USE OF AN ELECTRIC FIELD FOR DETACHING A PIEZOELECTRIC LAYER FROM A DONOR SUBSTRATE

Abstract

A method for transferring a piezoelectric layer from a donor substrate onto a support substrate comprises the steps of: a) providing a predetermined splitting area in a piezoelectric donor substrate, b) attaching the piezoelectric donor substrate to a support substrate to form an assembly, and c) detaching the piezoelectric layer from the piezoelectric donor substrate comprising applying an electric field. By using the electric field, the detachment step can be carried out at low temperatures. A detachment chamber for carrying out at least a portion of such a method includes one or two chucks comprising first and/or second electrodes for applying an electric field to a piezoelectric layer.

Claims

1. A method of transferring a piezoelectric layer onto a support substrate, comprising the steps of: a) providing a predetermined splitting area in a piezoelectric donor substrate; b) attaching the piezoelectric donor substrate to the support substrate to form an assembly; and c) detaching the piezoelectric layer from the piezoelectric donor substrate, detaching the piezoelectric layer comprising applying an electric field.

2. The method of claim 1, wherein the piezoelectric donor substrate comprises a bulk piezoelectric substrate.

3. The method of claim 1, wherein the piezoelectric donor substrate comprises a layer of piezoelectric material on a handle substrate.

4. The method of claim 1, wherein step b) comprises a heat treatment with a temperature of at most 100° C.

5. The method of claim 1, wherein step b) is carried out at a pressure below 10.sup.−2 mbar.

6. The method of claim 1, wherein step c) is carried out at a temperature of less than 100° C.

7. The method of claim 1, wherein applying the electric field comprises using a chuck comprising at least one electrode.

8. The method of claim 7, further comprising placing a surface of the piezoelectric donor substrate of the assembly is placed in direct contact with the chuck.

9. The method of claim 8, wherein the chuck comprises interdigitated electrodes separated by an electrically insulating material.

10. The method of claim 9, wherein the voltage applied to the chuck is up to 10 kV, in particular, in a range between 1 kV and 5 kV.

11. The method of claim 7, wherein the assembly is sandwiched between the chuck and a second electrode.

12. The method of claim 11, wherein the voltage applied to the electrostatic chuck is up to 5 kV.

13. The method of claim 1, wherein the electric field lines are essentially parallel to the polarization direction of the piezoelectric donor substrate.

14. The method of claim 1, wherein the piezoelectric donor substrate comprises a material chosen from among LiTaO.sub.3 (LTO), AlN, ZnO, Pb[Zr.sub.xTi.sub.1-x]O.sub.3 (0≤x≤1) (PZT) and LiNbO.sub.3 (LNO).

15. The method of claim 1, wherein the support substrate comprises a semiconductor substrate.

16. A detachment chamber for detaching a piezoelectric layer from a piezoelectric donor substrate, the detachment chamber comprising at least one chuck comprising at least one electrode for applying an electric field to the piezoelectric layer.

17. The detachment chamber of claim 16, wherein the at least one chuck comprises holding means for holding the piezoelectric donor substrate on the at least one chuck.

18. The detachment chamber of claim 17, wherein the at least one electrode is independent of the holding means.

19. The detachment chamber of claim 16, wherein the at least one chuck comprises a first chuck and a second chuck, each of the first and second chucks comprising at least one electrode.

20. The method of claim 4, wherein step b) is carried out between 15° C. and 25° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The disclosure will be described in more detail hereafter using advantageous exemplary embodiments in conjunction with the accompanying figures, wherein:

[0025] FIGS. 1a to 1e schematically illustrate an embodiment of a method of transferring a piezoelectric layer onto a support substrate;

[0026] FIG. 2 schematically illustrates a setup according to a second embodiment of the disclosure; and

[0027] FIG. 3 schematically illustrates a setup according to a third embodiment of the disclosure.

DETAILED DESCRIPTION

[0028] FIGS. 1a to 1e illustrate an embodiment of the method of transferring a piezoelectric layer onto a support substrate.

[0029] In the process step illustrated in FIG. 1a, corresponding to step a) of the method according to the disclosure, a predetermined splitting area 1 is created in a piezoelectric donor substrate 3 by implanting ions 5.

[0030] The piezoelectric donor substrate 3 can comprise a material chosen from among, for example, LiTaO.sub.3 (LTO), AlN, ZnO, Pb[Zr.sub.xTi.sub.1-x]O.sub.3 (0≤x≤1) (PZT) and LiNbO.sub.3 (LNO). In the following, only as an example according to the disclosure, the piezoelectric donor substrate is a bulk piezoelectric substrate comprising LTO.

[0031] According to a variant, the donor substrate could comprise a handle substrate with a piezoelectric layer on top of the handle substrate.

[0032] To form the predetermined splitting area 1 within the piezoelectric donor substrate 3, a dose of 5*10.sup.16 to 2*10.sup.17 H.sup.+ or He.sup.+ or a mix of H.sup.+/He.sup.+ ions/cm.sup.2 may be implanted with an energy of about 10 keV to 1 MeV as a function of the desired depth d of the predetermined splitting area 1. Under the implanting conditions mentioned above, the depth d of the predetermined splitting area 1 within the donor substrate 3 is of the order of 60 nm to 6 μm.

[0033] The next step, illustrated in FIG. 1b, is a first thermal treatment step to grow defects 7 that form the predetermined splitting area 1 created by the ion implantation. The roughness of the surface 9 is below 5 nm RMS. According to the disclosure, this first thermal treatment step is carried out at temperatures between 0° C. and 200° C. for a duration of about 1 hour to 24 hours.

[0034] Step b), according to the disclosure, is illustrated in FIG. 1c. It comprises attaching, in particular by bonding, the piezoelectric donor substrate 3 to a support substrate 11 to thereby form an assembly 13. The support substrate 11 can be a semiconductor substrate, such as a Si wafer, or an insulator, such as sapphire, or a metal, such as Mo.

[0035] The bonding step is carried out at ambient pressure or under vacuum, typically a primary vacuum of below 10.sup.−2 mbar, in particular, of the order of 10.sup.−3 to 10.sup.−4 mbar. In order to strengthen the bond between the two substrates 3 and 11, the bonding process is carried out at a temperature of up to 100° C.

[0036] FIG. 1d illustrates the next step in the manufacturing process. This step corresponds to step c) according to the disclosure. An electric field is applied to the assembly 13, with the electric field lines 15 essentially perpendicular to the predetermined splitting area 1.

[0037] According to an aspect of the disclosure, the electric field lines 15 are essentially parallel to the polarization axis 17 (or poling axis) of the piezoelectric donor substrate 3 to optimize the piezoelectric effect. Due to the piezoelectric properties, the presence of the electric field lines 15 will lead to a mechanical deformation in the direction z inside the piezoelectric support substrate 11. This deformation further weakens the predetermined splitting area 1. To obtain the desired electric field, voltages of up to 10 kV are applied (see description below with respect to FIGS. 2 and 3).

[0038] Depending on the strength of the electric field, a complete detachment of the remainder 19 of the piezoelectric donor substrate from the modified assembly 13′ comprising the support substrate 11 and a transferred piezoelectric layer 21 can occur at the predetermined splitting area as illustrated in FIG. 1e.

[0039] According to a variant, the detachment as shown in FIG. 1e can also be obtained by heating the assembly 13 during or after the application of the electric field lines 15. In this second heat treatment step, temperatures of up to 100° C. are used for the final detachment. The choice of the temperature depends on the conditions of the first heat treatment step and the strength of the electric field lines 15.

[0040] With the method according to the disclosure, it becomes possible to transfer thin piezoelectric layers 21 onto a support substrate 11 without suffering from an existing large difference in the thermal expansion coefficient between the material of the piezoelectric layer 21 and the support substrate 11.

[0041] The remainder 19 of the piezoelectric donor substrate can then be reused as a donor substrate 3 to restart the process as described with respect to FIGS. 1a to 1e.

[0042] FIG. 2 schematically illustrates a setup according to a second embodiment of the disclosure. FIG. 2 shows a detachment chamber 31 used to carry out at least step c) of the method according to the disclosure as illustrated in FIG. 1d.

[0043] The detachment chamber comprises a chuck 33 comprising positive electrodes 35 and negative electrodes 37 to be able to apply an electric field 39 to the assembly 13 comprising the piezoelectric donor substrate 3 and the support substrate 11 as described in detail with respect to the first embodiment. The description of the features of the first embodiment will not be repeated again, but is incorporated herewith by reference. The chuck may comprise further means for holding the assembly 13, e.g., a vacuum or a device configured to generate electrostatic forces. In this embodiment, those means for holding the assembly 13 are independent of the electrodes 35 and 37.

[0044] The assembly 13 is positioned on the chuck 33 such that the piezoelectric donor substrate 3 of the assembly 13 is placed onto the chuck 33.

[0045] The positive and negative electrodes 35, 37 are arranged such that the electric field 39 is essentially perpendicular to the surface of the chuck 33 at least within the thickness d′ of the piezoelectric donor substrate 3. With the polarization axis 17 of the piezoelectric donor substrate also being perpendicular to the chuck 33, the piezoelectric effect can be optimized, thereby creating mechanical strain in the predetermined splitting area 1 further leading to weakening.

[0046] According to a variant, it could also be the support substrate that is positioned on the chuck 33, especially in the case when the electric field is sufficiently strong. However, for an insulating support substrate 11, it is preferable to position the piezoelectric donor substrate 3 on the chuck 33.

[0047] In one variant, the positive electrodes 35 and negative electrodes 37 are interdigitated with an electrically insulating material (not shown), e.g., a thin ceramic layer, positioned between the positive electrodes 35 and negative electrodes 37.

[0048] The control unit of the detachment chamber 31 is configured such that voltage differentials of up to 10 kV can be applied to the electrodes, preferably, 1 kV to 5 kV. In this embodiment, only one electrostatic chuck is necessary, which simplifies the design of the detachment chamber 31.

[0049] FIG. 3 schematically illustrates a setup according to a third embodiment of the disclosure. FIG. 3 shows a second embodiment of a detachment chamber 51 used to carry out at least step c) of the method according to the disclosure as illustrated in FIG. 1d. The description of the features of the first and second embodiment will not be repeated again, but is incorporated herewith by reference.

[0050] In this embodiment, two chucks 53 and 55 are used. The lower chuck 53 comprises a positive electrode 57; the upper chuck 55 comprises a negative electrode 59. According to a variant, the polarization can be reversed. The assembly 13 is sandwiched between the two chucks 53, 55.

[0051] Also in this configuration, the electric field lines 61 are parallel to the polarization direction 17 of the piezoelectric donor substrate to optimize the piezoelectric effect leading to optimized weakening in the predetermined splitting area 1.

[0052] In this electrode configuration, voltages of up to 5 kV, especially 200 V to 1 kV, can be applied to the electrodes 57, 59 to obtain the desired effect in the predetermined splitting area 1 without observing a detachment at the interface between the piezoelectric donor substrate 3 and the support substrate 11.

[0053] The detachment chambers 31, 51 of the second and third embodiments may, according to further variants, be used for step b) of the method according to the disclosure, thus to realize the attachment step as illustrated in FIG. 1c. Furthermore it may, according to additional variants, also comprise heating means and/or a vacuum pump to be able to carry out the heat treatments and/or carry out the process steps under vacuum.

[0054] Features of any one of the first to third embodiments can be combined individually or in groups with any one of the other embodiments to form further variants of the method and/or splitting chamber according to the disclosure.