Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/21—Polarisation-affecting properties
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
  • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
  • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/21—Polarisation-affecting properties
  • G01N21/211—Ellipsometry
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y35/00—Methods or apparatus for measurement or analysis of nanostructures

Definitions

• the present invention relates to a device for two-dimensional ellipsometric display of a sample, a method of visualization and a method of ellipsometric measurement with spatial resolution. It is particularly well suited for viewing in ellipsometric contrast or in interference contrast.
• a sample receiving and reflecting light generally changes its polarization.
• r p and r s are the complex reflection coefficients of each of the polarizations on the substrate concerned which implicitly depend on x and y, ⁇ N ( ⁇ , NP) being the normalized flux reflected for an angle of incidence ⁇ , in non-polarized light.
• the object of the invention is therefore a two-dimensional ellipsometric display of an object of very small thickness invisible under an optical microscope under known observation conditions compatible with the use of a commercial optical microscope. Despite this, according to the invention, it is possible both to visualize the object and to measure its thickness and its index under a microscope.
• the object of study is deposited on a particular substrate, the association of the object of study and the substrate forming the observed set that we call - the sample -.
• the substrate is designed in such a way that the object of study, although very thin, suffices by its presence to modify the appearance of the substrate, thus leading to the visualization of the object.
• the substrate consists of a support covered with a stack of layers such that, on the one hand, the thickness e of the last layer satisfies the condition d 2 / of 2 [Ln
• ] 0 and such that, on the other hand, the minimum of the quantity
• the presence of the object is sufficient under these conditions to modify measurably under an optical microscope the parameters ⁇ and ⁇ of the substrate, so that the optical characteristics of the object can be extracted from the measurement of the parameters ⁇ and ⁇ of the sample.
• the substrate is designed in such a way that the sensitivity of the parameters ⁇ and ⁇ of the sample to a small perturbation of its constituent parameters is very large for low angles of incidence, therefore very different from the Brewster angle, while the visualization and measurement methods proposed are moreover designed in such a way that the radial geometry of the microscope is become compatible with the use of these ellipsometric characteristics.
• DIC differential interference microscope
• the contrast of the object is optimized thanks to the adjustment of a compensator included in the DIC device.
• This adjustment consists in extinguishing the interference between the two beams reflected by the non-interesting regions of the sample by adjusting their phase shift at the level of the device where they interfere, i.e. at the level of the analyzer, the quality of this extinction conditioning the quality of the visualization.
• the condition of maximum sensitivity over the thickness e of the last layer of the stack in this observation mode is d 2 / of 2 [Ln
• ] 0.
• the proposed visualization method is therefore generally optimal for all observations under a microscope between crossed polarizer and analyzer, including when a DIC device is included in the microscope.
• the invention therefore relates to a device for two-dimensional ellipsometric display of a sample, comprising an object, placed in an incident medium, observed between an analyzer and a polarizer crossed by reflection in convergent light, in which the ellipsometric parameters of the assembly formed by the object (4) and a substrate (8) on which it is placed, are used.
• a device for two-dimensional ellipsometric display of a sample comprising an object, placed in an incident medium, observed between an analyzer and a polarizer crossed by reflection in convergent light, in which the ellipsometric parameters of the assembly formed by the object (4) and a substrate (8) on which it is placed, are used.
• the substrate comprises a support and a stack of layers and that its ellipsometric properties are known
• the ellipsometric properties of the substrate being such that the variations in the ellipsometric parameters of the sample due to the object are displayed with a contrast greater than the contrast produced in the absence of this substrate.
• the sample is illuminated through a wide aperture objective such as a microscope objective,
• the microscope is a differential interference contrast microscope
• the microscope is a fluorescence microscope
• This embodiment is the most effective for viewing or detecting objects of nanometric dimensions. It is then a question of visualizing without solving. It allows in particular the visualization of all isolated filiform objects, that is to say distant by an amount greater than the lateral resolution of the microscope, whose length is greater than one micron (polymers, microtubules, collagen, bacteria, DNA , AN, carbon nanotubes, nanowires, etc.).
• the thickness e of the layer of the stack in contact with the object is such that the complex reflection coefficients r p and r s of the substrate satisfy the condition d 2 / of 2 [Ln
• ] 0,
• the optical properties of the substrate are such that the minimum value taken by the quantity
• the device comprises a polychromatic light source
• the device comprises a monochromatic light source
• the support is made of silicon, More generally, the support is advantageously an absorbent medium, a metal or a semiconductor whose real part of the optical index is greater than 3.3.
• the stack consists of a single layer, This layer is advantageously mineral, consisting of a mixture SiO / Si0 2 in suitable proportions.
• the layer is a layer of silica
• the thickness of the silica layer is of the order of 1025 ⁇ , the incident medium being air, the layer is a layer of magnesium fluoride,
• the thickness of the layer of MgF 2 is of the order of 1055 ⁇ , the incident medium being air,
• the layer is a layer of polymer
• the layer is a layer of polymer, with an optical index approximately equal to 1.343, the incident medium being air,
• the layer is a mineral layer, with an optical index approximately equal to 1.74, the incident medium being water,
• the layer is a mineral layer, with an optical index approximately equal to 1.945, the incident medium being an oil with an optical index 1.5,
• the layer is discontinuous and formed of silica pads and index 1.343, of the same height defining the thickness of the layer and of cross-sectional dimensions much less than a micrometer, the incident medium being air, - the layer is a mesoporous or nanoporous organic or mineral layer with an index approximately equal to 1.343, the incident medium being air,
• the layer is a mineral airgel with an index approximately equal to 1.343, the incident medium being air, - the device comprises a microscope comprising an aperture diaphragm in the form of a longitudinal slot orientable around the axis of the microscope making it possible to restrict the light cone to a single plane of incidence in a chosen direction, the device comprises a microscope comprising an aperture diaphragm in the form of a ring limiting the lighting cone of the sample around an angle of incidence,
• the object is a thin film and the stack comprises a beveled layer s whose thickness varies monotonously in one direction
• This display method and device are compatible and advantageously superimposable on any scanning optical microscopy technique, on any invisible light optical technique (UV 0 or IR), on any spectroscopy technique, on any non-linear optical technique, any diffusion or diffraction technique, and all their combinations. They are in particular compatible with the fluorescence, micro-Raman, confocal microscopy, two-photon microscopy techniques, and all their combinations.
• the implementation of the present invention with fluorescence microscopy is particularly advantageous. Indeed, the polarization of the light emitted by a fluorescent sample is often different from the polarization of the incident beam.
• the fluorescent marker therefore introduces a depolarization of the light to which the device of the invention is particularly sensitive.
• the extinction factor of the incident light specific to the device of the invention considerably reduces the noise accompanying the fluorescent signal.
• this implementation of the present invention with fluorescence microscopy makes it possible to recognize, among identical fluorescent objects, those of them which depolarize light, which corresponds to a very particular environment for molecules.
• the invention also relates to a measurement method in which:
• the display device is cut parallel to the s direction X into two elements, - the thin film is deposited on one of these elements,
• the two elements are placed between a crossed polarizer and an analyzer under a polarizing microscope lit in polychromatic light, so as to form fringes of colored interference on each of the elements,
• the invention further relates to a device for viewing a sample as specified above, in which the substrate is the bottom of a Petri dish.
• the invention further relates to a device for viewing a sample as specified above, in which the sample is a matrix multisensor, each pad or patch of the matrix possibly constituting the last layer of the stack.
• This multisensor can be a biochip with bacteria, viruses, antigens, antibodies, proteins, DNA, RNA, or chromosomes, the device then constituting a parallel reading device.
• the invention also relates to a method for ellipsometric measurement of a sample with spatial resolution under a polarizing microscope forming an image of the sample in which:
• the sample is illuminated by a linearly polarized light beam through an aperture diaphragm, - the light reflected by the sample is analyzed by a polarizer-analyzer, characterized by the relative orientation ⁇ of its direction of polarization compared to that of the polarizer,
• a modulation of the reflected intensity is ensured by the relative rotation of the polarization of the light beam and of the polarizer-analyzer.
• the aperture diaphragm of the lighting beam is a ring centered on the axis of the beam delimiting a single angle of incidence
• the average flux ⁇ M (x, y) reflected and its modulation amplitude ⁇ m (x, y) are measured simultaneously at each point of the image obtained from the sample
• the orientation of the analyzer relative to the polarizer is fixed at a value different from ⁇ / 2 modulo ⁇
• - the aperture diaphragm of the lighting beam is a slit orientable around the optical axis of the microscope superimposed on a ring delimiting a single angle of incidence
• the intensity of the reflected beam is measured for at least two different non non-redundant orientations of the slit, - these intensity measurements are processed from the relation:
• the aperture diaphragm of the lighting beam is a slit orientable around the optical axis of the microscope superimposed on a ring delimiting a single angle of incidence
• the orientation of the analyzer relative to the polarizer is fixed at a value different from ⁇ / 2 modulo ⁇ ,
• the invention also relates to a method for ellipsometric measurement of a sample with spatial resolution under a polarizing microscope forming an image of the sample, in which:
• the sample is illuminated by a linearly polarized light beam through an aperture diaphragm
• the light reflected by the sample is analyzed by a polarizer-analyzer, characterized by the relative orientation ⁇ of its direction of polarization with respect to that of the polarizer,
• the aperture diaphragm of the lighting beam is a disc centered on the axis of this beam
• the invention also relates to an ellipsometric measuring device under a microscope with lateral spatial resolution. According to this device:
• ⁇ are possibly effective parameters derived from means over all the angles of incidence present:
• the aperture diaphragm is a hole or a ring
• the image of the rear focal plane of the objective is formed in the focal plane of the eyepiece by a Bertrand lens
• the aperture diaphragm is a hole or a ring
• the image of the rear focal plane of the objective is formed in the focal plane of the eyepiece by a Bertrand lens
• the image of the rear focal plane of the objective is formed in the focal plane of the eyepiece by a Bertrand lens
• the camera is a tri-CCD color camera and the intensity measurement at each point is made and used for each of the colors.
• the object studied is placed on a substrate.
• the thickness e of the layer of the stack in contact with the object is such that the complex reflection coefficients r p and r s of the substrate satisfy the condition d 2 / of 2 [Ln
• ] 0.
• the object is placed on a substrate whose optical properties are such that the minimum value taken by the quantity jr p + r s
• FIG. 4 is a diagram of the polarizing microscope used according to the invention.
• FIG. 5 is a schematic representation of the device direct thickness measurement according to the invention
• FIGS. 1 and 2 are a schematic representation of the display device of a multisensor implemented in certain embodiments of the invention. The description of the invention will be made using the notations of FIGS. 1 and 2, where p is the polarization vector of the light carried by a radius of angle of incidence ⁇ on the sample.
• sample 1 denotes the assembly acting on the measurement.
• This sample is separated from objective 2 by an incident medium 3, it comprises, in order starting from the incident medium, a study object 4 (the one that we seek to visualize), a stack 5 of layers whose upper layer 6 is the layer in contact with the sample, and a support 7.
• the stack of layers and the support form the substrate 8.
• FIGS. 4A and 4B are representations of devices usable according to the invention; similar elements are represented there with the same reference numerals.
• a sample 1 assumed to be plane and isotropic is therefore placed under an optical microscope operating in reflection.
• the microscope is provided with an objective 10 and a Kôhler type lighting, comprising at least two lenses 12 and 13 and an aperture diaphragm or pupil 11 conjugated by the lens 13 of the rear focal plane of the objective 10, represented by a dotted line in Figure 4A.
• the polarizer P polarizes the light directed towards the sample by the semi-reflecting lamina 15.
• the direction of the polarizer P serves as a reference.
• the light returned by the object is subjected to an analyzer A.
• FIG. 4B corresponds to the implementation of a differential interference contrast microscope (DIC), it comprises a polarizing element 16 which is either an ollaston biprism or a prism and a Nomarski compensator.
• DIC differential interference contrast microscope
• the angle of incidence of a ray is ⁇ .
• the microscope is equipped with a linear polarizer and an analyzer located on either side of the sample on the light path.
• the lighting is episcopic and monochromatic.
• the analyzer is rotating and makes an angle ⁇ with the polarizer.
• the reference flux is that which would be obtained on the same instrument adjusted in the same way in the absence of a polarizer and an analyzer with a hypothetical perfectly reflecting sample.
• ⁇ N ( ⁇ , ⁇ ) cos 2 ⁇ (r p 2 +
• the second member of the formula (El) is directly interpretable. It is made up of two terms: The first, cos ⁇ (
• This reflectivity can be described as "inconsistent average reflectivity" because it would be obtained by ignoring the interferences between r p and r s , i.e. between the reflected parallel and perpendicular components, and by averaging over all possible azimuths ⁇ , i.e. over all possible orientations of the plane of incidence relative to the direction of the polarizer.
• Equation (El) describes the interference between r p and r s .
• Coherent reflectivity It translates the depolarization of the incident beam by the surface, which transforms the linear incident polarization into an elliptical polarization.
• the contrast of the edge of the film is:
• Our technique combines two extinction factors: i) the crossed or almost crossed polarizer and analyzer, ii) an anti-reflective substrate for this observation mode.
• Equation (E3) highlights the dual nature of our extinction: the crossed polarizer and analyzer extinguish the first term of the second member, our antireflective substrate extinguishes the second. It can therefore be defined as an antireflective substrate for coherent reflectivity.
• ⁇ e is the thickness of the film which can be assumed for the circumstance of optical index identical to that of the upper layer
• dl / de is the derivative of the intensity reflected by the bare substrate with respect to the thickness e of the last layer of the stack.
• e is therefore the thickness of this layer.
• the fact of taking an identical index for the film and for the last dielectric layer is not compulsory, but it simplifies the explanation and shows that our method does not exploit the reflection between the film and the substrate. The film is therefore considered here as a simple fluctuation in thickness of the upper layer.
• r p and r s for a solid covered with a single layer is conventional (ref. AZZAM for example):
• ⁇ y and Ily represent respectively the sum and the product of r ⁇ ) and r ij (s) .
• the sum ⁇ is a periodic function of the optical thickness
• Equation (E3) highlights the advantage of using a fluorescence microscope: in the presence of a fluorescence signal, the depolarized component of this fluorescence is added to the right member of equation (E3) without altering the extinction of the other two terms. The signal to noise ratio is therefore increased. This can also be transposed to a Raman signal.
• the invention also relates to an ellipsometric measurement method which can also operate without the need for a particular substrate being necessary:
• the ellipsometric angles ⁇ and ⁇ are defined by:
• Equation E3 shows that the reflected signal oscillates sinusoidally around the incoherent reflectivity with an amplitude
• the second step requires breaking the radial symmetry of the lighting, which can be done in two ways: either by physically modifying the geometry of the aperture diaphragm, which must become a slit or a cross formed by two perpendicular slits, or an angular sector ⁇ (modulo ⁇ ) of opening strictly less than ⁇ / 4, the apex of which coincides with the optical axis or the association of two or four identical angular sectors regularly arranged around the axis optics of the microscope, capable, like the analyzer, of rotating around the optical axis of the microscope, either by analyzing the intensity distribution present in a conjugate plane of the aperture diaphragm situated on the path of the reflected light, the microscope being in Koehler lighting.
• This solution also makes it possible, in the absence of the Bertrand lens, to carry out the first step of the analysis simultaneously on several regions of a heterogeneous sample, and therefore to determine by a parallel measurement the quantity (sin2 ⁇ cos ⁇ ) ( x, y).
• the Bertrand lens it is however necessary to select a homogeneous region of the sample by the use of a field diaphragm or a confocal geometry. This solution therefore does not allow the complete parallel analysis of the different points of the sample.
• the first solution on the other hand (diaphragm with rupture of radial symmetry), allows the total parallel analysis since one always keeps the image of the sample on the CCD camera.
• this intensity is a periodic function of ⁇ of period ⁇ and also includes terms of period ⁇ / 2.
• the relative orientation of the analyzer and the polarizer is fixed and: - if the slit has a uniform rotational movement around the optical axis at the frequency ⁇ , the intensity reflected by each point of the sample is modulated and this modulation allows different combinations of quantities to be extracted
• the signal I is modulated with a period ⁇ (on ⁇ ) and the measurement of I for different values of ⁇ becomes more precise;
• the measurement of I therefore makes it possible to determine the effective quantities and, in particular, the ellipsometric angles ⁇ eff and ⁇ eff , which can be compared with values calculated to deduce therefrom. properties of the object or sample, as is conventionally practiced with ellipsometric angles with single incidence.
• the sensitivity of the measurement to the physical parameters of the sample becomes excellent again, comparable in fact to that of traditional measurements around the Brewster angle, while the signal used remains little sensitive to the angle of incidence.
• the critical compositions of the substrates are defined by the existence of a solution to the equation
• 0.
• a critical substrate has a layer thickness close to a solution of this equation.
• 0 necessarily corresponds to a minimum of
• N 0 is the index of the ambient medium
• N 3 is the index of the substrate support
• N 2 is the index of the layer and e its thickness.
• the optimal thickness e is a linear function of ⁇ but is not not proportional to ⁇ .
• ⁇ 0.2.
• the layers of indices 1.74 and 1.945 can be produced by numerous methods, such as PECVD deposits.
• the layers of index 1.345 are more difficult to produce. They can be formed of a hydrogel, an airgel, a polymer, or be heterogeneous, for example formed of studs of constant thickness and very small dimensions. It can also be a solution in water, sugar, salt, polymer ...
• a particularly advantageous visualization method of the optical thickness (Ni x ej) of a very thin film can be carried out with the substrate used in the invention in the following manner shown in FIG. 5.
• a layer 21 of variable thickness in the form of a bevel is deposited on a support 20 (FIG. 5A, FIG. 5B).
• This substrate 20 is then cut so as to obtain two identical elements 22, 23 (23 not shown is then identical to 22) (FIG. 5C).
• these two elements are then observed under a microscope lit in white light with a disc-shaped pupil, after having positioned these two elements relative to each other, in their initial relative position, using a mark, notch or wedge 25.
• Each pellet has a surface of a few square microns and often a molecular thickness.
• the multisensor is used in the following way: it is brought into contact with the mixture that we want to analyze.
• Each patch 31, 32 ... fixes the species which it can recognize when it is present in The mixture.
• a fixed species creates an additional thickness, visible at the level of the stud, the position of the studs 31, 32 in the matrix informing us of the nature of the recognized species. This step is the step of reading the multisensor.
• biochips include, for example DNA chips, antibody chips, bacteria chips, virus chips, chromosome chips, protein chips, etc.
• each pad consists of a molecular layer of identical oligonucleotides capable of hybridizing with and only with their complementary strand.
• the analyzed DNA is cut into strands of suitable length, amplified by the PCR technique, which means that each strand is replicated a large number of times, then put in solution in contact with the chip.
• the recognized strands are fixed by the corresponding pads.
• the pellets whose thickness is regular and known are taken as elements of the multilayer building, so that the support + multilayer + patch or spot assembly constitutes an optimized substrate of very high sensitivity. Under these conditions, the presence of additional strands after hybridization is easily detected by the change in intensity or color that it causes in the observation of the pellet by our visualization process.
• the quantity of material present on a pellet can also be quantitatively evaluated by our measurement process.

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