Functional layer transfer process

Abstract

Functional Layer Transfer Method This description relates to a method for transferring a functional layer (110), comprising: - first transfer of the functional layer from a first substrate (112) onto a second substrate, including bonding a flexible temporary substrate (100) to the functional layer, the flexible temporary substrate comprising a first support layer (102) disposed between first and second adhesive layers (104, 106) and a second support layer (108) such that the second adhesive layer is disposed between the first and second support layers, the first adhesive layer being disposed between the functional layer and the first support layer; - removal of the second support layer and the second adhesive layer; - second transfer of at least a portion of the functional layer from the second substrate onto a third substrate;- Removal of the first backing layer and the first adhesive layer. Figure for the abbreviation: Figure 2;

Description

Title of the invention: Functional layer transfer method technical field

[0001] The present description relates in general to the field of functional layer transfer from a first substrate to a second substrate, for example to transfer a functional layer from an initial substrate to a final destination substrate. Previous technique

[0002] A functional layer refers to a single layer or a stack of several layers. More specifically, the functional layer may have a characteristic enabling the operation of at least one active component (e.g., a laser, a diode, a transducer, an actuator, a memory cell, a battery, etc.) or a passive component (e.g., an electrical capacitor, an optical waveguide, a lens, etc.). This characteristic may be related to the composition and / or structural organization of the functional layer, from which emerge remarkable properties that may be mechanical, thermal, electrical, dielectric, piezoelectric, magnetic, optical, etc., and which are fundamental to the operation of the component.

[0003] There are many situations where it is necessary to transfer a functional layer from an initial substrate to a final destination substrate.

[0004] For example, the fabrication of the functional layer may require specific processing conditions (e.g., in terms of temperature, pressure, chemistry, etc.) and / or specific substrates on which the composition and / or structural organization of the functional layer can be achieved. Thus, the optimal initial substrate used for the fabrication of the functional layer may differ from the final substrate on which the functional layer is integrated. For example, the final substrate may not withstand the processing conditions of the functional layer, or it may contain other components and / or elements that do not withstand these processing conditions, or it may not allow the fabrication of the functional layer at all.It is also possible that the initial substrate may not be suitable for the use of the functional layer once the product is finalized, for example because it is too fragile, too thick, not flexible enough, etc.

[0005] According to another example, it may be necessary to transfer the functional layer from the initial substrate used for its fabrication to the final substrate when a a step of processing the face of the functional layer against the initial substrate must be implemented.

[0006] By way of example, the functional layer may correspond to a layer of material comprising, for example, at least one of the following semiconductor materials: silicon, silicon carbide, germanium, a III-V compound such as GaAs, InP, or GaN, or a II-IV compound such as CdTe or ZnO. It may also correspond to a layer of material comprising, for example, at least one piezoelectric material such as LiNbO3, LiTaO3, PZT, or PMN-PT. It may also correspond to a layer of magnetic material or a functional oxide such as ZrO2, YSZ, yttrium-stabilized ZrO2, SrTiO3, or GaO2.

[0007] The functional layer material may be single-crystal. It is also possible for the functional layer material to be polycrystalline, for example when the processing conditions are optimized to obtain, for example, a particular density and size of crystalline grains and / or a preferred crystalline orientation.

[0008] According to another example, the functional layer may include at least one junction and, for example, a pn, npn, or pnp doping variation, or correspond to a power diode or a solar cell. The functional layer may also correspond to an optical stack that can be used to create a laser, for example, a VCSEL type laser, or a light-emitting diode (including a junction and a multi-quantum-well structure). The functional layer may also be used to create a piezoelectric actuator and / or sensor comprising a metal / piezoelectric material stack, or a solid-state battery. According to another example, the functional layer may include electronic components produced by monolithic 3D integration.

[0009] Such a transfer can be achieved by first transferring the functional layer from the initial substrate to a rigid temporary or sacrificial substrate. For example, such a transfer may involve creating a fracture or embrittlement interface in the initial substrate beneath the functional layer, then directly bonding the functional layer to the temporary substrate, and finally separating the initial substrate from the functional layer at the fracture interface. The functional layer is then transferred to the final substrate using the temporary substrate as a mechanical handle. The temporary substrate is then destroyed to release the functional layer.

[0010] The transfer process described above can be applied, for example, to perform a full-plate transfer of the functional layer onto the final substrate. It is also It is possible that this process could be implemented to achieve a collective transfer of several elements or portions of material, for example in chip format, and together forming a functional layer.

[0011] When the functional layer needs to be cut into several distinct portions, the second substrate onto which the functional layer is transferred is not the final destination substrate, but a second temporary substrate. The functional layer and the first temporary substrate are cut, for example by sawing, after the transfer to this second temporary substrate. The cut portions of the first temporary substrate and the functional layer are then individually transferred (a technique known as "pick and place") onto the final destination substrate. The first temporary substrate is then removed, leaving only the portions of the functional layer on the final destination substrate.

[0012] Alternatively, it is possible to attach the functional layer to a temporary substrate, to cut the first substrate and the functional layer, to transfer the cut portions of the first substrate and the functional layer individually onto the final substrate, and to remove the initial substrate to retain only the portions of the functional layer.

[0013] A common drawback of all the above transfer processes is their high cost due to the destruction of the temporary or initial substrate at the end of the process, these substrates being expensive because of the materials used. Furthermore, none of these processes is suitable for transferring a functional layer onto a curved or non-planar substrate.

[0014] US patent 2021 / 0260859 A1 describes another transfer method. Again, this method is not suitable for transferring a functional layer onto a curved or non-planar substrate.

[0015] US patent 6,100,166 A1 describes a method for transferring a functional layer using a flexible substrate to separate the functional layer from the initial substrate. However, this method is not suitable for manipulating the resulting structure, nor for further processing or transfer of the functional layer. Summary of the invention

[0016] There is a need to propose a functional layer transfer method that does not present at least some of the disadvantages of known functional layer transfer methods.

[0017] An embodiment overcomes all or part of the drawbacks of known methods and proposes a method for transferring a functional layer, comprising at least the steps of:

[0018] - first transfer of the functional layer from a first substrate onto a second substrate, including the bonding of a flexible temporary substrate to the functional layer, the flexible temporary substrate comprising at least a first support layer disposed between first and second adhesive layers and a second support layer such that the second adhesive layer is disposed between the first and second support layers, the first adhesive layer being disposed between the functional layer and the first support layer;

[0019] - removal of the second support layer and the second adhesive layer;

[0020] - second transfer of at least a portion of the functional layer from the second substrate on a third substrate;

[0021] - removal of the first support layer and the first adhesive layer.

[0022] According to a particular embodiment, the first transfer of the functional layer comprises at least, after the bonding of the flexible temporary substrate to the functional layer:

[0023] - a separation of the functional layer and the first substrate;

[0024] - a division of the functional layer into several distinct portions held mechanically between them by at least one of the layers of the flexible temporary substrate;

[0025] - a collective bonding of the portions of the functional layer on the second substrate.

[0026] According to a particular embodiment, the cutting is carried out through at least the functional layer, the first adhesive layer and the first support layer.

[0027] According to a particular embodiment, the second transfer is implemented individually for each of the portions of the functional layer.

[0028] According to a particular embodiment, the first transfer further comprises, before the bonding of the flexible temporary substrate to the functional layer, the creation of a region between the functional layer and the first substrate intended to facilitate a separation between the functional layer and the first substrate, and further comprises, after the bonding of the flexible temporary substrate to the functional layer, a separation of the functional layer and the first substrate at the level of said region.

[0029] According to a particular embodiment:

[0030] - during the first transfer, adhesion forces between the layers of the substrate temporary flexible layer between the first adhesive layer and the functional layer are greater than the adhesion force between the functional layer and the first substrate, and / or

[0031] - during the removal of the second backing layer and the second adhesive layer, the adhesion strength between the second adhesive layer and the first substrate layer is less than that between the first substrate layer and the first adhesive layer, between the first adhesive layer and the functional layer, and between the functional layer and the second substrate, and / or

[0032] - during the second transfer, the adhesion force between said at least a portion of the functional layer and the second substrate is less than those between the first support layer and the first adhesive layer and between the first adhesive layer and the functional layer, and / or

[0033] - during the removal of the first backing layer and the first adhesive layer, the adhesion strength between said at least a portion of the functional layer and the first adhesive layer is less than that between the functional layer and the third substrate.

[0034] According to a particular embodiment, the transfer process further comprises, during the process, the implementation of one or more treatment steps of at least one of the first and second adhesive layers, modifying the adhesive properties of said at least one of the first and second adhesive layers.

[0035] According to a particular embodiment, one of the first and second adhesive layers comprises a material whose adhesive properties are reduced by the implementation of a UV treatment, and the other of the first and second adhesive layers comprises a material whose adhesive properties are reduced by the implementation of a heat treatment.

[0036] According to a particular embodiment, the first transfer is implemented such that at least one third adhesive layer is disposed between the second substrate and the functional layer at the end of the first transfer.

[0037] According to a particular embodiment, the transfer process further comprises, prior to the first transfer and / or during the first transfer and / or during the second transfer, at least one functional layer processing step.

[0038] According to a particular embodiment, the bonding of the flexible temporary substrate to the functional layer is implemented by interposing at least one magnetic layer between the functional layer and the flexible temporary substrate, and / or the flexible temporary substrate comprises at least one magnetic layer.

[0039] According to a particular embodiment, the flexible temporary substrate comprises at least one marking layer configured to be laser-marked and interposed between the first support layer and the second adhesive layer and / or between the first adhesive layer and the first support layer, and the method comprises in addition to the implementation of at least one marking step in the marking layer before the second transfer.

[0040] According to a particular embodiment, the functional layer comprises at least one piezoelectric material.

[0041] According to a particular embodiment, the process for making a piezoelectric sensor includes the implementation of a process for transferring a functional layer according to a particular embodiment. Brief description of the drawings

[0042] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0043] [Fig.1], [Fig.2], [Fig.3], [Fig.4], [Fig.5], [Fig.6], [Fig.7], [Fig.8] and [Fig.9] represent steps in a process for transferring a functional layer according to a particular embodiment;

[0044] Figures 10, 11 and 12 represent steps in a transfer process of a functional layer according to different implementation variants. Description of the implementation methods

[0045] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0046] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been represented and are detailed.

[0047] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0048] In the following description, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", "on", "under", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures corresponding to a normal position of use.

[0049] In the figures, in order to facilitate their reading, the different elements and the different layers are not represented at the same scale relative to each other.

[0050] Unless otherwise specified, the expressions "approximately", "roughly", and "in the order of" mean within 10%, preferably within 5%.

[0051] Each layer of material can correspond to a single layer of material or a stack of several stacked layers.

[0052] An example of a functional layer transfer method is described below in relation to Figures 1 to 9.

[0053] The transfer process is implemented using a flexible temporary substrate, or soft substrate, 100 (hereafter referred to as "STF"), an example of which is shown in [Fig.1].

[0054] The STF 100 comprises a first support layer 102 disposed between first and second adhesive layers 104, 106. The STF 100 further comprises a second support layer 108 such that the second adhesive layer 106 is disposed between the first and second support layers 102, 108.

[0055] According to one embodiment, the total thickness of the STF 100 is, for example, on the order of 200 µm, with first and second support layers 102, 108 each having a thickness, for example, of 90 µm, and first and second adhesive layers 104, 106 each having a thickness, for example, of 10 µm. Alternatively, the thicknesses of the layers of the STF 100 may differ from these examples. Furthermore, alternatively, the thicknesses of the first and second support layers 102, 108 may differ from each other, and / or the thicknesses of the first and second adhesive layers 104, 106 may differ from each other. Generally speaking, the thickness of the STF 100 can range from 10 µm to 800 µm.

[0056] According to one embodiment, the first and second support layers 102, 108 comprise a polymer, for example PET (polyethylene terephthalate), PE (polyethylene), PP (polypropylene), PVC (polyvinyl chloride), PO (polyolefin), etc., and / or comprise a metallic material. Alternatively, the materials of the first and second support layers 102, 108 may be different from each other.

[0057] As described later, in the described transfer process, after a first transfer of the functional layer from a first substrate to a second substrate, the second support layer 108 and the second adhesive layer 106 are intended to be removed. Then, after a second transfer from the second substrate to a third substrate, the first support layer 102 and the first adhesive layer 104 are intended to be removed. The materials of the adhesive layers 104, 106 can therefore be such that:

[0058] - during the first transfer, of adhesion forces between the different layers of STF 100 and between the first adhesive layer 104 and the functional layer are greater than the adhesion force between the functional layer and the first substrate;

[0059] - during the removal of the second support layer 108 and the second layer adhesive 106, the adhesion force between the second adhesive layer 106 and the first support layer 102 is less than those between the first support layer 102 and the first adhesive layer 104, between the first adhesive layer 104 and the functional layer and between the functional layer and the second substrate;

[0060] - during the second transfer, the adhesion force between the functional layer and the second substrate is inferior to those between the first support layer 102 and the first adhesive layer 104 and between the first adhesive layer 104 and the functional layer;

[0061] - during the removal of the first support layer 102 and the first adhesive layer 104, the adhesion force between the functional layer and the first adhesive layer 104 is less than that between the functional layer and the third substrate.

[0062] Furthermore, during the aforementioned withdrawals implemented during the process, the cohesive force of the functional layer is greater than the adhesion force of the withdrawn layers.

[0063] According to one embodiment, the materials of the first and second adhesive layers 104, 106 may have by default adhesive properties, or adhesion properties, satisfying the above conditions. Alternatively, it is possible that the material(s) of at least one of the first and second adhesive layers 104, 106 may be such that their adhesive properties can be modified during the transfer process. For example, such a modification of the adhesive properties of a material of one of the adhesive layers 104, 106 may be achieved by exposing this material to a certain temperature and / or to radiation at a certain wavelength.

[0064] According to one embodiment, the material of the first adhesive layer 104 may comprise acrylic whose adhesive properties become very weak after exposure to a certain temperature, for example, above approximately 190°C when the first adhesive layer 104 comprises methacrylate monomer-based acrylic. The material of the second adhesive layer 106 may comprise nitrogen-based photodegradable compounds so that its adhesive properties become very weak after exposure to UV radiation. Alternatively, the materials of the first and second adhesive layers 104, 106 may be such that their adhesive properties become very weak when exposed to different temperatures or different wavelengths.

[0065] By way of example, the adhesive properties of the first and second adhesive layers 104, 106 may be such that their adhesive strength is between 0.01 N / cm and 15 N / cm. The adhesion strength of each of the first and second adhesive layers 104, 106 can be measured in accordance with the measurement method known as "Peel Adhesion", or peel adhesion, as described in ASTM D3330 or AFERA4001.

[0066] In the example of [Fig.1], the STF 100 has a first face 107 formed by one of the faces of the first adhesive layer 104, and a second face 109 formed by one of the faces of the second support layer 108. In the example described, unlike the second face 109, the first face 107 of the STF 100 has non-zero adhesive properties allowing this first face 107 of the STF 100 to be glued against an element to which the STF 100 is intended to be bonded.

[0067] In addition to the above characteristics relating to the adhesive properties of the first and second adhesive layers 104, 106, the layers 102 to 108 of STF 100 are such that STF 100 is flexible. Considering the flexural rigidity of STF 100, this can be defined by the equation:

[0068] n _ Eh3 U 12(1-.92)

[0069] with D the flexural stiffness of the STF 100, in GPa.pm3;

[0070] E the Young's modulus of STF 100, in GPa;

[0071] h the thickness of the STF 100, in pm;

[0072] v the Poisson coefficient of STF 100.

[0073] The flexural stiffness D of the STF 100 can be between 1 GPa.pm3 and 107 GPa.pm3.

[0074] In the example of [Fig.2], the STF 100 is attached, at the level of its first face 107, to the functional layer 110 intended to be transferred from a first substrate 112 to a second substrate 114 (visible on [Fig.5]). In the described embodiment, prior to the implementation of this bonding, a weakening region 116 is formed between the functional layer 110 and the first substrate 112. Different techniques can be implemented to create the weakening region 116, the choice of technique depending in particular on the material(s) of the functional layer 110 and the first substrate 112. According to a first example, the weakening region 116 can be formed by performing ion implantation in the first substrate 112, followed by annealing resulting in the formation of bubbles allowing the subsequent separation of the functional layer 110 from the first substrate 112.According to a second example, the embrittlement region 116 can be formed by porosification in the first substrate 112, the subsequent separation of the functional layer 110 from the first substrate 112 being achieved by etching. According to a third example, the embrittlement region 116 can be formed by laser. Lift-off, or laser delamination. Other techniques can be used to form the embrittlement region 116.

[0075] According to one embodiment, the functional layer 110 may correspond to a thin upper portion of the first substrate 112. In this case, it is the embrittlement region 116 that defines the functional layer 110, the material of which (or at least one of the materials) corresponds to that of the first substrate 112. For example, the first substrate 112 may correspond to a piezoelectric material substrate, and the functional layer 110 may correspond to a thin upper portion derived from the first substrate 112. According to another embodiment, the functional layer 110 may correspond to a layer of material produced by epitaxy on the first substrate 112. More generally, the material of the functional layer 110 may correspond to a single-crystal material that cannot be obtained directly, without transfer, on the final substrate.

[0076] Alternatively, it is possible that the embrittlement region 116 is replaced by a low adhesion force interface, such as for example that described in document FR3082997A1.

[0077] The thickness of the functional layer 110 may be less than 20 pm, or even less than or equal to 1 pm. Furthermore, the thickness of the functional layer 110 may depend on its nature, that is to say whether it corresponds to a single layer of material or to a stack of several layers of material, and / or whether it includes electrical and / or electronic elements and / or components.

[0078] The technique(s) used to bond the STF 100 to the functional layer 110 may depend, in particular, on the materials of the STF 100 and the functional layer 110. In the embodiment described here, the STF 100 is applied, for example, by lamination onto the functional layer 110. Other techniques may be used to achieve this bonding. The bonding between the STF 100 and the functional layer 110 is ensured by the adhesive properties of the first adhesive layer 104, on the first face 107 of the STF 100.

[0079] In the described embodiment, as shown in [Fig. 3], the functional layer 110 and the first substrate 112 are subsequently separated. During this separation, the adhesion forces between the different layers of the STF 100 and between the first adhesive layer 104 and the functional layer 110 are greater than the adhesion force between the functional layer 110 and the first substrate 112. According to one embodiment, this separation can be achieved by attaching a rigid peripheral element (not visible in the figures) to the STF 100 and using this element as a mechanical handle. Other separation methods are possible, whether mechanical, thermal, lift-off, etc.

[0080] In the described embodiment, as shown in [Fig. 4], the functional layer 110 is then cut into several distinct portions mechanically held together by at least one of the layers of the STF 100. This cutting step can be used to define the shape of elements, or portions, intended to be subsequently transferred onto different substrates. For example, when the functional layer 110 corresponds to a piezoelectric layer, this cutting step can be used to cut the shape of piezoelectric portions intended to serve as sensing elements of different piezoelectric sensors.

[0081] The cut (represented by cutting lines designated by reference numeral 118) can be made through at least the functional layer 110, the first adhesive layer 104 and the first support layer 102. In the example of [Fig. 4], the cut is also made through a part of the second adhesive layer 106. Alternatively, depending in particular on the thickness of the second support layer 108, this cut can also be made through the entire thickness of the second adhesive layer 106, or even through a part of the thickness of the second support layer 108.

[0082] According to one embodiment, the cutting is performed by laser. Other techniques for singulating portions of the functional layer 110, for example mechanical ones, can be implemented to perform this cutting.

[0083] As shown in [Fig.5], the functional layer 110 is transferred to a second substrate 120 using the STF 100 as a transport element for the functional layer 110. In the described embodiment, given the cutting of the functional layer 110 previously carried out, this transfer corresponds to a collective joining of the portions of the functional layer 110 on the second substrate 120.

[0084] In the example of [Fig. 5], the second substrate 120 corresponds to a rigid substrate on which an adhesive layer 122, comprising for example a silicone gel, is disposed to ensure bonding between the functional layer 110 and the second substrate 120. Alternatively, it is possible that the second substrate 120 corresponds to a flexible substrate, for example similar to or different from the first support layer 102 and / or the second support layer 108. Other variants are also conceivable, such as a second substrate 120 corresponding to a ceramic plate with which the adhesion of the functional layer 110 is ensured by suction, by electrostatic forces, etc.

[0085] The transfer process then involves removing the second support layer 108 and the second adhesive layer 106 (see [Fig. 6]). According to one embodiment, this removal corresponds to peeling achieved by applying a mechanical force pulling on the second support layer 108. Alternatively, other techniques can be implemented to achieve this removal.

[0086] In the described embodiment, when removing the second support layer 108 and the second adhesive layer 106, the bond strength between the second adhesive layer 106 and the first support layer 102 is less than those between the first support layer 102 and the first adhesive layer 104, between the first adhesive layer 104 and the functional layer 110 and between the functional layer 110 and the second substrate 120 (between the functional layer 110 and the adhesive layer 122 in the example shown in [Fig.6]).

[0087] According to one embodiment, the low adhesion strength between the second adhesive layer 106 and the first support layer 102 can be achieved by subjecting the second adhesive layer 106 to a treatment that reduces its initial adhesion strength. The nature of the treatment implemented may depend, in particular, on the nature of the material(s) of the second adhesive layer 106. For example, when the material of the second adhesive layer 106 comprises nitrogen-based photodegradable compounds, this treatment may consist of exposing the material of the second adhesive layer 106 (for example, through the second support layer 108) to UV radiation. In this example, the UV radiation used degrades the adhesive properties of the second adhesive layer 106 until they are very weak, or even nonexistent.It is then possible to remove the second support layer 108 and the second adhesive layer 106 without removing any other layers from the stack created at this stage of the transfer process. Furthermore, the material of the first adhesive layer 104 can be chosen such that its adhesive properties are not, or only minimally, affected by this treatment, as is the case, for example, when choosing a first adhesive layer 104 containing acrylic, the adhesive properties of which are not altered by UV treatment.

[0088] After removing the second support layer 108 and the second adhesive layer 106, the mechanical cohesion between the portions of the functional layer 110 is ensured by the second substrate 120 (and the adhesive layer 122 in the example described).

[0089] A second transfer of one or more portions of the functional layer 110 from the second substrate 120 to at least a third substrate 124 is then carried out (see Figures 7 and 8). In the described embodiment, this second transfer is carried out individually for each portion of the functional layer 110, for example, by a placement device 126, i.e., a "pick and place" type device. Alternatively, other transfer techniques are possible.

[0090] In the described embodiment, during this second transfer, the adhesion force between the portions of the functional layer 110 and the second substrate 120 is less than those between the first support layer 102 and the first adhesive layer 104 and between the first adhesive layer 104 and the functional layer 110. In the described embodiment, this translates into a force opposing the adhesion force between the second substrate 120 and the functional layer 110, applied to the second support layer 108 by the equipment 126, and which is greater than the adhesion force between the portion of the functional layer 110 and the second substrate 120. The force enabling this detachment of the portions of the functional layer 110 from the second substrate 120 corresponds, for example, to a suction force applied by the equipment 126 on each portion of the first support layer 102.

[0091] In the described embodiment, the third substrate 124 onto which the portions of the functional layer 110 are transferred corresponds to the final destination substrate of these portions. This third substrate 124 may be a rigid substrate, a flexible substrate, a PCB, etc. In a particular configuration different from that shown in Figures 7 and 8, the third substrate 124 may have a curved surface onto which one or more portions of the functional layer 100 are transferred.

[0092] In the described embodiment, the retention of the portions of the functional layer 110 on the third substrate 124 is ensured by a third adhesive layer 128 disposed between the third substrate 124 and the portion(s) of the functional layer 110. For example, the third adhesive layer 128 may comprise a solder paste or an electrically conductive film (deposited anisotropically or isotropically) allowing electrical contact to be restored with the portion(s) of the functional layer 110. If it is not necessary to restore electrical contact with the portion(s) of the functional layer 110, the third adhesive layer 128 may comprise, for example, an epoxy and / or acrylic resin.

[0093] As an alternative to the embodiment described above, after implementing the steps described above in connection with Figures 1 to 6, the portions of the functional layer 110 can be transferred not individually onto the third substrate 124, but collectively, for example by using equipment equipped with a roller against which the first support film 102 is secured and allowing the portions of the functional layer 110 to be transferred collectively onto the third substrate 124.

[0094] The first support layer 102 and the first adhesive layer 104 are then removed and separated from the functional layer 110 (see [Fig. 9]). According to one embodiment, this removal can correspond to a peeling action performed by applying a mechanical force pulling on the first support layer 102 and opposing the adhesion force between the first adhesive layer 104 and the functional layer 110. Alternatively, other techniques can be applied to achieve this removal of the first support layer 102 and the first adhesive layer 104.

[0095] In the described embodiment, during this removal, the adhesion force between the portion(s) of the functional layer 110 and the first adhesive layer 104 is lower than that between the functional layer 110 and the third substrate 124 (between the functional layer 110 and the third adhesive layer 128 in the example in [Fig. 9]). According to one embodiment, the low adhesion force between the first adhesive layer 104 and the functional layer 110 can be obtained by subjecting the first adhesive layer 104 to a treatment that reduces its initial adhesion force. The nature of the treatment applied may depend, in particular, on the nature of the material(s) of the first adhesive layer 104. For example, when the material of the first adhesive layer 104 contains acrylic, this treatment may correspond to a heat treatment, for example, carried out at a temperature of at least 190°C.In this example, the temperatures to which the first adhesive layer 104 is exposed degrade its adhesive properties until they are very low, or even nonexistent. It is then possible to remove the first support layer 102 and the first adhesive layer 104 without detaching the portion(s) of the functional layer 110 from the third substrate 124. Furthermore, the material of the third adhesive layer 128 can be chosen such that its adhesive properties are not, or only minimally, affected by this heat treatment, as is the case, for example, by choosing a third adhesive layer 128 made of a material comprising nitrogen-based photodegradable compounds whose adhesive properties are not altered by heat treatment.

[0096] Following the removal of the first support layer 102 and the first adhesive layer 104, the resulting stack(s) of portions of the functional layer 110 and the third substrate 124 can be used to create a device. For example, portions of the functional layer 110 can correspond to thin portions of piezoelectric material used to manufacture piezoelectric sensors. Numerous other applications are possible.

[0097] In the previously described example of a transfer process, treatment steps are described to reduce the adhesion forces of the first and second adhesive layers 104, 106 just before the removal steps of these layers are carried out. Alternatively, or in combination with these steps for reducing the initial adhesion forces of the adhesive layers, it is possible to carry out, during the transfer process, treatment steps on the adhesive layers that enhance their adhesion strength. For example, before the first transfer of the piezoelectric layer 110 onto the second substrate 120, it is possible to carry out One or more processing steps increasing the adhesion strength of the first and second adhesive layers 104, 106. As another example, before removing the second support layer 108 and the second adhesive layer 106, it is possible to implement one or more processing steps increasing the adhesion strength of the first adhesive layer 104 and / or the adhesive layer 122. As another example, before the second transfer of portions of the functional layer 110 onto the third substrate 124, it is possible to implement one or more processing steps increasing the adhesion strength of the first adhesive layer 104. By way of example, such a step for strengthening the adhesion strength of an adhesive layer could correspond to UV curing in the case of an adhesive layer comprising an acrylic adhesive, or temperature curing in the case of an adhesive layer comprising an epoxy adhesive.

[0098] As an alternative to the transfer process described above, it is possible to implement, for example before the bonding of the STF 100 to the functional layer 110, and / or between the separation of the functional layer 110 from the first substrate 112 and its bonding to the second substrate 120, and / or between the separation of the functional layer 110 from the second substrate 112 and its bonding to the third substrate 124, one or more processing steps for the functional layer 110. Such processing steps correspond, for example, to cleaning, etching (e.g., by laser, plasma, etc.), deposition, activation, etc., steps. Such processing steps can be implemented for one or both faces of the functional layer 110, since each face of the functional layer 110 is accessible during the transfer process.

[0099] According to an alternative embodiment illustrated in [Fig. 10], prior to the attachment of the STF 100 to the functional layer 110, a magnetic layer 130, i.e., a layer of material exhibiting magnetic properties, may be formed on the functional layer 110. This magnetic layer 130 may be a ferromagnetic layer and may include, for example, iron, nickel, or cobalt. It is also possible that the magnetic layer 130 may be a diamagnetic layer including, for example, carbon, copper, or silver. It is also possible that the magnetic layer 130 may be a paramagnetic layer including, for example, tungsten, aluminum, or lithium. It is also possible that the magnetic layer 130 may comprise several magnetic materials, combining or not these different magnetic properties.The magnetic layer 130 can be produced by depositing it onto the functional layer 110, for example by evaporation, PECVD (plasma-enhanced chemical vapor deposition), electrochemical deposition, etc. After the magnetic layer 130 has been deposited onto the functional layer 110, . The STF 100 can be bonded to the magnetic layer 130, as shown in [Fig. 10]. The other steps of the process can be similar to those previously described. At the end of the transfer process, the magnetic material remaining on the functional layer 110 can be removed or retained.

[0100] According to another embodiment illustrated in [Fig. 11], it is possible that the magnetic layer 130 is not formed on the functional layer 110 prior to the bonding of the STF 100, but is integrated into the STF 100, for example between the first support layer 102 and the first adhesive layer 104. In this case, the magnetic layer 130 can be removed when the first support layer 102 and the first adhesive layer 104 are removed. Alternatively, the magnetic layer 130 could be arranged between the first support layer 102 and the second adhesive layer 106, or between the second support layer 108 and the second adhesive layer 106.

[0101] According to another embodiment, it is possible to have at least one first magnetic layer interposed between the functional layer 110 and the STF 100, and at least one second magnetic layer disposed within the STF 100. Such a configuration can increase the overall magnetic power formed by these layers compared to a single layer of magnetic material, or allow the magnetic properties of two magnetic layers with different properties to be combined. It is also possible to have several magnetic layers present within the STF 100.

[0102] The presence of the magnetic layer 130 between the functional layer 110 and the STF 100 and / or within the STF 100 improves the handling and processing of the assembly produced and manipulated during the various stages of the process. The presence of the magnetic layer 130 can ensure the flatness of the assembly produced during the various stages, for example, by using a magnetic planar tool to which the assembly is held by the presence of the magnetic layer 130. The presence of the magnetic layer 130 can also allow other objects to be attached to this assembly, thanks to the magnetic forces generated, for example, for the implementation of certain processing steps of the functional layer 110 (for example, a mask for applying a coating to the functional layer 110).The presence of the magnetic layer 130 can also help maintain the cohesion of the different parts of the assembly obtained after the cutting step. According to a particular embodiment, it is also possible that the retention of the functional layer 110 on the second substrate 120 is ensured by magnetic forces exerted between the magnetic layer 130 and another magnetic material present on or in the second substrate 120.

[0103] According to an alternative embodiment illustrated in [Fig. 12], the STF 100 may include a marking layer 132 configured to be marked by laser engraving. The marking layer 132 is not transparent to the wavelength of the laser used to perform the desired marking. The marking layer 132 may be interposed between the first support layer 102 and the second adhesive layer 106, or between the first adhesive layer 104 and the first support layer 102. In the example of [Fig. 12], the marking is performed through the second support layer 108 and the second adhesive layer 106, which, in this example, are transparent to the wavelength of the laser used. For example, the marking layer 132 may include a metal such as aluminum, copper, nickel, gold, platinum, and / or a polymer such as PET, PVC, polyimide, PP, polycarbonate, etc., and / or glass, for example borosilicate, soda-lime glass, quartz glass, and / or a crystal such as silicon, quartz, or sapphire. Preferably, the marking layer material 132 can be inorganic, and / or metallic to allow for the dissipation of heat generated by the marking. Furthermore, the marking layer material 132 can be opaque to wavelengths in the visible range, which simplifies the alignment of the marked elements and / or subsequent marking recognition.

[0104] The marking of layer 132 can be carried out in one or more steps implemented before the second transfer from the second substrate 120 to the third substrate 124. According to one embodiment, this marking can correspond to an identifier used to identify the different portions of the functional layer 110 after the implementation of the second transfer, and / or can correspond to alignment marks. For example, this marking can indicate whether the portions of the functional layer 110 are intended for subsequent use or not.

[0105] According to one variant, the marking layer 132 can also serve as a magnetic layer capable of fulfilling the same functions as those previously described for the magnetic layer 130 if the material or materials are suitable for this, as is the case for example for a marking layer 132 comprising nickel.

[0106] In all embodiments, the substrates used in the transfer process can correspond to cylindrical wafers such as those used in the field of microelectronics.

[0107] Thus, in an example of an embodiment of this transfer process, from an initial substrate, a functional layer can be detached by being fixed to a flexible temporary substrate having a structure allowing a posteriori a singularization of the functional layer into smaller elements and their selective or collective transfer onto a final flat or curved substrate.

[0108] For all the embodiments described, the described transfer process can:

[0109] - a check of the flatness of the assembly during the different stages;

[0110] - a protection of the functional layer 110;

[0111] - facilitated manipulation of functional layer 110;

[0112] - a singularization of functional layer 110 into several facilitated elements by maintaining the assemblies;

[0113] - a collective or individual transfer of portions of the functional layer 110;

[0114] - access to both faces of the functional layer 110 during the process of transfer ;

[0115] - a transfer onto a final flat or curved substrate;

[0116] - a dissociation of the first and second transfers implemented, one of which may be of the pick and place type of portions of the functional layer 110 and the other which can correspond to a collective transfer of the functional layer 110 or portions of the functional layer 110, which allows for example to transfer portions of the functional layer 110 with a spacing, one with respect to the other ("pitch" in English), differ before and after the transfer.

[0117] Furthermore, compared to using two separate adhesive strips, using STF 100 to implement the functional layer 110 transfer process described above offers the following advantages:

[0118] - time saving (only one step of bonding the STF 100 to the layer functional 110, unlike the use of two separate adhesive strips requiring the implementation of two separate steps to attach them to the functional layer);

[0119] - reduction of defects (in particular the appearance of bubbles, particles, etc.);

[0120] - release of constraints (for example in terms of temperature, pressure, contamination, environment) of compatibility of the first substrate 112 with the steps related to the bonding of the STF 100 to the functional layer 110 (the bonding of the STF 100 to the functional layer 110 can be carried out without having to heat or apply pressure, unlike the successive bonding of two adhesive strips which may require a particular temperature and / or pressure to avoid the presence of bubbles between them).

[0121] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0122] Finally, the practical implementation of the embodiments and variants described is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

Demands

1. A method for transferring a functional layer (110), comprising at least the steps of: - first transfer of the functional layer (110) from a first substrate (112) onto a second substrate (120), including the bonding of a flexible temporary substrate (100) to the functional layer (110), the flexible temporary substrate (100) comprising at least a first support layer (102) disposed between first and second adhesive layers (104, 106) and a second support layer (108) such that the second adhesive layer (106) is disposed between the first and second support layers (102, 108), the first adhesive layer (104) being disposed between the functional layer (110) and the first support layer (102); - removal of the second support layer (108) and the second adhesive layer (106); - second transfer of at least a portion of the functional layer (110) from the second substrate (120) to a third substrate (124); - removal of the first support layer (102) and the first adhesive layer (104).

2. A transfer method according to claim 1, wherein the first transfer of the functional layer (110) comprises at least, after the bonding of the flexible temporary substrate (100) to the functional layer (110): - a separation of the functional layer (110) and the first substrate (112); - a cutting of the functional layer (110) into several distinct portions held mechanically together by at least one of the layers of the flexible temporary substrate (100); - a collective bonding of the portions of the functional layer (110) on the second substrate (120).

3. Transfer method according to claim 2, wherein the cutting is carried out through at least the functional layer (110), the first adhesive layer (104) and the first support layer (102).

4. Transfer method according to any one of claims 2 or 3, wherein the second transfer is carried out individually for each of the portions of the functional layer (110).

5. A transfer method according to any one of the preceding claims, wherein the first transfer further comprises, before the bonding of the flexible temporary substrate (100) to the functional layer (110), the creation of a region (116) between the functional layer (110) and the first substrate (112) intended to facilitate a separation between the functional layer (110) and the first substrate (112), and further comprises, after the bonding of the flexible temporary substrate (100) to the functional layer (110), a separation of the functional layer (110) and the first substrate (112) at the level of said region (116).

6. A transfer method according to any one of the preceding claims, wherein: - during the first transfer, the adhesion forces between the layers of the flexible temporary substrate (100) and between the first adhesive layer (104) and the functional layer (110) are greater than the adhesion force between the functional layer (110) and the first substrate (112), and / or - during the removal of the second support layer (108) and the second adhesive layer (106), the adhesion force between the second adhesive layer (106) and the first support layer (102) is less than those between the first support layer (102) and the first adhesive layer (104), between the first adhesive layer (104) and the functional layer (110), and between the functional layer (110) and the second substrate (120), and / or - during the second transfer,the adhesion force between said at least a portion of the functional layer (110) and the second substrate (112) is less than those between the first support layer (102) and the first adhesive layer (104) and between the first adhesive layer (104) and the functional layer (110), and / or - upon removal of the first support layer (102) and the first adhesive layer (104), the adhesion force between said at least a portion of the functional layer (110) and the first layer, adhesive (104) is less than that between the functional layer (110) and the third substrate (124).

7. Transfer method according to any one of the preceding claims, further comprising, during the process, the implementation of one or more processing steps of at least one of the first and second adhesive layers (104, 106), modifying adhesive properties of said at least one of the first and second adhesive layers (104, 106).

8. Transfer method according to claim 7, wherein one of the first and second adhesive layers (104, 106) comprises a material whose adhesive properties are reduced by the implementation of a UV treatment, and the other of the first and second adhesive layers (104, 106) comprises a material whose adhesive properties are reduced by the implementation of a heat treatment.

9. Transfer method according to any one of the preceding claims, wherein the first transfer is carried out such that at least one third adhesive layer (128) is disposed between the third substrate (124) and the functional layer (110) at the end of the second transfer.

10. A transfer method according to any one of the preceding claims, further comprising, prior to the first transfer and / or during the first transfer and / or during the second transfer, at least one functional layer processing step (110).

11. A transfer method according to any one of the preceding claims, wherein the bonding of the flexible temporary substrate (100) to the functional layer (110) is implemented by interposing at least one magnetic layer (130) between the functional layer (110) and the flexible temporary substrate (100), and / or wherein the flexible temporary substrate (100) comprises at least one magnetic layer (130).

12. A transfer method according to any one of the preceding claims, wherein the flexible temporary substrate (100) comprises at least one marking layer (132) configured to be laser-marked and interposed between the first support layer (102) and the second adhesive layer (106) and / or between the first adhesive layer (104) and the first support layer (102), and wherein the 23 process further includes the implementation of at least one marking step in the marking layer before the second transfer.

13. A transfer method according to any one of the preceding claims, wherein the functional layer (110) comprises at least one piezoelectric material.

14. Method for making a piezoelectric sensor, comprising implementing a method for transferring a functional layer (110) according to claim 13.

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