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

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

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

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

Internal structuring of silicon with ultrafast lasers

International audienc

Simple and robust method for determination of laser fluence thresholds for material modifications: An extension of Liu's approach to imperfect beams

awaiting peer reviewInternational audienceThe so-called D-squared or Liu's method is an extensively applied approach to determine the irradiation fluence thresholds for laserinduced damage or modification of materials. However, one of the assumptions behind the method is the use of an ideal Gaussian profile that can lead in practice to significant errors depending on beam imperfections. In this work, we rigorously calculate the bias corrections required when applying the same method to Airy-disk like profiles. Those profiles are readily produced from any beam by insertion of an aperture in the optical path. Thus, the correction method gives a robust solution for exact threshold determination without any added technical complications as for instance advanced control or metrology of the beam. Illustrated by two case-studies, the approach holds potential to solve the strong discrepancies existing between the laser-induced damage thresholds reported in the literature. It provides also an appropriate tool for new studies with the most extreme laser radiations

L’émergence de procédés d’écriture laser 3D dans les technologies silicium

International audienceLes lasers femtosecondes sont à la base des technologies d’écriture 3D permettant l'intégration de nombreuses fonctionnalités micro-optiques, fluidiques et mécaniques à l'intérieur des matériaux diélectriques transparents. Cependant, des défis importants restent à relever pour transposer ces technologies dans le silicium et les semiconducteurs avec les nouvelles sources infrarouges intenses. La forte non-linéarité de propagation inhérente aux semi-conducteurs limite intrinsèquement la localisation de l'énergie lumineuse à un niveau en dessous des régimes d’écriture dans les configurations conventionnelles. L’émergence récente de solutions à ce problème ouvre de nouveaux champs d’applications notamment dans la photonique sur silicium

Internal structuring of silicon by ultrafast laser irradiation

International audienceRecent demonstrations of internal structuring of silicon have open new perspectives for the important field of three-dimensional ultrafast laser writing. We discuss the applied methodologies and the remaining challenges to address microfabrication applications in silicon. An important challenge in the field of three-dimensional (3D) ultrafast laser processing is to achieve permanent modifications in the bulk of silicon (Si) and narrow-gap materials. Attempts by increasing the energy of infrared femtosecond pulses with conventional laser machining configurations have failed [1]-[3]. This paper concentrates on the limitations experienced in femtosecond interactions at 1300-nm wavelength to fully identify their origins. We present experimental investigations on the 3D reconstruction of the nonlinear pulse propagation and ionization of Si under tight focusing configurations. By comparison with simulations[4], we quantify the strong nonlinear and plasma effects in the pre-focal region causing the limitations [5]. With an extrapolation on the energy density that could be delivered with hyper-NA values (up to 3.5 in Si), we show that solid immersion focusing provides a solution to achieve ultrafast optical breakdown in Si [5]. By repeatedly illuminating the center of a Si sphere with pulses focused at apparent NA near 3, we exceed the breakdown threshold with sub-100 fs pulses. This leads to a highly-localized negative change of the refractive index as measured with an infrared phase microscopy arrangement. Beyond this proof-of-concept demonstration, the experiment can be translated with the astigmatic solid-immersion lens (ASIL) configuration consisting in focusing the laser radiation through an hemispherical Si sample while ensuring an appropriate optical contact with a planar wafer. This makes possible to achieve similar modifications in Si wafers with a long working distance focusing objective of modest NA (<0.3). It represents a critical step towards the fabrication of 3D photonic microdevices in silicon by a laser writing method. Another practical solution is to rely on longer pulses in the picosecond regime to reduce the peak power and the associated nonlinear effects limiting the energy delivery [6]-[8]. Compared to femtosecond lasers, the experiments confirm that picosecond sources lead to reduced thresholds for 3D writing inside silicon that is highly desirable. However, strong interplays between nonlinear effects persist and should not be ignored for the performance of the future technological developments. We illustrate this aspect by carefully retrieving from a studied case (2-ps pulses at 2-µm wavelength) the conditions for a demonstration of 3D data inscription inside a silicon wafer [9]. Despite the difficulties, refractive index engineering by ultrafast laser writing has the potential to make possible 3D architectures and monolithic Si platforms for the important field of Silicon Photonics. More generally, these developments have the potential to change the way silicon-based microsystems are today designed and fabricated

"Pulsed laser – particle – surface" interaction processes: from dry laser cleaning (DLC) to nanofabrication

International audienceDue to downscaling, the emerging nanotechnology industry requires new cleaning tools providing the ability to remove nanometer-size defects. The dry laser cleaning technique, which simply consists of the irradiation of materials with nanosecond laser pulses, is considered as a promising approach. Our study at LP3 laboratory contributes to a better understanding of the "laser–particles–surfaces" interaction processes. The experiments show that the removal results from a competition between several mechanisms. The ablation of molecular water trapped at the vicinity of contaminates was identified as the dominant cleaning mechanism in the low fluence regime. Among the optical damage mechanisms observed with larger fluences, we analyzed the substrate nanopatterning induced by near-field enhancement underneath the particles. Although this mechanism is not compatible with damage-free cleaning requirements, it may find numerous applications, like the fabrication of nanodevices