Method and system for characterizing a structure etched within a substrate

Abstract

The present invention relates to a method (200) for characterizing a structure etched in a substrate such as a wafer, the method (200) comprising, for at least one structure, - at least one interference measurement step (106, 108) carried out using a low coherence interferometer arranged on the upper side of the substrate in order to measure at least one depth data relating to the depth of the HAR structure using a measurement beam, the method (200) also including a first adjustment step (104) for adjusting the diameter of the measurement beam on the upper surface according to at least one upper CD data relating to the width of the HAR structure. 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 within 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 within a substrate, such as a wafer, for example structures etched within 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 within 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 having a narrow width and an elongated length, 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 HAR 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 HAR 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 within a silicon substrate, having a diameter of 2 - 3 μm and a depth of 40 - 50 μm.

[0005] These structures, particularly HAR structures, need to be measured and characterized, for example, by measuring their depth. The document, International Publication No. 2007 / 042676, describes a technique 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 an etched structure, particularly a HAR structure.

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

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

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

[0011] The present invention makes it possible to achieve at least one of these objects by a method for characterizing an etched structure, particularly a high aspect ratio, HAR, structure, in a substrate such as a wafer, said method being carried out with a low-coherence interferometer arranged above the substrate for at least one structure and comprising at least one interferometric measurement step of measuring at least one depth data regarding the depth of the structure using a measurement beam positioned on the structure.

[0012] According to a first aspect of the present invention, the method may also include a first adjustment step for adjusting the diameter of the measurement beam on the upper surface according to at least one upper CD data regarding the width of the structure.

[0013] Thus, according to this first aspect, the present invention proposes to adapt the diameter of the measurement beam to the width of at least one, in particular each, structure or HAR structure according to the upper CD data regarding the structure. The upper CD data represents useful information regarding the width or lateral dimension of the structure on the surface of the substrate. This upper CD or lateral dimension may be, for example, the diameter of a hole or the width of the minimum lateral dimension of a trench. Thus, as an advantageous feature, the present invention proposes to use the upper CD data of the structure to adjust the diameter of the interference measurement beam used for measuring the depth data of the structure. In that way, the interference measurement process can be carried out more quickly, even for structures with small critical dimensions, enabling a more accurate measurement of the depth of the structure. Furthermore, structures and HAR structures having a smaller CD and / or a larger aspect ratio can be efficiently measured.

[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 a silicon through-via (TSV), a trench, and more complex features etched in a support such as a wafer. Some non-limiting examples include TSVs in the form of cylindrical holes having a diameter of 2 - 3 μm and a depth of 40 - 50 μm etched in a silicon substrate.

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

[0017] The method according to the first aspect of the invention proposes, for at least one structure or HAR structure, to adjust the diameter on the upper surface of the substrate of the measurement beam emitted by the interferometer according to the upper CD of said HAR structure. This enables 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 causes 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 within 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 invention according to the first aspect makes it possible to optimize the sensitivity of the interferometric measurement by compensating for the many losses, especially in the HAR structure, and using most of the incident power to obtain a more stable interference signal.

[0018] 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 a TSV or the width of a 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.

[0019] 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.

[0020] This diameter may be adjusted so that at least 75%, or 80%, or 90% of the incident power is coupled to the structure.

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

[0022] 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, as well as HAR structures having a strongly curved bottom, 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.

[0023] Another advantage of adjusting the size of the measurement beam is that it can ensure that, even for an array of structures in close proximity to each other, the measurement beam is sufficiently restricted to cover only one structure, enabling the structures to be characterized individually.

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

[0025] In fact, in some cases, the upper CD data 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 the memory and can be read during the method according to the invention. In these embodiments, since pre-measurement of the upper CD data is not required, the characterization of the HAR structure can be performed more quickly.

[0026] In some cases, at least two, and in particular all, of the structures on the substrate may be identical. In such cases, the upper CD data is read once for at least two of said structures and can be used for each of said at least two structures.

[0027] Alternatively or additionally, at least two, in particular all, of the substrates may have different structures. In such a case, the upper CD data is read out individually for each structure and can be used for said structure.

[0028] 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.

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

[0030] The second adjustment step enables adjustment of the diameter of the measurement beam during the measurement step and, in particular, enables adjustment of the actual state and real-time measurement beam when the measured interference signal indicates that the diameter of the measurement beam does not match the structure being inspected.

[0031] 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 relative to the noise of the measured interference signal, and / or - The value of the depth data provided by the interference signal.

[0032] 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.

[0033] Alternatively or additionally, for example, an optimization process may 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.

[0034] In some embodiments, the method according to the invention may include a third adjustment step for adjusting the position of the measurement beam relative to the structure according to 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 enables the position of the measurement beam to be accurately adjusted during the measurement step, particularly in the actual situation and in real time, so as to optimize the measurement conditions for the depth data of the structure of interest.

[0037] 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, - The amplitude relative to the noise of the measured interference signal, - The value of the depth data provided by the interference signal.

[0038] 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 relative to the structure is not optimal. As a result, the position of the measurement beam can be adjusted.

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

[0040] According to a second aspect of the invention, which can be used alone or in combination with other aspects of the invention, the method according to the invention may further include at least one imaging step including the following steps. - Imaging at least one image of the upper surface using an imaging device disposed on the upper side of the substrate, and - Measuring first data regarding a structure from at least one captured image.

[0041] The first data regarding the structure represents useful information regarding the structure, as will be further explained. As an advantageous feature, the first data, i.e., the information regarding the structure, can be used to adjust a measurement beam for measuring the depth data of the structure. In that way, the interferometric measurement process can be carried out more quickly and enables a more efficient and accurate measurement of the depth of the structure.

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

[0043] In some embodiments, for at least one structure, at least one image captured by an imaging device may be related only to the structure, in which case the captured image contains only information regarding the structure and no information regarding any other structure.

[0044] Alternatively or additionally, at least one image captured by an imaging device may be related to several, in particular all, structures of the substrate, in which case the captured image contains information regarding each of the structures, and as a result, it is possible to determine the first data for each of the structures by processing the captured image. For example, an imaging step of capturing an image of the substrate can be carried out 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 the first data for each HAR structure of the substrate.

[0045] In some embodiments, for at least one structure, the first data regarding the structure may include top CD data that is used during a first adjustment process to adjust the diameter of the measurement beam.

[0046] Thus, the imaging process yields top CD data, which is then used during a first adjustment process to adjust the diameter of the measurement beam.

[0047] Thus, the method according to the present invention enables a quicker and more accurate measurement of the depth of the structure of the substrate when the top CD data of the structure is not known and / or when the substrate includes different structures having different top CDs.

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

[0049] Thus, the imaging process yields data information regarding the position of the structure by processing at least one image captured by the imaging device during the imaging process. Then, the position of the structure on the substrate is used for a quicker and more accurate positioning of the measurement beam so that the measurement of the depth of the structure of the substrate is performed more quickly and accurately compared to known techniques.

[0050] Then, the position of the measurement beam can be further optimized by performing a third adjustment process for positioning the measurement beam with respect to the structure according to at least one characteristic of the interference signal measured by the interferometer as described above. Thus, these fourth and third adjustment processes result in a coarse positioning and a fine positioning of the measurement beam that enable a quick and accurate measurement.

[0051] According to some embodiments, the imaging step and the interferometry step may be performed by respective optical paths having a common portion. In this case, the method according to the invention may also include synchronizing, by a synchronization unit, the imaging step and the interferometry step, whereby the steps are performed continuously or in sequence.

[0052] Such a method enables characterization of structures etched in a substrate with a system that is faster, less bulky, and less expensive than prior art systems. In fact, the imaging step and the interferometry 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] However, above all, synchronization enables the imaging step and the interferometry step to be performed in sequence, so that neither of these steps interferes with the other. In other words, the interferometry step can be performed without disturbances that may be caused by the imaging step. Similarly, the imaging step can be performed without disturbances that the interferometry beam may cause to the imaging step. Thus, the imaging step can perform more accurate imaging and, as a result, determine the first data in a more accurate form. Similarly, the interferometry step can perform more accurate interferometry and, as a result, determine the depth data in a more accurate form.

[0054] Synchronization between the imaging step and the interferometry step can be performed in various ways, either alone or in combination.

[0055] According to some embodiments, synchronization may be performed by controlling the position of a shutter located between the interferometer and the common portion. This shutter can move between: - a closed position that blocks the passage of the measurement beam, and - an open position that permits the passage of the measurement beam. When the imaging process is executed, the shutter can move to the closed position to block the passage of the measurement beam, and the measurement beam does not interfere with the imaging process. After the imaging process is executed, the shutter can move to the open position that permits the passage of the measurement beam so that the interferometry can be executed.

[0056] Alternatively or additionally, synchronization may be performed by controlling the position of a mirror located between the interferometer and the common portion. This mirror can move between: - a closed position that deflects the measurement beam away from the structure being inspected, and - an open position that directs the measurement beam towards the structure. When the imaging process is executed, the mirror can move to the closed position, and the measurement beam is deflected away from the HAR structure or further away from the substrate. After the imaging process is executed, the mirror can move to the open position that deflects the measurement beam towards the structure, and the interferometry can be executed.

[0057] Alternatively, or in addition to at least one of the aforementioned 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 portion. This filter can move between: - a closed position or a strong attenuation position that filters the measurement beam, and - an open position that allows the measurement beam to pass through. 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.

[0058] Alternatively, or in addition to at least one of the aforementioned synchronization options, synchronization may be performed by controlling the attenuation value of an attenuation device located between the interferometer and the common optical path portion, attenuating the measurement beam during the imaging process, and not attenuating the measurement beam otherwise.

[0059] 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 switched off during the imaging process and switched on for the interferometric measurement process.

[0060] Alternatively, or in addition to at least one of the aforementioned synchronization options, synchronization may be performed by triggering the acquisition of an (multiple) image by the imaging device with respect to the pulse 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 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.

[0061] The present invention proposes adjusting the diameter of the measurement beam on the upper surface in the first aspect of the present invention and optionally in the second aspect of the present invention. The adjustment of the diameter of the measurement beam on the upper surface can be carried out in various ways that can be carried out alone or in combination.

[0062] 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 arranged 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.

[0063] Alternatively or additionally, the adjustment of the diameter of the measurement beam on the top 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 top surface. The change in the focal length of the optical element may 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.

[0064] Alternatively, or in addition to at least one of the foregoing options, the adjustment of the diameter of the measurement 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 can be changed by using a beam expander in a collimated beam path or an aperture stop.

[0065] 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 being disposed above the substrate and using a measurement beam positioned on the structure to measure at least one depth data regarding the depth of the structure, particularly the HAR structure, with a low coherence interferometer.

[0066] According to a first aspect of the present invention, the system according to the present invention may also comprise an adjustment unit for adjusting the diameter on the top surface of the measurement beam according to at least one upper CD data regarding the width of the structure.

[0067] As described above, in some embodiments, for at least one structure, the upper CD data may be pre-known data. In this case, the system according to the present invention may comprise a memory for storing the upper CD data.

[0068] The memory may be a local memory or a remote memory.

[0069] The memory may or may not be a removable memory.

[0070] The memory may be a volatile medium or a permanent medium.

[0071] The upper CD data may be stored as numerical values in a data file in any format in a volatile memory, a non-volatile memory, or a permanent storage medium.

[0072] The memory may be integrated with an interferometer, or an adjustment unit, or another device of the system, or may be a stand-alone component belonging to the system.

[0073] According to a second aspect of the present invention, the system according to the present invention may also include an imaging unit. The imaging unit can include the following. - An imaging device disposed 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 from at least one image captured by the imaging device.

[0074] The imaging unit can be configured to perform the imaging process as described above.

[0075] Regarding at least one structure, the imaging unit may provide first data including or consisting of the upper CD data of the structure.

[0076] Regarding at least one structure, the imaging unit may provide first data including or consisting of position data regarding positions on the upper surface of the structure.

[0077] In some embodiments, the system according to the present invention may also include a positioning unit for adjusting the position of the measurement beam on the upper surface of the substrate.

[0078] The position of the measurement beam can be adjusted according to position data. This position data can be the following or can include the following. - For example, a predetermined value stored in a memory, - Position data provided by an imaging unit for at least one structure.

[0079] Alternatively or additionally, the position of the measurement beam may be adjusted according to at least one characteristic of the interference signal measured by an interferometer, as described above.

[0080] The positioning unit may comprise a holder for the substrate and / or a holder for the interferometer.

[0081] The positioning unit can adjust the position on the upper surface of the measurement beam by the following. - Moving the interferometer relative to the substrate and / or - Moving the substrate relative to the interferometer.

[0082] In some embodiments, to adjust the diameter on the upper surface of the measurement beam, the adjustment unit can comprise at least one of 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 or a zoom lens with an adjustable focal length 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.

[0083] In some embodiments, the optical paths of the imaging unit and the interferometer may each have a common portion. In this case, the system according to the invention may also comprise a synchronization unit so that the imaging unit and the interferometer are used continuously or in sequence.

[0084] To synchronize the imaging unit and the interferometer, the synchronization unit can include at least one of the following. - A shutter that is disposed between the interferometer and the common portion and is 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 that is disposed between the interferometer and the common portion and is 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 that is disposed between the interferometer and the common portion and is movable between a first position that filters the measurement beam to block or strongly attenuate the measurement beam and a second position that permits the measurement beam to pass through. - An attenuation device such as an electro-optic attenuator that is disposed between the interferometer and the common optical path portion and has a controllable attenuation value. - A controller that switches the interferometer light source on and off. - A controller that controls the imaging device and / or the light source so as to trigger the acquisition of an image by the imaging device with respect to the pulse of the pulsed light source of the interferometer such that image acquisition is performed between the pulses of the pulsed light source of the interferometer.

[0085] In some embodiments, the imaging unit can include a light source and a camera, optionally combined with a microscope optical device.

[0086] 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 fiber.

[0087] 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 optical path difference between two beams to be varied. When the optical path difference between the beams reflected respectively at the top and bottom of the structure, or between each of these beams and a reference beam, is reproduced by the delay line, interference bursts 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 said optical path difference.

[0088] 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 respectively 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 said optical path difference.

[0089] The interferometer 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, using this, the depth of the structure.

[0090] 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 upon examination of the detailed description of non-limiting embodiments and the accompanying drawings.

Brief Description of the Drawings

[0091]

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Mode for Carrying Out the Invention

[0092] It should be fully understood that the embodiments described below are in no way limiting. In particular, it is possible to envision variants 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.

[0093] In the figures, elements common to each figure retain the same reference numerals.

[0094] FIG. 1 is an illustration of a non-limiting example of a method according to the present invention.

[0095] The method 100 shown in FIG. 1 can be used to characterize structures etched in a substrate such as a wafer, particularly structures with a high aspect ratio, HAR. More specifically, the depth of a structure etched in a substrate can be measured using the method 100 of FIG. 1.

[0096] Method 100 includes a step 102 of reading out pre-known upper CD data from a memory for at least one structure. The upper CD data is data regarding the width of the structure, more specifically the upper side of the structure, i.e., the width of the structure on the upper surface of the substrate. For example, the upper CD data may be determined during the design or manufacture of the substrate and stored in the memory.

[0097] In some cases, at least two, particularly all, of the structures on the substrate may be the same. In such a case, the upper CD data is read out once for the structure and can be used for each of the structures in an interferometric measurement step for measuring depth data for each of the structures, i.e., during several repetitions.

[0098] In some cases, at least two, particularly all, of the structures on the substrate may be different. In such a case, the upper CD data can be read out individually for each of the structures.

[0099] Advantageously, method 100 includes a step 104 of adjusting the diameter of a measurement beam used for interferometric measurement of depth data according to the upper CD data on the upper surface of the substrate. The diameter of the measurement beam is adjusted to ensure that the measurement beam enters the structure and reaches the bottom of the structure with sufficient power, particularly for HAR structures, for measuring the depth of the structure.

[0100] After the adjustment step 104, method 100 includes an interferometric measurement step 106 for at least one structure, during which depth data regarding the depth of the structure is measured by an optical interference method.

[0101] Interferometric measurements are 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 of which yields depth data.

[0102] The measurement step 106 includes, as described above, at least one interferometric measurement 108 that provides a measurement signal. This measurement signal can then be processed to obtain depth data.

[0103] The method 100 may optionally include a second adjustment step 110 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 106. This second adjustment step 110 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, 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 provided by the interference signal.

[0104] 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 fit the structure being inspected. As a result, as described later, the diameter of the measurement beam can be adjusted. This step may be repeatedly iterated, for example, using 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.

[0105] Method 100 may optionally include a third adjustment step 112 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 106. This third adjustment step 120 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 depth value brought about by the interference signal.

[0106] 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 relative to the structure is not optimal. As a result, as described later, the position of the measurement beam relative to the structure can be adjusted. This step may be repeatedly iterated using, for example, a gradient-based algorithm to find the position of the measurement beam at which at least one characteristic of the measured interference signal is optimized or reaches a local extremum.

[0107] The second adjustment step 110 and the third adjustment step 112 may be executed simultaneously or in any order sequentially. Alternatively, only one of these may be executed, or neither may be executed. After at least one of these steps is executed, at least one another interference measurement 108 may be executed. In that way, steps 108 and 110, 120 can be repeated until the interference measurement is successful.

[0108] FIG. 2 is an illustration of another non-limiting example of the method according to the present invention.

[0109] 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, the depth of a structure etched in a substrate can be measured using the method 200 of FIG. 2.

[0110] The method 200 includes an imaging step 202 of the substrate.

[0111] The imaging step 202 includes a step 204 for imaging at least one image of the upper surface of the substrate, for example, by an imaging unit. The imaging unit 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 of the substrate.

[0112] Next, the captured image can be processed in a processing step 206 to identify position data related to the position of at least one structure visible in the captured image. The processing of the image to determine the position data can be performed by generally known image processing methods, for example, using segmentation, pattern recognition, or blob analysis algorithms.

[0113] The captured image can be processed in a processing step 208 to identify upper CD data related to at least one structure visible on the captured image. The processing of the image to determine the upper 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.

[0114] In some embodiments, only one of processing steps 206 and 208 may be performed. In some embodiments, both processing steps 206 and 208 may be performed. In the latter case, processing steps 206 and 208 may be performed during a single processing step.

[0115] Method 200 may include any step 210 for adjusting the position on the upper surface of the measurement beam according to the position data determined in step 206 so that the measurement beam is accurately positioned on the structure being characterized.

[0116] The position of the measurement beam on the upper surface can be adjusted by a positioning unit. The positioning unit can comprise the following. - A displacement stage for the interferometer and optionally the imaging unit, 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 unit.

[0117] Here too, since steps 206 and 210 are optional, in some embodiments, the method according to the invention may not include these steps.

[0118] If method 200 includes any step 208 for determining upper CD data of the structure being characterized, the upper CD data can be used during step 104 to adjust the diameter of the measurement beam on the surface of the substrate. Thus, step 102 for reading the upper CD data may not be performed.

[0119] If method 200 does not include any step 208 for determining upper CD data of the structure being characterized, method 200 can include step 102 for reading the upper CD data as described above for the structure.

[0120] Method 200 of FIG. 2 further includes steps 104 and 106 described above with reference to FIG. 1. In particular, this may include a step 112 of positioning the measurement beam according to the measurement signal, which is also executed by the positioning unit. This positioning step 120 may be executed after a step 210 of adjusting the position of the measurement beam according to the position data in order to improve or optimize the positioning. This may also be executed without step 210, for example, by using predefined or pre-stored position data.

[0121] FIG. 3 is an illustration of another non-limiting example of a method according to the present invention.

[0122] The method 300 shown in FIG. 3 can be used to characterize structures etched in a substrate such as a wafer, particularly HAR structures. More specifically, using the method 300 of FIG. 3, the depth of a structure etched in a substrate can be measured.

[0123] Method 300 includes the steps described with reference to method 200 of FIG. 2.

[0124] Method 300 further includes a synchronization step 302, whereby the imaging step 204 and the interferometric measurement step 108 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 capturing step 204 is executed. This is particularly important when the image capturing step and the interferometric measurement step are executed using respective optical paths having a common portion.

[0125] 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 capturing step 204, 〇 A second position that allows the passage of the measurement beam during at least the interferometric measurement step 108, - Controlling the position of the mirror located between the interferometer and the common part as follows, 〇 A first position that deflects the path of the measurement beam away from the upper surface during the image capturing step 204, 〇 A second position that deflects the measurement beam towards the upper surface during at least the interference measurement step 108, - Controlling the position of the optical density filter or spectral filter located between the interferometer and the common part as follows, 〇 A first position that filters or attenuates most of the measurement beam during the image capturing step 204, and 〇 A second position that allows the measurement beam to pass through during at least the interference measurement step 108, - Controlling the attenuation value of the attenuation device located between the interferometer and the common part as follows, 〇 During the image capturing step 204, the measurement beam does not pass through the common part at least excessively, and 〇 During at least the interference measurement step 108, 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 during at least the interference measurement step 108, - Triggering the imaging of the (multiple) images by the imaging unit 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.

[0126] Thus, in the method 300 of FIG. 3, the upper surface, or at least the image of the structure, is imaged by the imaging unit without interference from the measurement beam emitted by the interferometer.

[0127] FIG. 4a is an illustration of a non - limiting example of a system according to the present invention.

[0128] The system 400 shown in FIG. 4a 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.

[0129] The system 400 can be used to perform the method according to the present invention, particularly the method 100 of FIG. 1.

[0130] As shown in FIG. 4a, the system 400 is used to characterize structures etched in a substrate 402, such as a wafer, particularly HAR structures. Only one structure 404 is depicted in FIG. 4a for ease of understanding. Of course, the substrate may include two or more structures. The structure 404 may be, for example, a trench etched into the substrate 402 from the upper surface 406 of the substrate 402. The substrate 402 also has a bottom surface 408 opposite the upper surface.

[0131] FIG. 4b shows the information to be measured in the structure 404 etched in the substrate 402, which is namely the depth 450 and optionally the upper CD 452. In the illustrated example, the structure 404 may be, for example, a hole or a TSV, and the upper CD data 452 may represent the diameter at the upper surface 406. The structure 404 may also be an elongated trench, and the upper CD 452 may be its minimum lateral dimension, or its width at the upper surface 406.

[0132] The system comprises a low-coherence interferometer 410 disposed on the side of the upper surface 406 of the substrate 402. The low-coherence interferometer 410 is used to characterize each structure of the substrate, and more particularly to measure at least one data regarding the depth of the structure 404, and even more particularly to measure the depth of the structure 404.

[0133] The interferometer 410 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 optical path difference between two beams to be varied. When the optical path difference between the beams reflected respectively at the top and bottom of the structure 404, 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 404 is derived from said optical path difference.

[0134] 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 respectively by the top and bottom of the structure 404 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 404 is derived from said optical path difference.

[0135] 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 404.

[0136] The interferometer 410 may be, for example, similar to that described in WO 2007 / 042676.

[0137] Optionally but preferably, the measurement beam emitted by the interferometer 410 and the reflected light received from the substrate 402 may be transmitted to and received from the interferometer 410 using a single-mode fiber 412 coupled to the interferometer 410.

[0138] To measure narrow structures such as TSVs having a high aspect ratio (HAR) and a diameter smaller than 5 μm, the measurement light source may emit light in the visible spectrum range, for example, less than 900 nm, for better propagation into the structure.

[0139] System 400 also includes a holder 414, such as a wafer chuck, coupled to displacement means 416, such as a translation and / or rotation stage, to move and position the substrate 402 in the X-Y directions and optionally in the Z direction.

[0140] System 400 also includes means for adjusting the diameter of the measurement beam on the upper surface 406 of the substrate of the measurement beam emitted by the interferometer 410 to adjust the diameter of the measurement beam with respect to the structure under inspection.

[0141] In the example shown in FIG. 4a, the diameter of the measurement beam can be determined by the core of the fiber 412 or the mode field diameter of the light exiting the fiber, and the magnification provided by the combination of the collimator lens 418 and the front lens 420, such as a microscope objective lens. Thus, at least one of these lenses 418-420 can be changed to change the magnification and thereby adjust the diameter of the measurement beam on the upper surface 406.

[0142] System 400 includes a turret 422 for changing at least one of the lenses 418-420 and / or for changing the focal length of one of the lenses 418-420 and thereby changing the magnification accordingly.

[0143] System 400 may also include a beam expander (not shown) in the portion where the measurement beam is collimated, such as between the collimator lens 418 and the front lens 420. The beam expander changes the beam diameter and thus the numerical aperture (NA) at which the beam is focused. Thereby, the diameter of the measurement beam on the upper surface 406 is ultimately determined.

[0144] System 400 includes a control unit 424 for controlling means for adjusting the diameter of a measurement beam. In the illustrated example, control unit 424 is configured to control turret 422 to change at least one of lenses 418 - 420 in order to adjust the diameter of the measurement beam and obtain a desired diameter of the measurement beam on top surface 406.

[0145] In system 400 shown in FIG. 4a, the adjustment of the diameter of the measurement beam on the top surface can be performed according to previously known top CD data regarding structure 404 being characterized.

[0146] The previously known top CD data may or may not be part of system 400 and is stored in memory 426. Thus, control unit 424 reads the top CD data of structure 404 from memory 426 to adjust the diameter of the measurement beam emitted by interferometer 410 and obtain a desired beam diameter on top surface 406, optionally calculates the desired beam diameter of the measurement beam, or selects front lenses 418 - 420 according to a predefined recipe, and controls turret 422 to ensure that the appropriate lens is placed on the measurement beam.

[0147] Alternatively or additionally, the measurement beam diameter on the top surface may also be adjusted according to at least one characteristic of the signal measured by the interferometer.

[0148] Such an adjustment of the diameter of the measurement beam may be performed during the interferometric measurement, especially enabling real - time adjustment of the measurement beam in an actual situation when the measured interference signal indicates that the diameter of the measurement beam does not match structure 404 where the diameter is being measured.

[0149] At least one characteristic of the measurement signal that can be used to adjust the diameter of the measurement beam on top 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 interference fringes, or the modulation depth, or the spectral modulation of the measured interference signal, and / or - 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.

[0150] To do this, the interferometer 410 may be configured to measure the value of the characteristic of the measurement signal and compare the value with an assumed value or a previous value in an iterative process, or may include a module 428 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 424 to adjust the beam diameter by the turret 422 and / or the beam expander, as described above.

[0151] FIG. 5 is an illustration of another non-limiting example of a system according to the present invention.

[0152] The system 500 of FIG. 5 can be used to execute any one of the methods according to the present invention, particularly the method 100, 200, or 300 of FIGS. 1, 2, or 3.

[0153] The system 500 includes all the components of the system 400.

[0154] The system 500 further includes an imaging device for imaging at least one image of the substrate 402, more specifically, the upper surface 406 of the substrate 402, and processing the at least one imaged image to determine at least one first data about at least one HAR structure of the substrate 402.

[0155] The imaging device is arranged on the same side as the interferometer 410, that is, on the side of the upper surface 406 of the substrate 402.

[0156] In the non-limiting example shown in FIG. 5, the imaging device comprises a camera 502 and optionally a light source 504. The imaging device may also comprise a front lens 420 and a tube lens 506 for imaging the upper surface 406 of the substrate 402 with the camera 502.

[0157] The camera 502 is configured to image / acquire at least one image of the upper surface 406 of the substrate 402 comprising at least one HAR structure etched in the substrate. The captured image is processed by standard image processing techniques executed by a processing module 508 to measure first data regarding the at least one structure or HAR structure. The processing module can include a hardware module such as a processor or chip, or a software module such as a computer program.

[0158] For the at least one structure or HAR structure, the first data may include the position of the structure on the upper surface 406. In this case, the position of the structure can be transmitted to a control unit 424 to command / control the holder 414 and / or the stage 416 to accurately position the measurement beam emitted by the interferometer 410 onto the structure.

[0159] Alternatively or additionally, for the at least one structure or 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 424 to command / control the turret 422 to adjust the diameter on the upper surface 406 of the measurement beam emitted by the interferometer as described above. In this case, the system 500 may not comprise a memory 426 and the top CD may not be pre-known data.

[0160] As shown in FIG. 5, the interferometer 410 and the imaging device operate in respective optical paths having a common portion 510. In the example shown, this common portion 510 of the optical path starts at the plane of the mirror 512, and the mirror 512 is, - Reflect the measurement beam coming from the interferometer 410 towards the substrate 402 and reflect the reflected beam coming from the substrate towards the interferometer 410. - Pass the imaging light coming from the light source 504 towards the substrate 402 and pass the reflected imaging light coming from the substrate 402 towards the camera 502.

[0161] In the example of FIG. 5, the common portion 510 of the optical path includes the front lens 420.

[0162] FIG. 6 is an illustration of another non - limiting example of a system according to the present invention.

[0163] The system 600 shown in FIG. 6 includes all the components of the system 500 of FIG. 5 except for the memory 426.

[0164] In the system 600, the first data provided by the processing module 508 is assumed to include the top CD and / or position of the structure being characterized.

[0165] As also shown in FIGS. 6 and 5, the interferometer 410 and the imaging device operate in a common optical path portion 510. 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 cause blurring of the camera. At the same time, the imaging light may interfere with the interferometric measurements performed using the interferometer 410. Therefore, it can be advantageous to synchronize the interferometer 410 and the imaging device in order to perform the (multiple) interferometric measurements and the acquisition of the (multiple) images continuously or sequentially, more generally not simultaneously.

[0166] For this purpose, the system 600 includes a synchronization controller 602 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.

[0167] In the illustrated example, the synchronization controller 602 is configured to trigger the camera 502 between two pulses of a pulse beam source (not shown) of the interferometer 410, or to trigger the pulse light source during image acquisition by the camera, or to command both. Thus, the camera 502 captures or acquires at least one image when the measurement beam is not being emitted by the interferometer 410.

[0168] Alternatively or additionally, the mirror 512 may be controllably movable, particularly rotatable, and the synchronization controller 602 may be configured to command the position of the mirror. More specifically, the mirror 512 can be controllably rotated between. - A first position that deflects the measurement beam away from the structure or upper surface 406 being characterized, and - A second position that directs the measurement beam towards the structure or upper surface 406. When the imaging process is executed, the synchronization controller 602 commands the mirror to be in the first position, i.e., the measurement beam is deflected away from the structure, and the (plural) images can be captured by the camera. After the imaging process is executed, the synchronization controller 602 commands the mirror to be in the second position, i.e., the measurement beam is directed towards the structure and an interference measurement can be performed.

[0169] Alternatively or additionally, the system may include a controllable shutter 604 disposed between the interferometer 410 and the mirror 512 in the illustrated example. The synchronization controller 602 may be configured to command the position of the controllable shutter 604. This shutter 604 can be made controllable between. - A "closed" position that blocks the passage of the measurement beam coming from the interferometer, 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 604 can be commanded to a closed position that blocks the passage of the measurement beam. After the imaging process is executed, the shutter can be commanded to an open position that permits the passage of the measurement beam so that interferometry can be performed.

[0170] Alternatively or additionally, the system may include a movable optical filter 604, such as a neutral density filter or a spectral filter, attached to, for example, a filter wheel, and is arranged between the interferometer 410 and the mirror 512 in the illustrated example. The synchronization controller 602 may be configured to command the position of the movable optical filter 604 within the filter wheel. The position of this optical filter 604 can be controllable between the following. - A "closed" position that filters 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 movable optical filter 604 can be arranged to enter a closed position that blocks the passage of the measurement beam. After the imaging process is executed, the movable optical filter 604 can be commanded to move to an open position that permits the passage of the measurement beam so that interferometry can be performed.

[0171] Naturally, instead of or in combination with the synchronization means described with reference to FIG. 6, other synchronization means as further described above may be used.

[0172] FIG. 7 is an illustration of another non-limiting example of a system according to the present invention.

[0173] The system 700 shown in FIG. 7 includes all the components of the system 600 of FIG. 6 except for the turret 422.

[0174] In the system 700, the diameter of the measurement beam is not adjusted.

[0175] The first data provided by the imaging device, more specifically by the processing module 508, relates to the position of the structure. The position data is used by the control unit 424 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.

[0176] The system 700, on the other hand, comprises a synchronization controller 602 that controls the camera in relation to the pulse source of the interferometer and / or the mirror 512 and / or the shutter 604 so that imaging and interferometry are performed in sequence.

[0177] Of course, the present invention is not limited to the examples detailed above.

Claims

1. A method (100, 200, 300) for characterizing a structure (404) etched in a substrate (402) such as a wafer, said method (100, 200, 300) comprising, for at least one structure (404), - at least one interference measurement step (106, 108) carried out using a low coherence interferometer (410) arranged on the upper side (406) of said substrate (402) to measure at least one depth data regarding the depth of said structure (404) using a measurement beam positioned on said structure (404), said method (100, 200, 300) also including a first adjustment step (104) for adjusting the diameter of said measurement beam on said upper surface (406) according to at least one upper CD data regarding the width of said structure (404), method (100, 200, 300).

2. Characterized in that, for at least one structure (404), said upper CD data is pre-known data, and said method (100, 200) includes a step (102) of reading said upper CD data in a memory (426) before said first adjustment step (104), the method (100, 200, 300) according to Claim 1.

3. The method (100, 200, 300) according to Claim 1 or 2, further including a second adjustment step (110) for adjusting the diameter of said measurement beam according to at least one characteristic of the interference signal measured by said interferometer (410).

4. The method (100, 200, 300) according to any one of Claims 1 to 3, further including a third adjustment step (112) for adjusting the position of said measurement beam relative to said structure according to at least one characteristic of the interference signal measured by said interferometer (410).

5. - imaging at least one image of said upper surface (406) using an imaging device (502) arranged on the upper side of said substrate (402) (204), and - measuring first data regarding a structure (404) from at least one imaged image (206, 208) The method (200, 300) according to any one of Claims 1 to 4, further including at least one imaging step (202) including.

6. For at least one structure (404), the first data includes the upper CD data used during the first adjustment step (104) for adjusting the diameter of the measurement beam, the method (200, 300) according to claim 5.

7. For at least one structure (404), the first data includes position data regarding the position of the structure (404) on the upper surface (406), and the method (200, 300) further includes a fourth adjustment step (210) for adjusting the position of the measurement beam on the upper surface (406) according to the position data, the method (200, 300) according to claim 5 or 6.

8. The imaging step (202) and the interferometric measurement step (106) are performed through respective optical paths having a common portion (510), and the method further includes synchronization (302) of the steps by a synchronization unit (602) such that the imaging step (202) and the interferometric measurement step (106) are performed continuously or in sequence, the method (300) according to any one of claims 5 to 7.

9. The diameter of the measurement beam on the upper surface (406) is - at least one optical element (418, 420) such as a lens or a beam expander disposed between the interferometer (410) and the upper surface (406), - at least one focal length of an optical element (418, 420) such as a lens or a zoom device disposed between the interferometer (410) and the upper surface (406), and / or - the numerical aperture of the measurement beam on the upper surface, Adjusted by changing, the method (100, 200, 300) according to any one of claims 1 to 8.

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) is - A low coherence interferometer (410) disposed above the substrate (402) for measuring at least one depth data regarding the depth of the structure (404) using a measurement beam positioned on the structure (404), - An adjustment unit (424) for adjusting the diameter on the upper surface of the measurement beam according to at least one upper CD data regarding the width of the HAR structure (404), A system (400, 500, 600, 700) comprising the same. **Claim 11** Further comprising an imaging unit, wherein the imaging unit - An imaging device (502) disposed on the upper side of the substrate (402) for imaging at least one image of the upper surface (406) of the substrate (402), and - A processing unit (508) for measuring first data regarding the structure (508) from at least one image captured by the imaging device (502), The system (500, 600, 700) according to claim 10, comprising the same. **Claim 12** The system (500, 600, 700) further comprising a positioning unit (424, 414, 416) for adjusting the position on the upper surface (406) of the substrate (402) of the measurement beam, characterized in that, the system (500, 600, 700) according to claim 10 or 11. **Claim 13** In order to adjust the diameter on the upper surface (406) of the measurement beam, the adjustment unit - A turret (422) for changing at least one optical element (418, 420) such as a lens or a beam expander disposed on the path of the measurement beam between the interferometer (410) and the upper surface (406), - An optical element such as a lens or a zoom lens with an adjustable focal length disposed on the path of the measurement beam between the interferometer (410) and the upper surface (406), and / or - A beam expander with an adjustable numerical aperture disposed on the path of the measurement beam between the interferometer (410) and the upper surface (406) The system (400, 500, 600, 700) according to any one of claims 10 to 12, characterized in that it comprises at least one of the above. **Claim 14** Each optical path of the imaging unit and the interferometer (410) has a common part (510), and the system (600, 700) further comprises a synchronization unit (602) such that the imaging unit and the interferometer (410) are used continuously or in sequence, the system (600, 700) according to any one of claims 10 to 13. **Claim 15** The synchronization unit - A shutter (604) disposed between the interferometer (410) and the common portion (510), 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 (512) disposed between the interferometer (410) and the common portion (510), movable between a first position that deflects the path of the measurement beam away from the structure (404) and a second position that deflects the measurement beam toward the structure (404). - An optical filter such as a neutral density filter or a spectral filter, disposed between the interferometer (410) and the common portion (510), 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 (604) disposed between the interferometer (410) and the common optical path portion, whose attenuation value is controllable. - A controller (602) that switches the interferometer light source on and off. - A controller (602) that controls the imaging device and / or the light source so as to trigger the acquisition of an image by the imaging device with respect to the pulse of the pulsed light source such that the image acquisition is performed between the pulses of the pulsed light source of the interferometer (410). The system (600, 700) according to claim 14, characterized by comprising at least one of the above.

Images