Diffusion Barrier Properties Research Articles

Self-forming VOx layer as Cu diffusion barrier for low-k dielectrics

A Cu–V alloy is reported as a material for use in a self-forming barrier process. The diffusion barrier property of a V-based self-formed layer was investigated on various low-k dielectrics. Cu–V alloy films were directly deposited on various low-k dielectrics by co-sputtering, followed by annealing at various temperatures. X-ray diffraction revealed Cu (111), (200) and (220) peaks of the Cu–V alloys. Transmission electron microscopy showed that a uniform V-based interlayer self-formed at the interface after annealing. In order to evaluate the barrier property of the V-based interlayer, the thermal stability was measured with low-k dielectrics. The V-based interlayer formed on the low-k 3 dielectric that contained more oxygen had better thermal stability than that formed on the low-k 1 dielectric that contained less oxygen and more carbon. X-ray photoelectron spectroscopy analysis showed the chemical compositions of the self-formed layer. Furthermore, the results show that the formation of the V-based interlayers was strongly dominated by the oxygen concentration in the dielectric layers.

Structure–Diffusion Relationship of Magnetron-Sputtered WTi Barriers Used in Indium Interconnections

Tungsten-titanium (WTi) thin films are known as potential adhesion promoters and diffusion barriers. The barrier efficiency of WTi thin films against indium (In) diffusion was experimentally studied by x-ray diffraction (XRD) measurements during in situ annealing. Specific multilayered samples were designed to estimate the diffusion barrier properties using the Ni/In system. These diffusion samples were made up of a 100-nm-thick WTi layer prepared by magnetron sputtering from an alloyed target (W:Ti ≈ 70:30 at.%), sandwiched between Ni and Au/In layers. WTi film microstructures were observed to depend on the working pressure. Diffusion barrier breakdown was monitored upon annealing by the formation of intermetallic compounds (IMC) (intermixing between Ni and In). Annealing was performed at temperatures of 573 K, 623 K, and 673 K (homologous temperatures \(T/T_{\rm m}^{\rm In} \simeq 1.34, 1.45\), and 1.57, respectively) and under primary vacuum. The diffusion coefficients of In in WTi were determined. The correlation between WTi film microstructure and diffusion barrier efficiency was established. Better diffusion barrier performance was obtained for WTi films with dense microstructure associated with a compressive residual stress state. Hence, tuning the sputtering conditions allows significant improvement of barrier performance against diffusion through a change of the film microstructure.

An in vitro assay for entry into cilia reveals unique properties of the soluble diffusion barrier

Specific proteins are concentrated within primary cilia, whereas others remain excluded. To understand the mechanistic basis of entry into cilia, we developed an in vitro assay using cells in which the plasma membrane was permeabilized, but the ciliary membrane was left intact. Using a diffusion-to-capture system and quantitative analysis, we find that proteins >9 nm in diameter (∼100 kD) are restricted from entering cilia, and we confirm these findings in vivo. Interference with the nuclear pore complex (NPC) or the actin cytoskeleton in permeabilized cells demonstrated that the ciliary diffusion barrier is mechanistically distinct from those of the NPC or the axon initial segment. Moreover, applying a mass transport model to this system revealed diffusion coefficients for soluble and membrane proteins within cilia that are compatible with rapid exploration of the ciliary space in the absence of active transport. Our results indicate that large proteins require active transport for entry into cilia but not necessarily for movement inside cilia.

Amorphous thin film TaWSiC as a diffusion barrier for copper interconnects

A very thin and amorphous TaWSiC film with relatively low resistivity of 233 μΩ·cm was studied for its effectiveness as a diffusion barrier for copper interconnects. A 5 nm thick TaWSiC barrier effectively prevents copper diffusion and maintains structural integrity up to an annealing temperature of at least 550 °C, with copper silicide formation observed at 650 °C. In comparison, a barrier of 5 nm of nanocrystalline Ta already fails at 550 °C. Being very thin and amorphous, while having low resistivity and good thermal stability, are crucial properties of a good diffusion barrier for future technology, and this film meets these requirements.

Diffusion barrier properties of nitride-based coatings on fuel cladding

Abstract In this work, titanium nitride (TiN) and zirconium nitride (ZrN) coatings are proposed as diffusion barriers between stainless steel nuclear fuel cladding and lanthanide fission products. TiN and ZrN have been coated as barrier materials between pure Fe and Ce, i.e. diffusion couples of Fe/TiN/Ce and Fe/ZrN/Ce, annealed up to a temperature of 600 °C, and compared to the diffusion behavior of uncoated Fe/Ce. Backscattered electron images and energy dispersive X-ray spectroscopy measurements confirm that, with a 500 nm TiN or ZrN layer, no obvious diffusion is observed between Fe and Ce. Basic diffusion characteristics of the Fe/Ce couple have also been measured and compared with the TiN and ZrN coated ones. These preliminary results strongly advocate that TiN and ZrN coatings may be feasible as diffusion barriers against Ce and possibly other lanthanide fission products.

P.62: Effects of Amorphous InGaZnO Thin Film Transistors with Various Buffer Layers on Polyimide Substrate Under Negative Bias‐temperature Stresses

AbstractBuffer layers on flexible substrates have strongly affected to electrical performance and instability in oxide TFTs. The oxide TFT on proper buffer layer/PI substrate showed better electrical performance than that on other buffer layers because the buffer layer with high gas diffusion barrier properties can suppress to generate defect states in semiconductor and/or interface from hydrogen and water penetration. The origins of flexible oxide TFT instabilities were systematically investigated by using in‐situ/ex‐situ measurement and chemical/physical analysis.

Study of the effect of silica nanofillers on the sea-water diffusion barrier property of unsaturated polyester composites

With successful applications in every other field, composites have been used in making boats, offshore structures and various marine structural applications for past few decades, owing to their superior strength-to-weight ratio and performance-to-cost ratio. Usually, marine environment poses serious challenges to the choice of materials due to the presence of corrosive seawater which significantly decreases their life-time. Slowly, nanocomposites are increasingly becoming popular because of nanoscale effects, large interface area and strong interfacial interactions between nanoparticles and polymer. In the present study, Silicon dioxide nanofillers were used as additive in order to enhance the barrier property of composites against water diffusion and hence to prevent it from mechanical degradation. Being one of the most commonly used resin for making composites, unsaturated polyester was chosen for study. Resistance to sea-water diffusion and water absorption rate was studied while varying parameters like ambient temperature and salinity of water. It was observed that the presence of nanoparticles significantly decreases the maximum water uptake and moisture diffusivity in the composite. It was also found that as the salinity of sea-water increases and temperature decreases, degradation due to water absorption decreases.

Gas diffusion barrier characteristics of Al2O3/alucone films formed using trimethylaluminum, water and ethylene glycol for organic light emitting diode encapsulation

Al2O3/alucone barrier films were deposited by using atomic layer deposition and molecular layer deposition at 85 °C. Fourier transform infrared spectroscopy spectra reveal that the chemical bonding states, such as those of O–H, C–H, and C–O groups, changed rapidly in alucone films because the water vapor may absorb and/or react with the alucone film. The water vapor transmission rate (WVTR) measured by the calcium test of alucone film was similar to that of polyethylene naphthalate. However, the hybrid Al2O3/alucone films (2.08×10−2g/m2day) show better WVTR properties than that of Al2O3 single layer (3.73×10−2g/m2day) or that of alucone (1.14g/m2day). Hybrid layers can drastically improve the water vapor diffusion barrier property because the alucone layer may increase the water vapor diffusion path in the film and decrease the diffusion speed by trapping water vapor chemically. These promising hybrid layers can create a synergy effect to improve not only the WVTR property but also the flexible property.

Interfacial reaction between Sn–Ag–Cu solder and Co–P films with various microstructures

We electroplated Co–P films with nanocrystalline, amorphous and nanocrystalline/amorphous mixed structures and used them as under-bump metallization (UBM) joined with Sn–Ag–Cu lead-free solder. We systematically investigated the interfacial reaction between the Sn–Ag–Cu solder and the Co–P UBM and analyzed the growth mechanisms of the intermetallic compounds formed at the interfaces of the Sn–Ag–Cu/Co–P joints through multiple reflows. Among the three kinds of Co–P films, the film with a mixed structure shows the best diffusion-barrier properties and is a good candidate for the UBM joined with the Sn–Ag–Cu solder. For the nanocrystalline Co–P UBM, Co diffuses quickly toward the solder and Sn does not diffuse into the UBM, whereas for the amorphous Co–P film not only does Co diffuse into the solder, but also Sn diffuses into the Co–P film with a large diffusion rate. In addition, the first-principles calculation shows that the exchange coupling between Co(3d74s2) and Sn(5s25p2) electrons and between Sn(5s25p2) and P(3s23p3) electrons results in the formation of CoSn and SnP3, which originate from the diffusion and reaction of Co and Sn atoms, respectively; this is consistent with the experimental data of transmission electron microscopy characterization.

Self-forming barrier characteristics of Cu–V and Cu–Mn films for Cu interconnects

We investigated the influence of annealing on the diffusion barrier property in a Mn-based and V-based barrier layer. The samples were annealed at various temperatures for 1h in vacuum. X-ray diffraction revealed Cu (111), Cu (200) and Cu (220) peaks for the Cu–Mn and Cu–V alloys. Transmission electron microscopy showed that a 4–7nmV-based interlayer self-formed and a 2–5nm Mn-based interlayer self-formed at the interface after annealing. The resistivity of the annealed Cu–V alloy was reduced to 8.1μΩ-cm, which is greater than the resistivity of the annealed Cu–Mn alloy. The Mn-based interlayer and V-based interlayer showed excellent thermal stability. The results show that Mn and V based Cu alloys are suitable seed layer materials for Cu interconnects.

Enhanced growth and Cu diffusion barrier properties of thermal ALD TaNC films in Cu/low-k interconnects

For thermal ALD TaxNyCz films improved growth behaviour and Cu diffusion barrier performance are demonstrated by applying a plasma treatment prior to film deposition, in particular on low-k dielectrics. Two different kinds of ALD processes for depositing thermal ALD TaxNyCz films are applied in this study, involving either TBTDET or PDMAT as a precursor. Ammonia is used as a reactant and Ar as a purging gas in both processes. Within the experiment, two types of pre-treatments prior to ALD are investigated: a wet-chemical pre-treatment using diluted (0.5%) HF, and plasma pre-treatments using Ar/H2 or N2 plasmas. It is examined by transmission electron microscopy (TEM) from a microstuctural perspective whether improved growth behaviour of thermal ALD TaxNyCz films can be achieved by applying a plasma treatment prior to film deposition. The Cu diffusion barrier properties of 10-15nm ALD TaNC films are then evaluated by bias temperature stress (BTS) and triangular voltage sweep (TVS) measurements on metal-insulator-semiconductor (MIS) test structures, after annealing at up to 600^oC under H2/N2 atmosphere. The results imply that, from a process side, thermal ALD TaNC films can intrinsically achieve a Cu diffusion barrier performance similar to PVD TaN. However, if no treatment was applied, Cu drift occurred.

Electrografted insulator layer as copper diffusion barrier for TSV interposers

Introduction After many years as a hypothetical possibility, 3D Integrated Circuits (3D IC) stacking has emerged as a potential key enabler for maintaining semiconductor performance trends. Through Silicon Vias (TSVs) sit at the foundation of the 3D-IC revolution and are a key enabler for extending semiconductor integration trends into a new phase. Integrated Device Manufacturers and fabless design houses need small, high-density, fine-pitch vias for improved signal integrity and Si real-estate savings. They need them now, and cannot wait for very thin wafer processing and handling technologies to become mainstream – TSVs must cope with current mainstream wafer thickness. Deep TSVs with Aspect Ratio (AR) greater than 10:1 elegantly fulfill both requirements. But they cannot be manufactured with acceptable yield/cost using traditional dry processes for liner, barrier and seed deposition. Chemical and Physical Vapor Deposition techniques show basic shortcomings and impose high capital investments, holding back the industry-wide adoption of 3D-IC solutions. Beyond that, physical limitations of PVD and CVD techniques prevent to reach a good step coverage of the deposited layers inside the vias, which is required to perform void-free gap filling of electroplated copper. Electrografting polymer layer as copper diffusion barrier. To overcomes those limitation, Alchimer develops alternative wet solutions based on electrografting (eG™) and chemical grafting (cG™) proprietary technologies[1]. Electrografting is based on surface chemistry formulations and processes [2]. It is applied to conductive and semiconductive surfaces, and enables self-oriented growth of thin coatings of various materials, especially polymer and metals, initiated by in-situ chemical reactions between specific precursor molecules and the surface. Due to outstanding thermal, mechanical and electrical properties, electrografted polymer layers are an efficient insulation layer for TSV applications [3]. In this paper, we fill focus on the copper diffusion barrier properties of this eG polymer layer and the associated Cost of Ownership (CoO) reduction for TSV metallization. In fact, electrografted polymer layer can be used as insulator and copper diffusion barrier, involving the removal of copper diffusion barrier and copper seed layer deposition from the conventional process flow. TSV metallization process steps can thus be reduced to 2 steps:- Step 1: insulation and diffusion barrier all together (eGpolymer)- Step 2: Copper filling (electroless copper) We will describe in this paper the electrical, thermo-mechanical and barrier effect properties of the eG polymer film including breakdown voltage, capacitance, dielectric constant, young modulus, thermal stability and SIMS profiles after anneal to demonstrate the diffusion barrier efficiency. Complete metallization of TSV interposers, as an example of successful integration, will be highlighted by several characterizations including SEM cross sections. In addition, CoO comparison will be presented between conventional dry processes and this new wet approach for interposer metallization on the basis of 10:1 aspect ratio TSVs. New reliability data should also be presented, from test vehicles integrating eG layers, in extreme conditions where PECVD SiO2 cannot survive.

Electrografted insulator layer as copper diffusion barrier for TSV interposers

Alchimer develops alternative wet solutions based on electrografting (eG™) and chemical grafting (cG™) proprietary technologies. eG is based on surface chemistry formulations and processes. It is applied to conductive and semiconductive surfaces, and enables self-oriented growth of thin coatings of various materials, especially polymer and metals, initiated by in-situ chemical reactions between specific precursor molecules and the surface. Due to outstanding thermal, mechanical and electrical properties, electrografted polymer layers are an efficient insulation layer for TSV applications. In this paper, we fill focus on the copper diffusion barrier properties of this eG polymer layer and the associated Cost of Ownership (CoO) reduction for TSV metallization.

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.

Improved Diffusion Barrier Properties and NiSi Thermal Stability for the Cu Contact with the Ru/TaSiN Stack on NiSi/Si

Improved Diffusion Barrier Properties and NiSi Thermal Stability for the Cu Contact with the Ru/TaSiN Stack on NiSi/Si

Stress compensation in hafnia/silica optical coatings by inclusion of alumina layers

Hafnium dioxide films deposited using electron-beam evaporation tend to exhibit high tensile stresses, particularly when deposited on low-thermal-expansion substrates for use in a low-relative-humidity environment. Hafnia has been shown to be a critical material, however, for use in high-peak-power laser coatings, providing exceptional deposition control and laser-damage resistance. To correct for tensile thin-film stresses in hafnia/silica multilayer coatings, alumina compensation layers were incorporated in the multilayer design. Determination of the stresses resulting from alumina layers in different coating designs has led to the realization of the influence of water diffusion and the diffusion-barrier properties of alumina that must be considered. The inclusion of alumina layers in a hafnia/silica multilayer provides the ability to produce low-compressive-stress, high-laser-damage-threshold coatings.

Effect of sputtering bias voltage on the structure and properties of Zr–Ge–N diffusion barrier films

The diffusion barrier properties of Zr–Ge–N thin films are reported, focusing on issues relevant to their application as diffusion barriers for Cu interconnections in Si devices. The Zr–Ge–N films were prepared by reactive r.f. magnetron sputtering with different bias voltage. The analyses of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate that the final structure and composition of Zr–Ge–N film are very sensitive to the sputtering bias voltage. The N content in Zr–Ge–N film changes very little, and only decreases from 51.6 to 48.4at.% when sputtering bias voltage increases from 0V to −150V. However, the correlation between bias voltage change and the atomic ratio of Zr and Ge is very remarkable. These results clearly show that the Ge atoms are preferentially resputtered with increasing substrate bias voltage. The high sputtering bias appears to be in favor of the growth of ZrN grains. The copper diffusion barrier properties of Zr–Ge–N on Si have been examined and compared to ZrN. XRD and four-point probe method (FPP) both showed the onset of formation of copper silicide crystallites for ZrN barriers annealed at 650°C. In contrast, TEM on a Zr–Ge–N barriers annealed even at high annealing temperatures of 800°C revealed sharp interfaces and the energy dispersive X-ray spectroscopy (EDS) line scan showed no Cu diffusion through the barrier into Si substrate. The results suggest that Zr–Ge–N is superior to ZrN as a copper diffusion barrier on Si.

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.

Diffusion barrier properties of atomic-layer-deposited iridium thin films on Cu/Ir/Si structures

We investigated the diffusion barrier properties of an atomic-layer-deposited 12-nm-thick iridium (Ir) thin film as functions of the thermal treatment temperature. Up to a temperature of 500 °C, the Ir thin film maintained its initial configuration, preventing the penetration of the Cu layer into Si through the Ir layer. The thermal stability of the Ir layer up to 500 °C was confirmed by using high resolution transmission electron microscopy, Auger electron microscopy, and X-ray diffraction. In contrast, when the Ir layer was thermally annealed at 600 °C, copper silicide was formed, and interdiffusion of Cu and Ir was observed.

Growth of Ultrahigh Density Single-Walled Carbon Nanotube Forests by Improved Catalyst Design

We have grown vertically aligned single-walled carbon nanotube forests with an area density of 1.5 × 10(13) cm(-2), the highest yet achieved, by reducing the average diameter of the nanotubes. We use a nanolaminate Fe-Al(2)O(3) catalyst design consisting of three layers of Al(2)O(3), Fe, and Al(2)O(3), in which the lower Al(2)O(3) layer is densified by an oxygen plasma treatment to increase its diffusion barrier properties, to allow a thinner catalyst layer to be used. This high nanotube density is desirable for using carbon nanotubes as interconnects in integrated circuits.