In-vivo measurement of the human soft tissues constitutive laws. Applications to Computer Aided Surgery

In the 80's, biomechanicians were asked to work on Computer Aided Surgery applications since orthopaedic surgeons were looking for numerical tools able to predict risks of fractures. More recently, biomechanicians started to address soft tissues arguing that most of the human body is made of such tissues that can move as well as deform during surgical gestures [1]. An intra-operative use of a continuous Finite Element (FE) Model of a given tissue mainly faces two problems: (1) the numerical simulations have to be "interactive", i.e. sufficiently fast to provide results during surgery (which can be a strong issue in the context of hyperelastic models for example) and (2) during the intervention, the surgeon needs a device that can be used to provide to the model an estimation of the patient-specific constitutive behaviour of the soft tissues. This work proposes an answer to the second point, with the design of a new aspiration device aiming at characterizing the in vivo constitutive laws of human soft tissues. The device was defined in order to permit sterilization as well an easy intra-operative use

In vivo measurement of human brain elasticity using a light aspiration device

The brain deformation that occurs during neurosurgery is a serious issue impacting the patient "safety" as well as the invasiveness of the brain surgery. Model-driven compensation is a realistic and efficient solution to solve this problem. However, a vital issue is the lack of reliable and easily obtainable patient-specific mechanical characteristics of the brain which, according to clinicians' experience, can vary considerably. We designed an aspiration device that is able to meet the very rigorous sterilization and handling process imposed during surgery, and especially neurosurgery. The device, which has no electronic component, is simple, light and can be considered as an ancillary instrument. The deformation of the aspirated tissue is imaged via a mirror using an external camera. This paper describes the experimental setup as well as its use during a specific neurosurgery. The experimental data was used to calibrate a continuous model. We show that we were able to extract an in vivo constitutive law of the brain elasticity: thus for the first time, measurements are carried out per-operatively on the patient, just before the resection of the brain parenchyma. This paper discloses the results of a difficult experiment and provide for the first time in-vivo data on human brain elasticity. The results point out the softness as well as the highly non-linear behavior of the brain tissue.Comment: Medical Image Analysis (2009) accept\'

Global optimization in inverse problem of scatterometry

International audienceIn the current work, we consider the inverse problem in scatterometry which consists in determining the feature shape from an experimental ellipsometric signature. The reformulation of the given nonlinear identification problem was considered as a parametric optimization problem using the Least Square criterion. In this work, a design procedure for global robust optimization is developed using Kriging and global optimization approaches. Robustness is determined by Kriging model to reduce the number of real functional calculations of Least Square criterion. The technical of the global optimization methods is adopted to determine the global robust optimum of a surrogate model

Analysis of Defect in Extreme UV Lithography Mask Using a Modal Method Based on Nodal B-Spline Expansion

This paper details to an electromagnetic modeling of an extreme ultraviolet (EUV) lithography mask. For that purpose, a modal method based on a spline nodal expansion (MMSNE) is presented. The results obtained using first, and second-order splines as basis functions are compared with those obtained using other modal methods, such as modal method by Fourier expansion (MMFE). The agreement between the results obtained using different methods is very good, and a convergence test is also performed. The spline nodal basis function implemented in this paper is the first step toward the realization of a multiresolution scheme that is expected to perform much more efficiently than conventional schemes

Real time scatterometry: a new metrology for in situ microelectronics process control

In situ and real time control of the different process steps in semiconductor device manufacturing becomes a critical challenge, especially for the lithography and plasma etching processes. Real time scatterometry is among the few solutions able to meet the requirement for in line monitoring. In this paper we demonstrate that real time scatterometry can be used as a real time monitoring technique during the resist trimming process. For validation purposes the real time scatterometry measurements are compared with 3D Atomic Force Microscopy measurements made in the same process conditions. The agreement between both is excellent

Real-time profile shape reconstruction using dynamic scatterometry

International audienceIn-line process control in microelectronic manufacturing requires real-time and non-invasive monitoring techniques. Among the different metrology techniques, the scatterometry, based on the ellipsometric signatures (i.e stokes coefficients vs. wavelengths) of light scattered by a patterned structures, seems to be well adapted to address this kind of problem. For instance, the shape evolution of a grating in real time during etch processing can be monitored. Traditionally, the direct problem of defining the shape and computing the signature is dealt with modal methods. However, the inverse problem can not be solved as easily. Different classes of algorithms have been introduced (evolutionary, simplex), but the method of library searching is more commonly used in industry. The main limit of this method is the acquisition time of data for different wavelengths. Then, a lack of data can leads to the method failure and several database patterns can be matched to the experimental data. In this article, a technique for real time reconstruction of grating shape variation using dynamic scatterometry is presented. The different tools to realize this reconstruction, such as Modal Method by Fourier Expansion, regularization technique and mostly the specific soft and hardware architecture are also developed. Results of a dynamic experiments will illustrated these presentations

OPC model error study through mask and SEM measurement error

International audienceMask and metrology errors such as SEM (Scanning Electron Microscopy) measurement errors are currently not accounted for when calibrating OPC models. Nevertheless, they can lead to erroneous model parameters therefore causing inaccuracies in the model prediction if these errors are of the same order of magnitude than targeted modeling accuracy. In this study, we used a dedicated design of hundreds of features exposed through a Focus Exposure Matrix (FEM). We measured the mask bias from target for these structures and investigated its impact on the model accuracy. For the metrology error, we compared the SEM measurements to AFM measurements for as much as 105 features exposed in various process conditions of dose and defocus. These data have then been used in a OPC model calibration procedure. We show that the impact of the metrology error is not negligible and demonstrate the importance of taking into account these errors in order to improve the reliability of the OPC models

Fabrication of High Q Microdisk Resonators using Thermal Nanoimprint Lithography

International audienceWe demonstrate the fabrication of high Q microdisk resonators on an SOI platform using thermal nanoimprint lithography. The achieved Q factor is 60000 for 2µm radius disks. Arrays of 32 resonators show uniform spectral response

Microscale adhesion patterns for the precise localization of amoeba

In order to get a better understanding of amoeba-substrate interactions in the processes of cellular adhesion and directional movement, we engineered glass surfaces with defined local adhesion characteristics at a micrometric scale. Amoeba (Dictyostelium dicoideum) is capable to adhere to various surfaces independently of the presence of extracellular matrix proteins. This paper describes the strategy used to create selective adhesion motifs using an appropriate surface chemistry and shows the first results of locally confined amoeba adhesion. The approach is based on the natural ability of Dictyostelium to adhere to various types of surfaces (hydrophilic and hydrophobic) and on its inability to spread on inert surfaces, such as the block copolymer of polyethylene glycol and polypropylene oxide, named Pluronic. We screened diverse alkylsilanes, such as methoxy, chloro and fluoro silanes for their capacity to anchor Pluronic efficiently on a glass surface. Our results demonstrate that hexylmethyldichlorosilane (HMDCS) was the most appropriate silane for the deposition of Pluronic. A complex dependence between the physicochemistry of the silanes and the polyethylene glycol block copolymer deposition was observed. Using this method, we succeed in scaling down the micro-fabrication of pluronic-based adhesion motifs to the amoebaComment: Microelectronic Engineering (2008) in pres