Method for adjusting a device for measuring interfaces of an element

Abstract

The invention relates to a method (100) for adjusting an interferometry system comprising a measurement head that can be moved in space and is configured to emit an optical measurement beam capable of illuminating an element to be characterised, in particular an optical element, the method comprising the following steps: • a) moving (102) the measurement head to a given position, • b) measuring (104) a plurality of return signals relating to a beam reflected by the element to be characterised when it is illuminated by the optical beam, • c) selecting (106) a plurality of peaks among the return signals, • d) determining (108) a quality factor associated with the given position.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for adjusting a device for measuring the interfaces of an element

[0003] Technical field.

[0004] The present invention relates to a method for adjusting a device for measuring the interfaces of an element to be characterized. It also relates to a device implementing such a method.

[0005] Prior art

[0006] During the manufacture of optical elements, such as lenses or objectives with multiple lenses, it may be necessary to control or measure the thicknesses or positions of component elements, or the spaces between component elements, along a measurement axis such as the optical axis of the optical element.

[0007] One well-known method for this is the use of low-coherence interferometry techniques. A measurement optical beam from a broad-spectrum optical source is propagated through the surfaces of the optical element. The reflections of the beam from these surfaces are collected and analyzed by interfering with each other and / or with a reference beam to determine the differences in optical path lengths between interfering beams, and from this, the positions and / or distances between corresponding surfaces or interfaces can be deduced. This allows, for example, the determination of lens thicknesses, distances between lenses, and / or lens positions within an optical assembly. Similarly, these techniques can be used to measure the thicknesses of layers or structures of complex objects.

[0008] Such measurement techniques generally operate using retroreflection. This requires that the optical beam be incident on all surfaces to be measured at a normal or perpendicular angle, so as to generate a reflected wave that can be detected by the measurement system. For measuring an optical assembly, this condition generally implies superimposing or aligning the measurement beam with the optical axis of the assembly, and in particular with the lenses that compose it. Therefore, an effective optical beam alignment procedure is necessary. In practice, it is essential to be able to position the measurement beam relative to the optical axis of an assembly with an accuracy, for example, on the order of a micron for objects several millimeters in size. A method for achieving this level of performance is therefore required.Similarly, when creating small structures on the substrate surface, it may be necessary to precisely search for one or more positions of best optical return, for all the layers of the structure whose thicknesses we want to know.

[0009] The aim of the present invention is to resolve at least one of the aforementioned drawbacks.

[0010] Description of the invention

[0011] At least one of these goals is achieved with a method for adjusting an interferometry system comprising a measuring head movable in space and configured to emit an optical measurement beam suitable for illuminating an element to be characterized, in particular an optical element, the method comprising the following steps:

[0012] a) move the measuring head to a given position,

[0013] b) measure a plurality of return signals relating to the beams reflected by the element to be characterized when it is illuminated by the optical beam, c) select a plurality of peaks from among the return signals,

[0014] d) determine a quality factor associated with the given position, characterized in that the quality factor is a function of the product of powers of the peak amplitudes.

[0015] The method allows a quality factor to be associated with the positions of the measuring head. The determined quality factor depends on the power product of the peak amplitudes and is therefore robust to amplitude disparities between peaks when the measuring head is placed in the optimal measurement position. Furthermore, the quality factor is simple to calculate and does not require prior knowledge of the interface encountered by the element to be characterized, such as its geometry, refractive index, etc. Indeed, the quality factor is determined solely from the peak amplitudes of the return signals. The quality factor determined by this method can be used within an automated search algorithm or to guide a human operator in positioning the measuring head in the optimal measurement position simply and efficiently.In the context of the present invention, an "element to be characterized" may refer to any type of object having optical properties, intended for example to be inserted into an optical beam, to shape an optical beam, and / or to produce an image. It may refer, for example:

[0016] a unique optical component such as a lens or a plate or a substrate exhibiting, for example, surface patterns,

[0017] an assembly of lenses and / or other optical components, such as an imaging lens, a camera lens, or a device for shaping an optical beam,

[0018] an optical waveguide, an optical fiber, etc.

[0019] An element to be characterized may, in particular, consist of, or include, refractive or diffractive elements such as lenses. It may then include an optical axis corresponding to the propagation axis of a beam passing through it. This optical axis may also be, particularly for optical elements with refractive lenses, the axis or the only axis perpendicular to all the surfaces or interfaces of the element to be characterized.

[0020] For example, the element to be characterized may include a stack of optical lenses, layers, or integrated structures, or integrated circuits or assemblies of integrated circuits. For example, the element to be characterized may include surface structures on a wafer or structures integrated into a plate—that is, a stack of layers or local or extended structures—whose thicknesses we seek to determine at specific locations within the produced elements. This could involve measuring passage diameters in microfluidic circuits, or the wall thicknesses around these passage channels, for example. The element to be characterized may also, for example, correspond to integrated circuits fabricated on semiconductors, or to a structure assembling several integrated circuits.

[0021] In one embodiment, the peaks can be selected based on a predetermined measurement model. In particular, the method may include a step to match the feedback signals to signals in the measurement model.

[0022] For example, the number of selected peaks may correspond to the number of interfaces of the element to be characterized. Advantageously, the plurality of measured return signals may contain a number P of peaks. The method may include, in step c), the selection of a number n of peaks corresponding, for example, to the number of peaks expected in the predetermined measurement model.

[0023] According to an advantageous embodiment, the quality factor Q1 can be calculated using the following formula:

[0024]

[0025] with n being the number of peaks selected in step c) and A tbeing the amplitude of the peak having index i in the selection. In this case, each of the powers of the amplitudes is 1.

[0026] According to another advantageous embodiment, the quality factor Q2 can be calculated using the following formula:

[0027]

[0028] with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i. In this case, each of the powers of the amplitudes is 1.

[0029] According to yet another advantageous embodiment, the quality factor Q3 can be calculated using the following formula:

[0030]

[0031] with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i, a t being a weighting factor having the index i, and a being in particular equal to the sum of the a tfor all n indices i, or more generally being a constant number, such as an integer or a real number.

[0032] In particular, the weighting factor can be different from 1. Advantageously, the weighting factor can be between 0.8 and 1.2. Thus, it is possible to modulate the sensitivity to the amplitudes of the measured return signals, increasing this sensitivity when the weighting factor increases.

[0033] In one embodiment, the method may include determining the quality factor for a plurality of tested positions. The method may include moving the measuring head to maximize the quality factor. The measuring head may be moved automatically or manually by an operator. In another example, an ideal measuring position may be determined as the tested position associated with the highest quality factor.

[0034] Advantageously, the measurement model can include a predetermined number of useful peaks. The method can include, in step c), when for at least one useful peak of the model, none of the return signals exist that correspond to that useful peak(s) of the model, adding to the peak selection a chosen amplitude value corresponding to the missing peak(s). In other words, if a peak with index j is absent from the expected useful peaks, a chosen value is assigned to the missing amplitude A. For example, this value can be a fixed amplitude generated so as to be significantly lower than an expected amplitude. Thus, the quality factor is degraded to represent the absence of one or more peaks, but the sensitivity to the still visible optical returns is maintained.Similarly, if two or more peaks are missing, fixed amplitudes replace the lost peaks, so that the product of these fixed amplitudes is significantly lower than the product of the expected amplitudes when the measurement head is placed in the best measurement position, and all the expected peaks of the model are detected.

[0035] The chosen amplitude value can be different from zero and less than a predetermined threshold.

[0036] Optionally, the quality factor can be determined from a function applied to one of the Qi formulas, with i ranging from 1 to 3, such that the quality factor is obtained by the formula Ç'i = F(Çi), where F is said function. In particular, Qi, with i equal to 1, 2, or 3, can be considered an intermediate calculation quality factor formula, meaning that Qi is obtained according to one of the previously defined formulas. Such a function F could be, for example, a logarithmic function, y = ln(x). It could also be the inverse function I, defined by I(x) = 1 / x. In this last example, the directions of variation of the quality factor would be reversed; that is, the resulting quality factor would decrease when one of the amplitudes increases, due to the decreasing nature of the inverse function.

[0037] The measuring head can be specifically configured to move in an XY plane relative to the element being measured. The measuring head can also rotate in space relative to the element being measured. The element to be characterized can be mounted on a support, for example, that is movable in rotation and / or translation along the Z-axis perpendicular to the XY plane. The method may include a positioning step for the element being characterized instead of positioning the measuring head.

[0038] According to another aspect, the invention relates to a device for measuring interfaces of an element to be characterized, the device comprising: an imaging channel configured to produce a beam of light, and comprising imaging means configured to acquire images of an element to be characterized illuminated by said beam of light in a field of view of the imaging means,

[0039] a measuring head comprising a measuring channel configured to produce a measuring beam at a determined position relative to said field of view and comprising an optical distance sensor configured to produce distance and / or thickness measurements,

[0040] means for moving the measuring head configured to move the measuring head, and

[0041] a processing module configured to handle distance and / or thickness measurements, and images,

[0042] the processing module being configured to implement the aforementioned process.

[0043] The means of moving the measuring head can be configured to move the measuring beam along a predefined trajectory and for each position of the trajectory, a quality factor is determined.

[0044] The measuring head can be positioned at the position associated with the highest quality factor.

[0045] The element to be characterized may include at least one refractive or diffractive element.

[0046] The means for moving the measuring head can be replaced by means for moving the element to be characterized.

[0047] The means for moving the measuring head and / or the element to be characterized can be configured to move the measuring beam relative to the element to be characterized in space in translation along the XYZ direction and / or in rotation. Description of figures and embodiments Other advantages and features of the invention will become apparent upon reading the detailed description of non-limiting embodiments and the following accompanying drawings:

[0048] [Fig. 1] illustrates a schematic representation of a non-limiting example of an embodiment of a measuring device implemented in the present invention.

[0049] [Fig. 2] illustrates a schematic representation of an example of an optical sensor that can be used in the measuring device of Figure 1;

[0050] [Fig. 3] represents an example of measurement of an optical element obtained with the device in Figure 1;

[0051] [Fig. 4] is an illustration of an example of a method for adjusting the measuring device of figure 1 according to an example embodiment of the invention.

[0052] These embodiments are not exhaustive; in particular, variants of the invention may be considered that comprise only a selection of features described or illustrated hereafter, isolated from the other described or illustrated features (even if this selection is isolated within a sentence including these other features), provided that this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, and / or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0053] In particular, all the variants and embodiments described can be combined with each other if there are no technical obstacles to this combination.

[0054] In the figures, elements common to several figures retain the same reference. Figure 1 is a schematic representation of a non-limiting example of a measuring device that can be implemented within the framework of the present invention.

[0055] Device 1 is arranged to perform position measurements of interfaces, or thicknesses, along an optical axis, on an object 5 of optical element type, such as an optical assembly with a plurality of lenses.

[0056] The measurement device 1 comprises an imaging channel VI and a measurement channel VM. In the measurement channel VM, a measurement beam 11 from a distance optical sensor 2 is brought, for example by a single-mode optical fiber 21, to a collimator 20. The collimator 20 forms a substantially collimated beam which is directed towards the object to be characterized 5 by a beam splitter 7, preferably dichroic, or a beam splitter cube. The measurement beam 11 is focused onto the object by a distal objective 3.

[0057] The collimator 20 and the distal objective 3 constitute an imaging system which images the core of the fiber 21 from which the measurement beam 11 originates in or near the object 5.

[0058] When the measurement beam 11 is incident on a surface or interface of the object 5 to be characterized in a direction substantially perpendicular to this surface or interface, within tolerance limits depending in particular on the angular opening at the level of the distal objective 3, the reflections which occur on this surface or interface are recoupled in the optical fiber 21 and processed in the optical sensor 2.

[0059] The optical distance sensor 2 may include a low-coherence interferometer.

[0060] Figure 2 illustrates an example of a low-coherence time-domain interferometer usable within the framework of the present invention.

[0061] The low-coherence interferometer 2 can operate, for example, in the infrared. To measure optical assemblies with antireflective coatings, it can be advantageous to choose a different operating wavelength for the interferometer than the wavelengths for which the antireflective coatings are optimized, as these may exhibit high reflectivity. Thus, an interferometer operating in the infrared is well-suited for measuring optical assemblies intended for use in visible wavelengths. Furthermore, in the configuration illustrated in Figure 1, the interferometer 2 is designed to operate through imaging equipment, and in particular the distal objective 3, which are optimized for visible wavelengths, standard in microscopy.

[0062] Interferometer 2, as illustrated in Figure 2, comprises a double Michelson interferometer based on single-mode optical fibers. It is illuminated by a fiber optic light source 42. The light source 42 can be a superluminescent diode (SLD) with a central wavelength in the range of 1300 nm to 1350 nm. The choice of this wavelength is based, in particular, on component availability criteria.

[0063] The light from the source 42 is directed through a coupler 40 and the fiber 21 towards the collimator 20, to form the measurement beam 11. Part of the beam is reflected in the fiber 21 at the collimator 20, for example at the silica-air or glass-air interface forming the end of the optical fiber, to form the reference wave.

[0064] The retroreflections from object 5 are coupled in fiber 21 and directed with the reference wave towards a decoding interferometer built around a fiber coupler 41. This decoding interferometer has an optical correlator function whose two arms are, respectively, a fixed reference 44 and a time delay line 45. The signals reflected at the reference 44 and the time delay line 45 are combined, via the coupler 41, on a detector 43. The function of the time delay line 45 is to introduce an optical delay between the incident and reflected waves, which varies over time in a known manner, obtained, for example, by moving a mirror.

[0065] The length of the arms 44 and 45 of the decoding interferometer is adjusted so as to allow the reproduction with the delay line 45 of the differences in optical paths between the reference wave reflected at the collimator 20 and the retroreflections from the object 5, in which case an interference peak is obtained at the detector 43 whose shape and width depend on the spectral characteristics of the source 42.

[0066] Thus, the measurement range is determined by the optical length difference between the arms 44 and 45 of the decoding interferometer 2, and by the maximum stroke of the delay line 45. In addition, as the reference wave is generated at the collimator 20 outside the imaging system, spurious reflections in the measurement channel VM do not contribute significantly to the interference.

[0067] The imaging channel VI of the device 1 according to the embodiment shown in Figure 1 comprises a camera 6, equipped with a CCD matrix sensor 7, and optical imaging means capable of forming an image of the object 5, or at least of its entrance face, on the sensor 7 of the camera 6, according to a field of view on the object 5, the field of view being substantially proportional to the magnification of the optical imaging means and to the size of the sensor 7. These optical imaging means comprise a distal lens 3 disposed on the side of the object 5 and an optical relay 13.

[0068] The imaging channel VI of device 1 also includes a light source 8 whose emission spectrum includes visible and / or near-infrared wavelengths (around 1 pm). This light source 8 emits a beam of light 9 that illuminates the object 5 in such a way as to allow imaging by reflection. For clarity, the beam of light 9 is not shown in Figure 1 after the blade 10, which directs the light from the light source 8 towards the object 5 and the reflected light towards the camera 6.

[0069] The VM interferometric measurement channel comprising the measurement beam 11 is arranged so as to pass at least in part through the optical imaging means and in particular the distal objective 3. The measurement beam 11 is inserted into the optical imaging means by coupling means 7 such that it is incident on the object 5 according to a measurement area included in the field of view of the imaging channel.

[0070] The setup in Figure 1 thus allows an interferometric measurement beam 11 to be inserted into the field of view of an imaging system, consisting of the camera 6, the distal objective 3, and the relay 13 in the example shown. Thanks to this configuration, the position of the measurement beam 11 can be known or indexed, or at least fixed, relative to the images produced by the imaging system.

[0071] The collimator 20 can also optionally include displacement means 15 which allow the position of the measurement beam 11, and therefore the position of the measurement point, to be moved in a known manner on the object 5 relative to the field of view covered by the imaging means.

[0072] The device 1 further comprises a sample holder 30 for receiving the objects to be characterized 5, as well as movement means 14, such as translation and / or rotation tables, for moving the holder 30 in a plane perpendicular to the optical axis of the imaging means. The sample holder 30 includes a plurality of receptacles 31 for receiving a plurality of objects 5 to be characterized, in particular for inspecting objects 5 in the form of optical elements 5 such as volumetric camera lenses, or structures produced on the surface of a wafer corresponding to integrated structures produced in parallel.

[0073] According to one example, the elements to be measured 5 can be surface structures of a wafer or integrated into a plate, i.e. a stacking of layers or local or extended structures, whose thicknesses we seek to determine, in particular places of the produced elements.

[0074] In another example, these objects 5 could be lenses assembled in a barrel, and the receptacles could be openings with a diameter corresponding to that of the barrels, with a shoulder at the base on which the barrel rests. These objects could also correspond to the integrated optical production of one or more lenses on a wafer and / or be measured directly at the level of a support wafer.

[0075] Furthermore, objects 5 can be objects or structures produced on the surface or within a substrate (wafer, plate), or objects or structures exhibiting layers or specific patterns, whose thickness must be determined along a measurement axis at specific locations within the produced elements. This could involve measuring passage diameters in microfluidic circuits, or the wall thickness around these passage channels, for example. In the case of lenses to be characterized, these objects can also correspond to the integrated optical production of one or more lenses on a wafer and / or be measured directly on a substrate wafer.

[0076] Device 1 according to the invention further comprises a processing module 50, or computing module, configured to process distance and / or thickness measurements, and images. This computing module comprises at least one computer, a central processing unit or computing unit, a microprocessor (preferably dedicated), and / or suitable software. Device 1 according to the embodiment shown in Figure 1 can be used to implement the steps of the method according to the invention, which will be described below.

[0077] Figure 3 illustrates an example of an interferometric measurement obtained with a low-coherence interferometer 2 of Figure 2, for a camera lens-type element 5 formed by a stack of four microlenses along the same optical axis. These microlenses have respective thicknesses d1, d2, d3, and d4 and are separated by spacings 11, e2, and e3. The expected microlens surface position values, or the distances between interfaces, can be known by design or deduced from preliminary measurements. The continuous curve illustrates a measurement signal 51 with peaks 52 corresponding to interferogram envelopes, and representative of reflections of the measurement beam on lens interfaces of element 5. These peaks may correspond to real interfaces, or be due to multiple reflections within the system (virtual interfaces).To identify the actual interfaces, particularly for complex samples, prior knowledge about element 5, such as the expected surface position values, can be used. In the example in Figure 3, the respective positions of the expected microlens surfaces, as identified on the measurement signal 51, are indicated by crosses, corresponding to the peaks 52. Identifying the expected interfaces on the measurement signal and comparing the measured position and / or distance values ​​with expected values ​​allows validation of the measurement and the position of the measurement beam relative to the optical axis of the reference objective. Indeed, if the measurement beam is incorrectly positioned relative to the optical axis, there are generally no peaks detected on the measurement signal 51, or only a portion of them, and with potentially erroneous position or distance values.Furthermore, particularly for a measurement element 5, the absence of certain peaks or position or distance values ​​outside a tolerance range relative to the expected values ​​indicates a faulty optical element, with, for example, poorly positioned lenses.

[0078] Indeed, particularly when measuring the characteristics of a lens, or several lenses forming an optical objective, the return signal is at its strongest when the measurement beam 11 is located near all the vertices of the lenses. It is therefore essential to ensure the correct positioning of the measurement beam 11 relative to the object being measured 5.

[0079] The method 100 shown in Figure 4 aims to place the measuring beam in the best measuring position. In the following, the measuring head refers to the means for moving the measuring beam 11 in the plane 14 and / or the means for moving the measuring beam 11 by translation in the plane of the sample holder or by rotation about said plane, or any other means capable of modifying the incidence and / or the position of the measuring beam 11.

[0080] Process 100 includes the following steps:

[0081] - a step 102 of moving the measuring head to a position to be tested,

[0082] - a step 104 of measurement of the measurement signal 51,

[0083] - a step 106 of selecting one or more useful peaks, for example according to the model of the expected interfaces on the measurement signal. In particular, the number of peaks selected corresponds to the number of interfaces of the element to be characterized.

[0084] Next, process 100 includes a step 108 of determining a quality factor IQ, Q2, Q3 according to one of the following formulas.

[0085] "

[0086]

[0087] with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i. In this case, each of the powers of the amplitudes is 1.

[0088] n

[0089] Q2 = ]~[

[0090] i = l

[0091] with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i. In this case, each of the powers of the amplitudes is 1.

[0092]

[0093] with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i and a t being a weighting factor having index i, a being preferably equal to the sum of the at for all n indices i, or more generally being a constant number, such as an integer or a real number.

[0094] Note that an equivalent formulation of Q3 is:

[0095]

[0096] In particular, the ccj weighting factor can be different from 1 and range from 0.8 to 1.2. Thus, it is possible to modulate the sensitivity to the amplitudes of the measured return signals, increasing this sensitivity when the weighting factor has t increase.

[0097] Furthermore, if a peak with index J is absent among the expected useful peaks, the process may include a step of assigning a chosen value to the amplitude

[0098]

[0099] missing. For example, this value could be a fixed amplitude generated to be significantly lower than an expected amplitude. Thus, the quality factor is degraded to represent the absence of one or more peaks, but sensitivity to the still-visible optical returns is maintained. Similarly, if two or more peaks are missing, fixed amplitudes replace the lost peaks, so that the product of these fixed amplitudes is significantly lower than the product of the expected amplitudes when the measurement head is placed in the best measurement position and all the expected peaks of the model are detected.

[0100] The movement of the measuring head can be achieved by actuation of the movement means in the plane 14 and / or the movement means 15 of the measuring beam 11. The positions to be tested can be chosen according to a predetermined trajectory.

[0101] Steps 104 to 108 are repeated for a plurality of test positions. Procedure 100 includes a step 110 for determining the measurement position as the one to be tested with the highest quality factor. Procedure 100 can be used to position the measuring head at the best measurement position automatically or with operator assistance.

[0102] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

Claims

DEMANDS 1. Method (100) for adjusting an interferometry system comprising a measuring head movable in space relative to an element to be characterized (5) and configured to emit an optical measurement beam (11) suitable for illuminating the element to be characterized (5), in particular an optical element, the method comprising the following steps: a) move (102) the measuring head to a given position, b) measure (104) a plurality of return signals (51) relating to the beams reflected by the element to be characterized when it is illuminated by the optical beam (11), c) select (106) a plurality of peaks (52) from among the return signals, d) determine (108) a quality factor associated with the given position, characterized in that the quality factor is a function of the product of powers of the peak amplitudes.

2. Method (100) according to the preceding claim, wherein the peaks (52) are selected according to a predetermined measurement pattern.

3. Method (100) according to any one of the preceding claims, wherein the number of peaks selected corresponds to the number of interfaces of the element to be characterized (5).

4. A method (100) according to any one of the preceding claims, wherein the quality factor is calculated according to the following formula: with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i.

5. A method (100) according to any one of claims 1 to 3, wherein the quality factor is calculated according to the following formula: n Q2 = ]~[ i = l with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i.

6. A method (100) according to any one of claims 1 to 3, wherein the quality factor is calculated according to the following formula: <?3 = " " y with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i, a t being a weighting factor having the index i, and a being a constant integer or real number.

7. Method (100) according to the preceding claim, wherein the weighting factor is different from 1 and is between 0.8 and 1.

2.

8. Method (100) according to any one of claims 4 to 7, wherein the quality factor is determined from a function applied to one of the formulas Qi, with i ranging from 1 to 3, so that the quality factor is obtained by the formula Q'i = F(Qi), where F is said function.

9. Method (100) according to any one of the preceding claims, comprising determining the quality factor for a plurality of tested positions and moving the measuring head so as to maximize the quality factor.

10. Method (100) according to any one of the preceding claims taken in combination with claim 2, wherein the measurement model comprises a predetermined number of useful peaks, the method comprising, in step c), when for at least one useful peak of the model, there is none of the return signals which corresponds to that or those useful peak(s) of the model, adding to the selection of peaks a chosen amplitude value corresponding to the missing peak(s).

11. Method (100) according to the preceding claim, wherein the chosen amplitude value is different from zero and is less than a predetermined threshold.

12. Device (1) for measuring interfaces of an element to be characterized, the device comprising: an imaging channel (VI) configured to produce a beam of illumination, and comprising imaging means configured to acquire images of an element to be characterized illuminated by said beam of illumination within a field of view of the imaging means, a measuring head comprising a measuring channel (VM) configured to produce a measuring beam (11) at a predetermined position relative to said field of view and comprising an optical distance sensor (2) configured to produce distance and / or thickness measurements, means for moving the measuring head configured to move the measuring head, and a processing module configured to handle distance and / or thickness measurements, and images, the processing module being configured to implement the process according to one of the preceding claims.

13. Device (1) according to the preceding claim, wherein the means for moving the measuring head are configured to move the measuring beam (11) along a predefined trajectory and for each position of the trajectory, a quality factor is determined.

14. Device (1) according to the preceding claim, wherein the measuring head is positioned at the position associated with the highest quality factor.

15. Device (1) according to any one of claims 12 to 14, wherein the element to be characterized (5) comprises a stack of optical lenses or of layers or of integrated structures, or of integrated circuits or of assemblies of integrated circuits.

Images