed to evaluate the potential scalability of some Cu, Al, Ru and Mo based binary alloys to replace Cu. We evaluate the expected sensitivity of the resistivity of these binary alloys to reduced line dimensions with a figure of merit that is based on generalized finite-temperature transport tensors. These transport tensors allow for a straightforward comparison between highly anisotropic intermetallics with given transport directions and Cu, and are evaluated together with their resistance to electromigration. Based on the figure-of-merit analysis, we identify several aluminides that show potential to outperform Cu at reduced interconnect dimensions in terms of their electronic transport and reliability properties.

cond-mat.mtrl-sci↗

arXiv2024

Selecting Alternative Metals for Advanced Interconnects

Interconnect resistance and reliability have emerged as critical factors limiting the performance of advanced CMOS circuits. With the slowdown of transistor scaling, interconnect scaling has become the primary driver of continued circuit miniaturization. The associated scaling challenges for interconnects are expected to further intensify in future CMOS technology nodes. As interconnect dimensions approach the 10 nm scale, the limitations of conventional Cu dual-damascene metallization are becoming increasingly difficult to overcome, spurring over a decade of focused research into alternative metallization schemes. The selection of alternative metals is a highly complex process, requiring consideration of multiple criteria, including resistivity at reduced dimensions, reliability, thermal performance, process technology readiness, and sustainability. This tutorial introduces the fundamental criteria for benchmarking and selecting alternative metals and reviews the current state of the art in this field. It covers materials nearing adoption in high-volume manufacturing, materials currently under active research, and potential future directions for fundamental study. While early alternatives to Cu metallization have recently been introduced in commercial CMOS devices, the search for the optimal interconnect metal remains ongoing.

physics.app-ph↗

arXiv2024

Cu$_x$Al$_{1-x}$ films as Alternatives to Copper for Advanced Interconnect Metallization

Cu$_x$Al$_{1-x}$ thin films with $0.2 \le x \le 0.7$ have been studied as potential alternatives for the metallization of advanced interconnects. First-principles simulations were used to obtain the Cu$_x$Al$_{1-x}$ electronic structure and cohesive energy to benchmark different intermetallics and their prospects for interconnect metallization. Next, thin Cu$_x$Al$_{1-x}$ films were deposited by PVD with thicknesses in the range between 3 and 28 nm. The lowest resistivities of 9.5 $μΩ$cm were obtained for 28 nm thick stochiometric CuAl and CuAl$_2$ after 400$^\circ$C post-deposition annealing. Based on the experimental results, we discuss the main challenges for the studied aluminides from an interconnect point of view, namely the control of the film stoichiometry, the phase separation observed for off-stoichiometric CuAl and CuAl$_2$, as well as the presence of a nonstoichiometric surface oxide.

cond-mat.mtrl-sci↗

arXiv2024

Al$_3$Sc thin films for advanced interconnect applications

Al$_x$Sc$_{1-x}$ thin films have been studied with compositions around Al$_3$Sc ($x$ = 0.75) for potential interconnect metallization applications. As-deposited 25 nm thick films were x-ray amorphous but crystallized at 190°C, followed by recrystallization at 440°C. After annealing at 500°C, 24 nm thick stoichiometric Al$_3$Sc showed a resistivity of 12.6 $μΩ$cm, limited by a combination of grain boundary and point defect (disorder) scattering. Together with ab initio calculations that found a mean free path of the charge carriers of 7 nm for stoichiometric Al$_3$Sc, these results indicate that Al$_3$Sc bears promise for future interconnect metallization schemes. Challenges remain in minimizing the formation of secondary phases as well as in the control of the non-stoichiometric surface oxidation and interfacial reactions with underlying dielectrics.

cond-mat.mtrl-sci↗

arXiv2022

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

The resistivity scaling of metals is a crucial limiting factor for further downscaling of interconnects in nanoelectronic devices that affects signal delay, heat production, and energy consumption. Here, we generalize a commonly considered figure of merit for selecting promising candidate metals with highly anisotropic Fermi surfaces in terms of their electronic transport properties at the nanoscale. For this, we introduce a finite-temperature transport tensor, based on band structures obtained from first principles. This transport tensor allows for a straightforward comparison between highly anisotropic metals in nanostructures with different lattice orientations and arbitrary transport directions. By evaluating the temperature dependence of the tensor components, we also assess the validity of a Fermi surface-based evaluation of the transport properties at zero temperature, rather than considering standard operating temperature conditions.

cond-mat.mtrl-sci↗

arXiv2021

Ab initio screening of metallic MAX ceramics for advanced interconnect applications

The potential of a wide range of layered ternary carbide and nitride MAX phases as conductors in interconnect metal lines in advanced CMOS technology nodes has been evaluated using automated first principles simulations based on density functional theory. The resistivity scaling potential of these compounds, i.e. the sensitivity of their resistivity to reduced line dimensions, has been benchmarked against Cu and Ru by evaluating their transport properties within a semiclassical transport formalism. In addition, their cohesive energy has been assessed as a proxy for the resistance against electromigration and the need for diffusion barriers. The results indicate that numerous MAX phases show promise as conductors in interconnects of advanced CMOS technology nodes.

cond-mat.mtrl-sci↗

arXiv2018

Resistivity scaling model for metals with conduction band anisotropy

It is generally understood that the resistivity of metal thin films scales with film thickness mainly due to grain boundary and boundary surface scattering. Recently, several experiments and ab initio simulations have demonstrated the impact of crystal orientation on resistivity scaling. The crystal orientation cannot be captured by the commonly used resistivity scaling models and a qualitative understanding of its impact is currently lacking. In this work, we derive a resistivity scaling model that captures grain boundary and boundary surface scattering as well as the anisotropy of the band structure. The model is applied to Cu and Ru thin films, whose conduction bands are (quasi-)isotropic and anisotropic respectively. After calibrating the anisotropy with ab initio simulations, the resistivity scaling models are compared to experimental resistivity data and a renormalization of the fitted grain boundary reflection coefficient can be identified for textured Ru.

cond-mat.mes-hall↗

arXiv2017

Thickness dependence of the resistivity of Platinum group metal thin films

We report on the thin film resistivity of several platinum-group metals (Ru, Pd, Ir, Pt). Platinum-group thin films show comparable or lower resistivities than Cu for film thicknesses below about 5\,nm due to a weaker thickness dependence of the resistivity. Based on experimentally determined mean linear distances between grain boundaries as well as ab initio calculations of the electron mean free path, the data for Ru, Ir, and Cu were modeled within the semiclassical Mayadas--Shatzkes model [Phys. Rev. B 1, 1382 (1970)] to assess the combined contributions of surface and grain boundary scattering to the resistivity. For Ru, the modeling results indicated that surface scattering was strongly dependent on the surrounding material with nearly specular scattering at interfaces with SiO2 or air but with diffuse scattering at interfaces with TaN. The dependence of the thin film resistivity on the mean free path is also discussed within the Mayadas--Shatzkes model in consideration of the experimental findings.

cond-mat.mtrl-sci↗