Method for monitoring the weakening of an interface between a substrate and a layer, and device enabling such monitoring

Abstract

The invention relates to a method for monitoring the weakening of an interface (13) between a layer (12) and a substrate (11) while a weakening anneal is being carried out, the method comprising the following steps: illuminating the first face (10A) of the substrate (ll) / layer (12) assembly (10) with a monochromatic light beam (25) in a first direction (25A); measuring the intensity of the light beam (25) scattered by the substrate (ll) / layer (12) assembly (10) in at least a second direction (25B), the second direction (25B) forming a non-zero angle (20) with the first direction (25A); and determining a state of weakening of the interface (13) from the intensity. The invention further relates to a device for monitoring the weakening, suitable for implementing such a method.

Description

[0001] METHOD FOR MONITORING THE EMPTIBILIZATION OF AN INTERFACE BETWEEN A SUBSTRATE AND A LAYER AND DEVICE ALLOWING SUCH MONITORING

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The invention relates to the field of manufacturing microelectronic and optoelectronic structures and in particular that of the transfer of semiconductor layers capable of being used in the context of such manufacturing.

[0005] The invention thus relates more particularly to a method for monitoring the weakening of an interface between a substrate and a layer, a method for weakening such an interface, a device for monitoring the weakening of this same interface and a system for fracturing an interface between a substrate and a layer.

[0006] STATE OF THE PRIOR ART

[0007] It is not uncommon, in the context of the manufacture of microelectronic and / or optoelectronic structures, to carry out a transfer of a semiconductor layer from a donor substrate to a host substrate by a Smart Cut™ type process comprising an implantation step in the donor substrate to create a buried fragile interface delimiting the semiconductor layer to be transferred.

[0008] Such a transfer requires, after bonding of the donor substrate / layer assembly to the host substrate by said layer, fracturing between the donor substrate and the layer to be transferred at the buried fragile interface. This fracturing is generally carried out by embrittlement annealing allowing the growth and coalescence of micro-cavities formed at said interface.

[0009] Figure 1 illustrates the variation in roughness along the layer after fracturing. This variation in roughness is notably the consequence of differences in crack size at the time when fracturing occurs at the wafer scale. It can have different sources and in particular the inhomogeneity of the implantation or the embrittlement annealing or even the stress variations in the stack. Therefore, it would be interesting to be able to monitor the embrittlement of the interface between the donor substrate and the layer to be transferred during the embrittlement annealing. Currently, such monitoring can be obtained by infrared microscopy. If such imaging makes it possible to obtain an image of the micro-cavities and therefore to quantify the characteristics of their population and their evolution, it is not really adapted to in-situ measurements in a fracturing furnace, particularly when the latter is of the industrial type.

[0010] Indeed, for such imaging, it is necessary to have a low objective / sample distance (i.e. the donor substrate / layer / host substrate assembly) (a few millimeters at most), which particularly complicates its integration into an industrial fracturing furnace.

[0011] Furthermore, in temperature, the IR radiation emitted by the plates and the oven can interfere with the IR signal used for visualization and therefore requires very powerful sources to illuminate the wafers.

[0012] STATEMENT OF THE INVENTION

[0013] The invention aims to overcome the above drawback and thus aims to provide a method for monitoring embrittlement which is compatible with the constraints of a fracturing furnace, particularly an industrial one, and which does not require, in particular, the installation of an objective at a short distance from the substrate / layer assembly whose interface must be monitored and particularly powerful radiation sources.

[0014] The invention relates to this end to a method for monitoring the embrittlement of an interface between a layer and a substrate during embrittlement annealing of said interface, the substrate / layer assembly having at least a first and a second face, the method comprising the following steps:

[0015] - illumination of the first face with a monochromatic beam of light in a first direction,

[0016] - measurement of an intensity of the light beam diffused by the substrate / layer assembly in at least a second direction, the second direction having a non-zero angle with the first direction, determination of a state of embrittlement of the interface from said intensity.

[0017] The inventors identified that the intensity of the scattered light at a given angle with respect to the first direction was characteristic of the size of the micro-cavities and the distance between them. Therefore, by monitoring the variation of this intensity during embrittlement annealing, it is possible to monitor the embrittlement of the interface between the layer and the substrate. Such illumination and such a measurement can be carried out at a distance from the substrate / layer assembly and the method therefore has the advantage of being perfectly compatible with the constraints linked to the fracturing furnace, in particular of the industrial type. It will be noted in particular that the method according to the invention makes it possible to carry out such monitoring from outside the enclosure of the fracturing furnace, since the light source and the detector can be arranged at a distance from the substrate / layer assembly and are compatible with the use of portholes.

[0018] It should be noted that the first direction corresponds to a direction of incidence of the monochromatic light beam while the second direction(s) correspond to one or more observation directions used for monitoring fracturing. Thus, in this document, it is perfectly possible to substitute “first direction” with “incident direction” and “second direction” with “observation direction” without changing the teaching.

[0019] When measuring the intensity of the light beam, the intensity may be measured along a plurality of second directions each having a non-zero angle with the first direction, and preferably at least two of said second directions may have angles distinct from each other with respect to the first direction.

[0020] In this way, it is possible to obtain a more precise measurement, when these at least two directions have an identical angle with respect to the first direction, and to be interested in at least two second directions of interest corresponding to states of embrittlement of interest, in the case where said at least two directions have angles distinct from each other with respect to the first direction. This possibility allows the intensity measurement to be carried out according to a range of second directions such as will be discussed in connection with Figures 3 to 5.

[0021] A preliminary calibration step may be planned, carried out before the embrittlement annealing, comprising the following sub-steps:

[0022] - illumination of the first face with the light beam in the first direction,

[0023] - measurement of a reference intensity of the light beam diffused by the substrate / layer assembly in at least one second direction,

[0024] - in which, during the step of determining a state of embrittlement, a sub-step of correction of the measured intensity from the reference intensity is provided.

[0025] In this way, the diffusion peak linked to the cavities formed during the embrittlement of the interface can easily be identified and it is therefore easy to determine the state of embrittlement of the interface.

[0026] When illuminating the first face with the light beam in the first direction, the light beam may be moved into at least two regions, or zones, of the first face.

[0027] Thus, it is possible to verify the homogeneity of the embrittlement of the interface along the first face.

[0028] Alternatively, to such a measurement in two locations by moving the light beam, it may be provided, to allow such a measurement in at least two regions:

[0029] - the illumination of the first face by the beam of light and another beam of light both in the first direction,

[0030] - measuring the intensities of the light beam and of the other light beam scattered by the substrate / layer assembly in at least the second direction,

[0031] - determination of a state of weakening of the interface from said intensities at the level of said at least two regions.

[0032] The monochromatic light beam may have a wavelength included in the infrared wavelength range, preferably near infrared, said wavelength being even more advantageously between 1050 nm and 1550 nm.

[0033] Such a wavelength is particularly suitable when the substrate and / or the layer is / are made of silicon, germanium or a silicon-germanium alloy.

[0034] Note that alternatively, the light beam can have a visible wavelength.

[0035] Such an alternative is particularly suitable when the substrate and / or the layer is / are made in a wide gap semiconductor such as gallium nitride, aluminum nitride, an alloy of the two, or silicon carbide.

[0036] The invention further relates to a method for weakening an interface between a layer and a substrate comprising a step of weakening annealing the substrate / layer assembly in order to weaken said interface, in which during said annealing step a method for monitoring weakening according to the invention is implemented.

[0037] Such a method benefits from the advantages linked to the monitoring enabled by a monitoring method according to the invention. With such a method, it is thus easy to monitor the maturation of the cavities present at the interface and, if necessary, to provide feedback.

[0038] It is thus possible to adjust the embrittlement annealing conditions accordingly, in particular to obtain a desired distribution of micro-cracks. For example, the furnace heating profile can be modified in real time.

[0039] The embrittlement annealing step can be stopped when a state of embrittlement of the interface measured by the embrittlement monitoring method reaches a given threshold, the state of embrittlement preferentially corresponding to a fracturing of the interface, said fracturing then being detected by a variation in intensity along at least one second direction and / or a shift in the diffusion peak.

[0040] In this way, it is possible to optimize the fracturing, as the annealing can be stopped at the most opportune moment.

[0041] It will be noted in particular that, according to one possibility of the invention, the state of embrittlement can be chosen in such a way as to carry out the fracturing outside the furnace in which the embrittlement annealing is carried out. In this way, if the embrittlement process requires it, it will be possible to carry out the invoicing outside the furnace. The annealing conditions used during the annealing step can be modified depending on the state of embrittlement of the interface determined during the implementation of the embrittlement monitoring process.

[0042] In this way, it is possible to optimize the embrittlement annealing, and in particular the heating profile of the furnace, according to the state of embrittlement of the interface in order to obtain a desired distribution of micro-cracks at the interface.

[0043] The invention further relates to an interface embrittlement monitoring device for monitoring the embrittlement of an interface between a layer and a substrate during embrittlement annealing of said interface, the substrate / layer assembly having at least a first and a second face, comprising:

[0044] - an optical source capable of emitting a monochromatic light beam towards the first face in a first direction,

[0045] - an electromagnetic radiation detector capable of measuring an intensity of the light beam after diffusion by the substrate / layer assembly, the electromagnetic radiation detector being arranged to measure said intensity of the light beam in a second direction having a non-zero angle with the first direction.

[0046] Such a device is suitable for implementing a monitoring method according to the invention and therefore makes it possible to benefit from the advantages associated therewith.

[0047] The electromagnetic radiation detector may be arranged to allow measurement of the intensity of the light beam after diffusion in a plurality of second directions each having a non-zero angle with the first direction and, preferably, at least two of said second directions have angles distinct from each other with respect to the first direction.

[0048] In this way, it is possible to obtain a more precise measurement, when these at least two directions have an identical angle with respect to the first direction, and to be interested in at least two second directions of interest corresponding to states of embrittlement of interest, in the case where said at least two directions have angles distinct from each other with respect to the first direction.

[0049] It will be noted that such an arrangement of the electromagnetic radiation detector may be provided by the use of at least two electromagnetic radiation detection units each arranged to detect the intensity of the light beam after scattering in a respective second direction.

[0050] The detector can thus, for example, take the form of a matrix of such units (or pixels) in order to allow measurement in a plurality of second directions.

[0051] It should be noted that each of these units can be equipped with dedicated optics to enable the measurement of the intensity of the light beam after diffusion in the corresponding second direction.

[0052] The embrittlement tracking device may further comprise a processing unit configured to retrieve a light beam intensity value measured by the detector and to determine an embrittlement state of the interface from said light beam intensity value.

[0053] Such a processing unit facilitates the use of the tracking device according to the invention, the technician implementing the embrittlement annealing having direct access to a state of embrittlement of the interface.

[0054] The processing unit may further be configured to, when determining the state of embrittlement of the interface, correct the measured intensity from a reference intensity determined before the embrittlement annealing.

[0055] In this way, the diffusion peak linked to the cavities formed during the weakening of the interface can easily be identified.

[0056] The invention further relates to an annealing furnace 40 capable of carrying out embrittlement annealing in order to embrittle an interface between a layer and a substrate, the furnace comprising an embrittlement monitoring device according to the invention.

[0057] With such an embrittlement monitoring device, such an annealing furnace allows in-situ embrittlement monitoring which is perfectly suited to industrial type annealing furnaces.The annealing furnace may comprise a first location for the substrate / layer assembly and at least one second location for another substrate / layer assembly in order to allow simultaneous embrittlement annealing of the substrate / layer assembly and the other substrate / layer assembly, the second location being arranged so that a face of the other substrate / layer assembly is illuminated by the light beam after the light beam has passed through the substrate / layer assembly, and the electromagnetic radiation detector being further capable of measuring an intensity of the light beam after scattering by the other substrate / layer assembly, the electromagnetic radiation detector being arranged to measure said intensity of the light beam in another second direction having a non-zero angle with the first direction.

[0058] With such an annealing furnace, it is possible to perform interface embrittlement annealing for a plurality of substrate / layer assemblies by monitoring the embrittlement of at least two of said interfaces, or even all of said interfaces.

[0059] It will be noted that in such a configuration, the electromagnetic radiation detector may comprise at least two detection units each dedicated to a corresponding location among the first and second locations.

[0060] The annealing furnace may be configured so that, when implementing an embrittlement anneal, an anneal of the substrate / layer assembly is stopped when the embrittlement tracking device determines that the embrittlement state of the measured interface reaches a given threshold.

[0061] In this way, it is possible to provide an optimized embrittlement annealing since it is based on monitoring the embrittlement of the interface.

[0062] The annealing furnace may include a control unit configured to communicate with a processing unit of the embrittlement tracking device and to adjust the conditions of the embrittlement annealing based on the embrittlement state provided by the embrittlement tracking device. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] The present invention will be better understood by reading the description of exemplary embodiments, given purely for informational purposes and in no way limiting, with reference to the appended drawings in which:

[0064] [Fig. 1] illustrates a roughness map carried out on a semiconductor layer after fracturing its interface with a donor substrate from which said semiconductor layer originates, a clear value corresponding to maximum roughness;

[0065] [Fig. 2] illustrates an embrittlement furnace equipped with an embrittlement monitoring device according to the invention;

[0066] [Fig. 3] graphically illustrates the variations in intensity of the beam diffused by a layer / substrate assembly as a function of the diffusion angle obtained from the embrittlement monitoring device according to the invention measured respectively before and during embrittlement annealing;

[0067] [Fig. 4] graphically illustrates the differential intensity variation as a function of the diffusion angle calculated by subtracting the intensity measured during embrittlement annealing from the intensity measured before embrittlement annealing;

[0068] [Fig. 5] graphically compares the intensity of the scattered beam measured from a device according to the invention with a Fourier transform of a confocal microscopy image as implemented in the prior art.

[0069] Identical, similar or equivalent parts of different figures bear the same numerical references so as to facilitate the transition from one figure to another.

[0070] The different parts represented in the figures are not necessarily on a uniform scale, to make the figures more readable.

[0071] The various possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0072] Figure 2 illustrates a weakening furnace 40 in which a weakening annealing of an interface 13 between a donor substrate 11 and a layer 12 is carried out, said weakening furnace 40 being equipped with a weakening monitoring device 30 according to the invention in order to enable monitoring of the weakening of said interface 13.

[0073] It will be noted that in a usual configuration of the invention, as illustrated in Figure 2, the elements of the embrittlement monitoring device 30 are arranged outside the enclosure 40A of the embrittlement furnace 40, the enclosure 40A then being equipped with portholes, not illustrated, in order to allow embrittlement monitoring by the embrittlement monitoring device 30 according to the invention. Such a usual configuration is in no way limiting and it is perfectly conceivable, without departing from the scope of the invention, that at least some of the elements of the embrittlement monitoring device 30 are at least partly arranged in the enclosure 40A of the embrittlement furnace 40.

[0074] In the context of the present exemplary embodiment, the substrate, called the donor substrate, and the layer to be transferred are respectively a substrate and a layer of monocrystalline silicon Si. Therefore, the wavelengths, values ​​and other measurements indicated below and in the rest of this document are adapted for such a material. Of course, from such a teaching, the person skilled in the art is able to adapt the present teaching to other types of material. Thus, the invention is also particularly suitable in the context of embrittlement of an interface between a layer and a substrate both made of germanium Ge, in a silicon-germanium alloy Si-Ge or even in a silicon carbide SiC, or even for a silicon Si substrate and a layer of silicon carbide SiC.

[0075] Of course, if the invention concerns the monitoring of the embrittlement of an interface 13 between a substrate 11 and the layer 12 that it supports, in a conventional application of the invention, the embrittlement annealing follows a step of bonding said layer to a host substrate 14, the substrate 11 being the donor substrate used in the context of the transfer of the layer 12 to the host substrate 14. Thus, if in the general context of the invention the assembly 10 substrate 11 / layer 12 comprises the substrate 11 and the layer 12, in the conventional application of the invention, the assembly 10 also comprises the host substrate as shown in FIG.

[0076] Such a weakening monitoring device 30 comprises:

[0077] - an optical source 31 capable of emitting a monochromatic light beam 25 towards the first face 10A, the wavelength of said light beam 25 being chosen so that the layer 12 and the substrates 11 or 14 are substantially transparent at said wavelength,

[0078] - an electromagnetic radiation detector 32 capable of measuring an intensity of the light beam 25 after diffusion by the assembly 10 substrate 11 / layer 12, the electromagnetic radiation detector being arranged to measure said intensity of the light beam 25 in a second direction having a non-zero angle 20 with the first direction 25A.

[0079] Of course, such a second direction 25B for detecting a light beam 25 diffused by the assembly 10 substrate 11 / layer 12 crosses the first direction 25A, along which the light beam 25 is emitted, at the level of the diffusing element at the origin of said diffusion, that is to say the assembly 10 substrate 11 / layer 12 (or more precisely the interface 13 between the layer 11 and the substrate 12).

[0080] In a usual diffusion configuration, the second direction 25B may, as illustrated in FIG. 2, extend from the second face of the support away from the latter. In a variant not illustrated in which the diffusion measured by the detector is a backscattering, the second direction 25B may extend from the first face away from the latter. Such a possibility is particularly interesting in order to allow the observation of the diffusion with an opaque host / receiver substrate or when the angles in transmission are not accessible.

[0081] It will thus be noted that by diffusion of the light beam by the assembly 10 substrate 11 / layer 12, it must be understood, here and in the rest of this document, both a diffusion as such, that is to say that the light beam is diffused from the interface 13 in the direction of the second face 10B, and a backscattering, that is to say that the light beam is diffused from the interface 13 in the direction of the first face 10B.

[0082] As described below, a processing unit 33 may also be provided capable of controlling the optical source and the electromagnetic radiation detector 32 in order to calibrate, from the intensity measured by the electromagnetic radiation detector 32, a state of weakening of the interface 13.

[0083] The optical source 31 is a light source capable of providing / emitting the light beam 25 with a wavelength adapted to the transparency of the material(s) of the substrate 11 and of the layer 12. In the case of the present exemplary embodiment, that is to say a silicon layer and substrate, the wavelength of the light beam may be an infrared wavelength, preferably a near infrared wavelength. Thus, the light beam 25 may have a wavelength between 1050 nm and 1550 nm. and be for example equal to 1.2 pm, 1.5 pm, or 1.3 pm. To enable such a provision, the optical source may be a laser source, such as a semiconductor laser, laser diode; or a light-emitting diode.Preferably, the optical source 31 may comprise a light beam guidance system 25, such as an optical fiber, advantageously comprising a collimation system (lenses, mirrors) to define the size and divergence of the light beam after its emission.

[0084] As illustrated in Figure 2, the first direction 25A is preferably perpendicular to the first surface. Of course, other first directions 25A are conceivable without departing from the scope of the invention.

[0085] The electromagnetic radiation detector 32 is configured to receive electromagnetic radiation in a wavelength range including the wavelength of the light beam 25 emitted by the optical source 31 and provide a signal representative of the intensity of the received radiation. Thus, the electromagnetic radiation detector may comprise a photodetector such as a photodiode or a plurality of photodiodes organized in a matrix. Thus, for example, the electromagnetic radiation detector 32 may comprise a CMOS or CCD sensor whose spectral response is adapted to the source used. In such a configuration, the different photodiodes or pixels form detection units.

[0086] The electromagnetic radiation detector 32 may comprise, in addition to such a photodetector, an objective in order to concentrate the part of the light beam 25 diffused in the second direction 25B on said photodetector.

[0087] According to a first possibility of the invention, the electromagnetic radiation detector can be arranged to receive the part of the beam scattered in a second predetermined direction 25B and selectively image the light-emitting zone. According to this possibility, the second direction is chosen to correspond to a direction of interest, that is to say having an angle 20 of interest with respect to the first direction 25A, corresponding to a predetermined state of weakening of the interface 13.

[0088] It will be noted that, in the case where the electromagnetic radiation detector 32 comprises a plurality of detection units, the radiation detector may comprise a plurality of optical systems each dedicated to one or a group of respective detection units. Said optical systems are each arranged to allow a measurement of the intensity of the light beam 25 diffused by the substrate 11 / layer 12 assembly 10 in a second direction 25B which is respective to it.

[0089] In accordance with the present exemplary embodiment, the inventors have identified that, within the framework of such a possibility, a second direction having an angle 20 of between 5 and 15°, preferably between 8 and 12° and substantially equal to 10° corresponded to a state of embrittlement of the interface 13 suitable for providing optimized fracturing. The inventors have in fact identified that such an angle value of 10° of the second direction 25B with respect to the first direction 25A, corresponds to micro-cracks of 10 pm and to a maturity of the embrittlement of the interface 13 suitable for its fracturing.

[0090] According to a second possibility of the invention, the electromagnetic radiation detector and its optics can be arranged to receive a portion of the beam scattered along a plurality of second directions 25B, 25B' each having a non-zero angle 20 with the first direction. In this way, it is possible to precisely monitor the state of embrittlement of the interface. This plurality of second directions can correspond to a range of angle 20 with the first direction corresponding to several states of embrittlement of the interface 13 of interest (thus including, for example, 10° as mentioned above in the context of the first possibility).

[0091] According to a third possibility of the invention, the electromagnetic radiation detector 32 can be arranged to be movable so as to allow a measurement of the intensity of the beam after its diffusion according to a plurality of second directions 25B, 25B' each having a non-zero angle 20 with the first direction. In the same way as for the second possibility set out above, this plurality of second directions can correspond to a range of angle 20 with the first direction corresponding to several states of weakening of the interface 13 of interest (thus including, for example, 10° as mentioned above in the context of the first possibility).

[0092] It will also be noted, according to another possibility, compatible with the three possibilities above, that the embrittlement tracking device 30 can be configured to move the light beam 25 in at least two locations, or regions, of the first face 10A, the detector then being arranged to allow the measurement of the intensity of the light beam 25 diffused by the substrate 11 / layer 12 assembly 10 in the at least one second direction 25B for said at least two regions. Such a possibility allows mapping of the embrittlement state of the interface 13 along the first face 10A. Such a movement of the light beam 25 can be obtained by a suitable configuration of the optical source 31, the latter being either arranged to be movable or comprising an optic, such as an optical fiber and / or a lens, movable in order to allow movement of the light beam 25.Likewise, the electromagnetic radiation detector 31 is adapted to allow either by presenting an arrangement adapted to measure the intensity according to the at least one second direction 25B for all of the measurement locations of the first face 10A, or by being movable to allow a measurement for each of these locations.

[0093] It will be noted that if, in the present embodiment, the embrittlement furnace 40 accommodates a single substrate / layer assembly, it is perfectly conceivable that the embrittlement furnace 40 is adapted to allow embrittlement annealing of a number of assemblies greater than or equal to two. According to this possibility, not illustrated, the embrittlement furnace 40 may comprise a first location for the substrate 11 / layer 12 assembly and one or more second locations for one or more other substrate / layer assemblies in order to allow simultaneous embrittlement annealing of the substrate 11 / layer 12 assembly and of the other substrate / layer assemblies.

[0094] According to this same possibility, said second location(s) are arranged so that one face of the other substrate / layer assembly(s) is illuminated by the light beam after the latter has passed through the substrate 11 / layer 12 assembly. The electromagnetic radiation detector 32 is furthermore capable of measuring an intensity of the light beam 25 after scattering by the other substrate / layer assembly(s), the electromagnetic radiation detector 32 being arranged to measure said intensity of the light beam 25 in another second direction having a non-zero angle 20 with the first direction 25A. Such an arrangement can in particular be obtained by means of an electromagnetic radiation detector 32 comprising, for each location, at least one respective unit and a respective optical system dedicated to said unit.

[0095] Of course, as a variant, the embrittlement monitoring device 30 may comprise one or more other electromagnetic radiation detectors 32 in order to measure an intensity of the light beam 25 for one or more of the other substrate / layer assemblies.

[0096] The embrittlement monitoring device 30 may further comprise a processing unit 33 configured to recover an intensity value of the light beam measured by the detector and to determine a state of embrittlement of the interface from said intensity value of the light beam.

[0097] This same processing unit can further be configured to, when determining the state of embrittlement of the interface, correct the measured intensity from a reference intensity determined before the embrittlement annealing. Similarly, depending on the possibility implemented among the different possibilities described above, the processing unit is able to determine the state of embrittlement of the interface 13 from the intensity values ​​measured along the plurality of second directions 25B, 25B' and at different locations of the first face 10A. To do this, when the optical source 31 is configured to allow movement of the light beam 25, and / or when the electromagnetic radiation detector 32 is configured to measure the intensity along a plurality of second directions, control the optical source 31 and / or the electromagnetic radiation detector 32 in accordance with said possibility(s).

[0098] It will be noted that according to one possibility of the invention, the processing unit can be configured to provide the embrittlement furnace 40 with the embrittlement state of the determined interface 13. According to this possibility, the embrittlement furnace 40 can be configured to stop the embrittlement annealing when the embrittlement state of the interface 13 determined by the processing unit 33 reaches a given threshold.

[0099] According to a variant of this possibility of the invention, the processing unit can further be configured to detect the spontaneous fracturing of the assemblies at the end of annealing. Indeed, this event is associated with a sudden variation in the intensity and position of the diffusion intensity which can be detected by the embrittlement monitoring device 30 according to the invention. Thus, according to this variant, the given threshold of the embrittlement state corresponds to a fracturing of the interface 13, said fracturing being detected by a sudden variation in intensity along at least a second direction 25B and / or a shift in the diffusion peak. In an identical manner, the furnace can comprise a control unit configured to communicate with the processing unit of the embrittlement monitoring device and to adjust the conditions of the embrittlement annealing according to the embrittlement state provided by the embrittlement monitoring device.

[0100] According to this latter possibility, it is therefore possible to adjust the annealing conditions used during the annealing step as a function of the state of embrittlement of the interface 13 determined during the implementation of the embrittlement monitoring method. Thus, it is possible to optimize the embrittlement annealing and in particular the heating profile of the furnace, as a function of the state of embrittlement of the interface in order to obtain a desired distribution of microcracks at the interface. This is particularly advantageous when seeking to obtain fracturing outside the furnace. The embrittlement monitoring device 30 according to the invention is capable of allowing the implementation of an embrittlement monitoring method 30 comprising the following steps:

[0101] - illumination of the first face 10A with the monochromatic light beam 25 in the first direction 25A, the wavelength of the light beam 25 being chosen so that the layer 12 and the substrate 13 are substantially transparent at said wavelength,

[0102] - measurement of the intensity of the light beam 25 diffused by the substrate 11 / layer 12 assembly 10 according to at least one second direction 25B, the second direction 25B having a non-zero angle 20 with the first direction 25A,

[0103] - determination of a state of weakening of the interface 13 from said intensity.

[0104] Of course, in accordance with the possibilities described in connection with the embrittlement monitoring device 30, the method is compatible with these different possibilities. In particular, the method according to the invention may also comprise a preliminary calibration step carried out before the embrittlement annealing comprising the following sub-steps:

[0105] - illumination of the first face with the monochromatic light beam 25 in the first direction 25A,

[0106] - measurement of a reference intensity of the light beam 25 diffused by the assembly 10 substrate 11 / layer 12 according to the at least one second direction 25B. During the step of determining a state of embrittlement, a sub-step of correction of the measured intensity from the reference intensity is then provided.

[0107] If such an embrittlement monitoring device 30 and the corresponding method can be used in production in the context of monitoring a fracturing step of an interface 13 between a layer and a support, it can also be used in more specific cases such as during calibration of an embrittlement furnace 40 in the context of an installation or an overhaul of said furnace. In this context, the embrittlement monitoring device 30 is not necessarily integrated into said embrittlement furnace 40 and can be installed in a removable manner in order to implement the calibration step. The embrittlement monitoring device 30 can thus be perfectly removed after carrying out said calibration step.

[0108] As indicated, in a usual configuration, the entire embrittlement monitoring device 30 can be installed outside the enclosure 40A of the embrittlement furnace 40, said enclosure 40A then being provided with portholes transparent to the incident light 25A and diffused light 25B.

[0109] Examples of implementation of the invention

[0110] In order to illustrate the principle of implementation by the monitoring method according to the invention and to provide an example of determining the state of weakening of an interface, an example of measurements obtained by the inventors in the context of such an implementation is described below.

[0111] Thus, as illustrated in Figure 3, in the context of implementing such a method, the inventors measured the variation in intensity 102, 103 of the scattered light beam 25 as a function of the angle 20 between the second direction 25B and the first direction 25A, this during a weakening annealing of a silicon layer 12 supported by a silicon substrate 11 for two different samples, the interface 13 between said layer and said substrate having been implanted beforehand to form micro-cavities at said interface 13. For comparison, the inventors have shown in this same figure the variation in intensity 101 of the scattered light beam 25 as a function of the angle 0 between the second direction 25B and the first direction 25A obtained on a substrate 11 / layer 12 assembly before weakening annealing, such a measurement being able to form, as discussed below in link with figure 4, a reference measurement.

[0112] It can thus be seen that the coalescence of the micro-cavities and the increase in the size of the latter due to this coalescence and at the origin of a significant increase in the scattered light over an angular range 20 from 1° to 12°. Thus, as discovered by the inventors, the scattered light is characteristic of the size and distribution of the cavities at the interface 13 (such a characteristic can be formalized on the basis of a Fraunhofer approximation).

[0113] In order to better illustrate this phenomenon, the inventors have shown in Figure 4 the variation of the difference between the intensity of the light beam measured 102 during embrittlement annealing and that measured 101 before annealing as a function of the angle 20 between the second direction 25B and the first direction 25A. It can be seen that the intensity of scattered light linked to embrittlement annealing is maximum at around 9°, i.e. a micro-cavity size of around 8 microns.

[0114] For comparison, the inventors used a confocal microscope to obtain an infrared image of this same interface 13 which was characterized by the embrittlement tracking device during embrittlement annealing. The inventors performed a Fourier transform of this image and radially averaged the image thus obtained.

[0115] Figure 5 graphically compares the result of this Fourier transform 111 with the variation in intensity as a function of twice the angle between the second direction 25B and the first direction 25A. This comparison shows that these two techniques make it possible to obtain similar results and therefore both make it possible to characterize the state of embrittlement of the interface 13. The method according to the invention has, with respect to such confocal imaging, the advantage of not requiring the placement of an objective close to the sample and therefore of being perfectly capable of equipping a large industrial embrittlement furnace.

[0116] It will be noted that within the framework of the invention, the state of embrittlement of the surface determined from the method according to the invention can be, for example, provided in the form of one of the following values:

[0117] - the angle of the second direction 25B with respect to the first direction for which the increase in diffusion intensity is maximum with respect to a reference intensity determined before the embrittlement annealing,

[0118] - a micro-cavity size value estimated from the intensity of the light beam 25 diffused in the second direction(s) 25B, 25b', an intensity value of the light beam 25 diffused in a second reference direction 25B or a plurality of reference directions 25B, 25B'.

Claims

DEMANDS 1. Method for monitoring the embrittlement of an interface (13) between a layer (12) and a substrate (11) during embrittlement annealing of said interface (13), the substrate (11) / layer (12) assembly having at least a first and a second face (10A, 10B), the method comprising the following steps: - illumination of the first face (10A) with a monochromatic beam of light (25) along a first direction (25A), the wavelength of said beam of light (25) being chosen so that the layer (12) and the substrate (13) are substantially transparent at said wavelength, - measurement of the intensity of the light beam (25) scattered by the substrate (11) / layer (12) assembly (10) along at least a second direction (25B), the second direction (25B) having a non-zero angle (20) with the first direction (25A), - determination of a state of embrittlement of the interface (13) from said intensity.

2. A method for monitoring embrittlement according to claim 1, wherein, when measuring the intensity of the light beam (25), the intensity is measured along a plurality of second directions (25B, 25B') each having a non-zero angle with the first direction (25A), and wherein, preferably, at least two of said second directions (25B, 25B') have distinct angles from each other with respect to the first direction (25).

3. A method for monitoring embrittlement according to claim 1 or 2, wherein a preliminary calibration step is carried out before embrittlement annealing, comprising the following substeps: - illumination of the first face with the beam of light (25) along the first direction (25A), - measurement of a reference intensity of the light beam (25) scattered by the assembly (10) substrate (ll) / layer (12) along at least a second direction (25B), in which, during the step of determining a state of embrittlement, a sub-step is provided for correcting the measured intensity from the reference intensity.

4. Embrittlement monitoring method according to any one of claims 1 to 3, wherein when the first face (10A) is illuminated with the light beam (25) in the first direction, the light beam (25) is displaced in at least two regions of the first face (10A).

5. Embrittlement monitoring method according to any one of claims 1 to 4, wherein the monochromatic light beam (25) has a wavelength within the infrared wavelength range, preferably near infrared, said wavelength being more advantageously between 1050 nm and 1550 nm.

6. A method for embrittling an interface (13) between a layer (12) and a substrate (11) comprising an annealing step for embrittling the entire substrate (11) / layer (12) assembly (10) in order to embrittlead said interface (13), wherein during said annealing step a embrittlement monitoring method according to any one of claims 1 to 6 is implemented.

7. A method for embrittling an interface (13) according to claim 6, wherein the embrittling annealing step is stopped when an interface embrittlement state determined by the embrittlement monitoring method reaches a given threshold, the embrittlement state corresponding preferably to a fracturing of the interface (13), said fracturing then being detected by a variation in intensity along at least a second direction (25B) and / or a diffusion peak shift.

8. Method for weakening an interface (13) according to claim 6 or 7, in which the annealing conditions used during the annealing step are modified according to the embrittlement state of the interface (13) determined during the implementation of the embrittlement monitoring process.

9. Interface embrittlement monitoring device (30) for monitoring the embrittlement of an interface (13) between a layer (12) and a substrate (11) during embrittlement annealing of said interface (13), the substrate (11) / layer (12) assembly (10) having at least a first and a second face (10A, 10B), comprising: - an optical source (31) capable of emitting a monochromatic beam of light (25) in the direction of the first face (10A) along a first direction, - an electromagnetic radiation detector (32) capable of measuring an intensity of the light beam (25) after scattering by the assembly (10) substrate (11) / layer (12), the electromagnetic radiation detector being arranged to measure said intensity of the light beam (25) along a second direction having a non-zero angle (20) with the first direction (25A).

10. Embrittlement monitoring device (30) according to claim 9, wherein the electromagnetic radiation detector is arranged to allow measurement of the intensity of the light beam (25) after scattering along a plurality of second directions (25B, 25B') each having a non-zero angle with the first direction (25A), and wherein, preferably, at least two of said second directions (25B, 25B') have distinct angles from each other with respect to the first direction (25).

11. Embrittlement monitoring device (30) according to claim 9 or 10 further comprising a processing unit (33) configured to retrieve a light beam intensity value (25) measured by the detector (32) and to determine an interface embrittlement state (13) from said light beam intensity value (25).

12. Embrittlement monitoring device (30) according to claim 11 wherein the processing unit (33) is further configured to, when determining the embrittlement state of the interface, correct the measured intensity from a reference intensity determined before embrittlement annealing.

13. Annealing furnace (40) capable of carrying out embrittlement annealing in order to embrittlead an interface between a layer and a substrate, the annealing furnace (40) comprising an embrittlement monitoring device according to any one of claims 9 to 12.

14. Annealing furnace (40) according to claim 13, comprising a first location for the substrate (ll) / layer (12) assembly and at least a second location for another substrate / layer assembly to permit simultaneous embrittling annealing of the substrate (ll) / layer (12) assembly and the other substrate / layer assembly, wherein the second location is arranged so that a face of the other substrate / layer assembly is illuminated by the light beam after the light beam has passed through the substrate (ll) / layer (12) assembly and wherein the electromagnetic radiation detector (32) is further capable of measuring an intensity of the light beam (25) after scattering by the other substrate / layer assembly, the electromagnetic radiation detector (32) being arranged to measure said intensity of the light beam (25) along another second direction having a non-zero angle (20) with the first direction (25A).

15. Annealing furnace (40) according to claim 13 or 14 configured so that, when implementing embrittlement annealing, annealing of the substrate (11) / layer (12) assembly (10) is stopped when the embrittlement monitoring device (30) determines that the embrittlement state of the measured interface (13) reaches a given threshold.

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