Thinning process

Abstract

Thinning Process This description relates to a process for thinning a first layer (10) into a piezoelectric material comprising: a. ion implantation in the first layer (10) so as to amorphize an upper portion (10a) of the first layer (10), and b. removal of the upper portion (10a) by a mechanochemical polishing step. Figure for the abstract: Fig. 1C

Description

Title of the invention: Thinning process technical field

[0001] This description relates generally to electronic devices and their manufacturing processes. More specifically, this description relates to electronic devices comprising piezoelectric layers and their manufacturing processes. Previous technique

[0002] There are known methods for manufacturing a device comprising a thin layer of a piezoelectric material on a substrate. For example, document WO 2019 / 002080 describes a method called Smart Cut™ for transferring a thin film from a support onto a substrate.

[0003] The Smart Cut™ process, as well as other methods for manufacturing a device comprising a layer of piezoelectric material on a substrate, include a grinding step of the piezoelectric material layer. This grinding step results in surface defects on the piezoelectric material layer. Summary of the invention

[0004] One embodiment provides a process for thinning a first layer into a piezoelectric material comprising: a. the implantation of ions in the first layer so as to amorphize an upper part of the first layer, and b. the removal of the upper part by a mechanochemical polishing step.

[0005] According to one embodiment, the first layer is made of a material among LiNbO3, LiTaO3, quartz, langasite, langatate, KNbO3, K(Ta, Nb)O3, SrTiO3 or Pb(Zr, Ti)O3.

[0006] According to one embodiment, the ions comprise hydrogen and / or helium and / or oxygen ions.

[0007] According to one embodiment, the first layer is located on a substrate.

[0008] According to one embodiment, the first layer is obtained by a step of grinding.

[0009] According to one embodiment, the process includes an annealing step between steps a. and b.

[0010] According to one embodiment, the characteristics of step a. are such that the rate of removal of the upper part of the first layer by polishing is at least 10% faster than the rate of removal of a lower part not having received ions from the first layer by polishing.

[0011] According to one embodiment, the lower part has a thickness of less than 10 pm.

[0012] According to one embodiment, the lower part has a thickness of less than 1 pm.

[0013] According to one embodiment, the process comprises several distinct steps ion implantation.

[0014] Another embodiment provides for a method of manufacturing a surface acoustic wave filter comprising: the formation of a first layer of a piezoelectric material on a substrate; the thinning of the first layer by a process as described above; the formation of electrodes having interdigitated comb shapes on the first layer.

[0015] Another embodiment provides for a method of manufacturing a volume acoustic wave filter comprising: the formation of a second layer on a substrate; the formation of a first conductive or semiconductive region in the second layer; the formation of a first layer on the second layer; the thinning of the first layer by a process as described above; the formation of a cavity through the first layer so as to reach the first conductive or semiconductive region; the formation of a second conductive region on the first layer.

[0016] According to one embodiment, the second layer is a Bragg mirror.

[0017] According to one embodiment, the process comprises the formation of a cavity comprising a gaseous element between a part of the first region and the second layer.

[0018] According to one embodiment, the filter is adapted to radio frequencies. Brief description of the drawings

[0019] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0020] [Fig.1A] represents a step in a thinning process;

[0021] [Fig.1B] represents another step in the process of [Fig.1A];

[0022] [Fig.1C] represents another step in the process of [Fig.1A];

[0023] [Fig.2] represents a step in another thinning process;

[0024] [Fig.3] represents a filter comprising a piezoelectric layer;

[0025] Figure 4 represents a filter comprising a piezoelectric layer; and

[0026] [Fig.5] represents a filter comprising a piezoelectric layer. Description of the implementation methods

[0027] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0028] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been represented and are detailed.

[0029] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0030] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0031] Unless otherwise specified, the expressions "approximately", "roughly", and "in the order of" mean within 10%, preferably within 5%.

[0032] A piezoelectric material is defined as a material having the property of becoming electrically polarized under the action of mechanical stress and, conversely, of deforming when an electric field is applied to it. One category of piezoelectric material corresponds to ferroelectric materials, that is, materials possessing an electrical polarization in their natural state, a polarization that can be reversed by the application of an external electric field. Another category of piezoelectric material corresponds to pyroelectric materials, that is, materials in which a change in electrical polarization can be generated by a change in the material's temperature.

[0033] Figures IA, IB, and IC represent steps, preferably successive, of a process for thinning a layer of a piezoelectric material. The process shown in Figures IA, IB, and IC makes it possible, for example, to obtain a so-called thin layer of a piezoelectric material. The desired thin layer is preferably planar, that is, having opposite, parallel, and planar upper and lower faces.

[0034] Fig. 1A represents a step in a thinning process.

[0035] During this step, a layer 10 of a piezoelectric material is fixed onto a support 12.

[0036] The support 12 is, for example, a semiconductor substrate, for example made of silicon (Si), silicon carbide (SiC), or diamond. For example, the support 12 corresponds to the manipulator substrate, also called the handle substrate, or base, of the thinning process.

[0037] Alternatively, the support 12 may comprise several materials, for example, several layers of different materials. The support 12 corresponds, for example, to the substrate of a chip on which a filter can be formed.

[0038] Layer 10 is made of a piezoelectric material, preferably a single-crystal piezoelectric material. Layer 10 is, for example, made of a ferroelectric material or a pyroelectric material. For example, layer 10 is made of LiNbO3, LiTaO3, quartz, langasite, langatate, KNbO3, K(Ta,Nb)O3, SrTiO3, or Pb(Zr,Ti)O3.

[0039] Layer 10 corresponds, for example, to a solid block of piezoelectric material. Layer 10 is obtained, for example, from an ingot of piezoelectric material that has been cut and thinned to obtain said solid block.

[0040] The layer 10 is fixed to the support 12. The layer is fixed, for example, by molecular adhesion. The layer 10 is fixed, for example, to the support 12 by a fixing layer 14, or bonding layer 14. The layer 14 is, for example, made of a dielectric material, for example, silicon oxide (SiO2), silicon nitride (SiN), Al2O3 or HfO2, a polymer or a metal, for example, gold, tungsten, platinum or titanium.

[0041] In other words, the support 12 comprises an upper face, that is to say the face closest to the layer 10, covered by the fixing layer 14, more precisely by a lower face of the fixing layer 14. The fixing layer 14 is covered by the layer 10. More precisely, the upper face of the fixing layer 14 is covered by a lower face of the layer 10.

[0042] The thickness of the support 12 is for example between 50 pm and 2000 mm, for example substantially equal to 100 pm, 150 pm or 200 pm.

[0043] The thickness of layer 10 is greater than the desired thickness after the application of the thinning process. Layer 10 has, for example, a thickness between 5 and 2000 pm.

[0044] Fig.1B represents another step in the process of Fig.1A.

[0045] The step in [Fig. 1B] corresponds to a first thinning step. This thinning step removes, for example, a significant portion of the thickness of layer 10, for example, at least half of layer 10. It is preferably a grinding step.

[0046] The step in [Fig. 1B], i.e., the grinding step, results in the formation of defects on the upper surface of layer 10, i.e., on the ground surface. These surface defects correspond, for example, to a lack of uniformity in the thickness of layer 10, such as cracks in layer 10. Thus, some areas of layer 10 after grinding contain unwanted cavities on the upper surface. Furthermore, the grinding step may have caused degradation of the electrical characteristics of layer 10 on the upper surface.

[0047] The thickness of layer 10 after the grinding step is greater than the desired thickness after the application of the thinning process. More precisely, the grinding step is such that the thickness of layer 10 after grinding is greater than the sum of the desired thickness after the application of the thinning process and the maximum thickness of the defects generated by the grinding. For example, the thickness of layer 10 after the step in [Fig. 1B] is between 15 µm and 50 µm.

[0048] Fig.1C represents another step in the process of Fig.1A.

[0049] During this step, an upper part 10a is formed in layer 10. The Part 10a extends from the upper face of layer 10. Part 10a extends towards the lower face of layer 10. Part 10a corresponds to the entire upper part of layer 10.

[0050] The layer 10 further has a lower part 10b. The part 10b corresponds to the entire portion of the layer 10 extending between the part 10a and the support 12. Thus, the layer 10 corresponds to a stacking of the part 10b and the part 10a.

[0051] Part 10b has a thickness greater than or equal to, preferably substantially equal to, the desired height of layer 10 after the thinning process. Part 10a has a thickness greater than or equal to, preferably greater than, the maximum height of the surface defects generated by grinding.

[0052] Part 10a is obtained by introducing at least one so-called light species into layer 10. The introduction of said light species corresponds, for example, to implantation, that is, ion bombardment of the upper surface of layer 10 by light ions, for example, hydrogen and / or helium and / or oxygen ions, and possibly by heavier ions, for example, argon or carbon. For example, part 10a is obtained by cointegration, that is, the integration of several ions. Part 10a thus corresponds to a so-called amorphized, or damaged, part of layer 10.

[0053] The nature and dose of the implanted species and the implantation energy are chosen according to the thickness of the defects and the desired thickness of the thinning. It is thus possible to form a layer, corresponding to part 10b, having, depending on the application, a thickness greater than 10 pm, a thickness between 1 pm and 10 pm, or a thickness less than 1 pm.

[0054] The ion implantation process, which is very homogeneous on the scale of a plate, ensures that part 10a has a flat lower face, preferably parallel to the lower face of layer 10, preferably parallel to the upper face of layer 10.

[0055] The step in [Fig. IC] includes, for example, an annealing step of the structure.

[0056] The thinning process comprises, after the step in [Fig. 1C], a step Chemical mechanical polishing (CMP). The step The polishing process allows the removal of part 10a. The layer formed by the thinning process thus corresponds to part 10b.

[0057] The degradation of part 10a of the piezoelectric material layer 10 results in a change in the etching rate, or removal rate, of the piezoelectric material in part 10b. Thus, the material in part 10a is etched faster, for example at least 10% faster than the material in part 10a. For example, in the case of a LiNbO3 layer 10, part 10a is etched 30% faster than part 10b.

[0058] It is thus possible to remove part 10a without engraving or damaging part 10b. The difference in engraving speed ensures that height variations in part 10a caused by surface defects do not affect the upper surface of part 10b. Part 10b therefore has a flat upper surface, free of surface defects caused by grinding.

[0059] As an alternative, the process of figures IA to IC can be used to reduce non-uniformity after polishing and before a local abrasion step ("trimming").

[0060] As an alternative, layers 10 and 14 can be replaced by a layer of piezoelectric material obtained by physical deposition (Physical Vapor Deposition) or chemical deposition (Chemical Vapor Deposition).

[0061] Figure 2 represents a step in another thinning process. More specifically, Figure 2 illustrates a variant of the manufacturing process for figures IA to IC. The variant in Figure 2 is, for example, particularly suitable for forming a thin layer, for example, less than 10 pm. Figure 2 more specifically illustrates a variant of the step in Figure 1C.

[0062] The process illustrated by [Fig.2] includes, like the process of figures IA to IC, the steps of figures IA and IB.

[0063] The step in [Fig. 2] differs from the step in [Fig. 1C] in that the layer 10 undergoes several ion implantations before the polishing step, each implantation being represented by a dashed line in [Fig. 2]. More precisely, the dashed lines indicate the lower level of the portion receiving the ions for each implantation. Each implantation is, for example, followed by annealing. Each implantation is carried out at a different depth.

[0064] At least some of the different implantations are for example carried out with different ions, and / or different energy levels.

[0065] Figure 3 represents a filter 15 comprising a piezoelectric layer 10b. More specifically, Figure 3 represents a surface acoustic wave (SAW) filter 15.

[0066] The filter 15 comprises the layers 12 and 14 described above and a layer 10b obtained by one of the embodiments described above.

[0067] The manufacturing process, and in particular the characteristics of the ion implantation, is for example configured so that the layer 10b has a thickness between 15 pm and 50 pm.

[0068] The filter 15 further comprises electrodes 16 located on the upper face of the layer 10b. The electrodes 16 have interdigitated comb shapes, such that the acoustic waves propagate on the surface of the piezoelectric material of the layer 10b.

[0069] Figure 4 represents another filter 17 comprising a piezoelectric layer 10b. More specifically, Figure 4 represents a bulk acoustic wave (BAW) filter 17. The filter 17 is, for example, of the self-suspended film bulk acoustic resonator (FBAR) type, in which acoustic insulation is provided by an air cavity 22. For example, the filter 17 is suitable for radio frequency waves.

[0070] The filter 17 comprises the layers 12 and 14 described above and a layer 10b obtained by one of the embodiments described above.

[0071] The filter 17 further comprises a layer 18 situated between the fixing layer 14 and the layer 10b. The layer 18 is, for example, a layer made of an insulating material. The layer 18 is, for example, made of silicon oxide.

[0072] The filter 17 further includes a conductive or semiconducting region 20 and a cavity 22 in the layer 18, i.e. between the layer 14 and the layer 10b.

[0073] Region 20 constitutes a lower electrode of the filter. Layer 20 is, for example, made of metal. Layer 20 is preferably flush with the upper face of layer 18. Thus, the upper face of region 20 is preferably coplanar with the upper face of layer 18. Preferably, region 20 rests partially on layer 18. Thus, a portion of the lower face of region 20 is in contact with layer 18.

[0074] The cavity 22 is, for example, filled with a gaseous element, for example, air. The cavity 22 extends under a portion of the region 20. Thus, a portion of the lower face of the region 22 forms part of the walls of the cavity 22. The cavity 22 extends, for example, to the upper face of the layer 18, for example, to a lateral wall of the region 20. The cavity 22 thus reaches the lower face of the layer 10b. The cavity is delimited by the layer 18, the region 20, and the layer 10b. The cavity 22 is thus, for example, closed.

[0075] Region 20 and cavity 22 are, for example, formed before the formation of layer 10b. Alternatively, cavity 22 is filled with sacrificial material until the end of the formation of layer 10b. A release hole, not shown, passing through layer 10b at the level of layer 22 is then formed, so as to remove the sacrificial material through said release hole.

[0076] The filter 17 further includes a cavity 24 passing through the layer 10b so as to reach the region 20.

[0077] The filter 17 further comprises a conductive or semiconducting region 26 resting on the layer 10b, preferably opposite at least a part of the region 20. The region 26 constitutes an upper electrode of the filter 17.

[0078] Figure 5 represents a filter 30 comprising a piezoelectric layer 10b. More precisely, Figure 5 represents a bulk acoustic wave (BAW) filter 30. The filter 30 is, for example, of the solidly mounted resonator (SMR) type. For example, the filter 30 is suitable for radio frequency waves.

[0079] The filter 30 comprises the layers 12 and 14 described above and a layer 10b obtained by one of the embodiments described above.

[0080] The filter 30 further comprises the layer 18 located between the fixing layer 14 and the layer 10b. The layer 18 is, for example, a layer made of an insulating material. The layer 18 is, for example, made of silicon oxide.

[0081] The filter 30 further includes the conductive or semiconducting region 20 in the layer 18, that is to say between the layer 14 and the layer 10b.

[0082] Region 20 constitutes, as before, a lower electrode of the filter. Layer 20 is, for example, made of metal. Layer 20 is preferably flush with the upper face of layer 18. Thus, the upper face of region 20 is preferably coplanar with the upper face of layer 18.

[0083] The filter 30 differs from the filter 17, among other things, in that the filter 30 does not include the cavity 22. Thus, the region 20 rests entirely on the layer 18. In other words, the lower face, and preferably the lateral walls, of the region 20 are entirely in contact with the layer 18.

[0084] Region 20 is formed, for example, before the formation of layer 10b. The filter 30 further includes the cavity 24, or release hole 24, passing through layer 10b so as to reach region 20, allowing access to the lower electrode 20.

[0085] The filter 30 further comprises the conductive region 26 resting on the layer 10b, preferably opposite at least a part of the region 20. The region 26 constitutes an electrode of the filter 30. The layer 18 constitutes the Bragg mirror, i.e. an alternation of thin layers of materials having a low acoustic impedance, for example SiO2, SiOC, SiON, and thin layers of materials having a high acoustic impedance, for example AIN, W, TaN, Ta2O5, WO2, WN, HfO2, or HfN, allowing the resonator to be acoustically isolated from the substrate.

[0086] An advantage of the embodiments described above is that they allow the formation of thin layers of piezoelectric material without surface defects.

[0087] Various embodiments and variations have been described. A person skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will become apparent to a person skilled in the art.

[0088] Finally, the practical implementation of the described embodiments and variants is within the reach of a person skilled in the art, based on the functional indications given above.

Claims

Demands

1. A method for thinning a first layer (10) into a piezoelectric material comprising: a. at least two ion implantations in the first layer (10) so as to amorphize an upper portion (10a) of the first layer (10), the upper portion extending from an upper face of the first layer, the implantations being made at different depths, and b. the removal of the upper portion (10a) by a mechanochemical polishing step.

2. Method according to claim 1, wherein the first layer (10) is in a material among LiNbO3, LiTaO3, quartz, langasite, langatate, KNbO3, K(Ta, Nb)O3, SrTiO3 or Pb(Zr, Ti)O3.

3. A method according to claim 1 or 2, wherein the ions comprise hydrogen and / or helium and / or oxygen ions.

4. A method according to any one of claims 1 to 3, wherein the first layer (10) is located on a substrate (12).

5. A method according to any one of claims 1 to 4, wherein the first layer (10) is obtained by a grinding step.

6. A method according to any one of claims 1 to 5, wherein the method comprises an annealing step between steps a. and b.

7. A method according to any one of claims 1 to 6, wherein the characteristics of step a. are such that the rate of removal of the upper part (10a) of the first layer by polishing is at least 10% faster than the rate of removal of a lower part (10b) not having received ions from the first layer by polishing.

8. Method according to claim 7, wherein the lower part (10b) has a thickness of less than 10 pm.

9. Method according to claim 7 or 8, wherein the lower part (10b) has a thickness of less than 1 pm.

10. A method according to any one of claims 1 to 9, wherein the method comprises several distinct ion implantation steps.

11. Method of manufacturing a surface acoustic wave filter comprising: the formation of a first layer of a piezoelectric material on a substrate;

12.

13.

14.

15. the thinning of the first layer by a process according to any one of claims 1 to 10; the formation of electrodes (16) having interdigitated comb shapes on the first layer. Method for manufacturing a volume acoustic wave filter comprising: the formation of a second layer (18) on a substrate; the formation of a first conductive (20) or semiconductive region in the second layer; the formation of a first layer on the second layer; the thinning of the first layer by a process according to any one of claims 1 to 10; the formation of a cavity (24) passing through the first layer in order to reach the first conductive or semiconducting region; the formation of a second conductive region (26) on the first layer (10b). Method according to claim 12, wherein the second layer (18) is a Bragg mirror. A method according to claim 13, wherein the method comprises the formation of a cavity (22) comprising a gaseous element between a portion of the first region and the second layer. A method according to any one of claims 11 to 14, wherein the filter is adapted to radio frequencies.

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