Showing papers on "Annealing (metallurgy) published in 1987"

Reproducible technique for fabrication of thin films of high transition temperature superconductors

Abstract: We report on a new process to make films of Y1Ba2Cu3O7 using coevaporation of Y, Cu, and BaF2 on SrTiO3 substrates. The films have high transition temperatures (up to 91 K for a full resistive transition), high critical current densities (106 A/cm2 at 81 K), and a reduced sensitivity to fabrication and environmental conditions. Because of the lower reactivity of the films, we have been able to pattern them in both the pre‐annealed and post‐annealed states using conventional positive photoresist technology.

Mesotaxy: single-crystal growth of buried CoSi2 layers

Abstract: Buried single‐crystal CoSi2 layers in silicon have been formed by high dose implantation of cobalt followed by annealing. These layers grow in both the (100) and (111) orientations—those in (111) have better crystallinity, but those in (100) are of higher electrical quality. Electrical transport measurements on the layers give values for the resistance ratios and superconducting critical temperatures that are better than the best films grown by conventional techniques and comparable to bulk CoSi2.

Enhancement of Elongation by Retained Austenite in Intercritical Annealed 0.4C-1.5Si-O.8Mn Steel

Abstract: An excellent combination of elongation over 30% and high strength about 100kgf/mm2 is achieved in processing of a 0.4C-1.5Si-0.8Mn steel by intercritical annealing, rapid cooling into bainite transformation temperature to soak several minutes. This combination is caused by transformation induced plasticity of retained austenite. Sufficient amount of stable austenite is a requisite for the good ductility. For the rapid cooling after annealing, the soaking temperature for the best combination of strength and ductility is immediately above Ac1. On the other hand, a delay before rapid cooling provides good properties if the soaking temperature is near Ac3 and the subsequent cooling is performed at a lower rate before pearlite transformation; in this case the critical cooling rate is reduced. These phenomena are discussed in terms of the growth of ferrite and the diffusion of alloying elements inclusive of Mn during slow cooling.

Three-dimensional quantum-size effect in chemically deposited cadmium selenide films.

Abstract: Optical band gaps, ${E}_{g}$, up to 0.5 eV higher than in single-crystal samples, are observed for chemically deposited films of CdSe and explained in terms of a quantum-size effect, whereby the electrons are localized in individual crystallites. The increase in ${E}_{g}$ depends strongly on deposition temperature, with the greatest increase obtained at the lowest temperature. Annealing at temperatures above the deposition temperature causes a decrease in ${E}_{g}$; this decrease is stronger at higher annealing temperature. Structural studies of the as-deposited layers showed them to be composed of microcrystalline, cubic CdSe, and electron microscopy resolved them into individual crystallites of typically 40--80-A\r{} diameter, depending on deposition temperature. This is the first example reported of a three-dimensional quantum-size effect in a film.

Amorphous Ti-Si alloy formed by interdiffusion of amorphous Si and crystalline Ti multilayers

Abstract: Reactions upon rapid thermal annealing of sputtered Ti‐Si multilayers have been studied by cross‐section and through‐foil transmission electron microscopy, glancing‐angle Rutherford backscattering, and x‐ray diffraction. The compositions of the samples are 40 at. % Ti, 60 at. % Si and 60 at. % Ti, 40 at. % Si, and the bilayer periodicity is about 10 nm. The silicon layers in the as‐deposited films are amorphous; the titanium layers are polycrystalline hcp. After a 30‐s anneal at 455 °C, significant interdiffusion occurs and we observed the formation of an amorphous Ti‐Si alloy by interfacial reaction. The metastable disilicide, C49 TiSi2, nucleated along with a small amount of TiSi in the sample with higher silicon content (60%) upon annealing at 550 °C for 10 s, but the amorphous alloy remained as the only product of reaction in the 40‐at. % Si sample.

Defect reduction by thermal annealing of GaAs layers grown by molecular beam epitaxy on Si substrates

Abstract: Post growth thermal annealing has been used to reduce the defect density of GaAs layers grown on Si substrates by molecular beam epitaxy. Transmission electron microscopy indicates a 100× reduction of the true defect density. Twins and stacking faults were eliminated entirely. Most misfit dislocations were confined within the first ∼150 A GaAs layer and formed a regular and narrow network along the Si/GaAs interface. Similar results were obtained from an ion implanted and annealed specimen.

Production of YBa2Cu3O7−y superconducting thin films in situ by high‐pressure reactive evaporation and rapid thermal annealing

Abstract: A high‐pressure reactive evaporation process has been used to produce smooth YBa2Cu3O7−y high Tc superconducting films without the necessity of a post‐deposition oven anneal cycle. Augmented in some cases by rapid thermal annealing, the process has yielded films with zero resistance transition temperatures above 80 K, and critical current densities above 106 A/cm2 at 4.2 K on both cubic zirconia and SrTiO3 substrates.

Rapid annealing and the anomalous diffusion of ion implanted boron into silicon

Abstract: The anomalous diffusion of ion implanted boron into silicon is shown to be a transient effect with a decay time that decreases rapidly with increasing anneal temperature. The decay time is approximately 45 min at 800 °C and decreases to the order of a second at 1000 °C. The anomalous displacement in the low concentration region is greater at low temperatures but a larger fraction of the boron is redistributed at high temperature. Sheet resistance measurements agree with the idea that the moving fraction of the boron atoms is electrically active and limited to the intrinsic carrier concentration at the anneal temperature. The activation energy for the decay of the transient is greater than that for the diffusion coefficient, which makes an appropriate rapid thermal anneal cycle an important practical process in the fabrication of shallow p‐n junctions.

Effects of interfacial microstructure on uniformity and thermal stability of AuNiGe ohmic contact to n-type GaAs

Abstract: As part of the investigation of the use of AuNiGe as the ohmic contact to n‐type GaAs at a high integration level, cross‐sectional transmission electron microscopy was used to explore the uniformity at the metal/GaAs interface and the thermal stability of the AuNiGe contact after the ohmic contact formation. A close relation between spread of the contact resistance and nonuniformity of the interfacial microstructure of the contact was found. Deposition of 5‐nm‐thick Ni as the first layer of the AuNiGe ohmic contact significantly reduced the spread of the contact resistance and led to the formation of a uniform interface without large protrusions. The improvement in uniformity of compound distribution and the reduction of interface roughness are believed to be due to a change in the sequence of alloying reactions, compared to those in the contact without a Ni first layer. This suggests an ideal interface structure for a low resistance AuNiGe ohmic contact after alloying to be a uniform two layer structure: a high density of the NiAs(Ge) grains contacting the GaAs substrate, and a homogeneous β‐AuGa phase close to the top surface. However, due to the existence of β‐AuGa phases with a low melting point of around 375 °C, the thermal stability of the contact at 400 °C is of serious concern. Segregation of the NiAs(Ge) grains was observed after annealing at 400 °C for 10 h, which reduced the contact areas between the NiAs(Ge) grains and GaAs. During subsequent annealing at this temperature for up to 90 h, liquidlike flow of the β‐AuGa phase was observed which deteriorated the interface uniformity, causing an increase in contact resistance. A typical contact edge slide distance after contact alloying at 440 °C for 2 min was measured to be 0.2 μm and the longest distance among specimens examined was 0.47 μm. This edge deterioration could limit the use of the AuNiGe contact in GaAs submicron devices.

Mechanisms of Pearlite Spheroidization

Abstract: A study of the mechanisms of pearlite spheroidization under static annealing conditions was carried out in two materials — AISI 1080 steel and pure Fe-C alloy. By electrolytically etching away the ferrite matrix, the morphology of the cementite phase was directly investigatedvia SEM and TEM techniques. It was clearly observed that the initiation and development of spheroidization are associated with morphological faults such as terminations, holes, and fissures in the cementite plates. During spheroidization the recession of terminations and the expansion of holes and fissures led to the break-up of large cementite plates into small segments. The migration of these faults is anisotropic. The preferred orientations, [010] and [210] directions in the (001) cementite plane, were determined by TEM analysis. This anisotropic morphological change is attributed to the anisotropy of the α/Fe3C interfacial energy. All the experimental evidence strongly supports the idea that the fault migration theory is the main mechanism governing spheroidization.

Grain growth and grain size distributions in thin germanium films

Abstract: We have observed and characterized normal and secondary grain growth in thin films of germanium on silicon dioxide. Films were deposited on thermally oxidized silicon wafers, encapsulated with 1000‐A‐thick sputtered SiO2 films and annealed in evacuated ampoules at 900 and 915 °C. After 5 min, the films had developed a columnar grain structure as a result of normal grain growth. The grain size distributions were lognormal with mean grain diameters of about 2.5 times the film thickness. The standard deviation of the normal grain size distribution did not change significantly with annealing time and temperature. Secondary grain growth, which can lead to grains that are much larger than the film thickness, occurred in films that were annealed for longer periods of time. The normal grain size distribution remained stationary, i.e., the peak height and width did not increase with annealing time. Secondary grains were few in number compared to normal grains, and were manifest as a small tail on the normal grain size distribution. The rate of secondary grain growth was constant and largest in the thinnest films.

Effect of in situ and ex situ annealing on dislocations in GaAs on Si substrates

Abstract: Gallium arsenide layers grown by molecular beam epitaxy on (100) Si substrates were subjected to annealing under As overpressure at 650, 750, and 850 °C for 1/2 h A substantial reduction in the dislocation density near the interface and in the bulk of the epitaxial layers was observed for the 850 °C anneal In situ annealing at 700 °C for 1/2 h after 1/2 h of growth followed by a deposition of InGaAs/GaAs strained‐layer superlattices and bulk layers also resulted in reduced dislocation densities

Titanium disilicide formation on heavily doped silicon substrates

Abstract: Titanium disilicide formation on heavily doped silicon substrates was investigated with sheet resistance measurements, elemental depth profiling, and transmission electron microscopy. As found in a previous study [H.K. Park, J. Sachitano, M. McPherson, T. Yamaguchi, and G. Lehman, J. Vac. Sci. Technol. A 2, 264 (1984)], the TiSi2 growth rate depended on the dopant concentration. The growth rate was highest on undoped substrates, intermediate on heavily phosphorus‐doped substrates, and lowest on heavily arsenic‐doped substrates. However, the critical dopant concentration effect reported by Park et al. was not observed. The uniformity of the titanium‐silicon reaction was not seriously affected by heavy substrate doping. For heavily arsenic‐doped substrates (3.0×1021 As/cm3), TiAs precipitates formed at C49 TiSi2 grain boundaries, and the C49‐to‐C54 transformation temperature increased to 850 °C. For heavily phosphorus‐doped substrates (1.0×1021 P/cm3), no phosphides were unambiguously detected, and the C49‐to‐C54 transformation temperature remained below 800 °C. Discrete blocking layers at the silicide‐silicon interface, such as the native silicon oxide or a dopant‐rich phase, did not cause the reduction in silicide growth. Thus, it is concluded that dopant and knock‐on oxygen atoms in solid solution in both the silicide and the silicon retard TiSi2 growth.

Variations of stoichiometry and cell symmetry in YBa2Cu3O7−x with temperature and oxygen pressure

Abstract: The mixed valence of copper (Cu(II)–Cu(III)) seems to be important in the recently discovered high-critical-temperature superconductivity of the yttrium barium copper oxide, YBa2Cu3O7−x; several authors have noted the influence of synthesis procedures on the superconducting critical temperature Tc (refs 1, 2). Recent structure determinations3–5 have shown the presence of oxygen vacancies, changing the copper coordination number from 6 in an ideal stoichiometric perovskite-type compound to 4 and 5 in YBa2Cu3O7−x. Here we report a thermogravimetric study of YBa2Cu3O7−x carried out at various temperatures and oxygen partial pressures, along with single-crystal X-ray diffraction data showing evidence of a crystallographic transformation as a function of temperature. The optimum copper valence is not reached under usual annealing conditions (800–1,000 °C), even in an oxygen atmosphere, but only below ∼350 °C. A change in the rate of oxygen loss with temperature may be related to an orthorhombic to tetragonal structural transformation occurring at ∼600 °C in air.

Article having surface layer of uniformly oriented, crystalline, organic microstructures

Abstract: Article comprising a substrate bearing a microlayer which comprises uniformly oriented, crystalline, solid, organic microstructures and a method for preparing said article. The microstructures may be mono- or polycrystalline. In the preferred embodiment, the microstructures are of uniform shape and size. The articles can be prepared by (1) depositing a vapor of an organic compound as a thin, continuous film onto a substrate to provide a composite, and (2) annealing the composite in a vacuum sufficiently such that a physical change is induced in the orginal deposited film to form the microstructures. The microlayer can be overcoated with other materials to provide desired properties to the article. The articles of this invention are useful for many forms of light trapping, energy absorption, imaging, data transmission and storage, and gradient index applications.

Deep levels of copper in silicon

Abstract: Defect impurity levels have been examined in copper‐diffused p‐and n‐type silicon using deep level transient spectroscopy. Levels at Ev+0.09, Ev+0.23, and Ev+0.42 eV have been observed in both types of material, although the deeper levels were only oberved in n‐type material after post‐diffusion annealing at 200 °C. Associated with the appearance of these levels in n‐type material was another level at Ec−0.16 eV. This may be a further charge state of the center responsible for the Ev+0.23 eV and Ev+0.42 eV levels or the two centers may be decomposition products of a thermally unstable complex. Luminescence measurements have revealed the previously reported Cu‐Cu spectrum in all the copper‐diffused samples. The occurrence of this signal could not be correlated with the presence of the levels at Ev+0.23, Ev+0.42, or Ec−0.16 eV; this leaves the center at Ev+0.09 eV as the likely origin of the signal.

Recrystallization of ion-implanted α-SiC

Abstract: The annealing behavior of ion-implanted α-SiC single crystal was determined for samples implanted with 62 keV 14N to doses of 55X1014/cm2 and 80X1016/cm2 and with 260 keV 52Cr to doses of 15X1014/cm2 and 10X1016/cm2 The high-dose samples formed amorphous surface layers to depths of 017 μm (N) and 028 μm (Cr), while for the low doses only highly damaged but not randomized regions were formed The samples were isochronically annealed up to 1600°C, holding each temperature for 10 min The remaining damage was analyzed by Rutherford backscattering of 2 MeV He+, Raman scattering, and electron channeling About 15% of the width of the amorphous layers regrew cpitaxially from the underlying undamaged material up to 1500°C, above which the damage annealed rapidly in a narrow temperature interval The damage in the crystalline samples annealed linearly with temperature and was unmeasurable above 1000°C

Preparation of superconducting YBa2Cu3Ox thin films by oxygen annealing of multilayer metal films

Abstract: Superconducting thin films consisting predominantly of YBa2Cu3Ox have been prepared by oxygen annealing of metal films formed by using electron beam evaporation to deposit a three‐layer sequence of Cu, Ba, and Y in nominally stoichiometric proportions, then repeating the sequence five times. For the best superconducting films, which were prepared on yttria‐stabilized cubic zirconia substrates, the onset of superconductivity occurred at 94 K and zero resistivity was observed at 72 K. For the best films prepared on sapphire substrates, the corresponding temperatures were 95 and 40 K.

Annealing effects on the crystallinity of polyetheretherketone (PEEK) and its carbon fiber composite

Abstract: The degree of crystallinity of polyetheretherketone (PEEK) has been measured using both the density gradient technique (DGT) and differential scanning calorimetry (DSC). The difference in results between the methods was shown to depend on crystallization taking place during the heating scan in the DSC. By freezing the sample at different stages of the DSC thermogram and measuring its crystallinity in the density gradient column, the existence of induced crystallization for PEEK was established. Though this induced crystallization is not visible in the DSC thermogram, it must be taken into account when comparing the degree of crystallinity measured by the two methods. The induced crystallization was in turn interpreted as a result of an increase in crystal perfection that is also commonly observed during the initial stages of the annealing process. Accordingly, the effect of annealing on the crystallinity was also investigated. DSC scans on annealed samples exhibited a small endothermic peak at approximately 10°C above the annealing temperature. This peak was observed in both neat PEEK and its carbon fiber-reinforced composite. Annealed PEEK shows, therefore, two melting transitions, a low one which depends on the annealing temperature and a high one which is independent of annealing temperature conditions. Collectively, the results of this study demonstrate that processing conditions and morphological features must be considered in characterizing semicrystalline-based matrix polymers for high performance composites.

Evidence for EL6 (Ec− 0.35 eV) acting as a dominant recombination center in n‐type horizontal Bridgman GaAs

Abstract: Horizontal Bridgman grown n‐type GaAs is shown to contain two important electron traps EL6 (035 eV) and EL2 (080 eV) in the 1015 cm−3 concentration range A heat treatment at 800 °C for 1 h results in the reduction of EL6 to about 1013 cm−3 to a depth of at least 10 μm and an increase in EL2 by an amount about equal to the reduction of EL6 Measurement of the minority‐carrier (hole) diffusion lengths in this depth range by an electron beam induced current (EBIC) technique shows an inverse correlation with the concentration of the EL6 trap The results may be explained if EL6 is assumed to be VGa‐VAs, EL2 to be AsGa‐VAs, and the interaction between the two traps to involve Asi

Mechanisms of buried oxide formation by ion implantation

Abstract: We have studied the process of buried oxide formation as a function of implantation and annealing conditions. Concentrating on substoichiometric implants (<1×1018 O/cm2), we varied the implantation energies from 100 keV to 1 MeV. Some apparent precipitation of SiO2 similar to that observed in Czochralski‐grown silicon occurs on implantation. This means that formation of the buried oxide layer and perfection of the overlying crystalline Si layer depend more strongly on the substrate temperature during the implant than on the annealing temperature.

In situ study of the molecular beam epitaxy of CoSi2 on (111) Si by transmission electron microscopy and diffraction

Abstract: The growth of CoSi2 has been studied by deposition and reaction of Co on clean Si (111) surfaces in situ in a modified ultrahigh vacuum transmission electron microscope. On deposition of nominally 20 A Co at room temperature, strong interaction between Si and Co occurs yielding an epitaxial film which is believed to be a hexagonally distorted form of the Co2Si structure. On heating to ∼350 °C the growth of epitaxial CoSi is observed, which transforms to CoSi2 at ∼450 °C. Silicon‐rich phases propagate by lateral motion of phase boundaries. Substantial pinhole density arises in films only after annealing at higher temperatures. The B orientation dominates under similar annealing conditions. In contrast to NiSi2, the growth of cobalt silicide films on Si is dominated by bulk phase formation, with interfacial energy minimized in all cases by epitaxy.

Effects of electron irradiation and annealing on ferroelectric vinylidene fluoride-trifluoroethylene copolymers

Abstract: It is shown that the Curie point of the ferroelectric vinylidene fluoride‐trifluoroethylene copolymer can be shifted to the low temperatures by electron radiation. This effect was studied by in situ dielectric measurements as a function of the dose and of the irradiation temperature. An additional effect of the irradiation, in particular when performed at high temperature, was to noticeably decrease e’. We also have studied annealing at temperatures around the melting point and shown that most of the irradiation damage was nonreversible and cumulative whereas part of it could be annealed. We have shown that it was apparently impossible to shift the Curie temperature lower than a limit temperature of the order of 0 °C. We discuss this effect and suggest the hypothesis of a competition with the glassy transition occuring in this temperature region.