An original method is developed to investigate vibrational properties of thin films using infrared (IR) ellipsometry. The procedure is based on in-situ measurements as a function of deposition time. Out of absorption bands, the IR refractive index can be determined and related both to film density and oscillator strengths of electronic transitions. Thanks to band decomposition performed for a given film at different thicknesses, line frequency, band width and intensity of each vibration can be precisely determined, even in case of band overlapping or low IR oscillator strengths. As an illustration, C-H bonding of 1000 Å-thick plasmadeposited polymerlike hydrogenated carbon (PLC) films has been studied. Analysis of the interface between highly saturated PLC films and crystalline silicon reveals the formation of a 20 Å interlayer. Bulk analysis evidences weak vibrations located at 1405 and 1440 cm−1 which had not been observed so far and which are related to π bonds. By combining elastic recoil detection measurements and IR analysis, effective charges of sp3 CHn groups have been calculated. For methyl and methylene groups, these charges are similar to those of hydrocarbon compounds. As far as the sp3 CHn group is concerned, a strong decrease of the effective charge versus film density is evidenced and attributed to the formation of distorted weakly hydrogenated regions induced by ion bombardment.

Gold eutectic bonding of silicon wafers is a good candidate for wafer level vacuum packaging of vibrating MEMS: in this paper we investigated several e-beam evaporated metallizations stacks including a titanium adhesion layer, an optional diffusion barrier (Ni or Pt) and a gold film for eutectic bonding on Si and SiO2/Si wafers. Interdiffusion in the multilayers for annealing temperatures (380–430°C) larger than the Au–Si eutectic temperature (363°C) and times corresponding to a bonding process was characterized by RBS, roughness and resistivity measurements. Au/Pt/Ti and Au/Ti/SiO2 were found to have the best characteristics for bonding. This was confirmed by bonding experiments.

The structural effects of single and cyclic thermal annealings on relaxed Ge epilayers on Si(001) are investigated. The structural morphology of the films is studied ex situ by Rutherford back scattering spectrometry in channelling geometry (RBS-C), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The effects on optical properties are demonstrated by optical transmission spectroscopy. Thermal cycles between 750 and 870°C were found to be efficient for reducing the threading dislocations density. But, in return for it, thermal cycles result in a strong interdiffusion and a high disorder at the Ge/Si interface, as shown through a χmin value of 14.4%. On the contrary, a single annealing at 720°C decreases the density of dislocations but does not induce any new disorder. Moreover, the single annealing does not alter the near-IR optical absorption of the Ge layer.

The growth of germanium at low temperature by ultrahigh vacuum chemical vapor deposition on Si(001) is investigated in real time by reflection high-energy electron diffraction. These observations are complementarily checked by atomic force microscopy, Rutherford backscattering spectrometry, transmission electron microscopy, and x-ray diffraction experiments. It can be seen that the currently observed Stranski–Krastanov-related two-dimensional (2D) to three-dimensional transition is avoided at 330°C and that the major part of the relaxation process occurs during the deposition of the first two monolayers. Then, the measured in-plane lattice parameter evolves slowly and approaches that of bulk Ge after deposition of 50 monolayers. The corresponding relaxation equals 83%. The resulting surface is flat, with a rms roughness of 0.55nm. The relaxation is found to be mainly due to misfits dislocations located at the Ge∕Si interface. Regrowth experiments at 600°C show that the low-temperature films are not stable for thicknesses below 27nm. In spite of the nearly complete relaxation observed for 7.5nm, a much higher thickness is needed to enable a continuous 2D growth at 600°C. Finally, a 500-nm-thick film, obtained with a low-temperature Ge buffer and with a Ge regrowth at high temperature, exhibits a channeling-to-random Rutherford backscattering spectrometry ratio (χmin) of 4%, which indicates a good crystalline quality.

The structural effects of single and cyclic thermal annealings on relaxed Ge epilayers on Si(001) are investigated. The structural morphology of the films is studied ex situ by Rutherford back scattering spectrometry in channelling geometry (RBS-C), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The effects on optical properties are demonstrated by optical transmission spectroscopy. Thermal cycles between 750 and 870 degrees C were found to be efficient for reducing the threading dislocations density. But, in return for it, thermal cycles result in a strong interdiffusion and a high disorder at the Ge/Si interface, as shown through a chi(min) value of 14.4%. On the contrary, a single annealing at 720 degrees C decreases the density of dislocations but does not induce any new disorder. Moreover, the single annealing does not alter the near-IR optical absorption of the Ge layer. (c) 2004 Elsevier B.V. All rights reserved.

The Ge growth at 330 °C by ultrahigh vacuum chemical vapour deposition is investigated in real time by reflection high energy electron diffraction (RHEED) in combination with atomic force microscopy and Rutherford back scattering spectrometry (RBS). The Stranski-Krastanov-related 2D to 3D transition is avoided at low temperature and the major part of the relaxation process occurs during the deposition of the first two monolayers. The very low growth rate observed during this first step is related to the deposition of Ge on Si. Beyond 2 deposited MLs, the growth rate increases drastically due to a complete coverage of Si by Ge. Finally, the deposition of Ge at 330 °C results in an in-plane lattice parameter approaching 90% of that of Ge bulk and a flat surface with rms roughness of 0.6 nm for a film thickness lower than 30 nm.

In this paper, we studied the roughening of SiGeC surface revealed by in situ reflection high energy electron diffraction (RHEED) measurements, that happens during ultra-high vacuum chemical vapor deposition (UHV-CVD) growth under certain growth conditions. A high growth rate and a low temperature are found to be favorable for smooth surfaces. Roughening is accompanied by a dramatic decrease of the substitutional C content and, further, stacking faults develop within the epilayer. According to these observations, we proposed a model of surface roughening based on the formation of carboneous complexes on the film surface and a way to maximize substitutional C incorporation in very thin layers by using RHEED as a probe for monitoring the development of lattice defects. By this means, more than 2% of substitutional C atoms can be incorporated in 5nm Si1−yCy films (assuming Vegard’s law).

In this paper, we study the kinetics of carbon incorporation in Si1−x−yGexCy/Si(001), by ultra high vacuum-chemical vapor deposition. Layers were grown with a Ge content of 3% and substitutional C content up to 1.7%. All the layers were tensily strained. Using a simple model derived from the commonly accepted growth mechanism for silicon from SiH4, we deduced an expression for the growth rate as a function of the temperature and the SiH4 partial pressure. A qualitative model for surface roughening due to carbon incorporation is proposed. From that, we observed that the surface diffusion of carbon adatoms is limited by hydrogen coverage.

In this work, we investigated electrical and morphological properties of W/p-type Si Schottky diodes with intentional inhomogeneities introduced by macroscopic Ge-islands embedded beneath the interface. The Si-cap layer thickness (or the island-distance to the interface) was progressively reduced by successive chemical etching cycles. Electrical characterizations were achieved through reverse current-voltage ( I-V ) at room temperature and forward I-V measurements as a function of the temperature. In parallel, Rutherford backscattering spectroscopy analyses were performed to follow the Si-cap/Ge islands chemical thinning down with increasing the number of etching cycles. In addition, the comparison of topographical and electrical properties of the etched silicon-cap layer was carried out by conductive atomic force microscopy analyses with a nanometer-scale resolution. Our results indicate that the areas on the top of islands exhibit lower resistance than those which covered the wetting layer. This lateral variation of resistance at the surface of the semiconductor may correspond to Schottky barrier height inhomogeneities observed on broad area I-V characteristics of Schottky contacts.

In this work, we investigated the Schottky barrier height at W/p-type Si contacts with the presence of Ge-dots located below the interface. The effect of the dots is controlled by reducing the thickness of the Si-cap layer by successive chemical oxidation/etching cycles. The surface morphology of the samples is investigated by using atomic force microscopy and the Ge-content is determined by Rutherford backscattering spectroscopy. Nonideal behaviors in current–voltage characteristics are observed and explained in terms of inhomogeneities due to the presence of the Ge-dots.

We report our first results using a ultra high vacuum chemical vapor deposition (UHV-CVD) system to form Ge quantum dots on off-axis SiC substrates. Pure SiH4 and hydrogen-diluted GeH4 were used as gas precursors. The SiC substrates were chemically cleaned using the modified RCA process and the SiO2 layer was removed in-situ under a low SiH4 flow rate at a temperature between 1030°C and 1080°C. The Ge quantum dots were grown at a temperature of 750°C. In-situ reflection high-energy electron diffraction (RHEED) was used to monitor the surface cleaning and the Ge quantum dot growth. Ex-situ scanning electron microscope and atomic force microscopy were used to confirm the presence of Ge dots. The observed dots are smaller (350 Å width and 100 Å height) than similar Ge dots grown on Si.

Using in situ reflection high-energy electron diffraction, we have studied the surface roughening of SiGeC that occurs in ultrahigh vacuum chemical vapor deposition under certain growth conditions. For a given SiH3CH3 fraction in the gas phase, high growth rates and low temperatures are found to be favorable to obtain smooth surfaces. Roughening is accompanied by a dramatic decrease of the substitutional C content. According to these observations, we propose a model of surface roughening based on the formation of carboneous complexes on the film surface, limited by the growth rate and the diffusion length of C adatoms. From that, a critical ratio between the growth rate and the C diffusion coefficient was assumed. Its temperature dependence was determined. The activation energy of C adatoms diffusion was found to be close to the well known value for hydrogen desorption.

SixOyNz, Si3N4 and SiO2 films deposited on silicon in a low frequency PECVD reactor (187.5 kHz) from a SiH4, N2O and/or NH3 gas mixture are always in compressive mechanical stress state after deposition because of ion bombardment of the growing film during deposition. The stress value is, as expected, a decreasing function of oxygen content. It is demonstrated that by reducing drastically the deposition temperature down to 200 degreesC, stoechiometric silicon nitride films and silicon oxynitride films (0 less than or equal to O/Si less than or equal to 1.8) with a low tensile stress can be obtained after high temperature annealing (800 degreesC). Rutherford backscattering experiments (RBS), elastic recoil detection analyses (ERDA) and infrared spectrometry measurements show that this stress variation is related to the initial composition, to hydrogen desorption from Si-H, N-H and O-H bonds and to cross-linking. By controlling the initial hydrogen concentration with the deposition temperature, the stress value after annealing can be tuned precisely, This simple process was applied to the fabrication of flat dielectric membranes with a thickness in the range of 90-400 nm by KOH bulk micromachining. (C) 2002 Elsevier Science B.V. All rights reserved.

In this work, we investigated W/p-type Si Schottky contacts with intentional inhomogeneities beneath the interface. These inhomogeneities are related to the presence of Ge-dots located just below the contact. The size and the density of the inhomogeneities can be controlled either through the deposition conditions (Ge-coverage, here) or the thickness of the Si-cap layer. Electrical characterizations of contacts were achieved through current–voltage measurements in a temperature range 100–300 K. These experimental results are compared to numerical simulations using the Atlas-Silvaco package. To describe the contact, we have chosen a cylindrical geometry. The Schottky current takes into account the contributions of small circular patches of lower Schottky barrier height (SBH) embedded in a large area of uniform higher SBH. Our results evidence a correlation between the parameters of the Ge-dots (size, density, distance to the interface) and those of the patches introduced in the model. The well-known linear correlation between SBHs and ideality factors, ΦB (n), is observed for all the samples.

Polymer-like hydrogenated amorphous carbon (a-C:H) films have been grown in a dual-plasma [radio frequency (rf)–microwave (MW)] reactor using butane as a carbon precursor and different mixtures (H2–Ar or He–Ar) in the MW plasma in order to vary the atomic hydrogen flux impinging on the growing film. Decreasing the rf power (i.e., the energy of ion bombardment on a-C:H) or increasing the H atom flux both result in a wide band gap H-rich polymer-like a-C:H network. Nuclear techniques have been combined with UV-visible ellipsometry to determine the stoichiometry, density and growth rate of a-C:H films as a function of the plasma parameters. Parametrization of UV-visible optical properties allows to monitor the changes in the optical parameters (optical gap and density of π states) attributed to the formation of structural units containing C=C double bonds. C–H bonds observed by in situ infrared ellipsometry have been used to investigate the role of ions in the growth processes (densification, cross linking) and to interpret the observed changes in optical parameters in terms of a two-phase microscopic description of polymer-like a-C:H. In order to understand the kinetic results, a phenomenological growth model is proposed including the respective roles of ion bombardment and H atom flux in the activation and deactivation of surface sites available for CxHy radical incorporation (chemisorption) to the growth zone. The activation mechanism corresponds to a chemical modification at the growth zone sites. This adlayer model includes the physisorption of both H atoms and CxHy radicals and explains why the temperature dependence of the deposition rate is found to be opposite for the limiting cases of low and high H atom fluxes. Some consequences of the model on the film stoichiometry (H/C ratio) and microstructure (sp2 C/sp3 C ratio) have also been evaluated.

The authors demonstrate, using pump-probe experiments, that defects created by a 200 MeV Au+ ion beam in bulk GaAs reduce the relaxation time of the saturable absorption of the material to as little as 200 fs. The sample absorption is modulated over a spectral width of 50 nm. The integrated value of the absorption modulation thus shows the high absorption efficiency of the irradiated material. A very small variation in relaxation time is found when the density of photocreated carriers is increased to similar to 5 x 10(18)cm(-3). This material appears to be very promising for applications in optical processing and ultrafast measurement at high pulse repetition rates.

Electronic properties of polymer-like hydrogenated amorphous carbon films, grown in a RF-assisted microwave plasma reactor, have been studied using optical absorption and photoluminescence spectroscopies. Using a Forouhi-Bloomer parametrization of π-π* transitions, two regimes are evidenced for increasing C atom density: a decrease of the optical gap E ππ * at constant (H/H+C) content attributed to sp 2 C clustering , followed by some H elimination with minor changes in E ππ * due to cross-linking of polymer chains. The photoluminescence efficiency in the visible range (peak at ≈ 2.3 eV) is found to decrease over four orders of magnitude at the onset of the cross-linking regime. This quenching is attributed to stress-induced non-radiative centers.

Hydrogen incorporation in amorphous silicon oxide thin films a-SiOx:H (0.5 < x < 2.0) was studied quantitatively by combining nuclear analysis (Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA)) and IR absorption spectroscopy. The films were obtained at low temperatures (40-250 degrees C) and high growth rates (R(d)) up to 55 Angstrom s(-1) using a dual-plasma-enhanced chemical vapour deposition (dual-PECVD) reactor. Hydrogen atoms were bonded to Si in Si-rich films, whereas in nearly stoichiometric films H atoms were only bonded to oxygen in Si-OH and H2O configurations. The intensity of the OH broad absorption band increased for films produced at low temperatures and high oxygen flow rates (high deposition rates). No modification of the spectrum was observed after thermal annealing at 250 degrees C, even for thin films deposited at 70 degrees C, indicating good stability of the bonded H. Quantitative analysis of the stoichiometry of the films was undertaken, and the proportionality constants between the atomic concentration and the integrated absorbance for Si-O-Si, Si-O-H and H-O-H stretching modes and the H-O-H bending mode are given.

Si1−x−yGexCy films have been grown by pulsed laser induced epitaxy (PLIE) from C+ implanted pseudomorphic Si1−xGex films and from hydrogenated amorphous a-SiGeC:H films deposited on Si(001). The laser treated samples are examined by electron channelling patterns analysis, X-ray diffraction, channelling Rutherford backscattering spectroscopy and atomic force microscopy (AFM). If laser fluence exceeds a threshold for which the melted zone is thicker than the initial SiGeC layer, the laser induced epitaxy is effective. We show that laser fluence strongly influences germanium profiles. Germanium and carbon atoms are redistributed over the melted depth with a graded profile. Strain profiles, deduced from X-ray dynamical diffraction simulations, exhibit the same gradual evolution from the surface down to the substrate. AFM measurements show a strong decrease of rugosity obtained with suitable PLIE operating conditions.

The stoichiometry of amorphous hydrogenated silicon oxide films, grown in a dual-plasma system, has been investigated using elastic recoil detection (ERD), Rutherford backscattering, and infrared transmission. During ERD measurement of H profiles, using a 4He2+ beam of 3.0 MeV, ion-induced depletion of hydrogen atoms was observed, homogeneous over the 1 μm film thickness. Si-rich films (with H essentially bonded as Si–H) and nearly stoichiometric films (with H only bonded in Si–OH configurations) have been compared. The depletion is more pronounced in nearly stoichiometric oxides, whereas the apparent cross sections (≊1–2 nm2) are similar for both types of films. These observations are discussed in terms of an electron excitation process, with a subsequent chemical reconstruction via electron-hole recombination.