Procédés laser-particules : décontamination et nanofabrication

Les propriétés particulières des interactions entre une impulsion laser et des particules submicrométriques apportent de nouvelles solutions dans la course à la miniaturisation. Les travaux réalisés au laboratoire LP3 intéressent plus particulièrement les applications de nettoyage extrême pour l'industrie des semi-conducteurs et participent au développement de nouvelles techniques de nanofabrication

Analyses of femtosecond laser ablation of Ti, Zr, Hf

Femtosecond laser ablation of Ti, Zr and Hf has been investigated by means of in-situ plasma diagnostics. Fast plasma imaging with the aid of an intensified charged coupled device (ICCD) camera was used to characterise the plasma plume expansion on a nanosecond time scale. Time- and spaceresolved optical emission spectroscopy was employed to perform time-of-flight measurements of ions and neutral atoms. It is shown that two plasma components with different expansion velocities are generated by the ultra-short laser ablation process. The expansion behaviour of these two components has been analysed as a function of laser fluence and target material. The results are discussed in terms of mechanisms responsible for ultra-short laser ablation

Wavelength-independent performance of femtosecond laser dielectric ablation spanning over three octaves

Ultrafast laser breakdown of wide bandgap dielectrics is today a key for major technologies ranging from 3D material processing in optical materials to nanosurgery. However, a contradiction persists between the strongly nonlinear character of energy absorption and the robustness of processes to the changes of the bandgap/wavelength ratio depending on applications. While various materials and bandgaps have been studied, we concentrate here the investigations on the spectral domain with experiments performed with wavelength drivers varied from deep-ultraviolet (258 nm) to mid-infrared (3.5 $\mu$m). The measured fluence thresholds for single shot ablation in dielectrics using 200-fs pulses exhibit a plateau extending from the visible domain up to 3.5-$\mu$m wavelength. This is accompanied, after ablation crater analysis, by a remarkable invariance of the observed ablation precision and efficiency. Only at the shortest tested wavelength of 258 nm, a twofold decrease of the ablation threshold and significant changes of the machining depths are detected. This defines a lower spectral limit of the wavelength-independence of the ablation process. By comparison with simulations, avalanche ionization coefficients are extracted and compared with those predicted with the Drude model. This must be beneficial to improve predictive models and process engineering developments exploiting the new high-power ultrafast laser technologies emitting in various spectral domains

Jetting regimes of double-pulse laser-induced forward transfer

International audienceWe use the double-pulse laser-induced forward transfer (DP-LIFT) process, combining a quasi-continuous wave (QCW) and a femtosecond (fs) laser pulse to achieve jetting from a 1-µm thick copper film. The influence of the fs laser fluence on the dynamics of the liquid copper jetting is experimentally investigated by time-resolved shadowgraphy and theoretically analyzed with a simple energy balance model. Different jetting regimes are identified when varying the fs laser fluence. We demonstrate that the adjustment of this latter parameter while keeping all the others constant, allows accurate control of the diameter of the printed droplets from 1.9 µm to 6.0 µm. This leads us to a demonstration in which we print debris-free micro-pillars with an aspect ratio of 19 onto a silicon receiver substrate set as far as 60 µm away from the donor film

Femtosecond Laser Backside Ablation of Gold Film on Silicon Substrate

Citation: Lei, S., Grojo, D., Ma, J., Yu, X., & Wu, H. (2016). Femtosecond Laser Backside Ablation of Gold Film on Silicon Substrate. Procedia Manufacturing, 5, 594-608. doi:10.1016/j.promfg.2016.08.049Femtosecond laser ablation of gold thin film on the front and backside of silicon substrate is investigated, with backside ablation being the focus and front side ablation for comparison. The experiments are performed using 100 fs pulses delivered through an ultrafast laser source combined with an OPA for wavelength conversion at 1300 nm. We create a single shot ablation matrix by varying focus position and pulse energy. The laser beam is characterized using an IR imaging technique at both the front and backside of the substrate. It is found that the pulse profile experiences little distortion after passing though the 1 mm silicon substrate, despite the high pulse energy used. However, a comparison of the front and back ablation site indicates significant attenuation of pulse energy due to nonlinear absorption. Two types of damage happen depending on laser fluence: ablation and burst. Burst damage is confirmed with finite element simulation. © 2016 The Author

Limitations to laser machining of silicon using femtosecond micro-Bessel beams in the infrared

Citation: Grojo, D., Mouskeftaras, A., Delaporte, P., & Lei, S. T. (2015). Limitations to laser machining of silicon using femtosecond micro-Bessel beams in the infrared. Journal of Applied Physics, 117(15), 7. doi:10.1063/1.4918669We produce and characterize high-angle femtosecond Bessel beams at 1300-nm wavelength leading to nonlinearly ionized plasma micro-channels in both glass and silicon. With microjoule pulse energy, we demonstrate controlled through-modifications in 150-mu m glass substrates. In silicon, strong two-photon absorption leads to larger damages at the front surface but also a clamping of the intensity inside the bulk at a level of approximate to 4 x 10(11) W cm(-2) which is below the threshold for volume and rear surface modification. We show that the intensity clamping is associated with a strong degradation of the Bessel-like profile. The observations highlight that the inherent limitation to ultrafast energy deposition inside semiconductors with Gaussian focusing [Mouskeftaras et al., Appl. Phys. Lett. 105, 191103 (2014)] applies also for high-angle Bessel beams. (C) 2015 AIP Publishing LLC

Laser-fabricated porous alumina membranes (LF-PAM) for the preparation of metal nanodot arrays

We report on an efficient photonic-based method to prepare nanodot array of functional materials, independently of the nature of the substrate.Comment: Small (2008) Accepte

The so-called dry laser cleaning governed by humidity at the nanometer scale

Illumination with single nanosecond pulses leads to the detachment of silica particles with 250nm radii from siliconsurfaces. We identify two laser-energy dependent cleaning regimes by time-of-flight particle-scattering diagnostics. For the higher energies, the ejection of particles is produced by nanoscale ablation due to the laser field enhancement at the particle-surface interface. The damage-free regime at lower energy is shown to be governed by the residual water molecules, which are inevitably trapped on the materials. We discuss the great importance that the humidity plays on the cleaning force and on the adhesion in the experiments.Peer reviewe

Three-dimensional writing inside silicon using a 2-µm picosecond fiber laser

International audienc