Microstructure examination of copper wafer bonding

The microstructure morphologies and oxide distribution of copper bonded wafers were examined by means of transmission electron microscopy (TEM) and energy dispersion spectrometer (EDS). Cu wafers exhibit good bond properties when wafer contact occurs at 400°C/4000 mbar for 30 min, followed by an anneal at 400°C for 30 min in N₂ ambient atmosphere. The distribution of different defects showed that the bonded layer became a homogeneous layer under these bonding conditions. The oxidation distribution in the bonded layer is uniform and sparse. Possible bonding mechanisms are discussed.     

Temperature and duration effects on microstructure evolution during copper wafer bonding

Interfacial morphologies during Cu wafer bonding at bonding temperatures of 300–400°C for 30 min followed by an optional 30-min or 60-min nitrogen anneal were investigated by means of transmission electron microscopy (TEM). Results showed that increased bonding temperature or increased annealing duration improved the bonding quality. Wafers bonded at 400°C for 30 min followed by nitrogen annealing at 400°C for 30 min, and wafers bonded at 350°C for 30 min followed by nitrogen annealing at 350°C for 60 min achieve the same excellent bonding quality.     

Thermal stability of heavily tellurium-doped InP grown by metalorganic molecular beam epitaxy

The thermal stability of tellurium in InP has been examined in samples doped with Te up to an electron concentration of 1.4 × 10²⁰ cm⁻³. Annealing was conducted using rapid thermal annealing for a period of one minute at temperatures over the range 650–800°C. Secondary ion mass spectroscopy analysis showed virtually no change in the Te profile before and after annealing, even at the highest annealing temperatures. High resolution x-ray diffraction and Hall measurements revealed a general decrease in the lattice strain and carrier concentration for annealing temperatures above 650°C. No evidence of strain relief was found in the form of cross-hatching or through the formation of a dislocation network as examined by scanning electron microscopy or transmission electron microscopy (TEM). These results are most likely due to the formation of Te clusters, though such clusters could not be seen by crosssectional TEM.     

A Study on Sputtered Bi-Te Thermoelectric Films with Various Compositions: Microstructure Evolution and the Effects on Thermoelectric and Electrical Properties

This study examined the sensitive effects of composition on the microstructure evolution and thermoelectric properties of sputtered Bi-Te films. Bi-Te films of various Te compositions (49 at.% to 60 at.%) were grown by cosputtering deposition and annealed at 200°C for different durations. We examined the microstructure of the films using x-ray diffraction (XRD) and transmission electron microscopy (TEM), and measured the electronic transport and thermoelectric properties. As the Te composition of the films changed from 49 at.% to 60 at.%, the phase of the as-sputtered film changed from the rhombohedral BiTe-type phase to the metastable rock-salt phase, which eventually transformed to the Bi₂Te₃-type phase upon annealing, instigating microstructure evolution. This phase transformation profoundly influenced the electrical and thermoelectric properties of the films.     

Strain relief in compositionally graded Si1-xGex formed by high dose Ion implantation

Strain relief mechanisms have been investigated in alloys of Si and Ge formed by high dose ion implantation followed by solid phase epitaxy. Both compressive and tensile strain states were studied by implanting: (i) 200 keV Ge into (001) Si to form Si-rich alloys and (ii) 150 keV²⁹Si into (001) Ge to form Ge-rich alloys. We report that Si-rich compressively strained alloys above a critical implant dose relax via the introduction of a/6(112) partials (bounding stacking faults) when regrown by solid phase epitaxy below ≈600° C. Alloys formed by implanting Si into (001) Ge and regrown at 450° C also undergo strain relaxation above a critical dose but, in this case, relaxation proceeds via the introduction of planar defects + partials, Lomers, and 60° dislocations. The high dose ion implantation technique produces alloys in which the concentration, and hence lattice mismatch, is a Gaussian function of depth from the surface. In this work we present a modification of the conventional critical thickness calculation which includes: (i) balancing forces acting on defects in a strain gradient to define an interface above which strain relief occurs and (ii) integration of the strain energy in the portion of the compositionally graded film above this interface. Critical dose implant plots based on these calculations are presented. The model provides a good fit to cross-sectional and TEM observations of regrown alloys with implant doses above and below the predicted critical dose. A TEM characterization of the strain relieving defects for both compressive and tensile films is presented.     

Large‐Scale Synthesis,Annealing, Purification,and Magnetic Properties of Crystalline Helical Carbon Nanotubes with Symmetrical Structures

Crystalline helical carbon nanotubes (HCNTs) are synthesized as the main products in the pyrolysis of acetylene at 450 °C over Fe nanoparticles generated by means of a combined sol–gel/reduction method. Transmission electron microscopy (TEM) images reveal that there are two HCNTs attached to each Fe₃C nanoparticle, and that the two HCNTs are mirror images of each other. Annealing in Ar at 750 °C and purification by immersion in hot (90 °C) HCl solution do not significantly change the structure of the HCNTs, despite the partial removal of Fe nanoparticles by the latter treatment. The magnetic properties of the as‐prepared, annealed, and purified HCNTs have been systematically examined. The annealed sample shows relatively high magnetization due to the ferromagnetic α‐Fe nanoparticles encapsulated in the HCNT nodes. In the case of HCl treatment, relatively pure HCNTs are obtained by the removal of ferromagnetic nanoparticles from the double‐HCNT nodes. The effects of the amount of catalyst used in the synthesis process on the morphology and yield of the carbon products have also been investigated.     

Preparation and Characterization of Silica-Coated CaCu3Ti4O12

Silica was homogeneously coated on the surface of CaCu₃Ti₄O₁₂ (CCTO) particles via the sol–gel method. The obtained powders were characterized by x-ray diffraction analysis, Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM), energy-dispersive spectroscopy, scanning electron microscopy, and zeta potential analysis. The results demonstrate that there were silica layers on the surface of the CCTO particles. Physical and dielectric properties of silica-coated CCTO were also studied. TEM imaging showed that the thickness of the silica layer on the CCTO particles was about 20 nm to 35 nm. The specimen coated with 1.0 wt.% silica showed the maximum relative density of 96.7% with high dielectric constant (12.78 × 10⁴) and low dielectric loss (0.005) at 20°C after sintering at 1000°C for 6 h.     

Morphology and defect structures of GaSb islands on GaAs grown by metalorganic vapor phase epitaxy

The initial nucleation of GaSb on (001) GaAs substrates by metalorganic vapor phase epitaxy has been investigated using transmission electron microscopy (TEM) and high resolution electron microscopy (HREM). TEM results showed that the GaSb islands experience a morphological transition as the growth temperature increases. For growth at 520°C, the islands are longer along the [110] direction; at 540°C, they are nearly square, and at 560°C, they are longer along the direction. Possible mechanisms are proposed to describe such a transition. TEM and HREM examination showed that lattice misfit relaxation mechanisms depend on the growth temperature. For the sample grown at 520°C, the lattice mismatch strain was accommodated mainly by 90° dislocations; for the sample grown at 540°C, the misfit strain was relieved mostly by 90° dislocations with some of 60° dislocations, and for the sample grown at 560°C, the strain was accommodated mainly by 60° dislocations which caused a local tilt of the GaSb islands with respect to the GaAs substrate. The density of threading dislocations was also found to be dependent on the growth temperature. Mechanisms are proposed to explain these phenomena.     

Electroless CoWP as a Diffusion Barrier between Electroless Copper and Silicon

In this work, an electroless CoWP film deposited on a silicon substrate as a diffusion barrier for electroless Cu and silicon has been studied. Four different Cu 120 nm/CoWP/Si stacked samples with 30, 60, 75, and 100 nm electroless CoWP films were prepared and annealed in a rapid thermal annealing (RTA) furnace at 300°C to 800°C for 5 min. The failure behavior of the electroless CoWP film in the Cu/CoWP/Si sample and the effect of CoWP film thickness on the diffusion barrier properties have been investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and sheet resistance measurements. The composition of the electroless CoWP films was 89.4 at.% Co, 2.4 at.% W, and 8.2 at.% P, as determined by energy dispersive X-ray spectrometer (EDS). A 30 nm electroless CoWP film can prevent copper penetration up to 500°C, and a 75 nm electroless CoWP film can survive at least up to 600°C. Therefore, increasing the thickness of electroless CoWP films effectively increases the failure temperature of the Cu/CoWP/Si samples. The observations of SEM and TEM show that interdiffusion of the copper and cobalt causes the failure of the electroless CoWP diffusion barriers in Cu/CoWP/Si during thermal annealing.     

Improvements in the Sintering Behavior and Microwave Dielectric Properties of Geikielite-Type MgTiO3 Ceramics

Microwave dielectric ceramics based on geikielite-type MgTiO₃ were prepared by an aqueous sol–gel process. The precursor powders and dielectric ceramics were characterized by x-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and microwave methods. Highly reactive nanosized magnesium titanate powders with particle sizes of 20 nm to 40 nm were successfully obtained at 500°C as precursors. Sintering characteristics and microwave dielectric properties of MgTiO₃ ceramics were studied as a function of sintering temperature from 1100°C to 1300°C. With increasing sintering temperature, the density, ε _r, and Qf values increased, saturating at 1200°C with excellent microwave properties of ε _r = 17.5, Qf = 156,300 GHz, and τ _f  = ?44 ppm/°C. Correlations between the microstructure and dielectric properties of MgTiO₃ ceramics were also investigated.     

One step synthesis of ZnO nanoparticles in free organic medium: Structural and optical characterizations

Nano-sized ZnO particles are synthesized by the sol–gel method in aqueous medium without any annealing, ripening treatment or organic additive addition. The structure, morphology, and optical properties of these ZnO nanoparticles are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Ultraviolet–visible spectroscopy (UV–vis) respectively. The effect of the synthesis temperature on the morphological (shape and size) and optical properties of these nanoparticles have been examined for temperatures varying from 0 to 80 °C. XRD analysis shows that the as-prepared particles crystallize in the Würtzite hexagonal phase even at very low synthesis temperatures. Meanwhile, Transmission Electron Microscopy observations reveal that the particles present a significant change in shape and size as the temperature increases. They take a flower shape, at very low temperatures, a conical or ellipsoidal shape when the temperature is ranging from 20 °C to 50 °C and a rodlike shape with a hexagonal section at elevated temperatures (>50 °C). Moreover, it has been observed that the increasing of the synthesis temperature leads to a net increase in the average particle size. It affects especially the length in the minor axis direction while the length in the major direction (c-axis) remains nearly constant. Optical properties, carried out by spectrophotometric measurements, indicate that increasing the temperature results in lower band gap energy values.     

Synthesis and opto-electrical properties of Cu2NiSnS4 nanoparticles using a facile solid-phase process at low temperature

Cu2NiSnS4 nanoparticles were prepared for the first time using a facile solid-phase process at a temperature of 180 °C. The crystalline structure, morphology and optical properties of the Cu2NiSnS4 nanoparticles were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM) and ultraviolet-visible (UV-vis) spectrophotometer. The band gap and conversion efficiency of Cu2NiSnS4 nanoparticles were studied at various temperature. The results showed that the Cu2NiSnS4 nanoparticles exhibited an optimum band gap of 1.58 eV and a conversion efficiency of 0.64% at 180 °C, indicating that it maybe be useful in low-cost thin film solar cells.     

Ion implantation damage in GaAs: A TEM study of the variation with ion species and stoichiometry

GaAs samples have been implanted with a dose of 2 × 10¹⁴ cm^?2 of each ion in the following combinations: Ga, As, Ga + As, Se, Ga + Se and As + Se. Implantation was at 200°C, and post implantation annealing at 700°C. Subsequent examination by transmission electron microscopy (TEM) showed clear and reproducible differences in the dislocation loop size and density, depending on the ion species implanted. The simplest results were obtained with the single implants, particularly Ga and As. These observed variations could be explained in terms of point defect populations, and hence rates of annealing at a given anneal temperature, being affected significantly by the stoichiometric effect of the implant. These simpler aspects were also seen to be incorporated in the more complex “dual” implants.     

Investigation of Ti/Al and TiN/Al thin films as the stable ohmic contact for p-type 4H-SiC

Interfacial reactions, surface morphology, and current-voltage (I-V) characteristics of Ti/Al/4H-SiC and TiN/Al/4H-SiC were studied before and after high-temperature annealing. It was observed that surface smoothness of the samples was not significantly affected by the heat treatment at up to 900°C, in contrast to the case of Al/SiC. Transmission electron microscopy (TEM) observation of the Ti(TiN)/Al/SiC interface showed that Al layer reacted with the SiC substrate at 900°C and formed an Al-Si-(Ti)-C compound at the metal/SiC interface, which is similar to the case of the Al/SiC interface. The I-V measurement showed reasonable ohmic properties for the Ti/Al films, indicating that the films can be used to stabilize the Al/SiC contact by protecting the Al layer from the potential oxidation and evaporation problem, while maintaining proper contact properties.     

Structural and electrical properties of stable ni/cr thin films

The electrical and structural properties of nickel-chrome (NiCr) thin film resistors were studied for the effect of post-deposition annealing on stability. The temperature coefficient of resistance (TCR) of sheet resistivities in the range of 100 to 200 Ω/□ could be improved by both air and vacuum annealing to achieve 5 ± 5 ppm/°C over the temperature range of -180° C to +100° C. With stability tests, air annealing proved to be more favorable for stable TCR. Studies via SIMS and ESCA identified surface segregation of Cr whereas TEM micrographs revealed correlating structural transformation of the films upon annealing. An intentional impurity, Si, played an important role in achieving a low TCR.     

Growth of High-Density Self-Aligned Carbon Nanotubes and Nanofibers Using Palladium Catalyst

In this paper we demonstrate vertical self-aligned growth of carbon nanotubes (CNT) and carbon nanofibers (CNF) using 1 nm of Pd as the catalyst material. Results were compared with those obtained using traditional catalysts (Co, Fe, and Ni). Pd is of interest as it has been demonstrated to be an excellent material for electrical contact to nanotubes. CNT were grown using plasma-enhanced chemical vapor deposition (PECVD) at 450°C to 500°C and using atmospheric-pressure chemical vapor deposition (APCVD) between 450°C and 640°C. The results were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. High-density (10¹¹ cm⁻² to 10¹² cm⁻²) self-aligned CNT growth was obtained using APCVD and Pd as the catalyst, while Co and Fe resulted in random growth. TEM revealed that the CNT grown by Pd with PECVD form large bundles of tubes, while Ni forms large-diameter CNF. It was found that the CNT grown using Pd or Ni are of low quality compared with those grown by Co and Fe.     

Preparation and characterization of size controllable spherical silver nanoparticles

By adjusting pH values of reactant system, the mass ratio of stabilizer/water and aging temperature, size controllable spherical silver nanoparticles （NPs） were synthesized. The properties of silver NPs are characterized by X-ray diffrac- tion （XRD）, transmission electron microscope （TEM） and ultraviolet visible （UV-VIS） absorption spectra. Within the pH values of 7.0-11.0, the aging temperature of 80℃ is better to improve silver NPs in shape to nearly sphere, con- centrate size distribution and reduce aggregation than the aging temperature of 25 ℃. The shape and dispersibility of silver NPs are the best when the pH of the reactant system is within 7.0---8.0. With pH of 7.5, aging at 80 ℃, and sta- bilizer/water mass ratio of 1%, the spherical silver NPs with sizes of 50---70 nm were synthesized. The results are promising to be used to synthesize core/shell NPs when silver NPs are as core.     

Effects of high-temperature rapid thermal annealing for seed layers on the crystallographic evolution in hydrothermal ZnO nanostructures

In this work, we investigated effects of high temperature rapid thermal annealing for the zinc oxide (ZnO) seed layers on the growth morphology and crystal orientation of hydrothermal ZnO nanorods (NRs). The seed layers were prepared by sol–gel spin coating and annealed by two-step rapid thermal processes at different peak temperatures ranging from 600 to 900 °C for a short time period of 1 min. The seed layers annealed in a temperature range of 600–800 °C were all polycrystalline; however, they exhibited a highly Zn-deficient amorphous state when annealed at 900 °C as observed by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and cross-sectional transmission electron microscopy (TEM). The vertical NRs normal to the substrate were grown along [001] direction atop the polycrystalline seeds annealed at 600–800 °C, whereas different growth morphology of flower-like NRs was observed on the seeds annealed at 900 °C with the strongest XRD peak along the [100] orientation. From our cross-sectional TEM analysis, this flower-like architecture was initiated from the pioneer crystals laterally grown along [001] direction guiding the subsequent growth of petal NRs oriented by a slight difference in growth direction.     

Formation of nickel disilicide using nickel implantation and rapid thermal annealing

Transmission electron microscopy (TEM), secondary ion mass spectroscopy (SIMS), and x-ray photoemission spectroscopy (XPS) have been used to investigate the nucleation, growth, and ripening behavior of nickel-disilicide precipitates formed by Ni implantation in an amorphous-Si layer on (100) Si and followed by a two-step annealing treatment. The TEM and XPS results show that amorphous-disilicide precipitates are formed in a depth of ∼21 nm in the amorphous-Si layer when pre-annealed at 380°C for 30 sec. It is also shown that the second-step annealing at temperatures in the range of 450–600°C causes the amorphous precipitates to transform to randomly oriented crystalline ones embedded in the amorphous-Si layer. Annealing above 550°C is shown to induce the crystallization of amorphous Si by solid-phase epitaxial growth (SPEG). It is further shown that, in a prolonged annealing at high temperatures, the disilicide has dissolved and reprecipitated on the Si surface. Based on the roles of the silicide-mediated crystallization (SMC), the dissolution and reprecipitation of silicides, and SPEG, possible mechanisms are given to explain how the surface-disilicide islands are formed during annealing at temperatures of 550–950°C.     

Crystallization and failure behavior of Ta-TM (TM=Fe, Co) nanostructured/amorphous diffusion barriers for copper metallization

This work examined the thin-film properties and diffusion barrier behavior of sputtered Ta-TM (TM=Fe, Co) films, aiming at depositing a highly crystallization-resistant and conductive diffusion barrier film for Cu metallization. Four-point probe measurement, x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and a secondary ion mass spectrometer (SIMS) were used to examine the barrier properties. Structural examination indicated that intermetallic-compound-free amorphous Ta-TM films were obtained by magnetron sputtering, thus giving a resistivity of 146.82 μΩ-cm and 247.01 μΩ-cm for Ta_0.5Fe_0.5 and Ta_0.5Co_0.5 films, respectively. The Si/Ta_0.5Fe_0.5/Cu and Si/Ta_0.5Co_0.5/Cu stacked samples were observed to fail completely at temperature above 650°C and 700°C because of the formation of Cu₃Si protrusions between silicon and the Ta-TM interface. Ta_0.5Co_0.5 is thus superior to Ta_0.5Fe_0.5 in preventing copper from diffusion. Highly thermally stabilized amorphous Ta-TM thin film can thus be potentially adopted as a diffusion barrier for Cu metallization.