Effective Diffusion Barrier Research Articles

Effects of Co content on the Cu diffusion barrier property of electroless NiCoP film

The characteristics of electroless NiCoP films were investigated as a function of Co content. Sheet resistance of a multi-stacked film of SiO2/Ta/Cu/NiP dramatically increased after annealing at 500 °C, but as more Co was co-plated in NiCoP film, the change in sheet resistance of the stacked film of SiO2/Ta/Cu/NiCoP at 500 °C became smaller. A CoP/Cu film showed no change in resistance value after annealing, which indicates the CoP film is the most effective Cu diffusion barrier. X-ray diffraction analysis showed that an as-plated NiP film of amorphous structure is easily crystallized by thermal annealing over 300 °C, while CoP showed an insignificant change in crystal structure by thermal annealing up to 500 °C. This result reveals that the CoP film is capable of preventing the diffusion of Cu at 500 °C due to the thermal stability of CoP film.

Ablation mechanisms of interpenetrating Al20Si/graphite composites

In order to utilize the latent heat of metal fusion and evaporation, Al20Si/graphite was added into graphite by squeeze casting infiltration. Its ablation properties were tested by oxy-acetylene flame. Compared with graphite, linear ablation rates of Al20Si/graphite decrease nearly by one order of magnitude. However, linear ablation rate of Al20Si/graphite increases with ablation time, which is caused by the change of ablation mechanism. At the beginning of ablation process, thermal chemical erosion plays an important part and thermal protective effect comes from the melting of Al20Si, the alleviation of liquid Al2O3 towards flame scouring and the decrease of porosities compared with graphite, while with ablation processing thermal mechanical erosion turns to dominate and thermal protective effect is mainly presented on the prevention of oxygen diffusion by the molten Al4SiC4 covered on ablation surface and the oxygen diffusion barrier effect of Al4SiC4 stuffed into graphite pores.

Reducing copper leaching from treated wood by sol-gel derived TiO2 and SiO2 depositions

Abstract The antileaching efficacy of sol-gel-derived TiO2- and SiO2-based precursors has been evaluated through laboratory leaching trials with pine sapwood in two different ways. In a one-step process, wood was vacuum impregnated by the precursor solutions containing CuCl2. The copper (Cu) emission rates of the sol-gel-based impregnated woods were up to 70% lower than that of wood treated with pure CuCl2 solution at the same level of concentration. More improvement (80%) could be achieved in a two-step process, in which sol-gel precursors were introduced into an already CuCl2-treated wood. The refinement was attributed to several effects. In the one-step approach, Cu was embedded in the TiO2/SiO2 gels formed in the wood texture. During a two-step impregnation, gel layers that were formed in the wooden interior acted as an effective diffusion barrier. The sol-gel impregnations made wood more hydrophobic; therefore, the low amount of water that penetrated the cell wall was less efficient to leach out Cu.

Chemical Vapor Deposition of Manganese Metallic Films on Silicon Oxide Substrates

The growth of manganese-based films on silicon oxide substrates via the thermal decomposition of two Mn metalorganic complexes, bis(N,N′-diisopropylpentylamidinato)Mn(II) and methylcyclopentadienylmanganese(I) tricarbonyl, was characterized and contrasted by using an instrument equipped with a reactor coupled to a X-ray photoelectron spectroscopy (XPS) analytical chamber. The acetamidinate precursor proved highly reactive, affording the deposition of Mn at reasonable rates, higher at higher temperatures, but also leading to the incorporation of approximately 15% of nitrogen and additional carbon in the grown Mn(0) films. The methylcyclopentadienyl compound, by contrast, proved quite unreactive, even if an electron-impact gas-phase preactivation step recently developed in our laboratory was used. Slow deposition rates were seen with this precursor, appearing to be slower at higher temperature because of an unfavorable kinetic competition with Mn diffusion into the bulk. In both cases, a nonstoichiometric mixture of MnOx + SiOx and Mn silicate is formed first, possibly followed by the formation of a thin subsurface Mn silicide layer. The combined Mn silicate/Mn silicide structure acts as an effective diffusion barrier, after which Mn(0) metallic films can be grown on top. The implications of this behavior to the design of Mn chemical vapor deposition processes are briefly discussed.

Lignification of cell walls of infected cells in Casuarina glauca nodules that depend on symplastic sugar supply is accompanied by reduction of plasmodesmata number and narrowing of plasmodesmata

The oxygen protection system for the bacterial nitrogen-fixing enzyme complex nitrogenase in actinorhizal nodules of Casuarina glauca resembles that of legume nodules: infected cells contain large amounts of the oxygen-binding protein hemoglobin and are surrounded by an oxygen diffusion barrier. However, while in legume nodules infected cells are located in the central tissue, actinorhizal nodules are composed of modified lateral roots with infected cells in the expanded cortex. Since an oxygen diffusion barrier around the entire cortex would also block oxygen access to the central vascular system where it is required to provide energy for transport processes, here each individual infected cell is surrounded with an oxygen diffusion barrier. In order to assess the effect of these oxygen diffusion barriers on oxygen supply for energy production for transport processes, apoplastic and symplastic sugar transport pathways in C. glauca nodules were examined. The results support the idea that sugar transport to and within the nodule cortex relies to a large extent on the less energy-demanding symplastic mechanism. This is in line with the assumption that oxygen access to the nodule vascular system is substantially restricted. In spite of this dependence on symplastic transport processes to supply sugars to infected cells, plasmodesmal connections between infected cells, and to a lesser degree with uninfected cells, were reduced during the differentiation of infected cells.

Evaluation of Diffusion Barrier Between Pure Sn and Te

An electroless Ni layer is often chosen as an effective diffusion barrier in thermoelectric modules. Thermal aging can form a thick layer of NiTe. This study investigates the growth kinetics of NiTe intermetallic compounds (IMCs). The apparent activation energy was determined to be 70.9 kJ/mol. Ni/Co was also selected as an alternative barrier because Co-Te did not form IMCs. Results show that Co can effectively suppress the voids formed at the interfaces. After high-temperature annealing, a very thin Ni-Te IMC formed between Co-P and Te.

Temperature Jump Phenomenon During Plasmatron Testing of ZrB2-SiC Ultrahigh-Temperature Ceramics

U LTRAHIGH temperature ceramic (UHTC) materials containing hafnium diboride (HfB2) and zirconium diboride (ZrB2) with a silica former, most commonly silicon carbide (SiC), have been studied extensively over the last decade as materials for leading-edge and control surface components on hypersonic vehicles [1–3]. Such components experience extreme aerothermal heating in chemically aggressive, partially dissociated air environments. Promising aspects of diboride-based UHTC materials include the very high melting points of HfB2 and ZrB2 and their refractory oxides hafnia (HfO2) and zirconia (ZrO2), as well as the high thermal conductivities of HfB2 and ZrB2, which enables efficient heat conduction away from stagnation point regions [4]. Zirconium diboride has some advantages over hafnium diboride as an aerospace material, because it is lighter and less expensive. The oxidation of ZrB2 produces both zirconia and boron oxide (B2O3). Significant oxidation of ZrB2 in atmospheric air begins at about 1050 K. The softening temperature for amorphous B2O3 is in the range of 830–900 K [5]; below about 1500 K, the oxide scale consists of a porousZrO2 network filled with liquidB2O3 that acts as an effective oxygen diffusion barrier [6,7]. However, the vapor pressure of B2O3 increases rapidly with temperature [8], resulting in rapid loss of B2O3 above 1500 K. The residual porous zirconia scale provides little resistance to inward oxygen transport and further oxidation [9,10], making the oxidation resistance of pure ZrB2 insufficient for high-temperature hypersonic vehicle applications. The addition of a silica former to ZrB2 improves its oxidation resistance [11–14]. Compositions containing from 10 to 30% (by volume) SiC have generally been found to be optimal in this regard. The virgin ZrB2-SiC surfaces oxidize through parallel reactions that generate ZrO2,B2O3, and SiO2. LiquidB2O3 mixes with amorphous SiO2 to form a borosilicate glass that seals the ZrO2 scale [15]. With increasing temperature, boron oxide evaporates preferentially from Received 10 August 2011; revision received 13 February 2012; accepted for publication 19 February 2012. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0887-8722/12 and $10.00 in correspondence with the CCC. ∗Senior Research Scientist, Molecular Physics Laboratory, 333 Ravenswood Avenue; jochen.marschall@sri.com. Senior Member AIAA (Corresponding Author). Research Physicist, Molecular Physics Laboratory, 333 Ravenswood Avenue. Member AIAA. Professor, Department ofMaterials Science andEngineering, 223McNutt Hall; billf@mst.edu. Professor, Department ofMaterials Science andEngineering, 223McNutt Hall; ghilmas@mst.edu. Ph.D. Candidate, Aeronautics and Aerospace Department. Chaussee De Waterloo 72; panerai@vki.ac.be. ∗∗Associate Professor, Aeronautics and Aerospace Department, Chaussee De Waterloo 72; olivier.chazot@vki.ac.be. JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER Vol. 26, No. 4, October–December 2012

Engineered Coatings for Ni Alloys in High Temperature Reactors

Alloy 617 is a candidate material for the intermediate heat exchanger of the He-cooled very high temperature reactor. At target temperatures ≥1223 K (950 °C), low level impurities in the gas stream may cause carburization, decarburization, and/or oxidation of 617 with deleterious effects on its mechanical properties. The chromia scale formed naturally by 617 does not provide adequate protection in the expected environment. Alpha alumina offers a greater potential as an effective diffusion barrier with superior stability, but it requires modification of the alloy surface. This work explores two approaches to surface modification based on aluminizing, either alone or in combination with FeCrAlY cladding, followed by pre-oxidation to form alpha alumina. Both approaches yield coatings with promising diffusional stability on alloy 617. Initial corrosion studies in impure He environments reveal that the alpha alumina is stable and protects the underlying substrate in both carburizing and decarburizing environments.

Magic size effects of small Cu clusters diffusion on Ag (1 1 1) surface

Using embedded-atom-method (EAM) potential of Ag/Cu heterogeneous system, structural stabilities and diffusion behaviors of small Cu clusters on Ag (111) surface have been investigated by molecular dynamics studies. The binding energies, the effective diffusion barriers and the corresponding prefactors for Cu clusters have been calculated. Structural stabilities and the diffusion properties of small Cu clusters show significant magic size effects: the trimer and heptamer clusters with relatively higher effective diffusion barriers are more stable than the other sizes. Moreover, the dimer's and trimer's rotation mechanism have been investigated in this paper as well.

Ferromagnetic nanostructures of oxygen on Ag(111)

First principles calculations were performed to investigate the robustness of oxygen adsorbed structures that show ferromagnetic properties. These ferromagnetic properties are induced by ferromagnetic superexchange interactions and Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. Such ferromagnetic oxygen adsorbed structures appear only in the case of coverages higher than 0.5 ML, because the ferromagnetic superexchange interactions and RKKY interactions are appreciable between O-O only for short distances. In this work, we focused on single oxygen atom diffusion parallel and perpendicular to Ag(111) surfaces. The in-plane diffusion could induce associative desorption, which reduces the oxygen coverage. On the other hand, diffusion to the subsurface could quench the magnetic moment. These diffusion paths have effective diffusion barriers of 0.78 eV. Thus, such diffusion rarely occurs in low temperature regions.

Thermal Stability of Atomic Layer Deposited Ru Layer on Si and TaN/Si for Barrier Application of Cu Interconnection

The thermal stability of thin Ru single layer and Ru/TaN bilayers grown on bare Si by plasma enhanced atomic layer deposition (PEALD) have been studied with Cu/Ru, Cu/Ru/TaN structures as a function of annealing temperature. To investigate the characteristics as a copper diffusion barrier, a 50 nm thick Cu film was sputtered on Ru and Ru/TaN layers and each samples subjected to thermal annealing under N2 ambient with varied temperature 300, 400, and 500 degrees C, respectively. It was found that the single 5 nm thick ALD Ru layer acted as an effective Cu diffusion barrier up to 400 degrees C. On the other hand ALD Ru (5 nm)/TaN (3.2 nm) showed the improved diffusion barrier characteristics even though the annealing temperature increased up to 500 degrees C. Based on the experimental results, the failure mechanism of diffusion barrier would be related to the crystallization of amorphous Ru thin film as temperature raised which implies the crystallized Ru grain boundary served as the diffusion path of Cu atoms. The combination of ALD Ru incorporated with TaN layer would be a promising barrier structure in Cu metallization.

MNOS stack for reliable, low optical loss, Cu based CMOS plasmonic devices

We study the electro optical properties of a Metal-Nitride-Oxide-Silicon (MNOS) stack for a use in CMOS compatible plasmonic active devices. We show that the insertion of an ultrathin stoichiometric Si(3)N(4) layer in a MOS stack lead to an increase in the electrical reliability of a copper gate MNOS capacitance from 50 to 95% thanks to a diffusion barrier effect, while preserving the low optical losses brought by the use of copper as the plasmon supporting metal. An experimental investigation is undertaken at a wafer scale using some CMOS standard processes of the LETI foundry. Optical transmission measurments conducted in a MNOS channel waveguide configuration coupled to standard silicon photonics circuitry confirms the very low optical losses (0.39 dB.μm(-1)), in good agreement with predictions using ellipsometric optical constants of Cu.

A combined photovoltaic and Li ion battery device for continuous energy harvesting and storage

The design, fabrication, and initial analysis of a continuous energy harvesting and storage device for wireless sensor applications were undertaken. A Si nanowire-based photovoltaic (PV) device and Li ion battery were integrated onto a single Si substrate. The three terminal device consisted of separate positive terminals for each component and a shared negative electrode. The effect of Li+ incorporation into the planar PV electrode was evaluated. The current–voltage behavior of the PV device was tolerant to high Li+ concentrations. A titanium nitride layer between the battery and PV portions of the shared electrode was shown to be an effective diffusion barrier to Li+ incorporation.

TiN-based coatings on fuel cladding tubes for advanced nuclear reactors

Titanium nitride (TiN) thin films are coated on HT-9 and MA957 fuel cladding tubes and bars to explore their mechanical strength, thermal stability, diffusion barrier properties, and thermal conductivity properties. The ultimate goal is to implement TiN as an effective diffusion barrier to prevent the inter-diffusion between the nuclear fuel and the cladding material, and thus lead to a longer lifetime of the cladding tubes. Mechanical tests including hardness and scratch tests for the samples before and after thermal cycle tests show that the films have a high hardness of 28GPa and excellent adhesion properties despite the thermal treatment. Thermal conductivity measurements demonstrate that the thin TiN films have very minimal impact on the overall thermal conductivity of the MA957 and HT-9 substrates, i.e., the thermal conductivity of the uncoated HT-9 and MA957 substrates was 26.25 and 28.44Wm−1K−1, and that of the coated ones was 26.21 and 28.38Wm−1K−1, respectively. A preliminary Ce diffusion test on the couple of Ce/TiN/HT-9 suggests that TiN has excellent material compatibility and good diffusion barrier properties.

Effect of SnO–SiO2 composite coating on bonding of titanium–porcelain

The SnO–SiO2 composite coating was deposited on titanium (Ti) by sol–gel dipping process. The adhesion between the Ti and porcelain was evaluated by three point flexure bonding test. The results of thermogravimetry and differential scanning calorimetry analysis showed that the optimal heat treating temperature for SnO–SiO2 composite coating was 300°C. The SEM results revealed that the existence of microcracks on the SnO–SiO2 composite coatings surface after being treated at 300°C. The Ti oxide was formed along the crack. Failure of the Ti–porcelain predominantly occurred at the SnO–SiO2 composite coatings. SnO–SiO2 composite coatings served as an effective oxygen diffusion barrier, improved the chemical bonding between porcelain and Ti and resulted in the increased bonding strength of Ti–porcelain.

High-fidelity chemical patterning on oxide-free germanium

Oxide-free germanium can be chemically patterned directly with self-assembled monolayers of n-alkanethiols via submerged microcontact printing. Native germanium dioxide is water soluble; immersion activates the germanium surface for self-assembly by stripping the oxide. Water additionally provides an effective diffusion barrier that prevents undesired ink transport. Patterns are stable with respect to molecular exchange by carboxyl-functionalized thiols.

A bilayer diffusion barrier of Ru/WSixNy for advanced Cu interconnects

Bilayers of Ru (7nm)/WSixNy (8nm) prepared by sputtering were investigated as diffusion barriers between Cu and Si for direct-platable Cu interconnects. Four different WSixNy films were prepared by using various N2/Ar flow rate ratios during sputtering of a WSi2.7 target. Sheet resistance measurements and X-ray diffractometry analysis showed that Ru/WSixNy bilayer diffusion barriers prevented Cu diffusion during 30min of annealing at temperatures of up to 550–750°C, while the Ru single layer of the same thickness (15nm) failed after annealing at 400°C by the formation of copper silicide due to the diffusion of Cu into Si. It was shown that the performances of bilayer diffusion barriers were improved as the nitrogen content in the WSixNy films was increased, which can be explained based on the results from transmission electron microscopy and X-ray photoelectron spectroscopy analysis of WSixNy films deposited with different N2/Ar flow rate ratios. From the results, the SiN and WN chemical bonds are strengthened as the N contents in the WSixNy films are increased by increasing the N2 flow rate during the deposition. The results indicate that the formation of both SiN and WN bonds will give an effective diffusion barrier against Cu diffusion.

Electrical characterization and nanoscale surface morphology of optimized Ti/Al/Ta/Au ohmic contact for AlGaN/GaN HEMT

Good ohmic contacts with low contact resistance, smooth surface morphology, and a well-defined edge profile are essential to ensure optimal device performances for the AlGaN/GaN high electron mobility transistors [HEMTs]. A tantalum [Ta] metal layer and an SiNx thin film were used for the first time as an effective diffusion barrier and encapsulation layer in the standard Ti/Al/metal/Au ohmic metallization scheme in order to obtain high quality ohmic contacts with a focus on the thickness of Ta and SiNx. It is found that the Ta thickness is the dominant factor affecting the contact resistance, while the SiNx thickness affects the surface morphology significantly. An optimized Ti/Al/Ta/Au ohmic contact including a 40-nm thick Ta barrier layer and a 50-nm thick SiNx encapsulation layer is preferred when compared with the other conventional ohmic contact stacks as it produces a low contact resistance of around 7.27 × 10-7 Ω·cm2 and an ultra-low nanoscale surface morphology with a root mean square deviation of around 10 nm. Results from the proposed study play an important role in obtaining excellent ohmic contact formation in the fabrication of AlGaN/GaN HEMTs.

Effects of Surface Finishes and Current Stressing on Interfacial Reaction Characteristics of Sn-3.0Ag-0.5Cu Solder Bumps

The effects of surface finishes on the in situ interfacial reaction characteristics of ball grid array (BGA) Sn-3.0Ag-0.5Cu lead-free solder bumps were investigated under annealing and electromigration (EM) test conditions of 130°C to 175°C with 5.0 × 103 A/cm2. During reflow and annealing, (Cu,Ni)6Sn5 intermetallic compound (IMC) formed at the interface of electroless nickel immersion gold (ENIG) finish. In the case of both immersion Sn and organic solderability preservative (OSP) finishes, Cu6Sn5 and Cu3Sn IMCs formed. Overall, the IMC growth velocity of ENIG was much lower than that of the other finishes. The activation energies of total IMCs were found to be 0.52 eV for ENIG, 0.78 eV for immersion Sn, and 0.72 eV for OSP. The ENIG finish appeared to present an effective diffusion barrier between the Cu substrate and the solder, which leads to better EM reliability in comparison with Cu-based pad systems. The failure mechanisms were explored in detail via in situ EM tests.

The Influence of Oxygen Precipitates on the Diffusion Velocity of Copper in the Bottom Parts of mc-Si Ingots

In the present study, the influence of oxygen precipitates in the bottom part of multicrystalline silicon ingots on the metal diffusion has been studied. According to the well known haze test, an experimental setup for the measurement of diffusion velocity at 700°C was developed, in which the copper was detected using Total Reflection X-ray Fluorescence.Differences in the diffusion velocity and the gettering amount for copper in samples with low-oxygen and high-oxygen were observed. Thus gettering efficiency seems to be dependent on oxygen content. Metal precipitates detected were found to contain Si, O and Cu. Since these precipitates appear along grain boundaries, it is assumed that grain boundaries act as a diffusion channel. As a consequence, oxygen precipitates located at the grain boundary should be most effective for intrinsic gettering. The results of these studies are encouraging since they imply that an optimized oxygen precipitate concentration in the bottom zone of a multicrystalline silicon ingot can be used as an effective intrinsic diffusion barrier.