Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/01—Manufacture or treatment
  • H10N30/07—Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base
  • H10N30/072—Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base by laminating or bonding of piezoelectric or electrostrictive bodies
  • H10N30/073—Forming of piezoelectric or electrostrictive parts or bodies on an electrical element or another base by laminating or bonding of piezoelectric or electrostrictive bodies by fusion of metals or by adhesives
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/85—Piezoelectric or electrostrictive active materials

Definitions

• the invention relates to a method for manufacturing a donor substrate for transferring a piezoelectric layer and a method for transferring such a piezoelectric layer onto a support substrate.
• a piezoelectric on insulator (POI) substrate comprises a thin layer of piezoelectric material on a substrate.
• the process used comprises the transfer of the thin piezoelectric layer onto a support substrate from a thick substrate of piezoelectric material.
• a donor substrate is used in which a bulk substrate of piezoelectric material is assembled to a manipulation substrate by bonding using a polymer layer. Then, the donor substrate undergoes a step of thinning the bulk piezoelectric substrate to form a thinner piezoelectric layer before being assembled to the support substrate. Finally, the transfer of the piezoelectric layer on the support substrate is carried out mechanically or thermally at the level of a fracturing zone created beforehand in the thinned piezoelectric layer.
• the donor substrate is introduced into the process to limit the negative impact of the difference in 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 for the transfer of the thin layer, heat treatments are carried out. An example of this type of method is described in WO 2019/186032 A1.
• the donor substrate must undergo several stages of thermal and/or mechanical treatments and must have good mechanical resistance to the various treatments.
• a separation at the bonding interface between the piezoelectric material substrate and the polymer layer of the donor substrate can occur during the successive thermal and/or mechanical steps of the piezoelectric layer transfer process.
• An object 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 material piezoelectric on a support substrate which has better mechanical strength for the piezoelectric layer transfer process.
• the object of the invention is achieved by a process for 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, depositing a polymer layer on a free face of the piezoelectric substrate, assembling the piezoelectric substrate on the handling substrate such that the polymer layer is sandwiched between the piezoelectric substrate and the handling substrate, characterized in that that a step of surface activation treatment of the surface of the piezoelectric substrate coming into contact with the polymer layer is carried out before the step of assembling the piezoelectric substrate on the handling substrate.
• a surface treatment is a mechanical, chemical, electrochemical or physical operation which aims to modify the appearance or function of the surface of materials in order to adapt them to a given use.
• a surface treatment allows the functionalization, activation or cleaning of the surface, or a combination of these effects.
• the step of surface treatment of the piezoelectric substrate in the method according to the invention makes it possible to modify the appearance or the function of the surface of the piezoelectric substrate in order to adapt it to contact with the polymer layer, to obtain a better interface between the piezoelectric material and the polymer layer.
• the method according to the invention makes it possible to obtain a donor substrate having improved mechanical stability compared to the state of the art.
• the polymer layer can be deposited directly on the treated surface of the piezoelectric substrate.
• the treated surface of the piezoelectric substrate provides better adhesion to the polymer layer that will be deposited on it.
• a polymer layer can be deposited for example by a spin deposition process directly on the piezoelectric substrate.
• the polymer layer can be positioned directly on the manipulation substrate.
• the polymer layer alone makes it possible to achieve good adhesion to another layer or another substrate.
• a polymer layer can be deposited for example by a spin deposition process directly on the handling substrate.
• the assembly step of the method of manufacturing a donor substrate may comprise a step of processing the polymer layer to obtain a crosslinked polymer layer to bond the manipulation substrate to the piezoelectric substrate.
• the formation of a crosslinked polymer layer by a stage of treatment of the polymer layer is simple to implement and is inexpensive.
• the surface activation treatment step can be an oxygen-based surface activation treatment creating dangling bonds on the surface of the piezoelectric substrate coming into contact with the polymer layer.
• Oxygen-based surface activation treatment involves oxidation of the surface of a material. The oxidation of surface molecules makes it possible to increase the surface tension of a support.
• the oxygen-based surface activation treatment allows the creation of free radicals on the surface which promote the adhesion of a thin layer in contact with these free radicals.
• the surface activation treatment step of the piezoelectric substrate can be a treatment with ozone, in particular by wet process or assisted by UV.
• An ozone treatment is a treatment that allows the surface of the substrate to be modified piezoelectric to improve the interface between the polymer layer and the surface of the piezoelectric substrate.
• the surface activation treatment step of the piezoelectric substrate can be treatment with a solution based on hydrogen peroxide.
• a treatment with a solution based on hydrogen peroxide makes it possible to modify the surface of the piezoelectric substrate to improve the interface between the polymer layer and the surface of the piezoelectric substrate.
• a step of thinning the piezoelectric substrate of the donor substrate can be carried out after the assembly step, in particular after the step of processing the polymer layer of the assembly step, so as obtaining either a thinned piezoelectric substrate with a thickness t less than the thickness ti of the piezoelectric substrate, or a piezoelectric layer with a thickness t2 less than the thickness ti of the piezoelectric substrate.
• a thinner piezoelectric substrate or a piezoelectric layer of a desired thickness is obtained and the donor substrate produced according to the method of the invention can be used as a donor substrate for the transfer. of a thin piezoelectric layer on a supporting substrate to obtain a piezoelectric on insulator (POI) substrate.
• PPI piezoelectric on insulator
• the piezoelectric material and the material of the support substrate having very different coefficients of thermal expansion, a significant deformation of the assembly occurs.
• the thick piezoelectric substrate is held between the manipulation substrate and the support substrate.
• the choice of materials and thicknesses of the manipulation substrate and of the support substrate makes it possible to ensure a certain symmetry of the coefficients of thermal expansion, and thus to minimize the deformation of the assembly during the application of heat treatments during the manufacturing process. of a piezoelectric on insulator (POI) substrate.
• POI piezoelectric on insulator
• the object of the invention can also be achieved by a process for transferring a piezoelectric layer onto a support substrate comprising the steps of supplying a donor substrate obtained by the manufacturing process described above, forming a zone of weakness at the inside the piezoelectric substrate, providing a support substrate, in particular a silicon-based substrate, attaching the donor substrate to the support substrate to obtain a support substrate - donor substrate assembly, and producing the fracture along the weakened zone to separate a piezoelectric layer of the remainder of the donor substrate.
• a process for a POI substrate the piezoelectric material and the material of the support substrate having very different coefficients of thermal expansion, a significant deformation of the assembly occurs.
• the thick piezoelectric substrate is held between the manipulation substrate and the support substrate.
• the choice of materials and thicknesses of the manipulation substrate and of the support substrate makes it possible to ensure a certain symmetry of the coefficients of thermal expansion, and thus to minimize the deformation of the assembly during the application of heat treatments during the manufacturing process. of a piezoelectric on insulator (POI) substrate.
• Figure 1 schematically represents a method for manufacturing a donor substrate according to a first embodiment of the invention.
• FIG. 2 schematically represents a method of manufacturing a donor substrate according to a variant of the first embodiment of the invention.
• Figure 3 schematically represents a process for manufacturing a donor substrate according to a second embodiment of the invention.
• FIG. 4 schematically represents a method of transferring a piezoelectric layer according to a third embodiment of the invention.
• Figure 1 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.
• the method of manufacturing a donor substrate begins with step I) of providing a manipulation substrate 100, in particular a bulk substrate.
• a solid substrate is a substrate based on a single material typically with a thickness between 300 ⁇ m and 800 ⁇ m.
• the manipulation substrate 100 is made of a material whose coefficient of thermal expansion is close to that of the material of the support substrate on which the piezoelectric layer is intended to be transferred.
• close is meant a difference in coefficient of thermal expansion between the material of the manipulation substrate 100 and the material of the support substrate less than or equal to 5%, and preferably equal to or close to 0%.
• a piezoelectric substrate 106 is provided. It is preferably a solid substrate of piezoelectric material, the thickness of which is typically of the order of at least 300 ⁇ m, preferably at least 350 ⁇ m. According to a variant, the substrate of piezoelectric material 106 can also be a thick layer of piezoelectric material with a thickness of between 25 ⁇ m and 50 ⁇ m, deposited on another substrate.
• the piezoelectric material can, for example, be Lithium Tantalate (LTO), Lithium Niobate (LNO), Aluminum Nitride (AIN), Lead Titano-Circonate (PZT), Langasite or Langatate .
• LTO Lithium Tantalate
• LNO Lithium Niobate
• AIN Aluminum Nitride
• PZT Lead Titano-Circonate
• the piezoelectric substrate 106 may first undergo one or more steps of cleaning, brushing or polishing its free surface 110 to remove particles or dust and thus obtain a free surface 110 that is clean and of good quality in order to subsequently deposit a successive layer.
• the piezoelectric substrate 106 then undergoes a step III) of surface treatment 108 on one of its free surfaces 110 to obtain an activated surface 112.
• the surface treatment 108 of the surface 110 of the piezoelectric substrate 106 is a treatment which allows the activation of the surface to be treated.
• Such a surface activation treatment 108 makes it possible to prepare the surface of a material for contact with a successive layer either during a successive deposition, or during contact with another substrate.
• the surface activation treatment 108 modifies the properties of the surface.
• a surface activation treatment can be mechanical, chemical, electrochemical or physical.
• the surface activating treatment 108 may be an oxygen-based surface activating treatment.
• the oxidation of surface molecules increases the surface tension of a support creating dangling bonds on the surface.
• the 108 surface activation treatment based on oxygen allows the creation of free radicals on the surface which promote the adhesion of a thin layer in contact with these free radicals.
• the activated surface 112 of the piezoelectric substrate 106 comprises dangling bonds. These dangling bonds represent bond sites that allow a better bond to be obtained with the surface of a material brought into contact with the dangling bonds. Indeed, the dangling bonds of the activated surface 112 of the piezoelectric substrate 106 will make covalent bonds with the dangling bonds of the surface of the material brought into contact with the activated surface 112 of the piezoelectric substrate 106.
• step III) of surface activation treatment 108 of the piezoelectric substrate 106 can be a treatment with ozone, in particular wet or UV-assisted.
• ozone oxidizes surface molecules.
• UV irradiation creates free radicals.
• step III of surface activation treatment 108 of piezoelectric substrate 106 can be a treatment with a solution based on hydrogen peroxide. Hydrogen peroxide treatment is also known as active oxygen treatment, and allows the formation of free radicals by oxidation.
• step III of surface activation treatment 108 of piezoelectric substrate 106 can be treatment by plasma, in particular by plasma based on oxygen. Plasma treatment is a dry treatment that allows the activation of the surface. Plasma surface treatment consists of a very strong oxidation of the surface of a material.
• the surface treatment 108 of the method according to the invention makes it possible to improve the chemical characteristics of the surface 112 of the piezoelectric substrate 106 by creating bonding sites for better adhesion to a layer which is deposited or placed in contact with the activated surface 112 of the piezoelectric substrate 106 a posteriori in the process.
• a step IV) of depositing a polymer layer 104 on the activated surface 112 of the piezoelectric substrate 106 is then carried out.
• the free surface 110 of the piezoelectric substrate 106 has previously undergone the surface treatment step 108 for activation of the free surface 110 and thus obtain good adhesion of the polymer layer 104 on the free surface 110 of the piezoelectric substrate 106.
• the dangling bonds present on the activated surface 112 of the piezoelectric substrate 106 create bonding sites promoting the adhesion of the polymer layer 104 formed on the activated surface 112 of the piezoelectric substrate 106.
• the dangling bonds present on the activated surface 112 of the piezoelectric substrate 106 will form covalent bonds with the dangling bonds of polymer layer 104.
• the contact interface 116 between piezoelectric substrate 106 and polymer layer 104 is consolidated/strengthened.
• the assembly of the piezoelectric substrate 106 on the manipulation substrate 100 is made such that the polymer layer 104 is positioned sandwiched between the piezoelectric substrate 106 and the manipulation substrate 100.
• the contact interface 116 between the piezoelectric substrate 106 and the polymer layer 104 is consolidated/reinforced and results in a mechanical stability of the donor substrate 114 improved compared to the state of the art.
• a bonding step VI) is performed to bond the piezoelectric substrate 106 to the handling substrate 100 to form a stable donor substrate 122.
• Polymer layer 104 is cross-linked 118 to polymer layer 104 to modify the mechanical properties of polymer layer 104.
• Cross-linking 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 cross-linked, the polymer layer 104 becomes stiffer. Covalent chemical crosslinks are mechanically and thermally stable, so once formed they are difficult to break.
• a crosslinking treatment 118 can be carried out by using heat, pressure, by a change in pH or by irradiation. According to the invention, the crosslinking treatment 118 can be carried out by irradiation by a luminous flux 118 of the polymer layer 104. The irradiation 118 is carried out through the piezoelectric substrate 106 or the substrate 100 to crosslink the polymer layer 104 and obtain a crosslinked polymer layer 120 or also called polymerized layer 120 .
• the irradiation 118 of the donor substrate 114 is carried out using a light source, preferably a laser.
• the light radiation 118, or luminous flux is preferably ultraviolet (UV) radiation, preferably with a wavelength between 320 nm and 365 nm.
• the thickness of the crosslinked polymer layer 120 is preferably between 1 ⁇ m and 6.5 ⁇ m, in particular approximately 3.5 ⁇ m. This thickness depends in particular on the material of the polymer layer 104 deposited before bonding, on the thickness of said polymer layer and on the irradiation conditions.
• the crosslinking of the polymer layer 104 by UV irradiation 118 makes it possible to release 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 dangling bonds of the activated surface 112 of the piezoelectric substrate 106 and the crosslinked polymer layer 120 results in a mechanically and thermally stable bond.
• the interface 116 between the crosslinked polymer layer 120 and the piezoelectric substrate 106 presents an improvement in the adhesion between the polymer layer 120 and the surface of the piezoelectric substrate 106, the donor substrate 122 as well obtained by the manufacturing method according to the invention has improved mechanical stability at the polymer-piezoelectric interface.
• the thinning and treatment steps undergone by the donor substrate 122 can be carried out without the polymer-piezoelectric interface 116 being affected by these mechanical and/or thermal steps and the risk of take-off at this interface 116 is reduced, in particular eliminated.
• the donor substrate 128 obtained shows a mechanical stability which allows it to be used upstream in a process for transferring a piezoelectric layer 124 onto a support substrate 140.
• FIG. 3 shows the second embodiment of the invention in which the deposition step IV) of the polymer layer 152 is different with respect to the first embodiment.
• the step of deposition of the polymer layer 152 is carried out on the manipulation substrate 100. All the other steps I, II, III and V to VII are the same as in the first embodiment and its variant. All features common with the first embodiment and using the same reference number as above will not be described again, but reference is made to their detailed description above.
• step V) of assembly the polymer layer 152 of the handling substrate 100 is placed in direct contact with the activated surface 112 of the piezoelectric substrate 106.
• the contact interface 116 between the polymer layer 152 and the activated surface 112 of piezoelectric substrate 106 also exhibits better adhesion. Indeed, in the same way as previously described, the dangling bonds present on the activated surface 112 of the piezoelectric substrate 106 create bonding sites promoting the adhesion of the polymer layer 152 formed on the handling substrate 100 with the activated surface 112 of the piezoelectric substrate 106.
• the contact interface 116 between the piezoelectric substrate 106 and the polymer layer 152 is consolidated/reinforced and results in a mechanical stability of the donor substrate 114 improved compared to the state of the art.
• the support substrate 140 can be a solid substrate based on silicon, sapphire, aluminum nitride (AIN), silicon carbide (SiC) or even gallium arsenide (GaAs).
• Support substrate 140 can be a crystalline or polycrystalline substrate.
• the support substrate 140 can comprise a dielectric layer 142 previously deposited on the free surface 144 of the support substrate 140 by centrifuge deposition or by a deposition technique such as plasma deposition or evaporation.
• a heat treatment can also be carried out after the deposition of the dielectric layer 142 to optimize the adhesion of this dielectric layer 142 to the support substrate 140, or even a surface treatment to improve the quality of the surface of the dielectric layer 142 deposited.
• the support substrate 140 may include a layer of natural oxide which is formed on the free surface 144 of the support substrate 140.
• the dielectric layer 142 is for example a layer of silicon dioxide. But the dielectric layer 142 can also be a nitride layer, or a layer comprising a combination of nitride and oxide, or a superposition of an oxide layer and a nitride layer. For example, in the case of a silicon support substrate, an oxide layer, or a nitride layer SisN ⁇ a layer comprising a combination of nitride and oxide SiO x N y , or a superposition of an oxide layer and a SisN4 nitride layer.
• support substrate 140 may also include other layers.
• layers to produce a Bragg mirror or a trapping layer may/may be present on the support substrate 140.
• a trapping layer of polycrystalline, amorphous or porous silicon type may be present, with a thickness varying between 500nm and 5pm.
• a dielectric layer may be provided on piezoelectric layer 132 of donor substrate 138 instead of being provided on support substrate 140.
• This step of forming an embrittlement zone 130 is carried out by an implantation 134 of atomic or ionic species in the piezoelectric layer 124 of the donor substrate 128.
• the atomic or ion implantation 134 is carried out in such a way that the embrittlement zone 130 is located inside the piezoelectric layer 124 and separates a piezoelectric layer 136 from the rest 132 of the piezoelectric layer 124.
• the atomic or ionic species are implanted at a determined depth of the piezoelectric layer 124 which determines the thickness of the piezoelectric layer 136 to be transferred and the thickness t4 of the remainder 132 of the piezoelectric layer 124.
• the thickness is typically between 50 nm and 1 ⁇ m, in particular around 600 nm.
• Step C) of the transfer method according to the invention comprises assembling the donor substrate 138 to the support substrate 140 to obtain a support substrate-donor substrate assembly which forms the heterostructure 148.
• the assembly of the donor substrate 138 with the support substrate 140 is made at the level of the dielectric layer 142, such that the piezoelectric layer 136 of the donor substrate 138 is in contact with the dielectric layer 142 of the support substrate 140.
• the assembly is done in such a way that the piezoelectric layer 136 of the donor substrate 148 is in direct contact with the free surface 144 of the support substrate 140.
• the assembly takes place by molecular adhesion between the two substrates, at the piezoelectric interface - support substrate.
• the assembly of the donor substrate 138 with the substrate 140 takes place between the dielectric layer 142 and a dielectric layer formed on the donor substrate 140 as mentioned above.
• This dielectric layer is for example a layer of silicon oxide, a layer of silicon nitride SisN4 or a layer comprising a combination of nitride and silicon oxide also called silicon oxynitride SiO x N y , or a superposition of an oxide layer and a nitride layer.
• the formation of this dielectric layer can be followed by a heat treatment to improve the adhesion of the dielectric layer to the piezoelectric layer 124.
• a surface treatment to improve the quality of the surface of this dielectric layer can also be produced, in particular after the implantation step 134 and before the step C) mentioned above.
• a step D) of performing a fracture along the zone of weakness 130 of the donor substrate 148 to separate the piezoelectric layer 136 from the remainder 146 of the donor substrate 148 is carried out.
• This fracture step can be carried out thermally or mechanically. During a thermal separation, the temperature used is equal to or less than 300°C.
• the use of the donor substrate 128 manufactured according to the invention makes it possible to avoid detachment between the piezoelectric layer 124 and the polymer layer 120 of the donor substrate 128 during the fracturing of the donor substrate 128, thanks to the interface 116 between the layer polymer 120 and the piezoelectric layer 124 comprising better mechanical stability. This makes it possible to obtain an effective fracture of the donor substrate 148 at the zone of weakness 130 to obtain a POI substrate 150.
• the POI substrate 150 illustrated in step D) of Figure 4 is produced by the method of transferring a piezoelectric layer according to the invention and comprises a support substrate 140, a dielectric layer 142 and a piezoelectric layer 136.

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Citations (5)

• 2022
  • 2022-01-17 FR FR2200381A patent/FR3131980B1/fr active Active
  • 2022-12-22 TW TW111149571A patent/TW202418979A/zh unknown
• 2023
  • 2023-01-11 KR KR1020247027371A patent/KR20240135826A/ko active Pending
  • 2023-01-11 WO PCT/EP2023/050567 patent/WO2023135179A1/fr not_active Ceased
  • 2023-01-11 CN CN202380016766.6A patent/CN118525618A/zh active Pending
  • 2023-01-11 EP EP23700212.6A patent/EP4466966B1/fr active Active
  • 2023-01-11 JP JP2024540589A patent/JP2025501651A/ja active Pending
  • 2023-01-11 US US18/729,023 patent/US20250176431A1/en active Pending

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