Method of fabricating layers of single-crystal material
A process for fabricating a component includes an operation of transferring at least one layer of one or more piezoelectric or pyroelectric or ferroelectric materials forming part of a donor substrate to a final substrate, the process comprising a prior step of joining the layer to a temporary substrate via production of a fragile separating region between the donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material and the temporary substrate, the region comprising at least two layers of different materials in order to ensure two compounds apt to generate an interdiffusion of one or more constituent elements of at least one of the two compounds make contact, the fragile region allowing the temporary substrate to be separated.
1. A process for fabricating a component comprising transferring an assembly comprising one or more layers of one or more single-crystal piezoelectric or pyroelectric or ferroelectric materials to a final substrate, said process comprising at least:
a first set of steps comprising:
a step of implanting ions into a donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material at an implantation level so as to define a layer region in said single-crystal piezoelectric or pyroelectric or ferroelectric material;
a first joining step wherein said donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material is joined to a temporary substrate, said first joining step comprising producing a fragile separating interface region between said donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material and said temporary substrate, said region comprising at least two layers of different materials in order to ensure two compounds apt to generate an interdiffusion of one or more constituent elements of at least one of the two compounds make contact;
a step of thinning said donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material to the implantation level so as to define a layer of single-crystal piezoelectric or pyroelectric or ferroelectric material;
a step of healing residual defects via thermal annealing of said layer of single-crystal piezoelectric or pyroelectric or ferroelectric material;
and a second set of steps subsequent to the first set of steps, comprising at least:
a second joining step in which an assembly comprising the one or more layers of one or more single-crystal piezoelectric or pyroelectric or ferroelectric materials and said temporary substrate is joined to a final substrate;
a step of separating the temporary substrate from said layer of single-crystal piezoelectric or pyroelectric or ferroelectric material, via said fragile separating interface region,
wherein production of said fragile separating interface region between said donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material and said temporary substrate comprises at least:
producing a layer of oxide or of nitride;
depositing a layer of noble metal;
carrying out a thermal anneal apt to create said interdiffusion of one or more constituent elements of at least one of the two compounds,
wherein the step of separating the temporary substrate is carried out mechanically, via the fragile interface.
2. The fabricating process according to claim 1 , wherein the second set of steps comprises a step of producing a first functional structure on one of the layers of single-crystal piezoelectric or pyroelectric or ferroelectric material.
3. The process for fabricating a component according to claim 2 and comprising:
producing a first metal functional structure on a first face of said layer of single-crystal piezoelectric or pyroelectric or ferroelectric material, said structure being configured to be a continuous electrode or a series of discontinuous electrodes;
producing a second metal functional structure on the opposite face of said layer of single-crystal piezoelectric or pyroelectric or ferroelectric material or on an opposite face of another layer of single-crystal piezoelectric or pyroelectric or ferroelectric material, said structure being configured to be a continuous electrode or a series of discontinuous electrodes, said first face corresponding to the thinned face of the donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material.
4. The fabricating process according to claim 1 , wherein the second set of steps comprises a step of producing a second functional structure on one of the layers of single-crystal piezoelectric or pyroelectric or ferroelectric material.
5. The fabricating process according to claim 1 , wherein, after the step of thinning said donor substrate, which is made of a first single-crystal piezoelectric or pyroelectric or ferroelectric material, to the implantation level, so as to define a layer of single-crystal piezoelectric or pyroelectric or ferroelectric material, said process comprises producing an additional layer of second single-crystal piezoelectric or pyroelectric or ferroelectric material on the surface of said layer of single-crystal piezoelectric or pyroelectric or ferroelectric material, said first and second materials being identical or different.
6. The fabricating process according to claim 5 , wherein the thickness of the layer of first material is smaller than or equal to 1 micron, and the thickness of the additional layer of second material is comprised between 0.1 and 5 microns.
7. The fabricating process according to claim 1 , comprising:
producing a layer of silicon oxide or of silicon nitride;
depositing a layer of noble metal of Pt or of Au or of Rh or of Os or of Pd or of Ru or of Ir.
8. The fabricating process according to claim 1 , wherein the step of healing residual defects via thermal annealing is carried out with a thermal budget apt to cause the diffusion of the noble metal into the oxide or into the nitride, said thermal budget being spent at a temperature comprised between 300° C. and 700° C. for a time comprised between 1 hour and 10 hours.
9. The fabricating process according to claim 1 , wherein the first joining step, wherein step said substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material is joined to a temporary substrate, is carried out with a first bonding layer made of a constituent material of one of the materials in order to ensure two compounds apt to generate an interdiffusion or one or more constituent elements of at least one of the two compounds make contact.
10. The fabricating process according to claim 1 , wherein the first joining step, wherein step said substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material is joined to a temporary substrate, is carried out with a first bonding layer, said first bonding layer being a layer of silicon oxide (SiO 2 ), a metal layer (Cu, Au, Ti, Ag, etc.) or a layer of a polymer.
11. The fabricating process according to claim 1 , wherein the second joining step, wherein step an assembly comprising the one or more layers of one or more single-crystal piezoelectric or pyroelectric or ferroelectric materials and said temporary substrate is joined to a final substrate, is carried out with at least one second bonding layer, said second bonding layer being mineral.
12. The fabricating process according to claim 1 , wherein the donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material is made of lithium niobate, or lithium tantalate.
13. The fabricating process according to claim 1 , wherein the temporary substrate is made of the same material as the donor substrate of single-crystal piezoelectric or pyroelectric or ferroelectric material.
14. The fabricating process according to claim 1 , wherein the final substrate is made of lithium niobate, lithium tantalate or silicon or glass or sapphire.
15. The fabricating process according to claim 1 , said component being an acoustic wave resonator, said process comprising:
depositing a sacrificial layer on the surface of a layer of single-crystal piezoelectric or pyroelectric or ferroelectric material or on the surface of the additional layer of second single-crystal piezoelectric or pyroelectric or ferroelectric material and/or on the surface of the first metal functional structure;
producing at least one well in said sacrificial layer;
etching said well so as to produce a suspended membrane of single-crystal piezoelectric or pyroelectric or ferroelectric material.
16. The fabricating process according to claim 1 , said component being an acoustic-wave resonator, said process comprising producing cavities in said final substrate before the second joining step.
17. The fabricating process according to claim 1 , said component being an acoustic-wave resonator, said process comprising producing a stack with, in alternation, layers having different acoustic impedances on the surface of the layer of single-crystal piezoelectric or pyroelectric or ferroelectric material or on the surface of the additional layer of second single-crystal piezoelectric or pyroelectric or ferroelectric material, in order to produce a Bragg-mirror structure.
18. The fabricating process according to claim 1 , said component comprising a set of at least two stacked bulk-acoustic-wave resonators, said process comprising:
fabricating a resonator comprising at least a first layer of single-crystal piezoelectric or pyroelectric or ferroelectric material, a first metal functional structure, and a second metal functional structure, on a final substrate;
depositing one or more acoustically coupling or isolating layers on the surface of said first resonator;
producing a first metal functional structure apt to form a first electrode of a second resonator on the surface of said one or more acoustically coupling or acoustically isolating layers;
transferring a second layer of single-crystal piezoelectric or pyroelectric or ferroelectric material previously transferred, to a temporary substrate, via a fragile separating interface region to the surface of said temporary substrate;
removing said temporary substrate so as to leave a second face of said second active layer free;
producing a second metal functional structure, so as to define the second resonator.
19. The fabricating process according to claim 1 , said component being a pyroelectric sensor comprising, between two continuous electrodes, an active layer said process further comprises partially etching, from the back side, the final substrate, so as to define a membrane in said final substrate.
20. The fabricating process according to claim 1 , wherein the fragile interface region comprises a layer of noble metal and another layer comprising at least one of the following materials:
an oxide;
a nitride;
a silicon oxynitride;
a silicon oxycarbide (SiOC);
SiOF.