Method for manufacturing a donor substrate for transferring a piezoelectric layer and method for transferring a piezoelectric layer onto a supporting substrate
Patent Information
- Application Number
- FR2022000380
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-01-17
- Publication Date
- 2025-03-21
- Estimated Expiration
- 2042-01-17
Smart Images
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Abstract
Description
Title of the invention: Method for manufacturing a donor substrate for transferring a piezoelectric layer and method for transferring a piezoelectric layer onto a support substrate
[0001] The invention relates to a method of manufacturing a donor substrate for transferring a piezoelectric layer, a donor substrate and a method of transferring such a piezoelectric layer onto a support substrate.
[0002] A piezoelectric-on-insulator (POI) substrate comprises a thin layer of piezoelectric material on a substrate. To manufacture such a POI substrate, the method used comprises transferring the piezoelectric thin layer onto a support substrate from a thicker substrate of piezoelectric material.
[0003] For this, first a donor substrate is used in which a solid substrate of piezoelectric material is assembled to a handling substrate by bonding using a polymer layer. Then, the donor substrate undergoes a step of thinning the solid piezoelectric substrate to form a thinner piezoelectric layer before being assembled to the support substrate. Finally, the transfer of the piezoelectric layer to the support substrate is carried out mechanically or thermally at a fracturing zone previously created in the thinned piezoelectric layer. The donor substrate is introduced into the process to limit the negative impact of the difference in the thermal expansion coefficients between the piezoelectric material and the support substrate of the POI. Indeed, to reinforce the bonding interface between the different substrates and the transfer of the thin layer, heat treatments are carried out.An example of this type of method is described in WO 2019 / 186032 AL.
[0004] However, as the donor substrate must undergo several stages of thermal and / or mechanical treatments, detachment at the bonding interface between the piezoelectric substrate and the polymer layer may occur.
[0005] An aim of the invention is to remedy the aforementioned drawbacks and in particular to design a donor substrate for the transfer of a piezoelectric layer from a substrate of piezoelectric material onto a support substrate which has better mechanical strength.
[0006] The subject of the invention is achieved by a method of manufacturing a donor substrate for transferring a piezoelectric layer onto a support substrate comprising the steps of providing a handling substrate, in particular a silicon-based substrate, providing a piezoelectric substrate, forming an intermediate layer on a free surface of the piezoelectric substrate, depositing a polymer layer on the layer intermediate of the piezoelectric substrate, and assembling the piezoelectric substrate on the handling substrate to form the donor substrate.
[0007] The formation of an intermediate layer between the piezoelectric substrate and the polymer layer makes it possible to obtain a more stable bond between the piezoelectric material and the polymer layer, by choosing an intermediate layer which has good adhesion to the piezoelectric substrate as well as to the polymer layer. Thus, the method according to the invention makes it possible to obtain a donor substrate having improved mechanical stability between the piezoelectric substrate and the polymer layer of the handling substrate compared to the state of the art.
[0008] The object of the invention is also achieved by a method of manufacturing a donor substrate for transferring a piezoelectric layer onto a support substrate comprising the steps of providing a handling substrate, in particular a silicon-based substrate; depositing a polymer layer on a free face of the handling substrate, providing a piezoelectric substrate, forming an intermediate layer on a free surface of the piezoelectric substrate, assembling the piezoelectric substrate onto the handling substrate in such a way that the intermediate layer formed on the piezoelectric substrate is sandwiched between the polymer layer of the handling substrate and the piezoelectric substrate to form the donor substrate.
[0009] The formation of an intermediate layer between the piezoelectric substrate and the polymer layer of the handling substrate makes it possible to obtain a more stable bond between the piezoelectric material and the polymer layer, by choosing an intermediate layer which has good adhesion to the piezoelectric substrate as well as to the polymer layer. Thus, the method according to the invention makes it possible to obtain a donor substrate having improved mechanical stability between the piezoelectric substrate and the polymer layer of the handling substrate compared to the state of the art.
[0010] According to one embodiment, the formation of the intermediate layer may comprise the formation of a single layer or of several sub-layers.
[0011] According to one embodiment, the formation of the intermediate layer may comprise at least the formation of a dielectric layer, in particular a layer based on silicon oxide or nitride oxide or a combination of oxide nitride SiOxNy. The use of a dielectric layer formed on a piezoelectric material makes it possible to assemble the piezoelectric substrate to another substrate to form a donor substrate via this dielectric layer. Thanks to the presence of the dielectric layer providing the connection between the piezoelectric substrate and the handling substrate, the donor substrate obtained has improved mechanical stability for the various process steps that the donor substrate will then undergo.
[0012] According to one embodiment, a step of surface treatment of the inter layer mediate can be carried out, in particular a plasma treatment, even more in particular an oxygen O2 plasma. A plasma treatment is a dry treatment which allows the functionalization and / or activation of the surface. Plasma surface treatment consists of a very strong oxidation of the surface of a material. The oxidation of surface molecules makes it possible to increase the surface tension of a support. Plasma treatment allows the creation of free radicals on the surface which promote the successive adhesion of a thin layer in contact with these free radicals. Thus, plasma surface treatment makes it possible to improve the chemical characteristics of the material for better adhesion to a coating layer.Thus, the plasma treatment step of the method according to the invention makes it possible to improve the adhesion between the dielectric layer formed on the piezoelectric substrate and the polymer layer of the donor substrate, and results in improved mechanical stability of the donor substrate compared to the state of the art.
[0013] According to one embodiment, a step of thinning the piezoelectric substrate of the donor substrate may be carried out, so as to obtain either a thinned piezoelectric substrate with a thickness t less than h of the piezoelectric substrate, or a piezoelectric layer with a thickness t2 less than the thickness tj of the piezoelectric substrate. The thinning step may be carried out by a grinding process or by a chemical etching process of the piezoelectric substrate. Thus, from a thick piezoelectric substrate, a thinner piezoelectric substrate or a piezoelectric layer of a desired thinner thickness is obtained and the donor substrate thus manufactured by the method according to the invention may be used as a donor substrate in a subsequent layer transfer process for transferring a thin layer of the piezoelectric material onto a support substrate to thereby form a piezoelectric-on-insulator (POI) substrate.The use of a thinner piezoelectric substrate reduces subsequent problems due to non-symmetry of thermal expansion coefficients and thus minimizes assembly deformation when applying subsequent process steps.
[0014] According to one embodiment, the assembly step of the method for manufacturing a donor substrate may comprise a step of treating the polymer layer to obtain a crosslinked polymer layer for bonding the handling substrate to the piezoelectric substrate. The formation of a crosslinked polymer layer by a step of treating the polymer layer is simple to implement and allows adhesion that satisfies the conditions of the method.
[0015] The subject of the invention is also achieved by a donor substrate for the transfer of a piezoelectric layer comprising a handling substrate, in particular a silicon-based substrate, a piezoelectric substrate, a polymer layer sandwiched between the handling substrate and the piezoelectric substrate, and characterized in that the donor substrate further comprises an intermediate layer sandwiched between the piezoelectric substrate and the polymer layer. Due to the presence of the intermediate layer sandwiched between the piezoelectric substrate and the polymer layer, a better bond is achieved between the piezoelectric substrate and the polymer layer. This bond results in a donor substrate having improved mechanical stability and allows this donor substrate to be used in subsequent processes without encountering debonding problems at the polymer-piezoelectric interface.
[0016] According to one embodiment, the intermediate layer may comprise a single layer or several sub-layers.
[0017] According to one embodiment, the intermediate layer may comprise at least one dielectric layer, in particular a layer based on silicon oxide and / or silicon nitride or a combination of nitride and silicon oxide SiOxNy. The use of a dielectric layer formed on a piezoelectric material subsequently makes it possible to use the piezoelectric substrate for assembly to another substrate to form a donor substrate via this dielectric layer in a solid and stable manner for the various process steps that the donor substrate will subsequently undergo.
[0018] According to one embodiment, the dielectric layer of the intermediate layer may be in direct contact with the polymer layer of the donor substrate. Thus, the bond between the piezoelectric substrate and the polymer layer of the donor substrate is made via the dielectric layer, which makes it possible to obtain a stable bond so that the donor substrate subsequently undergoes thermal and / or mechanical process steps without suffering degradation at the piezoelectric-polymer bond.
[0019] According to one embodiment, the polymer layer may be a polymerized adhesive layer for bonding the piezoelectric substrate to the handling substrate via the intermediate layer of the piezoelectric substrate. The presence of a crosslinked polymer layer makes it possible to obtain a stable bond with the intermediate layer of the piezoelectric substrate.
[0020] According to one embodiment, the piezoelectric substrate may be a Lithium Tantalate (LTO), Lithium Niobate (LNO), Aluminum Nitride (AIN), Lead Titano-Circonate (PZT), Langasite or Langatate substrate. The donor substrate according to the invention may comprise these materials, which play a major role in devices exploiting the piezoelectric effect.
[0021] The subject of the invention can also be achieved by a method of transferring a piezoelectric layer onto a support substrate comprising the steps of providing a donor substrate as described previously with a thinned piezoelectric substrate or obtained by implementing the manufacturing method as described previously, forming a weakening zone inside the piezoelectric substrate, providing a substrate support, in particular a silicon-based substrate, attaching the donor substrate to the support substrate, to obtain a donor substrate - support substrate assembly, and performing the fracture along the weakening zone to separate a piezoelectric layer from the remainder of the donor substrate.
[0022] In such a method, thanks to the use of a donor substrate obtained according to the manufacturing method described earlier, which has better mechanical stability at the level of the bonding of the piezoelectric material with the polymer layer thanks to the presence of the intermediate layer, the risk of detachment of the piezoelectric material in the support substrate - donor substrate assembly during the performance of the various process steps applied a posteriori to the donor substrate - support substrate assembly and which is due to the differences in the thermal expansion coefficients is reduced. Thus, the use of donor substrates manufactured according to the invention allows the manufacture of POI substrates with a better yield.
[0023] The invention and its advantages will be explained in more detail hereinafter by means of preferred embodiments and with particular reference to the following accompanying figures, in which the reference numbers identify features of the invention.
[0024] [Fig. 1a] schematically represents a method of manufacturing a donor substrate and a donor substrate according to a first embodiment of the invention.
[0025] [Fig.lb] schematically represents a method of manufacturing a donor substrate and a donor substrate according to a first variant of the first embodiment of the invention.
[0026] [Fig.2] schematically represents a method of manufacturing a donor substrate and a donor substrate according to a second variant of the first embodiment of the invention.
[0027] [Fig.3] schematically represents a method of manufacturing a donor substrate and a donor substrate according to a second embodiment of the invention.
[0028] [Fig.4] schematically represents a method of transferring a piezo layer electric according to a third embodiment of the invention.
[0029] The invention will be described in more detail using advantageous embodiments in an exemplary manner and with reference to the drawings. The described embodiments are merely possible configurations and it should be borne in mind that individual features as described above may be provided independently of one another or may be omitted altogether when practicing the present invention.
[0030] [Fig.1a] schematically illustrates a method of manufacturing a donor substrate used for transferring a piezoelectric layer from the donor substrate to a support substrate according to a first embodiment of the invention.
[0031] The method for manufacturing a donor substrate begins with step I) of providing a handling substrate 100, in particular a solid substrate. A solid substrate is a substrate based on a single material typically with a thickness of between 300 μm and 800 μm, in particular between 350 μm and 800 μm. The handling substrate 100 is made of a material whose coefficient of thermal expansion is close to that of the material of the support substrate onto which the piezoelectric layer is intended to be transferred. By "close" is meant a difference in coefficient of thermal expansion between the material of the handling substrate 100 and the material of the support substrate of less than or equal to 5%, and preferably equal to or close to 0%.
[0032] The handling substrate 100 may be a substrate based on silicon, sapphire, aluminum nitride (AIN), silicon carbide (SiC) or gallium arsenide (GaAs). The handling substrate 100 may be a crystalline or polycrystalline substrate.
[0033] In step II) a piezoelectric substrate 106 is provided. It is preferably a solid substrate formed from a single piezoelectric material whose thickness is typically of the order of at least 300 pm, preferably at least 350 pm. According to a variant, the piezoelectric material substrate 106 may also be a thick layer of piezoelectric material between 25 pm and 50 pm, formed on another substrate.
[0034] The piezoelectric material may, for example, be Lithium Tantalate (LTO), Lithium Niobate (LNO), Aluminum Nitride (AIN), Lead Titano-Circonate (PZT), Langasite or Langatate.
[0035] According to the invention, a step III) of forming an intermediate layer 108 on a free surface 110 of the piezoelectric substrate 106 is carried out. The formation of the intermediate layer 108 on the free surface 110 of the piezoelectric substrate can be carried out by deposition by centrifugal coating, or "spin coating" in English terminology or by a thermal or plasma-assisted growth technique such as PECVD or PVD.
[0036] Before forming the intermediate layer 108, one or more steps of cleaning, brushing or polishing the surface of the piezoelectric substrate 106 may be carried out to remove the presence of particles and dust to thus obtain a cleaner free surface 110 which makes it possible to obtain an intermediate layer 108 of better quality.
[0037] According to the invention, the intermediate layer 108 formed on the piezoelectric substrate 106 is a dielectric layer, for example a layer based on silicon oxide, or based on silicon nitride Si3N4, or even a layer comprising a combination of nitride and silicon oxide SiOxNy.
[0038] According to a variant of the invention, a step 118 of activating the surface of the intermediate layer 108 formed on the piezoelectric substrate 106 can be carried out to activate the free surface 120 of the intermediate layer 108. In particular, this activation treatment 118 may be a plasma treatment, even more in particular an oxygen-based plasma treatment.
[0039] A plasma treatment is a dry treatment that allows the functionalization, activation or cleaning of the surface, or a combination of these effects by oxidation. The oxidation of the surface molecules makes it possible to increase the surface tension of a support creating dangling bonds on the surface. The plasma treatment allows the creation of free radicals on the surface which promote the successive adhesion of a thin layer in contact with these free radicals. Thus, the plasma surface treatment makes it possible to improve the chemical characteristics of the surface 120 of the dielectric layer 108 of the piezoelectric substrate 106 by creating dangling bond sites for better adhesion to a layer which is formed or brought into contact with the surface 120 of the layer 108 of the piezoelectric substrate 106 during the rest of the process.
[0040] According to the invention, a step IV) of depositing a polymer layer 104 on the intermediate layer 108 of the piezoelectric substrate 106 is carried out. The polymer layer 104 is thus in direct contact with the intermediate layer 108 of the piezoelectric substrate 106 at the interface 126. The presence of the intermediate layer 108 between the piezoelectric substrate 106 and the polymer layer 104 results in better adhesion with the polymer layer 104, and thus, with the piezoelectric substrate 106, compared to a direct bond between the polymer layer 104 and the piezoelectric substrate 106 of the state of the art. Indeed, it is possible to choose an intermediate layer 108 which has good adhesion to the piezoelectric substrate 106 as well as to the polymer layer 104.
[0041] The deposition of the polymer layer 104 is advantageously carried out by centrifugal coating, or “spin coating” in English terminology. This technique consists of rotating the substrate on which the deposition of the polymer layer 104 is planned on itself at a given speed, in order to spread said polymer layer 104 uniformly over the entire surface of the piezoelectric substrate 106 by centrifugal force. For this purpose, the piezoelectric substrate 106 is typically placed and held by vacuum on a rotating plate. The thickness of the polymer layer 104 obtained depends on the parameters used during the deposition of the layer, that is to say for example the speed and duration of rotation of the substrate and the volume of the polymer solution deposited on the surface of the substrate 106. The thickness of the polymer layer 104 is typically between 1 pm and 6 pm, preferably 3.5 pm.
[0042] The polymer layer 104 may be a photopolymerizable layer, in particular based on thiol-ene resin. For example, the layer marketed under the reference “NO A 61” by the company NORLAND PRODUCTS may be used in the present invention as polymer layer 104.
[0043] After spin-coating the polymer layer 104 onto the piezoelectric substrate 106, a heat treatment may be performed to improve the adhesion of the polymer layer 104 to the activated surface 120 of the intermediate layer 108 of the piezoelectric substrate 106.
[0044] In the variant where a step 118 of activating the surface 120 of the intermediate layer 108 is carried out, the step of depositing the polymer layer 104 is carried out after the step 118 of activating the surface 120 of the intermediate layer 108. Thus, the deposition of the polymer layer 104 is carried out on the activated surface 120 of the intermediate layer 108, in direct contact with the activated surface 120.
[0045] According to the invention, the piezoelectric substrate 106 obtained after step IV), is then assembled to the handling substrate 100 obtained in step I) during an assembly step V) to form the donor substrate 124.
[0046] The assembly of the piezoelectric substrate 106 on the handling substrate 100 is made such that the polymer layer 104 is positioned in contact with the layer 108 of the piezoelectric substrate 106 and the handling substrate 100.
[0047] Once the two substrates are assembled, a bonding step VI) is carried out to bond the piezoelectric substrate 106 to the handling substrate 100 to form a stable donor substrate 128.
[0048] The polymer layer 104 undergoes a crosslinking treatment 130 to modify the mechanical properties of the polymer layer 104. Crosslinking is the general term for the process of forming covalent bonds or relatively short sequences of chemical bonds to join two polymer chains. When the polymer chains are crosslinked, the polymer layer 104 becomes more rigid. Covalent chemical crosslinks are mechanically and thermally stable, so that once formed, they are difficult to break.
[0049] A crosslinking treatment 130 can be carried out by using heat, pressure, by a change in pH or by irradiation. According to the invention, the crosslinking treatment 130 can be carried out by irradiation with a light flux 130 of the polymer layer 104. The irradiation 130 is carried out through the piezoelectric substrate 106 or the substrate 100 to crosslink the polymer layer 104 and obtain a crosslinked polymer layer 132 or also called a polymerized layer 132.
[0050] The irradiation 130 can be carried out using a light source, preferably a laser. The light radiation 130, or light flux, is preferably ultraviolet (UV) radiation, preferably of a wavelength between 320nm and 365nm.
[0051] The thickness of the crosslinked polymer layer 132 is preferably between 1 pm and 6 pm, in particular approximately 3.5 pm. This thickness depends in particular on the material of the polymer layer 104 deposited before bonding, the thickness of said polymer layer 104 and the irradiation conditions.
[0052] Crosslinking the polymer layer 104 by UV irradiation 130 allows the release of radicals which will trigger the polymerization of the polymer layer 104. The polymerization of the polymer layer 104 results in chemical bonds which are mechanically and thermally stable, so that once formed, they are difficult to break. The bond between the polymerized layer 132 and the dielectric intermediate layer 108 thus ensures the mechanical cohesion of the donor substrate 128, by keeping the handling substrate 100 and the piezoelectric substrate 106 which form the donor substrate 128 bonded together.
[0053] In the variant where a surface activation treatment 118 is carried out on the surface 120 of the intermediate layer 108, the adhesion between the crosslinked polymer layer 132 and the dielectric layer 108 of the piezoelectric substrate 106 at the interface 126 is improved due to the activated surface of the intermediate layer 108. Indeed, the dangling bonds present on the activated surface of the dielectric intermediate layer 108 of the piezoelectric substrate 106 will form covalent bonds with the dangling bonds present on the surface of the polymer layer 104. Thus, the contact interface 126 between the intermediate layer 108 of the piezoelectric substrate 106 and the polymer layer 104 is consolidated / reinforced thanks to the surface activation treatment of the intermediate layer 108 and results in mechanical stability of the donor substrate 124 improved compared to the state of the art.
[0054] In a first variant of the first embodiment illustrated in [Fig. lb], step III) of the method for forming an intermediate layer 108 is replaced by the formation of a plurality 112 of sub-layers 114, each sub-layer 114 of the plurality 112 of sub-layers 114 being the same or being different in terms of their material or their properties or even their thicknesses. All other steps I to II and IV to VI are the same as those described for [Fig. la]. Thus, for a detailed description of these steps, reference is made to the description of [Fig. la]
[0055] At least one layer 116 of the sub-layers 114 of the plurality 112 of sub-layers is a dielectric layer 116, in particular a layer based on silicon oxide, or on nitride oxide Si3N4 or a combination of oxide nitride SiOxNy. In particular, the upper layer 116 which corresponds to the last layer of the plurality 112 of sub-layers 114 starting from the piezoelectric substrate 106, is a layer based on silicon oxide, or on silicon nitride Si3N4 or a combination of nitride and silicon oxide SiOxNy. The plurality 112 of sub-layers 114 may be a superposition of silicon oxide layer and silicon nitride layer Si3N4.
[0056] In this variant, the deposition of the polymer layer 104 is done on the upper layer 116 of the plurality 112 of sub-layers 114. Thus, the upper layer 116 is sandwiched between the polymer layer 104 and the rest of the sub-layers 114 of the plurality 112 of sub-layers 114 of the piezoelectric substrate 106.
[0057] In this variant, the assembly of the piezoelectric substrate 106 on the handling substrate 100 is made at the interface 136 between the free surface 102 of the handling substrate 100 and the polymer layer 104 formed on the upper layer 116 of the piezoelectric substrate 106. Thus, the upper layer 116 is sandwiched between the polymer layer 104 of the handling substrate and the rest of the sub-layers 114 of the plurality 112 of sub-layers 114 of the piezoelectric substrate 106 to form the heterostructure 134 which becomes after step VI) the donor substrate 138.
[0058] According to a variant, a surface activation treatment 118 can be carried out as in the method described with respect to [Fig.1a]. The plasma treatment 118 is carried out on the free surface 122 of the upper layer 116 of the plurality 112 of sub-layers 114.
[0059] The use of a dielectric layer 108, 116 formed on a piezoelectric material 106 subsequently makes it possible to assemble the piezoelectric substrate 106 to another handling substrate 100 via a polymer layer 104 deposited on this dielectric layer 108, 116 in a solid and stable manner to form a donor substrate. The mechanical stability of the donor substrate 128, 138 thus obtained thanks to the dielectric layer - polymer layer bonding allows this donor substrate 128, 138 to then be used in other processes and to undergo different thermal and mechanical process steps without undergoing deformation at the interface of the piezoelectric material 106.
[0060] [Fig.2] schematically represents a method of manufacturing a donor substrate for the transfer of a piezoelectric layer onto a support substrate according to a variant of the first embodiment of the invention.
[0061] All features common to the first embodiment using the same reference number as above will not be described again, but reference is made to their detailed description above.
[0062] The method illustrated in [Fig.2] comprises, after step VI) illustrated in [Fig.1a], a step VII) of thinning the piezoelectric substrate 106 of the donor substrate 128 obtained according to the method of the first embodiment and its first variant. In the same way, the donor substrate 138 can be used.
[0063] The thinning step VII) can be carried out by a grinding process or by a chemical etching process of the piezoelectric substrate 106 to reduce the thickness h of the piezoelectric material substrate 106 of the donor substrate 128 to obtain either a thinned piezoelectric substrate 140 with a thickness t less than / / or a piezoelectric layer 140 with a thickness t2 of the order of 20 pm, or between 5 pm and 25 pm. A treatment of the free surface 142 of the piezoelectric layer 140 obtained can be carried out once the thinning step VII) is completed to improve the quality of the free surface 142 of the piezoelectric layer 140.
[0064] [Fig. 3] illustrates the second embodiment of the invention in which the step of depositing the polymer layer 154 is carried out on the manipulation substrate 100, instead of being carried out on the piezoelectric substrate 106. All other steps I, II, III and V to VII are the same as in the first embodiment and its variants. All features common to the first embodiment and its variants and using the same reference number as above will not be described again, but reference is made to their detailed description above.
[0065] During step IV) of depositing the polymer layer 154, the polymer layer 154 is deposited directly in contact with the free surface 102 of the handling substrate 100. The handling substrate 100 may first be subjected to one or more steps of cleaning, brushing or polishing its free surface 102 to reduce the presence of particles or dust before depositing the polymer layer 154.
[0066] During the assembly step IV), the polymer layer 154 of the handling substrate 100 is brought into direct contact with the intermediate layer 108 of the piezoelectric substrate 106. Thus, the contact interface 126 between the polymer layer 154 and the intermediate layer 108 of the piezoelectric substrate 106 also has better adhesion. Indeed, in the same way as previously described, it is possible to choose an intermediate layer 108 which has good adhesion to the piezoelectric substrate 106 as well as to the polymer layer 154. Thus, the contact interface 126 between the piezoelectric substrate 106 and the polymer layer 154 via the intermediate layer 108 is consolidated / reinforced and results in improved mechanical stability of the donor substrate 124 compared to the state of the art.
[0067] [Fig. 4] schematically represents a method of transferring a piezoelectric layer according to a second embodiment of the invention using the donor substrate 144. According to variants, the method can be carried out with the donor substrate 128, 138 obtained according to the other variants described with respect to Figures 1a, 1b or 2.
[0068] In step A) the donor substrate 144 and a support substrate 156 are provided. The support substrate 156 may be a solid substrate based on silicon, sapphire, aluminum nitride (AIN), silicon carbide (SiC) or gallium arsenide (GaAs). The support substrate 156 may be a crystalline or polycrystalline substrate. The donor substrate 144 exhibits mechanical stability which allows it to be used in the method of transferring the piezoelectric layer 152 onto the support substrate 156.
[0069] As illustrated in [Fig. 4], the support substrate 156 may comprise a dielectric layer 158 previously formed on the free surface 160 of the support substrate 156, for example by spin coating or by a deposition technique such as plasma deposition or evaporation or thermal growth. The dielectric layer 158 is for example a layer of silicon oxide, a layer of silicon nitride Si3N4, or a layer comprising a combination of nitride and silicon oxide also called silicon oxynitride SiOxNy, or a superposition of an oxide layer and a nitride layer. According to a variant, the formation of the dielectric layer 158 may be followed by a heat treatment to improve the adhesion of the dielectric layer 158 to the support substrate 156. A surface treatment to improve the quality of the surface of the formed dielectric layer 158 may also be carried out.
[0070] The dielectric layer 158 may also be a natural oxide layer which is formed on the free surface 160 of the support substrate 156.
[0071] In one variant, other layers may be present on the support substrate 156 and / or the dielectric layer 158. For example, layers for making a Bragg mirror or a trapping layer. In yet another variant, the support substrate 156 is provided without a dielectric layer 158 and / or without a natural oxide layer.
[0072] Alternatively, a dielectric layer may be provided on the piezoelectric layer 140 of the donor substrate 144 instead of or in addition to the dielectric layer 158 formed on the support substrate 156.
[0073] In a variant, the support substrate 156 may also comprise other layers. For example, layers for producing a Bragg mirror or a trapping layer may be present on the support substrate 156. In particular, a trapping layer of polycrystalline, amorphous or porous silicon type may be present, with a thickness varying between 500nm and 5pm.
[0074] A step B) of forming a weakening zone 146 in the piezoelectric layer 140 of the donor substrate 144 is carried out so as to delimit the piezoelectric layer 152 to be transferred from the remainder 162 of the piezoelectric layer 140.
[0075] This step of forming a weakening zone 140 is carried out by an implantation 150 of atomic or ionic species in the piezoelectric layer 140 of the donor substrate 144. The atomic or ionic implantation 150 is carried out in such a way that the weakening zone 140 is located inside the piezoelectric layer 140 and separates a piezoelectric layer 152 from the remainder 162 of the piezoelectric layer 140. The atomic or ionic species are implanted at a determined depth of the piezoelectric layer 140 which determines the thickness t3 of the piezoelectric layer 152 to be transferred and the thickness t4 of the remainder 148 of the piezoelectric layer 140. The thickness t3 is typically between 50nm and 1pm, in particular the order of 600nm. In a non-limiting manner, a dielectric layer may be formed on the piezoelectric layer 140 obtained from the donor substrate 144. This dielectric layer is for example a layer of silicon oxide, a layer of silicon nitride Si3N4, or a layer comprising a combination of nitride and silicon oxide also called silicon oxynitride SiOxNy, or a superposition of an oxide layer and a nitride layer. According to a variant, the formation of this dielectric layer may be followed by a heat treatment to improve the adhesion of the dielectric layer to the piezoelectric layer 140. A surface treatment to improve the quality of the surface of this formed dielectric layer may also be carried out, in particular after the implantation step 150 and before step C) mentioned below.
[0076] During step C) of the transfer method according to the invention, the donor substrate 144 is assembled with the support substrate 156 to obtain a support substrate-donor substrate assembly 170. The assembly 170 of the donor substrate 144 with the support substrate 156 is done at the level of the dielectric layer 158, in such a way that the piezoelectric layer 140 of the donor substrate 144 is in direct contact with the dielectric layer 158 and the piezoelectric layer 152 to be transferred is sandwiched between the support substrate 156 and the remainder 162 of the donor substrate 144. In a variant, the assembly 170 of the donor substrate 144 with the support substrate 156 is done between the dielectric layer 158 and a dielectric layer formed on the donor substrate 144 as mentioned above.
[0077] The assembly is done by molecular adhesion between the two substrates, at the piezoelectric interface - support substrate in a known manner.
[0078] Then, a step D) of fracturing along the weakening zone 140 of the donor substrate 144 is carried out by supplying thermal and / or mechanical energy to separate the piezoelectric layer 152 from the remainder 162 of the donor substrate 144.
[0079] Thus, the POI substrate 174 is obtained comprising the support substrate 156, the dielectric layer 158 and the transferred piezoelectric layer 152.
[0080] Thanks to the presence of the dielectric intermediate layer 108 between the piezoelectric layer 140 and the polymer layer 120, 132 it becomes possible to reduce the risk of detachment between the piezoelectric layer 140 and the polymer layer 120, 132 of the donor substrate 144 during fracturing of the donor substrate 144. Thus, the use of the donor substrate 144 manufactured according to the invention allows the manufacture of a POI substrate 174 with a better yield.
[0081] The described embodiments are merely possible configurations and it should be borne in mind that individual features of the different embodiments may be combined with each other or provided independently of each other.
Claims
Claims
1. A method of manufacturing a donor substrate (128, 138, 144) for transferring a piezoelectric layer onto a support substrate comprising the steps of: - providing a handling substrate (100), in particular a silicon-based substrate; - providing a piezoelectric substrate (106), - forming an intermediate layer (108) on a free surface of the piezoelectric substrate (106), - depositing a polymer layer (104) on the intermediate layer (108) of the piezoelectric substrate (106), and assembling the piezoelectric substrate (106) onto the handling substrate (100) to form the donor substrate (128, 138, 144).
2. A method of manufacturing a donor substrate (128, 138, 144) for transferring a piezoelectric layer onto a support substrate comprising the steps of: - providing a handling substrate (100), in particular a silicon-based substrate;- depositing a polymer layer (154) on a free face of the handling substrate (100), - providing a piezoelectric substrate (106), - forming an intermediate layer (108, 112) on a free surface of the piezoelectric substrate (106), - assembling the piezoelectric substrate (106) on the handling substrate (100) in such a way that the intermediate layer (108, 112) formed on the piezoelectric substrate (106) is sandwiched between the polymer layer (132, 154) of the handling substrate (100) and the piezoelectric substrate (106) to form the donor substrate (128, 138, 144) wherein the method further comprises a step of surface treatment (118) of the intermediate layer (108, 112), in particular a plasma treatment, even more in particular an O2 plasma.;
3. A method of manufacturing a donor substrate (128, 138, 144) according to claim 1 or 2, wherein the formation of the intermediate layer (108, 112) on the piezoelectric substrate (106) comprises at least the formation of a dielectric layer, in particular based on silicon oxide, based on silicon nitride or based on a combination of silicon oxide and nitride SiOxNy.
4. A method of manufacturing a donor substrate (128, 138, 144) according to claim 1 or claim 3 in combination with claim 1, further comprising a step of surface treatment (118) of the intermediate layer (108, 112), in particular a plasma treatment, even more in particular an O2 plasma.
5. A method of manufacturing a donor substrate (128, 138, 144) according to one of claims 1 to 4, further comprising a step of thinning the piezoelectric substrate (106) of the donor substrate (124, 138, 144) to obtain a thinned piezoelectric substrate (140) or a piezoelectric layer (140), in particular by grinding.
6. A method of transferring a piezoelectric layer onto a support substrate comprising the steps of: - providing a donor substrate (144) obtained by implementing the manufacturing method according to claim 5, - forming a weakening zone (146) inside the piezoelectric substrate (140) of the donor substrate (144), - providing a support substrate (156), in particular a silicon-based substrate, - attaching the donor substrate (144) to the support substrate (156), to obtain a donor substrate - support substrate assembly (170), and - performing the fracture along the weakening zone (146) to separate a piezoelectric layer (152) from the remainder (162) of the donor substrate (144).