Mitsugu Hanabusa

Diamond-like carbon films prepared by pulsed-laser evaporation

Diamond-like carbon thin films were prepared by pulsed-laser evaporation. In this method a carbon target was irradiated by a XeCl laser with a power density of 3×108 W/cm2 and carbon atoms, together with a small number of ions, were produced. Deposition rates and film properties changed sensitively with substrate temperature. The films deposited at 50°C were diamond-like, having reasonable hardness, high refractive index (2.1–2.2 at 633 nm), optical transparency in the infrared, electrical resistivity of 108 Ω cm and chemical inertness (no dissolution in a HF∶HNO3 solution). The band gap measured from optical absorption was 1.4 eV. Raman spectrum and infrared absorption, whose features varied with the substrate temperature, were also measured. The films were amorphous and no crystallinity was observed, as confirmed by x-ray diffraction, transmission electron diffraction and Raman spectroscopy. Hydrogen atoms were incorporated in the films with a typical H/C ratio of 0.3. The application of a negative bias to the substrate modified the deposition due to the presence of ions.

Deposition of Diamond-like Carbon Films by Pulsed-Laser Evaporation

Diamond-like carbon thin films were deposited by pulsed-laser evaporation. A carbon target was irradiated by a Xe-Cl laser with a power density of 3×108 W/cm2. Ions were mixed with vaporized atoms. Deposition rates were typically 200 A/ min. Film properties changed with substrate temperature. The films deposited at 50°C were diamond-like, as confirmed by refractive index (2.1 to 2.2), optical transparenty and chemical resistance. Hydrogen-free films were produced. Optical band gap was 1.4 eV and electrical resistivity was 108 Ω-cm. No crystallinity was observed.

Laser‐induced vapor deposition of silicon

Silicon films were deposited when silane was irradiated with a pulsed CO2 laser. This laser‐induced vapor deposition occurs effectively when the laser is tuned to an absorption frequency of SiH4. Efficiency was so high that an unfocused beam of 1.3 MW/cm2 sufficed. Any thermal effects are ruled out. Deposition is induced efficiently at gas pressures above 100 Torr, indicating that a collision‐aided process is involved.

Dynamics of laser‐induced vaporization for ultrafast deposition of amorphous silicon films

Atomic vapor produced by a frequency‐doubled, pulsed Nd:YAG laser with its beam focused on a silicon plate has been used to deposit amorphous silicon films on substrate at room temperature. Time‐resolved measurements on the emission lines from vaporized Si show that the laser‐irradiated surface is kept at temperatures high enough to maintain a significant amount of vaporization for approximately 40 ns after the 7‐ns laser pulse. Since intense pulsed atomic beams are used, the silicon films grow at high speed in excess of 106 A/s.

Laser-induced deposition of silicon films

Abstract Recent advances in the laser-induced deposition of thin films are briefly reviewed in connection with the present experiment conducted for silicon films. Either gases or solids are used as starting materials. In the so-called laser chemical vapour deposition process, gases are decomposed by laser-induced photolysis or pyrolysis. Amorphous silicon films were deposited from silane using a CO 2 laser which was used to heat a quartz substrate and to excite gas molecules vibrationally; deposition rates are several micrometers per minute at about 10 W cm -2 . Ultrafast deposition of amorphous silicon films with instantaneous speeds as high as 10 μ m s -1 is made possible by laser sputtering, where a Q -switched laser irradiates solid silicon targets to generate atomic beams mixed with ions. The dynamics of laser sputtering have been studied through emissions from neutral silicon and silicon ions which show acceleration of ions by local electric fields followed by electronic recombination near the target. When gas molecules are introduced, they are decomposed by collisions with these energetic particles. This decomposition is responsible at least partly for the incorporation of atoms into films and for the modification of their physical properties.

Electrical and photovoltaic properties of iron-silicide/silicon heterostructures formed by pulsed laser deposition

Dark current–voltage characteristic showed a rectifying behavior for the iron-silicide/silicon heterostructures formed by pulsed laser deposition of iron on n-type silicon(100) substrates heated to 600°C. The polarity of the rectifier was reversed for the heterostructures formed at 800°C. The photosensitivity measured between 300 nm and 1100 nm was higher for the heterostructures formed at 800°C than those at 600°C. Also, the illumination of the silicon side gave higher photosensitivity than that of the silicide side. There were peaks near a wavelength of 1000 nm. In particular, the FeSi2/Si heterostructures formed at 800°C was the most sensitive (270 mA/W at a broad peak near 900 nm) with the spectrum extending from 400 nm to 1100 nm under the illumination of the silicon side. Open-circuit voltage, as well as short-circuit current density, was measured under AM 1.5, 100 mW/cm2 illumination.

Pulsed laser deposition of ZnO thin films using a femtosecond laser

Abstract Transparent, conductive ZnO films were deposited by pulsed laser deposition (PLD) using 790-nm, 130-fs laser pulses. An optical transmittance as high as 88% in the visible region was obtained when deposited above 150°C. The electrical resistivity of the films was 10−1 to 10−3 Ω cm between room temperature and 270°C. Sharp X-ray diffraction (XRD) peaks were observed for films deposited above 150°C on both quartz and Si. The results were obtained in absence of oxygen gas during the deposition, unlike in previous PLD where nanosecond laser pulses were used.

Deposition of aluminum thin films by photochemical surface reaction

Aluminum thin films have been deposited from dimethylaluminum hydride (DMAlH) on silicon substrates illuminated with a deuterium lamp or an ArF laser. DMAlH was found to be useful as a new source gas for photodeposition of aluminum films at a low carbon level if it was used with photons with wavelengths below 200 nm. Illumination is effective not only to produce films at a substrate temperature lower than required by thermal decomposition, but also to reduce the electrical resistivity of the deposited films. To emphasize surface, rather than gas‐phase, reactions, the vapor pressure in a reaction cell was lowered (typically at 6.7×10−3 Pa). Evidence for the photochemical surface reaction has been provided by area selectivity and the time needed to renew the adlayer on the surface. In spite of low vapor pressure, the deposition rate was typically 19 nm/min for the lamp and 0.06 nm/pulse for the laser at a substrate temperature of 200 °C. A rate equation, which included both photodissociation and photoinduce...

Photochemical Vapor Deposition of Aluminum Thin Films Using Dimethylaluminum Hydride

Using dimethylaluminum hydride as a source gas, aluminum thin films with low-electrical resistivity were deposited via photochemical reactions induced by a deuterium lamp. The best resistivity was 6.2 µΩcm, which was as low as 2.3 times the value of bulk aluminum. Deposition rates increased with substrate temperature. At 200°C the rate was 20 nm/min. A disk-like thickness profile, as well as the vapor pressure dependence of deposition rates, indicated that surface reactions dominated.

Laser-assisted chemical vapor deposition of titanium nitride films

We used a 193 nm ArF excimer laser to assist chemical vapor deposition of titanium nitride (TiN) films on Si (100) and SiO2. The source gases were tetrakis(dimethylamido)titanium (TDMAT) or tetrakis(diethylamido)titanium (TDEAT) mixed with ammonia. A correct stoichiometry was confirmed from Auger spectra. The laser helped to enhance TiN deposition rates at low temperatures (100 °C for TDMAT-NH3 and 200 °C for TDEAT-NH3). At higher temperatures the deposition rates decreased with an increasing laser energy density. Under irradiation the electrical resistivity of the TiN films was lowered. The laser-induced effect on electrical resistivity was particularly pronounced at low temperatures. A good conformality of the TiN films for contact holes with high aspect ratios was demonstrated.