Method and system for evaluating composite characteristics of structures etched in a substrate

Abstract

The present invention relates to a method (100) for characterizing a structure etched in a substrate such as a wafer, the method (100) comprising, for at least one structure etched in the substrate: - at least one imaging step (102), comprising the following steps: - imaging at least one image of the upper surface of the substrate using an imaging device disposed on the upper side of the substrate (104), and - measuring first data regarding the structure from at least one of the imaged images (106 - 110), - at least one interferometry step (130) carried out using a low coherence interferometer disposed on the upper side for measuring at least one depth data regarding the depth of the structure using a measurement beam positioned on the structure, wherein the method (100) also comprises a first adjustment step (120) for adjusting the measurement beam according to the first data. The present invention further relates to a system for implementing such a method.

Description

Technical Field

[0001] The present invention relates to a method for characterizing structures etched in a substrate, particularly structures with a high aspect ratio, HAR. The present invention also relates to a system for performing such a method.

[0002] The field of the present invention is the field of inspection and characterization of high aspect ratio structures etched in a substrate, such as a wafer, for example, structures etched in a substrate such as silicon through vias, TSVs, or trenches.

Background Art

[0003] In the semiconductor industry, or for example in the MEMS ("Micro-Electro-Mechanical Systems") industry, many processing steps are related to etched structures in a substrate such as silicon, sometimes having a high aspect ratio, HAR. Such HAR structures can be, for example, silicon through vias (TSVs), which are usually blind holes, and are used, for example, for interconnections in advanced packaging technologies, trenches with narrow widths and elongated lengths, and for more complex features. These can be made, for example, by deep reactive ion etching (Deep RIE) or photolithography techniques.

[0004] The aspect ratio of a structure is defined by the ratio between the depth and the lateral dimension, and is also referred to as the "critical dimension" (CD) of the structure. Some HAR structures may have an aspect ratio greater than 5, or greater than 10 or 20, and the lateral (critical) dimension is as narrow as 5 μm or less. Some non-limiting examples include TSVs in the form of cylindrical holes etched in a silicon substrate, with a diameter of 2 - 3 μm and a depth of 40 - 50 μm.

[0005] These structures, particularly HAR structures, need to be measured and their characteristics evaluated, for example, by measuring their depths. The document, International Publication No. 2007 / 042676, describes techniques for measuring the depth of HAR structures during a deep RIE process. However, this technique has several limitations for measuring HAR structures having very small critical dimensions (e.g., 4 μm or less). There are also known techniques for characterizing high-density arrays of HAR structures. These techniques cannot be used for individual characterization of HAR structures.

[0006] An object of the present invention is to overcome at least one of the drawbacks of the known techniques.

[0007] Another object of the present invention is to provide a solution for individually characterizing etched structures, particularly HAR structures.

[0008] Another object of the present invention is to provide a solution for characterizing etched structures, particularly HAR structures, having small critical dimensions.

[0009] Another object of the present invention is to provide a solution for measuring the depth and critical dimensions of etched structures, particularly HAR structures.

[0010] It is also an object of the present invention to provide a solution for more efficiently and / or more rapidly characterizing structures, particularly HAR structures. SUMMARY OF THE INVENTION

[0011] The present invention enables at least one of these objects to be achieved by a method of characterizing an etched structure, particularly a high aspect ratio, HAR, structure, within a substrate such as a wafer, the method comprising, for at least one structure etched within the substrate, - at least one imaging step, comprising the steps of: ■ imaging at least one image of the upper surface of the substrate using an imaging device disposed above the substrate, and - Measuring first data regarding the structure from at least one captured image At least one imaging step, including - At least one interference measurement step carried out using a low coherence interferometer arranged above to measure at least one depth data regarding the depth of the structure using a measurement beam positioned on the structure Including wherein the method also includes a first adjustment step for adjusting the measurement beam according to the at least one first data

[0012] Accordingly, the present invention proposes to adjust a measurement beam used to measure the depth of a structure, for example, adjusting the position and / or diameter of the measurement beam, according to first data previously measured about the structure from at least one image of the structure. The first data represents useful information about the structure as will be described later. Accordingly, as an advantageous feature, the present invention proposes to use the first data, i.e., information about the structure, to adjust the measurement beam used by an interferometer to measure the depth data of the structure. Thereby, the interference measurement step can be carried out more quickly, enabling a more rapid and efficient measurement of the depth of the structure.

[0013] Furthermore, the first data regarding the structure enables the measurement beam to be adapted to a single structure, thereby enabling the individual characterization of structures etched in a substrate, even for structures having small critical dimensions.

[0014] As used herein, "high aspect ratio structure" or "HAR structure" or "HARS" refers to a structure having an aspect ratio of 5, or 10, or even 20 or more.

[0015] For example, the HAR structure may be silicon through vias (TSVs), trenches, and even more complex features etched into a support such as a wafer. Some non-limiting examples include TSVs in the form of cylindrical holes etched into a silicon substrate, with a diameter of 2 - 3 μm and a depth of 40 - 50 μm.

[0016] As used herein, the “upper side” and “upper surface” of the substrate respectively correspond to the side and surface of the substrate on which the (plural) HAR structures are etched.

[0017] According to some embodiments, the imaging process and the interferometric measurement process may be performed by respective optical paths having a common portion. In this case, the method according to the present invention may also include synchronizing the imaging process and the interferometric measurement process by a synchronization unit, whereby the processes are performed continuously or in sequence.

[0018] Such a method enables the characterization of structures etched into a substrate in a system that is faster, less bulky, and less expensive than prior art systems. In fact, the imaging process and the interferometric measurement process can share common optical components and perform both measurements without the need to move the measurement system relative to the substrate between measurements.

[0019] However, above all, synchronization enables the imaging process and the interferometric measurement process to be performed in sequence, so that neither of these processes interferes with the other. In other words, the interferometric measurement process can be performed without disturbances that may be caused by the imaging process. Similarly, the imaging process can be performed without disturbances that may be caused by the interferometric measurement process, especially disturbances that the interferometric measurement beam may cause to the imaging process. Therefore, the imaging process can perform more accurate imaging and, as a result, determine the first data in a more accurate form. Similarly, the interferometric measurement process can perform more accurate interferometric measurements and, as a result, determine the depth data in a more accurate form.

[0020] The synchronization of the imaging and interferometric steps can be performed in a variety of ways, implemented alone or in combination.

[0021] According to some embodiments, the synchronization may be performed by controlling the position of a shutter located between the interferometer and the common part. This shutter can be moved between: a closed position which blocks the passage of the measurement beam, and an open position allowing passage of said measurement beam; When the imaging process is performed, the shutter can be moved to a closed position to block passage of the measurement beam so that the measurement beam does not interfere with the imaging process. After the imaging process is performed, the shutter can be moved to an open position to allow passage of the measurement beam so that interferometric measurements can be performed.

[0022] Alternatively or additionally, synchronization may be performed by controlling the position of a mirror located between the interferometer and the common part. This mirror can be moved between: a closed position, which deflects the measurement beam away from the structure under inspection, and An open position in which the measurement beam is directed towards the structure. When the imaging step is performed, the mirror can be moved to a closed position and the measurement beam is deflected away from the HAR structure or even away from the substrate. After the imaging step is performed, the mirror can be moved to an open position which deflects the measurement beam towards the structure and an interferometric measurement can be performed.

[0023] Alternatively, or in addition to at least one of the above mentioned synchronization options, synchronization may be performed by controlling the position of an optical filter, such as a neutral density filter or a spectral filter, located between the interferometer and the common part. This filter can be moved between: - a closed or strongly attenuated position for filtering the measurement beam, and - Open position, allowing the measurement beam to pass. When the imaging process is executed, the optical filter can move to the closed position, and the measurement beam is filtered or strongly attenuated and does not pass (at least excessively) towards the HAR structure. After the imaging process is executed, the optical filter can move to the open position, and the measurement beam passes through the filter, and as a result, the interferometry process can be executed.

[0024] Alternatively, or in addition to at least one of the aforementioned synchronization options, synchronization may be performed by controlling the attenuation value of the attenuation device located between the interferometer and the common optical path portion to attenuate the measurement beam during the imaging process and not attenuate the measurement beam otherwise.

[0025] Alternatively, or in addition to at least one of the aforementioned synchronization options, synchronization may be performed by switching the interferometer light source on and off. Thus, the light source can be turned off during the imaging process and turned on for the interferometry process.

[0026] Alternatively, or in addition to at least one of the aforementioned synchronization options, synchronization may be performed by triggering the acquisition of (a plurality of) images by the imaging device with respect to the pulses of the pulsed light source of the interferometer, and the image acquisition is performed between the pulses of the light source. In this case, the light source of the interferometer is a pulsed light source having a predetermined frequency for the pulses or a pulsed light source having pulses triggered by a synchronization unit. The imaging device may be triggered between the pulses, or the pulses may be controlled, or it may be triggered by a synchronization unit together with the pulsed light source so that at least one image is captured when the pulsed light source does not emit optical pulses.

[0027] In some embodiments, for at least one structure, the first data regarding the structure may be derived / calculated from a single image captured by the imaging device. Alternatively or additionally, for at least one structure, the first data regarding the structure may be derived from several images captured by the imaging device.

[0028] In some embodiments, for at least one structure, at least one image captured by the imaging device may be related only to said structure, in which case the captured image contains information only about said structure and no information about any other structure.

[0029] Alternatively or additionally, at least one image captured by the imaging device may be related to some, particularly all, of the structures of the substrate, in which case the captured image contains information about each of said structures, and as a result, it is possible to determine first data about each of said structures by processing the captured image. For example, an imaging step of capturing an image of the substrate can be performed before the first interferometric measurement step. The captured image may include the entire upper surface of the substrate. The captured image can then be processed to determine first data for each structure of the substrate.

[0030] In some embodiments, for at least one structure, the first data may include upper CD data regarding the width of said structure, and the first adjustment step includes adjusting the diameter of the measurement beam as a function of said upper CD data.

[0031] Thus, the imaging step provides upper CD data, which is then used during the first adjustment step to adjust the diameter of the measurement beam.

[0032] Thus, the method according to the invention enables a faster and more accurate measurement of the depth of the structures of the substrate, particularly when the upper CD data of said structures is not known and / or when the substrate includes different structures having different upper CDs.

[0033] In these embodiments, the method according to the invention proposes to adjust, for at least one structure or HAR structure, the diameter on the upper surface of the substrate of the measurement beam emitted by the interferometer according to the upper CD of said structure measured in advance during the imaging step. This allows most of the incident measurement beam to enter the structure, in particular the HAR structure, while at the same time only a very small part of it is reflected on the upper surface. Due to the fact that the ratio of the diameter or upper CD to the illumination wavelength, which results in a strong diffraction effect, is quite small (often less than 15), and also often due to the absorption characteristics of the materials involved, such as silicon, or more generally, due to the conditions of light propagation into these structures, there are many losses within these structures, and only a small part of the incident light is reflected from the bottom of the structure and coupled back to the interferometer. Therefore, the sensitivity of the interferometric measurement is optimized by using most of the incident power, in particular to compensate for the many losses in the HAR structure and obtain a more stable interference signal.

[0034] The diameter of the measurement beam on the upper surface may be adjusted, for example, to be from 0.8 times to 2 times the minimum lateral dimension of the structure, which may be, for example, the diameter or interval of the TSV, or the width of the trench. It may also be adjusted to be from 0.3 times or 0.5 times to 5 times the minimum lateral dimension of the structure, and still generate a usable signal.

[0035] The diameter of the measurement beam can be defined, for example, as the part of the beam having 90% or 99% of the incident power. In a Gaussian beam, the diameter of the measurement beam on the upper surface can also be defined, for example, as the 1 / e of the peak intensity corresponding to 86.5% of the power 2 or as the part of the beam having a higher local intensity.

[0036] This diameter may be adjusted so that at least 75%, or 80%, or 90% of the incident power is coupled to the structure.

[0037] As an example, a measurement beam diameter size of 5 μm or 3 μm can be used to measure structures with a diameter of 3 μm, particularly HAR structures, particularly TSVs.

[0038] The optimal portion of the light focused within the structure depends, inter alia, on the loss of light within the structure and thus on the shape of the structure (e.g., its aspect ratio). Deeper and narrower HAR structures, such as TSVs or trenches, and HAR structures with strongly curved bottoms require that most of the incident power be coupled into them and thus require a small beam diameter, while shallow or wide structures require that only a smaller portion of the incident power be coupled into them. This is the reason for selecting a beam size that can fit on the upper surface of the substrate.

[0039] Another advantage of adjusting the size of the measurement beam is that even in an array of structures in close proximity to each other, it can be ensured that the measurement beam is sufficiently restricted to cover only one structure, enabling the structures to be individually characterized.

[0040] In some embodiments, the method according to the invention may include a second adjustment step for adjusting the diameter of the measurement beam according to at least one characteristic of the interference signal measured by the interferometer.

[0041] The second adjustment step may be performed during or after the first adjustment step.

[0042] The second adjustment step enables, in particular, the adjustment of the diameter of the measurement beam during the measurement process and, in the case where the measured interference signal indicates that the diameter of the measurement beam does not match the structure being inspected, enables the adjustment of the measurement beam in the actual state and in real time.

[0043] At least one characteristic of the measured interference signal can include at least one of the following characteristics. - Optionally, the visibility of the interference fringes, or the modulation depth, or the spectral modulation of the measured interference signal, relative to the average value, and / or - The amplitude of the measured interference signal relative to the noise, and / or - The value of the depth data brought about by the interference signal.

[0044] For example, if one of these characteristics does not have an expected value or has a value outside the expected range, this indicates that the diameter of the measurement beam does not match the structure being inspected. As a result, the diameter of the measurement beam can be adjusted.

[0045] Alternatively or additionally, for example, an optimization process can be performed using a gradient-based algorithm to find the diameter of the measurement beam such that at least one characteristic of the measured interference signal is optimized or reaches a local extremum.

[0046] The adjustment of the diameter of the measurement beam on the upper surface can be carried out in various ways that can be implemented alone or in combination.

[0047] In some embodiments, the adjustment of the diameter of the measurement beam on the upper surface may be carried out by changing at least one optical element such as a lens or a beam expander disposed between the interferometer and the upper surface. The change of the optical element may be carried out by any means. For example, the change of the optical element may be carried out by the turret moving or supporting the at least one optical element.

[0048] Alternatively or additionally, the adjustment of the diameter of the measurement beam on the upper surface may be carried out by changing the focal length of at least one optical element such as a lens or a zoom device disposed between the interferometer and the upper surface. The change of the focal length of the optical element can be carried out, for example, by changing the shape or propagation characteristics of a deformable lens or a metasurface, or by changing the magnification of the optical element or the position of the components of the zoom device constituting the optical element.

[0049] Alternatively, or in addition to at least one of the aforementioned options, the adjustment of the diameter of the measurement on the upper surface may be performed by changing the numerical aperture of the measurement beam on the upper surface. The numerical aperture of the measurement beam can be changed by using a beam expander in a collimated beam path or an aperture stop.

[0050] In some embodiments, for at least one structure, the first data may include position data regarding the position of the structure on the upper surface. In this case, the first adjustment step can include adjusting the position of the measurement beam on the upper surface according to the position data.

[0051] Thus, the imaging step provides data information regarding the position of the structure by processing at least one image captured by the imaging device during the imaging step. Then, the position of the structure on the substrate is used for more rapid and accurate positioning of the measurement beam so that the measurement of the depth of the structure on the substrate is performed more rapidly and accurately compared to known techniques.

[0052] In some embodiments, the method according to the present invention may include a third adjustment step for adjusting the position of the measurement beam with respect to the structure according to at least one characteristic of the interference signal measured by an interferometer.

[0053] The third adjustment step may be performed during or after the first adjustment step.

[0054] The third adjustment step enables accurate adjustment of the position of the measurement beam during the measurement step, particularly in an actual state and in real time, so as to optimize the measurement conditions for the depth data of the structure of interest.

[0055] At least one characteristic of the measured interference signal can include at least one of the following characteristics. - Optionally, the visibility of the interference fringes, or the modulation depth, or the spectral modulation of the measured interference signal, with respect to the average value - The amplitude of the measured interference signal with respect to noise, - The value of the depth data brought about by the interference signal.

[0056] For example, if one of these characteristics does not have an expected value or has a value outside the expected range, this indicates that the position of the measurement beam with respect to the structure is not optimal. As a result, the position of the measurement beam can be adjusted.

[0057] Alternatively or additionally, for example, an optimization process can be performed using a gradient-based algorithm to find the position of the measurement beam where at least one characteristic of the measured interference signal is optimized or reaches a local extremum.

[0058] The adjustment of the position of the measurement beam on the upper surface can be carried out in various ways that can be implemented alone or in combination.

[0059] The position of the measurement beam can be adjusted by a positioning unit. The positioning unit may comprise a holder for the substrate and / or a holder for the interferometer.

[0060] The positioning unit can adjust the position of the measurement beam on the upper surface by the following. - Moving the interferometer relative to the substrate, and / or - Moving the substrate relative to the interferometer.

[0061] The present invention also relates to a system for characterizing a structure etched in a substrate such as a wafer, particularly a structure with a high aspect ratio, HAR, the system comprising the following. - An imaging device, comprising the following. ■ An imaging device arranged above the substrate for imaging at least one image of the upper surface of the substrate, and ■ A processing unit for measuring first data regarding the structure etched in the substrate from at least one captured image, and - A low coherence interferometer for measuring at least one depth data regarding the depth of the structure by using a measurement beam disposed on the upper side and positioned structurally. The system is also characterized by comprising an adjustment unit for adjusting the measurement beam according to the first data.

[0062] In some embodiments, for at least one structure, the first data may include upper CD data regarding the width of the structure. In this case, the adjustment unit may comprise means for adjusting the diameter on the upper surface of the measurement beam.

[0063] Alternatively or additionally, the diameter of the measurement beam may be adjusted according to at least one characteristic of the interference signal measured by the interferometer as described above.

[0064] According to some non - limiting examples, the adjustment unit may include the following. - A turret for changing at least one optical element such as a lens or a beam expander disposed on the path of the measurement beam between the interferometer and the upper surface. - An optical element such as a lens with an adjustable focal length or a zoom lens disposed on the path of the measurement beam between the interferometer and the upper surface, and / or - A beam expander with an adjustable numerical aperture disposed on the path of the measurement beam between the interferometer and the upper surface.

[0065] Alternatively or additionally, for at least one structure, the first data may include position data regarding the position of the structure on the upper surface. In this case, the adjustment unit may further comprise a positioning unit for adjusting the position on the upper surface of the measurement beam.

[0066] Alternatively or additionally, the position of the measurement beam may be adjusted according to at least one characteristic of the interference signal measured by the interferometer as described above.

[0067] The positioning unit may include a holder for the substrate and / or a holder for the interferometer.

[0068] The positioning unit can adjust the position on the upper surface of the measurement beam as follows. - Moving the interferometer relative to the substrate and / or - Moving the substrate relative to the interferometer.

[0069] In some embodiments, the optical paths of the imaging device and the interferometer may have a common portion. In this case, the system according to the present invention may also include a synchronization unit so that the imaging device and the interferometer are used continuously or in sequence.

[0070] To synchronize the imaging device and the interferometer, the synchronization unit can include at least one of the following. - A shutter disposed between the interferometer and the common portion, movable between a first position that blocks the passage of the measurement beam and a second position that permits the passage of the measurement beam. - A mirror disposed between the interferometer and the common portion, movable between a first position that deflects the path of the measurement beam away from the structure and a second position that deflects the measurement beam toward the structure. - An optical filter, such as a neutral density filter or a spectral filter, disposed between the interferometer and the common portion, movable between a first position that filters the measurement beam to block or strongly attenuate it and a second position that allows the measurement beam to pass through. - An attenuation device, such as an electro-optic attenuator, disposed between the interferometer and the common optical path portion, whose attenuation value is controllable. - A controller that switches on and off the interferometer light source. - A controller that controls the imaging device and / or the light source to trigger the acquisition of (a plurality of) images by the imaging device with respect to the pulses of the pulsed light source of the interferometer so that image acquisition is performed between the pulses of the pulsed light source of the interferometer.

[0071] In some embodiments, the imaging device can comprise a light source and a camera, optionally combined with a microscope optical device.

[0072] In some embodiments, the interferometer is coupled to optical fibers that transmit the measurement beam and the reflected light. The optical fiber may be a single-mode fiber.

[0073] The interferometer may be, for example, a time-domain interferometer. In that case, it comprises a broadband source (not shown) that emits polychromatic light. It further comprises an optical delay line that enables the change of the optical path difference between the two beams. When the optical path difference between the beams reflected at the top and bottom of the structure, or between each of these beams and a reference beam, is reproduced by the delay line, an interference burst or interference fringes can be observed on the photodetector, and this optical path difference can be measured. The depth of the structure is derived from the optical path difference.

[0074] The interferometer may also be a spectral-domain interferometer. In that case, it comprises a broadband source (not shown) that emits polychromatic light and a spectrometer for spectral analysis of the reflected light. On the spectrometer, the spectrum obtained by combining the light reflected by the top and bottom of the structure shows a known pattern such as modulation, and by analyzing it, the optical path difference between the overlapping beams can be obtained. The depth of the structure is derived from the optical path difference.

[0075] The interferometer may also comprise a swept-source interferometer having a wavelength-tunable laser that emits monochromatic light having an optical frequency that varies temporally over a spectral range. The intensity of the reflected light is measured by a photodetector so as to reconstruct the spectrum, and its analysis also enables the measurement of the optical path difference between the reflected beams and, using this, the depth of the structure.

[0076] The interferometer may be, for example, similar to the interferometer described in the document published under the number WO 2007 / 042676. Other advantages and features will become apparent by considering the detailed description of non-limiting embodiments and the accompanying drawings.

Brief Description of the Drawings

[0077]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0078] It is to be fully understood that the embodiments described below are in no way limiting. In particular, it is possible to envision variations of the present invention that include only the selection of the features described below, separated from the other features described. Such a selection is possible if this selection of features provides a technical advantage or is sufficient to distinguish the present invention with respect to the state of the prior art. Such a selection may include at least one, preferably functional, feature without structural details, or, if a part of the structural details alone provides a technical advantage or is sufficient to distinguish the present invention with respect to the prior art, such a selection may include at least one, preferably functional, feature together with only a part of the structural details.

[0079] In the figures, elements common to each figure retain the same reference numerals.

[0080] FIG. 1 illustrates a non-limiting example of a method according to the present invention.

[0081] The method 100 shown in FIG. 1 can be used to characterize structures etched in a substrate such as a wafer, particularly HAR structures. More specifically, using the method 100 of FIG. 1, the depth of a structure etched in a substrate can be measured.

[0082] The method 100 includes an imaging step 102 of the substrate.

[0083] The imaging step 102 includes a step 104 for capturing at least one image of the upper surface of the substrate, for example, by an imaging device. The imaging device can optionally include a camera associated with a microscope and a light source for imaging the upper surface of the substrate. The captured image can include the entire upper surface or only a part of the upper surface. The captured image can include only one structure etched in the substrate or several, particularly all, structures etched in the substrate.

[0084] Next, the captured image can be processed in a processing step 106 to identify first data regarding at least one structure.

[0085] More specifically, the first data may include position data regarding the position of at least one structure visible in the captured image. In this case, the processing step 106 can include a processing step 108 for processing the image to determine the position data. Such processing can be performed by generally known image processing methods, for example, using segmentation, pattern recognition, or blob analysis algorithms.

[0086] Additionally or alternatively, the first data may include top CD data regarding at least one structure visible on the captured image. In this case, processing step 106 can include a processing step 110 for processing the image captured to determine the top CD data. The processing of the image to determine the top CD data can be performed by generally known image processing methods. For example, once the structure is located and identified, its critical dimensions can be obtained using a pattern analysis algorithm and an imaging system calibrated with magnification or dimensions.

[0087] In some embodiments, only one of processing steps 108 and 110 may be executed. In some embodiments, both processing steps 108 and 110 may be executed. In the latter case, processing steps 108 and 110 may be executed during a single processing step.

[0088] Method 100 can include a first adjustment step 120 for adjusting the measurement beam according to the first data determined in processing step 106.

[0089] Adjustment step 120 may include an adjustment step 122 for adjusting the position on the upper surface of the measurement beam according to the position data determined in step 108 so that the measurement beam is accurately positioned on the structure being characterized.

[0090] Alternatively, if the first data does not include position data, the position data may be pre-known data read from a memory. In fact, in some cases, the position data of a structure etched in a substrate may be provided by the position data being determined during the design or manufacture of the substrate. In these cases, the position data is stored in a memory and can be read during the method according to the invention. In these embodiments, adjustment step 122 can be performed using the pre-known position data read from the memory.

[0091] The position of the measurement beam above can be adjusted by a positioning unit. The positioning unit can comprise the following. - A displacement stage for the interferometer and optionally the imaging device, configured to move at least the interferometer relative to the plane of the upper surface of the substrate, and / or - A displacement stage for the substrate, configured to move the substrate or the chuck holding the substrate relative to the interferometer and optionally the imaging device.

[0092] Repeatedly, since steps 108 and 122 are optional, in some embodiments, the method according to the invention may not include these steps, or may only include adjustment step 122 performed using position data read from memory.

[0093] The first adjustment step 120 may include an adjustment step 124 for adjusting the diameter of the measurement beam on the surface of the substrate according to the upper CD data, in particular according to the upper CD data determined in step 110. The diameter of the measurement beam can be adjusted to ensure that, in order to measure the depth of the structure, in particular for a HAR structure, the measurement beam enters the structure and reaches the bottom of the structure with sufficient power.

[0094] Alternatively, if the first data does not include the upper CD data, the upper CD data may be pre-known data read from memory. In fact, in some cases, the upper CD data of the structure etched in the substrate may be provided by the upper CD data being determined during the design or manufacture of the substrate. In these cases, the upper CD data is stored in memory and can be read during the method according to the invention. In these embodiments, adjustment step 124 can be performed using the pre-known upper CD data read from memory.

[0095] Adjustment of the diameter of the measurement beam on the upper surface may be performed by changing at least one optical element such as a lens or a beam expander disposed between the interferometer and the upper surface. The change of the optical element may be performed by any means. For example, the change of the optical element may be performed by the turret moving or supporting the at least one optical element.

[0096] Alternatively or additionally, adjustment of the diameter of the measurement beam on the upper surface may be performed by changing the focal length of at least one optical element such as a lens or a zoom device disposed between the interferometer and the upper surface. The change of the focal length of the optical element can be performed, for example, by changing the shape or propagation characteristics of a deformable lens or a metasurface, or by changing the magnification of the optical element or the position of the components of the zoom device constituting the optical element.

[0097] Alternatively, or in addition to at least one of the foregoing options, adjustment of the diameter of the measurement on the upper surface may be performed by changing the numerical aperture of the measurement beam on the upper surface. The numerical aperture of the measurement beam can be changed by using a beam expander in a collimated beam path or an aperture stop.

[0098] It should be repeated that since steps 110 and 124 are optional, in some embodiments, the method according to the present invention may not include these steps, or may only include the adjustment step 124 executed using the upper CD data read from the memory.

[0099] After the first adjustment step 120, method 100 includes an interferometric measurement step 130 for at least one structure, during which depth data regarding the depth of the structure is measured by optical interferometry.

[0100] Interferometric measurement is performed by a low-coherence light interferometer disposed above the substrate. Since the optical interference method is a well-known technique, it will not be described in detail here. Briefly, a measurement beam of broadband light is radiated onto the structure. At least a part of the measurement beam is reflected by the structure at the upper part or surface of the substrate and at the bottom of the structure, respectively. The reflected beams are interfered with each other or with a reference beam emitted from the same source to obtain an interference signal, and the analysis thereof yields depth data.

[0101] The measurement step 130 includes at least one interferometric measurement 132 that provides a measurement signal as described above. This measurement signal can then be processed to obtain depth data.

[0102] The method 100 may optionally include a second adjustment step 134 for adjusting the diameter of the measurement beam according to at least one characteristic of the interference signal measured by the interferometer, particularly during the measurement step 130. This second adjustment step 134 enables real-time adjustment of the diameter of the measurement beam according to the measurement signal. For example, the diameter of the measurement beam can be adjusted according to the following. - In some cases, the visibility of the interference fringes, or the modulation depth, or the spectral modulation of the measured interference signal, with respect to the average value, - The amplitude with respect to the noise of the measured interference signal, and / or - The value of the depth data provided by the interference signal.

[0103] For example, if one of these characteristics does not have an expected value or has a value outside the range of the expected value, this indicates that the diameter of the measurement beam does not match the structure being inspected. As a result, as will be described later, the diameter of the measurement beam can be adjusted. This step may be repeatedly iterated using, for example, a gradient-based algorithm to find the diameter of the measurement beam at which at least one characteristic of the measured interference signal is optimized or reaches a local extremum.

[0104] Method 100 may optionally include a third adjustment step 136 for adjusting the position of the measurement beam according to at least one characteristic of the interference signal measured by the interferometer, particularly during the measurement step 130. This third adjustment step 136 enables real-time adjustment of the position of the measurement beam according to the measurement signal. For example, the position of the measurement beam can be adjusted according to the following. - In some cases, the visibility of the interference fringes, or the modulation depth, or the spectral modulation of the measured interference signal, relative to the average value, and / or - The amplitude relative to the noise of the measured interference signal, and / or - The value of the depth data brought about by the interference signal.

[0105] For example, if one of these characteristics does not have an expected value or has a value outside the range of the expected value, this indicates that the position of the measurement beam with respect to the structure is not optimal. As a result, as described later, the position of the measurement beam with respect to the structure can be adjusted. This process may be repeatedly iterated using, for example, a gradient-based algorithm to find the position of the measurement beam where at least one characteristic of the measured interference signal is optimized or reaches a local extremum.

[0106] The second adjustment step 134 and the third adjustment step 136 may be executed simultaneously or in any order in sequence. Alternatively, only one of step 134 and step 136 may be executed, or neither may be executed. After at least one of these steps is executed, at least one another interference measurement step 132 may be executed. In that way, the interference measurement step 132 can be repeated until the interference measurement is successful.

[0107] FIG. 2 is an illustration of another non-limiting example of the method according to the present invention.

[0108] The method 200 shown in FIG. 2 can be used to characterize structures etched in a substrate, such as a wafer, particularly HAR structures. More specifically, using the method 200 of FIG. 2, the depth of a structure etched in a substrate can be measured.

[0109] The method 200 includes the steps of the method 100 described with reference to FIG. 1.

[0110] The method 200 further includes a synchronization step 202, whereby the imaging step 104 and the interferometry step 132 are executed in sequence so as not to interfere with each other. In particular, the synchronization step makes it possible to prevent the measurement beam of the interferometer from reaching the upper surface at least excessively when the image imaging step 104 is executed. This is particularly important when the image imaging step and the interferometry step are executed using respective optical paths having a common portion.

[0111] Such synchronization can be performed in various ways. The synchronization step can be performed as follows. - Controlling the position of a shutter located between the interferometer and the common portion as follows, 〇 A first position that blocks the passage of the measurement beam during the image imaging step 104, 〇 A second position that permits the passage of the measurement beam at least during the interferometry step 132, - Controlling the position of a mirror located between the interferometer and the common portion as follows, 〇 A first position that deflects the path of the measurement beam away from the upper surface during the image imaging step 104, 〇 A second position that deflects the measurement beam towards the upper surface at least during the interferometry step 132, - Controlling the position of an optical density filter or a spectral filter located between the interferometer and the common portion as follows, 〇 A first position that filters or attenuates most of the measurement beam during the image imaging step 104, and 〇 A second position that passes the measurement beam at least during the interferometry step 132, - Controlling the attenuation value of the attenuation device located between the interferometer and the common part as follows, 〇 During the image capturing step 104, the measurement beam does not pass at least excessively towards the common part, and 〇 During at least the interference measurement step 132, the measurement beam passes through. - Switching on and off the interferometer light source so that the measurement beam is not emitted during the image capturing step and is emitted at least during the interference measurement step 132, - Triggering the imaging of the (multiple) images by the imaging device with respect to the pulses of the pulsed light source of the interferometer, or vice versa, or synchronizing both so that image acquisition is performed between the pulses of the pulsed light source.

[0112] Thus, in the method 200 of FIG. 2, the top surface, or at least the image of the structure, is imaged by the imaging device without disturbance by the measurement beam emitted by the interferometer.

[0113] FIG. 3 shows a non-limiting example of a substrate including a structure etched in the substrate.

[0114] FIG. 3 shows a substrate 302 such as a wafer including one or more structures. For ease of understanding, only one structure 304 is depicted in FIG. 3. Of course, the substrate 302 may include two or more structures. The structure 304 may be, for example, a trench etched into the substrate 302 from the top surface 306 of the substrate 302. The substrate 302 also includes a bottom surface 308 opposite the top surface 306.

[0115] The information to be measured on the etched structure 304 includes the depth 310 and optionally the upper CD 312. In the illustrated example, the structure 304 may be, for example, a hole or a TSV, and the upper CD data 312 may represent the diameter at the top surface 306. The structure 304 may also be an elongated trench, and the upper CD 312 may be its minimum lateral dimension or its width at the top surface 306.

[0116] FIG. 4 is an illustration of a non-limiting example of a system according to the present invention.

[0117] The system 400 shown in FIG. 4 can be used to characterize structures etched in a substrate, such as a wafer, particularly HAR structures. More specifically, the system 400 can be used to measure the depth of a structure etched in a substrate, particularly substrate 302.

[0118] The system 400 can be used to perform a method according to the present invention, particularly method 100 of FIG. 1.

[0119] The system 400 includes a low-coherence interferometer 410 disposed on the side of the upper surface 306 of the substrate 302. The low-coherence interferometer 410 is used to characterize the structure of the substrate, particularly to measure at least one data regarding the depth of the structure 304, and more particularly to measure the depth of the structure 304.

[0120] The interferometer 410 may be, for example, a time-domain interferometer. In that case, it includes a broadband source (not shown) that emits polychromatic light. It further includes an optical delay line that enables changing the optical path difference between two beams. When the optical path difference between the beams reflected from the top and bottom of the structure 304, or between each of these beams and a reference beam, is reproduced by the delay line, an interference burst or interference fringes can be observed on the photodetector, and this optical path difference can be measured. The depth of the structure 304 is derived from the optical path difference.

[0121] The interferometer 410 may also be a spectral-domain interferometer. In that case, it includes a broadband source (not shown) that emits polychromatic light and a spectrometer for spectral analysis of the reflected light. On the spectrometer, the spectrum obtained by combining the light reflected from the top and bottom of the structure 304 shows a well-known pattern such as modulation, and by analyzing it, the optical path difference between the overlapping beams can be obtained. The depth of the structure 404 is derived from the optical path difference.

[0122] The interferometer 410 may also comprise a swept source interferometer having a wavelength tunable laser that emits monochromatic light having an optical frequency that varies in time over a spectral range. The intensity of the reflected light is measured by a photodetector so as to reconstruct the spectrum, and its analysis also makes it possible to measure the optical path difference between the reflected beams and thereby the depth of the structure 304.

[0123] The interferometer 410 may be similar to, for example, those described in WO 2007 / 042676.

[0124] Optionally but preferably, the measurement beam emitted by the interferometer 410 and the reflected light received from the substrate 302 may be transmitted to and from the interferometer 410 using a single mode fiber 412 coupled to the interferometer 410.

[0125] To measure narrow structures such as TSVs having a high aspect ratio (HAR) and a diameter less than 5 μm, the measurement light source may emit light in the visible spectral range, for example less than 900 nm, for better propagation into the structure.

[0126] The system 400 further comprises an imaging device for imaging at least one image of the substrate 302, more specifically of the upper surface 306 of the substrate 302, and for processing the at least one imaged image to determine at least one first data about at least one HAR structure of the substrate 302.

[0127] The imaging device is arranged on the same side as the interferometer 410, i.e., on the side of the upper surface 306 of the substrate 302.

[0128] In the non-limiting example shown in FIG. 4, the imaging device comprises a camera 420 and optionally a light source 422. The imaging device may also comprise a tube lens 424 for imaging the upper surface 306 of the substrate 302 with the camera 420.

[0129] The camera 420 is configured to image / acquire at least one image of the upper surface 306 of the substrate 302, which includes at least one structure etched within the substrate 302. To measure first data regarding the at least one structure, particularly the at least one HAR structure, the imaged image is processed by standard image processing techniques executed by the processing module 426. The processing module 426 can include a hardware module such as a processor or a chip, and / or a software module such as a computer program.

[0130] Regarding the at least one structure or the at least one HAR structure, the first data may include the position of the structure on the upper surface 306. In this case, the position of the structure can be transmitted to the control unit to command / control means for adjusting the position of the measurement beam on the upper surface 306 of the substrate 302 in order to accurately position the measurement beam radiated by the interferometer 410 onto the structure.

[0131] Alternatively, regarding the at least one structure, the position of the structure may be pre-known data stored in the memory 428. This data can be read by the control unit to command / control means for adjusting the position of the measurement beam on the upper surface 306.

[0132] Regarding the at least one structure or the at least one HAR structure, the first data may include the top CD of the structure. In this case, the top CD of the structure can be transmitted to the control unit to command / control means for adjusting the diameter of the measurement beam radiated by the interferometer 410.

[0133] Alternatively, regarding the at least one structure, the top CD of the structure may be pre-known data stored in the memory 428. This data can be read by the control unit to command / control means for adjusting the diameter of the measurement beam on the upper surface 306.

[0134] Optionally, system 400 may also include means for adjusting the position of the interferometric beam emitted by interferometer 410 on the upper surface 306 of substrate 302 in order to align the position of the measurement beam with the position of the structure being inspected.

[0135] In the example shown in FIG. 4, the position adjusting means comprises a holder 430, such as a wafer chuck, coupled to displacement means 432, such as a translation and / or rotation stage, for moving and positioning substrate 302 in the X-Y directions and optionally in the Z direction.

[0136] Optionally, system 400 may also include means for adjusting the diameter of the measurement beam in order to adjust the diameter of the interferometric beam emitted by interferometer 410 on the upper surface 306 of substrate 302 with respect to the structure being inspected.

[0137] In the example shown in FIG. 4, the diameter of the measurement beam can be determined by the core of fiber 412 or the mode field diameter of the light emerging from the fiber, and by the magnification provided by the combination of collimator lens 440 and a lens 442, referred to as a front lens, such as a microscope objective lens. Thus, at least one of these lenses 440-442 can be changed to change the magnification and thereby adjust the diameter of the measurement beam on upper surface 306.

[0138] System 400 includes a turret 444 for changing at least one of lenses 440-442 and / or for changing the focal length of one of lenses 440-442 and thereby changing the magnification accordingly.

[0139] System 400 may also include a beam expander (not shown) in a portion where the measurement beam is collimated, such as between collimator lens 440 and front lens 444. The beam expander changes the beam diameter and as a result the numerical aperture, NA, at which the beam is focused. This ultimately determines the diameter of the measurement beam on upper surface 306.

[0140] System 400 also includes a control unit 450.

[0141] The control unit 450 may be configured to control means for adjusting the position of the measurement beam on the upper surface 306 of the substrate according to the position data. As described above, the position data may be - provided by an imaging device, in particular by the processing module 426, or - read from the memory 428 as pre-known data. More specifically, the control unit 450 may be configured to control displacement means 432 for moving the holder 430 so that the substrate 302 moves relative to the measurement beam. In this way, the position of the measurement beam on the upper surface 306 can be adjusted.

[0142] Alternatively or additionally, the control unit 450 may also be configured to control means for adjusting the diameter of the measurement beam on the upper surface 306 of the substrate 302 according to the upper CD data. As described above, the upper CD data may be - provided by an imaging device, in particular by the processing module 426, or - read from the memory 428 if the upper CD data is pre-known data. More specifically, the control unit 450 is configured to control a turret 444 for changing at least one of the lenses 440 - 442 and / or for changing the focal length of one of the lenses 440 - 442 and accordingly changing the magnification. In this way, the diameter of the measurement beam on the upper surface 306 can be adjusted to obtain the desired diameter of the measurement beam on the upper surface 306.

[0143] Alternatively or additionally, the measurement beam diameter and / or the measurement beam position on the upper surface may also be adjusted according to at least one characteristic of the signal measured by the interferometer.

[0144] Such adjustment of the diameter and / or position of the measurement beam may be performed during the interferometric measurement, especially enabling real-time adjustment of the measurement beam in the actual situation if the measured interference signal indicates that the diameter and position of the measurement beam do not match the structure 404 being measured respectively.

[0145] At least one characteristic of the measurement signal that can be used to adjust the diameter and / or position of the measurement beam on the upper surface 406 may be at least one of the following characteristics, or may include at least one of the following characteristics. - In some cases, the visibility of the interference fringes, or the modulation depth, or the spectral modulation of the measured interference signal, with respect to the average value - The amplitude with respect to the noise of the measured interference signal, and / or - The value of the depth data brought about by the interference signal.

[0146] To do this, the interferometer 410 may be configured to measure the value of the said characteristic of the measurement signal and compare the value with an expected value or a previous value in an iterative process, or may include a module 452 configured in such a way (or may be coupled to such a module). The result of the comparison can be transmitted to the control unit 450 to adjust the beam diameter and / or beam position on the upper surface 306 as described above.

[0147] As shown in FIG. 4, the interferometer 410 and the imaging device operate in respective optical paths having a common portion 460. In the illustrated example, this common portion 460 of the optical path begins at the plane of the mirror 462, and the mirror 462 - reflects the measurement beam coming from the interferometer 410 towards the substrate 302 and reflects the reflected beam coming from the substrate towards the interferometer 410, - passes the imaging light coming from the light source 422 towards the substrate 302 and passes the reflected imaging light coming from the substrate 302 towards the camera 420.

[0148] In the example of FIG. 4, the common portion 460 of the optical path includes a front lens 442.

[0149] Figure 5 illustrates another non - limiting example of the system according to the present invention.

[0150] The system 500 shown in FIG. 5 includes all the components of the system 400 of FIG. 4.

[0151] As also shown in FIGS. 5 and 4, the interferometer 410 and the imaging device operate in a common optical path portion 460. When the interferometer beam is visible to the camera, due to the non - uniform illumination generated by the interferometer beam, it may degrade or even prevent proper imaging of the structure, or may even cause blurring of the camera 420. At the same time, the imaging light may interfere with the interferometry performed using the interferometer 410. Therefore, it may be advantageous to synchronize the interferometer 410 and the imaging device in order to perform the (multiple) interferometry measurements and the acquisition of the (multiple) images continuously or sequentially, more generally not simultaneously.

[0152] For this purpose, the system 500 includes a synchronization controller / unit 502 that can be a hardware unit such as a processor, a chip, or even a computer, or a software module such as a computer program.

[0153] In the illustrated example, the synchronization controller 502 is configured to trigger the camera 420 between two pulses of the pulse beam source (not shown) of the interferometer 410, or to trigger the pulsed light source during image acquisition by the camera, or to command both. Thus, the camera 420 captures or acquires at least one image when the measurement beam is not being emitted by the interferometer 410.

[0154] Alternatively or additionally, the mirror 462 may be controllably movable, particularly rotatable, and the synchronization controller 502 may be configured to command the position of the mirror 462. More specifically, the mirror 462 can be controllably rotated between the following. - a first position that deflects the measurement beam away from the structure or top surface 306 being characterized, and - a second position that directs the measurement beam toward the structure or top surface 306. When the imaging process is executed, the synchronization controller 502 commands the mirror 462 to be in the first position, i.e., the measurement beam is deflected away from the structure 304, and (a plurality of) images can be captured by the camera 420. After the imaging process is executed, the synchronization controller 502 commands the mirror 462 to be in the second position, i.e., the measurement beam is directed toward the structure 304 and an interferometric measurement can be performed.

[0155] Alternatively or additionally, the system may include a controllable shutter 504 disposed between the interferometer 410 and the mirror 462 in the illustrated example. The synchronization controller 502 may be configured to command the position of the controllable shutter 504. This shutter 504 can be made controllable between the following. - a "closed" position that blocks the passage of the measurement beam coming from the interferometer 410, and - an "open" position that permits the passage of the measurement beam coming from the interferometer 410. When the imaging process is executed, the shutter 504 can be commanded to enter a closed position that blocks the passage of the measurement beam. After the imaging process is executed, the shutter 504 can be commanded to enter an open position that permits the passage of the measurement beam so that an interferometric measurement can be performed.

[0156] Alternatively or additionally, the system may include a movable optical filter 504, such as a neutral density filter or a spectral filter, attached to, for example, a filter wheel and disposed between the interferometer 410 and the mirror 462 in the illustrated example. The synchronization controller 502 may be configured to command the position of the movable optical filter 504 within the filter wheel. The position of this optical filter 504 can be made controllable between the following. - The "closed" position that filters the measurement beam coming from the interferometer 410, and - The "open" position that permits the passage of the said measurement beam coming from the interferometer 410. When the imaging process is executed, the movable optical filter 504 can be arranged to enter the closed position that blocks the passage of the measurement beam. After the imaging process is executed, in order to enable interferometry to be executed, the movable optical filter 504 can be commanded to enter the open position that permits the passage of the measurement beam.

[0157] Of course, instead of, or in combination with, the synchronization means described with reference to FIG. 5, other synchronization means as described above may further be used.

[0158] FIG. 6 is an illustration of another non-limiting example of the system according to the present invention.

[0159] The system 600 shown in FIG. 6 includes all the components of the system 500 of FIG. 5 except for the turret 444.

[0160] In the system 600, the diameter of the measurement beam is not adjusted.

[0161] The first data provided by the imaging device, more specifically the processing module 426, relates to the position of the structure 304. The position data is used by the control unit 450 to adjust the position of the measurement beam on the upper surface and to accurately position the measurement beam on the structure or HAR structure being characterized.

[0162] The system 600 may, on the one hand, optionally include a synchronization controller 502 that controls the camera 420 in relation to the pulse source of the interferometer and / or the mirror 462 and / or the shutter 504 so that imaging and interferometry are executed in sequence.

[0163] Of course, the present invention is not limited to the examples detailed above.

Claims

1. A method (100, 200) for characterizing a structure (304) etched in a substrate (302) such as a wafer, said method (100, 200) comprising, for at least one structure (304) etched in said substrate (302), - at least one imaging step (102), comprising the steps of: 〇 Imaging at least one image of the upper surface (306) of said substrate (302) using an imaging device (420, 422) disposed on the upper side of said substrate (302) (104), and 〇 Measuring first data regarding said structure (304) from at least one of the imaged images (106 - 110) Including at least one imaging step (102), - At least one interferometry step (130) performed using a low coherence interferometer (410) disposed on the upper side to measure at least one depth data regarding the depth of said structure (304) using a measurement beam positioned on said structure (304) Including, wherein said method (100, 200) also includes a first adjustment step (120) for adjusting said measurement beam according to said at least one first data, Method (100, 200).

2. The imaging step (102) and the interferometry step (130) are performed through respective optical paths having a common portion (460), and said method (200) also includes synchronization (202) of said steps by a synchronization unit (502) for continuously or sequentially performing said imaging step and said interferometry step (102, 130). The method (200) according to claim 1, characterized in that it comprises.

3. For at least one structure (304), said first data includes upper CD data regarding the width of said structure (304), and said first adjustment step (120) includes adjusting the diameter of said measurement beam as a function of said upper CD data. The method (100, 200) according to claim 1 or 2, characterized in that it comprises.

4. The method (100, 200) according to any one of claims 1 to 3, further comprising a second adjustment step (134) for adjusting the diameter of said measurement beam according to at least one characteristic of the interference signal measured by said interferometer (410).

5. The diameter of said measurement beam on said upper surface (306) is - at least one optical element (440, 442), such as a lens or a beam expander, disposed between the interferometer (410) and the upper surface (306), - at least one focal length of an optical element (440, 442), such as a lens or a zoom device, disposed between the interferometer (410) and the upper surface (306), and / or - the numerical aperture of the measurement beam on the upper surface (306), The method (100, 200) according to claim 3 or 4, characterized in that it is adjusted by changing.

6. For at least one structure (304), the first data includes position data regarding the position of the structure (304) on the upper surface (306), and the first adjustment step (120) is the measurement beam according to the position data. The method (100, 200) according to any one of claims 1 to 5, characterized in that it includes adjustment of the position on the upper surface (306).

7. The method (100, 200) according to any one of claims 1 to 6, further comprising a third adjustment step (136) for adjusting the position of the measurement beam with respect to the structure (304) according to at least one characteristic of the interference signal measured by the interferometer (410).

8. The position of the measurement beam on the upper surface (306) is - moving the interferometer (410) relative to the substrate (302), and / or - moving the substrate (302) relative to the interferometer (410), The method (100, 200) according to claim 6 or 7, characterized in that it is adjusted by.

9. A system (400, 500, 600) for evaluating the characteristics of a structure (304) etched in a substrate (302) such as a wafer, the system (400, 500, 600) comprising: - an imaging device, 〇 An imaging device (420) disposed above the substrate (302) for imaging at least one image of the upper surface (306) of the substrate (302), and 〇 A processing unit (426) for measuring first data regarding a structure (304) etched in the substrate (302) from at least one captured image An imaging device comprising: - A low coherence interferometer (410) for measuring at least one depth data regarding the depth of the structure (304) by using a measurement beam disposed on the upper side and positioned on the structure (304). Including, the system also comprises an adjustment unit (440 - 444, 430 - 432, 450) for adjusting the measurement beam according to the first data, characterized in that System (400, 500, 600).

10. For at least one structure (304), the first data includes upper CD data regarding the width of the structure (304), and the adjustment unit (440 - 444, 430 - 432, 450) is - A turret (444) for changing at least one optical element (440, 442) such as a lens or a beam expander disposed on the path of the measurement beam between the interferometer (410) and the upper surface (306). - An optical element such as a lens with adjustable focal length or a zoom lens disposed on the path of the measurement beam between the interferometer (410) and the upper surface (306), and / or - A beam expander with adjustable numerical aperture disposed on the path of the measurement beam between the interferometer (410) and the upper surface (306). The system (400, 500, 600) according to claim 9, characterized in that it comprises means (440 - 444, 450) for adjusting the diameter on the upper surface (306) of the measurement beam as described above.

11. For at least one structure (304), the first data includes position data regarding the position of the structure (304) on the upper surface (406), and the adjustment unit (440 - 444, 430 - 432, 450) further comprises a positioning unit (430 - 432) for adjusting the position on the upper surface (306) of the measurement beam. The system (400, 500, 600) according to claim 9 or 10, characterized in that.

12. Each optical path of the imaging device and the interferometer (410) has a common part (460), and the system (500, 600) also comprises a synchronization unit (502) such that the imaging device and the interferometer (410) are used continuously or in sequence. The system (500, 600) according to any one of claims 9 to 11.

13. The synchronization unit is - A shutter (504) disposed between the interferometer (410) and the common portion (460), movable between a first position that blocks the passage of the measurement beam and a second position that permits the passage of the measurement beam. - A mirror (562) disposed between the interferometer (410) and the common portion (460), movable between a first position that deflects the path of the measurement beam away from the structure (304) and a second position that deflects the measurement beam toward the structure (304). - An optical filter, such as a neutral density filter or a spectral filter, disposed between the interferometer (410) and the common portion (460), movable between a first position that filters the measurement beam and a second position that allows the measurement beam to pass through. - An attenuation device (504) disposed between the interferometer (410) and the common optical path portion (460), whose attenuation value is controllable. - A controller (502) for switching on and off the interferometer light source. - A controller (502) for controlling the imaging device and / or the light source so as to trigger the acquisition of (a plurality of) images by the imaging device with respect to the pulses of the pulsed light source of the interferometer (410) such that image acquisition is performed between the pulses of the pulsed light source. The system (500, 600) according to claim 12, characterized by comprising at least one of the above.

Images