Showing papers on "Annealing (metallurgy) published in 1988"

Bonding of silicon wafers for silicon‐on‐insulator

Abstract: Several aspects of a new silicon‐on‐insulator technique utilizing bonding of oxidized silicon wafers were investigated. The bonding was achieved by heating in an inert atmosphere a pair of wafers with hydrophilic surfaces contacted face‐to‐face. A quantitative method for the evaluation of the surface energy of the bond based on crack propagation theory was developed. The bond strength was found to increase with the bonding temperature from about 60–85 erg/cm2 at room temperature to ≂2200 erg/cm2 at 1400 °C. The strength was essentially independent of the bond time. Bonds created during 10‐s annealing at 800 °C were mechanically strong enough to withstand the mechanical and/or chemical thinning of the top wafer to the desired thickness and subsequent device processing. A model was proposed to explain three distinct phases of bonding in the temperature domain. Electrical properties of the bond were tested using metal‐oxide‐semiconductor (MOS) capacitors. The results were consistent with a negative charge de...

Large grain polycrystalline silicon by low‐temperature annealing of low‐pressure chemical vapor deposited amorphous silicon films

Abstract: The crystallization of undoped amorphous silicon films deposited by low‐pressure chemical vapor deposition in the temperature range 580–530 °C and annealed from 550 to 950 °C has been studied by transmission electron microscopy. The average grain size of the crystallized films depends on the annealing temperature and the deposition conditions. The nucleation rate of new grains during annealing decreases as the deposition temperature decreases from 580 to 545 °C and/or when the deposition rate increases. The final grain size is also influenced by the annealing temperature with the largest grain size obtained at low annealing temperatures. A simple model is described which explains the dependence of grain size on the annealing temperature. An average grain size of 500 nm has been obtained in a 200‐nm film deposited at 545 °C and annealed at 550 °C.

Deposition of superconducting Y‐Ba‐Cu‐O films at 400 °C without post‐annealing

Abstract: Superconducting thin films of Y1Ba2Cu3O7−x were fabricated using the process of plasma‐assisted laser deposition. The substrate temperature was as low as 400 °C and high‐temperature post‐annealing in an O2 atmosphere was not necessary. The as‐deposited films have a Tc of ∼85 K, and are oriented mostly with the c axis perpendicular to the substrate surface. The measured Jc at 80 K was 105 A/cm2.

Formation of high Tc superconducting films by organometallic chemical vapor deposition

Abstract: The first growth of superconducting YBaCuO films by organometallic chemical vapor deposition is described. Metal β‐diketonates were decomposed thermally on MgO substrates in an oxygen‐rich atmosphere to produce amorphous brown films. Subsequent annealing in oxygen yielded dull gray films whose thickness corresponded to deposition rates of approximately 8 nm min−1. These films showed semiconductor‐like behavior at higher temperatures, followed by a broad resistive transition from 80 to 36 K with the resistance becoming zero at ∼20 K. Analysis of x‐ray data indicated the presence of the orthorhombic superconducting phase and various other metal oxides. Profilometer measurements yielded film thicknesses up to 950 nm, and scanning electron microscopy revealed faceted grains from 0.5 to 1.0 μm in size.

Defect reduction effects in GaAs on Si substrates by thermal annealing

Abstract: High quality GaAs films with dislocation densities of 2–3×106 cm−2 on (100) Si substrates have been obtained by thermal cycle growth using the metalorganic chemical vapor deposition method. Significant reduction effects of dislocation density in the GaAs layers on Si have been analyzed by a simple model, in which annihilation and coalescence of dislocations are assumed to be caused by dislocation movement under thermal stress. Relaxation of thermal stress in the GaAs films on Si during thermal annealing has also been observed.

High Tc superconductor/noble‐metal contacts with surface resistivities in the 10−10 Ω cm2 range

Abstract: Contact surface resistivities (product of contact resistance and area) in the 10−10 Ω cm2 range have been obtained for both silver and gold contacts to high Tc superconductors. This is a reduction by about eight orders of magnitude from the contact resistivity of indium solder connections. The contact resistivity is low enough to be considered for both on‐chip and package interconnect applications. The contacts were formed by sputter depositing either silver or gold at low temperatures (<100 °C) on a clean surface of Y1 Ba2 Cu3 O7−δ (YBCO) and later annealing the contacts in oxygen. Annealing temperature characteristics show that for bulk‐sintered YBCO samples there is a sharp decrease in contact resistivity after annealing silver/YBCO contacts in oxygen for 1 h at temperatures above ∼500 °C and gold/YBCO contacts for 1 h above ∼600 °C. Oxygen annealing for longer times (8 h) did not reduce the contact resistivity of silver contacts as much as annealing for 1 h. Auger microprobe analysis shows that indium...

Transient boron diffusion in ion-implanted crystalline and amorphous silicon

Abstract: Boron diffusion in ion‐implanted and annealed single‐crystal and amorphized Si is compared to determine the effect of amorphization on the initial transient boron motion reported for single crystal. The boron was implanted at 20 keV and at doses of 1×1015 and 3×1015cm−2. The Si was either preamorphized or postamorphized to a depth of 320 nm by implantation of Si ions at three different energies. In the amorphized samples the entire boron profile was always contained within this distance. The samples were annealed by furnace or rapid thermal annealing to 900–1100 °C with or without a preanneal at 600 °C. The initial rapid diffusion transient in the tail region of the boron profile was observed in all the crystal samples. This transient was totally absent in the amorphized samples. This is manifest by careful comparison of boron concentration profiles determined by secondary ion mass spectrometry of single‐crystal and amorphized samples after annealing. For anneals where significant motion occurs, the profi...

Thermal annealing of fission tracks in apatite 3. Variable temperature behaviour

Abstract: Despite considerable attention to isothermal behaviour in the literature, no satisfactory description of the variable temperature annealing behaviour of fission tracks in apatite has been given to date. Here, we show that our recently published constant-temperature annealing description can be adapted to temperatures which vary with time using the “principle of equivalent time”. This assumes that at any moment, a track which has been annealed to a certain degree r (= l/l0) behaves during further annealing in a manner which is independent of the conditions which caused the prior annealing, but which depends only on the degree of annealing that has occurred, and the prevailing conditions of temperature and time. Comparison of predictions of mean track length based on this assumption with observed values in a large number of laboratory variable-temperature annealing experiments shows good agreement, suggesting that the assumption is valid. Detailed inspection of the behaviour of tracks during heating and cooling shows that annealing is much more rapid at higher temperatures, and that temperature is the dominant factor in fission-track annealing in apatite. Extension of this treatment to geological situations is not straightforward and is left to a future paper.

Polymer-Polymer Miscibility and Enthalpy Relaxations

Abstract: Annealing of polymers below the glass transition temperature results in a decrease in enthalpy that is recovered during heating. The enthalpy recovery is visible as an endothermic peak in a differential scanning calorimetry (DSC) scan. The position of this peak depends on the thermal treatment given and on the structure of the material itself. Because different polymers behave differently, the phenomenon can be utilized to investigate polymel-polymer miscibility of polymers with similar Tg values. Therefore, by annealing the blends at the temperature of interest and subsequent sub-T, annealing, one can monitor phase behavior resulting from the initial treatment by inspection of the enthalpy recovery. Two systems were investigated to illustrate this: an immiscible blend of poly(viny1 chloride) and poly(isopropy1 methacrylate) and a miscible blend of poly(viny1 chloride) and poly(methy1 methacrylate).

Ion‐bombardment‐enhanced grain growth in germanium, silicon, and gold thin films

Abstract: Grain growth has been studied in polycrystalline thin films of Ge, Si, and Au during ion bombardment. The phenomenon has been characterized by varying the ion dose, ion energy, ion flux, ion species, substrate temperature, and thin‐film deposition conditions. Films bombarded with Si+, Ar+, Ge+, Kr+, and Xe+ exhibited enhanced grain growth which was weakly temperature dependent and proportional to the energy deposited in elastic collisions at or very near grain boundaries. The effect of these parameters on grain size and microstructure was analyzed both qualitatively and quantitatively using transmission electron microscopy. A transition state model describing the motion of grain boundaries during ion bombardment has been applied to the present experimental data. The results suggest that bombardment‐enhanced grain growth may be due to thermal migration of bombardment‐generated defects across the boundary. The calculated defect yield per incident ion was found to be directly related to enhanced grain growth...

Ion implantation and annealing of crystalline oxides and ceramic materials

Abstract: The response of several crystalline oxides or ceramic materials to ion implantation and subsequent thermal annealing is described. For both SrTiO 3 and CaTiO 3 single crystals, the near-surface region can be turned amorphous by relatively low doses of heavy ions (Pb, 10 15 /cm 2 , 540 keV). During annealing, the amorphous region recrystallizes epitaxially with the underlying substrate by simple solid-phase epitaxy, and the crystallization kinetics have been determined for both of these materials. In Al 2 O 3 , the amorphous phase of the pure material is produced by a stoichiometric implant at liquid nitrogen temperature. During annealing, the amorphous film crystallizes in the (crystalline) γ phase, followed by the transformation of the γ to the α phase at a well-defined interface. The kinetics characterizing the growth of α-Al 2 O 3 have been determined. Preliminary results are presented on the effect of impurities (Fe) on the nature and kinetics of the crystallization of amorphous Al 2 O 3 .

Modification of SiO through room-temperature plasma treatments, rapid thermal annealings, and laser irradiation in a nonoxidizing atmosphere

Abstract: We have studied the modification of a-SiO thin deposited films through Ar-plasma treatment at room temperature, through heating (rapid thermal annealing), or through irradiation (uv-laser treatment), in a nonoxidizing atmosphere. Rutherford backscattering spectroscopy, reflection high-energy electron diffraction, ir-absorption, and x-ray photoelectron spectroscopy techniques have been used in combination to investigate the atomic composition and the structural and chemical nature of SiO films after various nonoxidizing treatments. We show that the as-deposited oxide is not a mixture of Si and ${\mathrm{SiO}}_{2}$ and separates into phases as a result of processing. The effects of irradiation by low-energy electrons at room temperature (plasma treatment) are similar to those observed for high-temperature treatments. A possible microscopic mechanism, leading to silicon cluster growth, is proposed to explain the transition from a material rich in intermediate suboxides (as-deposited SiO) to the mixture structure (phase-separated Si and ${\mathrm{SiO}}_{2}$).

Effect of large boron additions to magnetically hard Fe‐Pt alloys

Abstract: Magnetic properties were investigated for the ternary (Fe0.6Pt0.4)100−xBx and (Fe1−yPty)83B17 alloy ribbons prepared by the twin roll technique. Boron changes the compositions of the ordered FePt (γ1) phase, which coexists with Fe2B at various alloy compositions so that the actual Pt content of γ1 in the ternary alloy goes up with increasing boron content. Coercive force increase due to boron addition is remarkable, in particular at low Pt concentration. Annealing time to get high coercivity becomes much shorter by boron addition. iHc=5.6 kOe and 4πMs=7.8 kG were obtained in the (Fe0.65Pt0.35)83B17 ribbon.

As-deposited superconducting Y-Ba-Cu-O thin films on Si, Al2O3, and SrTiO3 substrates

Abstract: We have developed an electron beam evaporator designed to deal with the special requirements of thin films of oxide superconductors. The growing surface is sprayed with plasma‐excited oxygen while the sources and rate monitors operate in a low background pressure. This allows us to reproducibly grow films of Y‐Ba‐Cu‐O on Si, Al2O3, and SrTiO3 substrates at a substrate temperature of 540 °C which are superconducting without the need for annealing. The resistive transitions of most films show an onset of 90 K and zero resistance by 68 K. X‐ray diffraction indicates a preferred orientation for growth on most Si and SrTiO3 substrates. A preliminary measurement yields critical currents of at least 104 A/cm2 at 4.2 K for a film on silicon.

Transient structural relaxation of amorphous silicon

Abstract: Transient structural relaxation of ion-implanted and vacuum-evaporated amorphous silicon has been studied over a wide range of times and temperatures using Raman spectroscopy. for ultra-fast, pulsed-laser induced heating at ≥ 1000°C relaxation occurs on a nanosecond time-scale. Thermal annealing at 200–600°C induces relaxation within seconds to hours. For heating at a certain temperature, the degree of relaxation (as defined by the bond-angle distortion) initially increases roughly logarithmically with time. Subsequently a pseudo-saturation level is reached which is temperature-dependent. The activation energy associated with the very first part of the relaxation is ≈ 0.5 eV for ion-implanted amorphous silicon and thermal annealing. Relaxation is enhanced in the case of pulsed-laser induced heating, which may be related to the formation of a high density of electrons and holes and the resulting network softening. It is suggested that the melting temperature of a-Si is influenced by the state of relaxation and that it varies with the heating procedure used. The initial state of relaxation of a-Si formed by vacuum evaporation is found to be strongly dependent on preparation conditions. Upon further annealing the films relax to a saturation level which is only slightly dependent on the initial conditions.

Thin films of Y‐Ba‐Cu‐O on silicon and silicon dioxide

Abstract: Thin films of the high‐temperature superconductor Y‐Ba‐Cu‐O near the 1:2:3 stoichiometry were deposited on single‐crystal silicon and oxidized silicon with a zirconia buffer layer. Zero‐resistance transition temperatures up to 83 K have been measured on the films formed by a process of sequential evaporation and furnace annealing.

The reduction of dislocations in oxygen implanted silicon‐on‐insulator layers by sequential implantation and annealing

Abstract: Reduction of the dislocation density in silicon‐on‐insulator layers produced by oxygen implantation has been achieved by sequentially implanting and annealing the wafers with oxygen doses less than a critical value of about 4×1017/cm2 at 150 keV between heat treatments. Anneals of 17 h duration at 1250 °C were employed. Dislocation densities of less than 103/cm2 were obtained by etching studies on thin epitaxial layers grown on these wafers, in comparison to values around 109/cm2 with single doses greater than the critical value. Since the dislocations in the epitaxial layer arise from those in the implanted silicon overlayer, we expect a six order of magnitude decrease in dislocations at the top of the overlayer as well. The absence of threading dislocations in transmission electron microscope cross sections and plan views reinforces this expectation.

Effect of the post‐deposition processing ambient on the preparation of superconducting YBa2Cu3O7−x coevaporated thin films using a BaF2 source

Abstract: We have investigated the effect of the post‐deposition processing ambient on the preparation of YBa2Cu3O7−x thin films from a BaF2 source. The role of H2O vapor during the high‐temperature anneal is understood through a thermodynamic analysis of the fluorine removal reaction. The role of a HF getter (e.g., SiO2) is understood through the same type of analysis. We have demonstrated that a zero resistance transition temperature at 77 K can be obtained for an annealing temperature as low as 690 °C for films deposited on SrTiO3 substrates by increasing the PH2O and decreasing PHF during the high‐temperature soak cycle.

Photo-Process of Tantalum Oxide Films and Their Characteristics

Abstract: TaOx film formation by a photo-CVD method using TaCl5 as a source material is examined. The deposition rate increases with increasing growth temperature and decreasing chamber pressure down to 1 Torr. The leakage current of the formed TaOx film decreases drastically with annealing in the presence of both UV-irradiation and an oxygen ambient after deposition (p-O2 annealing), when the underlying layer contains Si. The leakage current density is 10-8 A/cm2 at the 4 MV/cm electric field. The dielectric constant for MIS structure capacitors decreases with decreasing TaOx thickness, but does not decrease much with p-O2 annealing. In addition, the mechanisms of reduction of the leakage current with p-O2 annealing are discussed.

Rolled texture and magnetic properties of 3% silicon steel

Abstract: Conventional grain‐oriented silicon steels 0.3 mm thick were cold‐rolled to thicknesses from 0.18 to 0.08 mm, and the magnetic properties and grain textures of these sheets were observed before and after annealing. The results indicated that the magnetic induction B8 and the coercive force Hc were 1.8 T and 25 A/m, respectively, for a sheet 0.08 mm thick after primary recrystallization. When a 0.12‐mm‐thick sheet was annealed for more than 6 h at 1200 °C, the tertiary recrystallization had begun, and the (110)[001] texture occupied the whole surface of the sheet. The magnetic properties of this sheet were as follows : B8=1.97 T, Hc =1.7 A/m, W12.5/50 =0.21 W/kg, and W17/50 =0.43 W/kg under the application of a tensile stress of 4 kg/mm2 .

Processing of La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films by dual‐ion‐beam sputtering

Abstract: High quality La1.8Sr0.2CuO4 and YBa2Cu3O7 superconducting thin films, with zero resistance at 88 K, have been made by dual‐ion‐beam sputtering of metal and oxide targets at elevated temperatures. The films are about 1.0 μm thick and are single phase after annealing. The substrates investigated are Nd‐YAP, MgO, SrF2, Si, CaF2, ZrO2‐9% Y2O3, BaF2, Al2O3, and SrTiO3. Characterization of the films was carried out using Rutherford backscattering spectroscopy, resistivity measurements, transmission electron microscopy, x‐ray diffraction, and secondary ion mass spectroscopy. Substrate/film interaction was observed in every case. This generally involves diffusion of the substrate into the film, which is accompanied by, for example, the replacement of Ba by Sr in the YBa2Cu2O7 structure, in the case of SrTiO3 substrate. The best substrates were those that did not significantly diffuse into the film and which did not react chemically with the film. In general, the superconducting transition temperature is found to ...

Ferrite thin films for microwave applications

Abstract: Production of ferrite thin films is the key to integration of microwave ferrite devices (circulators for phased array antennas, for instance). The interesting materials are the usual microwave ferrites: garnets, lithium ferrites, barium hexaferrites. The required thicknesses are a few tens of micrometers, and it will be important to achieve high deposition rates. Different substrates can be used: silicon and alumina both with and without metallization. The films were deposited by rf sputtering from a single target. The as‐deposited films are amorphous and therefore require careful annealing in oxygen atmosphere. The sputtered films are a few micrometers thick on 4 in. substrates. The optimum annealing temperature was found by trying to obtain the highest possible magnetization for each ferrite. The precision on the value of magnetization is limited by the precision on the thickness of the film. We obtain magnetization values slightly lower than the target’s. The ferromagnetic resonance linewidth was measu...

GaAs heteroepitaxial growth on Si for solar cells

Abstract: Thermal annealing effects on the reduction of dislocation density in GaAs on Si substrates were investigated. The dislocation density in GaAs films grown on Si substrates by metalorganic chamical vapor deposition was reduced by in situ thermal annealing to 2×106/cm2. We have found that the cooling and heating cycle of the GaAs film is most important factor in reducing the dislocation density in thermal annealing. Solar cells fabricated using GaAs films with 5×106/cm2 etch pit density have 18% conversion efficiency for the active area under AM1.5 simulated illumination.

Ion implantation damage and annealing in InAs, GaSb, and GaP

Abstract: The characteristics of ion implantation induced damage in InAs, GaSb, and GaP, and its removal by rapid thermal annealing have been investigated by Rutherford backscattering and transmission electron microscopy. There is relatively poor regrowth of these materials if they were amorphized during the implantation, leaving significant densities of dislocation loops, microtwins, and in the case of GaSb, polycrystalline material. For implant doses below the amorphization threshold, rapid annealing produces good recovery of the lattice disorder, with backscattering yields similar to unimplanted material. The redistribution of the implanted acceptor Mg is quite marked in all three semiconductors, whereas the donor Si shows no measurable motion after annealing of InAs or GaP. In GaSb, however, where it appears to predominantly occupy the group III site, it shows redistribution similar to that of Mg.

The effect of phosphorous and sulfur treatment on the surface properties of InP

Abstract: Experimental results are presented for InP surfaces treated by using red phosphorus as a source to create an excess overpressure of phosphorus during annealing and prior to silicon dioxide deposition. The surface has been probed by in situ photoluminescence, noncontacting remote gate C-V, and conventional high-frequency and quasi-static C-V methods. A study has also been made of the surface of sulfurized InP following heating in aqueous (NH4)2S(x). MISFETs fabricated using the benefits of these surface treatments show high transconductances and stabilities approaching those of thermal SiO2/Si with less than 5-percent variation in drain current over a 12-hr period.

Thin-film Bi-Sr-Ca-Cu-O high-temperature superconductors using pulsed laser evaporation from sintered disks

Abstract: Films of the high‐temperature superconductor in the Bi‐Sr‐Ca‐Cu‐O system were deposited by pulsed laser evaporation from a ceramic disk. Films deposited onto (100) MgO show x‐ray diffraction patterns characteristic of c‐axis textured Bi2(Sr,Ca,Bi)3Cu2Ox phase following annealing for 10 min at 850 °C in 20% O2‐80% N2. These textured films have zero resistance at 78 K and show resistance drops near 110 K. The effects of the annealing environment on the electrical and structural properties are presented.

High-resolution and in situ tem studies of annealing of Ti-Si multilayers

Abstract: The solid state amorphization reaction in sputtered amorphous-siliconpolycrystalline-titanium multilayers has been studied in cross-section by high-resolution transmission electron microscopy (TEM). Heat treatments included rapid thermal annealing and in situ heating in the microscope. The bilayer spacing of the sample is 25.0 nm and the composition is 50at.%Ti-50at.%Si. Growth of the alloy is strictly planar. The amorphization does not occur preferentially along titanium grain boundaries. The reaction is diffusion controlled with an activation energy of about 2.0 eV atom−1. When the layers are partially reacted, the amorphous alloy composition is silicon rich, with an estimated Ti:Si atomic ratio of 1:2. Once all of the elemental silicon is consumed the alloy incorporates more titanium, reaching a composition of about Ti45Si55. In situ studies reveal that Kirkendall voids form at this point in place of the silicon layers. In situ annealing studies duplicate the microstructure observed in the bulk-annealed samples; from this we conclude that bulk diffusion dominated in the thin TEM foil.