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Resistance capacitance time delay in Cu interconnects is becoming a significant factor requiring further performance improvements in future nanoelectronic devices. Choice of alternate interconnect materials, for example, refractory metals, and subsequent integration with underlying barrier and liner layers are extremely challenging for the sub-10 nm nodes. The development of conformal deposition processes for alternate interconnects, liner, and barrier materials are crucial in order for implementation of a possible replacement for Cu interconnects for narrow line widths. In this study, the authors report on ultrathin (~3 nm) chemical vapor deposition (CVD) grown ruthenium films on 0.5 and 1 nm thick metal nitride (TiN, TaN) barrier layers deposited via atomic layer deposition (ALD). Using scanning electron microscopy, the authors determined the effect of the underlying barrier layer on the coverage of the ruthenium overlayer. The authors utilized synchrotron x-ray diffraction with in situ rapid thermal annealing to investigate the thermal stability of the barrier layers and determine the effective activation energies of barrier failure leading to ruthenium monosilicide formation. For Ru films deposited directly on Si and on 0.5 nm MN (M=Ti, Ta) covered Si substrates, silicide formation proceeds via a two-step crystallization process involving lateral nucleation above ~440 °C followed by thickening of the ruthenium monosilicide layer above ~520 °C. This silicidation temperature of ~440 °C could be potentially problematic in back-end-of-the-line (BEOL) processing since it is close to the typical thermal budget used. However ~1nm thick ALD MN (M=Ti, Ta) was found to be adequate to block silicide formation up to ~580 and ~620 °C for TiN and TaN, respectively, and also aided in superior coverage of the CVD ruthenium overlayer (>90%). The results reported here might be useful to ascertain annealing temperature and time for BEOL process and integration optimization without reaching a state where ruthenium silicides start forming. [ABSTRACT FROM AUTHOR]

An understanding of the aging and oxidation of the (0001) surface of Bi2Se3 is critical to a comprehensive physical picture of its topologically protected surface states. Here, the authors contribute new experimental observations about the aging and oxidation process. The authors find that surface aging in ambient conditions occurs in two major steps. Within 2 h of exfoliation, a series of ~3.2A ° high islands are observed by atomic force microscopy over approximately 10% of the surface. Subsequently, patch growth stops, and oxidation begins after the 2 h and continues until one quintuple layer has been oxidized. X-ray photoelectron spectroscopy shows no sign of oxidation before ~120 min of exposure to air, and the oxygen 1 s peak, as well as oxidized Se 3d and Bi 4d peaks, are clearly present after ~190 min of ambient exposure. Variable angle spectroscopic ellipsometry indicates that the oxidation of a full quintuple layer occurs on the time scale of days. These results are in good agreement with the time dependent changes observed in the surface crystal structure by second harmonic generation. In addition to providing the ability to nondestructively measure oxide on the surface of Bi2Se3 crystals, ellipsometry can be used to identify the thickness of Bi2Se3 flakes. With these methods, the authors have constructed a consistent, experimentally based model of aging process at the surface of Bi2Se3. [ABSTRACT FROM AUTHOR]

This paper will take a 'From the Lab to the FAB' approach for discussing the measurements and applications of nanoscale characterization and metrology. The nanoscale dimensions of features found in semiconductor materials and devices provide many challenges for characterization of physical properties as well as measurements for process control. The use of multiple measurement methods results in a more complete determination of the properties so that structure-function relationships can be elucidated. Here, the authors use pseudomorphic Si1-xGex on Si(001), nanoscale films of Ni, and nanoscale Hf oxide films to illustrate this principle. [ABSTRACT FROM AUTHOR]

With the replacement of SiO2 by high-k Hf-based dielectrics in complementary metal-oxide-semiconductor technology, the measurement of the high-k oxide bandgap is a high priority. Spectroscopic ellipsometry (SE) is one of the methods to measure the bandgap, but it is prone to ambiguity because there are several methods that can be used to extract a bandgap value. This paper describes seven methods of determining the bandgap of HfO2 using SE. Five of these methods are based on direct data inversion (point-by-point fitting) combined with a linear extrapolation, while two of the methods involve a dispersion model-based bandgap extraction. The authors performed all of these methods on a single set of data from a 40 Å HfO2 film, as well as on data from 20 and 30 Å HfO2 films. It was observed that the bandgap values for the 40 Å film vary by 0.69 eV. In comparing these methods, the reasons for this variation are discussed. The authors also observed that, for each of these methods, there was a trend of increasing bandgap with decreasing film thickness, which is attributed to quantum confinement. Finally, the authors observed a greater variation in bandgap values among the methods for the 40 Å films than among the methods for the 30 and 20 Å films. This is attributed to the larger tail in the extinction coefficient k curve for the 40 Å film. [ABSTRACT FROM AUTHOR]

In order to miniaturize metal oxide semiconductor field effect transistors even further and improve their performance, channel lengths and gate dielectric thicknesses must be decreased. Traditionally deployed SiO2 dielectrics face the difficulty of excessive leakage current and must be replaced by alternative (high-k) materials with larger dielectric permitivitties and smaller equivalent oxide thicknesses. A current focus of the industry is studying thin films of HfO2 because they are a main candidate for the next generation of gate dielectrics. Measuring the depth profiles of the constituents of these layered systems is instructive in that it provides information about the thicknesses of the layers and the degree of intermixing between them. Here we demonstrate the use of a novel characterization technique, grazing incidence extreme ultraviolet reflectometry (GIXUVR), which utilizes short wavelength radiation from non-synchrotron sources to measure the depth profile of such thin-film structures. Depth profiles of samples from the same wafers were also measured using angle resolved x-ray photoelectron spectroscopy, medium energy ion scattering, and synchrotron GIXUVR. These measurements show the compatibility and complementarity of the results. The benefits of GIXUVR are the short measuring time (on the order of milliseconds to seconds), as well as high thickness, density, and material sensitivity due to a very efficient interaction of extreme ultraviolet light with matter. [ABSTRACT FROM AUTHOR]