Method for adjusting a device for measuring interfaces of an element

Abstract

The invention relates to a method (100) for adjusting an interferometry system comprising a measurement head that can be moved in space relative to an element to be characterised, the element to be characterised being a semiconductor object comprising one or more chips and at least one composite layer for moulding at least some of the chips, and the measurement head being configured to emit an optical measurement beam capable of illuminating the element to be characterised, in particular an optical element.

Description

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

[0001] The present invention relates to a method for adjusting a device for measuring the thickness of a layer of molding composite of an element to be characterized, comprising one or more chips and one or more layers of molding composite of at least one of said chips. It also relates to a device implementing such a method. Prior art

[0002] During the manufacture of elements to be characterized, comprising one or more chips and one or more layers of molding composite of at least one of said chips, it may be necessary to control or measure the thicknesses of said layers or the positions of constituent elements, or even the spaces between constituent elements, along a measurement axis, during the molding process and possibly after the molding process.

[0003] One method known for this is the use of low-coherence interferometry techniques. A measurement optical beam from a broad-spectrum optical source is propagated through the surfaces of the chip molding composite layers. The beam reflections from these surfaces are collected and analyzed by interfering with each other and / or with a reference beam to determine the differences in optical path lengths between interfering beams, and from this, the positions and / or distances between corresponding surfaces or interfaces can be deduced. This allows, for example, the determination of the thicknesses of the chip molding composite layers.

[0004] Such measurement techniques generally operate using retroreflection. This requires that the optical measurement beam be incident on all surfaces to be characterized at a normal or perpendicular angle, so as to generate a reflected wave that can be detected by the measurement system. Therefore, an effective optical measurement beam alignment procedure is necessary. In practice, it is essential to be able to position the measurement beam relative to the optical axis of an assembly with an accuracy, for example, on the order of a micron for objects several millimeters in size. A method for achieving this level of performance is therefore required.

[0005] These issues arise in the context of molding a semiconductor sample, such as a wafer. The molding process involves depositing a molding composite onto the chip(s) to be molded. The molding composite layer is then thinned, for example, in several passes, to expose the top surface of the chips and the electrical connectors located above them. It is necessary to monitor the molding composite layer during the molding process, and particularly during the thinning of this composite layer, for example, to control its remaining thickness.

[0006] It may also be necessary to check the composite layer, and in particular the integrity of said composite layer, during operations carried out after the chip molding process.

[0007] The aim of the present invention is to resolve at least one of the aforementioned drawbacks.

[0008] Another objective of the invention is to provide a method for finding an optimal measurement position for the measurement beam. Description of the invention

[0009] At least one of these goals is achieved with a method for adjusting an interferometry system comprising a measuring head movable in space relative to an element to be characterized and configured to emit a measurement optical beam suitable for illuminating said element to be characterized, said element to be characterized being a semiconductor object comprising one or more chips and at least one layer of molding composite of at least a part of said chips, the interferometry system being configured for the inspection and / or characterization, and in particular the determination of the thickness, of one of the molding composite layers, the method comprising repeating the following steps until a stopping criterion is satisfied: a) select a scan position from among scan positions of a provided current scan grid, b) move the measuring head to the selected scan position, c) perform measurements from a measurement signal relating to the beams reflected or transmitted by the element when illuminated by the optical beam, and determine a quality factor associated with the scan position from the measurement signal.

[0010] The process allows for an exhaustive scan of a grid to find one or more optimal positions. From these measurements, it is possible to determine one or more of the most relevant points for taking, or considering, measurements based on a selection criterion, such as a quality factor. These measurements can be taken from those already performed during the grid scan and / or repeated, in a similar or different manner, in a subsequent phase, at the position(s) of the most relevant point(s).

[0011] In one embodiment, a reference position of the current scanning grid can be recalibrated to a predetermined position. For example, the predetermined position can be close to, or included within, an area where the quality factor is maximized or greater than a threshold. The reference position of the current scanning grid can be a central position of the current scanning grid, that is, located in the middle of the current scanning grid. Thus, the method ensures scanning completeness in an area around the measurement optimum.

[0012] According to a particular embodiment, a first scanning grid with a first spacing between scanning positions and a second scanning grid with a second spacing between scanning positions may be provided. The first spacing may be smaller than the second spacing. In this case, the process may include: i) selecting the current grid as the second grid, and repeating steps a) to c) until the quality factor reaches a first threshold, ii) select the current grid as the first grid and the second grid as a previous grid, re-align a reference position of the current grid to the scan position of the previous grid for which the first threshold is reached, and repeat steps a) to c) with the current grid until the stopping criterion is satisfied.

[0013] This allows for faster scanning of a relatively large area for positioning the measuring head. Furthermore, using multiple grids with varying spacing between positions makes it possible to start from a poorly defined point, or even one not returning a measurement signal, to determine the optimal measurement position while keeping the total setup time quite short. Therefore, it is not necessary to know a measurement area where the measurement signal is optimal beforehand.

[0014] The second spacing can be greater than or equal to twice the first spacing.

[0015] The second scanning grid can be scanned randomly by selecting the scanning position in step a). Alternatively, or in addition, the second scanning grid can be scanned according to a pre-established path pattern or according to the quality factor determined for the previously scanned positions.

[0016] Of course, it is possible to provide more than two scanning grids with different spacings between scanning positions. The process may include scanning the grids consecutively in descending order of their spacings; in other words, by scanning the grid with the widest spacing until the quality factor reaches a threshold, then scanning a grid with a narrower spacing, and so on. For example, a third scanning grid may be provided. This third scanning grid may have a spacing between its scanning positions that is smaller than the second spacing and larger than the first spacing. In this case, the process may include: i) select the current grid as the second grid, and repeat steps a) to c) until the quality factor reaches a first threshold, ii) select the current grid as the third grid and the second grid as the previous grid, re-align a reference position of the current grid to the scan position of the previous grid for which the first threshold is reached, and repeat steps a) to c) with the current grid until the quality factor reaches a second threshold, and iii) select the current grid as the first grid and the third grid as the previous grid, re-align a reference position of the current grid to the scan position of the previous grid for which the second threshold is reached, and repeat steps a) to c) with the current grid until the stopping criterion is satisfied.

[0017] In the examples above, the first grid may correspond to a fine-pitch grid and the second grid to a coarse-pitch grid, while the third grid may correspond to a medium-pitch grid.

[0018] Alternatively, if the stopping criterion is not met with the first grid, the procedure may include: returning to step i) by continuing the sweep of the second grid to the position where the first threshold is reached, or returning to step ii) by continuing the sweep of the third grid to the position where the second threshold is reached.

[0019] Thus, large-step and medium-step grids could continue to be swept after the threshold is reached, but with a systematic exploration of points around the area that triggered the threshold higher than the first threshold, or higher than the second threshold.

[0020] For example, the stopping criterion can be met when the determined quality factor exceeds a stopping threshold. In this case, the interferometry system adjustment is stopped when sufficient quality is achieved. This saves adjustment time.

[0021] According to another embodiment, the stopping criterion can be satisfied when the quality factor is determined for each of the scanning positions of the current scanning grid.

[0022] The process may include a step of selecting at least one optimal measurement position carried out after the stopping criterion is satisfied.

[0023] In particular, the step of selecting at least one optimal measurement position may depend on the quality factor and / or measurement noise. An optimal position may be one for which the quality factor is greater than a threshold. Alternatively, or in addition, an optimal position may be one for which the measurement noise is minimized or less than a threshold.

[0024] In one embodiment, the step of selecting at least one optimal measurement position may include interpolating the determined quality factors. Then, at least one optimal measurement position may be chosen at the maximum or minimum point of said interpolation. The optimal position may be chosen as the one whose interpolation yields an optimum. Several optimal positions may be chosen on and / or near this optimal position of the interpolation.

[0025] Each scanning grid can be a matrix of integer coordinate scanning positions contained within a predetermined area, for example of a square or circular shape.

[0026] According to one embodiment, the selection of the scanning position in step a) can be carried out so as to scan the predetermined area, for example according to a spiral scan or in parallel lines or in a zig-zag pattern, etc.

[0027] The process may include the following steps: i) repeat steps a) to c) for a sweep of the predetermined area along a first direction of traversal of the predetermined area until the quality factor reaches an optimal value, ii) repeat steps a) to c) for a scan of the predetermined area in a second direction of traversal of the predetermined area different from the first direction, until the quality factor reaches an optimal value, steps i) and ii) being repeated as long as the value of the quality factor remains increasing, or in the optimum direction.

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

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

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

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

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

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

[0032] In this document, "item to be characterized" means a sample, such as a wafer or semiconductor object or panel, comprising one or more chips and at least one layer of molding composite of at least one of said chips, deposited on said sample.

[0033] The molding composite can be of any shape / composition. Following a non-limiting example, the molding composite can, for example, be in the form of an epoxy filled with thermal expansion control elements, such as silica beads.

[0034] According to another aspect, a device is proposed for measuring the thickness of a molding composite layer of an element to be characterized, said element to be characterized being a semiconductor object comprising one or more chips and at least one molding composite layer of at least a part of said chips, the device comprising: -an imaging channel configured to produce a beam of illumination, and comprising imaging means configured to acquire images of the element to be characterized illuminated by said beam of illumination within a field of view of the imaging means, -a measuring head comprising a measuring channel configured to produce a measuring beam at a determined position relative to said field of view and comprising an optical distance sensor configured to produce distance and / or thickness measurements, -Measures for moving the measuring head configured to move the measuring head relative to the element to be characterized, and -a processing module configured to handle distance and / or thickness measurements, and images, the processing module being configured to implement the process as described above.

[0035] The means for moving the measuring head can be replaced by means for moving the element to be characterized.

[0036] The means of moving the measuring head and / or the element to be characterized can be configured to move the measuring beam relative to the element to be characterized in space in translation along the XYZ direction and / or in rotation.

[0037] The present invention is used for the adjustment of an inspection system for a composite layer of chip molding of a semiconductor object, or sample.

[0038] In particular, the invention allows the adjustment of a system to measure the thickness of said composite layer, during the molding of chip(s) of the sample with the molding composite, that is to say after deposition of said molding composite and / or during the thinning of the composite layer.

[0039] In particular, the invention allows the adjustment of a system to control said molding composite layer after the molding process is completed, during at least one measurement operation applied to said sample. Description of the figures and methods of implementation

[0040] Other advantages and features of the invention will become apparent upon reading the detailed description of implementations and embodiments, which are by no means limiting, and the following attached drawings: [Fig. 1] illustrates a schematic representation of a non-limiting example of an embodiment of a measuring device implemented in the present invention. [Fig. 2] illustrates a schematic representation of an example of an optical sensor that can be used in the measuring device in the figure. [Fig. 3] represents an example of a measurement of an element to be characterized obtained with the device in Figure 1; [Fig. 4] is an illustration of an example of a method for adjusting the measuring device of figure 1 according to an example embodiment of the invention. [Fig. 5] is an illustration of several examples of scanning grids. [Fig. 6] Figures 6a-6d are schematic representations of an example of a chip molding process of a sample, or a semiconductor device, with a molding composite, during which the thickness of the molding composite layer can be measured according to the invention.

[0041] These embodiments are not exhaustive; in particular, variants of the invention may be considered that comprise only a selection of features described or illustrated hereafter, isolated from the other described or illustrated features (even if this selection is isolated within a sentence including these other features), provided that this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, and / or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

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

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

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

[0045] The device 1 is arranged to perform a layer of molding composite thickness, along an optical axis, on an object to be characterized 5 of type a semiconductor object comprising one or more chips and at least one layer of molding composite of at least a part of said chips.

[0046] The measurement device 1 comprises an imaging channel VI and a measurement channel VM. In the measurement channel VM, a measurement beam 11 from a distance optical sensor 2 is brought, for example by a single-mode optical fiber 21, to a collimator 20. The collimator 20 forms a substantially collimated beam which is directed towards the object to be characterized 5 by a beam splitter 7, preferably dichroic, or a beam splitter cube. The measurement beam 11 is focused onto the object by a distal objective 3.

[0047] The collimator 20 and the distal objective 3 constitute an imaging system which images the core of the fiber 21 from which the measurement beam 11 originates in or near the object 5.

[0048] When the measurement beam 11 is incident on a surface or interface of the object 5 to be characterized in a direction substantially perpendicular to this surface or interface, within tolerance limits depending in particular on the angular opening at the level of the distal objective 3, the reflections which occur on this surface or interface are recoupled in the optical fiber 21 and processed in the optical sensor 2.

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

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

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

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

[0053] Interferometer 2, as illustrated in Figure 2, comprises a double Michelson interferometer based on single-mode optical fibers. It is illuminated by a fiber optic light source 42. The light source 42 can be a superluminescent diode (SLD) with a central wavelength in the range of 1300 nm to 1350 nm. The choice of this wavelength is based, in particular, on component availability criteria.

[0054] The light from the source 42 is directed through a coupler 40 and the fiber 21 towards the collimator 20, to form the measurement beam 11. Part of the beam is reflected in the fiber 21 at the collimator 20, for example at the silica-air or glass-air interface forming the end of the optical fiber, to form the reference wave.

[0055] The retro-reflections from object 5 are coupled in fiber 21 and directed with the reference wave towards a decoding interferometer built around a fiber coupler 41. This decoding interferometer has an optical correlator function whose two arms are, respectively, a fixed reference 44 and a time delay line 45. The signals reflected at the reference 44 and the time delay line 45 are combined, through the coupler 41, on a detector 43. The function of the time delay line 45 is to introduce an optical delay between the incident and reflected waves, which varies over time in a known way, obtained for example by moving a mirror.

[0056] The length of the arms 44 and 45 of the decoding interferometer is adjusted so as to allow the reproduction with the delay line 45 of the differences in optical paths between the reference wave reflected at the collimator 20 and the retroreflections from the object 5, in which case an interference peak is obtained at the detector 43 whose shape and width depend on the spectral characteristics of the source 42.

[0057] Thus, the measurement range is determined by the optical length difference between the arms 44 and 45 of the decoding interferometer 2, and by the maximum stroke of the delay line 45. In addition, as the reference wave is generated at the collimator 20 outside the imaging system, spurious reflections in the measurement channel VM do not contribute significantly to the interference.

[0058] The imaging channel VI of the device 1 according to the embodiment shown in Figure 1 comprises a camera 6, equipped with a CCD matrix sensor 7, as well as optical imaging means capable of forming an image of the object 5, or at least of its entrance face, on the sensor 7 of the camera 6, according to a field of view on the object 5, the field of view being substantially proportional to the magnification of the optical imaging means and to the dimension of the sensor 7. These optical imaging means comprise a distal lens 3 disposed on the side of the object 5 and an optical relay 13.

[0059] The imaging channel VI of the device 1 also includes a light source 8 whose emission spectrum includes visible and / or near-infrared wavelengths (around 1 pm). This light source 8 emits a beam of light 9 that illuminates the object 5 in such a way as to allow imaging by reflection. For clarity, the beam of light 9 is not shown in Figure 1 after the blade 10, which directs the light from the light source 8 towards the object 5 and the reflected light towards the camera 6.

[0060] The VM interferometric measurement channel comprising the measurement beam 11 is arranged so as to pass at least in part through the optical imaging means and in particular the distal objective 3. The measurement beam 11 is inserted into the optical imaging means by coupling means 7 such that it is incident on the object 5 according to a measurement area included in the field of view of the imaging channel.

[0061] The setup in Figure 1 thus allows an interferometric measurement beam 11 to be inserted into the field of view of an imaging system, consisting of the camera 6, the distal objective 3, and the relay 13 in the example shown. Thanks to this configuration, the position of the measurement beam 11 can be known or indexed, or at least fixed, relative to the images produced by the imaging system.

[0062] The collimator 20 can also optionally include displacement means 15 which allow the position of the measurement beam 11, and therefore the position of the measurement point, to be moved in a known manner on the object 5 relative to the field of view covered by the imaging means.

[0063] The device 1 further comprises a sample holder 30 for receiving the objects to be characterized 5, as well as movement means 14, such as translation and / or rotation tables, for moving the holder 30 in a plane perpendicular to the optical axis of the imaging means. The sample holder 30 comprises a plurality of receptacles 31 for receiving a plurality of objects 5 to be characterized, comprising at least one layer of composite material for molding chips of an object, or of a sample, for example, a semiconductor.

[0064] Device 1 according to the invention further comprises a processing module 50, or computing module, configured to process distance and / or thickness measurements, and images. This computing module comprises at least one computer, a central processing unit or computing unit, a microprocessor (preferably dedicated), and / or suitable software.

[0065] Device 1 according to the embodiment shown in Figure 1 can be used to implement the steps of the process according to the invention which will be described below.

[0066] Figure 3 illustrates an example of an interferometric measurement obtained with a low-coherence interferometer 2 of Figure 2, for an element 5 comprising four layers of chip-molding composite of a semiconductor sample along the same optical axis. These composite layers have respective thicknesses d1, d2, d3, and d4 and are separated by spacings 11, 12, and 13. The expected surface area values ​​of the composite layers, or the distances between interfaces, can be known by design or deduced from preliminary measurements. The continuous curve illustrates a measurement signal 51 with peaks 52 corresponding to interferogram envelopes, and representative of reflections of the measurement beam on interfaces of the composite layers of the element 5. These peaks may correspond to real interfaces, or be due to multiple reflections within the system (virtual interfaces).To identify the actual interfaces, particularly for complex samples, prior knowledge about element 5, such as the expected surface position values, can be used. In the example in Figure 3, the respective positions of the expected composite layer surfaces, as identified on the measurement signal 51, are indicated by crosses, corresponding to the peaks 52. Identifying the expected interfaces on the measurement signal and comparing the measured position and / or distance values ​​with expected values ​​allows validation of the measurement and the position of the measurement beam relative to the optical axis of the reference objective. Indeed, if the measurement beam is incorrectly positioned relative to the optical axis, there are generally no peaks detected on the signaled measurement 51, or only a portion of them, and with potentially erroneous position or distance values.Furthermore, the absence of certain peaks or position or distance values ​​outside a tolerance range relative to the expected values ​​indicates a faulty element or makes the position of the element in contact with the compound difficult to measure at the current position.

[0067] The method 100 shown in Figure 4 aims to place the measuring beam in the best measuring position. In the following, the measuring head refers to the means for moving the measuring beam 11 in the plane 14 and / or the means for moving the measuring beam 11 by translation in the plane of the sample holder or by rotation about said plane, or any other means capable of modifying the incidence and / or the position of the measuring beam 11.

[0068] The process 100 includes a step 102 for providing a scanning grid comprising a plurality of scanning positions. Examples of scanning grids are shown in Figure 5. The scanning grid 200 of Figure 5a comprises several scanning positions 202 distributed uniformly in a square area in parallel lines. Similarly to the scanning grid 200, the scanning grid 220 of Figure 5b comprises several scanning positions 222 distributed uniformly in a rectangular area in parallel lines. The scanning grid 240 of Figure 5c comprises several scanning positions 242 distributed uniformly in parallel lines and delimited by a circular area.

[0069] A current scan position is then selected in step 104. The current scan position can be chosen randomly. Alternatively, the current scan position can be chosen according to a scan strategy. For example, the 200 scan grid is traversed along parallel lines, first in a Dirl direction and then in a Dir2 direction when moving from one line to the next. Another example of a scan strategy is the 220 scan grid, where the grid is traversed in a spiral, for example, starting from a starting position 223.

[0070] In step 106, a measurement of the measurement signal is then carried out by the interferometry system as in device 1. A quality factor is then determined from the measurement signal.

[0071] The measurement signal can be stored in conjunction with the scan position. Specifically, the positions of the measurement signal peaks with their determined amplitudes can be stored at this stage. Furthermore, the shape of the measurement signal peak envelope, the acquired interferogram, and / or the quality factor can also be stored at this stage.

[0072] Determining the quality factor in step c) may include the following steps: - select a plurality of peaks from the measurement signal, and - calculate the quality factor as a function of the power product of the amplitudes of the selected peaks.

[0073] The process 100 then includes a step 108 to determine whether a stopping condition is satisfied at the current scanning position.

[0074] For example, the stopping condition can be satisfied when a measurement of the measurement signal is performed for each of the scan positions of the scanning grid.

[0075] In one embodiment, the quality factor depends on a measurement noise level. The stopping condition is considered satisfied when the noise level is below a threshold.

[0076] In another embodiment, the quality factor is determined based on the peak amplitudes present in the measurement signal. For example, the quality factor can be a function of the power product of the peak amplitudes. The stopping condition is satisfied when the quality factor exceeds a threshold.

[0077] If the stopping criterion is not met, step 104 is repeated. Otherwise, if the stopping criterion is met, process 100 includes a step 110 to determine the ideal measurement position.

[0078] In particular, selection step 104 depends on the quality factor and / or measurement noise. The optimal position may be the position for which the quality factor is above a threshold. Alternatively, or in addition, the optimal position may be the position for which the measurement noise is minimized or below a threshold.

[0079] According to another embodiment, step 104 may include an interpolation of the determined quality factors. Then, the optimal measurement position may be chosen at the maximum point of said interpolation.

[0080] In one embodiment, the process includes a step of recalibrating the scanning grid to a predetermined position. For example, the predetermined position may be close to, or included within, a zone for which the quality factor is maximized or greater than a threshold. In particular, the center of the scanning grid may be recalibrated to a position close to a measurement optimum.

[0081] Regulating the scanning grid near an area where the quality factor is maximized or greater than a threshold can be based on the use of at least two scanning grids. For example, a first and a second registration grid are used. The first registration grid has a first spacing between scanning positions, and the second scanning grid has a second spacing between scanning positions that is larger than the first spacing. In this case, the following steps are taken: i) select the current grid as the second grid, and repeat steps a) to c) until the quality factor reaches a first threshold, ii) select the current grid as the first grid and the second grid as the previous grid, recalibrate a reference position of the current grid to the scan position of the previous grid for which the first threshold is reached, and repeat steps a) to c) with the current grid until the stopping criterion is satisfied.

[0082] In the examples above, the first grid may correspond to a fine-pitch grid and the second grid to a coarse-pitch grid.

[0083] Alternatively, if the stopping criterion is not reached with the first grid, the process may include returning to step i) by continuing the sweep of the second grid to the position where the first threshold is reached.

[0084] The 100 method can be used for tuning an interferometry system to control a chip molding composite layer of a sample or object, after the chip molding process is complete, particularly during manufacturing steps that take place after the chip molding process.

[0085] Alternatively, process 100 can be used to control the chip molding composite layer of a sample or object, during the chip molding process, particularly after the molding composite has been deposited on the chips and / or during thinning steps of said molding composite.

[0086] Figures 6a-6d are schematic representations of a non-limiting example embodiment of a chip molding process of a sample, or a semiconductor device, with a molding composite.

[0087] The process shown in Figures 6a-6d allows at least one chip of a sample 1100 to be molded with a molding composite, referred to as compound in the following.

[0088] The object to be characterized 5 can be sample 1100.

[0089] Sample 1100, shown in figures 6a-6d, is by no means exhaustive and is given for illustrative purposes only.

[0090] Sample 1100 includes a support 1102, also called a carrier, which may be, for example, in the form of a metal plate or a glass plate.

[0091] Sample 1100 comprises one or more chips 1104 deposited on support 1102. In the example shown, only one chip 1104 is depicted. Of course, the sample may contain several chips arranged one on top of the other, or side by side, or a combination of these two configurations.

[0092] Optionally, an intermediate layer 1106, called an interposer, may be arranged between the support 1102 and the chip 1104.

[0093] Optionally, one or more electrical connections 1108, such as electrical connection pads or electrical disconnection tracks, may be located on the chip 1104, on the side opposite the support 1102. In the following, without loss of generality, it is assumed that the electrical connections are located on a top face of the chip 1104, opposite the support 1102.

[0094] Optionally, an electrical insulation layer 1110 may be deposited on the chip 1104, in particular on the top face of the chip 1104, between or around the electrical connections 1108.

[0095] Again, the sample example given in Figures 6a-6d is by no means limiting and sample 1100 may include only some of the elements described above and / or other element(s) than those described above.

[0096] In the example shown, chip 1104 is located on the side of a first face 1112 of sample 1100. This first face 1112 is referred to as the top face of sample 1100 hereafter. The opposite face 1114 of sample 1100 is referred to as the second face, or bottom face, hereafter.

[0097] The molding process, as known, aims to mold the chip 1104 in a molding composite 1120. The molding composite 1120 can be of any shape / composition. According to one embodiment, the molding composite 1120 can, for example, be in the form of an epoxy filled with thermal expansion control elements, such as silica beads.

[0098] Figure 6a represents sample 1100 before molding chip 1104 in molding composite 1120.

[0099] Figure 6b shows sample 1100 after the molding composite 1120 has been deposited onto chip 1104. The molding composite 1120 can be deposited using any known technique, for example, by depositing a paste. The molding composite 1120 is deposited onto chip 1104 so as to completely cover said chip 1104. Chip 1104 is then embedded in the molding composite 1120, as shown schematically in Figure 6b. In all cases, the molding composite 1120 has a significant thickness, which may be greater than chip 1104, resulting in a non-negligible thickness above chip 1104, for example, on the order of several tens of micrometers, for example, on the order of 50 micrometers or 100 micrometers above the chip.

[0100] Following a non-limiting embodiment example, the thickness of the molding composite 1120 is on the order of 900 pm, in a measurement position located at the periphery of the chip 1104.

[0101] The compound 1120 deposited on the sample has a first interface 1122, also a free interface or upper interface, on the side opposite the support 1102. The compound has a second interface 1124, also a buried interface or lower interface, in contact with the upper face 1112 of the support 1102.

[0102] Next, the molding composite 1120 is thinned to reduce the thickness of the molding composite 1120, until the upper face of the chip 1104, or the electrical connections 1108 located on said chip 1104, is exposed. The thinning of the molding composite 1120 is generally carried out in several passes, each pass removing a fraction of the thickness of the molding composite 1120, thus moving the upper interface 1122 of the compound 1120 towards the sample 1100.

[0103] The thinning, or removal, of the molding composite 1120 above the chip 1104 can be achieved by any known technique, for example by planing, grinding, and / or by a chemical process.

[0104] Figure 6c schematically represents the thinning stage.

[0105] The thinning step ends when all the molding composite 1120 above the chip 1104 has been removed so that the top face of the chip 1104 is apparent, where the electrical connections 1108 on said top face of the chip 1104 are apparent.

[0106] Figure 6d shows sample 1100 when the thinning step is complete. In this example, since chip 1104 has electrical connections 1108, the thinning step is terminated when these connections 1108 are visible. The molding composite 1120 is still present around chip 1104.

[0107] The invention is not limited to the example just described and the molding process may include other step(s) than the one(s) just described.

[0108] Generally, the chip molding process from a sample requires controlling the thickness of the composite 1120 during its thinning for obvious reasons. It is important not to damage the chip 1104, or the electrical connections 1108 if applicable, during the thinning step. Otherwise, the chip 1104 is unusable and the sample 1100 is discarded, resulting in a significant loss.

[0109] The invention makes it possible to measure the thickness of the composite layer 1120 at any time after the composite has been deposited, for example to control and / or guide the thinning.

[0110] The invention makes it possible to measure the thickness of the 1120 composite layer after the end of thinning, and / or when the molding process is complete.

[0111] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

Claims

DEMANDS 1. A method (100) for adjusting an interferometry system comprising a measuring head movable in space relative to an element to be characterized (5) and configured to emit a measurement optical beam (11) capable of illuminating said element to be characterized, said element to be characterized being a semiconductor object comprising one or more chips and at least one layer of molding composite of at least a portion of said chips, the interferometry system being configured for the inspection and / or characterization, and in particular the determination of the thickness, of one of the molding composite layers, the method comprising repeating the following steps until a stopping criterion is met: a) select (104) a scan position (202,222,242) from among the scan positions of a current scan grid (200,220,240) provided, b) move the measuring head to the selected scan position, (c) perform measurements (106) from a measurement signal relating to the beams reflected or transmitted by the element when illuminated by the optical beam, and determine a quality factor associated with the scan position from the measurement signal.

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

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

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

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

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

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

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

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

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

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

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

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

14. Device (1) for measuring the thickness of a molding composite layer of an element to be characterized, said element to be characterized being a semiconductor object comprising one or more chips and at least one molding composite layer of at least a part of said chips, the device comprising: an imaging channel (VI) configured to produce a beam of illumination, and comprising imaging means configured to acquire images of the element to be characterized illuminated by said beam of illumination within a field of view of the imaging means, a measuring head comprising a measuring channel (VM) configured to produce a measuring beam (11) at a determined position relative to said field of view and comprising an optical distance sensor (2) configured to produce distance and / or thickness measurements, means for moving the measuring head configured to move the measuring head relative to the element to be characterized (5), and a processing module configured to handle distance and / or thickness measurements, and images, the processing module being configured to implement the process (100) according to one of the preceding claims.

Images