Method for adjusting an element interface measurement device

Abstract

The invention relates to a method (100) for adjusting an interferometry system comprising a measurement head that can be moved in space and configured to emit an optical measurement beam capable of illuminating an element to be characterised, the element to be characterised being a semiconductor object comprising one or more chips and at least one moulding composite layer of at least some of the chips, the interferometry system being configured for the inspection and / or characterisation, and in particular the determination of the thickness, of one of the moulding composite layers, the method comprising the following steps: a) moving (102) the measurement head to a given position, b) measuring (104) a plurality of return signals relating to a beam reflected by the element to be characterised when it is illuminated by the optical beam, c) selecting (106) a plurality of peaks among the return signals, d) determining (108) a quality factor associated with the given position.

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 an element to be characterized, comprising one or more chips and a layer of composite molding 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 a layer of molding composite of at least one of said chips, it may be necessary to control or measure the thicknesses of said layer 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 the 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 measured 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 measurement axis of an assembly with an accuracy, for example, on the order of a micron for objects several millimeters in size. A method enabling this level of performance is therefore required.Similarly, when creating small structures on the substrate surface, it may be necessary to precisely search for one or more positions of best optical return, for all the layers of the structure whose thicknesses we want to know.

[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. Description of the invention

[0008] At least one of these goals is achieved with a method for adjusting an interferometry system comprising a measuring head movable in space and configured to emit a measurement optical beam suitable for illuminating an element to be characterized, the 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 the following steps: a) move the measuring head to a given position, b) measure a plurality of return signals relating to the beams reflected by the element to be characterized when it is illuminated by the optical beam, c) select a plurality of peaks from among the return signals, d) determine a quality factor associated with the given position, characterized in that the quality factor is a function of the product of powers of the peak amplitudes.

[0009] The method allows a quality factor to be associated with the positions of the measuring head. The determined quality factor depends on the power product of the peak amplitudes and is therefore robust to amplitude disparities between peaks when the measuring head is placed in the optimal measurement position. Furthermore, the quality factor is simple to calculate and does not require prior knowledge of the interface encountered by the element to be characterized, such as its geometry, refractive index, etc. Indeed, the quality factor is determined solely from the peak amplitudes of the return signals. The quality factor determined by this method can be used within an automated search algorithm or to guide a human operator in positioning the measuring head in the optimal measurement position simply and efficiently.

[0010] In this document, "item to be characterized" means a sample, such as a wafer or a semiconductor object or a 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.

[0011] 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.

[0012] In one embodiment, the peaks can be selected based on a predetermined measurement model. In particular, the method may include a step to match the feedback signals to signals in the measurement model.

[0013] For example, the number of peaks selected may correspond to the number of interfaces of the element to be characterized.

[0014] Advantageously, the plurality of measured return signals can contain a number P of peaks. The method can include, in step c), the selection of a number n of peaks corresponding, for example, to the number of peaks expected in the predetermined measurement model.

[0015] According to an advantageous embodiment, the quality factor Q1 can be calculated using the following formula: with n being the number of peaks selected in step c) and Ai being the amplitude of the peak with index i in the selection. In this case, each of the powers of the amplitudes is 1.

[0016] According to another advantageous embodiment, the quality factor Ç2 can be calculated using the following formula: with n being the number of peaks selected in step c) and Ai being the amplitude of the peak with index i. In this case, each of the powers of the amplitudes is 1.

[0017] According to yet another advantageous embodiment, the quality factor Q3 can be calculated using the following formula: with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i, a t being a weighting factor having the index i, and a being in particular equal to the sum of the a t for all n indices i, or more generally being a constant number, such as an integer or a real number.

[0018] In particular, the weighting factor can be different from 1. Advantageously, the weighting factor can be between 0.8 and 1.2. Thus, it is possible to modulate the sensitivity to the amplitudes of the measured return signals, increasing this sensitivity when the weighting factor has t increase.

[0019] In one embodiment, the method may include determining the quality factor for a plurality of tested positions. The method may include moving the measuring head to maximize the quality factor. The measuring head may be moved automatically or manually by an operator. In another example, an ideal measuring position may be determined as the tested position associated with the highest quality factor.

[0020] Advantageously, the measurement model can include a predetermined number of useful peaks. The method can include, in step c), when for at least one useful peak of the model, none of the return signals exist that correspond to that useful peak(s) of the model, adding to the peak selection a chosen amplitude value corresponding to the missing peak(s). In other words, if a peak with index j is absent from the expected useful peaks, a chosen value is assigned to the missing amplitude Aj. For example, this value can be a fixed amplitude generated so as to be significantly lower than an expected amplitude. Thus, the quality factor is degraded to represent the absence of one or more peaks, but the sensitivity to the still visible optical returns is maintained.Similarly, if two or more peaks are missing, fixed amplitudes replace the lost peaks, so that the product of these fixed amplitudes is significantly lower than the product of the expected amplitudes when the measurement head is placed in the best measurement position, and all the expected peaks of the model are detected.

[0021] The chosen amplitude value can be different from zero and less than a predetermined threshold.

[0022] Optionally, the quality factor can be determined from a function applied to one of the formulas Σi, with i ranging from 1 to 3, so that the quality factor is obtained by the formula Q'i = F(Qi), where F is said function. In particular, Qi, with i equal to 1, 2, or 3, can be considered an intermediate calculation quality factor formula, meaning that Qi is obtained according to one of the formulas defined previously. Such a function F could be, for example, a logarithmic function, y = ln(x). It could also be the inverse function I, defined by I(x) = 1 / x. In this last example, the directions of variation of the quality factor would be reversed; that is, the resulting quality factor would decrease when one of the amplitudes increases, due to the decreasing nature of the inverse function.

[0023] The measuring head can be specifically configured to move in an XY plane relative to the element being measured. The measuring head can also rotate in space relative to the element being measured. The element to be characterized can be mounted on a support, for example, that is movable in rotation and / or translation along the Z-axis perpendicular to the XY plane. The method may include a step of positioning the element to be characterized instead of positioning the measuring head.

[0024] According to another aspect, the invention relates to a device 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 portion 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, - means for moving the measuring head configured to move the measuring head, and - a processing module configured to handle distance and / or thickness measurements, and images, the processing module being configured to implement the aforementioned process.

[0025] The means of moving the measuring head can be configured to move the measuring beam along a predefined trajectory and for each position of the trajectory, a quality factor is determined.

[0026] The measuring head can be positioned at the position associated with the highest quality factor.

[0027] The element to be characterized may include at least one refractive or diffractive element.

[0028] The means for moving the measuring head can be replaced by means for moving the element to be characterized.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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 realization

[0033] 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 of Figure 1; [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] Figures 5a-5d are schematic representations of an example of a chip molding process of a sample, or of a semiconductor device, with a molding composite, during which the thickness of the molding composite layer can be measured according to the invention.

[0034] 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.

[0035] In particular, all the variants and embodiments described can be combined with each other if there are no technical obstacles to this combination.

[0036] In the figures, elements common to several figures retain the same reference.

[0037] 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.

[0038] Device 1 is arranged to perform measurements of the thickness of a layer of molding composite, along an optical axis, on an object 5 of the 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The optical distance sensor 2 may include a low-coherence interferometer.

[0043] Figure 2 illustrates an example of a low-coherence interferometer in the time domain, usable within the framework of the present invention.

[0044] The low-coherence interferometer 2 can operate, for example, in the infrared.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The imaging channel VI of 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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, each comprising at least one layer of composite material for molding chips of an object, or of a sample, for example, a semiconductor.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Process 100 includes the following steps: - a step 102 of moving the measuring head to a position to be tested, - a step 104 of measurement of the measurement signal 51, - a step 106 of selecting one or more useful peaks for example according to the model of the interfaces expected on the measurement signal.

[0062] In particular, the number of peaks selected corresponds to the number of interfaces of the element to be characterized.

[0063] Next, process 100 includes a step 108 of determining a quality factor çi, C2, Q3 according to one of the following formulas. <21 = with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i. In this case, each of the powers of the amplitudes is 1. with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i. In this case, each of the powers of the amplitudes is 1. <23 = “ J 1=1 with n being the number of peaks selected in step c) 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 t for all n indices i, or more generally being a constant number, such as an integer or a real number.

[0064] Note that an equivalent formulation of Q3 is: Q3 = F t=l

[0065] In particular, the weighting factor ai can be different from 1 and range from 0.8 to 1.2. Thus, it is possible to modulate the sensitivity to the amplitudes of the measured return signals, increasing this sensitivity when the weighting factor has t increase.

[0066] Furthermore, if a peak with index j is not found among the expected useful peaks, the process may include a step of assigning a chosen value to missing. For example, this value could be a fixed amplitude generated to be significantly lower than an expected amplitude. Thus, the quality factor is degraded to represent the absence of one or more peaks, but sensitivity to the still-visible optical returns is maintained. Similarly, if two or more peaks are missing, fixed amplitudes replace the lost peaks, so that the product of these fixed amplitudes is significantly lower than the product of the expected amplitudes when the measurement head is placed in the best measurement position and all the expected peaks of the model are detected.

[0067] The movement of the measuring head can be achieved by actuation of the movement means in the plane 14 and / or the movement means 15 of the measuring beam 11. The positions to be tested can be chosen according to a predetermined trajectory.

[0068] Steps 104 to 108 are repeated for a plurality of test positions. Procedure 100 includes a step 110 for determining the measurement position as the one to be tested with the highest quality factor. Procedure 100 can be used to position the measuring head at the best measurement position automatically or with operator assistance.

[0069] 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.

[0070] 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.

[0071] Figures 5a-5d 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.

[0072] The process shown in figures 5a-5d allows at least one chip of a sample 1100 to be molded with a molding composite, referred to as compound in the following.

[0073] The element to be measured or element to be characterized can be sample 1100.

[0074] Sample 1100, shown in figures 5a-5d, is by no means exhaustive and is given for illustrative purposes only.

[0075] 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.

[0076] 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.

[0077] Optionally, an intermediate layer 1106, called an interposer, may be arranged between the support 1102 and the chip 1104.

[0078] 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.

[0079] 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.

[0080] Again, the sample example given in figures 5a-5d 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.

[0081] 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.

[0082] 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.

[0083] Figure 5a represents sample 1100 before molding chip 1104 in molding composite 1120.

[0084] Figure 5b 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 5b. 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] Figure 5c schematically represents the thinning stage.

[0090] 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.

[0091] Figure 5d shows sample 1100 when the thinning step is complete. In the example shown, 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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 an optical measurement beam (11) suitable for illuminating the element to be characterized (5), 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, and the measuring head, 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 the following steps: a) move (102) the measuring head to a given position, b) measure (104) a plurality of return signals (51) relating to the beams reflected by the element to be characterized when it is illuminated by the optical beam (11), c) select (106) a plurality of peaks (52) from among the return signals, d) determine (108) a quality factor associated with the given position, characterized in that the quality factor is a function of the product of powers of the peak amplitudes.

2. Method (100) according to the preceding claim, wherein the peaks (52) are selected according to a predetermined measurement pattern.

3. Method (100) according to any one of the preceding claims, wherein the number of peaks selected corresponds to the number of interfaces of the element to be characterized (5).

4. A method (100) according to any one of the preceding claims, wherein the quality factor is calculated according to the following formula: with n being the number of peaks selected in step c) and Ai being the amplitude of the peak having index i.

5. Method (100) according to any one of claims 1 to 3, wherein the quality factor is calculated according to the following formula: with n being the number of peaks selected in step c) and Ai being the amplitude of the peak having the index i.

6. A method (100) according to any one of claims 1 to 3, wherein the quality factor is calculated according to the following formula: with n being the number of peaks selected in step c) and A t being the amplitude of the peak having the index i, a t being a weighting factor having the index i, and a being a constant integer or real number.

7. Method (100) according to the preceding claim, wherein the weighting factor is different from 1 and is between 0.8 and 1.

2.

8. Method (100) according to any one of claims 4 to 7, wherein the quality factor is determined from a function applied to one of the formulas Qi, with i ranging from 1 to 3, so that the quality factor is obtained by the formula Q'i = F(Qi), where F is said function.

9. Method (100) according to any one of the preceding claims, comprising determining the quality factor for a plurality of tested positions and moving the measuring head so as to maximize the quality factor.

10. A method (100) according to any one of the preceding claims taken in combination with claim 2, wherein the measurement model comprises a predetermined number of useful peaks, the method comprising, in step c), when for at least one useful peak of the model, there is none of the feedback signals that corresponds to that useful peak(s) of the model, adding to the selection of peaks a chosen amplitude value corresponding to the missing peak(s).

11. A method (100) according to the preceding claim, wherein the chosen amplitude value is non-zero and is less than a predetermined threshold.

12. 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, and - a processing module configured to handle distance and / or thickness measurements, and images, the processing module being configured to implement the process according to one of the preceding claims.

13. Device (1) according to the preceding claim, wherein the means for moving the measuring head are configured to move the measuring beam (11) along a predefined trajectory and for each position of the trajectory, a quality factor is determined.

14. Device (1) according to the preceding claim, wherein the measuring head is positioned at the position associated with the highest quality factor.

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