The growth mode of Si on GaAs(100) substrates and that of GaAs on very thin (1/4 ∼ 3 ML) Si films grown pseudomorphically on GaAs was investigated by observing the behavior of the reflection-high energy electron diffraction (RHEED) specular spot intensity. From the presence of RHEED oscillations during the initial stage of the growth of Si on GaAs we infer a two-dimensional growth with nucleation on the terraces up to a thickness of 3 ML. During the posterior growth of GaAs on the pseudomorphic Si films, a tendency towards three dimensional growth was observed. This tendency increased with the Si interlayer thickness. The causes of the formation of these islands are discussed.

The morphology and interface chemistry occurring during the initial stages of growth of GaN and A1N layers has been obtained. Films were grown using gas source MBE equipment containing an ECR plasma source to activate molecular nitrogen. The experiments consisted of sequential depositions of about one monolayer thick films and XPS analysis. Evidence for silicon nitride formation on the SiC surface was obtained from the studies of both the Si oxidation states and the substrate peak intensity dependence on film thickness. The growth of GaN on sapphire appeared to occur via the Stranski-Krastanov mode, while the growth on SiC showed characteristics of three-dimensional growth. AlN grew in a layer-by-layer mode on both substrates.

Cerium dioxide (CeO2) layers epitaxially grown on (100), (111) and (110) silicon substrates by electron beam evaporation in an ultra-high vacuum were investigated. CeO2 layers on Si (111) substrates were proved to be epitaxially grown at the substrate temperature above 200°C, and had considerably good crystalline quality. On the other hand, CeO2 layers grown on Si (100) at 800°C consisted of more than 98% volume fraction of (110) component. Cross-sectional high resolution transmission electron microscopy and selected area electron diffraction verified clearly the above crystallography orientation and that the <100> direction in the CeO2(110) plane was parallel with the <110> direction in the Si (100) plane. The cross-sectional lattice image confirmed the existence of ∼ 6 nm-thick intermediate amorphous layer between the CeO2 layer and the Si substrate.

GaAs/AlxGa1-xAs (x=0.5, 0.6, 1.0) superlattices used as buffer layers in HEMT devices have been grown by Metalorganic Chemical Vapor Deposition (MOCVD) at. atmospheric pressure, and characterized by cross-sectional transmission electron microscopy (XTEM). The initial stage of nucleation on the substrates has been clearly verified by examining the undulations of a 30na GaAs layer sandwiched between the substrate and the superlattice. Both Alo.5Gao.5As/GaAs and AlAs/GaAs superlattices can smooth out interface roughness caused by contaminations and dislocations on the substrate surface. The mechanism of smoothing effect has been discussed in detail.

Enhancement of solid-phase epitaxial growth (SPEG) due to hydrostatic pressures and bending stresses is explained by stress-enhanced mobility of point defects in the amorphous solid. The crystallization is by the adjustment of atomic positions in the vicinity of the crystallization/amorphous (c-a) interface due to self-diffusion in the amorphous phase, assisted by a free energy decrease equal to the difference in free energies between the amorphous and crystalline phases. Due to a mismatch in the bulk moduli between the amorphous and crystalline phases, the application of a hydrostatic pressure can develop tensile stresses in the amorphous layer near the c-a interface. Non-hydrostatic stresses in the amorphous layer enhance the mobility of point defects in the amorphous layer and, therefore, an enhancement of the SPEG rate. In the cases of both hydrostatic pressure and bending, the enhancement occurs in the tensile side, indicating that vacancy-like mechanism is predominant in SPEG.

The crystallization of sputter-deposited Si/Al amorphous alloys was examined by transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). In-situ high-resolution TEM reveals the existence of an Al layer between the amorphous matrix and the growing crystalline phase. The activation energy for the growth is about 1.2eV, roughly corresponding to the activation energy of Si diffusion in Al. These two observations support the view that a crystallization mechanism, in which an Al buffer layer provides the shortest reaction path, is responsible for the reaction. The product microstructure exhibits secondary crystallization at a higher temperature.

This paper describes a stability analysis of the solidification interface during graphite-strip zone-melting-recrystallization of Silicon-On-Insulator thin film structures. The study focused on instabilities induced by i) variations in the optical properties due to thickness perturbations in the structure and ii) changes in optical properties during phase change. Reflective and emissive interference effects between multilayers play a significant role in the temperature distributions during processing. The presence of a step perturbation imbedded within the film structure affects local heat absorption and resulting temperature profiles. Such disturbances that trigger instabilities at the solid-liquid interface were investigated numerically. Processing speeds which cause interface instability due to optical property variation during phase change were identified.

A new method for obtaining a planar silicon film on glass substrates (SOG) with controlled crystal orientation has been introduced. This technique uses solid phase epitaxy (SPE) with external seed to fabricate the orientation-controlled SOG structure. Heat treatment of amorphous SOG substrate in contact with mesa striped Si seed crystal was performed at 540°C for 16 hours to form the SPE layer. The planar surface of the SOG structure is due to the most important feature of the present technique-the separation of the seed from the substrate after SPE.

A detailed study by real time spectroellipsometry of the early stage of the growth of microcrystalline silicon (μc-Si) on various substrates is presented. In practical applications μc-Si films are generally deposited on hydrogenated amorphous silicon (a-Si:H) or on transparent conducting oxides (TCO). In the case of a-Si:H, the beginning of the deposition is described by an uniform growth of a 60 Å thick porous μc-Si. However a nucleation-coalescence mechanism is observed during the growth of the first 60–70 Å thick μc-Si on smooth crystalline silicon (c-Si) substrate. In contrast a strong chemical reduction of the TCO substrates is observed during the first 10–20s of the exposure to the hydrogen diluted plasma. Then the ellipsometric measurements reveal an induction period of 30–60 s for the nucleation of microcrystallites. The influence of the preparation conditions of μc-Si on the TCO / μc-Si interfaces formation is emphasized.

The early stages of the growth of plasma deposited amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si) on glass substrates are investigated by in situ infrared phase modulated ellipsometry (IRPME) in the silicon-hydrogen stretching mode region. μc-Si are prepared by alternating SiH4 and H2 plasmas. New insights on the plasma-surface interactions during the growth of these films are given. During the deposition of the first 20 Å of a-Si:H, the hydrogen is incorporated as SiH2. During the further growth of a-Si:H the SiH2 bonds are located at the film surface inside a very thin hydrogen rich overlayer. During the deposition of the first 10–20 Å of μc-Si, the SiH2 bonds are predominantly removed by the H2 plasma, the material being amorphous. After this selective removal of the SiH2 groups, a transition from amorphous to microcrystalline growm is observed. A systematic hydrogen etching during the further growth of μc-Si is observed.

A hydrogenated amorphous silicon (a-Si:H) interface fabrication technology for the plasma CVD method, which can produce low interface defect density, is presented. The relation between the interface defect density and radio frequency (RF) power was investigated. As a result, the difference between the interface defect density and the bulk defect density decreased with increasing the RF power. A high RF power (25 W) a-Si:H buffer layer 5 nm thick was deposited on the interface before depositing low RF power (5 W) a-Si:H layer with a low bulk defect density. It has been found that the ideal defect density distribution, which shows the uniform distribution with the very low defect density (4.2×1014 cm) from the i/i interface to the bulk, can be accomplished by 5 nm buffer layer.

The crystallization of an amorphous thin film, when it is annealed, can be described in terms of the latent heat of the transformation and an activation energy which depends upon the configurational entropy of the surface of the crystallizing interface. An expression is derived for anatase, the low temperature form of titanium oxide, which is consistent with the growth that is observed.

Thermal oxidation of Silicon in the thin regime is of vital importance to VLSI device engineers because thin layers of SiO2 are exclusively used as the gate dielectric for high performance of MOS devices. There exists a number of models to explain this kinetics of oxidation. However there is a considerable variance among the reported rate constants, which are supposed to describe the oxidation process. Rather than arriving at an alternative model, the present study aims at simulation of existing models of oxidation in dry oxygen, with a recent set of experimental data and arrive at the best possible model and provide accurate rate constants for oxidation in dry oxygen. These experimental data have been obtained, earlier, using high-resolution transmission electron microscopy (HRTEM) and ellip-sometry techniques to measure thicknesses of silicon oxide, grown at 800° in dry oxygen, in the thickness range of 2–20 nm.

We report the first kinetic study of metal-semiconductor interface reactions using in-situ, time resolved, laser interferometry. Diffusion couples with Co/Ge thicknesses of 1500 Å/1500 Å were sputter deposited on silicon wafers, and vacuum-annealed at temperatures between 300°C-400°C. Under these conditions polycrystalline CoGe was expected to form [1]. Real time laser (HeNe 6328 Å) interferograms for each anneal were recorded in-situ. These data were supplemented by information from AES and X-ray.

For temperatures below 400°C the diffusion controlled formation of CoGe was observed. The composition was confirmed by Auger depth profiling that showed uniform Co and Ge concentrations when the reaction went to completion. The well defined interferences fringes were formed by the dissolution of amorphous Ge. The activation energy = 1.6 eV for the formation of CoGe were determined with precision from the temperature dependence of the time required to anneal the fixed λ/4 distance between adjacent minima and maxima of the interferogram. We discuss the evidence for formation of an intermediate Co-rich compound following the initial diffusion of Co into Ge. The results of these experiments indicate that optical interferometry will be a valuable adjunct to other techniques used to study metal-semiconductor interface reactions.

The formation of suicides during the thermal reaction of Ti/polysilicon bilayers has been investigated using both in-stu four point sheet resistance measurements and ex-situ measurements including X-ray diffraction, cross-sectional transmission electron microscopy and Auger electron spectroscopy. For a series of samples annealed at a ramp rate of 10°C/min the following sequence of changes in the bilayers occurred. At temperatures exceeding 350°C and prior to the silicidation oxygen from the vacuum system diffuses into the Ti film forming a solid solution of Ti(O) with O levels up to 20 %. An amorphous TixSiy layer is the first major suicide reaction observed at temperatures near 440°C. The first major crystalline phase is observed at 500°C and identified as C49 TiSi2. This phase was found to coexist at these temperatures with the partially consumed Ti(O) and the amorphous TixSiy layers. Further annealing above 700 °C results in the final structural transformation from C49 TiSi2 to C54 TiSi2.

Vertical sections of multilayers (VSM) should provide excellent testing grounds for physics and chemistry on surfaces with densely populated heterogeneous interfaces. Although VSM can be obtained from usual horizontal multilayers stacks by crushing them into pieces or by partial ion etching through masks from the top surfaces, a better way to get VSM is to form vertical multilayers. Employing simultaneous oblique deposition of ZnTe and SiO2 from opposite azimuthal directions, we have obtained nanometer-scale heterogeneous structures with anisotropie optical properties for the light coming perpendicularly to the surface. TEM revealed that successive annealing caused relaxation and recrystalllzation of ZnTe in the framework of SiO2 porous nano-structure. The resultant mosaic image of dark ZnTe regions and bright Sio2 regions of 5–10 nm wide and 30nm (or more) long told the development of VSM over the substrate although the perfect periodicity and two-dimensionality were missing. The structural modification of these quasi-multilayers was studied making reference to the similar but horizontal system of ZnTe particles periodically buried between Sio2 isolation layers.

New metastable materials can be deposited using low temperature physical vapour deposition (PVD) techniques. During reactive sputtering, the atoms condensing in an intermixed state attempt to achieve a stable configuration. Due to low mobility of the adatoms, equilibrium phases cannot form and metastable structures are observed. Reactive sputtering can be used to deposit films with different stoichiometries and structures in the W-N system. The metastable phases α-W. β-W. W2N and WN1−x are obtained. All coatings are, however, thermally unstable. At temperatures above 570 °C. all phases are transformed into the a-W modification. By alloying chromium to the coatings in the W-N system, it is possible to stabilize all tungsten and tungsten nitride modifications as well as the interface layer between the substrate and the thin films.

We have studied the thermodynamics and kinetics of growth of Al-Ti phases in thin-film interdiffusion couples, A lOOnm thick aluminum layer is vapor-deposited on a poly- or single-crystal titanium substrate, previously etched by ion bombardment. The sample is then annealed during a time ranging from a few minutes to a few hours, at temperatures from 300 to 600°C. The Al atomic fraction vs depth is determined using a sputtering technique, associated with thermo-ionization mass spectrometry (STIMS). At low temperature (300–450°C), titanium diffuses along the grain boundaries of the micro-crystalline aluminum layer, to form an Al-rich phase. At higher temperature (450–500°C), the T1AI3 phase grows rapidly up to the surface. Above 460°C, an intermediate Ti-72at/Al phase grows between TiAl3 and Ti‥ At 600°C, the aluminum layer becomes morphologically unstable.