Effects of molybdenum, silver dopants and a titanium substrate layer on copper film metallization

Annealing of 100 nm-thick Cu, Cu(Mo) and Cu(Ag) films was carried out to investigate the effect of dopant atoms on the films. Molybdenum (Mo) and silver (Ag) were selected as immiscible dopants for out-diffusion studies. A thermally grown SiO₂ layer and a sputtered Ti layer were used as substrates. The dopant and substrate effects were characterized in terms of surface morphology, resistivity, preferred orientation, and diffusional characteristics. The lowest observed resistivity was 2.32 · cm in the Cu(Ag) film, which was lower than that in a pure Cu film of the same thickness. Ag addition enhanced the surface morphology and thermal stability of the Cu(Ag) films. The highest thermal stability was obtained in the case of a Cu(Mo)/Ti film which maintained film integrity to 800°C. A Ti substrate enhanced Cu(111) texture growth. A highly oriented Cu(111)-texture was obtained in the Cu(Mo)/Ti films. Cu diffusion through the Ti layer was limited in the (111)-textured Cu(Mo)/Ti films, which showed good potential as a diffusion barrier.     

Effects of temperature/humidity treatments on the peel strength of CuCr alloy films on polyimide

A single layer of CuCr alloy was sputter deposited on polyimide films instead of Cu/Cr double layers. The adhesion strengths of the metal/polyimide thin films were measured by the peel test. In order to study the effects of temperature and humidity on the adhesion strength, 85 C/85% R.H. (T/H) treatments were applied to the specimens. Results showed that the peel strength without T/H treatments increased proportionally with the Cr content in the CuCr alloy layer(x) up to 17 at%, and then saturated. Among the samples studied, the peel strength decreased with hold time under T/H conditions for all the cases, but most drastically for the sample with x=8.5. The very poor peel strength of that sample (x=8.5) was attributed to the occurrence of interfacial failures, which were thought to take place along CuCr oxide/polyimide interfaces.     

Diffusion and adhesion properties of Cu films on polyimide substrates

Copper thin films were prepared on polyimide (PI) substrates by physical vapor deposition (PVD) and chemical vapor deposition (CVD). Titanium nitride (TiN) diffusion barrier layers were deposited between the copper films and the PI substrates by PVD. Auger electron spectroscopy compositional depth profile showed that TiN barrier layer was very effective in preventing copper diffusion into PI substrate even after the Cu/TiN/PI samples were annealed at 300 °C for 5 h. For the as-deposited CVD-Cu/PI, CVD-Cu/TiN/PI, and as-deposited PVD-Cu/PI samples, the residual stress in Cu films was very small. Relatively larger residual stress existed in Cu films for PVD-Cu/TiN/PI samples. For PVD-Cu/TiN/PI samples, annealing can increase the peeling strength to the level observed without a diffusion barrier. The adhesion improvement of Cu films by annealing treatment can be attributed to lowering of the residual tensile stress in Cu films.     

Enhanced adhesion of plasma-sputtered copper films on polyimide substrates by oxygen glow discharge for microelectronics

Enhanced plasma-sputtered copper film adhesion onto polyimide substrates treated by oxygen glow discharge was investigated. The peel test demonstrates this improvement, with peel strengths of 0.7-1.2 g/mm for copper films prepared on un-modified polyimide substrates and 195.5-262.2 g/mm for copper films on oxygen plasma-modified polyimide substrates at certain plasma conditions. The enhanced adhesive strengths of plasma-sputtered copper films onto polyimide substrates by oxygen plasmas are due mainly to the increased surface energies of the polyimide substrates. Contact angle measurements indicate that the surface energies of polyimide substrates were greatly increased by oxygen plasmas. X-ray photoelectron spectroscopy analysis shows that the increased surface energies of polyimide substrates using oxygen plasmas occur because of the increased oxygen surface concentration and the increased C-O bond proportion.     

A study on the tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) coated with a Ni-P layer

The tribological behaviour of ultra-high molecular weight polyethylene (UHMWPE) has been investigated using friction and wear tests at room temperature (25 °C) and also at a low temperature (-20 °C) in air, vacuum or CO₂ saturated vapour for UHMWPE rubbing against itself and also against a steel counterpart. A sticking phenomenon took place in saturated CO₂ vapour at low temperature (-20°C), which was produced by severe adhesion between the UHMWPE polymer rubbing pair. The sticking phenomenon was prevented by a Ni-P coating deposited on the surface of the UHMWPE by means of high-speed electro-plating. Non-continuous transfer films of UHMWPE on the Ni-P surface layer and the steel surface were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The studied coating has a solid lubrication character, so that its sliding friction coefficient and relative wear weight loss of the pin w _t, decreased; the wear mechanism changed from adhesive wear to surface fatigue wear. It is concluded that the tribological behaviour of the UHMWPE polymer could be improved with a metallic coating, such as the Ni-P coating used in this study.     

Electrical properties of non c-axis oriented SrBi2(Ta0.95V0.05)2O9 thin films

Pulsed laser deposition technique was used to grow off c-axis oriented SrBi₂(Ta_0.95V_0.05)₂O₉ (SBTV) ferroelectric thin films. X-ray diffraction studies revealed the c-axis suppression in the films grown at lower substrate temperature (350°C) followed by annealing at higher temperatures (650°C). In-plane lattice parameters of the films were decreased with increase in annealing temperature. SBTV films annealed at 750°C exhibited enhanced ferroelectric properties with remanent polarization (2P _r) of 31.5 C/cm² and coercive field (E _c) of 157 kV/cm. The dielectric permmitivity of the films increased with increase in annealing temperature and it was attributed to the grain size dependence. The films annealed at 750°C showed maximum value of dielectric permittivity 172 with a tangential loss of 0.1, at 100 kHz. Higher value of dissipation factor at lower annealing temperature is explained in terms of space charge accumulation at grain boundaries. The leakage current densities of the films follow ohmic behavior at low field regime and space charge limited current dominates at higher fields.     

Low energy O2 and N2O ion beam modification of polyimide for improving adhesive strength of Cu/PI in roll-to-roll process

To enhance the weak mechanical durability of directly deposited copper layers on polyimide (PI) film due to their poor adhesive strength, a continuous roll-to-roll process involving surface modification using a reactive ion beam irradiation and in-situ deposition process is studied. The polyimide film is modified by an ion source with a linear stationary plasma thruster (LSPT) in the vacuum roll-to-roll process. An O₂ ion beam, with beam energy of 214 eV and beam current density of 0.78 mA/cm², and N₂O ion beam, with 220 eV and 0.69 mA/cm², irradiate PI film in winding speed of 0.5 m/min. The surface energy increases from 38 mN/m for the pristine PI film to 80 mN/m after beam irradiation at an ion fluence of 3.5 × 10¹⁶ ions/s. After beam irradiation, a 10 nm thick tie layer and 200 nm thick copper layer are successively deposited by in-situ DC magnetron web coating. The peel strength of the copper layer on the PI film is enhanced from 0.4 kgf/cm without ion beam treatment to 0.71 kgf/cm after O₂ beam treatment and to 0.75 kgf/cm after N₂O beam treatment. This enhancement is closely related to the increase in the polar force originating from the formation of hydrophilic CO (carbonyl) groups on the modified PI surface.     

Electrodeposition of n-type and p-type ZnSe thin films for applications in large area optoelectronic devices

ZnSe layers have been grown by a low temperature (65 °C) electrochemical deposition technique in an aqueous medium. The resulting thin films have been characterized using X-ray diffraction (XRD) and a photoelectrochemical (PEC) cell for determination of the bulk properties and electrical conductivity type. XRD patterns indicate the growth of ZnSe layers with (1 1 1) as the preferred orientation. PEC studies show p-type semiconducting properties for the as deposited layers and n-type ZnSe can be produced by appropriate doping. Annealing at 250 °C for 15 min improves the crystallinity of the layers and the photoresponse of the ZnSe/electrolyte junction. © 1998 Kluwer Academic Publishers     

Preparation and characterization of Ce-doped BaTiO3 thin films by pulsed laser deposition

Thin films of BaTiO₃ doped with 5.5 mol%CeO₂ have been deposited on Pt/Si substrate by pulsed laser deposition. These films crystallize on the tetragonal BaTiO₃ structure without any preferential orientation. Ce-doped BaTiO₃ films deposited by PLD at 675°C in 30 Pa ambient oxygen exhibits a smooth surface: mean surface roughness (Rms) of 48 nm, mean size of grain of 40 Å, average size of aggregates of 315 nm. Thin films as prepared presented good dielectric characteristics: dielectric constant and dielectrics loss (tan ) at a frequency of 1 KHz were 220 and 0.2, respectively. The temperature dependence of dielectric constant exhibited a diffuse ferroelectric to paraelectric phase transition at about 0–10°C. The ferroelectric nature of Ce-doped BaTiO₃ film was confirmed by the hysteresis of the C-V curves.     

Structural factors determining the change in young's modulus of polycrystalline carbon materials in heat treatment

The structural factors determining the change in Young's modulus of polycrystalline carbon materials based on fired coke (type ARV) and unfired coke (type MPG) in relation to treatment temperature t in the 1000–3200°C range were investigated. The microstructure of the specimens was characterized by the density and coefficient of coherence, which was determined from the ratio of the electrical conductivity of the material to the electrical conductivity of its porosity-free volumes. The degree of perfection of the layers of specimens with a graphitic structure was determined from the magnetic resistance. It was established that the change in Young's modulus in this range of treatment temperatures is determined by the change in Young's modulus of the porosity-free volumes E₀ c₄₄ and in the coefficient of coherence. The value of E₀ decreases sharply with an increase in t from 1000 to 1800°C and after 2400°C it is practically independent of the degree of perfection of the graphite-like layers. The coefficient of coherence increases in density with an increase in t from 1000 to 2000°C and decreases as the result of appearance of disk-shaped cracks in a change in t from 2400 to 3200°C. The physical reasons for the rules found were analyzed.Translated from Problemy Prochnosti, No. 1, pp. 69–73, January, 1990.     

Stability of nickel coated sapphire whiskers

The effect of high temperature annealing (1100 to 1300° C) on the stability of nickel coated purified sapphire whiskers has been investigated. It was found that the initially coherent coating spheroidized to form a series of partially adherent nickel particles, which increased in size with continued time at temperature. The time for complete adhesion of the particles, which was established from the product of the number and volume of particles per unit area of surface, decreased from 72 h at 1100° C to 3 h at 1300° C, giving an activation energy of 70 kcal/mol. In addition at 1300° C, after 8 h, there was evidence for whisker breakdown from a sapphire-nickel reaction.     

The effect of inductively coupled plasma treatment on the surface activation of polycarbonate substrate

The effect of inductively coupled plasma (ICP) treatment on the surface activation of the polycarbonate (PC) substrate was studied. At high working pressure and ICP power the wetting angle could be decreased as low as 5°. The wetting angle was decreased effectively when the impinging ions had proper energy ∼ 8 eV. Excess ion energy interfered with reducing the wetting angle. The polar functional group (CO) significantly affected the change of surface energy. Compared with the deposited Al₂O₃ film on the PC substrate treated at a low wetting angle, that on the PC substrate treated at a high wetting angle adhered very well.     

Polyimide-silica microcomposite films

Planarizing films of fine-grained silica embedded in polyimide have been prepared by a spincoating technique and their structure has been investigated by optical and electron microscopy. The films were found to be diphasic. A silica content near 9 vol% yields a well mixed silica/polyimide composite which is homogeneous down to nanometre scale and has good planarization characteristics. Films with contents of 3 and 6 vol% silica have rough surfaces and exhibit two forms of segregation. In the 3% case, elongated inclusions of such silica/polyimide material appear at 100-m islands in a pure polyimide matrix. In the 6% case, the pure polyimide appears as 100-m elongated lakes surrounded by silica/polyimide material.     

等离子体轰击致聚酰亚胺表面亲水性研究

等离子体轰击聚酰亚胺表面会提高挠性印制电路板中溅射铜膜与聚酰亚胺基板的附着力,同时聚酰亚胺表面亲水性随之改变.本文通过改变轰击等离子体种类、轰击电流、轰击时间和轰击气压等条件,研究这些工艺参数与聚酰亚胺表面亲水性的相互关系.在等离子体轰击处理后的聚酰亚胺上磁控溅射镀铜并电镀加厚,利用剥离强度测试仪测量铜膜与聚酰亚胺基板的附着力,并分析亲水性与附着力之间的关系.研究发现,等离子体轰击可以增强聚酰亚胺的亲水性及聚酰亚胺基板与铜膜的附着力,且亲水性越好的样品,溅射镀铜后铜膜与基板的附着力也越好,并得到了等离子体轰击参数与亲水性的关系;研究表明可以把测量亲水性作为聚酰亚胺表面等离子体轰击效果的一种评价方法.     

Corrosion resistance and microstructure of stainless steel modified by pulsed high energy density plasma

Pulsed high energy density plasma has been used to deposit aluminum nitride films on the surface of the 1Cr18Ni9Ti stainless steel (0.1% C, 18% Cr, 9% Ni, 0.8% Ti). The formed films are composed of nanocrystalline-structured aluminum nitride phase, whose crystal sizes are about 10 nm. Transition areas are formed across the film to the substrate and strengthen the adhesion between them. The nanocrystalline-structured aluminum nitride films contribute to the improvement of the corrosion resistance of the modified stainless steel, whose corrosion rate has been reduced by about ten times compared with that of the unmodified stainless steel.     

Air-plasma treated polyethylene fibres: effect of time and temperature ageing on fibre surface properties and on fibre-matrix adhesion

The effect of a low energy air-plasma treatment of extended chain polyethylene (ECPE) fibres (Spectra®900) on the adhesion with a matrix of epoxy resin has been studied. Surface energies of fibre and matrix were calculated by contact angles, measured with a Wilhelmy microbalance in different liquids, and the adhesion between fibres and the matrix was evaluated through a pull-out test. The results showed an increase in fibre-matrix adhesion by a factor of ca. 1.5 calculated by surface energy measurements, and by a factor of ca. 4 measured by the pull-out tests. Time (up to six months) and temperature (in the range 20–120 °C for 2 h) ageing caused some decrease in adhesion with respect to the values evaluated just after the fibre plasma treatment. The plasma treatment did not affect the fibre's mechanical properties.On leave from Dept. of Chemistry, University of Naples Federico II, Italy.     

Thickness dependence of H2 gas sensor in amorphous SnQx films prepared by ion-beam sputtering

Amorphous SnO_x films were deposited by ion-beam sputtering on sintered alumina substrates. Amorphous film sensors were prepared by annealing the films at 300° C for 2 h in air. The thickness dependence of resistivity and hydrogen gas sensitivity were measured at 150° C over the thickness range 1 to 700 nm. A resistivity maximum was observed in ultrathin films. Resistivity increased by three orders of magnitude with increasing film thickness from 0.9 to 7.4 nm and then decreased by five orders of magnitude from 7.4 to 35 nm. Ultrathin film sensors showed sensitivity maxima around a thickness of 10 nm. Sensitivity and resistivity of ultrathin films were significantly influenced by the thermal expansion coefficient and the surface state of the substrate.     

Low-temperature plasma-enhanced chemical vapor deposition of tungsten and tungsten nitride

Tungsten and tungsten nitride layers have been deposited by plasma-enhanced chemical vapor deposition (PECVD). Tungsten layers deposited at low deposition temperatures T150 °C using this method showed good uniformity over dielectric and silicon substrate areas. As the deposition temperature decreased, the silicon consumed during the deposition reaction decreased, at T150 °C no silicon consumption was measurable. PECVD tungsten nitride layers were deposited directly on oxidized silicon substrates with no requirement for a nucleation layer. As the NH₃ flow rate was increased, whilst maintaining all other parameters constant, deposited layers were found to change from metal tungsten to tungsten-rich amorphous layer to W₂N. The resistivity of the layers was found to be high compared to published literature for higher-temperature deposited layers. The high resistivity is attributed to the incorporation of fluorine into the layer at low deposition temperatures. A deposition process was established for smooth amorphous tungsten-rich W _x N layers at 150 °C.     

Growth of n-type and p-type ZnSe thin films using an electrochemical technique for applications in large area optoelectronic devices

ZnSe layers have been grown by a low temperature (65 °C) electrochemical deposition technique in an aqueous medium. The resulting thin films have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive analysis by X-rays (EDAX), glow discharge optical emission spectroscopy (GDOES) and X-ray fluorescence (XRF) for bulk material properties. A photo-electrochemical (PEC) cell and an optical absorption method have been used for determination of the electrical and optical properties of the thin films. XRD patterns indicate the growth of ZnSe layers with (1 1 1) as the preferred orientation. The XPS spectra are similar to those of commercially available ZnSe and the EDAX, GDOES and XRF also indicate the presence of Zn and Se in the layers. PEC studies show p-type semiconducting properties for the as deposited layers and n-type ZnSe can be produced by appropriate doping. Optical absorption is maximum around 460 nm indicating a band gap of 2.7 eV. Annealing at 200 °C for 15 mins improves both the crystallinity of the layers and the photoresponse of the electrolyte/ZnSe liquid/solid Schottky junction. © 1998 Chapman & Hall     

Preparation of CuInSe2 thin films by selenization of co-sputtered Cu–In precursors

CuInSe2 thin films have been prepared by high Se vapor selenization of co-sputtered Cu–In alloy precursors within a partially closed graphite container. Cu–In alloys with different compositions were investigated. X-ray diffraction (XRD) analysis of the films showed mainly CuIn2 and Cu11In9 phases and the Cu11In9 peak intensity was found to increase as the alloy composition tended towards Cu-rich. A linear dependence of the alloy composition on the Cu/In deposition power was observed from energy dispersive analysis by X-rays (EDX). A three-fold volume expansion was exhibited by all the CuInSe2 films after selenization at 500–550 °C. Scanning electron microscopy (SEM) analysis of the films showed large and densely packed crystal structures with sizes above 5 m. The CuInSe2 films exhibited single phase chalcopyrite structure with preferential orientation in the (1 1 2) direction. The EDX composition analyses of the films showed Cu/In ratio ranging from 0.43 to 1.2, and Se/(Cu+In) ratios from 0.92 to 1.47. The measured film resistivities varied from 10-1 to 105 cm. The Cu–In alloy precursors with Cu/In ratio less than 0.70 were found to form CuIn3Se5 a defect chalcopyrite compound. All films were Se rich, with the exception of samples with very high Cu content.© 1998 Kluwer Academic Publishers