Method for monitoring the weakening of the interface between a substrate and a layer and device enabling such monitoring - Patents.com

Abstract

The invention relates to a method for monitoring the weakening of an interface (13) between a layer (12) and a substrate (11) during a weakening anneal, comprising the steps of illuminating a first surface (10A) of a substrate (11) / 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 (11) / layer (12) assembly (10) in at least a second direction (25B), which second direction (25B) forms a non-zero angle (20) with the first direction (25A), and determining from the intensity the weakening state of the interface (13). The invention further relates to a weakening monitor device suitable for carrying out such a method.

Description

[Technical field]

[0001] The present invention relates to the field of manufacturing structures in microelectronics and optoelectronics, and in particular to the field of semiconductor layer transfer that can be used in such manufacturing situations.

[0002] The present invention therefore aims more particularly to provide a method for monitoring the weakening of an interface between a substrate and a layer, a method for weakening such an interface, an apparatus enabling the weakening of this same interface to be monitored, and a system for fracturing the interface between a substrate and a layer. [Background technology]

[0003] In the context of manufacturing structures in microelectronics and / or optoelectronics, semiconductor layers are often transferred from a donor substrate to a host substrate by a Smart Cut® type method involving an implantation step in the donor substrate providing a buried brittle interface that bounds the semiconductor layer to be transferred.

[0004] Such transfer requires bonding of the donor substrate / layer assembly to the host substrate by a layer followed by fracture between the donor substrate and the layer to be transferred at the buried brittle interface, which is typically performed by a weakening anneal that allows growth and coalescence of the microcavities formed at this interface.

[0005] Figure 1 illustrates the change in roughness in a layer after fracture. This change in roughness is the result of differences in crack size, especially at the wafer scale, at the moment when fracture occurs. This can have different causes, especially inhomogeneities in the implantation or weakening annealing, or changes in stress in the stack.

[0006] For this reason, it would be advantageous to be able to monitor the weakening of the interface between the donor substrate and the layer transferred during the weakening anneal. Currently, such monitoring can be performed by infrared microscopy. Such imaging makes it possible to obtain images of the microcavities and therefore to quantify their number and the characteristics of their development, but is not really suited to in situ measurements, especially when the spallation furnace is of industrial type.

[0007] This is because such imaging requires a short distance (at most a few millimeters) between the lens and the sample (i.e. the donor substrate / layer / host substrate assembly), making the introduction into industrial crushing furnaces even more complicated.

[0008] Moreover, at temperature, the IR radiation emitted by the plate and the furnace interferes with the IR signal used for viewing, therefore necessitating a very high power source to illuminate the wafer. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention seeks to remedy the above-mentioned drawbacks. The present invention therefore has the object of providing a method for monitoring the fragility of substrate / layer assemblies, in particular those whose interfaces have to be monitored, that is particularly compatible with the constraints of industrial spallation furnaces and does not require the placement of lenses at close distances from a very high power radiation source. [Means for solving the problem]

[0010] To this end, the invention relates to a method for monitoring the weakening of an interface between a layer and a substrate during a weakening anneal of said interface, the method comprising the following steps: illuminating the first surface with a monochromatic light beam in a first direction; measuring an intensity of the light beam scattered by the substrate / layer assembly in at least one second direction, the second direction having a non-zero angle with respect to the first direction; determining a weakened state of the interface from the strength; Includes:

[0011] The inventors have determined that the intensity of the light scattered at a given angle in the first direction is characterized by the size of the microcavities and the distance between them. It is therefore possible to monitor the weakening of the interface between the layer and the substrate by monitoring the change in this intensity during the weakening anneal. Such illumination and such measurements can be carried out at a distance from the substrate / layer assembly, which is therefore an advantage that this method is perfectly compatible with the constraints associated with industrial-type crushing furnaces in particular. It should be noted in particular that the method according to the invention allows such monitoring to be carried out from outside the enclosure of the crushing furnace, since the light source and the sensor can be placed at a distance from the substrate / layer assembly and is compatible with the use of a viewing window.

[0012] It should be noted that the first direction corresponds to the direction of incidence of the monochromatic light beam, while the second direction or directions correspond to one or more observation directions used to monitor the fracture. Thus, it is entirely possible herein to use "direction of incidence" instead of "first direction" and "observation direction" instead of "second direction" without changing the teachings thereof.

[0013] When the intensity of the light beam is measured, the intensity may be measured in a number of second directions, each of which has a non-zero angle with respect to the first direction, and preferentially, at least two of the second directions may have different angles from each other with respect to the first direction.

[0014] In this way, it is possible to obtain a more precise measurement when these at least two directions have the same angle with respect to the first direction, and to focus on the at least two second directions of the object, which correspond to a weakened state of the object, when the at least two directions have different angles from each other with respect to the first direction.

[0015] This possibility allows the intensity to be measured in a range of second directions, as will be discussed in connection with FIGS.

[0016] The calibration step described above is provided and is performed before the weakening anneal; illuminating the first surface with a light beam in a first direction; measuring a reference intensity of the light beam scattered in at least one second direction by the substrate / layer assembly; Including, During the step of determining the weakened state, a sub-step is provided of correcting the measured intensity by a reference intensity.

[0017] Thus, the scattering peaks associated with the cavities formed during the weakening of the interface are easily identified, and therefore the weakened state of the interface is easy to determine.

[0018] During illumination of the first surface with a light beam in a first direction, the light beam may move in at least two regions or zones of the first surface.

[0019] It is therefore possible to check the homogeneity of the interfacial weakening along the first surface.

[0020] In a variant, such a measurement at two points by moving the light beam is Illuminating the first surface with a light beam and a different light beam, both in a first direction; measuring the intensity of the light beam and another light beam scattered in at least a second direction by the substrate / layer assembly; determining a weakened state of the interface based on the intensities in at least two regions; To this end, a setup may be made that allows such measurements in at least two regions.

[0021] The monochromatic light beam may have a wavelength comprised in the infrared, preferentially near infrared wavelength range, and even more advantageously the wavelength is between 1050 nm and 1550 nm.

[0022] Such wavelengths are particularly suitable when the substrate and / or layers are made from silicon, germanium, or silicon germanium alloys.

[0023] It should be noted that, alternatively, the light beam may have a wavelength in the visible range.

[0024] Such an alternative is particularly applicable when the substrate and / or layers are fabricated from large gap semiconductors such as gallium nitride, aluminum nitride, or alloys of the two, or silicon carbide.

[0025] The invention further relates to a method for weakening an interface comprising a step of performing a weakening anneal of a substrate / layer assembly to weaken the interface between the layer and the substrate, during which annealing step the method for monitoring the weakening according to the invention is performed.

[0026] Such a method enjoys the advantages associated with the monitoring made possible by the monitoring method according to the invention, since in such a method it is easy to monitor and, if applicable, retrospectively identify the growth of cavities present at the interface.

[0027] It is therefore possible to adjust the weakening annealing conditions accordingly, in particular to obtain the required distribution of microcracks, for example by modifying the furnace heating profile in real time.

[0028] The weakening annealing step may be stopped when the weakened state of the interface measured by the weakening monitoring method reaches a given threshold, the weakened state preferentially corresponding to a fracture of the interface, and this fracture is detected by a change in intensity and / or a shift in the scattering peak in at least one second direction.

[0029] In this way it is possible to optimize the fracturing and to stop the annealing at the most appropriate moment.

[0030] It should be noted in particular that, according to one possibility of the invention, the weakening conditions can be selected so that the fracturing is carried out outside the furnace in which the weakening annealing is carried out. In this way, it will be possible to carry out the fracturing outside the furnace if the weakening method requires it.

[0031] The annealing conditions used during the annealing step may be modified according to the weakened state of the interface determined during the weakening monitoring method.

[0032] In this way it is possible to optimize the weakening anneal, and in particular the furnace heating profile, according to the weakening state of the interface in order to obtain the required distribution of microcracks at the interface.

[0033] The present invention further provides an interface weakening monitor for monitoring weakening of an interface between a layer and a substrate during a weakening anneal of the interface, the interface weakening monitor comprising a substrate / layer assembly having at least a first surface and a second surface, an optical source capable of emitting a monochromatic light beam in a first direction toward the first surface; an electromagnetic radiation detector capable of measuring the intensity of the light beam after scattering by the substrate / layer assembly, the electromagnetic radiation detector being positioned to measure the intensity of the light beam in a second direction having a non-zero angle with respect to the first direction; The present invention relates to an interface weakening monitoring device comprising:

[0034] Such an apparatus is adapted to carry out the monitoring method according to the invention and therefore to enjoy the associated advantages.

[0035] The electromagnetic radiation detector may be arranged to enable measurement of the intensity of the light beam after scattering in a plurality of second directions, each of which has a non-zero angle with respect to the first direction, and preferentially at least two of the second directions have different angles with respect to the first direction.

[0036] In this way, it is possible to obtain more precise measurements when these at least two directions have the same angle with respect to the first direction, and to focus on at least two second directions of the object that correspond to a weakened state of the object when the at least two directions have different angles with respect to the first direction.

[0037] It should be noted that such an arrangement of electromagnetic radiation detectors may be provided by using at least two electromagnetic radiation detection units, each arranged to detect the intensity of the light beam after scattering in a respective second direction.

[0038] The detector may thus for example take the form of a matrix of such units (or pixels) to allow measurements in a number of second directions.

[0039] It should be noted that each of these units may comprise an optical component so as to enable measurement of the intensity of the light beam after scattering in a corresponding second direction.

[0040] The attenuation monitor may further comprise a processing unit configured to retrieve intensity values ​​of the light beam measured by the detector and to determine an attenuation state of the interface from the intensity values ​​of the light beam.

[0041] Such a processing unit facilitates the use of the monitoring device according to the invention, so that the technician performing the weakening anneal has direct access to the weakened state of the interface.

[0042] The processing unit may further be configured, when a weakened state of the interface is determined, to correct the measured intensity based on a reference intensity determined before the weakening anneal.

[0043] In this way, scattering peaks associated with cavities formed during interface weakening can be easily identified.

[0044] The invention further relates to an annealing furnace 40 capable of performing a weakening anneal to weaken the interface between a layer and a substrate, the furnace being equipped with a weakening monitor according to the invention.

[0045] Such a weakening monitor allows for in situ weakening monitoring with such annealing furnaces, which is perfectly suited for industrial type annealing furnaces.

[0046] To allow simultaneous weakening annealing of the substrate / layer assembly with another substrate / layer assembly, the annealing furnace may comprise a first location for the substrate / layer assembly and at least one second location for another substrate / layer assembly, the second location is positioned such that a surface of another substrate / layer assembly is illuminated by the light beam after the light beam has passed through the substrate / layer assembly; The electromagnetic radiation detector is further capable of measuring the intensity of the light beam after scattering by another substrate / layer assembly, the electromagnetic radiation detector being positioned to measure the intensity of the light beam in a different, second direction having a non-zero angle relative to the first direction.

[0047] In such an annealing furnace it is possible to perform interface weakening anneals for multiple substrate / layer assemblies while monitoring the weakening of at least two of the interfaces, or even all of the interfaces.

[0048] It should be noted that in such a configuration, the electromagnetic radiation detector may comprise at least two detection units, each dedicated to a corresponding one of the first and second locations.

[0049] When a weakening anneal is performed, the annealing furnace may be configured to stop annealing the substrate / layer assembly when the weakening monitor determines that the measured interface weakened state has reached a given threshold.

[0050] In this way it is possible to provide a weakening anneal that is optimized since it is based on monitoring the weakening of the interface.

[0051] The annealing furnace may comprise a control unit configured to communicate with the processing unit of the weakening monitor and to adjust the conditions of the weakening anneal according to the weakening state provided by the weakening monitor.

[0052] The invention will be better understood on reading the description of example embodiments, given by way of indication only and not limiting in any respect, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0053] [Figure 1] 1 shows roughness mapping performed on a semiconductor layer after fracture at its interface with the donor substrate from which the semiconductor layer originated, with the light intensity value corresponding to the maximum roughness. [Diagram 2] 1 shows an attenuation furnace equipped with an attenuation monitoring device according to the invention. [Diagram 3] 1 shows a graph of the change in intensity of a light beam scattered by a layer / substrate assembly as a function of scattering angle obtained from a weakening monitor according to the present invention and measured respectively before and during the weakening annealing. [Figure 4] The difference in intensity change, calculated by subtracting the intensity measured before the weakening anneal from the intensity measured during the weakening anneal, is plotted as a function of scattering angle. [Diagram 5] 1 is a graph comparing the intensity of a scattered light beam measured using a device according to the invention with the Fourier transform of a confocal microscope image carried out in the prior art. In order to facilitate the transition from one figure to another, identical, similar or equivalent parts of the various figures are given the same reference numbers. In order to make the figures easier to read, the various parts shown in the figures are not necessarily drawn to uniform scale. The various possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with one another. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] FIG. 2 shows a weakening furnace 40 in which a weakening anneal of the interface 13 between the donor substrate 11 and the layer 12 is performed, the weakening furnace 40 being equipped with a weakening monitoring device 30 according to the invention to enable monitoring of the weakening of the interface 13.

[0055] In a typical configuration of the present invention, as shown in Fig. 2, the elements of the weakening monitor 30 are arranged outside the housing 40A of the weakening furnace 40, and the housing 40A is equipped with a viewing window (not shown) to enable weakening monitoring by the weakening monitor 30 according to the present invention. Such a typical configuration is not limiting in any way, and it can be fully envisaged that at least some of the elements of the weakening monitor 30 are at least partially arranged in the housing 40A of the weakening furnace 40 without departing from the scope of the invention.

[0056] In the context of this embodiment example, the substrate, referred to as the donor substrate, and the layer to be transferred are, respectively, a substrate and a layer of monocrystalline silicon Si. Therefore, the wavelengths, numerical values, and other measurements indicated below and in the remainder of this document are adapted to such materials. Naturally, from such teachings, the skilled artisan is in a position to adapt the teachings to other types of materials. Therefore, the invention is particularly adapted to situations of weakening of the interface between a layer and a substrate, both made from silicon germanium Si-Ge alloys or germanium Ge of silicon carbide SiC, or for a silicon Si substrate and a layer of silicon carbide SiC.

[0057] Of course, in conventional applications of the invention, where the invention is concerned with monitoring the weakening of the interface 13 between substrate 11 and the layer 12 it supports, the step of bonding this layer to a host substrate 14 is followed by a weakening anneal, and substrate 11 is the donor substrate used in the context of transferring layer 12 to host substrate 14. Thus, in the general context of the invention, where substrate 11 / layer 12 assembly 10 comprises substrate 11 and layer 12 in conventional applications of the invention, assembly 10 also comprises a host substrate as shown in FIG.

[0058] Such a weakening monitor 30 includes: an optical source 31 capable of emitting a monochromatic light beam 25 in the direction of the first face 10A, the wavelength of the light beam 25 being selected such that the layers 12 and the substrate 11 of 14 are substantially transparent to said wavelength; an electromagnetic radiation detector 32 capable of measuring the intensity of the light beam 25 after scattering by the substrate 11 / layer 12 assembly 10, the electromagnetic radiation detector being arranged to measure the intensity of the light beam in a second direction having a non-zero angle 2θ with respect to the first direction 25A; Equipped with:

[0059] Naturally, such second direction 25B for detection of the light beam 25 scattered by the substrate 11 / layer 12 assembly 10 intersects the first direction 25A in which the light beam 25 is emitted at the level of the scattering element at the starting point of this scattering, i.e. the substrate 11 / layer 12 assembly 10 (more precisely the interface 13 between layer 11 and substrate 12).

[0060] In a normal scattering configuration, the second direction 25B extends from the second surface on its way away from the support, as shown in Figure 2. In a variant not shown in which the scattering measured by the detector is backscattering, the second direction 25B may extend from this on its way away from the first surface. Such a possibility is particularly advantageous to enable observation of scattering by opaque host / receiver substrates or when the transmission angle is not available.

[0061] It should therefore be noted that with respect to scattering of a light beam by the substrate 11 / layer 12 assembly 10, both such scattering, i.e., scattering of the light beam from interface 13 in the direction of second surface 10B, and back scattering, i.e., scattering of the light beam from interface 13 in the direction of first surface 10B, must be understood here and in the remainder of this document.

[0062] A processing unit 33 may further be provided capable of controlling the optical source and the electromagnetic radiation detector 32 to calibrate the weakened state of the interface 13 based on the intensity measured by the electromagnetic radiation detector 32, as described below.

[0063] The optical source 31 is a light source capable of providing / emitting a light beam 25 with a wavelength adapted to the transparency of the material or materials of the substrate 11 and the layer 12. In the present embodiment, as an example, i.e. in the case of a layer and substrate of silicon, the wavelength of the light beam may be an infrared, preferably near-infrared wavelength. The light beam 25 may thus have a wavelength between 1050 nm and 1550 nm, for example equal to 1.2 μm, 1.5 μm or 1.3 μm. To allow such a setting, the optical source may be a laser source, such as a semiconductor laser, a laser diode or a light-emitting diode. Preferentially, the optical source 31 may comprise a system for guiding the light beam 25, such as an optical fiber, advantageously equipped with a collimation system (lenses, mirrors) that defines the size and divergence of the light beam after emission.

[0064] 2, the first direction 25A is preferentially perpendicular to the first surface. Naturally, other first directions 25A may be envisaged without departing from the scope of the invention.

[0065] 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 to provide a signal representative of the intensity of the received radiation. The electromagnetic radiation detector may thus comprise a photodetector such as a photodiode or a number 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 an arrangement, various photodiodes or pixels form the detection units.

[0066] In addition to such a photodetector, the electromagnetic radiation detector 32 may comprise a lens to focus the portion of the light beam 25 scattered in the second direction 25B onto the photodetector.

[0067] According to a first possibility of the invention, the electromagnetic radiation detector can be arranged to receive a part of the beam scattered in a predetermined second direction 25B and to selectively image the light emitting zone. According to this possibility, the second direction is chosen to have an angle of interest 2θ with respect to the first direction 25A, which corresponds to a direction of interest, i.e. to a predetermined weakening state of the interface 13.

[0068] It should be noted that in case the electromagnetic radiation detector 32 comprises multiple detection units, the radiation detector may comprise multiple optical systems, each dedicated to a respective one or group of detection units, each arranged to allow measurement of the intensity of the light beam 25 scattered by the substrate 11 / layer 12 assembly 10 in the second direction 25B in question.

[0069] According to this embodiment example, the inventors have determined that in such a scenario of possibility, a second direction having an angle 2θ between 5° and 15°, preferentially between 8° and 12° and substantially equal to 10°, corresponds to a weakened state of the interface 13 adapted to provide an optimized fracture. The inventors have indeed determined that an angle value of 10° of the second direction 25B with respect to such a first direction 25A corresponds to a microcrack of 10 μm and to a completed state of weakening of the interface 13 adapted to said fracture.

[0070] According to a second possibility of the invention, the electromagnetic radiation detector and its optics can be arranged to receive a part of the light beam scattered in a number of second directions 25B, 25B', each having a non-zero angle 2θ with respect to the first direction. In this way, it is possible to precisely monitor the weakened state of the interface. The number of second directions can correspond to an angle range 2θ with respect to the first direction that corresponds to several weakened states of the interface 13 of interest (thus including, for example, the 10° mentioned above in the context of the first possibility).

[0071] According to a third possibility of the invention, the electromagnetic radiation detector 32 may be movably arranged so as to allow measurement of the intensity of the beam after scattering in a number of second directions 25B, 25B', each having a non-zero angle 2θ with respect to the first direction. Similar to the second possibility disclosed above, this number of second directions may correspond to an angular range 2θ with respect to the first direction corresponding to several weakening states of the interface 13 of interest (thus including, for example, the 10° mentioned above in the context of the first possibility).

[0072] It should also be noted that according to another possibility compatible with the above three possibilities, the attenuation monitor 30 can be configured to move the light beam 25 at least two points or areas of the first surface 10A, the detector being arranged to allow measurement of the intensity of the light beam 25 scattered by the substrate 11 / layer 12 assembly 10 in at least one second direction 25B for these at least two areas. Such a possibility allows mapping of the attenuation state of the interface 13 at the first surface 10A. Such a movement of the light beam 25 is obtained by an adapted configuration of the optical source 31, which is arranged to be movable or which comprises optical components such as optical fibers and / or lenses that are movable to allow the movement of the light beam 25. Similarly, the electromagnetic radiation detector 31 is adapted by having an adapted configuration to measure the intensity in at least one second direction 25B for all measurement points of the first surface 10A or by being movable to allow measurement for each of these points.

[0073] It should be noted that, although in this embodiment the weakening furnace 40 accommodates a single substrate / layer assembly, it may be fully envisioned that the weakening of the furnace 40 is adapted to allow weakening annealing for a number of assemblies greater than or equal to two.

[0074] According to this possibility, not shown, the weakening furnace 40 may include a first location for the substrate 11 / layer 12 assembly and one or more second locations for one or more other substrate / layer assemblies to enable simultaneous weakening annealing of the substrate 11 / layer 12 assembly with one or more other substrate / layer assemblies.

[0075] According to this same possibility, the second location or locations are arranged such that the surface of the other substrate / layer assembly or locations is illuminated by the light beam after passing through the substrate 11 / layer 12 assembly. The electromagnetic radiation detector 32 is furthermore capable of measuring the intensity of the light beam 25 after scattering by the other substrate / layer assembly or locations, the electromagnetic radiation detector 32 being arranged to measure the intensity of the light beam 25 in another second direction having a non-zero angle 2θ with the first direction 25A. Such an arrangement is in particular obtained by the electromagnetic radiation detector 32 comprising, for each location, at least one respective unit and a respective optical system dedicated to this unit.

[0076] Of course, in variants, the attenuation monitor 30 may include one or more other electromagnetic radiation detectors 32 for measuring the intensity of the light beam 25 for one or more of the other substrate / layer assemblies.

[0077] The attenuation monitor 30 may further comprise a processing unit 33 configured to retrieve intensity values ​​of the light beam measured by the detector and to determine the attenuation state of the interface from the intensity values ​​of the light beam.

[0078] This same processing unit may further be configured to correct the measured intensity during the determination of the weakened state of the interface on the basis of a reference intensity determined before the weakening annealing. Similarly, according to an implemented possibility among the various possibilities described above, the processing unit is capable of determining the weakened state of the interface 13 from the intensity values ​​measured in a number of second directions 25B, 25B' and at various points of the first surface 10A. To do this, it controls the optical source 31 and / or the electromagnetic radiation detector 32 according to one or more of the above possibilities, when the optical source 31 is configured to enable the movement of the light beam 25 and / or when the electromagnetic radiation detector 32 is configured to measure the intensity in a number of second directions.

[0079] It should be noted that according to one possibility of the invention, the processing unit may be configured to provide the determined weakened state of the interface 13 to the weakening furnace 40. According to this possibility, the weakening furnace 40 may be configured to stop the weakening annealing when the weakened state of the interface 13 determined by the processing unit 33 reaches a given threshold value.

[0080] According to a variant of this possibility of the invention, the processing unit may further be configured to detect spontaneous fracture of the assembly at the end of the annealing process. In fact, this event is associated with a sudden change in intensity and a position of the scattering intensity, which can be detected by the weakening monitor 30 according to the invention. Thus, according to this variant, a given threshold of a weakened state corresponds to a fracture of the interface 13, which is detected by a sudden change in intensity in at least one second direction 25B and / or a shift of the scattering peak. In exactly the same way, the furnace may comprise a control unit configured to communicate with the processing unit of the weakening monitor and to adjust the weakening annealing conditions according to the weakening state provided by the weakening monitor.

[0081] According to this last possibility, it is therefore possible to adjust the annealing conditions used during the annealing step according to the weakened state of the interface 13, which is determined during the implementation of the weakening monitoring method. It is thus possible to optimize the weakening anneal, in particular the heating profile of the furnace, according to the weakened state of the interface in order to obtain the required distribution of microcracks at the interface. This is particularly advantageous when spalling is to be obtained outside the furnace.

[0082] The weakening monitor 30 according to the invention comprises the following steps: illuminating the first surface 10A with a monochromatic light beam 25 in a first direction 25A, the wavelength of the light beam 25 being selected such that the layer 12 and the substrate 13 are substantially transparent to the wavelength; measuring the intensity of the light beam 25 scattered by the substrate 11 / layer 12 assembly 10 in at least one second direction 25B, the second direction 25B having a non-zero angle 2θ with respect to the first direction 25A; determining the weakened state of the interface 13 from its strength; This makes it possible to implement a weakening monitoring method 30 including the above.

[0083] Naturally, in compliance with the possibilities described in relation to the attenuation monitor 30, the method is compatible with these various possibilities. In particular, the method according to the invention comprises the following sub-steps: illuminating the first surface with a monochromatic light beam 25 in a first direction 25A; measuring a reference intensity of the light beam 25 scattered by the substrate 11 / layer 12 assembly 10 in at least one second direction 25B; It may also include a pre-calibration step carried out before the weakening anneal, comprising: a step of correcting the measured intensity by a reference intensity during the step of determining the weakening state.

[0084] Whereas the weakening monitor 30 and the corresponding method may be used in production in the context of monitoring a step of fracturing the interface 13 between the layer and the support, they may also be used in more specific cases, such as during the calibration of a weakening furnace 40 in the context of installation or maintenance of this furnace. In this context, the weakening monitor 30 is not necessarily integrated into the weakening furnace 40, but may be removably installed in order to carry out a calibration step. It may therefore be entirely sufficient if the weakening monitor 30 is removed after carrying out the calibration step.

[0085] As noted, in a typical configuration, the attenuation monitor 30 is located entirely outside the housing 40A of the attenuation furnace 40 and may include a viewing window that is transparent to the incident light 25A and the scattered light 25B.

[0086] Example of the invention To illustrate the principles of implementation of the monitoring method of the present invention and to provide examples of determining an interface weakening condition, example measurements taken by the inventors in the context of such implementation are described below.

[0087] Thus, as illustrated in Fig. 3, in the context of the implementation of such a method, the inventors measured the variation in intensity 102, 103 of the scattered light beam 25 as a function of the angle 2θ between the second direction 25B and the first direction 25A in two different samples during weakening annealing of a layer 12 of silicon supported by a silicon substrate 11, the interface 13 between the layer and the substrate having been previously implanted so as to form a microcavity at the interface 13. By way of comparison, the inventors show in this same figure the variation in intensity 101 of the scattered light beam 25 as a function of the angle θ between the second direction 25B and the first direction 25A obtained in the substrate 11 / layer 12 assembly 10 before weakening annealing; such a measurement can form a reference measurement, as will be discussed below in connection with Fig. 4.

[0088] Thus, one sees the aggregation of microcavities, their increase in size due to this aggregation, and the onset of a significant increase in the scattered light over the angular range 2θ from 1° to 12°. Thus, as the inventors have discovered, the scattered light is characteristic of the size and distribution of the cavities at the interface 13 (such a feature can be formalized based on the Fraunhofer approximation).

[0089] To better illustrate this phenomenon, we plot the change in the difference between the intensity 102 of the light beam measured during the weakened anneal and the intensity 101 measured before the anneal as a function of the angle 2θ between the second direction 25B and the first direction 25A. It can be seen that the scattered light intensity associated with the weakened anneal is maximum at approximately 9°, i.e., a microcavity size of approximately 8 microns.

[0090] As a comparison, the inventors used a confocal microscope to obtain an infrared image of this same interface 13 that was characterized by the weakening monitor during the weakening annealing. The inventors took a Fourier transform of this image and radially averaged the image thus obtained.

[0091] 5 is a graphical comparison of the result 111 of this Fourier transform and the intensity variation 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 are capable of characterizing the weakened state of the interface 13. The method according to the invention has the advantage that for such confocal images, it is not necessary to place the lens close to the sample, and therefore it is fully possible to equip large industrial weakening furnaces.

[0092] In the context of the present invention, the weakened state of a surface determined using the method according to the invention can, for example, be determined by the following values: the angle of the second direction 25B with respect to the first direction at which the increase in scattered intensity is greatest with respect to a reference intensity determined before the weakening anneal; a microcavity size value estimated from the intensity of the light beam 25 scattered in one or more second directions 25B, 25B′; the intensity value of the light beam 25 scattered in a second reference direction 25B or in a plurality of reference directions 25B, 25B′; It should be noted that the present invention may be provided in one of two forms: [Explanation of symbols]

[0093] 10 Assembly 10A 1st side 10B 2nd side 11 Donor Substrate 12 layers 13 Interface 14 Host Board 25 Monochromatic Light Beam 25A 1st direction 25B,25B' 2nd direction 30 Weakening Monitoring Device 31 Optical source 32 Electromagnetic Radiation Detector 33 Processing Unit 40 Weakening Furnace 40A housing 2θ non-zero angle

Claims

1. A method for monitoring the weakening of an interface (13) between a layer (12) and a substrate (11) during a weakening anneal of said interface (13), said substrate (11) / layer (12) assembly having at least first and second surfaces (10A, 10B), the method comprising: - irradiating said first surface (10A) with a monochromatic light beam (25) in a first direction (25A), the wavelength of said light beam (25) being selected such that said layer (12) and said substrate (13) are substantially transparent to said wavelength; measuring the intensity of the light beam (25) scattered by the substrate (11) / layer (12) assembly (10) in at least one second direction (25B), the second direction (25B) having a non-zero angle (2θ) with respect to the first direction (25A); determining a weakened state of said interface (13) from said strength; The method includes:

2. 2. The method for monitoring attenuation according to claim 1, wherein during the measurement of the intensity of the light beam (25), the intensity is measured in a plurality of second directions (25B, 25B') each having a non-zero angle with respect to the first direction (25A), and preferentially at least two of the second directions (25B, 25B') have mutually different angles with respect to the first direction (25).

3. The calibration step described above is provided and is performed before the weakening anneal; the sub-step of illuminating said first surface with a light beam (25) in said first direction (25A); measuring a reference intensity of said light beam (25) scattered in said at least one second direction (25B) by said substrate (11) / layer (12) assembly (10), During the step of determining the weakened state, a sub-step of correcting the measured intensity based on the reference intensity is provided. The weakening monitoring method according to claim 1 or 2.

4. The method for monitoring weakening according to any one of claims 1 to 3, wherein during irradiation of the first surface (10A) with the light beam (25) in the first direction, the light beam (25) moves in at least two regions of the first surface (10A).

5. The method for monitoring attenuation according to any one of claims 1 to 4, wherein the monochromatic light beam (25) has an infrared wavelength, preferentially a wavelength in the near infrared range, said wavelength being even more advantageously between 1050 nm and 1550 nm.

6. A method for weakening an interface (13) between a layer (12) and a substrate (11), comprising the step of subjecting the substrate (11) / layer (12) assembly (10) to a weakening annealing in order to weaken said interface (13), wherein during said annealing step a method for monitoring weakening as claimed in any one of claims 1 to 6 is implemented.

7. 7. The method for weakening an interface (13) according to claim 6, wherein the weakening annealing step is stopped when a weakened state of the interface (13) determined by the weakening monitoring method reaches a given threshold, the weakened state preferentially corresponding to a fracture of the interface (13), the fracture being detected by an intensity change and / or a shift of the scattering peak in the at least one second direction (25B).

8. 8. A method for weakening an interface (13) according to claim 6 or claim 7, wherein annealing conditions used during the annealing step are modified according to the weakened state of the interface (13) determined during performance of the weakening monitoring method.

9. 1. An apparatus (30) for monitoring weakening of an interface (13) between a layer (12) and a substrate (11) for monitoring weakening of said interface (13) during weakening annealing of said interface, said substrate (11) / layer (12) assembly (10) having at least one first side (10A) and one second side (10B), an optical source (31) capable of emitting a monochromatic light beam (25) in a first direction towards said first face (10A); an electromagnetic radiation detector (32) capable of measuring the intensity of the light beam (25) after scattering by the substrate (11) / layer (12) assembly (10), the electromagnetic radiation detector being arranged to measure the intensity of the light beam (25) in a second direction having a non-zero angle (2θ) with respect to the first direction (25A); An apparatus (30), comprising:

10. 10. The weakening monitor (30) of claim 9, wherein the electromagnetic radiation detector is arranged to enable measurement of the intensity of the light beam (25) after scattering in a plurality of second directions (25B, 25B') each having a non-zero angle with respect to the first direction (25A), and preferentially at least two of the second directions (25B, 25B') have mutually different angles with respect to the first direction (25).

11. The weakening monitoring device (30) of claim 9 or claim 10, further comprising a processing unit (33) configured to collect intensity values ​​of the light beam (25) measured by the detector (32) and to determine a weakening state of the interface (13) based on the intensity values ​​of the light beam (25).

12. The weakening monitor (30) of claim 11, wherein the processing unit (33) is further configured to correct the measured intensity during the determination of the weakened state of the interface from a reference intensity determined before the weakening anneal.

13. An annealing furnace (40) capable of performing a weakening anneal to weaken an interface between a layer and a substrate, the annealing furnace (40) comprising a weakening monitor according to any one of claims 9 to 12.

14. a first location for the substrate (11) / layer (12) assembly and at least one second location for another substrate / layer assembly to enable simultaneous weakening annealing of the substrate (11) / layer (12) assembly with another substrate / layer assembly; the second location is arranged such 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; 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 the intensity of the light beam (25) in a different, second direction having a non-zero angle (2θ) with respect to the first direction (25A); The annealing furnace (40) of claim 13.

15. 15. An annealing furnace (40) as claimed in claim 13 or claim 14, which, when performing a weakening anneal, stops annealing the substrate (11) / layer (12) assembly (10) when the weakening monitor (30) determines that the measured weakened state of the interface (13) has reached a given threshold value.

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