E. D'Anna

Deposition of CN films by reactive laser ablation

Abstract A study of the characteristics of films deposited at room temperature on Si and KBr substrates by XeCl laser ablation of graphite in low pressure (0.25–2.5 mbar) N2 and NH3 is presented. Hard films, with a very high electrical resistivity were obtained. N C atomic ratios up to 0.6 were calculated from backscattering measurements. Different diagnostic techniques (XPS, IR absorption spectroscopy, etc.) prove the formation of carbon nitride with a prevalent graphitic structure.

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.

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.

Study of CN binding states in carbon nitride films deposited by reactive XeCl laser ablation

Carbon nitride films, deposited on 〈111〉 Si substrates at room temperature by XeCl laser ablation of graphite targets in low pressure (1, 5, 10 and 50 Pa) N2 atmosphere at the fluence of 16 J/cm2 (∼0.5 GW/cm2) have been submitted to accurate X-ray photoelectron spectroscopy (XPS) investigations in order to study the CN chemical bonding in the films. Multiple binding energy values have been obtained. The N 1s peak of the XPS spectra indicates three different binding states of nitrogen atoms to C atoms, while the C 1s peak, apart from the binding states to nitrogen atoms, indicates other bonding states with regard to carbon atoms.

Pulsed laser deposition of Co- and Fe-based amorphous magnetic films and multilayers

Abstract Magnetic films and multilayers were prepared by pulsed laser ablation of Co- and Fe-based amorphous magnetic ribbons with compositions Co 67 Cr 7 Fe 4 Si 8 B 14 and Fe 73.5 Nb 3 Cu 1 Si 13.5 B 9 , respectively. Targets were ablated in vacuum (∼10 −5 Pa) by KrF excimer laser pulses at fluences from 3 to 7 J/cm 2 . Films were deposited on oxidized silicon wafers, placed 80 mm apart from the target. From X-ray diffraction spectra it follows that all the films are amorphous, while Rutherford backscattering spectrometry analyses confirm that their composition is close to the respective target when they are deposited at the lower fluence. In the case of higher fluence, the concentrations of both Si and B in the films decrease. From ferromagnetic resonance studies it results that the effective magnetizations 4 πM eff and g -factors of the films are close to the values of the respective ribbon only in the case of Fe-dominating composition. Nanometric multilayers (4-nm magnetic alloy/6 nm Cu) ×5 were also deposited and electrically and magnetically characterized.

Multilayer titanium nitride and silicide structures synthesized by multipulse excimer laser irradiation

Abstract We report a study of the formation of titanium nitride/titanium silicide multistructure layers on silicon single crystals covered with thin (140 and 400 nm) titanium films, by single step multipulse (100 to 5000) XeCl excimer laser irradiation in N 2 atmosphere at a moderate laser fluence (∼ 0.6 J/cm 2 ) and a pulse repetition rate of 50 Hz. After irradiation the samples were submitted to different investigations: optical and electron microscopy, surface resistivity, Rutherford backscattering spectrometry and nuclear reaction analysis. It is shown that the thickness of the silicide and nitride layers can be adjusted by a proper choice of the number of subsequent laser pulses. Optical spectroscopy investigations and temperature profile calculations indicate that titanium nitride is formed at the sample surface through a liquid-phase reaction.

Synthesis of thin films of semiconductor and refractory metal nitrides by laser irradiation of solid samples in ambient gases

Abstract A review is presented of the results obtained of the formation of nitride surface layers on semiconductor (silicon, germanium) and refractory metal (titanium, ziconium, hafnium) samples by laser irradiation in nitrogen-containing atmospheres. These results show the great efficiency of the laser-induced nitridation process.

Characterization of TiAlN films deposited by reactive pulsed laser ablation

Abstract We have deposited TiAlN films by using the reactive laser ablation technique. TiAl targets were ablated in low-pressure N2 (0.1–10 Pa) atmosphere by 2×104 XeCl excimer laser pulses at the repetition rate of 10 Hz. The laser fluence at the target was set at 6 J/cm2, corresponding to a power density of 0.2 GW/cm2. The films were deposited on Si substrates at room temperature, placed at 40 mm from the target. Their characteristics were investigated by many different techniques. Scanning electron micrographs show that surfaces are plane without cracks or corrugations. From Rutherford backscattering spectra it results that the thickness vary from ∼100 nm for films deposited at 0.1–0.5 Pa to 50 nm for the film deposited at 10 Pa. The mean composition is close to TiAlN for the film deposited at 0.1 Pa and close to TiAlN2 for the film deposited at 0.5 Pa. X-Ray diffraction analysis points to an amorphous structure of the film deposited at the lowest pressure (0.1 Pa), while peaks of fcc TiN and hexagonal Ti3Al2N2 appear in the spectra of the films deposited at higher N2 pressures. The complex chemical bonding of the top surface layer of the films was studied by X-ray photoelectron spectroscopy.

Tungsten silicide formation by XeCl excimer-laser irradiation of W/Si samples

We report a study of the formation of tungsten silicide at the W-Si interface, induced by multipulse (up to 300 shots) XeCl excimer-laser irradiation of W(150 nm)/Si and W(500 nm)/Si samples. Laser fluences ranging from 0.6 to 1.8 J/cm2 were used. After laser treatment the samples were examined by different diagnostic techniques: Rutherford backscattering spectrometry, X-ray scattering, resistometry, and surface profilometry. Numerical computations of the evolution and depth profiles of the temperature in the samples as a consequence of a single 30 ns laser pulse were performed as well. The results indicate that it is possible to obtain a tungsten silicide layer at the W-Si interface at quite low fluences. The layer thickness increases with the number of laser pulses. Complete reaction of the 150 nm thick W film with silicon was obtained at the fluence of 1.2 J/cm2 between 30 and 100 laser pulses and at 1.5 J/cm2 after 30 laser pulses. The sheet resistance of these silicides was 5–10 Ω. At the used fluences for the 500 nm thick W film only the onset of silicide synthesis at the W-Si interface was observed.

Nitridation of titanium by multipulse excimer laser irradiation

We report a study of the formation of nitride surface layers on titanium foils by multipulse (100 to 2500) XeCl excimer laser (λ = 308 nm) irradiation in N2 and NH3 atmosphere. After irradiation the samples were analyzed by Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA) and then examined by electron microscopy (SEM, TEM). The nitridation process was shown to be very efficient with both gases. The amount of nitride has been observed to depend on the number of subsequent laser pulses, on the pulse repetition rate and on the nature of the ambient gas.