G. Leggieri

Pulsed laser deposition of active waveguides

We report on the pulsed laser deposition (PLD) of thin films of chalcogenide and tellurite glasses doped with RE ions. The depositions were performed in vacuum, for chalcogenide films, and in a low oxygen pressure for the tellurite films by using an excimer laser. After the deposition, the morphological, structural, optical and spectroscopical characteristics are analysed by different techniques: Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Rutherford Backscattering Spectrometry (RBS), optical profilometry, m-lines spectroscopy, photoluminescence etc. The experimental results demonstrated that PLD is a suitable technique for the realisation of films of complex materials for optoelectronic and photonic applications.

Synthesis of pure titanium nitride layers by multipulse excimer laser irradiation of titanium foils in a nitrogen-containing atmosphere

Experimental results are reported concerning the synthesis of pure, hard, and adherent titanium nitride layers by multipulse excimer (λ=308 nm) laser irradiation in a nitrogen or ammonia atmosphere. It is shown that the process is more efficient when the irradiation is performed in a nitrogen atmosphere. The general characteristics of synthesized surface compound layers are compatible with the requirements of utilization in microelectronics.

Laser synthesis of metal silicides

The relevant results obtained in the field of laser synthesis of metal silicides are reviewed. Particular emphasis is given to the work using a pulsed laser in the nanosecond regime and to the results obtained in our laboratory. Formation of stable and metastable compounds, their structure and the surface morphology of the irradiated materials are discussed. The reaction kinetics is investigated through a comparison of the experimental results with the heat flow and temperature calculations.

Laser-reactive ablation deposition of silicon-nitride films

Silicon-nitride films were deposited on silicon waters by XeCl (308 nm) excimer-laser ablation of silicon in low-pressure (0.05–5 mbar) ammonia atmospheres. Series of 10 000 pulses at the repetition rate of 8 Hz were directed to the target surface. The fluence was set at about 5 J/cm2. Pulse duration was about 30 ns. The deposited films were characterized by different techniques (X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, scanning electron microscopy, profilometry). Silicon-nitride films with thickness close to 1 μm were obtained under specific experimental conditions.

Oxidation interference in direct laser nitridation of titanium: relative merits of various ambient gases

Abstract A comparison is performed between the relative merits of using an ambient NH 3 atmosphere or a stoichiometrically equivalent N 2 -H 2 (1:3) mixture for the direct laser nitridation of titanium samples by multipulse excimer laser ( λ = 308nm) irradiation. It is shown that the N 2 -H 2 mixture proves more effecient in inhabiting the unwanted interference of the oxidation process and that the whole process proceeds through the action of an erosion plasma on a molten layer covering the laser-irradiated area.

The optical band gap of semiconducting iron disilicide thin films

Abstract Optical transmittance and reflectance measurements have been carried out on semiconducting β-iron disilicide layers formed by annealing of iron films evaporated onto silicon substrates and capped with amorphous silicon or SiOx thin overlayers. The dependence of the absorption coefficient on the energy of photons favours direct allowed transitions with the forbidden energy gap of 0.87 ± 0.04 eV.

Characterization of C-N thin films deposited by reactive excimer laser ablation of graphite targets in nitrogen atmosphere

Abstract Carbon nitride films were deposited at room temperature on 〈111〉 Si substrates by XeCl laser ablation of graphite in low pressure (1–50 Pa) N2 atmosphere at a fluence of 12 J/cm2. N/C atomic ratios up to 0.5 were inferred from Rutherford backscattering measurements. Different diagnostic techniques (ARXPS, FTIR transmission spectroscopy, EDS, SEM and XRD) were used to characterize the deposited films. XRD spectra indicate a polycrystalline structure of the films.

Excimer laser reactive ablation: An efficient approach for the deposition of high quality TiN films

The successful deposition of TiN films on Si wafers by excimer (λ=308 nm) multipulse laser ablation of Ti in a low pressure N2 jet is reported in this article. The films are particularly pure, entirely consisting of polycrystalline fcc TiN. One difficulty still seems to be related to the presence of small droplets probably ejected in a liquid phase. According to the analyses, TiN is formed on Ti target with small contributions only, if any, of the next transit through gas and final deposition onto the Si wafer support.

Compounds in the Pd‐Si and Pt‐Si system obtained by electron bombardment and post‐thermal annealing

Thin Pt, Pd, Pt2 Si, and Pd2Si films deposited on Si were reacted by using electron beam pulses of 60 nsec duration in the 0.4–2.4 J/cm2 energy density range. Irradiaton of Pd/Si structure produces at the same time PdSi, Pd2Si, Pd3Si, and Pd4Si, while PdSi is the only phase observed starting from the Pd2Si/Si structure. Post‐thermal annealing of these layers up to 600 °C induces the growth of Pd2Si phase at the expense of the other phases. PdSi seems to be a metastable phase at least up to 600 °C. PtSi, Pt2Si, Pt3Si compounds are formed after irradiation of Pt/Si structure. Post‐thermal annealing at 500 °C produces PtSi. A Si‐enriched metastable phase Pt2Si3 is present after irradiation of Pt2Si/Si or PtSi/Si structure. Post‐thermal annealing at 450 °C produces the growth of Pt2Si3. Further annealing at 500 °C induces the formation of PtSi and Si polycrystal.

Carbon nitride films deposited by reactive laser ablation

Abstract Carbon nitride films were deposited at 20, 250 and 500°C on 〈111〉 Si substrates by XeCl laser ablation of graphite in low pressure (1–50 Pa) N2 atmosphere at fluences of 12 and 16 J/cm2. Different diagnostic techniques (SEM, TEM, RBS, XPS, XRD) were used to characterize the deposited films. Films resulted plane and well adhesive to their substrates. N/C atomic ratios up to 0.7 were inferred from RBS measurements in films deposited at 20°C and 16 J/cm2. Nitrogen concentration increases with increasing ambient pressure and laser fluence. The N 1s peak of the XPS spectra indicate two different bonding states of nitrogen atoms to C atoms, while the C 1s peak, apart from the two bonding states to nitrogen atoms, indicates one bonding state with regard to carbon atoms. XRD and TEM analyses point to an oriented microcrystalline structure of the films. Heating of the substrate results in a lower nitrogen concentration in respect of films deposited at 20°C in otherwise identical experimental conditions. Optical emission studies of the laser plasma plume indicate a correlation between the emission intensity of the CN radicals in the plume and the nitrogen atom concentration in the films.