Method for transferring a useful layer into a supporting substrate

Abstract

A process for transferring a useful layer to a carrier substrate including a first surface is provided, the process including the steps of: providing a donor substrate including a first surface, a weakened zone including implanted species, the useful layer, which is bounded by the weakened zone and by the first surface of the donor substrate, and an amorphous zone disposed, in the useful layer, parallel to the weakened zone; assembling, on a side of the first surface of the donor substrate and on a side of the first surface of the carrier substrate, the donor substrate with the carrier substrate by bonding, such that the amorphous zone is at least partially facing at least one cavity that is partially bounded by the first surface of the donor substrate; and splitting the donor substrate along the weakened zone so as to reveal the useful layer.

Claims

1. A process for transferring a useful layer to a carrier substrate including a first surface, the process comprising successive steps of: a) providing a donor substrate comprising a crystalline first material including: a first surface, a weakened zone comprising implanted species, the useful layer comprising a portion of the crystalline first material of the donor substrate bounded by the weakened zone and by the first surface of the donor substrate and having a first thickness of the crystalline first material in a direction from the first surface to the weakened zone, and an amorphous zone disposed, in the useful layer, parallel to the weakened zone and having a second thickness in the direction less than the first thickness; b) assembling, on a side of the first surface of the donor substrate and on a side of the first surface of the carrier substrate, the donor substrate with the carrier substrate by bonding, step b) being executed such that the amorphous zone is at least partially facing at least one cavity that is partially bounded by the first surface of the donor substrate; and c) splitting the donor substrate along the weakened zone so as to reveal the useful layer.

2. The process according to claim 1, wherein the at least one cavity is produced in the first surface of the carrier substrate, and wherein the bonding of step b) is carried out between the first surface of the donor substrate and the first surface of the carrier substrate.

3. The process according to claim 1, wherein the carrier substrate includes pillars extending to the first surface of the carrier substrate and partially bounding the cavity, and wherein the bonding of step b) is carried out between the first surface of the donor substrate and the pillars of the carrier substrate.

4. The process according to claim 1, wherein the donor substrate provided in step a) includes pillars extending to the first surface of the donor substrate and partially bounding the cavity, and wherein the bonding of step b) is carried out between the pillars of the donor substrate and the first surface of the carrier substrate.

5. The process according to claim 1, wherein the carrier substrate includes pillars extending to the first surface of the carrier substrate and partially bounding a first cavity, wherein the donor substrate provided in step a) includes pillars extending to the first surface of the donor substrate and partially bounding a second cavity, and wherein the bonding of step b) is carried out between the pillars of the donor substrate and the pillars of the carrier substrate so as to join the first and second cavities and form said at least one cavity.

6. The process according to claim 1, further comprising a step d) consisting of crystallizing the amorphous zone, with step d) being executed after step c).

7. The process according to claim 6, wherein step d) is executed by solid-phase epitaxial regrowth.

8. The process according to claim 1, wherein step a) includes the steps of: a.sub.0) providing the donor substrate including the first surface, a.sub.1) forming the weakened zone in the donor substrate, and a.sub.2) forming the amorphous zone in the useful layer.

9. The process according to claim 8, wherein step a.sub.1) consists of implanting ionized species in the donor substrate, through the first surface of the donor substrate.

10. The process according to claim 9, wherein the ionized species includes at least one species selected from among H.sup.+, He.sup.+, and B.sup.+.

11. The process according to claim 8, wherein step a.sub.2) consists of implanting species in the useful layer, through the first surface of the donor substrate.

12. The process according to claim 11, wherein the species includes silicon ions or germanium ions.

13. The process according to claim 8, wherein step a.sub.2) is executed such that the amorphous zone is disposed at a distance from the first surface of the donor substrate.

14. The process according to claim 8, wherein the useful layer of the donor substrate provided in step a) has a volume density, denoted ρ.sub.1, and wherein step a.sub.2) is executed such that the amorphous zone has a volume density, denoted ρ.sub.2, satisfying ρ.sub.2≥ρ.sub.1/10.

15. The process according to claim 8, wherein the thickness of useful layer of the donor substrate provided in step a) is denoted t, defining a maximum theoretical width of the at least one cavity, denoted W.sub.lim, that is proportional to t.sup.2, and wherein step a.sub.2) is executed such that the amorphous zone forms a periodic array of zones with a pitch between the zones, denoted p, satisfying p<W.sub.lim, the periodic array being disposed parallel to the first surface of the donor substrate.

16. The process according to claim 8, wherein step a.sub.2) is executed by one of implantation of a species into the crystalline first material of the useful layer and deposition of an amorphous material in the crystalline first material of the donor substrate.

17. The process according to claim 1, wherein step c) is executed by applying a thermal anneal after the assembling of step b).

18. The process according to claim 1, wherein the useful layer comprises the crystalline first material and the amorphous zone is entirely disposed within boundaries of the useful layer.

19. A process for transferring a useful layer to a carrier substrate including a first surface, the process comprising successive steps of: a) providing a donor substrate made from a first material selected from a crystalline semiconductor and a piezoelectric material including: a first surface, a weakened zone comprising implanted species, the useful layer, which is bounded by the weakened zone and by the first surface of the donor substrate, is comprised of the first material, and has a first thickness in a direction from the first surface to the weakened zone, and an amorphous zone disposed, in the useful layer, parallel to the weakened zone and having a second thickness less than the first thickness; b) assembling, on a side of the first surface of the donor substrate and on a side of the first surface of the carrier substrate, the donor substrate with the carrier substrate by bonding, step b) being executed such that the amorphous zone is at least partially facing at least one cavity that is partially bounded by the first surface of the donor substrate; and c) splitting the donor substrate along the weakened zone so as to reveal the useful layer.

20. The process according to claim 19, wherein the semiconductor is selected from among Si, Ge, GaAs, InP, and GaN, and wherein the piezoelectric material is selected from among LiNbO.sub.3 and LiTaO.sub.3.

21. The process according to claim 19, wherein the first material of the donor substrate is a single crystal material.

22. A process for transferring a useful layer to a carrier substrate including a first surface, the process comprising successive steps of: a) providing a donor substrate comprising a crystalline first material including: a first surface, a weakened zone comprising implanted species, the useful layer comprising a portion of the crystalline first material of the donor substrate bounded by the weakened zone and by the first surface of the donor substrate, and an amorphous zone disposed, in the useful layer, parallel to the weakened zone; b) assembling, on a side of the first surface of the donor substrate and on a side of the first surface of the carrier substrate, the donor substrate with the carrier substrate by bonding, step b) being executed such that the amorphous zone is at least partially facing a plurality of cavities that are each partially bounded by the first surface of the donor substrate; and c) splitting the donor substrate along the weakened zone so as to reveal the useful layer, wherein the amorphous zone comprises a plurality of zones each being formed to be surrounded by the crystalline first material, and each partially facing one of the plurality of cavities.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages will become apparent from the detailed description of various embodiments of the invention, the description being coupled with examples and references to the appended drawings.

(2) FIGS. 1a to 1g are views of schematic cross sections cut along the normal to the first surfaces—and second surfaces—of the donor and carrier substrates, illustrating steps of a process according to the invention.

(3) FIGS. 2a to 2f are views of schematic cross sections cut along the normal to the first surfaces—and second surfaces—of the donor and carrier substrates, illustrating steps of a process according to the invention.

(4) FIGS. 3a to 3f are views of schematic cross sections cut along the normal to the first surfaces—and second surfaces—of the donor and carrier substrates, illustrating steps of a process according to the invention.

(5) FIGS. 4a to 4g are views of schematic cross sections cut along the normal to the first surfaces—and second surfaces—of the donor and carrier substrates, illustrating steps of a process according to the invention.

(6) FIG. 5 is a view of a schematic cross section cut along the normal to the first surfaces—and second surfaces—of the donor and carrier substrates, illustrating an amorphous zone forming a periodic array.

(7) The figures have not been drawn to scale in order to simplify comprehension thereof.

DETAILED DESCRIPTION OF EMBODIMENTS

(8) Elements that are identical or that perform the same function in the various embodiments have been given the same references, for the sake of simplicity.

(9) One subject of the invention is a process for transferring a useful layer 1 to a carrier substrate 2 including a first surface 20, the process including the successive steps of: a) providing a donor substrate 3 including: a first surface 30, a weakened zone ZS comprising implanted species, the useful layer 1, which is bounded by the weakened zone ZS and by the first surface 30 of the donor substrate 3, an amorphous zone 4 lying, in the useful layer 1, parallel to the weakened zone ZS; b) assembling, on the side of the first surface 30 of the donor substrate 3 and on the side of the first surface 20 of the carrier substrate 2, the donor substrate 3 with the carrier substrate 2 by bonding; step b) being executed so that the amorphous zone 4 is at least partially facing at least one cavity 200 that is partially bounded by the first surface 30 of the donor substrate 3; c) splitting the donor substrate 3 along the weakened zone ZS so as to reveal the useful layer 1.
Carrier Substrate

(10) As illustrated in FIG. 1d, according to one embodiment, the one or more cavities 200 are formed in the first surface 20 of the carrier substrate 2, preferably by steps of photolithography and of etching. The carrier substrate 2 includes a second surface 21, opposite the first surface 20.

(11) The first surface 20 of the carrier substrate 2 may be covered with an oxide layer. The oxide layer may be a thermal oxide. By way of variant, the first surface 20 of the carrier substrate 2 may be covered with a metal layer. The metal layer is made of a metal that is preferably selected from Au, Cu, Ti and W.

(12) Donor Substrate

(13) The donor substrate 3 provided in step a) includes a second surface 31, opposite to the first surface 30. The donor substrate 3 provided in step a) is advantageously made from a material selected from: a semiconductor, preferably Si, Ge, GaAs, InP or GaN; a piezoelectric material, preferably LiNbO.sub.3, LiTaO.sub.3.

(14) When the first surface 20 of the carrier substrate 2 is covered with an oxide layer, the first surface 30 of the donor substrate 3 is advantageously covered with an oxide layer in order to promote hydrophilic bonding in step b). When the first surface 20 of the carrier substrate 2 is covered with a metal layer, the first surface 30 of the donor substrate 3 is advantageously covered with a metal layer, preferably of the same metal, in order to promote thermocompression bonding in step b).

(15) The donor substrate 3 has a single-crystal structure.

(16) Step a) advantageously includes the steps of: a.sub.0) providing the donor substrate 3 including the first surface 30 and the opposite second surface 31; a.sub.1) forming the weakened zone ZS in the donor substrate 3; a.sub.2) forming the amorphous zone 4 in the useful layer 1.

(17) Steps a.sub.1) and a.sub.2) may be inverted. Step a.sub.0) is illustrated in FIG. 1a. Step a.sub.1) is illustrated in FIG. 1b. Step a.sub.2) is illustrated in FIG. 1c.

(18) Step a.sub.1) advantageously consists in implanting ionized species in the donor substrate 3, through the first surface 30 of the donor substrate 3, said ionized species preferably including at least one species selected from H.sup.+, He.sup.+ and B.sup.+. It is therefore possible to carry out a co-implantation with a plurality of ionized species (e.g. H.sup.+ and B.sup.+), or even to carry out a multi-implantation of the same ionized species. By way of nonlimiting example, when the donor substrate 3 is made of single-crystal silicon and when the implanted species are H.sup.+ ions, step a.sub.1) may be executed using the following parameters: an energy comprised between 60 keV and 200 keV, a dose comprised between 5×10.sup.16 at.Math.cm.sup.−2 and 10.sup.17 at.Math.cm.sup.−2.

(19) The parameters will be adapted depending on the thickness desired for the useful layer 1. For example, when the donor substrate 3 is made of single-crystal silicon, an energy of 160 keV and a dose of 6×10.sup.16 at.Math.cm.sup.−2 lead to a thickness of 1.5 μm for the useful layer 1.

(20) Step a.sub.2) advantageously consists in implanting species in the useful layer 1, through the first surface 30 of the donor substrate 3, said species preferably being silicon ions or germanium ions. The species are implanted in step a.sub.2) through a mask 5 (illustrated in FIG. 1c). The mask 5 may be a hard mask or a thick photoresist (of thickness of about 3 μm). Step a.sub.2) is advantageously executed so that the amorphous zone 4 lies at distance from the first surface 30 of the donor substrate 3. By way of nonlimiting example, when the donor substrate 3 is made from single-crystal silicon and when the implanted species are silicon ions, step a.sub.2) may be executed using the following parameters: an energy comprised between 10 keV and 150 keV, a dose comprised between 10.sup.14 at.Math.cm.sup.−2 and 5×10.sup.15 at.Math.cm.sup.−2.

(21) The parameters will be adapted depending on the desired amorphization depth.

(22) According to one variant, step a.sub.2) includes the steps of: a.sub.20) etching a portion of the first surface 30 of the donor substrate 3; a.sub.21) depositing an amorphous layer in said etched portion so as to form the amorphous zone 4.

(23) The useful layer 1 of the donor substrate 3 provided in step a) has a volume density, denoted ρ.sub.1. Step a.sub.2) is advantageously executed so that the amorphous zone 4 has a volume density, denoted ρ.sub.2, satisfying ρ.sub.2≥ρ.sub.1/10.

(24) The useful layer 1 of the donor substrate 3 provided in step a) has a thickness, denoted t, defining a maximum theoretical width of the cavity, denoted W.sub.lim, that is proportional to t.sup.2, as described in D1. According to one embodiment, which is illustrated in FIG. 2, step a.sub.2) is executed so that the amorphous zone 4 forms a periodic array with a pitch, denoted p, satisfying p<W.sub.lim, the periodic array lying parallel to the first surface 30 of the donor substrate 3. By way of nonlimiting example, when the donor substrate 3 is made of single-crystal silicon, and when the thickness t of the useful layer 1 is about 1.5 μm, then W.sub.k is about 40 μm.

(25) Step b) of Bonding

(26) Step b) is illustrated in FIG. 1e. Steps a.sub.2) and b) are configured so that the following cases may present themselves at the end of step b): (i) all the amorphous zone 4 is located facing all the cavity 200, (ii) all the amorphous zone 4 is located facing a portion of the cavity 200, (iii) a portion of the amorphous zone 4 is located facing all the cavity 200, (iv) a portion of the amorphous zone 4 is located facing a portion of the cavity 200.

(27) Case (i) will be preferred in order to optimize the inhibition of the blistering of the implanted species.

(28) When the one or more cavities 200 are produced in the first surface 20 of the carrier substrate 2, the bonding of step b) is carried out between the first surface 30 of the donor substrate 3 and the first surface 20 of the carrier substrate 2. When the carrier substrate 2 is provided with a single cavity 200, step b) is executed so that the amorphous zone 4 is at least partially facing the cavity 200. When the carrier substrate 2 is provided with a plurality of cavities 200, step b) is executed so that the amorphous zone 4 is at least partially facing each cavity 200.

(29) The side of the first surface 30 of the donor substrate 3 is defined by the orientation of the normal to the first surface 30 of the donor substrate 3. In the same way, the side of the first surface 20 of the carrier substrate 2 is defined by the orientation of the normal to the first surface 20 of the carrier substrate 2.

(30) As illustrated in FIG. 1e, at the end of step b), each cavity 200 is bounded: partially by the first surface 30 of the donor substrate 3, partially by the first surface 20 of the carrier substrate 2.

(31) The bonding carried out in step b) is advantageously bonding by direct adhesion between the first surface 30 of the donor substrate 3 and the first surface 20 of the carrier substrate 2. By “direct adhesion”, what is meant is spontaneous bonding resulting from bringing two surfaces into contact, i.e. in the absence of an additional element such as an adhesive, a wax or a solder. The adhesion mainly results from van der Waals forces due to the electronic interaction between the atoms or molecules of two surfaces, from hydrogen bonds because of preparation of the surfaces or from covalent bonds established between two surfaces. Bonding by molecular adhesion or direct bonding are also spoken of. Bonding by direct adhesion is to be contrasted with thermocompression bonding, eutectic bonding, or even anodic bonding.

(32) However, the bonding carried out in step b) may be thermocompression bonding or eutectic bonding depending on the nature of the first surface 30 of the donor substrate 3 and of the first surface 20 of the carrier substrate 2.

(33) Step b) is advantageously preceded by a preparation of the first surface 30 of the donor substrate 3 and by a preparation of the first surface 20 of the carrier substrate 2. By way of example, for direct bonding, it is possible to chemically activate the first surfaces 20, 30, for example using a Caro's acid (produced by mixing H.sub.2SO.sub.4 and H.sub.2O.sub.2), then to clean the first surfaces 20, 30 using a standard RCA process. By way of variant, for direct bonding, it is possible to activate the first surfaces 20, 30 by chemical-mechanical polishing (CMP), then to clean the first surfaces 20, 30 with a scrubber.

(34) Step b) is advantageously executed in a controlled atmosphere. By way of nonlimiting example, step b) may be executed under a high vacuum such as a secondary vacuum at a pressure lower than 10.sup.−2 mbar.

(35) Step c) of Splitting

(36) Step c) is illustrated in FIG. 1f. Step c) of splitting is advantageously executed by applying a thermal anneal to the assembly obtained at the end of step b).

(37) The thermal anneal is applied with a thermal budget suitable for splitting the donor substrate 3 along the weakened zone ZS. The thermal-anneal temperature is preferably comprised between 350° C. and 550° C. The duration of the thermal anneal is preferably comprised between 5 minutes and 3 hours.

(38) Step c) is advantageously preceded by a step consisting in applying a thermal anneal to the assembly obtained in step b) with a thermal budget suitable for strengthening the bonding without initiating the splitting of the donor substrate 3 along the weakened zone ZS.

(39) Step d) of Recrystallizing

(40) The process advantageously includes a step d) consisting in recrystallizing the amorphous zone 4, step d) being executed after step c). Step d) is illustrated in FIG. 1g. Step d) is advantageously executed by solid-phase epitaxial regrowth. Thus, one procured advantage is the ability to easily reconstruct a crystal structure for the useful layer 1. Step d) is essential when it is desired to form an electronic device from the useful layer 1. For this application, step a.sub.2) is advantageously executed so that the amorphous zone 4 has a degree of mass crystallinity lower than or equal to 20%, this allowing the quality of the recrystallization to be improved. Step d) is executed by applying a thermal anneal. By way of nonlimiting example, when the amorphous zone 4 is of amorphous silicon, the recrystallization starts at 450° C.

(41) By way of variant, step d) may be executed: using a rapid microwave thermal anneal, or using laser recrystallization.
Finishing

(42) The process according to the invention advantageously includes: a step of sacrificial oxidation of the useful layer 1, which is executed after step d), so as to adjust the final thickness of the useful layer 1 and to remove portions damaged by the implantation of the ionized species; a step of chemical-mechanical polishing in order to improve the surface finish of the useful layer 1.

(43) The method may also include steps of dry or wet etching, and steps of cleaning the useful layer 1.

(44) Application to the Formation of a Protective Cover

(45) According to the embodiment illustrated in FIGS. 2a to 2f, the carrier substrate 2 includes pillars 6 extending to the first surface 20 of the carrier substrate 2 and partially bounding the cavity 200. The bonding of step b) is carried out between the first surface 30 of the donor substrate 3 and the pillars 6 of the carrier substrate 2. The pillars 6 of the carrier substrate 2 may partially bound a plurality of cavities 200. As illustrated in FIG. 2e, at the end of step b), each cavity 200 is bounded: partially by the first surface 30 of the donor substrate 3, partially by the first surface 20 of the carrier substrate 2, partially by the pillars 6 of the carrier substrate 2.

(46) The technical features described above with respect to steps a), b) and c) apply to this subject matter, with the exception of the direct bonding of step b) which is not conceivable in this case. Step d) is optional. Specifically, when the useful layer 1 forms a protective cover, an electronic device is not necessarily formed from the useful layer 1. For this application, step a.sub.2) may be executed so that the amorphous zone 4 has a degree of mass crystallinity lower than or equal to 80%. In other words, a polycrystalline structure of the amorphous zone 4 is perfectly recommendable provided that an electronic device does not need to be formed from the useful layer 1.

(47) The pillars 6 are advantageously made from a metal, and preferably from copper. By way of nonlimiting example, the pillars 6 are formed in the first surface 20 of the carrier substrate 2 by electrochemical deposition (ECD). The bonding carried out in step b) is advantageously thermocompression bonding.

(48) Thus, such a transferred useful layer 1 forms locally a, preferably hermetic, protective cover on the carrier substrate 2, so as to form an encapsulating means. Such a transferred useful layer 1 forms an encapsulating means that is more effective than an ad hoc, deposited, pierced then plugged layer.

(49) By way of variant, as illustrated in FIGS. 3a to 3f, the donor substrate 3 provided in step a) includes pillars 6′ extending to the first surface 30 of the donor substrate 3 and partially bounding the cavity 200. The bonding of step b) is carried out between the pillars 6′ of the donor substrate 3 and the first surface 20 of the carrier substrate 2. The pillars 6′ of the donor substrate 3 may partially bound a plurality of cavities 200. As illustrated in FIG. 3e, at the end of step b), each cavity 200 is bounded: partially by the first surface 30 of the donor substrate 3, partially by the first surface 20 of the carrier substrate 2, partially by the pillars 6′ of the donor substrate 3.

(50) The technical features described above with respect to steps a), b) and c) apply to this subject matter, with the exception of the direct bonding of step b) which is not conceivable in this case. Step d) is optional. Specifically, when the useful layer 1 forms a protective cover, an electronic device is not necessarily formed from the useful layer 1. For this application, step a.sub.2) may be executed so that the amorphous zone 4 has a degree of mass crystallinity lower than or equal to 80%. In other words, a polycrystalline structure of the amorphous zone 4 is perfectly recommendable provided that an electronic device does not need to be formed from the useful layer 1.

(51) The pillars 6′ are advantageously made from a metal, and preferably from copper. By way of nonlimiting example, the pillars 6′ are formed in the first surface 30 of the donor substrate 3 by electrochemical deposition (ECD). The bonding carried out in step b) is advantageously thermocompression bonding.

(52) Thus, such a transferred useful layer 1 forms locally a, preferably hermetic, protective cover on the carrier substrate 2, so as to form an encapsulating means. Such a transferred useful layer 1 forms an encapsulating means that is more effective than an ad hoc, deposited, pierced then plugged layer.

(53) By way of variant, as illustrated in FIGS. 4a to 4g, the carrier substrate 2 includes pillars 6 extending to the first surface 20 of the carrier substrate 2 and partially bounding a first cavity 200a. The donor substrate 3 provided in step a) includes pillars 6′ extending to the first surface 30 of the donor substrate 3 and partially bounding a second cavity 200b. The bonding of step b) is carried out between the pillars 6′ of the donor substrate 3 and the pillars 6 of the carrier substrate 2 so as to join the first and second cavities 200a, 200b and form the cavity 200. The pillars 6 of the carrier substrate 2 may partially bound a plurality of first cavities 200a. The pillars 6′ of the donor substrate 3 may partially bound a plurality of second cavities 200b. Joining the first and second cavities 200a, 200b forms a plurality of cavities 200. As illustrated in FIG. 4f, at the end of step b), each cavity 200 is bounded: partially by the first surface 30 of the donor substrate 3, partially by the first surface 20 of the carrier substrate 2, partially by the pillars 6′ of the donor substrate 3, partially by the pillars 6 of the carrier substrate 2.

(54) The technical features described above with respect to steps a), b) and c) apply to this subject matter, with the exception of the direct bonding of step b) which is not conceivable in this case. Step d) is optional. Specifically, when the useful layer 1 forms a protective cover, an electronic device is not necessarily formed from the useful layer 1. For this application, step a.sub.2) may be executed so that the amorphous zone 4 has a degree of mass crystallinity lower than or equal to 80%. In other words, a polycrystalline structure of the amorphous zone 4 is perfectly recommendable provided that an electronic device does not need to be formed from the useful layer 1.

(55) The pillars 6 of the carrier substrate 2 and the pillars 6′ of the donor substrate 3 are advantageously made from a metal, and preferably from copper. By way of nonlimiting example, the pillars 6 of the carrier substrate 2 and the pillars 6′ of the donor substrate 3 are formed in the first surface 20 of the carrier substrate 2 and in the first surface 30 of the donor substrate 3 by electrochemical deposition (ECD) respectively. The bonding carried out in step b) is advantageously thermocompression bonding.

(56) Thus, such a transferred useful layer 1 forms locally a, preferably hermetic, protective cover on the carrier substrate 2, so as to form an encapsulating means. Such a transferred useful layer 1 forms an encapsulating means that is more effective than an ad hoc, deposited, pierced then plugged layer.

(57) The invention is not limited to the described embodiments. Those skilled in the art will be able to consider technically possible combinations thereof, and to substitute equivalents thereof.