Vacuum Furnace Annealing Research Articles

Interdiffusion, reaction, and stability in a thin film iron-aluminium bilayered system

In this work we describe the results of Rutherford backscattering spectrometry, sheet resistivity measurements, X-ray diffractometry and conversion electron Mossbauer spectroscopy performed on thin film Fe-Al bilayered samples submitted to high vacuum furnace annealing. Isothermal anneals were performed at 570 K for time intervals ranging from 60 to 600 min. It is demonstrated that the diffusion of Al into Fe is smaller than the diffusion of Fe into Al for temperatures below 600 K. Sequential isochronous thermal anneals of 60 min were performed at temperatures ranging from 570 to 870 K, in order to study the stability of the formed phases. The stable Fe2Al5 intermetallic compound formed at 570 K decomposes at about 650 K, and the FeAl6 intermetallic compound appears at temperatures around 750 K.

NiAl3 formation in Al/Ni thin-film bilayers with and without contamination

The interfacial reactions induced by vacuum furnace annealing and rapid thermal annealing in sequentially deposited Al/Ni bimetallic thin-film diffusion couples have been investigated with MeV 4He+ backscattering spectrometry, cross-sectional transmission electron microscopy, and Auger electron spectroscopy. Upon annealing, NiAl3 is the first aluminide phase to grow. In uncontaminated samples, the NiAl3 growth proceeds in uniform planar fashion, governed by diffusion-limited kinetics. The kinetics data fit well with those for NiAl3 growth on large-grained Al substrates, yielding a common kinetics law of x2=kt, where x is the thickness of the NiAl3 grown at the interface, t is the annealing duration, and k is the growth constant, which is given by k=2.24(cm2/s) exp(−1.5±0.1 eV/kBT), in which T is the annealing temperature and kB is the Boltzmann constant. Microscopic examination reveals slight nonuniformity at the Al/NiAl3 interface resulting from shallow local protrusions of NiAl3 grains into the Al layer at grain boundaries. When either the Al film or the Al/Ni interface is purposely contaminated during sample preparation, the roughness at this Al/NiAl3 interface becomes very pronounced, and the reaction rate is significantly reduced. Meanwhile, Ni motion becomes appreciable as NiAl3 grains and/or Ni severely penetrate the Al layer. In contrast, the NiAl3/Ni interface remains sharp in all samples. The irregular morphology and nonuniform reaction cannot be attributed uniquely to the presence of grain boundaries in the Al film, but rather are a combined effect of impurities and Al grain boundaries. Short-term rapid thermal annealing at elevated temperatures appreciably alleviates the nonuniformity at the Al/NiAl3 interface in contaminated samples.

Surface metallurgy with high energy heavy ion beams

High energy noble gas ion beams are currently used to induce the formation of specific surface alloys from vacuum deposited multilayered thin film structures on metallic or insulating engineering components. We discuss in this paper the formation of metastable and stable, amorphous and crystalline phases by ion beam mixing. In particular we discuss the intermetallic compounds of the Fe-Al thin film bilayer system formed on the surface of insulating substrates by means of high vacuum furnace annealing, ion bombardment of the bilayer interface and the simultaneous combination of these two metallurgical treatments.

Reaction of evaporated Ti films with large-grained Al substrates

We have studied the reaction kinetics of titanium films on large-grained aluminium substrates during furnace annealing in vacuum for temperatures between 450–550°C. Oxygen was profiled by elastic resonance16O(α, α)16O backscattering. A TiAl3 aluminide layer always forms at the Ti/Al interface. In addition, a second TiAl3 layer grows at the free Ti surface when the contamination of the annealing ambient by oxygen-carrying species is reduced during annealing. Otherwise, the nucleation of the second compound layer is inhibited by an oxygen-rich surface layer of the Ti.

Growth of WSi2 in phosphorous-implanted W/«Si» couples

The thermal reaction of rf-sputter-deposited tungsten films with a (100) silicon substrate is investigated by vacuum furnace annealing and rapid thermal annealing. An irradiation of the W/Si interface by a phosphorous ion beam at room temperature prior to annealing promotes a uniform interfacial growth of WSi2. The growth of WSi2 follows diffusion-controlled kinetics during both furnace annealing and rapid thermal processing. A growth law of x2 = kt is obtained for furnace annealing between 690 and 740° C, where x is the thickness of the compound, t is the annealing duration after an initial incubation period and k = 62 (cm2/s) exp (−-3.0 eV/kT). The surface smoothness of the suicide films improves with increasing ion dose.

Thin film reactions on silicon surfaces and the quality of metal-semiconductor interfaces

We have studied the formation of thin silicide layers on silicon surfaces by thermal treatments of thin evaporated metal films. Examples are given for Pt/Si, V/Si, and Ti/Si. The treatments studied were vacuum furnace annealing, electron-beam annealing, and xenon lamp illumination. The compositional depth profiles of the resulting structures were analyzed with RBS and Auger/ sputter profiling. Impurities, oxygen and carbon, are present in Ti and V before annealing, and may also become incorporated during the treatment. Thus the quality of the annealing procedures depends strongly on the thermodynamics of the ternary or quarternary mixtures of metal, silicon and impurities. Best results, in terms of silicide homogeneity, purity, and interface sharpness (epitaxy) were obtained for PtSi, xenon lamp annealed for very short times. Also for V and Ti, rapid thermal annealing was found to produce much better structures than vacuum furnace annealing. The influence of oxygen in the systems studied is discussed in terms of ternary phase diagrams.

Arsenic out-diffusion during TiSi2 formation

The behavior of implanted As atoms during high-temperature (800–900 °C) TiSi2 formation was investigated by helium backscattering. A significant As loss was observed during TiSi2 formation by vacuum furnace annealing. The main factors influencing the As loss were the initial As profiles and Ti film thickness. Most of the As loss was caused by rapid As out-diffusion through the TiSi2 layer; the remaining As atoms were only observed in the Si substrate after TiSi2 formation. As long as the As distribution was deeper than the TiSi2 layer, the loss of As atoms was kept to a minimum. Careful selection of the As implantation energy and the Ti film thickness can achieve high As concentration at the TiSi2/Si interface.