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 is movable in space relative to a wafer to be inspected for the characterisation of at least one structure formed in the wafer and configured to emit an optical measurement beam able to illuminate the wafer, the method comprising repeating the following steps until a stop criterion is met: a) selecting (104) a scanning position from scanning positions of a provided current scanning grid, b) moving the measurement head to the selected scanning position, c) taking measurements (106) on the basis of a measurement signal relating to the beams reflected or transmitted by the wafer when the wafer is illuminated by the optical beam, and determining a quality factor associated with the scanning position on the basis of the measurement signal.

Description

DESCRIPTION TITLE: Method for adjusting a device for measuring the interfaces of an element Technical field.

[0001] The present invention relates to a method for adjusting a device for measuring interfaces of a structure formed in an element to be characterized. It also relates to a device implementing such a method. Prior art

[0002] During the manufacture of semiconductor elements comprising at least one structure formed from said semiconductor elements, it may be necessary to control or measure thicknesses or positions of at least one structure, along a measurement axis.

[0003] 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 element to be characterized. 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, to deduce the positions and / or distances between corresponding surfaces or interfaces. These techniques can be used to measure the thickness of layers or structures of complex objects.

[0004] Such measurement techniques generally operate using retroreflection. This requires that the optical measurement beam be incident on all surfaces to be characterized at a normal or perpendicular angle, so as to generate a reflected wave that can be detected by the measurement system. Therefore, an effective optical measurement beam alignment procedure is necessary. In practice, it must be possible to position the measurement beam relative to the 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.

[0005] The aim of the present invention is to resolve at least one of the aforementioned drawbacks.

[0006] Another objective of the invention is to provide a method for finding an optimal measurement position for the measurement beam. Description of the invention

[0007] At least one of these goals is achieved with a method for adjusting an interferometry system comprising a measuring head movable in space relative to a wafer to be inspected for the characterization of at least one structure formed in said wafer, and configured to emit an optical measurement beam capable of illuminating said wafer, the method comprising repeating the following steps until a stopping criterion is satisfied: a) Select a scan position from among the scan positions of a provided current scan grid, b) move the measuring head to the chosen scanning position, c) perform measurements from a measurement signal relating to the beams reflected or transmitted by the wafer when illuminated by the optical beam, and determine a quality factor associated with the scanning position from the measurement signal.

[0008] The process allows for an exhaustive scan of a grid to find one or more optimal positions. From these measurements, it is possible to determine one or more of the most relevant points for taking, or considering, measurements based on a selection criterion, such as a quality factor. These measurements can be taken from those already performed during the grid scan and / or repeated, in a similar or different manner, in a subsequent phase, at the position(s) of the most relevant point(s).

[0009] In one embodiment, a reference position of the current scanning grid can be recalibrated to a predetermined position. For example, the predetermined position can be close to, or included within, an area where the quality factor is maximized or greater than a threshold. The reference position of the current scanning grid can be a central position of the current scanning grid, that is, located in the middle of the current scanning grid. Thus, the method ensures scanning completeness in an area around the measurement optimum.

[0010] According to a particular embodiment, a first scanning grid with a first spacing between scanning positions and a second scanning grid with a second spacing between scanning positions may be provided. The first spacing may be smaller than the second spacing. In this case, the process may include: i) selecting the current grid as the second grid, and repeating steps a) to c) until the quality factor reaches a first threshold, ii) select the current grid as the first grid and the second grid as a previous grid, re-align a reference position of the current grid to the scan position of the previous grid for which the first threshold is reached, and repeat steps a) to c) with the current grid until the stopping criterion is satisfied.

[0011] This allows for faster scanning of a relatively large area for positioning the measuring head. Furthermore, using multiple grids with varying spacing between positions makes it possible to start from a poorly defined point, or even one not returning a measurement signal, to determine the optimal measurement position while keeping the overall setup time quite short. Therefore, it is not necessary to know in advance a measurement area where the measurement signal is optimal.

[0012] The second spacing can be greater than or equal to twice the first spacing.

[0013] The second scanning grid can be scanned randomly by selecting the scanning position randomly in step a). Alternatively, or in addition, the second scanning grid can be scanned according to a pre-established path pattern or according to the quality factor determined for the previously scanned positions.

[0014] Of course, it is possible to provide more than two scanning grids with different spacings between scanning positions. The process may include scanning the grids consecutively in descending order of their spacings, or by scanning the grid with the widest spacing until the quality factor reaches a threshold, then scanning a grid with a narrower spacing, and so on. For example, a third scanning grid may be provided. This third scanning grid may have a spacing between its scanning positions that is smaller than the second spacing and larger than the first spacing. In this case, the process may include: i) selecting the current grid as the second grid, and repeating steps a) through c) until the quality factor reaches a first threshold. ii) select the current grid as the third grid and the second grid as the previous grid, re-register a reference position of the current grid to the scan position of the previous grid for which the first threshold is reached, and repeat steps a) to c) with the current grid until the quality factor reaches a second threshold, and iii) select the current grid as the first grid and the third grid as the previous grid, re-align a reference position of the current grid to the scan position of the previous grid for which the second threshold is reached, and repeat steps a) to c) with the current grid until the stopping criterion is satisfied.

[0015] In the examples above, the first grid may correspond to a fine-pitch grid and the second grid to a coarse-pitch grid, while the third grid may correspond to a medium-pitch grid.

[0016] Alternatively, if the stopping criterion is not met with the first grid, the procedure may include: returning to step i) by continuing the sweep of the second grid to the position where the first threshold is reached, or returning to step ii) by continuing the sweep of the third grid to the position where the second threshold is reached.

[0017] Thus, large-step and medium-step grids could continue to be swept after the threshold is reached, but with a systematic exploration of points around the area that triggered the threshold higher than the first threshold, or higher than the second threshold.

[0018] For example, the stopping criterion can be met when the determined quality factor exceeds a stopping threshold. In this case, the interferometry system adjustment is stopped when sufficient quality is achieved. This saves adjustment time.

[0019] According to another embodiment, the stopping criterion can be satisfied when the quality factor is determined for each of the scanning positions of the current scanning grid.

[0020] The process may include a step of selecting at least one optimal measurement position carried out after the stopping criterion is satisfied.

[0021] In particular, the step of selecting at least one optimal measurement position may depend on the quality factor and / or measurement noise. An optimal position may be one for which the quality factor is greater than a threshold. Alternatively, or in addition, an optimal position may be one for which the measurement noise is minimized or less than a threshold.

[0022] In one embodiment, the step of selecting at least one optimal measurement position may include interpolating the determined quality factors. Then, at least one optimal measurement position may be chosen at the maximum or minimum point of said interpolation. The optimal position may be chosen as the one whose interpolation yields an optimum. Several optimal positions may be chosen on and / or near this optimal position of the interpolation.

[0023] Each scanning grid can be a matrix of integer coordinate scanning positions contained within a predetermined area, for example of a square or circular shape.

[0024] According to one embodiment, the selection of the scanning position in step a) can be carried out so as to scan the predetermined area, for example according to a spiral scan or in parallel lines or in a zig-zag pattern, etc.

[0025] The process may include the following steps: i) repeat steps a) to c) for a sweep of the predetermined area along a first direction of traversal of the predetermined area until the quality factor reaches an optimal value, ii) repeat steps a) to c) for a scan of the predetermined area in a second direction of traversal of the predetermined area different from the first direction, until the quality factor reaches an optimal value, steps i) and ii) being repeated as long as the value of the quality factor remains increasing, or in the optimum direction.

[0026] For example, each of the first and second directions can be a straight line. The first direction can be perpendicular to the second direction. In particular, in the scanning grid, the scanning positions can be distributed along parallel lines. For example, the first direction can be a horizontal or vertical line, and the second direction can be a vertical or horizontal line, respectively. For example, the direction of travel of the first direction can be changed after each travel of the second direction, and vice versa. This allows the optimal measurement position to be reached more quickly. The optimal value of the quality factor can be a maximum or minimum value, depending on the method used to determine the quality factor.

[0027] The method may include, in step c), a step for storing the measured signal, in particular the positions of the peaks of the measured signal with the determined amplitudes, in association with the swept position. Furthermore, the shape of the envelope of the peaks of the measured signal, the acquired interferogram, and / or the quality factor may also be stored in this step.

[0028] Determining the quality factor in step c) may include the following steps: - select a plurality of peaks from the measurement signal, and - calculate the quality factor as a function of the power product of the amplitudes of the selected peaks.

[0029] In particular, the number of peaks selected may correspond to the number of interfaces of the element to be characterized.

[0030] The quality factor, denoted QI, Q2 or Q3, can be determined according to one of the following formulas. with n being the number of selected peaks and A t being the amplitude of the peak having the index i. with n being the number of selected peaks and A t being the amplitude of the peak having the index i. with n being the number of selected peaks 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 a's, for all n indices i, or more generally being a constant number, such as an integer or a real number. In particular, the weighting factor may be different from 1. Advantageously, the weighting factor may be between 0.8 and 1.2.

[0031] The quality factor obtained from these formulas can correspond to a maximum value when the overall amplitudes are optimal, meaning that the amplitudes of the selected peaks are generally large, which typically improves the measurement quality. Conversely, it is possible to consider the inverse function of the previous formulas, in the sense of the function y(x) = 1 / x, applied to these formulas. This can lead to a minimum quality factor when the overall amplitudes are optimal.

[0032] The elements to be characterized may also, for example, correspond to integrated circuits made on semiconductor, or to a structure making an assembly of several integrated circuits.

[0033] The invention is used for the adjustment of an inspection system of at least one structure formed in a wafer comprising one or more structures, such as TSVs (Through Silicon Vias), trenches, etc.

[0034] The invention is particularly used for the adjustment of a system for inspecting structures located on a wafer, such as, for example, a via, a TSV, or any other structure.

[0035] For example, the invention can be used for tuning an inspection system capable of measuring at least one characteristic of at least one structure provided on the wafer, such as: • the width of the structure, for example of the TSV or the via; • the depth of the structure, for example of the TSV or the via; • the position of the structure, for example the TSV or the via; • the number of structures planned on, or in, the wafer; • etc.

[0036] In particular, the invention can be used for the adjustment of a structural inspection system located on a wafer, the aspect ratio of which, i.e. the depth / width ratio, is greater than or equal to 4, in particular 8, and more particularly 15.

[0037] According to another aspect, a device is proposed for measuring the interfaces of a wafer to be inspected for the characterization of at least one structure formed in said wafer, the device comprising: - an imaging channel configured to produce a beam of illumination, and comprising imaging means configured to acquire images of the wafer illuminated by said beam of illumination in a field of view of the imaging means, -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, -Measures for moving the measuring head configured to move the measuring head relative to the wafer, and -a processing module configured to handle distance and / or thickness measurements, and images, the processing module being configured to implement the process as described above.

[0038] The means for moving the measuring head can be replaced by means for moving the wafer.

[0039] The means of moving the measuring head and / or the wafer 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 the figures and methods of implementation

[0040] Other advantages and features of the invention will become apparent upon reading the detailed description of implementations and embodiments, which are by no means limiting, and the following attached drawings: [Fig. 1] illustrates a schematic representation of a non-limiting example of an embodiment of a measuring device implemented in the present invention. [Fig. 2] illustrates a schematic representation of an example of an optical sensor that can be used in the measuring device in the figure. [Fig. 3] represents an example of a measurement of a wafer obtained with the device in Figure 1; [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. [Fig. 5] is an illustration of several examples of scanning grids.

[0041] 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.

[0042] In particular, all the variants and embodiments described can be combined with each other if there are no technical obstacles to this combination.

[0043] In the figures, elements common to several figures retain the same reference.

[0044] Figure 1 is a schematic representation of a non-limiting example embodiment of a measuring device that can be implemented within the framework of the present invention.

[0045] Device 1 is arranged to perform position measurements of interfaces, or thicknesses, along an optical axis, on a wafer 5.

[0046] 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 wafer 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.

[0047] 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 wafer 5.

[0048] When the measurement beam 11 is incident on a surface or interface of the wafer 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.

[0049] The optical distance sensor 2 may include a low-coherence interferometer.

[0050] Figure 2 illustrates an example of a low-coherence interferometer in the time domain, usable within the framework of the present invention.

[0051] The low-coherence interferometer 2 can operate, for example, in the infrared.

[0052] Furthermore, in the configuration illustrated in Figure 1, the interferometer 2 is intended to operate through the imaging means, and in particular the distal objective 3, which are optimized for visible wavelengths, standard in microscopy.

[0053] 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.

[0054] 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.

[0055] The retro-reflections 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, through 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 way, obtained for example by moving a mirror.

[0056] 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 optical path differences between the reference wave reflected at the collimator 20 and the retroreflections from the wafer 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.

[0057] 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.

[0058] 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, as well as optical imaging means capable of forming an image of the wafer 5, or at least of its entrance face, on the sensor 7 of the camera 6, according to a field of view on the wafer 5, the field of view being substantially proportional to the magnification of the optical imaging means and to the dimension of the sensor 7. These optical imaging means comprise a distal lens 3 disposed on the side of the wafer 5 and an optical relay 13.

[0059] The imaging channel VI of the 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 an illumination beam 9 that illuminates the wafer 5 in such a way as to enable imaging by reflection. For clarity, the illumination beam 9 is not shown in Figure 1 after the blade 10, which directs the light from the light source 8 towards the wafer 5 and the reflected light towards the camera 6.

[0060] 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 wafer 5 according to a measurement area included in the field of view of the imaging channel.

[0061] 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.

[0062] 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 wafer 5 relative to the field of view covered by the imaging means.

[0063] The device 1 further comprises a sample holder 30 for receiving the wafers 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 wafers 5 to be characterized, in particular for the inspection of structures produced on the surface of the wafer, corresponding, for example, to integrated circuits.

[0064] 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.

[0065] Furthermore, device 1 can be used to characterize structures on the surface or within the wafer, or objects or structures exhibiting layers or particular patterns, whose thickness along a measurement axis is to be determined at specific locations on the wafers. This could involve measuring passage diameters in microfluidic circuits, or the wall thickness around these passage channels, for example. These objects could also, for instance, correspond to integrated circuits fabricated on semiconductors, or to a structure assembling several integrated circuits.

[0066] 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.

[0067] Device 1 according to the embodiment shown in Figure 1 can be used to implement the steps of the process according to the invention which will be described below.

[0068] Figure 3 illustrates an example of an interferometric measurement obtained with a low-coherence interferometer 2 of Figure 2, for a multilayer wafer 5. These multilayers have respective thicknesses d1, d2, d3, and d4 and are separated by spacings 11, 12, and 13. The expected surface position values ​​of the multilayers, 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 interfaces of the wafer layers 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 the wafer 5, such as the expected surface position values, can be used. In the example in Figure 3, the respective positions of the expected multilayer 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.

[0069] 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 angle and / or position of the measuring beam.

[0070] The process 100 includes a step 102 for providing a scanning grid comprising a plurality of scanning positions. Examples of scanning grids are shown in Figure 5. The scanning grid 200 of Figure 5a comprises several scanning positions 202 distributed uniformly in a square area in parallel lines. Similarly to the scanning grid 200, the scanning grid 220 of Figure 5b comprises several scanning positions 222 distributed uniformly in a rectangular area in parallel lines. The scanning grid 240 of Figure 5c comprises several scanning positions 242 distributed uniformly in parallel lines and delimited by a circular area.

[0071] A current scan position is then selected in step 104. The current scan position can be chosen randomly. Alternatively, the current scan position can be chosen according to a scan strategy. For example, the 200 scan grid is traversed along parallel lines, first in a Dirl direction and then in a Dir2 direction when moving from one line to the next. Another example of a scan strategy is the 220 scan grid, where the grid is traversed in a spiral, for example, starting from a starting position 223.

[0072] In step 106, a measurement of the measurement signal is then carried out by the interferometry system as in device 1. A quality factor is then determined from the measurement signal.

[0073] The measurement signal can be stored in conjunction with the scan position. Specifically, the positions of the measurement signal peaks with their determined amplitudes can be stored at this stage. Furthermore, the shape of the measurement signal peak envelope, the acquired interferogram, and / or the quality factor can also be stored at this stage.

[0074] Determining the quality factor in step c) may include the following steps: - select a plurality of peaks from the measurement signal, and - calculate the quality factor as a function of the power product of the amplitudes of the selected peaks.

[0075] The process 100 then includes a step 108 to determine whether a stopping condition is satisfied at the current scanning position.

[0076] For example, the stopping condition can be satisfied when a measurement of the measurement signal is performed for each of the scan positions of the scanning grid.

[0077] In one embodiment, the quality factor depends on a measurement noise level. The stopping condition is considered satisfied when the noise level is below a threshold.

[0078] In another embodiment, the quality factor is determined based on the peak amplitudes present in the measurement signal. For example, the quality factor can be a function of the power product of the peak amplitudes. The stopping condition is satisfied when the quality factor exceeds a threshold.

[0079] If the stopping criterion is not met, step 104 is repeated. Otherwise, if the stopping criterion is met, process 100 includes a step 110 to determine the ideal measurement position.

[0080] In particular, selection step 104 depends on the quality factor and / or measurement noise. The optimal position may be the position for which the quality factor is above a threshold. Alternatively, or in addition, the optimal position may be the position for which the measurement noise is minimized or below a threshold.

[0081] According to another embodiment, step 104 may include an interpolation of the determined quality factors. Then, the optimal measurement position may be chosen at the maximum point of said interpolation.

[0082] In one embodiment, the process includes a step of recalibrating the scanning grid to a predetermined position. For example, the predetermined position may be close to, or included within, a zone for which the quality factor is maximized or greater than a threshold. In particular, the center of the scanning grid may be recalibrated to a position close to a measurement optimum.

[0083] Regulating the scan grid near an area where the quality factor is maximized or greater than a threshold can be based on the use of at least two scan grids. For example, a first registration grid and a second registration grid are used. The first registration grid has a first spacing between scan positions, and the second scan grid has a second spacing between scan positions that is larger than the first spacing. In this case, the following steps are performed: i) select the current grid as the second grid, and repeat steps a) to c) until the quality factor reaches a first threshold. ii) select the current grid as the first grid and the second grid as the previous grid, re-align a reference position of the current grid to the scan position of the previous grid for which the first threshold is reached, and repeat steps a) to c) with the current grid until the stopping criterion is satisfied.

[0084] In the examples above, the first grid may correspond to a fine-pitch grid and the second grid to a coarse-pitch grid.

[0085] Alternatively, if the stopping criterion is not reached with the first grid, the process may include returning to step i) by continuing the sweep of the second grid to the position where the first threshold is reached.

[0086] 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. A method (100) for adjusting an interferometry system comprising a measuring head movable in space relative to a wafer to be inspected for the characterization of at least one structure formed in said wafer, and configured to emit a measurement optical beam (11) capable of illuminating said wafer, the method comprising repeating the following steps until a stopping criterion is met: a) select (104) a scan position (202,222,242) from among the scan positions of a current scan grid (200,220,240) provided, b) move the measuring head to the selected scan position, (c) perform measurements (106) from a measurement signal relating to the beams reflected or transmitted by the wafer when illuminated by the optical beam, and determine a quality factor associated with the scan position from the measurement signal.

2. Method (100) according to the preceding claim, wherein a reference position of the current scanning grid (200,220,240) is recalibrated to a predetermined position.

3. A method (100) according to claim 1, wherein a first scanning grid with a first spacing between the scanning positions and a second scanning grid with a second spacing between the scanning positions are provided, the first spacing being smaller than the second spacing, the method comprising i) select the current grid as the second grid, and repeat steps a) to c) until the quality factor reaches a first threshold, ii) select the current grid as the first grid, the second grid as a previous grid, recalibrate a reference position of the current grid to the scan position of the previous grid for which the first threshold is reached, and repeat steps a) to c) with the current grid until the stopping criterion is satisfied.

4. Method (100) according to any one of the preceding claims, wherein the stopping criterion is satisfied when the determined quality factor is greater than a stopping threshold.

5. Method (100) according to any one of claims 1 to 3, wherein the stopping criterion is satisfied when the quality factor is determined for each of the scanning positions (202,222,242) of the current scanning grid (200,220,240).

6. Method (100) according to the preceding claim, comprising a step (110) of selecting at least one optimal measuring position carried out after the stopping criterion is satisfied.

7. Method (100) according to the preceding claim, wherein the step of selecting at least one optimal measurement position depends on the quality factor and / or measurement noise.

8. Method (100) according to the preceding claim, wherein the step (110) of selecting at least one optimal measurement position includes an interpolation of the determined quality factors, at least one optimal measurement position being chosen at the maximum or minimum point of said interpolation.

9. Method (100) according to any one of the preceding claims, wherein each scanning grid (200,220,240) is a matrix of scanning positions (202,222,242) with integer coordinates contained within a predetermined area, for example of square or circular shape.

10. Method (100) according to the preceding claim, wherein the selection of the scanning position (202,222,242) in step a) is carried out so as to scan the predetermined area, for example according to a spiral scan or parallel line scan.

11. Method (100) according to claim 9, comprising the following steps: iii) repeating steps a) to c) for a sweep of the predetermined area along a first direction of traversal of the predetermined area until the quality factor reaches an optimal value, (iv) Repeat steps (a) to (c) for a scan of the predetermined area in a second direction of traversal of the predetermined area different from the first direction, until the quality factor reaches an optimal value, steps i) and ii) being repeated as long as the value of the quality factor remains increasing, or in the optimum direction.

12. Method (100) according to any one of the preceding claims, wherein, in step c), the determined quality factor is stored for each scan position (202,222,242), in particular, in association with a related attribute such as a peak amplitude of the measurement signal, a shape of the measurement signal and / or an interferogram based on the measurement signal.

13. A method (100) according to any one of the preceding claims, wherein step c) comprises the following steps: select a plurality of peaks from the measurement signal, and calculate the quality factor as a function of the power product of the amplitudes of the selected peaks.

14. Device (1) for measuring interfaces of a wafer to be inspected for the characterization of at least one structure formed in said wafer, the device comprising: an imaging channel (VI) configured to produce a beam of illumination, and comprising imaging means configured to acquire images of the wafer 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 relative to the wafer (5), and a processing module configured to handle distance and / or thickness measurements, and images, the processing module being configured to implement the process (100) according to one of the preceding claims.

Images