Method and system for characterizing structure etched in substrate

Abstract

The invention relates to a method (200) for characterizing structures etched in a substrate (e.g. A wafer), said method (200) comprising, for at least one structure:-at least one interferometric step (106, 108) carried out with a low coherence interferometer located on a top side of said substrate, the depth measuring module is used for measuring at least one piece of depth data related to the depth of the HAR structure by using a measuring light beam; wherein the method (200) further comprises a first adjustment step (104) for adjusting the diameter of the measurement beam at the top surface according to at least one top-CD data relating to the width of the HAR structure. The invention also 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, in particular high aspect ratio HAR structures. The present invention also relates to a system for implementing such a method.

[0002] The field of the invention is that of inspecting and characterizing structures etched in a substrate, such as high aspect ratio structures such as through silicon vias, TSVs or trenches etched in a substrate, such as a wafer. Background Art

[0003] In the semiconductor industry, or for example in the microelectromechanical systems (MEM) industry, many process steps involve etching structures that sometimes have a high aspect ratio in a substrate (e.g., silicon). Such structures with a high aspect ratio (hereinafter referred to as "HAR structures") can include, for example, through silicon vias (TSVs) (usually blind vias, used for interconnects, for example in advanced packaging technologies), trenches with narrow widths and elongated lengths, and more complex features. Such trenches can be realized, for example, by deep radiation ion etching (Deep RIE) or photolithography.

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

[0005] There is a need to measure and characterize these structures, in particular HAR structures, by measuring, for example, the depth of these structures. Document WO 2007 / 042676 describes a technique for depth measurement of HAR structures during a deep RIE process. However, this technique has some limitations when measuring HAR structures with very small critical dimensions (e.g., 4µm or less). There are also known techniques for characterizing dense arrays of HAR structures. These techniques cannot be used to characterize HAR structures individually.

[0006] It is an object of the present invention to overcome at least one of the disadvantages of the known art.

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

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

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

[0010] Another object of the present invention is to provide a solution for more efficiently and / or faster characterization of structures, in particular HAR structures. Summary of the invention

[0011] The present invention achieves at least one of these objectives by a method for characterizing structures etched in a substrate, such as a wafer, in particular high aspect ratio HAR structures, the method comprising, for at least one structure, at least one interferometric measurement step performed by a low coherence interferometer located on the top side of the substrate, for measuring at least one depth datum related to the depth of the structure with a measuring beam located on the structure.

[0012] According to the first aspect of the present invention, the method may further comprise a first adjusting step for adjusting a diameter of the measuring beam at the top surface according to at least one top-CD data related to a width of the structure.

[0013] Therefore, according to this first aspect, the present invention proposes to adapt the diameter of the measuring beam to the width of at least one structure or HAR structure, in particular the width of each structure or HAR structure, based on top-CD data related to the structure. The top-CD data represent valuable information about the width or lateral dimension of the structure at the substrate surface. This top-CD or lateral dimension can be, for example, the diameter of a hole, or the width of the smallest lateral dimension of a groove. Therefore, as an advantageous feature, the present invention proposes to use the top-CD data of the structure to adjust the diameter of the interferometric measurement beam used to measure the depth data of the structure. Therefore, the interferometric measurement step can be realized faster and allows to measure the depth of the structure more accurately, even for structures with smaller critical dimensions. In addition, structures and HAR structures with smaller CD and / or larger aspect ratios can be measured efficiently.

[0014] As used herein, a “high aspect ratio structure” or “HAR structure” or “HARS” refers to a structure having an aspect ratio greater than or equal to 5, or 10, or even 20.

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

[0016] In this document, the "top side" or "top surface" of a substrate corresponds to the side or surface, respectively, of a structure etched on the substrate.

[0017] The method according to the first aspect of the invention proposes that, for at least one structure or HAR structure, the diameter of the measuring beam emitted by the interferometer on the top surface of the substrate is adjusted according to the top-CD of the HAR structure. This allows a large part of the incident measuring beam to enter the structure, in particular the HAR structure, while only a small part is reflected at the top surface. Due to the relatively small ratio of the diameter or top-CD to the illumination wavelength (usually below 15), which leads to strong diffraction effects, and usually also due to the absorption characteristics of the materials involved (such as silicon), or more generally due to the conditions under which the light propagates into these structures, the losses within these structures are high, and only a small part of the incident light is reflected from the bottom of the structure and coupled into the interferometer. Therefore, the invention according to the first aspect allows to optimize the sensitivity of the interferometric measurement by using a large part of the incident power to compensate for the high losses, in particular in HAR structures, and to obtain a more balanced interference signal.

[0018] The diameter of the measurement beam on the top surface can be adjusted to, for example, 0.8 to 2 times the smallest lateral dimension of the structure, such as the diameter or cross section of a TSV, or the width of a trench. The diameter of the measurement beam on the top surface can also be adjusted to 0.3 or 0.5 to 5 times the smallest lateral dimension of the structure and still produce a usable signal.

[0019] For example, the diameter of the measurement beam can be defined as the beam portion with 90% or 99% of the incident power. For a Gaussian beam, the diameter of the measurement beam at the top surface can also be defined, for example, as the beam portion with a local intensity above 1 / e² of the peak intensity, corresponding to 86.5% of the power.

[0020] The diameter can also be adjusted so that at least 75%, or 80%, or 90% of the input power is coupled into the structure.

[0021] As an example, a measurement beam having a diameter size of 5 µm or 3 µm can be used to measure a HAR structure, in particular a TSV, having a diameter of 3 µm.

[0022] The optimal portion of light focused into the structure depends primarily on the light losses inside the structure and therefore on the structure shape (e.g. its aspect ratio). Deeper and narrower HAR structures, such as TSVs or trenches, and HAR structures with strongly curved bottoms need to couple most of the input power into them and therefore require a smaller beam diameter, while shallower or wider structures only need to couple a smaller portion of the input power into them. This is why an adaptable beam size is chosen on the top surface of the substrate.

[0023] Another advantage of adjusting the measurement beam size is that, even for arrays of structures close to each other, the measurement beam is sufficiently constrained to cover only one structure, which allows ensuring that the structures can be individually characterized.

[0024] In some embodiments, for at least one structure, the top-CD data may be a priori known data. In this case, the method according to the invention may comprise, before the first adjustment step, a step for reading the top-CD data in a memory.

[0025] Indeed, in some cases, top-CD data may be provided because they are determined during the design or manufacturing of the substrate. In these cases, the top-CD data may be stored in a memory and read during the method according to the invention. In these embodiments, characterization of the HAR structure may be completed more quickly because no prior measurement of the top-CD data is required.

[0026] In some cases, at least two, in particular all structures of the substrate may be identical. In this case, top-CD data may be read once for at least two of the structures and used for each of the at least two structures.

[0027] Alternatively or additionally, at least two of the substrates, in particular all structures of the substrates can be different. In this case, top-CD data can be read separately for each structure and used for the structure.

[0028] In some embodiments, the method according to the invention may comprise a second adjustment step for adjusting the diameter of the measuring beam depending on at least one characteristic of the interference signal measured by the interferometer.

[0029] The second adjustment step may be performed during or after the first adjustment step.

[0030] The second adjustment step allows adjusting the diameter of the measuring beam during the measuring step and in real time, in particular under practical conditions, when the measured interference signal indicates that the size of the measuring beam is not suitable for the inspected structure.

[0031] The at least one characteristic of the measured interference signal may include at least one of the following characteristics: - visibility or modulation depth of the interference fringes (possibly relative to an average value) or spectral modulation of the measured interference signal, and / or - the amplitude of the noise relative to the measured interference signal, and / or - The value of the depth data provided by the interferometric signal.

[0032] Therefore, if one of these features does not have the expected value, or its value is not within the expected range, this indicates that the diameter of the measuring beam is not appropriate for the structure being inspected. The diameter of the measuring beam can be adjusted accordingly.

[0033] Alternatively or additionally, an optimization process may be performed, for example using a gradient-based algorithm, to find a diameter of the measurement beam for which at least one characteristic of the measured interference signal is optimized, or reaches a local minimum.

[0034] In some embodiments, the method according to the invention may comprise a third adjustment step for adjusting the position of the measuring beam relative to the structure depending on at least one characteristic of the interference signal measured by the interferometer.

[0035] The third adjustment step may be performed during or after the first adjustment step.

[0036] The third adjustment step allows to adjust the position of the measuring beam during the measuring step accurately, in particular in real time under real conditions, in order to optimize the measurement conditions of the depth data of the target structure.

[0037] The at least one characteristic of the measured interference signal may include at least one of the following characteristics: - visibility or modulation depth of the interference fringes (possibly relative to the average value) or spectral modulation of the measured interference signal, - the amplitude of the noise relative to the measured interference signal, - The value of the depth data provided by the interferometric signal.

[0038] Therefore, if one of these features does not have the expected value, or its value is not within the expected range, this indicates that the position of the measurement beam relative to the structure is not optimal. The position of the measurement beam can be adjusted accordingly.

[0039] Alternatively or additionally, an optimization process may be performed, for example using a gradient-based algorithm, to find a position of the measuring beam for which at least one characteristic of the measured interference signal is optimized, or reaches a local minimum.

[0040] According to the second aspect of the present invention, which can be used alone or in combination with other aspects of the present invention, the method may further comprise at least one imaging step, the imaging step comprising the following steps: - capturing at least one image of said top surface with an imaging device located on the top side of said substrate, and - Measuring first data related to the structure from at least one captured image.

[0041] As will be further explained, the first data related to the structure represent valuable information about the structure. As an advantageous feature, the first data, i.e. the information about the structure, can be used to adjust the measuring beam used to measure the depth data of the structure. Thus, the interferometric measurement step can be realized faster and allows a more efficient and accurate measurement of the depth of the structure.

[0042] In some embodiments, for at least one structure, first data related to the structure may be inferred from a single image captured by an imaging device. Alternatively or additionally, for at least one structure, first data related to the structure may be inferred from several images captured by an imaging device.

[0043] In some embodiments, for at least one structure, at least one image captured by the imaging device may relate only to said structure: in this case, the captured image only includes information about said structure and does not include information about any other structure.

[0044] Alternatively or additionally, at least one image captured by the imaging device may relate to several, in particular all, structures of the substrate: in this case, the captured image comprises information about each of said structures, so that first data for each of said structures can be determined by processing said captured image. For example, an imaging step of capturing an image of the substrate may be performed before the first interferometric measurement step. The captured image may comprise the entire top surface of the substrate. The captured image may then be processed to determine first data for each HAR structure of the substrate.

[0045] In some embodiments, for at least one structure, the first data related to the structure may include top-CD data used during a first adjustment step for adjusting a diameter of the measuring beam.

[0046] Hence, the imaging step provides top-CD data which are then used in a first adjustment step to adjust the diameter of the measuring beam.

[0047] Therefore, the method according to the invention allows a faster and more accurate measurement of the depth of structures of a substrate when the top-CD data of the structures are unknown and / or when the substrate comprises different structures with different top-CDs.

[0048] Alternatively or additionally, for at least one structure, the first data may include position data relating to the position of the structure on the top surface. In this case, the method according to the invention may include a fourth adjustment step for adjusting the position of the measuring beam on the top surface according to the position data.

[0049] Thus, the imaging step provides data information related to the position of the structure by processing at least one image captured by the imaging device during the imaging step. The position of the structure on the substrate is then used to position the measuring beam more quickly and accurately, so that the depth of the structure of the substrate is measured more quickly and more accurately than with known techniques.

[0050] Then, as previously described, the position of the measuring beam can be further optimized by performing a third adjustment step for positioning the measuring beam relative to the structure according to at least one feature of the interference signal measured by the interferometer. These fourth and third adjustment steps then provide a coarse and fine positioning of the measuring beam, thereby allowing fast and accurate measurements.

[0051] According to some embodiments, the imaging step and the interferometric step may be performed by respective optical paths having a common portion. In this case, the method according to the invention may further comprise synchronizing the imaging step and the interferometric step by a synchronization unit so as to be performed in sequence and sequentially.

[0052] This approach allows characterizing structures etched in a substrate faster and using a smaller, cheaper system than prior art systems. In fact, the imaging step and the interferometric measurement step can share common optical components and both measurements can be performed without the need to move the measurement system relative to the substrate between measurements.

[0053] But most importantly, synchronization enables the imaging step mixed with the interferometric step to be performed sequentially so that none of these steps interferes with the other. In other words, the interferometric step can be performed without being interfered with by the imaging step. Likewise, the imaging step can be performed without the interferometric step, and in particular the interferometric beam, possibly interfering with the imaging step. Thus, the imaging step can be performed more accurately, so that the first data can be determined in a more accurate manner. Likewise, the interferometric step can perform the interferometric measurement more accurately, so that the depth data can be determined in a more accurate manner.

[0054] The synchronization of the imaging step and the interferometric measurement step can be performed in different ways, either alone or in combination.

[0055] According to some embodiments, synchronization can be performed by controlling the position of a shutter located between the interferometer and the common part. The shutter can be moved between the following positions: - a closed position which blocks the passage of the measuring beam, and - Open position allowing the measurement beam to pass.

[0056] When the imaging step is performed, the shutter can be moved to a closed position preventing the measurement beam from passing: the beam does not interfere with the imaging step. After the imaging step is performed, the shutter can be moved to an open position allowing the measurement beam to pass, so that an interferometric measurement can be performed.

[0057] Alternatively or additionally, synchronization can be performed by controlling the position of a mirror located between the interferometer and the common part. The mirror can be moved between the following positions: - a closed position that deflects the measuring beam away from the structure being inspected, and - directing the measuring beam towards the open position of the structure.

[0058] While the imaging step is being performed, the mirror can be moved to the closed position: the measurement beam is deflected away from the HAR structure and even away from the substrate. After the imaging step is performed, the mirror can be moved to the open position, deflecting the measurement beam towards the structure: interferometric measurements can be performed.

[0059] Alternatively or in addition to at least one of the previous synchronization options, synchronization may be performed by controlling the position of a filter, such as a neutral optical density filter or a spectral filter, located between the interferometer and the common part. The filter may be moved between the following positions: - an off or strongly attenuated position for filtering the measuring beam, and - Open position that lets the measuring beam through.

[0060] When the imaging step is performed, the filter can be moved to the closed position: the measuring beam is filtered out or strongly attenuated and does not pass (at least significantly) towards the HAR structure. After the imaging step is performed, the filter can be moved to the open position, the measuring beam passes through the filter, so that the interferometric measurement step can be performed.

[0061] Alternatively or additionally to at least one of the previous synchronization options, the synchronization may be performed by controlling an attenuation value of an attenuation device located between the interferometer and the common optical path portion, attenuating the measuring beam during the imaging step, or not attenuating the measuring beam.

[0062] Alternatively or in addition to at least one of the previous synchronization options, synchronization may be performed by switching the interferometer light source on and off. Thus, the light source may be switched off during the imaging step and switched on during the interferometric step.

[0063] Alternatively or in addition to at least one of the previous synchronization options, the acquisition of one or more images by the imaging device is triggered relative to a pulsed light source of the interferometer, such that the image acquisition is performed between pulses of said light source. In this case, the light source of the interferometer is a pulsed light source with a given pulse frequency or with pulses triggered by the synchronization unit. The imaging device can be triggered between pulses, or the pulses are controlled, or triggered by the synchronization unit together with the pulsed light source, such that at least one image is captured when the pulsed light source does not emit light pulses.

[0064] In the first aspect and the optional second aspect of the invention, the invention proposes adjusting the diameter of the measuring beam on the top surface. The adjustment of the diameter of the measuring beam on the top surface can be performed in different ways, either individually or in combination.

[0065] In some embodiments, the adjustment of the diameter of the measuring beam on the top surface can be performed by changing at least one optical element (such as a lens or a beam expander) placed between the interferometer and the top surface. The change of the optical element can be achieved in any way. For example, the change of the optical element can be achieved by moving or supporting a turntable of the at least one optical element.

[0066] Alternatively or additionally, the adjustment of the diameter of the measuring beam on the top surface can be performed by changing at least one focal length of an optical element (e.g. a lens or a zoom device) placed between the interferometer and the top surface. The change of the focal length of the optical element can be achieved, for example, by modifying the shape or propagation properties of a deformable lens or metalens, or by changing the magnification of the optical element, or by changing the position of components of the zoom device constituting the optical element.

[0067] Alternatively or additionally to at least one of the previous options, the adjustment of the measurement diameter on the top surface may be performed by changing the numerical aperture of the measurement beam on the top surface. The numerical aperture of the measurement beam may be changed by using a beam expander or an aperture stop in the collimated beam path.

[0068] The present invention also relates to a system for characterizing a structure etched in a substrate (such as a wafer), in particular a high aspect ratio HAR structure, the system comprising a low coherence interferometer, which is arranged on the top side of the substrate and is used to measure at least one depth data related to the depth of the structure, in particular the HAR structure, using a measuring beam located on the structure.

[0069] According to the first aspect of the invention, the system according to the invention may further comprise an adjusting unit for adjusting a diameter of the measuring beam at the top surface according to at least one top-CD data related to a width of the structure.

[0070] As mentioned above, in some embodiments, the top-CD data may be a priori known data of at least one structure. In this case, the system according to the invention may include a memory for storing said top-CD data.

[0071] The storage may be local or remote storage.

[0072] The memory may be removable memory or may not be removable memory.

[0073] Memory can be volatile or permanent media.

[0074] Top-CD data may be stored as numerical values ​​in volatile or non-volatile memory, or in a data file of any format in a permanent storage medium.

[0075] The memory may be integrated into the interferometer, into the adjustment unit, or into another device of the system, or may be an independent component belonging to the system.

[0076] According to the second aspect of the present invention, the system of the present invention may further include an imaging unit. The imaging unit may include: - an imaging device arranged on the top side of said substrate for capturing at least one image of the top surface of the substrate, and - A processing unit for measuring first data related to the structure from at least one image captured by the imaging device.

[0077] The imaging unit may be configured to perform the imaging steps as described above.

[0078] For at least one structure, the imaging unit may provide first data comprising or consisting of top-CD data of said structure.

[0079] For at least one structure, the imaging unit may provide first data comprising or consisting of position data relating to the position of said structure on the top surface.

[0080] In some embodiments, the system according to the present invention may further include a positioning unit for adjusting the position of the measuring beam on the top surface of the substrate.

[0081] The position of the measuring beam may be adjusted based on the position data. The position data may be or include: - e.g. a predefined value stored in a memory; - The imaging unit provides position data for at least one structure.

[0082] Alternatively or additionally, as previously described, the position of the measuring beam may be adjusted depending on at least one characteristic of the interference signal measured by the interferometer.

[0083] The positioning unit may comprise a support for the substrate and / or a support for the interferometer.

[0084] The positioning unit can adjust the position of the measuring beam on the top surface by: - moving the interferometer relative to the substrate; and / or - Move the substrate relative to the interferometer.

[0085] In some embodiments, in order to adjust the diameter of the measuring beam on the top surface, the adjusting unit may include at least one of the following: - a turntable for changing at least one optical element, such as a lens or a beam expander, placed on the path of the measuring beam between the interferometer and the top surface; - an optical element with adjustable focal length, such as a lens or zoom lens, placed in the path of the measuring beam between the interferometer and the top surface; and / or - A beam expander with adjustable numerical aperture placed in the path of the measurement beam between the interferometer and the top surface.

[0086] In some embodiments, the respective optical paths of the imaging unit and the interferometer may have a common part. In this case, the system according to the invention may comprise a synchronization unit such that the imaging unit and the interferometer are used sequentially or one after the other.

[0087] In order to synchronize the imaging unit and the interferometer, the synchronization unit may include at least one of the following: - a shutter located between the interferometer and the common part and movable between a first position blocking the passage of the measuring beam and a second position allowing the passage of said measuring beam; - a mirror situated between the interferometer and the common part and movable between a first position deflecting the passage of the measuring beam away from the structure and a second position deflecting said measuring beam towards said structure; - a filter, such as a neutral density filter or a spectral filter, which is located between the interferometer and the common part and is movable between a first position in which the measuring beam is filtered so as to block it or to strongly attenuate it, and a second position in which the measuring beam is passed; - an attenuation device, such as an optoelectronic attenuator, located between the interferometer and the common optical path portion, the attenuation value of which is controllable; - A controller to turn the interferometer light source on and off; - A controller controlling the imaging device and / or the light source to trigger the imaging device for acquisition of one or more images relative to the pulsed light source of the interferometer so that image acquisition is performed between pulses of said light source.

[0088] In some embodiments, the imaging unit may include a light source and a camera, optionally in combination with microscope optics.

[0089] In some embodiments, the interferometer is coupled to an optical fiber that transmits the measurement beam and the reflected light. The optical fiber may be a single mode optical fiber.

[0090] For example, the interferometer can be a time domain interferometer. In this case, the interferometer comprises a broadband light source (not shown) emitting polychromatic light. The interferometer also comprises an optical delay line that allows the optical path difference between the two beams to be varied. When the optical path difference between the beams reflected at the top and at the bottom of the structure, respectively, or between these respective beams and a reference beam, is reproduced by the delay line, an interference burst or fringe can be observed on the photodetector, allowing the optical path difference to be measured. The depth of the structure is inferred from the optical path difference.

[0091] The interferometer can also be a spectral domain interferometer. In this case, the interferometer includes a broadband light source (not shown) emitting polychromatic light and a spectrometer for spectral analysis of the reflected light. The spectrum obtained by combining the light reflected by the top and bottom of the structure on the spectrometer exhibits a known pattern (e.g., modulation), and analysis of the spectrum can provide the optical path difference between the superimposed beams. The depth of the structure is inferred from the optical path difference.

[0092] The interferometer can also include a swept source interferometer, which has a tunable laser that emits monochromatic light with an optical frequency that varies over time within a spectral range. The intensity of the reflected light is measured by a photodetector, thereby recovering the spectrum, and analysis of the spectrum also allows the optical path difference between the reflected beams to be measured, and thus the depth of the structure to be measured.

[0093] The interferometer may for example be similar to the one described in document published under number WO 2007 / 042676. BRIEF DESCRIPTION OF THE DRAWINGS AND DETAILED DESCRIPTION

[0094] Other advantages and features will become apparent from a reading of the detailed description of non-limiting embodiments and the accompanying drawings, in which: - Figure 1-3 is a schematic diagram of a non-limiting example of a method according to the present invention; and - Figure 4a , Figure 4b , Figure 5-7 is a schematic diagram of a non-limiting example of a system according to the present invention.

[0095] It should be understood that the embodiments described below are non-limiting. In particular, if the selection of the features described below is sufficient to give a technical advantage or distinguish the present invention from the prior art, it is conceivable that the variant of the present invention only includes the selection of features (independent of the other features described). This selection includes at least one preferred functional feature, which has no structural details or only some of the structural details - as long as the partial details themselves are sufficient to give a technical advantage or distinguish the present invention from the prior art.

[0096] In the figures, elements common to several figures may use the same reference numerals.

[0097] Figure 1 is a schematic diagram of a non-limiting example of a method according to the invention.

[0098] Figure 1 The method 100 shown can be used to characterize structures etched in a substrate (e.g., a wafer), particularly high aspect ratio HAR structures. More specifically, Figure 1 The method 100 may be used to measure the depth of a structure etched in a substrate.

[0099] The method 100 comprises a step 102 for reading a priori known top-CD data of at least one structure from a memory. The top-CD data is data related to the width of the structure, more specifically, data related to the width of the structure at the top side (i.e., on the top surface of the substrate). For example, the top-CD data may be determined during the design or manufacturing process of the substrate and stored in the memory.

[0100] In some cases, at least two, in particular all, structures of the substrate may be identical. In this case, the top-CD data may be read once for the structure and used for each of the structures, i.e. for multiple iterations of the interferometric measurement step, to measure depth data for each of the structures.

[0101] In some cases, at least two, in particular all structures of the substrate may be different. In this case, top-CD data may be read separately for each of the structures.

[0102] Advantageously, the method 100 comprises a step 104 for adjusting the diameter of a measuring beam on the top surface of the substrate for interferometric measurement of the depth data according to the top-CD data. The diameter of the measuring beam is adjusted to ensure that the measuring beam enters the structure with sufficient power and reaches the bottom of the structure, in particular for HAR structures, to measure the depth of the structure.

[0103] After the adjusting step 104 , the method 100 comprises an interferometric measurement step 106 for at least one structure, during which depth data relating to the depth of said structure are measured by optical interferometry.

[0104] The interferometric measurement is performed by a low coherence optical interferometer arranged on the top side of the substrate. Optical interferometry is a well-known technique and will not be described in detail here. In short, a measuring beam of broadband light is sent to the structure. At least a portion of the measuring beam is reflected by the structure at the top or surface of the substrate and at the bottom of the structure, respectively. The reflected beams are caused to interfere with each other or with a reference beam emitted from the same source to obtain an interference signal, the analysis of which provides depth data.

[0105] The measuring step 106 comprises at least one interferometric measurement 108 providing a measurement signal as described above. The measurement signal may then be processed to obtain depth data.

[0106] The method 100 may optionally comprise a second adjustment step 110, in particular during the measuring step 106, for adjusting the diameter of the measuring beam according to at least one characteristic of the interference signal measured by the interferometer. This second adjustment step 110 allows the diameter of the measuring beam to be adjusted in real time according to the measured signal. For example, the diameter of the measuring beam may be adjusted according to: - visibility or modulation depth of the interference fringes (possibly relative to an average value) or spectral modulation of the measured interference signal; and / or - the amplitude of the noise relative to the measured interference signal; and / or - The value of the depth data provided by the interferometric signal.

[0107] Therefore, if one of these features does not have an expected value, or its value is not within the expected range of values, it indicates that the diameter of the measurement beam is not appropriate for the structure being inspected. As described later, the diameter of the measurement beam can be adjusted accordingly. This process can be iteratively repeated using, for example, a gradient-based algorithm to find a diameter of the measurement beam for which at least one feature of the measured interference signal is optimized, or reaches a local minimum.

[0108] The method 100 may optionally include a third adjustment step 112 for adjusting the position of the measuring beam according to at least one characteristic of the interference signal measured by the interferometer, in particular during the measuring step 106. This third adjustment step 120 allows the position of the measuring beam to be adjusted in real time according to the measured signal. For example, the position of the measuring beam may be adjusted according to: - visibility or modulation depth of the interference fringes (possibly relative to an average value) or spectral modulation of the measured interference signal; and / or - the amplitude of the noise relative to the measured interference signal; and / or - The value of the depth data provided by the interferometric signal.

[0109] Therefore, if one of these features does not have an expected value, or its value is not within an expected range of values, this indicates that the position of the measurement beam relative to the structure is not optimal. As described later, the position of the measurement beam relative to the structure can be adjusted accordingly. This process can be iteratively repeated using, for example, a gradient-based algorithm to find a position of the measurement beam for which at least one feature of the measured interference signal is optimized, or reaches a local minimum.

[0110] The second adjustment step 110 and the third adjustment step 112 may be performed simultaneously or sequentially in any order. Alternatively, only one of them may be performed or none of them may be performed at all. After performing at least one of these steps, at least one further interferometric measurement 108 may be performed. Thus, steps 108 and 110, 120 may be repeated until the interferometric measurement is successful.

[0111] Figure 2 is a schematic diagram of another non-limiting example of a method according to the present invention.

[0112] Figure 2 The method 200 shown may be used to characterize a structure, particularly a HAR structure etched in a substrate (e.g., a wafer). More specifically, Figure 2 The method 200 may be used to measure the depth of a structure etched in a substrate.

[0113] The method 200 includes a step 202 of imaging a substrate.

[0114] The imaging step 202 comprises a step 204 for capturing at least one image of the top surface of the substrate, for example by an imaging unit. The imaging unit may comprise a camera, optionally associated with a microscope and a light source, for imaging the top surface of the substrate. The captured image may comprise the entire top surface or only a portion of the top surface. The captured image may comprise only one structure etched in the substrate, or several structures of the substrate, in particular all structures of the substrate.

[0115] The captured image may then be processed to identify position data relative to the position of at least one structure visible in the captured image in a processing step 206. Image processing for determining position data may be performed according to known image processing methods, for example using segmentation, pattern recognition or blob analysis algorithms.

[0116] At processing step 208, the captured image may be processed to identify top-CD data associated with at least one structure visible on the captured image. Image processing for determining top-CD data may be performed according to known image processing methods. For example, once a structure is located and identified, its critical dimensions may be obtained by using a pattern analysis algorithm and a magnification calibrated or size calibrated imaging system.

[0117] In some embodiments, only one of process steps 206 and 208 may be performed. In some embodiments, both process steps 206 and 208 may be performed. In the latter case, process steps 206 and 208 may be performed during a single process step.

[0118] The method 200 may include an optional step 210 for adjusting the position of the measurement beam on the top surface based on the position data determined in step 206 so as to accurately position the measurement beam on the structure being characterized.

[0119] The position of the measuring beam on the top surface can be adjusted using a positioning unit. The positioning unit may include: - a translation stage for the interferometer and possibly the imaging unit, arranged to move at least the interferometer relative to the plane of the substrate top surface, and / or - A translation stage for the substrate, arranged to move the substrate or a chuck holding the substrate relative to the interferometer and possibly the imaging unit.

[0120] Likewise, steps 206 and 210 are optional, and thus in some embodiments, the method according to the present invention may not include these steps.

[0121] When method 200 includes optional step 208 of determining top-CD data of the characterized structure, said top-CD data may be used to adjust the diameter of the measuring beam on the substrate surface during step 104. Thus, step 102 for reading top-CD data may not be performed.

[0122] If the method 200 does not include the optional step 208 of determining top-CD data of the structure being characterized, the method 200 may include the step 102 of reading top-CD data of the structure as described above.

[0123] Figure 2 The method 200 also includes as described above with reference to Figure 1 The method 200 may include steps 104 and 106 described above. In particular, the method 200 may include a step 112 of positioning the measuring beam according to the measurement signal, which step is performed by means of a positioning unit. This positioning step 120 may be performed after a step 210 for adjusting the position of the measuring beam according to the position data, in order to refine or optimize the positioning. The method 200 may also be performed without step 210, for example by using predefined or previously stored position data.

[0124] Figure 3 is a schematic diagram of another non-limiting example of a method according to the present invention.

[0125] Figure 3 The method 300 shown may be used to characterize structures etched in a substrate (eg, a wafer), particularly HAR structures. More specifically, Figure 3 The method 300 may be used to measure the depth of a structure etched in a substrate.

[0126] Method 300 includes referring to Figure 2 The steps of method 200 are described.

[0127] The method 300 further comprises a synchronization step 302, so that the capturing step 204 and the interferometric measurement step 108 are performed sequentially, so that the steps do not interfere with each other. In particular, the synchronization step allows preventing the measuring beam of the interferometer from reaching the top surface at least significantly when performing the image capturing step 204. This is particularly important when the image capturing step and the interferometric measurement step are performed by using corresponding optical paths having common parts.

[0128] This synchronization can be done in different ways. The synchronization step can be done by following these steps: - Control the position of the shutter located between the interferometer and the common part: o at a first position where the measurement beam is blocked from passing during the image capturing step 204, and o a second position through which the measuring beam is allowed to pass at least during the interferometric measurement step 108; - Control the position of the mirror located between the interferometer and the common part: o deviating the passage of the measuring beam from the first position of the top surface during the image capturing step 204; and o a second position in which the measuring beam is deflected towards the top surface at least during the interferometric measurement step 108; - Control the position of the optical density filter or spectral filter between the interferometer and the common section: o filtering or attenuating a majority of the measurement beam during the image capture step 204, at a first position; and o at a second position through which the measuring beam is passed at least during the interferometric measurement step 108; - Control the attenuation value of the attenuation device located between the interferometer and the common section in order to: o during the image capturing step 204, the measuring beam does not pass at least significantly towards the common portion; and o the measuring beam passes at least during the interferometric measurement step 108; - switching the interferometer light source on and off so that the measuring beam is not emitted during the image capturing step and the measuring beam is emitted at least during the interferometric measurement step 108; - triggering the capturing of one or more images by the imaging unit with respect to the pulses of the pulsed light source of the interferometer, or inversely, or synchronizing both so that image acquisition is performed between the pulses of said pulsed source.

[0129] Therefore, in Figure 3 In the method 300 , the imaging unit captures an image of the top surface or at least the structure without being disturbed by the measuring beam emitted by the interferometer.

[0130] Figure 4a is a schematic diagram of a non-limiting example of a system according to the present invention.

[0131] Figure 4a The system 400 shown can be used to characterize structures etched in a substrate (eg, a wafer), particularly HAR structures. More specifically, the system 400 can be used to measure the depth of the structures etched in the substrate.

[0132] System 400 can be used to perform the method according to the present invention, in particular Figure 1 Method 100.

[0133] like Figure 4a As shown, system 400 is used to characterize structures etched in a substrate (e.g., a wafer), particularly HAR structures. Figure 4a In the figure, for ease of understanding, only one structure 404 is shown. Of course, the substrate may include more than one structure. The structure 404 may be, for example, a groove etched in the substrate 402 from the top surface 406 of the substrate 402. The substrate 402 also includes a bottom surface 408 opposite to the top surface.

[0134] Figure 4b Information to be measured on a structure 404 etched in a substrate 402 is shown, namely a depth 450 and possibly a top-CD 452. In the example shown, the structure 404 may be, for example, a hole or a TSV, and the top-CD data 452 may represent a diameter at a top surface 406. The structure 404 may also be an elongated trench, and the top-CD 452 may be its smallest lateral dimension, or its width at the top surface 406.

[0135] The system includes a low coherence interferometer 410 placed on the top surface 406 side of the substrate 402. The low coherence interferometer 410 is used to characterize each structure of the substrate, and in particular to measure at least one data related to the depth of the structure 404, and even more specifically to measure the depth of the structure 404.

[0136] For example, the interferometer 410 can be a time domain interferometer. In this case, the interferometer 410 comprises a broadband light source (not shown) emitting polychromatic light. The interferometer 410 also comprises an optical delay line that allows the optical path difference between the two beams to be varied. When the optical path difference between the beams reflected at the top and at the bottom of the structure 404, respectively, or between these respective beams and a reference beam is reproduced by the delay line, an interference burst or fringe can be observed on a photodetector, allowing the optical path difference to be measured. The depth of the structure is inferred from the optical path difference.

[0137] The interferometer can also be a spectral domain interferometer. In this case, the interferometer includes a broadband light source (not shown) emitting polychromatic light and a spectrometer for spectral analysis of the reflected light. The spectrum obtained by combining the light reflected by the top and bottom of the structure on the spectrometer exhibits a known pattern (e.g., modulation), and analysis of the spectrum can provide the optical path difference between the superimposed beams. The depth of the structure is inferred from the optical path difference.

[0138] Interferometer 410 may also include a swept source interferometer having a tunable laser that emits monochromatic light whose optical frequency varies over time within a spectral range. The intensity of the reflected light is measured by a photodetector to recover the spectrum, and analysis of the spectrum also allows measurement of the optical path difference between the reflected beams, and thus measurement of the depth of the structure.

[0139] For example, interferometer 410 may be similar to the interferometer described in WO 2007 / 042676.

[0140] Optionally but preferably, a single mode optical fiber 412 coupled to the interferometer 410 may be used to transmit the measuring beam emitted by the interferometer 410 out of the interferometer 410 and to transmit the reflected light received from the substrate 402 to the interferometer 410 .

[0141] To measure narrow structures with a high aspect ratio (HAR) and a diameter of less than 5 µm, such as TSVs, the measurement light source may, for example, emit light in the visible spectral range (eg < 900 nm) in order to better propagate into these structures.

[0142] The system 400 also includes a support 414 associated with a displacement device 416 (eg, a translation and / or rotation stage), such as a wafer chuck, to move and position the substrate 402 in the xy direction, and optionally in the z direction.

[0143] The system 400 further comprises means for adjusting the diameter of the measurement beam emitted by the interferometer 410 on the substrate top surface 406, so as to adjust the diameter of the measurement beam reaching the inspected structure.

[0144] exist Figure 4a In the example shown, the diameter of the measurement beam can be determined by the core of the optical fiber 412 or the mode field diameter of the light leaving the optical fiber and the magnification provided by the combination of the collimating lens 418 and the front lens 420 (such as a microscope objective lens). Therefore, at least one of these lenses 418-420 can be changed to change the magnification and thus adjust the diameter of the measurement beam on the top surface 406.

[0145] The system 400 includes a turret 422 for changing at least one of the lenses 418 - 420 and / or changing the focal length of one of the lenses 418 - 420 to correspondingly change the magnification.

[0146] The system 400 may also include a beam expander (not shown) located in the portion of the measurement beam where it is collimated (e.g., between the collimator lens 418 and the front lens 420). The beam expander modifies the beam diameter, thereby changing the numerical aperture (NA) at which the beam is focused. This ultimately defines the diameter of the measurement beam on the top surface 406.

[0147] The system 400 includes a control unit 424 for controlling the device for adjusting the diameter of the measuring beam. In the example shown, the control unit 424 is configured to control the turntable 422 for changing at least one of the lenses 418-420, thereby adjusting the diameter of the measuring beam and obtaining a desired diameter of the measuring beam on the top surface 406.

[0148] exist Figure 4a In the illustrated system 400 , adjustment of the diameter of the measurement beam at the top surface may be accomplished based on a priori known top-CD data associated with the structure 404 being characterized.

[0149] A priori known top-CD data is stored in memory 426, which may or may not be part of system 400. Therefore, control unit 424 reads the top-CD data of structure 404 from memory 426, optionally calculates the desired beam diameter of the measurement beam, or selects front side lenses 418-420 according to a predefined recipe, and controls turntable 422 to ensure that the correct lens is positioned at the measurement beam, thereby adjusting the diameter of the measurement beam emitted by interferometer 410 and obtaining the desired beam diameter on top surface 406.

[0150] Alternatively or additionally, the diameter of the measuring beam on the top surface can also be adjusted as a function of at least one characteristic of the signal measured by the interferometer.

[0151] Such an adjustment of the diameter of the measuring beam may be performed during the interferometric measurement and allows real-time adjustment of the measuring beam, in particular under practical conditions, when the measured interference signal indicates that the diameter of the measuring beam is not suitable for the structure 404 being measured.

[0152] At least one characteristic of the measured signal that can be used to adjust the diameter of the measurement beam on the top surface 406 can be or include at least one of the following characteristics: - visibility or modulation depth of the interference fringes (possibly relative to an average value) or spectral modulation of the measured interference signal, and / or - the amplitude of the noise relative to the measured interference signal, and / or - The value of the depth data provided by the interferometric signal.

[0153] To this end, the interferometer 410 may be configured to, or may include (or may be coupled to) a module 428 configured to measure the value of the characteristic of the measured signal and compare the value with one or more expected values ​​or one or more previous values ​​in an iterative process. As described above, the comparison result may be transmitted to the control unit 424 to adjust the diameter of the light beam by means of the turntable 422 and / or the beam expander.

[0154] Figure 5 is a schematic diagram of another non-limiting example of a system according to the present invention.

[0155] Figure 5 The system 500 can be used to perform the method according to the present invention, in particular Figure 1 , Figure 2 or Figure 3 Any of methods 100, 200 or 300.

[0156] System 500 includes all components of system 400 .

[0157] The system 500 also includes an imaging device for capturing at least one image of the substrate 402 , more specifically at least one image of the top surface 406 of the substrate 402 , and processing the at least one captured image for determining at least one first data associated with at least one HAR structure of the substrate 402 .

[0158] The imaging device is arranged on the same side as the interferometer 410 , ie on the side of the top surface 406 of the substrate 402 .

[0159] exist Figure 5 In the non-limiting example shown, the imaging device includes a camera 502 and an optional light source 504. The imaging device may also include a front lens 420 and a tubular lens 506 to image the top surface 406 of the substrate 402 on the camera 502.

[0160] The camera 502 is configured to capture / acquire at least one image of a top surface 406 of a substrate 402 including at least one HAR structure etched therein. The captured image is processed by standard image processing techniques performed by a processing module 508 to measure first data associated with at least one structure or HAR structure. The processing module may include a hardware module, such as a processor or chip, or a software module, such as a computer program.

[0161] For at least one structure or HAR structure, the first data may include the position of the structure on the top surface 406. In this case, the position of the structure may be transmitted to the control unit 424 to command / control the support 414 and / or the stage 416 for accurately positioning the measurement beam emitted by the interferometer 410 on the structure.

[0162] Alternatively or additionally, for at least one structure or HAR structure, the first data may include a top-CD of the structure. In this case, as described above, the top-CD of the structure may be transmitted to the control unit 424 to command / control the turntable 422 for adjusting the diameter of the measurement beam emitted by the interferometer on the top surface 406. In this case, the system 500 may not include the memory 426, and the top-CD may not be a priori known data.

[0163] like Figure 5 As shown, the interferometer 410 and the imaging device operate with respective optical paths having a common portion 510. In the example shown, the common portion 510 of the optical path begins at a mirror 512, which: - reflecting the measuring beam from the interferometer 410 towards the substrate 402 and reflecting the reflected beam from the substrate towards the interferometer 410; - passing imaging light from light source 504 towards substrate 402 and passing reflected imaging light from substrate 402 towards camera 502; exist Figure 5 In the example of FIG. 4 , the common portion 510 of the optical path includes the front lens 420 .

[0164] Figure 6 is a schematic diagram of another non-limiting example of a system according to the present invention.

[0165] Figure 6 The illustrated system 600 includes Figure 5 All components of system 500 except memory 426.

[0166] In system 600, the first data provided by processing module 508 is considered to include the top-CD and / or the location of the structure being characterized.

[0167] like Figure 6 and Figure 5As shown, the interferometer 410 and the imaging device operate using a common optical path portion 510. If the interferometer beam is visible to the camera, the interferometer can degrade or even prevent proper imaging of the structure due to the uneven illumination produced by the interferometer, or even cause camera blur. At the same time, the imaging light can interfere with the interferometric measurements performed using the interferometer 410. Therefore, it can be advantageous to synchronize the interferometer 410 and the imaging device so that one or more interferometric measurements and image acquisitions are performed sequentially or successively, and more generally not simultaneously.

[0168] To this end, the system 600 includes a synchronization controller 602, which may be a hardware unit such as a processor, a chip or even a computer, or a software module such as a computer program.

[0169] In the example shown, the synchronization controller 602 is configured to trigger the camera 502 between two pulses of a pulsed beam source (not shown) of the interferometer 410, or to trigger the pulsed light source between image acquisitions by the camera, or to command both. Thus, when the interferometer 410 is not emitting a measurement beam, the camera 502 captures or acquires at least one image.

[0170] Alternatively or additionally, the mirror 512 may be controllably movable, in particular rotatable, and the synchronization controller 602 may be configured to command the position of the mirror. More specifically, the mirror 512 may be controllably rotatable between: - deflecting the measurement beam away from a first position of the structure or top surface 406 being characterized, and - directing the measuring beam towards a second location of the structure or top surface 406 .

[0171] When performing the imaging step, the synchronization controller 602 commands the mirror to be in a first position: the measurement beam deviates from the structure and one or more images can be captured by the camera. After performing the imaging step, the synchronization controller 602 controls the mirror to be in a second position: the measurement beam points to the structure: interferometry can be performed.

[0172] Alternatively or additionally, in the example shown, the system may include a controllable shutter 604 placed between the interferometer 410 and the mirror 512. The synchronization controller 602 may be configured to control the position of the controllable shutter 604. The controllable shutter 604 may be controlled between: - an "off" position that blocks the passage of the measuring beam from the interferometer, and - an "on" position allowing the measurement beam from the interferometer 410 to pass through.

[0173] When the imaging step is performed, the shutter 604 can be commanded to a closed position, preventing the measurement beam from passing through. After the imaging step is performed, the shutter can be commanded to an open position, allowing the measurement beam to pass through, so that interferometric measurements can be performed.

[0174] Alternatively or additionally, the system may include a movable optical filter 604, such as a neutral density or spectral filter, placed between the interferometer 410 and the mirror 512 in the example shown and mounted, for example, in a filter wheel. The synchronization controller 602 may be configured to control the position of the movable optical filter 604 within the filter wheel. The position of the filter 604 may be controllable between: - an "off" position for filtering the measuring beam from the interferometer 410, and - an "on" position allowing the measurement beam from the interferometer 410 to pass through.

[0175] When performing the imaging step, the movable optical filter 604 can be positioned into a closed position preventing the measurement beam from passing through. After performing the imaging step, the movable optical filter 604 can be commanded to an open position allowing the measurement beam to pass through so that interferometry can be performed.

[0176] Of course, other synchronization devices can be used instead of reference Figure 6 The described synchronization devices or in combination therewith, such as those further indicated above.

[0177] Figure 7 is a schematic diagram of another non-limiting example of a system according to the present invention.

[0178] Figure 7 The illustrated system 700 includes Figure 6 All components of system 600 except turntable 422.

[0179] In system 700, the diameter of the measurement beam is not adjusted.

[0180] The first data provided by the imaging device, more specifically the processing module 508, is related to the position of the structure. The control unit 424 uses the position data to adjust the position of the measuring beam on the top surface and accurately place the measuring beam on the structure being characterized or the HAR structure.

[0181] However, the system 700 includes a synchronization controller 602 that controls the camera relative to the pulse source and / or the mirror 512 and / or shutter 604 of the interferometer, thereby achieving image capture and interferometry in sequence.

[0182] Of course, the present invention is not limited to the examples detailed above.

Claims

1. A method (100; 200; 300) for characterizing structures (404) etched in a substrate (402), the substrate being, for example, a wafer, the method comprising, for at least one structure (404): - at least one interferometric measurement step (106, 108), the at least one interferometric measurement step being performed with a low coherence interferometer (410) located on the top side (406) of the substrate (402) for measuring at least one depth data related to the depth of the structure (404) with a measuring beam located on the structure (404); The method (100; 200; 300) further comprises a first adjustment step (104) for adjusting the diameter of the measuring beam at the top surface (406) according to at least one top-CD data related to the width of the structure (404).

2. The method (100; 200; 300) according to the preceding claim, characterized in that For at least one structure (404), top-CD data are a priori known data, and before the first adjustment step (104), the method (100; 200) comprises a step (102) for reading said top-CD data in a memory (426).

3. The method (100; 200; 300) according to any of the preceding claims, further comprising a second adjustment step (110) for adjusting the diameter of the measuring beam depending on at least one characteristic of the interference signal measured by the interferometer (410).

4. The method (100; 200; 300) according to any of the preceding claims, further comprising a third adjustment step (112) for adjusting the position of the measuring beam relative to the structure depending on at least one characteristic of the interference signal measured by the interferometer (410).

5. The method (200; 300) according to any one of the preceding claims, further comprising at least one imaging step (202), the at least one imaging step comprising the following steps: - capturing at least one image of the top surface (406) using an imaging device (502) located on the top side of the substrate (402), and - measuring (206, 208) first data related to the structure (404) from at least one captured image.

6. The method (200; 300) according to the preceding claim, characterized in that For at least one structure (404), the first data include top-CD data, which are used during a first adjustment step (104) for adjusting a diameter of a measuring beam.

7. The method (200; 300) according to any one of claims 5 or 6, characterized in that For at least one structure (404), the first data comprises position data related to the position of the structure (404) on the top surface (406), and the method (200; 300) further comprises a fourth adjustment step (210) for adjusting the position of the measuring beam on the top surface (406) according to the position data.

8. The method (300) according to any one of claims 5 to 7, characterized in that The imaging step (202) and the interference measurement step (106) are performed through corresponding optical paths having a common part (510), and the method also includes synchronizing (302) the imaging step (202) and the interference measurement step (106) by a synchronization unit (602) so that the steps are performed in sequence or one after another.

9. The method (100; 200; 300) according to any one of the preceding claims, characterized in that The diameter of the measurement beam on the top surface (406) is adjusted by varying: - at least one optical element (418, 420) placed between the interferometer (410) and the top surface (406), the at least one optical element being, for example, a lens or a beam expander; - at least one focal length of an optical element (418, 420), such as a lens or a zoom device, placed between the interferometer (410) and the top surface (406); and / or - the numerical aperture of the measuring beam on the top surface.

10. A system (400; 500; 600; 700) for characterizing a structure (404) etched in a substrate (402), such as a wafer, the system (400; 500; 600; 700) comprising: - a low coherence interferometer (410) arranged on the top side of the substrate (402) for measuring at least one depth data related to the depth of the structure (404) using a measuring beam located on the structure (404); - an adjustment unit (424) for adjusting a diameter of the measuring beam at the top surface according to at least one top-CD data related to a width of the HAR structure (404).

11. The system (500; 600; 700) according to the preceding claim, further comprising an imaging unit comprising: - an imaging device (502) arranged on the top side of the substrate (402) for capturing at least one image of the top surface (406) of the substrate (402), and - a processing unit (508) for measuring first data related to a structure (508) from at least one image captured by the imaging device (502).

12. The system (500; 600; 700) according to any one of claims 10 or 11, characterized in that The system (500; 600; 700) further comprises a positioning unit (424, 414, 416) for adjusting the position of the measuring beam on the top surface (406) of the substrate (402).

13. The system (400; 500; 600; 700) according to any one of claims 10 to 12, characterized in that In order to adjust the diameter of the measuring beam on the top surface (406), the adjustment unit includes at least one of the following: - a turntable (422) for changing at least one optical element (418, 420) placed on the path of the measuring beam between the interferometer (410) and the top surface (406), the at least one optical element being, for example, a lens or a beam expander; - an optical element with adjustable focal length, for example a lens or a zoom lens, placed in the path of the measuring beam between the interferometer (410) and the top surface (406); and / or - a beam expander with an adjustable numerical aperture placed in the path of the measuring beam between the interferometer (410) and the top surface (406).

14. The system (600; 700) according to any one of claims 10 to 13, wherein the respective optical paths of the imaging unit and the interferometer (410) have a common part (510), and the system (600; 700) further comprises a synchronization unit (602) so that the imaging unit and the interferometer (410) are used sequentially or one after the other.

15. System (600; 700) according to the preceding claim, characterized in that The synchronization unit includes at least one of the following: - a shutter (640) located between the interferometer (410) and the common part (510) and movable between a first position blocking the passage of the measuring beam and a second position allowing the passage of the measuring beam; - a mirror (512) located between the interferometer (410) and the common part (510) and movable between a first position in which the passage of the measuring beam is deflected away from the structure (404) and a second position in which the measuring beam is deflected towards the structure (404); - a filter, located between the interferometer (410) and the common part (510) and movable between a first position for filtering the measurement beam and a second position for passing the measurement beam, the filter being, for example, a neutral density filter or a spectral filter; - an attenuation device (604), the attenuation device being located between the interferometer (410) and the common optical path portion, the attenuation value of the attenuation device being controllable; - a controller (602) for turning the interferometer light source on and off; - a controller (602) controlling the imaging device and / or the light source to trigger the acquisition of one or more images by the imaging device relative to the pulsed light source of the interferometer (410), so that image acquisition is performed between pulses of the light source.

Images