Phosphorous doped Ru film for advanced Cu diffusion barriers

Copper diffusion barrier properties of phosphorous doped Ru film are studied. Phosphorous out-diffusion to Ru from underneath phosphosilicate glass (PSG) layer results in P doped Ru film. The doped Ru film improves copper barrier properties and has excellent thermal stability. XRD graph indicates that there is no copper silicide and ruthenium silicide formations after annealing at 550 °C for 30 min in vacuum. This result is consistant with AES depth profiles which show no Cu, Ru, O and Si inter-diffusion. The phosphorous doped Ru barrier also blocks oxygen's diffusion to copper from the PSG layer. The phosphorous doped Ru film could be an alternative Cu diffusion barrier for advanced Cu interconnects.     

Effect of Ag-alloying addition on the stress-temperature behavior of electroplated copper thin films

The effect of Ag-alloying on the microstructural and thermo-mechanical properties of electrochemically deposited Cu thin films was investigated using the focused ion beam technique, scanning electron microscopy and the electron back scatter diffraction (EBSD) technique as well as the substrate curvature method to study their stress-temperature and stress relaxation behavior. The results show that the linear elastic behavior of 1 μm thick Cu films is significantly improved by alloying. Additionally, after annealing such films have an excellent low electrical resistivity of 1.9-2.0 μΩ cm, which meets the requirements of the roadmap ITRS [International Technology Roadmap for Semiconductors, Edition 2003, part: interconnect, available at http://public.itrs.net/].     

Surface morphology and reaction at Cu/Si interface—Effect of native silicon suboxide

Copper thin films are deposited by thermal evaporation on unetched and etched monocrystalline silicon. The study by alpha particles backscattering (RBS) raises a strong diffusion of copper in silicon substrates with and without native suboxide layer. On the other hand, the X-rays diffraction shows the formation and the growth of Cu₃Si and Cu₄Si silicides. Whereas the scanning microscopy underlines large crystallites growth surrounded by black zones of silicon coming from the uncovered substrate, independently to the surface state of the substrate, after annealing at high temperature. The presence of native silicon suboxide at Cu/Si interface, influences in a drastic way the minimal temperature to which the interfacial reaction occurs. The oxygen impurities detected by microanalysis, after heat treatment under vacuum, are closely related to the growth of silicides crystallites.     

Characterization of thin Ta-Si-Nx layers of different nitrogen content using XPS, UPS and STM

Reactively sputtered Ta-Si-N_x barrier systems of different nitrogen content on copper were investigated by photoelectron spectroscopy (XPS, UPS) and scanning tunnelling microscopy (STM). The measured photoelectron spectra (excitation He-I) showed a clear dependence of the electron state density near the Fermi edge on the content of nitrogen. These results correlate with the I(U) characteristics of the STM measurements and the electrical conductivity of these layers.     

Improved electromigration failure in Al based interconnects

Electromigration (EM) failure in Al interconnects is significantly improved by inserting a WN film between Al and the interlayer dielectric: over 90% of test samples failed with the Al/TiN/Ti interconnects, whereas the failure rate of the Al film on WN is reduced to less than 13% under the stress con‐ ditions of 9 MA/cm² and 225 °C, and the EM lifetime is also much extended at the same conditions. Experimental results suggest that higher activation energy, no hillocks and compressive stress are responsible for the improved electromigration performance in the Al/WN interconnect. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Oxygen diffusion barriers using a new sacrificial design concept for future high-density memory devices

We emphasize the importance of the new design concept for diffusion barriers in high-density memory capacitors. RuTiN and RuTiO films are proposed as sacrificial oxygen diffusion barriers. They showed much lower sheet resistance up to 800 °C than various barriers including binary and ternary nitrides, reported by others. The contact resistance for both the Pt/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si and the Pt/RuTiO/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si contact structures, the most important electrical parameter for the diffusion barrier in the bottom-electrode structure of capacitors, exhibited values as low as 5 kΩ, even after annealing up to 750 °C. When each RuTiN and TiN film is inserted as a glue layer between the bottom electrode Pt layer in the CVD–BST simple stack-type structure, the thermal stability of the RuTiN glue layer is observed to be 150 °C higher than that of the TiN glue layer. Moreover, the capacitance of the PVD–BST simple stack-type structure with a TiN glue layer initially degrades after annealing at 500 °C, and thereafter failed completely. In the case of RuTiN and the RuTiO/RuTiN glue layers, however, the capacitance continuously increased up to 550 °C. These new experimental results accommodate the introduction of the sacrificial design concept of diffusion barriers against oxygen in high-density memory capacitors. Received: 6 February 2002 / Accepted: 4 March 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +82-31/360-4545, E-mail: dongsoo.yoon@hynix.com     

Investigation of organic impurities adsorbed on and incorporated into electroplated copper layers

At room temperature electroplated copper layers exhibit changes in resistivity, residual stress, and microstructure. This process, known as self-annealing, is intimately linked to the release of organic impurities, which stem from the incorporation of organic additives into the Cu layer in the course of the electroplating process. The behavior of these impurities during self-annealing, represented by the carbon content, could be detected by analytical radio frequency glow discharge optical emission spectrometry (GD-OES) and carrier gas hot extraction (CGHE). The precondition of a quantitative determination is a surface cleaning procedure to remove adsorbed organics from the copper surface. It was observed that at first almost all impurities have to leave the Cu metallization before an accelerated abnormal grain growth can start. The small amount of remaining organic species after self-annealing could be quantified by both examination techniques, GD-OES and CGHE.     

Investigation of ultrathin tantalum based diffusion barrier films using AES and TEM

Reliably acting diffusion barrier films are basically for the functionality of the copper inter-connect technology. Tantalum (Ta) and Tantalum nitride (TaN) are established materials for diffusion barriers against copper diffusion. In this study, the characterization of TaN like films produced using N⁺ plasma immersion ion implantation (PIII) was performed using Auger electron spectroscopy (AES). Chemical information was extracted from the Auger data using linear least square fit (LLS). The capability of the method in order to detect very little changes in the film composition dependent on small process changes was demonstrated. The nitrogen incorporation by PIII into high aspect ratio contact holes was proven using analytical TEM.     

Composition spread metal thin film fabrication technique based on ion beam sputter deposition

A composition spread metal thin film fabrication technique based on ion beam sputter deposition method was developed. The technique enables us to fabricate any desired part or a complete binary/ternary composition spread metal thin films onto a single substrate by sequentially sputtering different target materials. Composition spread metal thin films can be deposited directly on a dielectric film in patterned electrode shape for C-V and I-V measurements. The system could be especially useful in the search for new multi-component metal gate materials.     

Copper nanocluster diffusion in carbon nanotube

The diffusion of copper nanocluster in carbon nanotube was investigated using a classical molecular dynamics simulation and three empirical potential functions. The results indicated a growth mechanism of the copper-filled ultra-thin carbon nanotubes: the copper nanoclusters inserted into carbon nanotubes swiftly migrate along the tube axis, and then the copper nanowires grow in the ultra-thin carbon nanotubes. Periodic energy barriers in the carbon nanotubes induced the directional movement of copper nanoclusters in the carbon nanotubes. The diffusion speeds of copper nanocluster in the carbon nanotube showed the Arrherius relation.     

Direct patterning of gold oxide thin films by focused ion-beam irradiation

For direct writing of electrically conducting connections and areas into insulating gold oxide thin films a scanning Ar⁺ laser beam and a 30 keV Ga⁺ focused ion beam (FIB) have been used. The gold oxide films are prepared by magnetron sputtering under argon/oxygen plasma. The patterning of larger areas (dimension 10–100 μm) has been carried out with the laser beam by local heating of the selected area above the decomposition temperature of AuO_x (130–150 °C). For smaller dimensions (100 nm to 10 μm) the FIB irradiation could be used. With both complementary methods a reduction of the sheet resistance by 6–7 orders of magnitude has been achieved in the irradiated regions (e.g. with FIB irradiation from 1.5×10⁷ Ω/□ to approximately 6 Ω/□). The energy-dispersive X-ray analysis (EDX) show a considerably reduced oxygen content in the irradiated areas, and scanning electron microscopy (SEM), as well as atomic force microscopy (AFM) investigations, indicate that the FIB patterning in the low-dose region (10¹⁴ Ga⁺/cm²) is combined with a volume reduction, which is caused by oxygen escape rather than by sputtering. Received: 30 May 2000 / Accepted: 31 May 2000 / Published online: 13 July 2000     

Photoluminescence of very thin oxide/a-Si:H structures passivated in HCN solutions

In this contribution we present new experimental facts concerning evolution of the a-Si:H photoluminescence (PL) spectra, recorded at 6 K, induced by both formation of very thin oxide layer in the surface region of the semiconductor by nitric acid solutions and passivation of a-Si:H defect states using HCN aqueous solutions. a-Si:H layers were deposited on both n-type of crystalline Si and the Corning glass. The analysis of the set of PL spectra - their interpretation - indicates that two explanations of blue shifts of the PL band maxima are possible. The first is connected with formation of several structurally different a-Si:H-based phases inside the amorphous matrix and/or with the Street model of recombination of localized electron-hole pairs coupled with the optical phonon in Si.Additionally, as it was stated, the wet chemical oxidation of 1 μm thick a-Si:H layers deposited on the glass can induce formation of hydrogenated micro-sized a-Si grains. Passivation procedure performed in the HCN solution can transform an equivalent part of the a-Si:H semiconductor to a-Si:CN. If the multiphase model is accepted for interpretation of the PL spectra then the following main PL transitions related with different phases were observed: 1.20, 1.25, 1.38, 1.41, 1.44, and 1.48 eV.     

The effect of hydrogen peroxide on polishing removal rate in CMP with various abrasives

The effect of hydrogen peroxide in chemical mechanical planarization slurries for shallow trench isolation was investigated. The various abrasives used in this study were ceria, silica, alumina, zirconia, titania, silicon carbide, and silicon nitride. Hydrogen peroxide suppresses the polishing of silicon dioxide and silicon nitride surfaces by ceria abrasives. The polishing performances of other abrasives were either unaffected or enhanced slightly with the addition of hydrogen peroxide. The ceria abrasives were treated with hydrogen peroxide, and the polishing of the work surfaces with the treated abrasive shows that the inhibiting action of hydrogen peroxide is reversible. It was found that the effect of hydrogen peroxide as an additive is a strong function of the nature of the abrasive particle.     

Adjustable thermal conductivity in carbon nanotube nanofluids

Homogeneous and stable nanofluids have been produced by suspending well dispersible multi-walled carbon nanotubes (CNTs) into ethylene glycol base fluid. CNT nanofluids have enhanced thermal conductivity and the enhancement ratios increase with the nanotube loading and the temperature. Thermal conductivity enhancement was adjusted by ball milling and cutting the treated CNTs suspended in the nanofluids to relatively straight CNTs with an appropriate length distribution. Our findings indicate that the straightness ratio, aspect ratio, and aggregation have collective influence on the thermal conductivity of CNT nanofluids.     

Single-particle thermal diffusion of charged colloids: Double-layer theory in a temperature gradient

The double-layer contribution to the single-particle thermal diffusion coefficient of charged, spherical colloids with arbitrary double-layer thickness is calculated and compared to experiments. The calculation is based on an extension of the Debye-Hückel theory for the double-layer structure that includes a small temperature gradient. There are three forces that constitute the total thermophoretic force on a charged colloidal sphere due to the presence of its double layer: i) the force F _W that results from the temperature dependence of the internal electrostatic energy W of the double layer, ii) the electric force F _el with which the temperature-induced non-spherically symmetric double-layer potential acts on the surface charges of the colloidal sphere and iii) the solvent-friction force F _sol on the surface of the colloidal sphere due to the solvent flow that is induced in the double layer because of its asymmetry. The force F _W will be shown to reproduce predictions based on irreversible-thermodynamics considerations. The other two forces F _el and F _sol depend on the details of the temperature-gradient-induced asymmetry of the double-layer structure which cannot be included in an irreversible-thermodynamics treatment. Explicit expressions for the thermal diffusion coefficient are derived for arbitrary double-layer thickness, which complement the irreversible-thermodynamics result through the inclusion of the thermophoretic velocity resulting from the electric- and solvent-friction force.     

Comment on: “Dynamical analysis of Cohen-Grossberg neural networks with continuously distributed delays” [Phys. Lett. A 364 (2007) 38]

Recently, Mao and Zhao [Z. Mao, H. Zhao, Phys. Lett. A 364 (2007) 38] considered the existence and uniqueness of the equilibrium point of the Cohen-Grossberg neural network model with continuously distributed delays. Mao and Zhao established Theorem 1. In this Letter, we would like to point out that Theorem 1 given by Mao and Zhao is incorrect in general.     

Oxygen diffusion through thin Pt films on Si(100)

We have investigated the diffusion of oxygen through evaporated platinum films on Si(100) upon exposure to air using substrates covered with Pt films of spatially and continuously varying thickness (0–500 Å). Film compositions and morphologies before and after silicidation were characterized by modified crater edge profiling using scanning Auger microscopy, energy-dispersive X-ray microanalysis, scanning tunneling microscopy, and transmission electron microscopy. We find that oxygen diffuses through a Pt layer of up to 170 Å forming an oxide at the interface. In this thickness range, silicide formation during annealing is inhibited and is eventually stopped by the development of a continuous oxide layer. Since the platinum film consists of a continuous layer of nanometer-size crystallites, grain boundary diffusion of oxygen is the most probable way for oxygen incorporation. The diffusion constant is of the order of 10^–19 cm²/s with the precise value depending on the film morphology.     

Application of the modified electrostatic model to the impurity diffusion in nickel

The modified electrostatic model (Neumann and Tölle 1995) is applied to the impurity diffusion in nickel.Z ₀ = 0.4 is used for the effective charge of the nickel ion.The comparison of calculated and experimental diffusion parameters reveals that the sign of J Q, the difference between impurity diffusion and self-diffusion energy, and the sign of the difference between impurity diffusion and self-diffusion coefficient is correctly predicted in all cases. On the other hand the comparison exhibits some systematic deviations for 5p impurities, which cannot be explained in terms of the current impurity diffusion models.     

Aluminium diffusion in titanium nitride films. Efficiency of TiN barrier layers

Two kinds of reactively evaporated titanium nitride films with columnar (B ₀ films) and fine-grained (B ₊ films) film structures, respectively, have been examined as diffusion barriers for preventing aluminium diffusion. The aluminium diffusion profiles have been investigated by 2 MeV ⁴He⁺ Rutherford backscattering spectrometry (RBS) at temperatures up to 550° C. The diffusivity from 300° C to 550° C is: D[m²s^–1]=3×10^–18 exp[–30/(RT)] in B ₀ layers and D[m²s^–1]=1.4×10^–16 exp[–48/(RT)] in B ₊ TiN layers. The activation-energy values determined indicate a grain boundary diffusion mechanism. The difference between the diffusion values is determined implicitly by the microstructure of the layers. Thus, the porous B ₀ layers contain a considerable amount of oxygen absorbed in the intercolumnar voids and distributed throughout the film thickness. As found by AES depth profiling, this oxygen supply allows the formation of Al₂O₃ during annealing the latter preventing the subsequent diffusion of the aluminium atoms.