Pierre Barritault

A new analysis strategy for CD metrology using rapid photo goniometry method

In the present paper, we use a new photo goniometric method capable to measure the entire diffracted pattern of a sub micron grating at fixed wavelength very rapidly. The complete reflectance pattern is obtained versus incidence angle (0-80°) and azimuth angle (0-360°). Regression software based on RCWA simulations has been developed. It is used to adjust automatically the grating profile with an unprecedented rapidity. Regressions have been applied to our polarimetric measurements versus incidence angle θ and versus azimuth angle φ. Results are compared to those provided by spectroscopic ellipsometry (SE) and scanning electron microscopy (SEM). We show that fixed incidence angle specular reflection coefficients versus azimuth angle R(φ) curves are very sensitive to the profiles especially when the CD is reduced mainly because of the occurrence of diffracted orders matching the CD at given azimuths even if the wavelength is much larger than the CD. Mid space illumination measurements in a large angular aperture (0<θ<80° and 0<φ<180°) can be also used to deduce profile information. We show that specular reflection coefficients can be fitted in the entire angular aperture to provide precise structural shapes. Out of specular contribution which is measured simultaneously can also be used in the analysis. We show that it is more sensitive to the grating imperfections than the specular contribution.

Robust sub-50-nm CD control by a fast-goniometric scatterometry technique

Sub-50 nm half pitch critical dimension metrology of resist lines by a fast goniometric scatterometry technique in the visible range has been investigated. The goniometric optical instrumentation allows illumination and reflection of patterned objects from almost all angles of view (0°/80° polar angles, and 0°/360° azimuthal angles) simultaneously. Applied to scatterometry, this tomography-like technique ensures a robust lines profiles reconstruction. Sensitivity and correlation analysis show that this technique exhibits at least equal performances compared to ellipsometry. Since the technique uses a single wavelength, no spurious assumptions about the refractive index of the materials illuminated is introduced is the modeling process. So the technique is believed to be more robust than ellipsometry. We present a demonstration of CD measurement with this technique on 30 nm CD resist lines with various pitches. The results are compared to CDSEM.

Determination of surface-bound-fluorophore orientation by goniometric fluorescence polarization: application to quantification of DNA-chip readouts.

We present a polarized goniofluorimeter designed to measure the observation-angle and polarization-dependent intensity emitted by a group of surface-bound fluorescent molecules. We studied two types of surface bonding: In one case, dyes were adsorbed into the surface by spin coating, and in the other, dyes were covalently immobilized to DNA strands. Fluorescent dyes consisted of Cy3 and Alexa546. The substrate was a silicon wafer bearing a silicon dioxide layer. The different samples presented a wide panel of reproducible experimental behavior. By confronting experimental behavior with theory and simulation, we can explain these differences as directly linked to the mean orientation of fluorophores with respect to the surface.

Optical thin films serving biotechnology: fluorescence enhancement of DNA chip

Over the past years, DNA-chip technology has exploded. Yet scientists using such devices have to face many problems. One of them, due to the very low concentration of biological species to be detected, is the weakness of fluorescence signal collected through the reading system (microscope or scanner). To solve this problem, we proposed to use optical thin films technology. We studied the potentialities of this method step by step. The first step was to be able to understand, explain and forecast the fluorescence emitted by a DNA-chip in terms of fluorescence angular patterns. A theoretical and experimental study enabled us to master this issue even in the case of multi-layers substrates. Using this knowledge we were then able to explain, through simulations, the potentialities of this new type of substrates in terms of fluorescence enhancement. Thus we showed that a theoretical enhancement of twenty-fold (compare to a glass substrate) was achievable.

Fluorescence of mitigated laser damage in fused silica

In the field of laser-induced surface damage, it has been shown that localized re-fusion of silica can be used as a mean to mitigate the damage and therefore stop its growth before the use of the optical component is impaired. In this paper, this localized re-fusion was produced using a continuous CO2 laser. As the damage is reshaped, we observed that a ring of evaporated silica is systematically deposited around the mitigated damage. This evaporated silica is likely to be non-stoechiometric and therefore to present absorption and luminescence properties. Thus we decided to perform photoluminescence measurements in order to analyse the mitigated damages. We performed fluorescence imaging and spectroscopy using 351nm continuous laser excitation. Different experimental conditions were used for the re-fusion process and the consequences on the photoluminescence properties were studied. We also compared these properties to the properties of non-mitigated damages.

Polarized gonio fluorimetric measurements of DNA-chip: a step forward towards fluorescence quantification

Quantifying hybridization and therefore fluorescence signals has become a key-issue in DNA-chip technology. Thus a better understanding of fluorescence near a surface has become a necessity. To study this issue, we modeled the fluorophore after an electromagnetic dipole radiating over the substrate; we then developed a simulation code which enabled us to calculate the observation-angle-dependent-intensity radiated by a population and altitude. In the mean time we developed a polarized-gonio-fluoimeter which permits angular fluorescence patterns and fluorescence polarization measurements. We studied DNA-chips obtained by covalent grafting of labeled oligonucleotides. Simulation curves perfectly matched experimental ones, enabling an accurate determination of fluorophore localization on the substrate. Once achieved a better understanding of the fluorophore emission, we designed and realized a thin-film-coated microscope slide dedicated to the enhancement of DNA-chip fluorescence. This substrate was used in a c-DNA gene analysis. Fluorescence enhancement was clearly observed enabling the detection of Cart1 and P2A which are undetectable when using non-coated microscope slides.