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EP-4736604-A1 - METHOD FOR PRODUCING A DONOR SUBSTRATE FOR TRANSFERRING A PIEZOELECTRIC LAYER ONTO A SUPPORT SUBSTRATE

EP4736604A1EP 4736604 A1EP4736604 A1EP 4736604A1EP-4736604-A1

Abstract

The invention relates to a method for producing a donor substrate (1) for transferring a piezoelectric layer onto a support substrate, which comprises the following successive steps: • (a) providing a piezoelectric substrate (5) and a manipulation substrate (2); • (b) depositing a photo-polymerisable adhesive layer (6) on a main face of the manipulation substrate (2) or the piezoelectric substrate (5); • (c) bonding the piezoelectric substrate (5) with the manipulation substrate (2) via the adhesive layer (6) to form a heterostructure (7); • (d) irradiating the heterostructure (7) with a luminous flux to polymerise the adhesive layer (6); • (e) thermally treating the irradiated heterostructure (7); and • (f) thinning the piezoelectric substrate (5) by its face opposite the manipulation substrate (2), so as to form the donor substrate (1).

Inventors

  • CHARLES-ALFRED, Cédric
  • CAULMILONE, RAPHAEL
  • VEILLY, Maxime
  • THIEFFRY, Stéphane
  • GUERIN, Rénald

Assignees

  • SOITEC

Dates

Publication Date
20260506
Application Date
20240625

Claims (19)

  1. 1. Method for manufacturing a donor substrate (1) for transferring a piezoelectric layer onto a support substrate comprising the following successive steps: (a) providing a piezoelectric substrate (5) and a manipulation substrate (2), (b) depositing a photopolymerizable adhesive layer (6) on a main face of the handling substrate (2) or the piezoelectric substrate (5), (c) bonding the piezoelectric substrate (5) with the handling substrate (2) via the adhesive layer (6) to form a heterostructure (7), (d) irradiating said heterostructure (7) with a light flux to polymerize the adhesive layer (6), (e) heat treatment of the irradiated heterostructure (7), (f) thinning the piezoelectric substrate (5) by its face opposite the handling substrate (2), so as to form said donor substrate (1).
  2. 2. Method according to the preceding claim, further comprising a step (g) of chemical-mechanical polishing of the free surface of the thinned piezoelectric substrate (4).
  3. 3. Method according to one of the preceding claims, in which the heat treatment (e) is carried out so as to increase the degree of crosslinking of the polymer in the photopolymerized adhesive layer (3) and/or the rigidity of said photopolymerized adhesive layer (3).
  4. 4. Method according to one of the preceding claims, in which the heat treatment (e) is carried out so that the Young's modulus of the adhesive layer (3) after irradiation and heat treatment is between 3.5 GPa and 10 GPa, said Young's modulus being measured by nanoindentation.
  5. 5. Method according to one of the preceding claims, in which the heat treatment (e) comprises the application of a temperature between 90°C and 110°C for a duration between 1 hour and 12 hours, in a nitrogen atmosphere.
  6. 6. Method according to one of the preceding claims, in which the luminous flux is applied through the piezoelectric substrate (5).
  7. 7. Method according to one of the preceding claims, in which the luminous flux has a wavelength between 200 nm and 500 nm.
  8. 8. Method according to one of the preceding claims, in which the thickness of the photopolymerizable adhesive layer (6) is between 1 pm and 50 pm and the irradiation energy received by said adhesive layer (6) during the irradiation step is between 0.7 J/cm 2 and 10 J/cm 2 .
  9. 9. Method according to one of the preceding claims, in which the deposition of the photo-polymerizable adhesive layer (6) is carried out by centrifugal coating.
  10. 10. Method according to one of the preceding claims, in which the photo-polymerizable adhesive layer (6) comprises an isocyanurate, acrylate or epoxy glue crosslinkable by ultraviolet radiation with or without a hardening agent.
  11. 11. Method according to one of the preceding claims, in which the bonding step is carried out at a temperature between 10°C and 50°C and/or in which the irradiation step is carried out at a temperature between 10°C and 50°C.
  12. 12. Method for transferring a piezoelectric layer onto a support substrate comprising: - the formation of a donor substrate (1) by implementing the method according to any one of the preceding claims, - the formation of a weakening zone in the thinned piezoelectric substrate (4) so as to delimit the piezoelectric layer to be transferred (9), - the supply of the support substrate (8), - bonding said donor substrate (1) to the support substrate (8), the piezoelectric layer to be transferred (9) being located at the bonding interface, - detaching the donor substrate (1) along the weakening zone so as to transfer the piezoelectric layer to be transferred (9) onto the support substrate (8).
  13. 13. Method according to the preceding claim, comprising, before bonding, the formation of an oxide layer, or a nitride layer, or a layer comprising a combination of nitride and oxide, or a superposition of at least one oxide layer and one nitride layer on the support substrate (8).
  14. 14. Method according to one of claims 12 or 13, in which the formation of the weakening zone is carried out by implantations of atomic species in the thinned piezoelectric substrate (4).
  15. 15. Manufacturing method according to one of claims 12 to 14, in which the handling substrate (2) and the support substrate (8) are manufactured from materials such that the difference in thermal expansion coefficient between the material of the handling substrate (2) and the support substrate (8) is less than or equal to 5%, preferably approximately equal to 0%.
  16. 16. Method for manufacturing a bulk acoustic wave device comprising the deposition of electrodes on two opposite faces of a piezoelectric layer, characterized in that it comprises the manufacturing of said piezoelectric layer by a method according to one of claims 12 to 15.
  17. 17. Donor substrate for the transfer of a piezoelectric layer, consisting of a heterostructure comprising a piezoelectric substrate bonded to a handling substrate (2), said substrate being characterized in that it comprises, at the interface between the piezoelectric substrate and the handling substrate, a polymerized adhesive layer (3) whose Young's modulus is between 3.5 GPa and 10 GPa.
  18. 18. Substrate according to the preceding claim, in which the thickness of the polymerized adhesive layer (3) is between 1 pm and 50 pm.
  19. 19. Substrate according to one of claims 17 or 18, in which the polymerized adhesive layer (3) comprises an isocyanurate, acrylate or epoxy glue crosslinkable by ultraviolet radiation with or without a hardening agent.

Description

DESCRIPTION Method of manufacturing a donor substrate for transferring a piezoelectric layer onto a support substrate TECHNICAL AREA The invention relates to a method of manufacturing a donor substrate for transferring a piezoelectric layer onto a support substrate, a method of transferring a piezoelectric layer onto such a support substrate and a method of manufacturing a bulk acoustic wave device comprising such a transfer. The invention finally relates to a donor substrate for transferring a piezoelectric layer. STATE OF THE ART The transfer of an active layer, i.e. intended for the formation of components for electronic, optical or optoelectronic devices, onto a support substrate via an electrically insulating layer, is widely used in the microelectronics industry. An example of a well-known active layer transfer process is the Smart Cut™ process. This process comprises forming a weakening zone by implanting atomic species into a donor substrate, in order to delimit a layer of interest to be transferred, bonding the donor substrate to the support substrate, and then detaching the donor substrate along the weakening zone, so as to transfer the layer of interest to the support substrate. In some situations, it is not possible to directly bond the donor substrate to the support substrate. More particularly, the bonding of the donor substrate to the support substrate can be carried out by means of oxide layers previously formed on the surface of each of the two substrates. To strengthen the oxide-oxide bonding between the piezoelectric substrate and the support substrate, it is known to carry out, after bonding, a consolidation annealing. Said consolidation annealing is typically carried out at a temperature between 100 °C and 300 °C. The Smart Cut™ process may also require annealing to achieve detachment of the layer of interest to be transferred, in a temperature range of 100°C to 600°C. When the donor substrate and the donor substrate have different coefficients of thermal expansion - which is the case for example between a donor substrate in a piezoelectric material and a silicon support substrate - such annealing causes significant deformation of the assembly of the two substrates, which is detrimental to the transfer since it can induce breakage of the substrates. To minimize such deformation, it is possible to form an intermediate substrate called a pseudo-donor substrate, in which the donor substrate is assembled on a temporary handling substrate (“handle substrate” in English). The method for manufacturing the pseudo-donor substrate generally comprises several steps. Thus, a layer of a thick piezoelectric material is bonded to the handling substrate, for example a silicon substrate. Then, the layer of piezoelectric material is thinned and possibly trimmed. Finally, the free surface of the thinned layer of piezoelectric material is polished, for example in a chemical-mechanical polishing (CMP) process, and possibly covered with a thin layer of oxide so as to achieve the oxide-oxide bonding previously described with the support substrate. The bonding of the piezoelectric substrate and the handling substrate to form the pseudo-donor substrate could be carried out by means of oxide layers previously formed on the surface of each of the two substrates. However, the deposition of an oxide layer on the piezoelectric substrate causes a significant curvature ("bow" according to the English terminology) of said piezoelectric substrate which is not very compatible with the subsequent steps of the process. Furthermore, the formation of oxide layers necessary for bonding is long and costly. Finally, as mentioned above, the heterostructure cannot be subjected to consolidation annealing due to the differences in thermal expansion coefficients between the piezoelectric substrate and the handling substrate. However, in the absence of consolidation annealing, the bonding energy of the oxide layers of the two substrates remains very low, so that the mechanical strength of the pseudo-donor substrate is insufficient. Therefore, failure at the bonding interface may occur during the thinning step of the thick piezoelectric substrate. An interesting alternative to oxide-oxide bonding for assembling the heterostructure constituting the donor pseudo-substrate is the implementation of a photopolymerizable adhesive layer: the photopolymerizable adhesive layer is deposited on one face of the handling substrate or the piezoelectric material layer, the handling substrate is bonded with the piezoelectric material layer via the adhesive layer and then the heterostructure thus formed is irradiated by a light flux so as to polymerize the adhesive layer. The photopolymerized adhesive layer ensures good mechanical strength of the donor pseudo-substrate. It also eliminates the need for high-temperature process steps that could cause significant curvature of the substrate. Moreover, the formation of such an adhesive layer is very simp