7319. formation of continous CoSi2 layers by high Co dose implantation into Si(100)

7319. formation of continous CoSi2 layers by high Co dose implantation into Si(100)

Classified abstracts 7318-7325 state. Silicon recrystallization in the silicide layer can be suppressed if the polysilicon is doped with phosphorus p...

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Classified abstracts 7318-7325

state. Silicon recrystallization in the silicide layer can be suppressed if the polysilicon is doped with phosphorus prior to metal deposition, or the phenomenon can be alleviated by an arsenic or boron implantation into the silicide. S Nygren and S Johansson, J Appl Phys, 68, 1990, 105~1058. 34 7318. Influence of elastic stress on the growth kinetics of planar thin-film binary diffusion couples Some possible effects of elastic stress, engendered by epitaxial strain and compositional inhomogeneity, on the kinetics of intermediate phase formation in a planar thin-film binary diffusion couple are identified. A simple quasistatic approximation to the diffusion equation is used to estimate the thickening rate of the intermediate phases when elastic effects are incorporated into both the diffusion equation and the interracial boundary conditions for diffusion using the thermodynamics of stressed solids. The various growth regimes of the phases are visualized using a simple graphical representation of the phase growth velocities (phase plot). Growth kinetics are shown to depend on both the strain engendered by and the crystallographic orientation of the substrate. It is also proposed that elastic stresses could influence the sequence of phase formation in thin-film systems including such observations as the absence of those phases appearing in the equilibrium phase diagram and the initial disappearance and subsequent reappearance of equilibrium phases. W C Johnson and G Martin, J Appl Phys, 68, 1990, 1252-1264. 34 7319. formation of continuous CoSi2 layers by high Co dose implantation into Si(100) We have studied the mechanisms for formation of continuous CoSi2 layers by high dose ( ~ 10 ~7 cm -2) Co implantation into Si(100). For single dose implantations, a critical dose exists above which coalescence into a single layer occurs after a vacuum anneal at 1000°C for 30 min, but below which disconnected, strongly { 111 } faceted precipitates form. Transmission electron microscopy and Rutherford backscattering suggest that the key condition for continuous layer coalescence to occur is the formation of a connected array of small silicide precipitates either asimplanted or during an intermediate 600°C anneal. This postulate is supported by the observation that super-critical doses which are builtup by successive subcritical doses and 1000°C anneals do not coalesce into single layers. R Hull et al, JApplPhys, 68, 1990, 1629 1634. 34 7320. Epitaxial relations between in situ superconducting YBa2Cu3OT_x thin films and BaTiO3/MgAIzO4/Si snbstrates In situ superconducting YBa2Cu307_x films with To0 up to 87 K and Je,77K up to 6 X 1 0 4 A cm- 2were prepared on Si substrates with MgA120 4 and BaTiO ~double-buffer layers. The epitaxial relations between various layers were established by transmission electron microscopy. The MgAlzO4 layer is heavily faulted. The subsequent BaTiO3 layer stops most of the faults, provides a template for the YBa2Cu3OT_x growth, and partially screens off the stress due to different thermal expansion coefficients. The mierostructure of the YBa2Cu 307_x layer is very similar to that of the films deposited directly on SrTiO3, exhibiting a homogeneous heavily faulted single-crystaMike structure free from secondary phases and grain boundaries. The slight degradation of the transport properties is attributed to residual thermal stress. D M Hwang et al, JApplPhys, 68, 1990, 1772-1774. 34 7321. Structure and magnetic properties of Co/Al multilayered films We report on an investigation of Co/A1 multilayered films (MLFs). The samples had periodic layered structures and had in-plane easy axes. Nonmagnetic CoAl compound was formed at the Co/A1 interfaces. Co/A1 MLFs had a perpendicular interface anisotropy. This interface anisotropy energy (Ks) was estimated to be 0.25 erg cm- 2. Taking account the volume contribution of Co layers, it was suggested that perpendicular magnetism would appear when the remaining unmixed Co layer thickness was under 6 A. However, this surface anisotropy energy vanished when the Co layers were thinner than 9 A.. In Co/A1 MLFs with thin Co layers, the island growth of Co on the initial stage was considered to be the reason for K, = 0. T Mitsozuka et al, J Appl Phys, 68, 1990, 1787-1790.

34 7322. lnterdiffusion and resistivity of Cu]Au, Cu]Co, Co[Au, and Cu/Co/Au thin films at 25-550°C The interdiffusion and resistivity of Cu/Au, Cu/Co, Co/Au, and Cu/Co/Au thin-film structures were studied, at temperatures ranging from 25 to 550°C, using Rutherford backscattering spectroscopy, Auger analysis, and four-point probe resistance measurements. Intermetallic phase formation was studied by X-ray diffraction and changes in microstructure were analyzed by scanning electron microscopy. Interdiffusion of Cu and Au in the Cu/Au structure is observed at temperatures as low as 150°C and is accompanied by an increase in resistivity. No significant reactions occur in the Cu/Co, Co/Au, and Cu/Co/Au thin-film structures up to 400°C, after which the resistivity increases. The very rapid increase in resistivity observed at 250°C for the Cu/Au system and at 450°C for Cu/Co/Au, is associated with structural changes in the films which result in large grains and the formation of AuCu, Cu3Au, and Cu3 Au2 compounds. The structural changes in the Cu/Co/Au system occur at a higher temperature because of the time needed for Cu and Au to diffuse through the Co barrier, which did not react significantly with either Au or Cu. P Madakson and J C Liu, JAppl Phys, 68, 1990, 2121-2124. 34 7323. Experimental verification of temperature calculations in multilayers used for Co2 laser recrystallization of silicon-on-insulator films Temperature profiles were calculated numerically for a three-layer stack of SiO2-Si-SiO2 on top of a monocrystalline Si substrate. The stack was locally heated by a CO2 laser whereas the wafer background temperature was controlled by a heat chuck. The calculation method makes it possible to simulate temperatures as functions of laser power, spot radius, scan speed, substrate bias temperature, and layer thickness. These parameters play a major role in COz laser recrystallization of polycrystalline silicon for making single crystalline silicon films on insulator films. It is shown that under conditions of maximum absorption experimental verification of the calculations is possible by measuring the recrystallized track width. A good agreement was found between the calculated and measured results. M J J Thennissen et al, J Appl Phys, 68, 1990, 806-813. 34 7324. Interfacial reactions in Ag-Zn thin film couples Interracial reactions in Ag-Zn thin film couples have been investigated by measuring the contact resistance and composite electrical resistance with time and temperature in order to understand the kinetic behaviour of the system. The resistivity measurements have been supplemented by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The activation energy of diffusion has been found to be 6.1 x 10 20 j from electrical resistivity measurements where the model assumes rapid grain boundary diffusion followed by a defect-assisted path for diffusion into the grain and 8.3 x 10-2o J from contact resistance measurements where the model is based on grain boundary diffusion. XRD indicates the growth of/T-AgZn phase even at room temperature which changes to the/t phase above 250°C. SEM confirms the diffusion of silver through zinc grain boundaries, especially at the interface boundary. TEM indicates the growth of grain size with annealing and confirms the presence of the/~' phase. A K Bandyopadhyay et al, Thin Solid Films, 186, 1990, 87-98. 34 7325. Oxygen impurity effects on the formation of thin titanium silicide films by rapid thermal annealing The behaviour of oxygen impurities during rapid thermal processing of Ti/Si diffusion couples has been studied between 480 and 800°C. Samples were prepared by sputter deposition of 40 nm of titanium on (001) silicon wafers which were then annealed in ambient argon. The investigation techniques included depth profiling using Auger electron spectroscopy, transmission electron microscopy, and electrical sheet resistance measurements. The oxygen impurity effects are mainly controlled by kinetic parameters, i.e. the silicide reaction rate and the oxygen diffusivity in titanium. At low temperatures, the oxygen contamination originating from the annealing furnace is the cause of major impurity effects. Below 550°C the oxygen that spreads into the metal film blocks the silici& reaction while above 650°C, silicide formation dominates over oxygen diffusion and contamination-free silicide is produced. From 550 to 600°C, the competition between silicide reaction and oxygen diffusion results in the formation of a silicon-deficient, oxygen-rich T~Si~:) sublayer on top of the silicide. This layer appears to be composed of TiOx and TiSi2. In some cases, all Ti is reacted by oxygen remains in the layer and the

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