Dielectric layers are deposited on semiconductor materials for many applications, either in the active stacks of the devices (e.g. the gate dielectric in a metal-oxide-semiconductor transistor) or as passivation solutions (e.g. in image sensors [ 1 ], solar cells [ 2 ] etc.). The progress at the material and technology levels must be accompanied by the development of new characterization tools. One of the challenges in terms of characterization is to obtain the information on the electrical quality of the dielectric-on-semiconductor interface during the fabrication flow, non-destructively, just after the corresponding deposition step (if possible) and without needing to fully fabricate a particular test structure. At wafer level, a typical electrical evaluation method is the Corona characterization of semiconductors [ 3 ] that provides the interface state density (D it ) and the “total” charge responding in the structure. Its main drawback is the charging of the surface during the measurement. Optical methods (like the photoconductance decay or the photoluminescence) are non-destructive, but they are directly related to material and interface quality through the carrier lifetime [ 4 ] and they don’t allow a simple separation between fixed charge in the oxide (Q ox ) and D it . However optical-based methods are still a recommended strategy, since they ensure non-destructive measurements. In this context, the second harmonic generation (SHG) is a good option, because it can be sensitive to the “static” electric field induced between layers. In the SHG, the surface of the sample is irradiated with a femtosecond laser and a second harmonic wave is then generated and detected. In general, the SHG contains both bulk and surface contributions, but for centrosymmetric materials (such as silicon, silicon dioxide, alumina, etc.) in the dipolar approximation, the interface signal is dominant and it is related to the symmetry breaking due to both the interface itself and to the “static” electric field [ 5 ]. The SHG has already been used for dielectric characterization using various modalities: SHG versus power, time, wavelength, etc. [ 6 ], [ 7 ], [ 8 ]. In this paper, we focus on the analysis of the interface electric field, which is related to Q ox and D it . If trapping/detrapping phenomena occur during the illumination of the sample, this field can actually depend on time. The value of the SHG (proportional to the square of the field) will then be related to Q ox and its evolution in time should correlate to D it . The technique is promising but it triggers two questions: (1) how to separate optical phenomena (absorption, interferences) specific to multi-layer structures and access electrical field only and (2) how to actually extract Q ox and D it . During the presentation we explain recent results in these two areas, using simulation results obtained with our “home-made” code and a wide panel of samples for the experiments. Alternative electrical characterization performed through capacitance versus voltage measurements gives hints for future calibration. Acknowledgements This work was supported by Region Rhône Alpes (ARC6 program), the French National Research Agency within the framework of the OXYGENE project (ANR-17-CE05-0034) and French National Plan Nano2022, within the IPCEI Nanoelectronics for Europe program. [1] J. L. Regolini, D. Benoit, and P. Morin, "Passivation issues in active pixel CMOS image sensors," Microelectronics Reliability, vol. 47, pp. 739-742, 2007. [2] A. G. Aberle, "Surface passivation of crystalline silicon solar cells: a review," Progress in Photovoltaics: Research and Applications, vol. 8, pp. 473-487, 2000. [3] M. Wilson, J. Lagowski, L. Jastrzebski, et al. , "COCOS (corona oxide characterization of semiconductor) non-contact metrology for gate dielectrics," AIP Conference Proceedings, vol. 550, pp. 220-225, 2001. [4] D. K. Schroder, "Carrier lifetimes in silicon," Electron Devices, IEEE Transactions on, vol. 44, pp. 160-170, 1997. [5] J. E. Sipe, D. J. Moss, and H. M. van Driel, "Phenomenological theory of optical second- and third-harmonic generation from cubic centrosymmetric crystals," Physical Review B, vol. 35, pp. 1129-1141, 1987. [6] J. Price, M. Lei, P. S. Lysaght, et al. , "Charge trapping defects in Si/SiO2/Hf(1−x)SixO2 film stacks characterized by spectroscopic second-harmonic generation," Journal of Vacuum Science & Technology B, vol. 29, p. 04D101, 2011. [7] N. M. Terlinden, G. Dingemans, V. Vandalon, et al. , "Influence of the SiO2 interlayer thickness on the density and polarity of charges in Si/SiO2/Al2O3 stacks as studied by optical second-harmonic generation," Journal of Applied Physics, vol. 115, p. 033708, 2014. [8] H. Park, J. Qi, Y. Xu, et al. , "Boron induced charge traps near the interface of Si/SiO2 probed by second harmonic generation," Physica Status Solidi (b), vol. 247, pp. 1997-2001, 2010.

The second harmonic generation (SHG) proved to be a very promising characterization technique for dielectric-semiconductor interfaces because it is sensitive, non-destructive, can be applied directly on wafer, at different stages of wafer processing. The method, based on non-linear optics effects, is measuring a signal encompassing the “static” electric field at the dielectric-semiconductor interface which is directly related to the oxide charges Qox and to the interface state density Dit. A general methodology for Qox and Dit extraction from SHG measurements requires (i) calibration based on parameters obtained by classical electrical methods and (ii) modeling to capture the optical propagation phenomena that impact the SHG signal. In this paper, we discuss these issues based on a review of our recent advances on how to exploit SHG for dielectrics on semiconductor characterization.

This paper investigates the ability of second harmonic generation (SHG) to probe the passivation quality of atomic layer deposited Al2O3 on Si by estimating the induced interface electric field due to fixed charges in the oxide. Samples with various oxide charges (Q(ox)) and interface state densities (D-it) were fabricated, using different deposition parameters. The samples were characterized by capacitance-voltage (C-V) and microwave photoconductance decay measurements in order to evaluate Q(ox) and D-it as well as the effective minority carrier lifetime tau(eff). The SHG results were consistent with Q(ox), D-it and tau(eff) values, proving the ability of the technique to monitor the interfacial quality in a contactless and non-destructive way. Optical simulations which use the electric field values obtained from the C-V measurements could reproduce the measured SHG signal. This demonstrates that SHG coupled with optical simulation can give access to the electric field magnitude and thus characterize the electrical properties of oxide/Si interfaces. Published by AIP Publishing.

In this study, we report the use of Al2O3 nanoparticles in combination with fluorine doped tin oxide (F:SnO2, aka FTO) thin films to form hazy Al2O3-FTO nanocomposites. In comparison to previously reported FTO-based nanocomposites integrating ZnO and sulfur doped TiO2 (S:TiO2) nanoparticles (i.e., ZnO-FTO and S:TiO2-FTO nanocomposites), the newly developed Al2O3-FTO nanocomposites show medium haze factor HT of about 30%, while they exhibit the least loss in total transmittance Ttot. In addition, Al2O3-FTO nanocomposites present a low fraction of large-sized nanoparticle agglomerates with equivalent radius req > 1 μm; effectively 90% of the nanoparticle agglomerates show req < 750 nm. The smaller feature size in Al2O3-FTO nanocomposites, as compared to ZnO-FTO and S:TiO2-FTO nanocomposites, makes them more suitable for applications that are sensitive to roughness and large-sized features. With the help of a simple optical model developed in this work, we have simulated the optical scattering by a single nanoparticle agglomerate characterized by bottom radius r0, top radius r1, and height h. It is found that r0 is the main factor affecting the HT(λ), which indicates that the haze factor of Al2O3-FTO and related FTO nanocomposites is mainly determined by the total surface coverage of all the nanoparticle agglomerates present.

Controlling plasmonic systems with nanometer resolution in transparent films and their colors over large nonplanar areas is a key issue for spreading their use in various industrial fields. Using light to direct self-organization mechanisms provides high-speed and flexible processes to meet this challenge. Here, we describe a route for the laser-induced self-organization of metallic nanostructures in 3D. Going beyond the production of planar nanopatterns, we demonstrate that ultrafast laser-induced excitation combined with nonlinear feedback mechanisms in a nanocomposite thin film can lead to 3D self-organized nanostructured films. The process, which can be extended to complex layered composite systems, produces highly uniform large-area nanopatterns. We show that 3D self-organization originates from the simultaneous excitation of independent optical modes at different depths in the film and is activated by the plasmon-induced charge separation and thermally induced NP growth mechanisms. This laser color marking technique enables multiplexed optical image encoding and the generated nanostructured Ag NPs:TiO2 films offer great promise for applications in solar energy harvesting, photocatalysis, or photochromic devices.

This paper describes a model to simulate changes in the size distribution of metallic nanoparticles (NPs) in TiO2 films upon continuous wave light excitation. Interrelated laser induced physical and chemical processes initiated directly by photon absorption or by plasmon induced thermal heating are considered. Namely the model takes into account the NP coalescence, Ostwald ripening, the reduction of silver ions and the oxidation of metallic NPs, competitive mechanisms that can lead to counter-intuitive behaviors depending on the exposure conditions. Theoretical predictions are compared successfully to the experimental results deduced from a thorough analysis of scanning transmission electron microscopy (STEM) pictures of Ag:TiO2 films processed with a scanning visible laser beam at different speeds. Ag:TiO2 systems are considered for many applications in solar energy conversion, photocatalysis or secured data printing. Numerical investigations of such a system provide a better understanding of light induced growth and shrinking processes and open up prospects for designing more efficient photocatalytic devices based on metal NP doped TiO2 or for improving the size homogeneity in self-organized metallic NP patterns, for instance.

Mesoporous thin films of TiO2 doped with silver can undergo spectacular microstructural modifications upon laser scanning at visible wavelengths through the excitation of a localized surface plasmon resonance in Ag nanoparticles (NPs). The latter can result in competitive physicochemical mechanisms, leading either to the shrinkage or to the growth of NPs depending on the exposure conditions. Contrary to intuition, we provide evidence that the speed of the laser scan controls the size of NPs as follows: low speeds lead to silver oxidation and a decrease in the NP size, whereas high speeds induce rapid temperature rises and a spectacular growth of NPs. Both regimes are separated by a speed threshold that depends on extrinsic and intrinsic parameters such as laser power, beam diameter, and initial size of Ag NPs. We propose here a comprehensive model based on a set of coupled differential equations describing the transformations of silver under laser excitation between the Ag-0, Ag+, and metallic NP states, which provides a convincing physicochemical explanation of the experimental findings. This study constitutes a significant advance in the understanding of oxidationreduction processes involved during laser exposure of metallic NPs and opens new directions to control their growth rate and their final size.

Using a monochromatic plane wave to generate periodic arrays of metallic nanoparticles with tunable features buried in thin films is the original work we report here. We focus on the way such waveguiding metallic photonic crystals can self-emerge from thin films homogeneously loaded with metallic precursors under continuous-wave and homogeneous laser excitation. This paper fully describes the conditions leading to the formation of periodic structures and highlights the role of several parameters in the underlying physical mechanisms. The laser exposure parameters, especially, fix the geometrical and optical properties of the generated structures. Grating lines are parallel to the laser polarization and the period is directly linked to the laser wavelength. Both electron resonances of metal nanoparticles and optical resonances of guided modes interact to form the periodic patterns under homogeneous exposure. A model, based on the coupled mode theory, can be proposed to predict the spontaneous generation of such periodic nanostructures. It concludes that the guided waves exponentially enhance during illumination due to a positive feedback loop with the ordered growth of particles. This process opens up new fabrication techniques for making optical devices and may find applications in various fields such as polarization imaging, displays, security or lighting.

This paper deals with the colorimetric properties of silver nanoparticle gratings buried in a dense titania film that result from a continuous wave laser-induced self-organization process. The samples exhibit shining colors in the direction of the specular reflection, which are very sensitive to polarization. We show that a large color gamut and a tunable dichroism can be reached by varying the exposure conditions. We also discuss the physical meaning of the observed variations in the dichroism. This laser process produces a single pass marking with a micrometer resolution and could be useful for developing innovative solutions in fields like active color displays, security, polarization imaging, or design.

In this work, we evaluate through rigorous coupled-wave analysis simulations the effect of various process-related inaccuracies on plasmonic filters performance, especially regarding cross-shaped-hole arrays. Focusing exclusively on CMOS-compatible materials, we demonstrate the potential of these structures for reliable integration and fabrication at wafer level. A high monitoring of the deposition parameters is required to control the transmission level and the resonant wavelength of the filters. Optical proximity calculations show that double patterning is a way to limit corner rounding and to avoid losing the resonant mode of the crosses. The impacts on plasmon resonances of the metal oxidation, or a sloped profile after metal etching, are evaluated. These results allow for a good anticipation regarding process issues to realize efficient plasmonic filters.

Hole arrays metallic filters can be made independent to polarization at normal incidence. However they may lose this property for a non-normal incidence, being dependent to both polar and azimuthal incident angles. These variations of the filter characteristics according to light orientation and polarization are not desirable for most optical applications. Yet, for specific geometric parameters, high-stability can be obtained for cruciform-holes Ag-SiO2 filters. In this article, we propose a review of cross-holes metallic filters, working with CMOS-compatible materials in the visible range. We find out the main geometrical parameters impacting the filters sensitivity to the incident angles and polarization and link their role to spectral stability. We give proper design rules to realize stable filters which may lead to optical sensors with very low spectral variations whatever the incidence and the polarization of the source.

In the present paper, we will show how diffractive microstructures can lead to efficient lenses which present several advantages with respect to other proposed solutions. Also, they only require wavelength-scale resolution and not very small nanostructuring. Nevertheless we obtain comparable performances as plasmonics lenses and we show that the diffraction phenomenon which is at the origin of the observed effects can indeed lead to efficient focusing in the Fresnel region. The structures we proposed in this paper consist of pairs of parallel metallic nanowires fabricated by direct laser writing technique. The fabrication set-up is based on a metallic photoreduction initiated by two photon absorption using a nanosecond Q-Switched Nd-YAG laser. We show for instance experimentally that this pair of metallic nanowires separated by 2 μm when irradiated with an unpolarized light (at λ=546 nm) lead to a focusing at 2 μm with a diffraction limited resolution and an intensity enhancement at the focusing point of about 2.2 times the incoming intensity. Two different theoretical models were used to corroborate our experimental measurement. The first one is the diffraction theory based on the Rayleigh-Sommerfeld integral and the second one is the well kwon FDTD simulations, which are in very good agreement with experiments and confirm the origin of the focusing process. In addition they show that, in the case of our microstructures, plasmonic effects do not contribute to the focusing process. Finally, we propose a 2D array of microlenses based on a grid of metallic nanowires separated by a distance D. This device has slightly the same lens characteristics as a pair of metallic nanowires but with an intensity enhancement higher than 5, and thus may present practical interest in view of applications.

Measurements of optical tweezers forces on biological micro-objects can be used to develop innovative biodiagnostics methods. In the first part of this report, we present a new sensitive method to determine A, B, D types of red blood cells. Target antibodies are coated on glass surfaces. Optical forces needed to pull away RBC from the glass surface increase when RBC antigens interact with their corresponding antibodies. In this work, measurements of stripping optical forces are used to distinguish the major RBC types: group O Rh(+), group A Rh(+) and group B Rh(+). The sensitivity of the method is found to be at least 16-folds higher than the conventional agglutination method. In the second part of this report, we present an original way to measure in real time the wall thickness of bacteria that is one of the most important diagnostic parameters of bacteria drug resistance in hospital diagnostics. The optical tweezers force on a shell bacterium is proportional to its wall thickness. Experimentally, we determine the optical tweezers force applied on each bacteria family by measuring their escape velocity. Then, the wall thickness of shell bacteria can be obtained after calibrating with known bacteria parameters. The method has been successfully applied to indentify, from blind tests, Methicillinresistant Staphylococcus aureus (MRSA), including VSSA (NCTC 10442), VISA (Mu 50), and heto-VISA (Mu 3)

It has been shown in literature that cross-shaped holes arrays can be made insensitive to polarization at normal incidence, and can even feature good stability for off-normal incidence. In this work we look for the optimal design rules to obtain high spectral stability conditions in the visible for those structures, through a complete review of all geometrical parameters using CMOS-compatible materials. Rigorous Coupled Wave Analysis (RCWA) simulations have been used to identify the most-impacting parameters and to determine typical ranges allowing for the realization of low-color errors image sensors whatever the light incidence. It appears that the two main parameters are the ratio of the arm width to the arm length of the crosses and the distance between crosses, which both have to be low to ensure stable responses of the filters. We demonstrate the results with CIE chromaticity diagrams reporting the responses of a RGB filter designed with the established rules under various illumination conditions.

We report on the optimization of ultrasmall microlenses based on the diffraction of two parallel metallic nanowires. The Rayleigh–Sommerfeld integral is used in the visible range to simulate the near field diffraction patterns induced by single and paired planar silver wires. We demonstrate that the wire width w affects only the diffraction efficiency and the contrast of the diffraction pattern. The wire interdistance D controls the focal length and the depth of focus, which are equal and vary in the 0.1 to 10 μm range when D/λ increases from 1 to 8. The transversal FWHM increases from 200 to 700 nm, and a normalized intensity greater than 2.2 is obtained at the focal point when w is about 300 nm and D/λ=3. There is excellent agreement between these calculated properties and the experimental results obtained for single and paired parallel silver nanowires. We show that in our microsized geometry, the plasmon contribution is negligible with respect to pure diffraction effect. In addition, these nanowire microlenses have focusing properties similar to those of ideal refractive lenses limited by diffraction.

Miniature optical components at the wavelength scale remain today a theoretically opened challenging problem of great technological interest. Appart from refractive micro-optics, plasmonics have been proposed to realize micro lenses with properly designed planar metallic nano-patterns. We show in this paper that efficient light focusing at the diffraction limit with higher transmission can be obtained with micro-structures much easier to fabricate than nano ones, such as a simple micro-slit studied here as an example. Optical properties are attributed to diffraction and a quantitative excellent agreement between experiment and theory is obtained.

We theoretically and experimentally demonstrate that the diffraction of microstructures based on silver nanowires leads to very efficient microfocusing effects. Pairs of parallel nanowires act as ultrasmall cylindrical microlenses with diffraction-limited resolution in the Fresnel region. This is a new diffraction scheme to make micron-sized optical lenses with higher transmittance than plasmonic microlens based on nano-aperture arrays. Calculations based on the scalar Rayleigh-Sommerfeld integral highlights the pure scalar diffractive contribution. Thus, the plasmon contribution is negligible in such micron-sized metallic geometry. We demonstrate that two-dimensional grids of nanowires can be used to fabricate dense arrays of microlenses, i.e. 10000x10000 DPI (dots per inch).

Archimedes micro-screws have been fabricated by three-dimensional two-photon polymerization using a Nd:YAG Q-switched microchip laser at 532nm. Due to their small sizes they can be easily manipulated, and made to rotate using low power optical tweezers. Rotation rates up to 40 Hz are obtained with a laser power of 200 mW, i.e. 0.2 Hz/mW. A photo-driven micropump action in a microfluidic channel is demonstrated with a non-optimized flow rate of 6 pL/min. The optofluidic properties of such type of Archimedes micro-screws are quantitatively described by the conservation of momentum that occurs when the laser photons are reflected on the helical micro-screw surface.

A continuous-wave dual-wavelength solid-state microlaser is presented and a technique for regulating the gain competition between the two wavelengths is proposed, based on the angular tilt of the laser cavity output mirror. Laser behavior is studied and balanced dual-wavelength emission is obtained with output power levels as high as 200 mW for 2 W pump power. Sum frequency mixing is demonstrated making the source promising for Terahertz generation in the 0.5-0.7 THz range through difference frequency generation.

Recent intensive theoretical and experimental studies shed light on possible new physics beyond the standard model of particle physics, which can be probed with sub-eV energy experiments. In the second run of the OSQAR photon regeneration experiment, which looks for the conversion of photon to axion (or Axion-Like Particle), two spare superconducting dipole magnets of the Large Hadron Collider (LHC) have been used. In this paper we report on first results obtained from a light beam propagating in vacuum within the 9 T field of two LHC dipole magnets. No excess of events above the background was detected and the two-photon couplings of possible new scalar and pseudo-scalar particles could be constrained.