Showing papers on "Annealing (metallurgy) published in 1994"

Low resistance ohmic contacts on wide band‐gap GaN

Abstract: We report a new metallization process for achieving low resistance ohmic contacts to molecular beam epitaxy grown n‐GaN (∼1017 cm−3) using an Al/Ti bilayer metallization scheme. Four different thin‐film contact metallizations were compared during the investigation, including Au, Al, Ti/Au, and Ti/Al layers. The metals were first deposited via conventional electron‐beam evaporation onto the GaN substrate, and then thermally annealed in a temperature range from 500 to 900 °C in a N2 ambient using rapid thermal annealing techniques. The lowest value for the specific contact resistivity of 8×10−6 Ω cm2, was obtained using Ti/Al metallization with anneals of 900 °C for 30 s. X‐ray diffraction and Auger electron spectroscopy depth profile were employed to investigate the metallurgy of contact formation.

Visible photoluminescence in Si+‐implanted silica glass

Abstract: We have investigated visible photoluminescence excited by Ar‐ion laser (488 nm, 2.54 eV) at room temperature from Si+‐implanted silica glass, as‐implanted and after subsequent annealing in vacuum. We found two visible luminescence bands: one peaked around 2.0 eV, observed in as‐implanted specimens and annealed completely after heating to about 600 °C, the other peaked around 1.7 eV observed only after heating to about 1100 °C, the temperature at which Si segregates from SiOx. It was found that the 2.0 eV band anneals parallel to the E’ centers, as detected by electron spin resonance studies. It was also found that Raman lines around 520 cm−1, due to Si—Si bonds, grow and that interference patterns are induced by annealing Si+‐implanted silica glass. Based on these studies, we ascribe the 2.0 eV band to the electron‐hole recombination in Si‐rich SiO2 and the 1.7 eV band to the electron‐hole recombination in the interface between the Si nanocrystal and the SiO2 formed by segregation of crystalline Si from SiOx.

Dynamic recrystallization in high-strain, high-strain-rate plastic deformation of copper

Abstract: When copper is deformed to high plastic strain (y ~ 34) at high strain rates (~ ~ I04 s -1) a microstructure with grain sizes of ~0.1 am can be produced. It is proposed that this microstructure develops by dynamic recrystallization, which is enabled by the adiabatic temperature rise. By shock-load- ing the material, and thereby increasing its flow stress, the propensity for dynamic recrystallization can be enhanced. The grain size-flow stress relationship observed after cessation of plastic deformation is consistent with the general formulation proposed by Derby (Acta metall, mater. 39, 955 (1991)). The temperatures reached by the specimens during dynamic deformation are calculated from a constitutive equation and are found to be, for the shock-loaded material, in the 500-800 K range; these temperatures are consistent with static annealing experiments on shock-loaded specimens, that show the onset of static recrystallization at 523 K. A possible recrystallization mechanism is described and its effect on the mechanical response of copper is discussed.

A study of residual stresses in Zircaloy-2 with rod texture

Abstract: The development of high grain-to-grain interactions in Zircaloy-2 polycrystals is due to the anisotropy of the thermal, elastic and plastic properties of the constituent grains. These residual stresses modify the mechanical performance of the materials as well as its response under neutron irradiation. Here we simulate the evolution of internal stresses in Zircaloy-2 with rod texture, when the aggregate is cooled down from the annealing temperature, and also when it is subjected to tensile and compressive deformation. We implement for that purpose an elasto-plastic self-consistent scheme that accounts for grain interactions, and compare our predictions with experimental determinations of residual strains obtained by neutron diffraction. Our results are in good quantitative agreement with the experimental evidence, and represent a qualitative improvement over the predictions of the more rigid upper-bound approach. We discuss the role that slip and twinning systems play in the macroscopic response of the aggregate and in the evolution of internal stresses.

Orientation of rapid thermally annealed lead zirconate titanate thin films on (111) Pt substrates

Abstract: The nucleation, growth, and orientation of lead zirconate titanate thin films prepared from organometallic precursor solutions by spin coating on (111) oriented platinum substrates and crystallized by rapid thermal annealing was investigated. The effects of pyrolysis temperature, post-pyrolysis thermal treatments, and excess lead addition are reported. The use of post-pyrolysis oxygen anneals at temperatures in the regime of 350–450 °C was found to strongly affect the kinetics of subsequent amorphous-pyrochlore-perovskite crystallization by rapid thermal annealing. The use of such post-pyrolysis anneals allowed films of reproducible microstructure and textures [both (100) and (111)] to be prepared by rapid thermal annealing. It is proposed that such anneals and pyrolysis temperature affect the oxygen concentration/average Pb valence in the amorphous films prior to annealing. Such changes in the Pb valence state then affect the stability of the transient pyrochlore phase and thus the kinetics of perovskite crystallization.

Visible photoluminescence in Si+‐implanted thermal oxide films on crystalline Si

Abstract: We have investigated visible photoluminescence excited by Ar ion laser (488 nm, 2.54 eV) at room temperature from Si+‐implanted thermal oxide films grown on crystalline Si wafer, as‐implanted and after subsequent annealing in vacuum. We found two types of visible luminescence bands similar to those of silica glasses; one band is observed in as‐implanted specimens and disappears after heating to about 600 °C, and the other band is observed only after heating the specimens to about 1100 °C. Though the shapes of these luminescence spectra are different from those having been observed in Si+‐implanted silica glass, the origins of these bands are the same as in silica glass. We discuss the similarities and the differences of luminescence bands in Si+‐implanted silica glasses and thermal oxide films grown on crystalline Si.

Investigation of Pt/Ti bilayer metallization on silicon for ferroelectric thin film integration

Abstract: The stabilities of Pt/Ti bilayer metallizations in an oxidizing atmosphere have been investigated with several thicknesses of interfacial Ti‐bonding layers. Reactions in the Pt/Ti/SiO2/Si interface were examined as a function of various annealing conditions in the temperature range 200–800 °C by using Rutherford backscattering spectrometry, Auger electron spectroscopy, x‐ray diffraction, and transmission electron microscopy. Thermal treatment in oxygen was found to cause rapid oxidation of the Ti layer, accompanied by the migration of Ti into the Pt film. Diffusion of oxygen through the Pt grain boundaries was mainly responsible for the adverse reactions at the interface and loss of mechanical integrity. Thin Ti (10 nm) layers resulted in the depletion of the interfacial bonding layer causing serious adhesion problems, whereas thicker Ti films (100 nm) caused the formation of TiO2−x in the Pt‐grain boundaries, ultimately encapsulating the Pt surface with an insulating TiO2 layer. Improved stability and adhesion in the Pt/Ti bilayer metallization compatible with ferroelectric thin film processing, were achieved by incorporating well reacted thin TiO2 layers in situ, and depositing Pt films at a high temperature.

Process for fabricating thin film transistor

Abstract: After a pattern is transferred on silicon film crystallized by annealing, the silicon film is annealed by radiation of intense rays for a short time. Especially, in the crystallizing process by annealing, an element which promotes crystallization such as nickel is doped therein. The area not crystallized by annealing is also crystallized by radiation of intense rays and a condensed silicon film is formed. After a metal element which promotes crystallization is doped, annealing by light for a short time is performed by radiating intense rays onto the silicon film crystallized by annealing in an atmosphere containing halide. After the surface of the silicon film is oxidized by heating or by radiating intense rays in a halogenated atmosphere and an oxide film is formed on the silicon film, the oxide film is then etched. As a result, nickel in the silicon film is removed.

Diffusion barrier effects of transition metals for Cu/M/Si multilayers (M=Cr, Ti, Nb, Mo, Ta, W)

Abstract: In order to find appropriate diffusion barrier materials for Cu, the diffusion of Cu into Si through various barrier metals M (M=Cr, Ti, Nb, Mo, Ta, W) was investigated. The behavior of Cu in Cu/M/Si multilayers was measured after annealing using x‐ray diffraction analysis, secondary ion mass spectroscopy, Rutherford backscattering spectroscopy, and electric resistance change. Only Cu/Ta/Si and Cu/W/Si multilayers retained their multilayer structures after annealing at 600 °C×1 h in H2 without resistivity increases. Multilayers of the other metals did not retain their structures after the same annealing condition. This difference in the barrier properties of the transition metals appeared to be related to the metal‐Cu binary phase diagrams and their self‐diffusion coefficients.

Electrochemical Er doping of porous silicon and its room‐temperature luminescence at ∼1.54 μm

Abstract: We present a new electro‐chemical method for incorporating high concentration Er ions deep into porous silicon layers and its intense photoluminescence at ∼1.54 μm at room temperature. Porous silicon layers prepared by anodic etching of p‐type silicon substrates in HF/H2O are immersed in ErCl3/ethanol solution. Then the negative bias relative to a counter platinum electrode is applied to the samples. Er3+ ions are drawn into fine pores of the porous silicon layers by the electric field. After thermal annealing at ∼1300 °C in an O2/Ar atmosphere, the samples show sharp and intense Er3+‐related photoluminescence at ∼1.54 μm at room temperature upon excitation with an Ar ion laser.

Magnetic and Mössbauer studies of single‐crystal Fe16N2 and Fe‐N martensite films epitaxially grown by molecular beam epitaxy (invited)

Abstract: Single‐phase, single‐crystal Fe16N2(001) films and Fe‐11 at. %N martensite films of 200–900 A thickness have been epitaxially grown on In0.2Ga0.8As(001) substrates by evaporating Fe in an atmosphere of mixed gas of N2 and NH3, followed by annealing. The saturation magnetizations 4πMs’s for Fe16N2 and Fe‐N martensite films have been measured to be around 29 and 24 kG at room temperature, respectively, and almost constant in the above thickness range by using a vibrating sample magnetometer. 4πMs for Fe‐N martensite films has been increased with ordering of N atoms caused by annealing and finally reached around 29 kG for Fe16N2. Mossbauer spectra have been measured for those films. The spectrum for Fe‐N martensite films was a superposed one with hyperfine fields of 360, 310, and 250 kOe, similar to those previously reported for martensite. While the spectrum became simpler with ordering, finally reaching a single hyperfine field of 330 kOe for Fe16N2. 4πMs of 29 kG for Fe16N2 (3.2 μB/Fe atom) and 4πMs of 24...

Interaction of aluminum with hydrogenated amorphous silicon at low temperatures

Abstract: Annealing effects on aluminum/hydrogenated amorphous silicon (a‐Si:H) contacts in the temperature range from 100 to 300 °C were studied. Al was evaporated on device‐quality, phosphorus‐doped (n+) a‐Si:H films deposited in a UHV plasma‐enhanced chemical‐ vapor‐deposition system. Both electrical measurements and surface morphological analyses were performed to characterize the interaction. The transmission line model technique was used to measure sheet resistance and contact resistivity. For samples where Al covered the entire a‐Si:H surface during annealing, sheet resistance and contact resistivity were found to decrease monotonically with annealing temperature; whereas, samples annealed after patterning of the Al pads exhibited a minimum in sheet resistance and contact resistivity at temperatures between 150 and 200 °C. Optical and scanning electron microscopy, surface profilometry, and Raman spectroscopy were used to study the surface morphology. Interaction of Al with a‐Si:H was observed to initiate at ...

Conversion of chemically deposited photosensitive CdS thin films to n‐type by air annealing and ion exchange reaction

Abstract: A method is presented for the deposition of CdS thin films of 005–07 μm thickness from solutions at 50–70 °C containing citratocadmium(II) complex ions and thiourea The films show an optical band gap Eg≳26 eV Optical transmittance is about 80% for photon energy

Influence of defect passivation by hydrogen on the Schottky barrier height of GaAs and InP contacts

Abstract: The change in barrier height caused by sputter metallization of contacts on both GaAs and InP substrates, and using evaporated contacts as a reference, is investigated. It has been found that by annealing, the reference barrier height can be restored. A model is proposed, wherein sputter metallization leads to passivation of interfacial defects by hydrogen. Accordingly, the Fermi level pinning caused by these defects is removed and the barrier height changes and is determined by other mechanisms. Annealing produces a removal of hydrogen and reactivates the amphoteric defects. Additional evidence is given for the assumption that sputter metallization leads to passivation, by hydrogen, of dopants and defects in the semiconductor.

Temperature–Time Texture Transition of Pb(Zr1−xTix)O3 Thin Films: II, Heat Treatment and Compositional Effects

Abstract: Texture transition of Pb(Zr1−xTix)O3 thin films grown from a metallo–organic solution onto Pt/Ti/SiO2/Si substrates has been studied. The orientation obtained depends on the crystallization temperature and time and can be drastically altered by modifying the heat treatment schedule. A [100] texture requires an initial seeding treatment in the intermediate temperature range. This is attributed to a nucieation advantage associated with the formation of an intermediate PbO[001] texture that tends to form at intermediate temperature over time. A [111] texture develops at higher temperature during rapid heating and can be rationalized by the formation of an epitaxial intermetallic phase Pt5–7Pb, at the PZT/Pt interface that provides lattice matching between PZT(lll), Pt5–7Pb(lll), and Pt(lll). Temperature–time transformation texture (TTT) diagrams of PZT texture have been constructed for seeding various orientations. The effect of composition (Pb excess and Zr/Ti ratio) and the possible manipulation of these texture selection relations by combining compositional tailoring and heat treatment schedules are illustrated.

Intermetallic compounds at aluminum-to-copper electrical interfaces: effect of temperature and electric current

Abstract: The effects of intermetallic compounds on the electrical and mechanical properties of bimetallic friction welded Al-Cu joints was studied. The formation and growth of intermetallic compounds was studied in the temperature ranges 200-525/spl deg/C. In addition, the effect of electrical current on the morphology and kinetics of formation of intermetallic compounds of bimetallic friction welded aluminum-copper joints was studied in the temperature ranges 200-500/spl deg/C that was realized by heating Al-Cu joints with an ac current of different intensities (400-1000 A). The contact resistance was found to increase linearly with the thickness of the intermetallics. The presence of an electrical field greatly accelerates the kinetics of formation of intermetallic phases and alters significantly their morphology. The growth kinetics of intermetallic phases under the influence of electrical current is much higher than that under diffusion annealing in furnace. >

Effect of atmosphere on the PTCR properties of BaTiO3 ceramics

Abstract: The influence of low-temperature annealing, at < 360 °C, in various reducing and oxidizing atmospheres for a series of BaTiO3 ceramics with a positive temperature coefficient of resistance (PTCR) is discussed. Combined impedance and modulus spectroscopy is used to analyse a.c. impedance data and shows that the total resistance of the sample can be composed of up to three components, dependent on the cooling rate from the sintering temperature. For quickly cooled samples the PTCR response is dominated by an outer shell on individuals grains, whereas for slowly cooled samples the grain boundary resistance dominates. Annealing in reducing atmospheres destroys the grain boundary PTCR effect whereas the outer-shell grain PTCR effect is relatively insensitive to the reducing atmosphere. It is proposed that the acceptor states responsible for the outer-grain and grain-boundary PTCR effects are predominantly intrinsic metal vacancies, i.e. Ba and/or Ti, and adsorbed oxygen, respectively.

Fabrication and characterization of low-loss, sol-gel planar waveguides.

Abstract: Applications of planar integrated optical waveguide (IOW) technology to problems in surface spectroscopy and optical chemical sensing have been partly limited by the difficulty of producing high-quality glass IOWs. The fabrication of IOWs by the sol-gel method from methyltriethoxysilane and titanium tetrabutoxide precursors is described here. The physical, chemical, and optical properties of the films during and after high-temperature annealing were studied using a variety of analytical techniques. The results show that the catalyst used to accelerate the sol-gel reaction strongly influenced the optical quality of the IOW. HCl catalysis produced waveguides with propagation losses of approximately 1 dB/cm, whereas in the case of SiCl4 catalysis, propagation losses were < 0.2 dB/cm, a value significantly less than any previously reported for sol-gel-derived IOWs. An examination of film surface structure and morphology by scanning electron microscopy and atomic force microscopy showed that the SiCl4-catalyzed IOWs were significantly smoother and more homogeneous on a submicrometer scale than the HCl-catalyzed IOWs. The use of SiCl4 is thought to retard formation of a microheterogeneous network containing Si-rich and Ti-rich domains, which is favored with HCl catalysis and contributes to the higher observed losses.

Hydrophobic silicon wafer bonding

Abstract: Wafers prepared by an HF dip without a subsequent water rinse were bonded at room temperature and annealed at temperatures up to 1100 °C. Based on substantial differences between bonded hydrophilic and hydrophobic Si wafer pairs in the changes of the interface energy with respect to temperature, secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM), we suggest that hydrogen bonding between Si‐F and H‐Si across two mating wafers is responsible for room temperature bonding of hydrophobic Si wafers. The interface energy of the bonded hydrophobic Si wafer pairs does not change appreciably with time up to 150 °C. This stability of the bonding interface makes reversible room‐temperature hydrophobic wafer bonding attractive for the protection of silicon wafer surfaces.

Effects of barrier layer and annealing on abnormal grain growth in copper thin films

Abstract: Abnormal (100) grain growth has been characterized in predominantly (111)‐textured Cu thin films as a function of deposition temperature, annealing temperature and the presence of a Ta or W underlayer. For films deposited at room temperature, bimodal grain size distributions are observed at annealing temperatures at or above 150 °C for Cu on Ta and 100 °C for Cu on W. Suppression of (100) abnormal grain growth was achieved by depositing Cu on either barrier layer at 150 °C. A bimodal grain size distribution was still observed for the film deposited on W at 150 °C but the large grains forming this distribution were found to be (111) oriented. These results are explained as the result of competition between strain energy minimization and surface and interface energy minimization. The (100) growth is shown to be driven by a reduction of the orientation‐dependent strain energy that builds up due to the elastic anisotropy of Cu. Films deposited at higher temperatures have a lower yield stress which limits the ...

Method of making semiconductor device/circuit having at least partially crystallized semiconductor layer

Abstract: Amorphous silicon in impurity regions (source and drain regions or N-type or p-type regions) of TFT and TFD are crystallized and activated to lower electric resistance, by depositing film having a catalyst element such as nickel (Ni), iron (Fe), cobalt (Co) or platinum (Pt) on or beneath an amorphous silicon film, or introducing such a catalyst element into the amorphous silicon film by ion implantation and subsequently crystallizing the same by applying heat annealing at an appropriate temperature.

Surface-Induced Ordering in Asymmetric Block Copolymers

Abstract: The surface-induced ordering in thin films of asymmetric deuterated polystyrene (dPS)--poly(vinylpyridine) (PVP) diblock and triblock copolymers of comparable polymerization index and PVP volume fraction (f [approximately] 0.25) was studied using transmission electron microscopy, atomic force microscopy, secondary ion mass spectrometry, and neutron reflectivity. The morphology of both di- and triblock copolymer films was found to be cylindrical except for the layer adjacent to the silicon oxide surface, which due to the strong interaction of silica with PVP, was lamellar. The spacing between adjacent cylindrical layers was found to be consistent with mean field theory predictions. In the triblock copolymer films the cylindrical layers were oriented parallel to the silicon oxide surface, and no decay of the ordered structure was observed for at least 12 periods. If the total film thickness t[prime] deviated from t = [(n + 0.71)210 + 182] [angstrom], where n is an integer, islands or holes formed at the vacuum interface. The height of the holes or islands reached its equilibrium value, 210 [angstrom], after annealing 24 h at 180 C. In contrast, it was far more difficult to orient parallel to the silicon oxide surface the microphase-separated cylindrical domains in the diblock copolymer films. As amore » result no islands or holes were observed even after annealing for 5 days at 180 C. The authors concluded that the difference in ordering behavior was due to the ability of the triblock copolymer to form an interconnected micelle network while the diblock copolymer formed domains that were free to move with respect to each other. This conclusion was further confirmed by diffusion measurements which showed that the PS homopolymer penetrated easily into the ordered diblock copolymer films and was excluded from the ordered triblock copolymer films.« less

Nb3Al Multifilamentary Wires Continuously Fabricated by Rapid-Quenching

Abstract: The Nb tube process has recently been developed at NRIM(Japan) for fabricating Nb3Al multifilamentary superconductors,1–3 which are characterized by the heat treatment at low temperature ( 1700°C), many attempts were made to form Nb3A1 by heat treating Nb/AI composite at high temperatures.4–6 However, rapid grain growth decreased the density of pinning center (grain boundary) in Nb3A1 and thereby degraded Jc in particular at low magnetic fields. To overcome this problem, Nb3A1 conductors fabricated through a rapid-quenching process have been studied. In this process the A15 Nb3A1 phase with fine grain structure can be precipitated from the supersaturated Nb-Al bcc phase by aging at ~800°C. However, no attempt was made to fabricate a practical-structure conductor such as a long multifilamentary wire through continuous rapid-quenching and subsequent annealing (post annealing) process.

Tin dioxide thin-film gas sensor prepared by chemical vapour deposition : Influence of grain size and thickness on the electrical properties

Abstract: Tin dioxide films are elaborated by a chemical vapour deposition (CVD) method. An accurate control of deposition parameters (temperature, total pressure, duration) so that appropriate annealing conditions (duration, temperature) can be used to modify the structural properties of the films: grain size, thickness, and stoichiometry. Important modifications of electrical performances in tin dioxide films for gas-sensing applications are observed. A correlation between structural properties of CVD films and their electrical behaviour is proposed. The main results are: (i) a sharp increase in the electrical conductance under pure air G0 from a critical value of the grain size D=2L, due to the apparition of a conduction channel between adjacent grains; the depletion layer L is evaluated to 35 A; (ii) a dependence of the electrical conductance G0 with stoichiometry observed for various deposition temperatures and various annealing conditions; the predominant effect of stoichiometry variations for films deposited at high temperature (100–300 A grain size range) is responsible for the decrease of G0, and (iii) a strong influence of film thickness e, with a maximum of sensitivity for the thinnest films, in which tin dioxide is more discontinuous and disordered, and an increase in G0 with e due to the increase of the number of percolation paths up to 3000 A corresponding to a percolation threshold.