Vincent Senez

Strain determination in silicon microstructures by combined convergent beam electron diffraction, process simulation, and micro-Raman spectroscopy

Test structures consisting of shallow trench isolation (STI) structures are fabricated using advanced silicon (Si) technology. Different process parameters and geometrical features are implemented to investigate the residual mechanical stress in the structures. A technology computer aided design homemade tool, IMPACT, is upgraded and optimized to yield strain fields in deep submicron complementary metal–oxide–semiconductor devices. Residual strain in the silicon substrate is measured with micro-Raman spectroscopy (μ-RS) and/or convergent beam electron diffraction (CBED) for large (25 μm) and medium size (2 μm), while only CBED is used for deep submicron STI (0.22 μm). We propose a methodology combining CBED and technology computer aided design (TCAD) with μ-RS to assess the accuracy of the CBED measurements and TCAD calculations on the widest structures. The method is extended to measure (by CBED) and calculate (by TCAD) the strain tensor in the smallest structures, out of the reach of the μ-RS technique....

Engineering Sticky Superomniphobic Surfaces on Transparent and Flexible PDMS Substrate

Following the achievement of superhydrophobicity which prevents water adhesion on a surface, superomniphobicity extends this high repellency property to a wide range of liquids, including oils, solvents, and other low surface energy liquids. Recent theoretical approaches have yield to specific microstructures design criterion to achieve such surfaces, leading to superomniphobic structured silicon substrate. To transfer this technology on a flexible substrate, we use a polydimethylsiloxane (PDMS) molding process followed by surface chemical modification. It results in so-called sticky superomniphobic surfaces, exhibiting large apparent contact angles (>150°) along with large contact angle hysteresis (>10°). We then focus on the modified Cassie equation, considering the 1D aspect of wetting, to explain the behavior of droplets on these surfaces and compare experimental data to previous works to confirm the validity of this model.

Analysis and application of a viscoelastic model for silicon oxidation

The numerical modeling of the oxidation of silicon is analyzed from a nonlinear viscoelastic approach. Its mechanical and stress dependent parameters are determined for silicon dioxide and nitride. The study focuses on the rheological behavior of the materials. The two dimensional simulations of silicon cylinders oxidation and local oxidation of silicon processing reveal that at 1000 °C, a nonlinear viscous modeling is equivalent to the nonlinear viscoelastic one. But, for lower temperatures, the discrepancies between these two models, observed in the stress calculation and final oxide shape, demonstrate the necessity for a complete nonlinear viscoelastic formulation. Finally, the calibrated model is used to study the growth of a recessed isolation structure. The investigations quantify the influence of geometrical parameters of the silicon groove on the shape of the final isolation oxide (e.g., parameters such as the silicon overetch under the pad oxide, the depth of silicon etching, the slope of the sil...

Zipping Effect on Omniphobic Surfaces for Controlled Deposition of Minute Amounts of Fluid or Colloids

When a drop sits on a highly liquid-repellent surface (super-hydrophobic or super-omniphobic) made of periodic micrometer-sized posts, its contact-line can recede with very weak mechanical retention providing that the liquid stays on top of the microsized posts. Occurring in both sliding and evaporation processes, the achievement of low-contact-angle hysteresis (low retention) is required for discrete microfluidic applications involving liquid motion or self-cleaning; however, careful examination shows that during receding, a minute amount of liquid is left on top of the posts lying at the receding edge of the drop. For the first time, the heterogeneities of these deposits along the drop-receding contact-line are underlined. Both nonvolatile liquid and particle-laden water are used to quantitatively characterize what rules the volume distribution of deposited liquid. The experiments suggest that the dynamics of the liquid de-pinning cascade is likely to select the volume left on a specific post, involving the pinch-off and detachment of a liquid bridge. In an applied prospective, this phenomenon dismisses such surfaces for self-cleaning purposes, but offers an original way to deposit controlled amounts of liquid and (bio)-particles at well-targeted locations.

Two-dimensional simulation of local oxidation of silicon: calibrated viscoelastic flow analysis

Local Oxidation of Silicon (LOCOS) remains the common isolation technology for mass-production of integrated circuits. The work reported in this paper contributes to the improvement of the numerical modeling of the LOCOS process. A physical two-dimensional (2-D) modeling of the thermal oxidation of silicon has been developed based on the explicit treatment of the reaction expansion. The originality of this modeling is to propose a general solution taking into account of the silicon deformation, incorporating the viscoelastic behaviour of oxide and nitride and, particularly, giving a complete calibration of the stress-dependent parameters. The prediction capabilities are demonstrated by the calculations of oxide shapes and oxidation-induced stresses in a silicon substrate for very advanced isolation techniques.

Formation of silicon islands on a silicon on insulator substrate upon thermal annealing

Starting from silicon on insulator substrates, we show that a thermal treatment (in the 600–900 °C range) induces the creation of silicon islands. To characterize the island formation as well as the initial silicon layer thickness, we use in situ Auger electron spectroscopy analysis in an ultrahigh vacuum chamber. The island size and density are studied with an ex situ atomic force microscope. We show that the formation temperature of the islands increases from 575 to 875 °C as the initial silicon layer thickness increases from 1 to 19 nm. For the 1 nm thickness, the minimum island size is reached (semispherical shape with a 16 nm diameter). The phenomena involved in the island formation are discussed and the study of the variations of the calculated stress tensor (IMPACT software) as a function of the thermal treatment explain the behavior of the top silicon layer.

Contact angle hysteresis origins: Investigation on super-omniphobic surfaces

Contact angle hysteresis of liquid droplets is investigated on sticky and flexible super-omniphobic surfaces made up of PDMS–Si3N4 microstructures. Up to now, extensive studies have been focusing on the relation between hysteresis and surface properties such as roughness or defect density. However, little attention has been paid to the dependence of hysteresis with respect to the liquid surface tension. In this work, advancing and receding apparent contact angles are measured on surfaces displaying 4 different defect densities with 10 water–ethanol mixtures (surface energy ranging from 72 to 21.7 mN m−1). While advancing angles are found to be constant whatever the defect density and the liquid surface energy, receding angles exhibit more complex variations. Surprisingly, we noticed a saturation of this receding angle at low surface energy. In order to explain this phenomenon, we address the receding contact line distortion from the point of view of micro capillary bridges formation and breakage. The model is supported by fine SEM observation of the local deformation and offers a new perspective to explain the underlying mechanism of the saturation phenomenon.

Techniques for mechanical strain analysis in sub-micrometer structures: TEM/CBED, micro-Raman spectroscopy, X-ray micro-diffraction and modeling

In this paper, three techniques are discussed that provide information on process-induced local mechanical stress in silicon: the convergent beam electron diffraction technique of transmission electron microscopy, X-ray micro-diffraction and micro-Raman spectroscopy. We discuss the principles of these techniques, their spatial resolution, the ease-of-use, the information that can be obtained, the required sample preparation, the measurement time, and the complementarities of these techniques. We demonstrate this for stress induced by shallow trench isolation and correlate the results to finite element analysis results.

Modeling of the transient enhanced diffusion of boron implanted into preamorphized silicon

We present a physically based modeling of the transient enhanced diffusion (TED) of boron implanted into preamorphized silicon. We start by describing the nucleation and growth of a supersaturation of Si interstitial atoms into dislocation loops. Our modeling of the nucleation and growth of the dislocation loops is divided into three distinct stages: the nucleation, the “pure growth,” and the Ostwald ripening. The implementation of this modeling into the process simulator IMPACT-4 allows one to correctly predict the size and density evolutions of the dislocation loops observed by transmission electron microscopy for a variety of annealing times and temperatures. This simulation also gives access to the concomitant behavior of the free Si interstitials atoms responsible for TED. Implementation of this model into IMPACT-4 shows that TED in preamorphized Si can be simulated for a variety of experimental conditions by assuming boron diffusion occurs through the coupling of boron atoms with this fast evolving ...

Thermally assisted formation of silicon islands on a silicon-on-insulator substrate

We report the self-formation of nanometer-size silicon islands on a silicon-on-insulator (SOI) substrate that is associated with simple thermal treatment in the range of 500–900 °C. We study the island formation process versus the temperature of the thermal annealing, the thickness of the top silicon layer, and the presence of a native oxide on this top layer. The island size distribution is also studied. To follow the chemical evolution of the top layer, we used in situ Auger electron spectroscopy in an ultrahigh vacuum chamber. The island morphology is studied using ex situ atomic force microscopy (AFM). The formation temperature increases with the thickness of the top silicon layer and can be explained by thermal stress induced at the Si/SiO2 interface. From a technological point of view, this study shows the limitation of a SOI substrate with a thin silicon top layer under thermal treatment. On the other hand, it opens up an easy way in which to build silicon dots on an insulator. Finally, we present ...