Copper Silicide Research Articles

Feasibility study on the use of Cu(Co) alloy for barrierless copper metallization

In the present study, the properties of Cu(Co) alloy films were studied to evaluate their potential use as alloying elements for copper metallization. The Cu(Co) films were deposited on SiO2/Si substrates using magnetron sputtering technique. Cu(Co)/SiO2/Si structures were subsequently annealed in the temperature range of 300–600°C to determine the diffusion barrier characteristics of the films. Thereafter samples were characterized using four-point probe measurements, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron and transmission electron microscopy. It was found that the Cu(Co) films were preferentially orientated at (111) plane. No copper silicide was detected in the Cu(Co) films annealed up to 500°C. A Co-containing thin layer was found at the Cu (Co)/SiO2 interface. In addition, well-defined interfaces were obtained for the sample annealed at 500°C. There was no evidence of inter-diffusion between Cu and the substrate.

Magnetic properties of Co films grown on the modified Si(111) surface

The magnetic properties and domain structure of epitaxial Co films grown on a modified Si(111) surface were studied. First, the processes of growth of copper silicide nanostructures on the Si(111) surface were investigated. Copper silicide clusters were formed on the Si(111)-5.55 × 5.55-Cu surface at a substrate temperature of ∼550°C. It was established that the nanostructures formed have a perfect faceting, and the lateral edges and long wire side are oriented along the Si〈110〉 crystallographic directions. Then, Co films were deposited on the formed structures. The investigation of the coercive force and reduced remanent magnetization showed that the Co(111) films have the sixth-order crystalline anisotropy. It was found that the coercive force of the Co films deposited on the Cu buffer layer is approximately six times less than that of the Co films deposited on the Si(111)-5.55 × 5.55-Cu surface and Si(111)−5.55 × 5.55-Cu/(Cu-Si) cluster surface.

Preparation and Performance of the Room‐Temperature‐Cured Heat‐Resistant Phosphate Adhesive for C/C Composites Bonding

Carbon/carbon(C/C) composites were bonded with a phosphate adhesive prepared from H3PO4 (orthophosphoric acid) and Al(OH)3 as the matrix and Si and CuO as the inorganic fillers. The mechanical properties were tested at room temperature after the bonded specimens were treated from RT to 1500°C. The results showed that the addition of CuO could greatly improve the adhesive's mechanical properties due to the formation of CunSi (copper silicides). The shear strength of bonded specimens could be up to 8.2 MPa without heat treatment and remain above 2 MPa within the whole heat‐treatment temperature range.

Catalyst-free synthesis of Si-SiOx core-shell nanowire anodes for high-rate and high-capacity lithium-ion batteries.

Si-SiOx core-shell nanowires (NWs) ranging from 10 to 30 nm in diameter are prepared by a simple evaporation of silicon monoxide and control of substrate temperatures without any catalyst. The Si-SiOx NWs grown at 735 and 955 °C are strongly anchored to the Cu current collector by forming copper silicide at the interface between Si and Cu, and subsequently used as anodes in lithium-ion batteries, in which no binder or conducting materials are used. The Si-SiOx NWs anodes show excellent electrochemical performances in terms of capacity retention and rate capability. In particular, the Si-SiOx NW anode grown at 955 °C shows a reversible capacity of ∼1000 mAh g(-1) even at a high-rate of 50 C. This catalyst-free synthetic route of Si-SiOx NWs that are strongly anchored to the Cu current collector opens up an effective process for fabricating other high-capacity anodes in lithium-ion batteries (LIBs).

The effects of nitrogen incorporation on the properties of atomic layer deposited Ru thin films as a direct-plateable diffusion barrier for Cu interconnect

N-incorporated Ru films were deposited by atomic layer deposition (ALD) at a deposition temperature of 270°C using 1-isopropyl-4-methylbenzene-cyclohexa-1,3-dienyl ruthenium and N2/H2 mixture plasma as the precursor and reactant, respectively. The N content in the ALD-Ru films was controlled by changing the gas ratio [N2 versus the total gas (N2+H2) flow rates] in the reactant from 0.82 to 1. Secondary ion mass spectrometry depth profiling revealed an increase in N content in the film with increasing gas ratio. The amount of N in the ALD-Ru films had a considerable effect on the film properties, such as resistivity, crystallinity and microstructure. Although the resistivity of the pure ALD-Ru film was ~19μΩcm, the N-incorporated ALD-Ru films deposited with a gas ratio of 0.86 (N/Ru: ~0.38) showed a resistivity of ~340μΩcm, which increased continuously with increasing gas ratio. X-ray and electron diffraction revealed degradation in film crystallinity and decrease in grain size with increasing N incorporation into ALD-Ru films. Transmission electron microscopy showed that N-incorporated ALD-Ru films formed nanocrystalline and non-columnar grain structures. This is in contrast to that observed in the pure ALD-Ru film, which had a polycrystalline columnar grain structure. The growth rate of a representative N-incorporated Ru film deposited with a gas ratio of 0.86 showed a linear dependency on the number of ALD cycles; growth rate of 0.051nm/cycle at short incubation cycles of ~3. The step coverage was approximately 98% over the trench structure (aspect ratio: 4.5) with a top opening width of 25nm. The direct plating of Cu on an optimized N-incorporated ALD-Ru film (5nm in thickness) was possible. The structure of Cu (80nm)/N-incorporated ALD-Ru (8nm)/Si was found to be stable without the formation of copper silicide after annealing at 600°C for 30min.

Investigation of the Co Films Growth on Si (111) Surface with Copper Silicide Nanostructures

In this study the features of the growth processes of copper silicide nanostructures on Si (111) were investigated. The nanostructures were grown by molecular beam epitaxy. It has been shown that the islands and nanowires are formed at the substrate temperature 550°C. The nanostructures have ideal facets and lateral edges. The long side of nanowires is oriented along the crystallographic direction <110> Si. We have shown that there is a range of thicknesses at which nanowires generally grow.

TaCx Thin Films Prepared by Atomic Layer Deposition as Diffusion Barriers for Cu Metallization

TaCx films were deposited by atomic layer deposition (ALD) using tris (neopentyl) tantalum dichloride, (Ta[CH2C(CH3)3]3Cl2) and H2 plasma as the precursor and reactant, respectively, at substrate temperatures ranging from 200°C to 400°C. The ALD–TaCx films with the formation of nanocrystalline structures and a rock‐salt phase were confirmed by X‐ray and electron diffraction. The ALD temperature window was found to be 225°C–300°C with a growth rate of ~0.11 nm per cycle. The resistivity of the ALD–TaCx films was dependent on the microstructural features, such as the grain size and crystallinity, as well as their composition (C/Ta ratio), and the presence of impurities in the films, which could be controlled by varying the deposition parameters, such as the deposition temperature and reactant pulse conditions. With increasing deposition temperature and reactant pulse time, Ta‐rich films with a low Cl impurity concentration and larger grain size were obtained. The film with a resistivity less than 400 μΩ cm was obtained at 300°C, which was within the ALD temperature window, by optimizing the H2 plasma pulse time. The step coverage of the film deposited at 300°C was approximately 100% over the trench structure (top opening width of 25 nm) with an aspect ratio of ~4.5. The performance of the ALD–TaCx films deposited under the optimized conditions was evaluated as a diffusion barrier for the Cu interconnects. The structure of Cu (100 nm)/ALD–TaCx (5 nm)/ Si was stable without the formation of copper silicide after annealing at 600°C for 30 min.

Growth kinetics and interface structure of copper silicides studied by atom probe tomography

AbstractLaser‐assisted atom probe shows a unique potential in the analysis of embedded Si/metal interfaces, owing to its ability to deliver 3D information with atomic resolution. The interface structures in tri‐layer specimens Cu/amorphous Si/Cu are investigated by this technique. For amorphous Si (a‐Si) deposited on Cu, a sharp transition occurred with an interface width of 2.4 nm. On the contrary, a much broader mixed zone, 5.3 nm wide, is formed when Cu is deposited on top of a‐Si. Only in the latter case, brief annealing leads to immediate nucleation of the Cu3Si. Secondary neutral mass spectrometry confirmed independently the existence of this asymmetry in phase formation and demonstrates linear growth kinetics of the silicide. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Carbon mediated reduction of silicon dioxide and growth of copper silicide particles in uniform width channels

We show that surface arc-discharge deposited carbon plays a critical intermediary role in the breakdown of thermally grown oxide diffusion barriers of 90 nm on a silicon wafer at 1035 °C in an Ar/H2 atmosphere, resulting in the formation of epitaxial copper silicide particles in ≈ 10 μm wide channels, which are aligned with the intersections of the (100) surface of the wafer and the {110} planes on an oxidized silicon wafer, as well as endotaxial copper silicide nanoparticles within the wafer bulk. We apply energy dispersive x-ray spectroscopy, in combination with scanning and transmission electron microscopy of focused ion beam fabricated lammelas and trenches in the structure to elucidate the process of their formation.

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.

Cu induced morphology changes at Pb/Si (1 1 1) interface: Separation of “5 × 5”-Cu structure into individual domains

The adsorption of small amount of Cu onto 1×1-Pb/Si (111) and √3×√3R30°-Pb/Si (111) coexisting phases was studied with variable temperature scanning tunnelling microscopy and spectroscopy. The most significant features connected with the deposition of copper at room temperature appeared as tiny clusters randomly scattered over smooth 1×1-Pb islands. Behaviour of the clusters at room at low temperature assumed that Cu penetrates through inert 1×1-Pb layer and mixes up with silicon. Moderate thermal treatment of (Cu, Pb)/Si (111) system induced the formation of shallow depressions of variable shape and size that are embedded into 1×1-Pb phase. Tunnelling spectra taken over a particular depression showed the peaks typical for the copper silicides. Moreover, the temperature rise causes the formation of large objects of distinctive hexagonal shape on neighbouring √3×√3R30°-Pb/Si (111) structure. Filled and empty state STM images of the hexagons differ strongly suggesting covalent bonding between constituent atoms. Detailed analysis of the hexagonal objects (and their agglomerates) reveals the specific features of quasi-commensurate 5×5-Cu structure.

Copper silicide/silicon nanowire heterostructures: in situ TEM observation of growth behaviors and electron transport properties

Copper silicide has been studied in the applications of electronic devices and catalysts. In this study, Cu3Si/Si nanowire heterostructures were fabricated through solid state reaction in an in situ transmission electron microscope (TEM). The dynamic diffusion of the copper atoms in the growth process and the formation mechanism are characterized. We found that two dimensional stacking faults (SF) may retard the growth of Cu3Si. Due to the evidence of the block of edge-nucleation (heterogeneous) by the surface oxide, center-nucleation (homogeneous) is suggested to dominate the silicidation. Furthermore, the electrical transport properties of various silicon channel length with Cu3Si/Si heterostructure interfaces and metallic Cu3Si NWs have been investigated. The observations not only provided an alternative pathway to explore the formation mechanisms and interface properties of Cu3Si/Si, but also suggested the potential application of Cu3Si at nanoscale for future processing in nanotechnology.

Low-temperature growth of bamboo-like multi-walled carbon nanotubes over an atomic layer epitaxy-Cu/SiO2catalystvia metal-support interaction

The well-controlled growth of carbon nanotubes (CNTs) at low temperature (< 1073 K) using non-iron group metal catalysts remains a challenge. Here, we report that CNTs can be grown at 773–1173 K over an atomic layer epitaxy (ALE) prepared copper catalyst (ALE-Cu/SiO2) using chemical vapour deposition in helium diluted ethylene. At the same reaction conditions, only amorphous carbon can be generated over an impregnation (IM) method prepared copper catalyst (IM-Cu/SiO2). A metal-support interaction (MSI) model is proposed to describe the interaction between the ALE prepared Cu nanoparticles (NPs) and SiO2 support through the results of temperature programmed reduction profiles, X-ray photoelectron spectra and in situ X-ray diffraction (XRD) patterns. Structurally stabilised CuNPs in ALE-Cu/SiO2 catalyst indicate that the strong MSI site of CuNPs and/or copper silicide (Cu3Si) evidenced by in situ XRD patterns would be the active centers to fabricate CNTs. Our observations provide new insights into controlling the CNT growth at low-temperatures over non-ferromagnetic catalysts.

Solution-phase synthesis of single-crystal Cu3Si nanowire arrays on diverse substrates with dual functions as high-performance field emitters and efficient anti-reflective layers

There is strong and growing interest in applying metal silicide nanowires as building blocks for a new class of silicide-based applications, including spintronics, nano-scale interconnects, thermoelectronics, and anti-reflective coating materials. Solution-phase environments provide versatile materials chemistry as well as significantly lower production costs compared to gas-phase synthesis. However, solution-phase synthesis of silicide nanowires remains challenging due to the lack of fundamental understanding of silicidation reactions. In this study, single-crystalline Cu3Si nanowire arrays were synthesized in an organic solvent. Self-catalyzed, dense single-crystalline Cu3Si nanowire arrays were synthesized by thermal decomposition of monophenylsilane in the presence of copper films or copper substrates at 420 to 475 °C and 10.3 MPa in supercritical benzene. The solution-grown Cu3Si nanowire arrays serve dual functions as field emitters and anti-reflective layers, which are reported on copper silicide materials for the first time. Cu3Si nanowires exhibit superior field-emission properties, with a turn-on-voltage as low as 1.16 V μm(-1), an emission current density of 8 mA cm(-2) at 4.9 V μm(-1), and a field enhancement factor (β) of 1500. Cu3Si nanowire arrays appear black with optical absorption less than 5% between 400 and 800 nm with minimal reflectance, serving as highly efficient anti-reflective layers. Moreover, the Cu3Si nanowires could be grown on either rigid or flexible substrates (PI). This study shows that solution-phase silicide reactions are adaptable for high-quality silicide nanowire growth and demonstrates their promise towards fabrication of metal silicide-based devices.

Transmission electron microscopy analysis of extended defects in multicrystalline silicon using in‐situ EBIC/FIB sample preparation

AbstractThis paper reports results of microstructural investigations of block cast multicrystalline silicon materials deliberately contaminated with iron and copper impurities from the melt. Electron microscopy techniques have been used to study interactions of grain boundaries, light element impurities such as nitrogen and oxygen, and metal impurities. The key to get access to extended defects typically present in a small density is the recently developed in‐situ EBIC/FIB approach to sample preparation.Special attention is drawn to oxygen and nitrogen containing precipitates at grain boundaries and resulting secondary defects. Strong accumulation of copper impurities is observed which is related to reduced excess carrier lifetimes in these regions. It is shown that copper silicide precipitation mainly accounts for local dislocation networks with a high recombination activity. These observations provide evidence that decoration of grain boundaries with light element contaminants leads to efficient nucleation of metal impurity precipitates. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Growth of Crystalline Copper Silicide Nanowires in High Yield within a High Boiling Point Solvent System

Here, we report the formation of high density arrays of Cu15Si4 nanowires using a high boiling point organic solvent based method. The reactions were carried out using Cu foil substrates as the Cu source with nanowire growth dependent upon the prior formation of Cu15Si4 crystallites on the surface. The method shows that simple Si delivery to metal foil can be used to grow high densities of silicide nanowires with a tight diameter spread at reaction temperatures of 460 °C. The nanowires were characterized by high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), and X-ray photoelectron spectroscopy (XPS), and electrical analysis showed that they possess low resistivities.

Copper Silicides with the Highest Lithium Content: Li7CuSi2 Containing the 16‐Electron Group [CuSi2]7− and Li7.3CuSi3 with Heterographene Nets ${{{\hfill 2\atop \hfill \infty }}}$[CuSi]3.3−

Jede Menge Lithium: Die Silicide Li7CuSi2, mit dem linearen Zintl-Anion [Si-Cu-Si]7− (siehe Bild), und Li7.3CuSi3 sind die Verbindungen mit dem höchsten Lithiumgehalt in diesem ternären System. Die Kristallstrukturen und Bindungsverhältnisse beider Verbindungen werden besprochen.

Copper Silicides with the Highest Lithium Content: Li7CuSi2 Containing the 16‐Electron Group [CuSi2]7− and Li7.3CuSi3 with Heterographene Nets ${{{\hfill 2\atop \hfill \infty }}}$[CuSi]3.3−

Incredibly rich in lithium: The ternary silicides Li7CuSi2 with the linear [Si-Cu-Si]7− Zintl anion (see picture) and Li7.3CuSi3 are compounds with the highest lithium content in the ternary system. The crystal and electronic structures of both compounds are discussed.

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.

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.