Valery M. Dubin

High-frequency electrical properties of individual and bundled carbon nanotubes

Bundles of single wall carbon nanotubes have been proposed as an interconnect that could potentially replace copper in state-of-the-art ultralarge-scale-integrated circuits if theoretically predicted inductance, resistance, and capacitance scale with the number of carbon nanotubes within the bundle. The authors report direct measurement of the kinetic inductance of individual single wall carbon nanotubes and measurement of the high-frequency impedance of bundles showing that the bundle inductance scales with the number of individual carbon nanotubes.

Effects of local Joule heating on the reduction of contact resistance between carbon nanotubes and metal electrodes

We report here a practical application of known local Joule heating processes to reduce the contact resistance between carbon nanotubes and metallic electrical contacts. The results presented in this study were obtained from a series of systematic Joule heating experiments on 289 single-walled carbon nanotubes (SWCNTs) and 107 multiwalled carbon nanotubes (MWCNTs). Our experimental results demonstrate that the Joule heating process decreases the contact resistances of SWCNTs and MWCNTs to 70.4% and 77.9% of their initial resistances, respectively. The I-V characteristics of metallic nanotubes become more linear and eventually become independent of the gate voltages (Vgs). For semiconducting nanotubes, the contact resistance has a similar decreasing tendency but the dependency of source-drain current (Ids) on Vgs does not change with the Joule heating process. This suggests that the reduction of the contact resistance and the decrease of the transport potential barrier are largely attributed to the thermal...

Influence of phonon, geometry, impurity, and grain size on Copper line resistivity

The authors report on the resistivity of submicron copper lines ranging from 75to500nm linewidths as a function of temperature in the 10Kto380K interval. Their estimate of the contributions to electron scattering at 20K for the narrowest line (75nm linewidth) is 29% from copper surfaces, 25% from grain boundaries, and 30% from impurities, with the bulk resistivity making up the remaining 16%. It should be noted that at 300K, the contribution of electron-phonon scattering is about 60% illustrating the benefit of studying different scattering mechanisms at cryogenic temperatures.

Electroless deposition of novel Ag-W thin films

The seedless electroless deposition of silver-tungsten (Ag-W) thin films on silicon dioxide substrate was performed using wet palladium activation from ammonia-acetate and benzoate solutions. Introducing tungsten in the plating bath catalyzes the deposition for benzoic acid solution and decreases the deposition rate for ammonia-acetate solution. The tungsten content in the deposit was 0-1.0 at%, mainly in WOx form. It was found that the electrical, optical, and mechanical properties of the Ag-W films depends on the W content in the deposit. The optimal Ag-W thin films that were deposited from either the ammonia-acetate or benzoate bath demonstrate good adhesion to the substrate, high brightness, and do not corrode at temperatures up to 350 °C in air. Sub-100 nm thick Ag-W deposits have demonstrated resistivity of about 4 µΩ cm after vacuum annealing at 350 °C for 1 h. Finally, we present the film microstructure characterization and discuss the possibility of using Ag-W thin films for advanced microelectronics metallization.

Material properties of very thin electroless silver–tungsten films

a Abstract Thin electroless silver-tungsten (Ag-W) films were deposited on silicon dioxide substrate from the benzoate solution. The layer composition and microstructure as well as the film deposition rate were studied as a function of the bath formulation. The tungsten concentration in the deposit was up to ;2.1 atm% with corresponding oxygen concentration approximately 4 atm%. It was found that electrical, optical, and mechanical properties of Ag-W films depend on the W content in the deposit. Ag-W films of sub 120 nm thickness with ;0.6 atm% tungsten and 1.8 atm% oxygen have demonstrated the resistivity of ;4 mVOcm. Finally, the possibility to use the Ag-W thin films for microelectronic metallization is discussed. 2003 Elsevier Science B.V. All rights reserved.

Advanced Electrochemical Processes for Sub-50 nm On-chip Metallization

Electrodeposition of copper in the presence of additives (e.g., a suppressor, an accelerator, and a leveler) is being used for the fabrication of on-chip copper interconnects. For current generation interconnects, the via and trench aspect ratios required to be filled using electroplating are accessible using conventional additives chemistries and plating conditions. For future generation sub-50 nm technology nodes, however, the via aspect ratios will be significantly higher (>10:1 in some cases due to the overhang caused by the PVD copper seed). For filling such aggressive geometries, conventional plating chemistries and approaches have, as of yet, shown little promise. In the present talk, several alternatives for addressing this issue will be outlined. These will include: (i) Development of advanced electroplating chemistries, (ii) Direct copper deposition on new liner metals (such as ruthenium), and (iii) Electroless copper plating. Decreasing feature sizes and scaling causes increase in the current density through Cu interconnects, requiring enhanced Cu electromigration resistance. Electroless Co caps will be discussed as a potential solution for improving Cu electromigration performance. Electroplating on Cu seed. Techniques for optimization of additives chemistries for sub-50 nm gap-fill will be discussed. Additives screening is performed using two techniques: (i) Linear sweep voltammetry on rotating disc electrode to characterize the additives suppression and/or interactions characteristics, and (ii) Gap-fill experiments on a patterned wafer. Correlating LSV data with SEM cross-sections provide valuable information regarding the additives chemistry, and its effect on the gap-fill. Electroplating on Ruthenium. Direct plating on new liner materials such as ruthenium is attractive since it provides reduced via/trench aspect ratios without significant seed overhang, thereby facilitating ‘defectfree’ gap-fill. In the present talk, the effects of current density, bath composition, and pretreatment on the nucleation site density of copper on ruthenium will be addressed. The influence of the terminal effect (caused by the resistive ruthenium seed) on the location-dependent nucleation density will be discussed. Electroless Cu deposition. Electroless copper provides two major advantages: (i) Improved wafer-scale uniformity (no resistive seed effects), and (ii) Extendibility of gap fill down to sub-50nm feature sizes. E-test data show comparable resistance of electroless Cu films to electroplated Cu, in addition to good gap fill on 6:1 aspect ratio features. Cu interconnects reliability. We have successfully demonstrated electroless deposition of cobalt on Cu lines with good uniformity on patterned wafers (Figure 3). The Co caps showed low leakage, improved electromigration resistance without any appreciable penalty in the Cu line resistance.