E. Fogarassy

A thermal description of the melting of c- and a-silicon under pulsed excimer lasers

Abstract The thermal melting calculations for crystalline and amorphous silicon under pulsed UV excimer lasers include the most recent values for the thermal and optical parameters of Si in the UV range. The melting threshold, melt duration and depth of fusion are calculated in different irradiation conditions and compared to the various experimental values already published or measured in our laboratory. The influence of photochemical reactions which can take place in the gas phase at UV wavelength, on the purely thermal process will be also briefly discussed.

Laser‐induced forward transfer of high‐Tc YBaCuO and BiSrCaCuO superconducting thin films

For the first time, the deposition of YBaCuO and BiSrCaCuO thin films has been performed by the single‐laser pulse‐induced forward transfer technique. In addition, the BiSrCaCuO films were successfully converted into the superconducting phase, with an onset critical temperature of about 90 K and a zero resistance at 80 K, by a subsequent thermal anneal in oxygen atmosphere in the 850–900 °C temperature range.

Silicon solar cells realized by laser induced diffusion of vacuum‐deposited dopants

A technique for solar cell preparation based on vacuum deposition of thin films of dopants on silicon, followed by irradiation with a high‐energy (∼1.5 J/cm2) ruby laser pulse is described. Several dopants like phosphorus, antimony, bismuth, aluminium, gallium, and indium have been investigated. Electrical and Rutherford backscattering measurements indicate that the dopant is dissolved in the silicon and becomes electrically active, as a result of the irradiation. The P‐N junctions which are formed are shallow (depth <4000 A) but heavily doped, since after the laser treatment the solubility of the dopant is generally higher than after a thermal diffusion. Therefore good diode characteristics can be achieved by this simple method, and solar cells up to 14 % efficiency under AM1 (air mass 1) illumination have been realized using dopants like phosphorus, antimony, bismuth, aluminium, or gallium.

LOW-TEMPERATURE SYNTHESIS OF SILICON OXIDE, OXYNITRIDE, AND NITRIDE FILMS BY PULSED EXCIMER LASER ABLATION

Silicon oxide, oxynitride, and nitride films are deposited, at low temperature (≤450 °C) by pulsed ArF excimer laser ablation from silicon, silicon monoxide, fused silica, and silicon nitride targets, performed under vacuum and in an oxygen atmosphere. The specific influence of laser fluence, target materials, substrate temperature, and oxygen pressure on the composition and final properties of SiOxNy grown layers is investigated using various complementary experiments such as infrared optical absorption, Rutherford backscattering, Auger electron spectroscopy, ellipsometry, and scanning electron microscopy. The process conditions are optimized in order to deposit good quality silicon oxide and silicon nitride thin films.

SiO2 thin‐film deposition by excimer laser ablation from SiO target in oxygen atmosphere

Silicon dioxide thin films are deposited, for the first time, by reactive laser ablation from a silicon monoxide target in oxygen atmosphere, with a high‐power pulsed ArF (λ=193 nm) excimer laser. The specific influence of oxygen in the chamber during the laser processing on the stoichiometry and final properties of the oxide films deposited at ambient temperature is demonstrated.

Pulsed laser crystallization and doping for the fabrication of high-quality poly-Si TFTs

Abstract We review the various applications of pulsed lasers, working in the nanosecond regime, to prepare high-quality poly-Si TFTs. It is shown that the best device performances (field-effect mobilities in excess of 140 cm2/V·s) are achieved by pulsed excimer laser crystallization of unhydrogenated amorphous Si thin films. In addition, for source and drain formation, we demonstrate that the excimer laser induced diffusion of dopant from a solid source (spin-on phosphorus-doped silicate glass) is very attractive to achieve good electrical properties of the n-channel TFTs.

Numerical and experimental analysis of pulsed excimer laser processing of silicon carbide

In this work, we investigated the thermal behaviour of both crystalline and amorphous SiC under pulsed excimer laser treatment at different wavelengths (193, 248 and 308 nm) and for pulse durations ranging from 20 to 200 ns. Numerical analysis was performed by solving the heat flow equation and using the appropriate optical and thermal parameters for SiC. The reasonable agreement found between the simulations and experimental results confirms the adequacy of such a type of numerical analysis for predicting the thermal behaviour of SiC under excimer laser processing.

Melting threshold of crystalline and amorphized Si irradiated with a pulsed ArF (193 nm) excimer laser

Modifications induced by a pulsed ArF excimer laser at surface of implanted silicon were investigated by a new and simple optical method which consists to follow the evolution of solid reflectivity, at 633 nm wavelength, resulting from the amorphouspolycrystalline (or monocrystalline) transition during the laser melting process. These results, which have been compared to those obtained using time resolved reflectivity experiments have demonstrated the capability of this simple technique to determine the melting threshold of implanted silicon.

Pulsed laser crystallization of hydrogen-free a-Si thin films for high-mobility poly-Si TFT fabrication

The possibility to fabricate high-mobility polysilicon TFTs by nanosecond pulsed laser crystallization of unhydrogenated amorphous Si thin films has been investigated. Two types of lasers have been used: a large area (≈ 1 cm2) single ArF excimer laser pulse and a small diameter (≈ 100 μm) frequency-doubled Nd:YAG laser beam, working in the scanning regime. Processed films have been characterized in detail by different optical and microscopic techniques. Device performances indicate that the best results are achieved with the excimer laser leading to high mobility values (up to 140 cm2/Vs) which are much larger than in polysilicon TFTs fabricated onto the same quartz substrates by low-temperature thermal (630° C) crystallization of amorphous Si films (μfe≈55 cm2/Vs).

Ablation dynamics of silicon based targets in oxygen and nitrogen atmospheres

Abstract The optical emission from plasma produced by excimer laser (ArF, λ = 193 nm) ablation of Si, SiO and Si3N4 targets was studied in the visible range. We present results of the time integrated optical spectroscopy measurements and time-of-flight analysis of the particle expansion dynamics. Both methods show the formation of diatomic molecules within the laser induced plasma plume. The velocities of the ejected species are strongly affected by a chemical reaction inside the plasma plume.