Amorphous Si/Ti multilayers transform at high temperatures (above 700°C) to TiSi2-C54. This phase is important for microelectronics applications because of its low resistivity, stability up to 900°C, and compatibility with silicon processing. However, an unfavorable metastable TiSi2-C49 phase is usually formed at lower temperatures. Thus, an understanding of the C49 phase formation kinetics is useful to the device processing strategy. The kinetics of the transformation of TiSi2-C49 phase can be characterized as a process of nucleation and growth, using the well known Johnson Mehl Avrami (JMA) equation. In the present work the formation kinetics of the C49 phase has been studied by an in situ x-ray diffraction technique. Isothermal annealing in vacuum was done at four temperatures, in the range of 275"C to 310°C. A position sensitive detector (PSD) was used to simultaneously collect the diffracted beams of (131) and (150) peaks of the C49 phase. From the data, the Avrami exponent, n, was determined to be 2.0±0.1. The reaction rate constant k follows a familiar Arrhenius-type equation with a measured activation energy of 2.5eV. Comparison of our x-ray results with kinetic data obtained by other means will be discussed.

In this study, the phase transformation and the surface and interface morphologies of TiSi2 formed on atomically clean Si substrates are investigated. 200Å Ti and 400A Si films on Si(111) have been co-deposited at elevated temperatures (400°C - 800°C) in ultrahigh vacuum. The phase transition of TiSi2 is characterized with using XRD. The results distinguish the formation of the C49 and C54 crystalline titanium silicides. The surface and interface morphologies of titanium silicides have been examined with SEM and TEM. A relatively smooth surface is observed for the C49 phase while a rough surface and interface are observed for the C54 phase. The islanding of the C54 phase becomes severe at high temperature (800°C). Islands of TiSi2 have been observed at temperatures above 700°C but no islands are observed at temperatures below 600°C. For films deposited at 400TC and 500°C, weak XRD peaks corresponding to TiSi were observed and TEM micrographs exhibited small crystalline regions of titanium silicide at the interface.

The microstructure and kinetics of the polymorphic C49 to C54-TiSi2 phase transformation have been studied using samples prepared as in self-aligned silicide applications. For C49-TiSi2 thin films formed at temperatures of 600°C and 625°C on (100) single-crystal silicon substrates, the effective activation energy was 5.6 ± 0.3 and 5.7 ± 0.08 eV, respectively, for this phase transformation carried out in the temperature range of 600°C to 700°C. The transformation process was observed to occur by nucleation and growth of the orthorhombic face-centered (C54) phase from the as-formed orthorhombic base-centered (C49) phase.

The energetics associated with the formation of CoSi2 have been investigated by using the equilibrium shape of isolated precipitates. Two types of precipitates were studied: CoSi2 equilibrated at the Si surface and CoSi2 equilibrated within the Si lattice. CoSi2 precipitates form by facetting along {111} and {1100} planes in Si. Using a reverse Wulff approach, a ratio of interfacial free energies of γ{100} / γ{111) has been measured to be 1.43 ± 0.07.

Cubic FeSi2 precipitates were produced in Si (001) wafers by Fe implantation at room temperature, followed by ion beam-induced crystallization at 320°C, and their stability upon thermal annealing was examined by transmission electron microscopy. We found that the cubic phase remains relatively stable for a 650°C anneal, but the precipitates tend to change from an aligned to a twinned orientation with respect to the Si matrix. For higher temperature (800 and 900°C) anneals, most of the precipitates are transformed into β-FeSi2, accompanied by substantial precipitate coarsening. For platelet-shaped precipitates, the coarsening activation energy was determined to be 3.48 eV.

Recently, a generalized kinetic model for silicide formation has been developed and a principle of the largest free energy degradation rate (largest FEDR) has been proposed. Free energy change rate as a function of diffusion flux has been derived from the kinetic model so that the principle can be justified not only for first phase formation but also for the subsequent processes. Silicide formation sequence predictions, from the model and the FEDR principle, for 15 metal-Si systems have shown very good agreement with the experimental results reported in the literature. In this paper, a brief introduction to the model and the principle is given, followed by examples of the predictions for several metal-Si systems and comparison with experimental results.

Co silicide formed via selective diffusion of Co through a Ti interfacial layer has been reported by several groups. In this report, phase identification of the silicide has been further studied for both Co/Ti and Ti/Co multi- and bilayers deposited on p(100)-Si substrates. The samples were either vacuum furnace or RTA annealed from 550°C to 900°C. The Co silicide formation sequence in the Co/Ti-Si systems follows CoSi2→Co2Si→CoSi→CoSi2 with the formation temperature increasing for each phase. The Co/Ti bilayer CoSi to CoSi2 transformation temperature was lower than that for the six layer Co/Ti system. For the multilayer sample with Co as the first layer in contact with the Si substrate, CoSi2 formed at 550°C and then CoSi was observed at higher temperatures due to the effect of Co supply on disilicide phase instability. Epitaxial CoSi2 growth occured at higher temperatures after the removal of the unreacted upper layers. A 15 μΩ-cm film resistivity was obtained from 50 nm epitaxial CoSi2.

The reaction rate kinetics of the thin film solid-state reaction between 120 nm of Pd and 100 or 300 nm of a-Si:H(18at%) to form Pd2Si were studied in situ using x-ray diffraction and four-point probe resistivity measurements during isothermal annealing. These two techniques yielded activation energies and prefactors of Ea=1. 36±:0.11 eV with ko=4.29 cm2/sec for the x-ray diffraction experiments; and Ea=0.97±0.22 eV with ko=3.42x10-4 cm2/sec for the resistivity measurements. The activation energy and prefactor obtained from the c-Si substrate of the resistivity measurements yielded Ea=l.41±0.31 eV and ko=10.6 cm2/sec. Comparisons showed that the silicide formed from the a-Si:H reacted approximately 1.4 times faster than the silicide formed from the c-Si in the same sample, but three times faster than silicide formed on pure c-Si(111). The crystalline texture and grain size of the metal and silicide films were examined.

The aim of this paper is to investigate phase formation and growth kinetics in thin film Cu/a-Ge difflusion couples (150 nm Cu / 150 nm Ge) by means of cross-sectional transmission electron microscopy. During annealing in the temperature range between 100 and 180°C a highly supersaturated ζ-phase was formed first; the growth of this phase exhibits a parabolic dependence, thus indicating diffusion controlled growth; further annealing leads to a transformation into the orthorhombic ε1-phase. The first phase formed during the contact reaction probably depends on the texture and orientation of the copper layer with (111) Cu favouring the formation of the ζ-phase. When in contact with crystalline Ge the orthorhombic ε1-phase is formed directly, probably caused by a lack of driving force for the formation of the ζ-phase.

Crystallization of Cu-contaminated amorphous Ge is characterized by the formation of an extremely fine-grained microstructure; higher Cu contents lead to primary crystallization of the ε1-phase (orthorhombic Cu3Ge) followed by polymorphous crystallization of the amorphous matrix into crystalline Ge. These results indicate that the early formation of a crystalline interlayer is not due to the reduced crystallization temperature of an amorphous Ge(Cu) film as formed by Cu diffusion into the amorphous Ge.

Simultaneous occurrence of multiphases was observed in the interfacial reactions of ultrahigh vacuum deposited Ti, Hf and Cr thin films on (111)Si by high resolution transmission electron microscopy in conjunction with fast Fourier transform diffraction analysis and image simulation. For the three systems, an amorphous interlayer as well as a number of crystalline phase were found to form simultaneously in the early stages of interfacial reactions. The formation of multiphases appeared to be quite general in the initial stages of interfacial reactions of UHV deposited refractory thin films. The results called for a reexamination of generally accepted “difference” in reaction sequence between bulk and thin film couples.

W or Mo directly deposited on Si cold substrate by electron-beam gun at a base pressure of 10-6 torr is not able to form silicide even annealed at 900 °C in either N2 or H2 ambient. We present an easy way that Mo and W silicides can be formed on the same depositing and annealing conditions with the help of an intervened layer of cobalt or its alloy. Investigation was made on various metallizations of Mo (or W)/Co/Si, W/Co-Mo/Si, and Co/Mo/Si in normal flowingnitrogen or in H2 ambient at various temperatures. In the systems of Mo (or W)/Co/Si and W/Co-Mo/Si, the overlying Mo (or W) can be transformed into silicide at 900 °C, while in the Co/Mo/Si system, where stable Co-Mo compounds are formed in advance, no silicide can be formed. Why silicide is formed in preference to metal oxide in N2 environment at higher temperature is based on Ellingham diagram.

Silicide formation through deposition of Ni onto hot Si substrates has been investigated. Ni was deposited onto <100> oriented Si wafers, which were heated up to 300°C, by e-beam evaporation under a vacuum of <2x10-6 Torr. The deposition rates were varied from 0.1 nm/s to 6 nm/s. The samples were then examined by both cross sectional and plan view transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy and electron diffraction. The experimental results are discussed in terms of a new kinetic model.

The Cu/a-Si:H system has been studied by gas effusion method, elastic recoil detection analysis (ERDA), in situ sheet resistance measurements and scanning electron microscopy. Cu layers of 15 and 90 nm in thickness were deposited by e-beam evaporation onto 1 μm a-Si:H films produced by RF glow discharge on Si(100) substrates at 250 °C. The most important effects are observed in the effusion measurements, when pure a-Si:H samples and Cu/a-Si:H samples are compared. For the Cu/a-Si:H samples, three well-defined peaks are observed, one at very low temperature (T=200 °C), another at 380 °C and a high temperature peak at about. However, pure a-Si:H shows only one effusion maxima at 550 °C. The low temperature effusion peaks are directly correlated with steps increases in the sheet resistance measurements. The first one (T=200 °C) is due to the beginning of silicide formation. The H2 evolution at 380 °C is correlated to phase transition in the a-Si:H film. The hydrogen depth profiles obtained by ERDA and SEM observations are also used to describe the aspects of the Cu/a-Si:H interaction.

Detailed relationship between the fractal dimension and the excess noise frequency exponent has been considered for metal-silicon interfacial structures during the phase transformation to the initial compound phase formation in thin film systems. In the estimation of the fractal dimension of the thin film structures, a technique has been used, which basically employs a digital image processing of highly magnified micrographs of the structures. Previously measured frequency exponent data of the excess noise power spectral density for the same thin film systems has been interpreted by introducing a multiplication process which combines the fractal dimension variations and cluster interactions of the interfaces. It has been assumed that the fractal dimension plays a role as a multiplication factor in the multiplication process.

Diffusion of atoms and molecules on surfaces plays an important role in the growth of thin films. In the present study, the surface vacancy diffusion on Cu and Ni (100) and (111) planes is investigated via atomistic simulations. This investigation is performed using the Embedded Atom Method (EAM) interatomic potentials and the finite temperature properties are determined within the local harmonic and quasiharmonic frameworks. This study helps reveal fundamentals of surface vacancy diffusion in the thin film growth. Our results show that the vacancy diffusion is important on (100) surface but it is not the dominant diffusion mechanism on (111) plane.

The crystal structure of sputter deposited chromium thin films on Coming 7059 glass, polytetrafluoroethylene, and cold rolled (110) oriented low carbon steel α-Fe substrates was investigated as a function of O and C incorporation into the growing Cr film. The as-deposited crystal structure of the films was found by X-ray diffraction to be either highly oriented (110) BCC α-Cr or (200) oriented A-15 δ-Cr. Chemical analysis of the films by Auger electron spectroscopy determined that the δ-Cr phaseformed when the combined O and C impurity concentration in the film was ∼15-30 at.%. At total impurity concentrations above ∼30 at.% or below ∼10 at.% standard BCC α-Cr formed. The crystal structure of the films was not influenced by the substrate material. X-ray photoelectron spectroscopy of the Cr 2pl/2-2p3/2 orbitals indicated that the dominate binding state of both the BCC α-Cr and A-15 δ-Cr films was characteristic of elemental Cr. Vacuum annealing of the A-15 δ-Cr films at 500º for one hour transformed the crystal structure into BCC α-Cr without a measurable change in chemical composition. The incorporation of O and C into the growing Cr film is believed to impurity stabilize the A-15 structure and favor its formation over the BCC structure.

Oxygen plays an essential role in the growth of a variety of oxides such as high-Tc superconductors, ferroelectrics, ferrites and dielectrics. The oxygen available for film growth during laser ablation can come from two sources: the target material and the ambient deposition atmosphere. The amount of oxygen incorporated from these two sources at room temperature has been investigated over a range of deposition pressures. Thiswas accomplished using 18O as a tracer during pulsed laser deposition of amorphous filmsfrom Cu and CuO targets. It was found that the total amount of oxygen incorporated by the amorphous films increases with chamber pressure up to approximately 35 mTorr. For pulsed laser deposition from the oxide target, the major fraction of the oxygen within the deposited material comes from the target. For the oxide target, the amount of oxygen incorporated from the ambient atmosphere is strongly pressure dependent with a maximum near 35 mTorr. These results are compared to earlier work with YBa2Cu3O7.

We present a microstructural study of boron nitride films grown by ion-assisted pulsed laser deposition. Fourier transform infra-red spectroscopy, electron energy loss spectroscopy, and electron diffraction measurements indicate that within the irradiated region of the substrate, the film consists of high fraction of cBN with a small amount of the turbostratic phase; outside of the irradiated region, only the turbostratic phase is detected. Conventional and high resolution electron microscopic observations of the boron nitride microstructure indicate that the cBN is in the form of twinned crystallites, up to 30 nm in diameter. We also observe particulates, formed by the laser pulse, that reduce the yield of cBN in the irradiated regions by shadowing local areas from the ion beam.

The microstructure of Si thin films, deposited on in-situ cleaned Si(100) surfaces by remote plasma-enhanced chemical-vapor deposition (RPECVD), is dependent on the process pressure, substrate temperature and H2 flow rate. Surface characterization by on-line low energy electron diffraction, LEED, has been used to detect changes in the character of the deposited films which can either be amorphous, microcrystalline or crystalline, hereafter designated as a-Si, Sμc-Si, and c-Si, respectively. We have used these results to generate phase diagrams for the Si microstructure as a function of the process pressure and substrate temperature, including the flow rate of H2 as an additional deposition parameter.

Thin In46Sb54 films have been prepared on glass substrates by flash evaporation. Films of 1000 Å were deposited at room temperature. After 7 mins' thermal annealing at 450ºC, an average grain size increased from 20 nm to 200 nm. Under exposure to a Fraunhofer diffracted pulsed Nd-YAG laser beam, the films showed different microstructures for different applied laser power. In general, five regions are identified: ablation region, regions with grain sizes less than 20 nm, grain sizes ranging from 400 to 1000 nm, grain sizes ranging from 200 to 400 nm and unchanged region. The previous five regions are counted from the center of the exposed area outward. The pulse duration is 16 ns. In this paper, an atomic migration mechanism is proposed to explain the power dependent microstructures changes. Transmission electron microscopy was mainly used to characterize the films. The application of this type of phase transformations in the phase change optical storage is also discussed.