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.Comment: 28 pages, 9 figure

Low-lying resonances in electron-argon scattering: Measurements at 5-meV resolution and comparison with theory

Combining a laser photoelectron source with a triply differentially pumped supersonic beam target and several electron multipliers for simultaneous detection of electrons elastically scattered into the angles 22.5°, 45°, 90°, 112.5°, and 135° and of metastable atoms due to inelastic scattering, we have carried out an improved study of electron-argon scattering over the energy range 11.0–13.7  eV with experimental energy widths around 5  meV. In addition, the Fribourg scattering apparatus has been used for careful remeasurements of the differential cross section and the resonance structure in the energy range of the two lowest anion resonances over the full angular range at a resolution of about 13  meV. Accurate values for the energies, the widths (2.3±0.2  meV), and the fine-structure separation (172.7±0.2  meV) of the low-lying Ar⁻(3p⁵4s²  ²P3/2,1/2) Feshbach resonances have been determined from the two experiments by detailed partial-wave analyses of the resonance profiles using several sets of energy-dependent background phase shifts; these include an accurate set obtained with a coupled-cluster calculation involving a soft box potential. Moreover, the excitation function for the production of metastable Ar*(3p⁵4s  ³P2,0) atoms has been measured from threshold to 13.7  eV. From a fit to its onset, the absolute electron energy scale is established to within ±0.3  meV; in addition, the energies and widths of some higher-lying resonances (12.9–13.5  eV) have been determined and are compared with the results of earlier experiments and of a recent B-spline R-matrix calculation. In connection with calibration experiments involving He atoms, we carried out an improved measurement of the He⁻(1s2s²  ²S1/2) resonance and deduced a natural width of 10.9±0.3  meV

Efficient long-term laser excitation of a collimated beam of potassium atoms on the D2 line

With the aim to provide a reliable scheme for efficient laser excitation of the potassium D2 line over long periods of time, we have developed a robust stabilization of a single mode laser of frequency $f_{0}=(f_{12}+f_{23})/2$ onto a crossover peak in the saturation spectrum of the 39K(D2) line (4s 2S$_{1/2}, F \to 4p~^{2}$P$_{3/2}, F^{\prime} )$. The two hyperfine transitions $F=1\to F^{\prime} =2$ (frequency $f_{12})$ and $F=2\to F^{\prime} =3$ (frequency $f_{23})$ are simultaneously excited by the first order sidebands $f_{\pm }=f_{0}\pm f_{EOM}$ of the laser beam (f0), generated by its electro-optical modulation at the frequency $f_{EOM}= (f_{12}-f_{23})/2$. In this way stable excitation of the two transitions on their proper frequencies is achieved and hyperfine pumping compensated

Constant voltage electromigration for advanced BEOL copper interconnects

© 2015 IEEE. For characterizing the electromigration (EM) reliability of advanced interconnects, we propose a constant voltage approach (CV-EM) as an alternative method to traditional constant current tests (CI-EM). As extremely scaled interconnects require very thin barriers, their current shunting capabilities will be reduced. When close to full void formation, we show that this lack of current shunting capability leads to unrealistically high stress conditions during CI-EM while more realistic stresses are induced during CV-EM. We also demonstrate that the void detection capability is highly improved after CV-EM. We use simulations and experiments to compare CV-EM with CI-EM where we obtain a) slightly longer lifetimes for CV-EM, b) the same failure mechanisms and c) similar Ea and n values.status: publishe

A novel electron scattering apparatus combining a laser photoelectron source and a triply differentially pumped supersonic beam target: characterization and results for the He

A novel electron scattering apparatus for high resolution studies of angle-differential elastic and inelastic electron scattering from atoms and molecules in the gas phase is described and its performance characterized. It combines a laser photoelectron source, a triply differentially pumped collimated supersonic beam target (half angle 0.015 rad, background to beam density ratio <0.01), and several electron multipliers for simultaneous detection of elastically scattered electrons and metastable atoms (or molecules) due to inelastic scattering. In detailed test measurements of the yield for the production of metastable He*(23S1) atoms around its threshold, the dependence of the overall energy width on various experimental parameters has been investigated. So far a resolution down to 7 meV (FWHM) has been obtained. Under such conditions we have investigated the profile of the He- $(1s\ 2s^2\ ^2{\rm S}_{1/2})$ resonance at the scattering angles 22°, 45°, and 90°. From a consistent fit of the measured profiles by resonant scattering theory we determine a new value for the resonance energy ($E_r = 19.365(1)$ eV) and an accurate resonance width ($\Gamma = 11.2(5)$ meV). These results are consistent with the previously recommended values

In-situ scanning electron microscope observation of electromigration-induced void growth in 30 nm 1/2 pitch Cu interconnect structures

In-situ electromigration tests have been performed inside a scanning electron microscope on 30 nm wide single damascene interconnects without vias, where a good resolution was obtained and drift velocities during void growth could be measured at 300 C. These tests showed direct evidence that the cathode end of the line, where a polycrystalline grain cluster encounters a bigger grain, can act as a flux divergent point of Cu diffusion. Moreover, it was found that a thicker barrier suppresses barrier/interface diffusivity of Cu atoms, thereby slowing down electromigration-induced void growth. It was also demonstrated that Cobalt based metal caps are beneficial to electromigration for advanced interconnects where thinner barriers are required.status: publishe