Showing papers on "Annealing (metallurgy) published in 1981"

Macroscopic theory of pulsed-laser annealing. I. Thermal transport and melting

Abstract: Pulses of radiation from ruby and Nd:YAG $Q$-switched lasers have been used recently to anneal the lattice damage caused by ion implantation of semiconductors. Other similar applications include the laser-induced diffusion of thin dopant films deposited on the surface of samples, recrystallization of doped amorphous films deposited on single-crystal substrates, and the removal of precipitates present after conventional high-temperature dopant diffusion. All of these processes can be understood in terms of models and calculations based on macroscopic diffusion equations for heat and mass transport, cast in a finite-difference form to allow for the temperature and spatial dependences of the thermal conductivity, absorption coefficient, reflectivity, and other quantities. Results of calculations on silicon with the models show that the near-surface region of a sample can melt and stay molten for times of the order of 100 nsec during which dopant diffusion in the liquid state and nonequilibrium segregation during ultrarapid recrystallization are sufficient to explain the major features of the experimental results. In this paper, a description of the model used in our heat-transport calculations is given. Results of the modeling are illustrated by a variety of calculations which should be of particular interest to experimentalists working with pulsed-laser annealing. These results include, e.g., the effects of pulse duration, shape, and energy density, the effects of assumptions made about the latent heat of amorphous silicon, the effects of substrate heating, the role played by the absorption coefficient in determining melt-front penetration, and the duration of surface melting.

Effects of morphology on the mechanical behavior of a dual phase Fe/2Si/0.1C steel

Abstract: A study has been made on the effects of morphology on the mechanical behavior of a dual phase Fe/2Si/0.1C steel. The coarse dual phase structure obtained by continuously annealing in the two phase region directly from the austenite region results in poor elongation ductility with relatively high strength. However, upon obtaining a fine fibrous or fine globular dual phase structure by following different transformation paths, significant improvements occur in elongation ductility without much sacrifice in strength. The poor elongation ductility of the coarse dual phase structure is due to the initiation of cleavage cracks in the ferrite region where maximum localized stress concentration took place. But, in steels with both fine fibrous or globular morphologies, fracture occurred by void nucleation and coalescence after large amounts of plastic deformation.

Controlled Transient Solid Second‐Phase Sintering of Yttria

Abstract: Compositions of La2O3-Y2O3 were sintered to full density by a process which uses a controlled transient solid phase to retard grain growth sufficiently that pores remain on grain boundaries and are eliminated by solid-state diffusion. The temperature is then decreased into a single-phase region and the structural transition yields a pore-free, single-phase body. Optimum compositions are 8.1 to 12.1 mol% La2O3 for a sintering temperature of 2170°C and annealing temperatures of 1920° to 2020°C, resulting in materials with near-theoretical total transmittances and specular transmittance within 6% of theoretical.

Measurement of Lattice Temperature of Silicon during Pulsed Laser Annealing

Abstract: A classical time-of-flight method was used to determine the temperature of evaporated Si atoms and thus the lattice temperature of Si during pulsed laser annealing. The resulting temperatures between 1200 and 3000 K for energy densities between 1.0 and 2.5 J/${\mathrm{cm}}^{2}$ clearly support a strictly thermal annealing model including melting of the surface region of Si.

Characterization of Plasma‐Deposited Silicon Dioxide

Abstract: Silicon dioxide films have been deposited by reacting silane and nitrous oxide in a parallel‐plate, radial flow, plasma reactor. Deposition parameters (temperature, power, and gas composition) have been systematically varied, and the films characterized by measuring the infrared spectra, deposition rate, density, etch rate, stress, refractive index, step coverage, breakdown voltage, and annealing behavior. The films, deposited at 100°–340°C and at rates of 200–360 A/min, contain 2–9 a/o H bonded as , , and . The films have densities of about 2.3 g/cm3, refractive indexes of about 1.47, a compressive stress usually less than , and etch rates about twelve times faster than thermally grown silicon dioxide. Films deposited below 200°C or at high power etch nonuniformly with part of the film etching very fast, possibly indicating a two‐phase mixture. The step coverage is not conformal and the films are thin along vertical step walls. The films breakdown at fields of 4–10 MV/cm. During annealing in air at temperatures up to 400°C, the films lose hydrogen and become less dense, but do not crack. The properties of the plasma‐deposited silicon dioxide are strongly dependent on the specific deposition conditions. In addition, simple correlations between the properties do not exist. Thus in characterizing plasma deposited silicon dioxide, the exact deposition conditions must be specified and all the film properties of interest must be measured.

On mechanisms of structural relaxation in a Pd48Ni32P20 glass

Abstract: Structural relaxation processes are investigated calorimetrically for a pre-conditioned Pd48Ni32P20 glass over a wide temperature range from well below to just above the glass transition. The low temperature anneals further stabilize the glassy structure. Upon heating, the annealed sample shows an excess endothermic specific heat ΔCp above the annealing temperature and completely recovers the initial enthalpy before any manifestation of glass transition, Tg. Significantly the ΔCp peak evolves in a continuous manner with annealing time. A physically reasonable activation energy spectrum N 0 ∗ (Q) is obtained with the proper choice of coupling constants which are dependent on annealing temperature. Results suggest the existence of localized relaxation modes which do not contribute to macroscopic flow. A concept of distribution in glass transition temperatures H(Tg,m) is conceived to account for the reversible relaxation with temperature. A model glass transition based on percolation theory is proposed and is found to reproduce the calorimetric relaxation phenomena well.

Macroscopic theory of pulsed-laser annealing. II. Dopant diffusion and segregation

Abstract: The radiation from $Q$ -switched ruby and Nd:YAG (yttrium aluminum garnet) lasers can anneal the lattice damage produced by ion implantation of semiconductors. In the first paper of this series, we described the models and methods we have been using for heat-transport calculations during pulsed-laser annealing and gave numerous illustrations of the type of results which are obtained. In this paper, we discuss dopant-diffusion calculations in detail, with particular emphasis on the incorporation of segregation effects into the modeling. From the forms of the experimental dopant profiles, it is established that pulsed-laser annealing is a nonequilibrium process, but in this paper the interface segregation coefficient is treated as an adjustable parameter and no attempt is made to justify the values obtained. Approximate analytical and finite-difference solutions to the diffusion equation are discussed and compared. It is argued here that the excellent fit between theory and experiment which is obtained is a strong indication of the basic validity of the melting model of pulsed-laser annealing.

Ion implantation and low‐temperature epitaxial regrowth of GaAs

Abstract: Channeling and transmission electron microscopy have been used to investigate the parameters that govern the extent of damage in ion‐implanted GaAs and the crystal quality following capless furnace annealing at low temperature (∼400 °C). The implantation‐induced disorder showed a strong dependence on the implanted ion mass and on the substrate temperature during implantation. When the implantation produced a fully amorphous surface layer the main parameter governing the regrowth was the amorphous thickness. Formation of microtwins after annealing was observed when the initial amorphous layer was thicker than 400 A. Also, the number of extended residual defects after annealing increased linearly with the initial amorphous thickness and extrapolation of that curve predicts good regrowth of very thin (<400 A) GaAs amorphous layers produced by ion implantation. A model is presented to explain the observed features of the low‐temperature annealing of GaAs.

Thermal stability of titanium nitride for shallow junction solar cell contacts

Abstract: To demonstrate the thermal stability of titanium nitride as a high‐temperature diffusion barrier, the TiN‐Ti‐Ag metallization scheme has been tested on shallow‐junction (∼2000 A) Si solar cells. Electrical measurements on reference samples with the Ti‐Ag metallization scheme show serious degradation after a 600 °C, 10‐min annealing. With the TiN‐Ti‐Ag scheme, no degradation of cell performance is observed after the same heat treatment if the TiN layer is ≳1700 A. The glass encapsulation of cells by electrostatic bonding requires such a heat treatment.

Metastable Au-Si alloy formation induced by ion-beam interface mixing

Abstract: An amorphous Au-Si alloy with composition Au-28·5 at. % Si (Au5Si2) has been formed by inplanting energetic Xe, Ar or Ne ions through a thin layer of Au deposited on a Si substrate. The ion-induced amorphous Au-Si alloy is uniform in composition and in thickness as indicated by 4He+ backscattering measurement. The Au-Si alloys so obtained were studied by resistivity measurements and by transmission electron microscopy and diffraction. Two distinct stages of phase transformation are observed as revealed by a sudden change of resistivity with increasing annealing temperature. In the first stage, a transformation from amorphous to a metastable crystalline Au5Si2 phase occurs in a narrow temperature range around 100°C. The second stage, which appears broader near 180°C, involves the transformation to the equilibrium two-phase state of Au and Si. The kinetics of the amorphous to metastable crystalline transformation has been determined by isothermal annealing over the temperature interval 85-101°C. An...

Gold gettering in silicon by phosphorous diffusion and argon implantation: Mechanisms and limitations

Abstract: The ability of phosphorus diffusion or argon implantation to remove gold from a silicon wafer has been studied. Both the gettering layer and the gettered substrate have been analyzed for their gold content by complementary techniques such as Rutherford backscattering, neutron activation analysis, and deep level transient spectroscopy. Phosphorus diffusion allows a very efficient gold removal when surface concentration CS and temperature T are kept in a well‐defined domain (high CS , low T). On the contrary, the gettering is ineffective in the low CS , high T domain. The boundary between these two domains is found to be an iso‐Fermi level curve corresponding to Ec −EF = 0.15 eV. These results are explained by the formation of a negatively charged (P, Au) pair. Argon implantation induces a damaged layer which is found to accomodate large amounts of metal. However, at annealing temperatures higher than 800 °C, gold is found to remain in the bulk at noticeable concentrations which increase with temperature. S...

Rapid isothermal annealing of ion implantation damage using a thermal radiation source

Abstract: The rapid annealing of ion implantation damage in silicon using the radiation from a graphite heater has been demonstrated. Complete 3‐in.‐diam wafers were annealed in a single 10‐sec exposure with high activation for implants of boron (50 keV; 1×1015 cm−2) and moderate activation for high‐dose arsenic implants (140 keV; 6×1015 cm−2). Dopant redistribution was ∼1000 A for boron and ∼200 A for arsenic. Leakage currents of implanted p+n and n+p diodes were comparable to those of furnace‐annealed control wafers and indicate good crystallinity in the depletion region near the junction. Diode leakage uniformity across the wafers was also excellent. C‐V measurements on oxides annealed by this technique showed flatband voltages within 0.5 V of those measured on control wafers. This method of annealing implant damage is a practical alternative to those involving more elaborate power sources such as lasers, electron beams, or high‐intensity arc lamps.

Heat-pulse annealing of arsenic-implanted silicon with a CW arc lamp

Abstract: A new annealing method is introduced whereby a silicon wafer is irradiated by a short heat pulse generated by CW lamps. Results of the annealing process obtained from medium-dose arsenic-implanted silicon are similar to those obtained from nonmelting short heat treatments-complete activation of the implanted dopant with no diffusion or distortion of the impurity profile. Investigation of the crystal structure by means of TEM indicates a lack of any defects down to a resolution of 10 A. Because of its simplicity, heat-pulse annealing has the potential of higher throughput in comparison to equivalent laser or electron-beam irradiation.

Interference enhanced Raman scattering study of the interfacial reaction of Pd on a‐Si:H

Abstract: The application of interference enhanced Raman scattering to probe the structure of metal/semiconductor interfaces is described. This technique is used to study the interface structures of Pd on hydrogenated amorphous Si (a‐Si:H) with particular attention to the effects of a native oxide layer on the a‐Si:H. It is found that for deposition on lightly oxidized a‐Si:H, ∠20 A of Pd is consumed to form a crystalline silicide interfacial structure with composition near Pd2Si. Annealing causes growth of this phase and further consumption of Pd until a second phase of Pd2Si is observed. If the deposition is repeated on more heavily oxidized a‐Si:H, no silicide formation is observed even at annealing temperatures of 400 °C.

Mechanical properties and superstructure of high‐modulus and high‐strength PET fiber prepared by zone annealing

Abstract: The relationships between mechanical properties and superstructure of the poly(ethylene terephthalate) fiber prepared by a new annealing method called zone annealing method were investigated. The effectiveness of zone annealing was compared with three other annealing methods, namely, annealing under release, annealing at constant length, and annealing under tension. The very high modulus and strength of the zone-annealed fiber were directly attributed to the large number of tie molecules connecting the crystallites and to the high orientation of the amorphous region.

Electrical Properties and Stability of Supersaturated Phosphorus‐Doped Silicon Layers

Abstract: Supersaturated solutions of phosphorus in silicon were obtained by ion implantation and pulsed ruby laser annealing. The dependence of electron mobility and electrical resistivity on carrier density was accurately determined by Hall effect and resistivity measurements. Maximum dopant concentration was , corresponding to a resistivity of 110 μΩ cm and to an electron mobility of 11 cm2/V sec. The stability of these alloys was analyzed by isochronal and isothermal annealing. In the more heavily doped samples a remarkable deactivation of the dopant was verified also for thermal treatments of 1 hr at 300°C. TEM examinations showed a large amount of precipitates with density and size depending on supersaturation. Finally it was observed that the electron mobility depends only on the carrier density and is unaffected by the electrically inactive phosphorus, even when present at very high concentrations.

Growth interface breakdown during laser recrystallization from the melt

Abstract: Morphological instability occurring during high‐velocity Si crystal growth from an impurity containing melt is examined in detail. The experimental conditions are achieved by annealing an ion‐implanted Si layer with pulsed laser radiation. Computer modeling is employed to understand the heat flow and impurity diffusion behavior that occurs. The stability and size of impurity segregation cells observed to occur under particular conditions are related to the predictions of morphological stability theory.

Kinetics of low temperature structural relaxation in two (Fe‐Ni)‐based metallic glasses

Abstract: Structural relaxation processes below the glass transition temperature have been investigated calorimetrically via isothermal annealing and the time shift method for (Fe.5Ni.5)75P16B6Al3 and Fe40Ni40P14B6 glasses. The relaxation spectra are described by broad distributions in both activation energies and frequency factors. The low temperature anneals stabilize a portion of the relaxation spectrum and the annealed sample upon heating shows an endothermic reaction above the annealing temperature. The effects of successive annealing are additive provided that the anneals are followed by a lower temperature one. The results may account for many aging behaviors, such as the wide variation in activation energies, ’’reversibility’’ in Curie temperature and the cross‐over phenomenon.

Radiation Annealing of GaAs Implanted with Si

Abstract: The use of radiation from halogen lamps to anneal implanted GaAs has been studied. Semi-insulating GaAs wafers implanted with 3×1012 cm-2 silicon at 70 keV were completely activated by 5 seconds rediation with or without encapsulation. The wafer temperature reached 950°C. This annealing method minimizes the thermal conversion of semi-insulating GaAs wafers.

Temperature dependence of the reflectance of solid and liquid silicon

Abstract: The reflectivity of silicon plays an important role in laser annealing. Results from literature are limited either to 225 °C in the solid phase or to 1410 °C in the liquid phase. Measurements, at 633 nm wavelength in a large temperature range near melting point, are reported here.

Scattering loss reduction in ZnO optical waveguides by laser annealing

Abstract: We report successful laser annealing of ZnO optical waveguides deposited on an amorphous SiO2 layer thermally grown on Si. A significant improvement in the optical attenuation of the fundamental mode from several dB/cm before laser annealing to as low as 0.01 dB/cm after laser annealing is observed. Scattering loss measurements for the m = 1 and m = 2 mode are also reported. We attribute the reduction in loss primarily to an improvement in the quality of the ZnO film in the region near the ZnO‐SiO2 interface.

Sub‐sub Tg structural relaxation in glassy polymers

Abstract: Structural relaxation in a temperature range from 32 to 62° K glass transition has been investigated, for the first time, for a nearly monodisperse polystyrene using a differential scanning calorimeter and a thermal mechanical analyzer. Low temperature anneals in the vicinity of 320 K stabilize the glassy structure and lead to volume contraction. Upon heating, the annealed samples show an excess endothermic peak and exhibit a gradual expansion associated with structural recovery above the annealing temperature. Significantly, the samples recover the initial heat content and volume without reheating through the glass transition temperature. This sub‐Tg structural relaxation behavior is in many respects distinct from that commonly observed near the glass transition. Kinetics of relaxation processes are also discussed.

Fundamental absorption edge of evaporated amorphous WO3 films

Abstract: The fundamental absorption edge of evaporated WO3 films is investigated. The optical gap of the virgin film is estimated to be 3.41 eV at room temperature and it decreases with increase of annealing temperature up to 200°C. Annealing at 300°C leads to change in the spectral shape, which is caused by crystallization. For the films annealed at 200°C, temperature coefficient of the optical gap is estimated to be −2×10−4 eV/K and the slope of Urbach's tail is found to be independent of measuring temperature up to 200°C. With electrolytic coloration, shift of the optical gap toward higher energy is observed. Magnitude of this shift is estimated to be 0.05 eV at the color center concentration of 7.5×1021 cm−3 when H+ electrolyte is used. If Li+ electrolyte is used, the magnitude of this shift is about three times larger than in the case of H+ electrolyte. This fact is interpreted by a small change in the host matrix structure owing to the injection of proton or Li+ during coloration.

Formation of pin holes in hydrogenated amorphous silicon at high temperatures and the yield strength of a‐Si:H.

Abstract: The formation of holes in sputtered hydrogenated amorphous silicon films after isochronal annealing has been investigated. The holes are caused by the breaking of hydrogen‐containing bubbles formed at the film‐substrate interface as hydrogen diffuses from the film. The diameter of the holes is dependent on the film thickness, and the number of holes depends linearly on the initial hydrogen concentration. These simple relationships are used to derive the yield strength of a‐Si:H to be about 1.3×109 dyn/cm2.