Method for preparing residues from a donor substrate after layers have been removed by delamination.

Abstract

The invention relates to a method for preparing a residue (1') of a donor substrate, the residue (1') comprising a peripheral ring on a peripheral zone (13) of its main surface (10). The method comprises a first step of removing at least a part of the peripheral ring, a second step of treating the main surface (10) of the residue (1') with the aim of removing a surface layer, and, after the second step, a third step of grinding the peripheral zone (13) of the main surface (10) of the residue (1'), with the aim of reducing the height of the peripheral zone (13).

Description

Technical Field

[0001] The present invention relates to a method for preparing a residue of a donor substrate.

Background Art

[0002] U.S. Patent Application Publication No. 2020 / 0186117 describes a method for preparing a thin layer, including pre-forming a composite donor substrate formed by a thick layer of material on an intermediate support, removing a thin layer from the thick layer of the donor substrate, and transferring this thin layer to a final support. The removal step and the transfer step are carried out by Smart Cut (trademark) technology.

[0003] This preparation method is particularly suitable when the material forming the thin layer has a thermal expansion coefficient completely different from that of the material forming the final support.

[0004] The step of removing and transferring the thin layer includes introducing a light species into the donor substrate, in this case the thick layer of the composite donor substrate, through the surface (or surface) called the "main surface" of this substrate to form an embedded weak plane. The layer to be transferred is defined between this embedded weak plane and the main surface of the donor substrate. In a subsequent step, the donor substrate is assembled on the final support through its main surface, heat treatment is applied to this assembly, and optionally mechanical force is additionally applied to separate the thin layer at the weak plane and transfer this thin layer to the final support.

[0005] The residue from the donor substrate, i.e., the remaining portion of the substrate after the thin layer has been removed, can be reconditioned for use in another removal-reconditioning cycle. Such methods for reconditioning the residue obtained upon completion of the SmartCut™ method are known, for example, from European Patent Nos. 1427002, 1427001, U.S. Patent Publication Nos. 2009 / 0061545, 2010 / 0200854, and 2018 / 0033609. These methods generally attempt to prepare the main surface of the residue by removing peripheral steps, often called rings, corresponding to peripheral portions of the donor substrate that are not transferred to the final support, in order to remove surface defects generated by material fracturing at the brittle surface.

[0006] In the method proposed in U.S. Patent Application Publication No. 2020 / 0186117, the composite donor substrate generally tends to have a curvature that gives the substrate convex strength, because the thick layer and the intermediate support have different coefficients of thermal expansion, and the main surface of the substrate (the exposed surface of the thick layer) is slightly curved outward.

[0007] When the assembly step is performed by molecular bonding, the donor substrate is brought into contact with the final support at the apex of a protrusion located in the central part of the main surface of the substrate. A bonding wave is then initiated, which tends to bring the two opposing surfaces into contact with each other, and this wave propagates concentrically from the initial contact point toward the outer edges of the donor substrate and the final support.

[0008] In this configuration, bonding defects tend to appear at the interface between the donor substrate and the final support. These defects take the form of small bubbles located near the edges of the assembly at the propagation ends of the bonding wave. These bubbles locally hinder proper adhesion of the donor substrate to the final support, and as a result, portions of the thin layer covering or near these defects are not completely removed and transferred to the final support. Consequently, the thin layer exhibits "pore" type defects or has a very irregular contour.

[0009] The applicant has observed that the density of pores in the thin layer, or the non-uniformity of the contour of the thin layer, tends to increase with the degree of recycling of the donor substrate, i.e., the number of removal-reconditioning cycles the substrate has undergone.

[0010] Of course, this defect is undesirable, and if it exceeds a certain threshold, the hybrid substrate composed of the thin layer and the final support becomes unusable. At the same time, being able to use the same substrate a considerable number of times is economically beneficial, especially when composite donor substrates are used, as preparing them is far more expensive than readjusting the residue. [Overview of the project] [Problems that the invention aims to solve]

[0011] The object of the present invention is to enable the donor substrate to be used multiple times and to suppress the degradation of the quality of the removed and transferred thin layers despite these multiple uses, as has been observed with conventional methods. The present invention is of particular interest when the donor substrate is a hybrid substrate formed by a thick layer placed on an intermediate support. [Means for solving the problem]

[0012] To achieve this objective, the subject of the present invention proposes a method for preparing a donor substrate residue in which a layer has been removed from the donor substrate by peeling at a fragile surface formed by the introduction of a light seed, the residue including a peripheral ring on the peripheral zone of the main surface corresponding to the unremoved portion of the donor substrate.

[0013] This method, - A first step of removing at least a portion of the peripheral ring, -A second step involves treating the main surface of the residue with the aim of removing the surface layer, - A third step, following the second step, in which the peripheral zone of the main surface of the residue is ion-etched and ground, wherein the third grinding step is aimed at reducing the height of the peripheral zone. Includes.

[0014] According to other advantageous and non-limiting features of the present invention, the following can be obtained individually or in any technically feasible combination: -The second processing step is after the first removal step, -The first step is performed by grinding the peripheral ring, -The second step is carried out by chemical mechanical polishing of the main surface. - The thickness of the removed surface layer was less than 5 microns. - Ion etching involves argon ions, -The third grinding step aims to shape the peripheral zone into a predetermined profile. - The peripheral zone, upon completion of the third grinding step, has a maximum height less than or equal to the height of the average height surface of the central portion. -The residue includes a thick layer of material placed on the intermediate support. -The material of the thick layer is a ferroelectric material. - The thicker layers are assembled onto the intermediate support by a layer of adhesive material. [Brief explanation of the drawing]

[0015] Further features and advantages of the present invention will become apparent from the following detailed description of the invention with reference to the accompanying drawings. [Figure 1a] This diagram schematically shows the residues from the donor substrate. [Figure 1b] This diagram schematically shows the residues from the donor substrate. [Figure 2a] This figure shows the residue after applying the first removal step of the preparation method according to the present invention. [Figure 2b] This figure shows the residue after applying the second processing step of the preparation method according to the present invention. [Figure 2c] This figure shows the reprocessed residue after applying the preparation method according to the present invention. [Figure 3]Figure showing the steps of a method for removing and transferring a thin layer, in which the prepared residue according to the present invention can be used.

DETAILED DESCRIPTION OF THE INVENTION

[0016] Figures 1a and 1b schematically show a donor substrate, i.e., the residue 1' of a substrate from which a thin layer has been removed by peeling at a weak plane formed by the introduction of a light species, according to the steps of a method for implementing Smart Cut™ technology.

[0017] On the main surface 10 of this residue 1', there is a peripheral ring 11, which is annular in the case of the illustrated example, and the residue 1' is in the form of a circular wafer corresponding to the non-removed part of the donor substrate. More specifically, the peripheral ring 11 is accommodated in the peripheral zone 13 of the residue 1' and does not adhere sufficiently to the final support during the assembly step of the transfer method, and as a result, it cannot be removed from the donor substrate and corresponds to the part of the thin layer defined in the donor substrate. The cross-section of Figure 1a shows the weak plane 3 defining this part of the non-removed thin layer below the peripheral ring 11.

[0018] The peripheral ring 11 forms a step, and its width l can be in the range of 0.5 mm to 8 mm, and its height h can reach from 100 nm to 1.5 microns. The peripheral zone has a width l' on the main surface that is larger than the width of the ring, typically 1 to 3 times the width l of the ring, and more generally a width in the range of 0.5 mm to 2.5 cm.

[0019] The presence of this step prevents the residue 1' from being used directly to remove a new thin layer. Furthermore, the central portion 12 of the main surface 10, i.e., the surface contained within the peripheral ring 11 of the peripheral zone 13, has a particularly rough surface finish and hardened surface thickness, which also must be prepared before the residue 1' can be used again. This surface finish of the central portion 12 is the result of the thin layer removal step, which in particular corresponds to a brittle surface P generated by the light seed introduced into the donor substrate, and the thin layer is removed along this brittle surface P.

[0020] The present invention aims to make such residue 1' suitable for further use in the application of a method for removing and transferring thin layers to implement the SmartCut™ method by readjusting the residue 1'. More specifically, the present invention aims to prevent the occurrence of bonding defects in the peripheral areas of the interface formed by assembling a readjusted donor substrate (more specifically, the readjusted residue of the donor substrate) onto a final substrate, or to limit the density of such defects.

[0021] A method for preparing the residue 1' includes a first step of removing at least a portion of the peripheral ring 11. This step can be carried out by grinding. In such embodiments, the grinding wheel of the grinding machine is equipped with abrasive particles (e.g., diamond). The grinding wheel is positioned relative to a portion of the main surface 10 of the residue to be processed, in this case the peripheral ring 11, and rotates relative to the residue to gradually remove the material forming the ring 11 by mechanical grinding. This removal exposes the peripheral zone 13 of the residue 1', as seen in Figure 2a, which shows the residue after this first removal step has been applied.

[0022] The removal step may involve techniques other than preferred grinding techniques. For example, this may include polishing techniques such as double-sided chemical mechanical polishing.

[0023] Therefore, once this first removal step is complete, the peripheral ring 11 is at least partially removed, and the exposed surface 13 of the peripheral zone of the residue 1' can have substantially the same height as the central portion 12 of the residue 1'. The peripheral zone 13 is also roughened, especially if the ring has been removed by grinding.

[0024] The method for preparing the residue 1' also provides a second step of treating the main surface 10 of the residue 1', i.e., the central portion 12 and peripheral zone 13 of the residue 1', in order to remove the surface layer 4. This surface layer 4 is thick enough to include the cured thickness of the central portion 12 and is generally thick enough to provide the main surface with a surface finish smooth enough to allow assembly to the final support by molecular adhesion. This surface finish can be characterized by a roughness of less than 0.5 nm (favorably less than 0.3 nm) as the root mean square value over a measuring range of 5 microns × 5 microns. This second treatment step can be carried out by chemical mechanical polishing. Thus, the thickness of the removed surface layer 4 may be in the range of 100 nm to 5 microns.

[0025] If the first removal step is separate from the second treatment step, the second treatment step is performed after the removal step. Alternatively, these two steps can be combined using techniques that include chemical mechanical polishing of the exposed surface of the residue.

[0026] Furthermore, while these two steps are performed using chemical mechanical polishing techniques, it is also possible to perform each of these steps using separate parameters and / or consumables (especially polishing cloths).

[0027] In either case, once the second step of processing the main surface 10 of the residue is complete, a partially reconditioned residue 1' is obtained that exhibits a main surface 10 that is smooth and flat enough to be bonded to another substrate by molecular adhesion, as shown in Figure 2b.

[0028] However, upon close inspection of the residue 1' at the completion of the second processing step, it was found that the residue 1' has a "rising" edge flange, that is, the height profile of the exposed surface of the substrate is the average plane of a portion of the central part 12 of the substrate that is contained within the peripheral zone 13. F It becomes clear that it has a maximum value M greater than the height of the peripheral surface 3 that defines the edge flange. This height profile of the peripheral surface 3 that defines the edge flange can generally be seen by observing the height profile of the exposed surface established along several distinct radii, in all angular directions of these radii. Thus, the point M of the maximum height of the peripheral zone is the average plane of the remaining portion of the central portion 12 of this substrate (i.e., the portion contained inside the peripheral zone 13). F It can rise even higher, up to 500nm.

[0029] There are numerous possible causes for this "rising" edge flange. This edge flange may be related to the incomplete removal of the peripheral ring 11 during the first step of the method. However, even if the peripheral ring is completely and entirely removed during the first step, this edge flange may also be related to the edge effect that appears during the second processing step, especially if this processing step is carried out by chemical mechanical polishing.

[0030] It should be noted that this profile does not prevent the partially reconditioned residue shown in Figure 2b from being assembled to the final support by molecular adhesion during further application of the method for removing and transferring the thin layer. In particular, its surface is flat and smooth enough to carry out the steps of contact and propagation of bonding waves. However, this “rising” edge flange tends to promote the occurrence of bonding defects as described at the beginning of this application.

[0031] Furthermore, the maximum height M of the surrounding zone 13 and the average surface of the central part 12 FThe magnitude of the difference between the heights tends to increase with the degree of donor substrate recycling, i.e., the number of removal-reconditioning cycles performed on the same donor substrate.

[0032] Furthermore, in order to prevent this phenomenon and enable such donor substrates to be reused multiple times (preferably three, five, or even more than ten times), the method for preparing the residue according to the present invention provides a third step of rectifying a peripheral zone 13, following a second step of processing the main surface 10, the third step of which aims to reduce the height of the peripheral zone.

[0033] This third step differs from the first and third steps (more generally, these three steps are distinct from one another), namely, these steps do not use the same techniques and the same equipment to apply to residue 1'.

[0034] Advantageously, upon completion of the third step, the peripheral zone 13 is equal to the average surface of the central portion 12. F It has a maximum height M' which is less than or equal to the height of the central portion 12. Experiments conducted tend to show that such edge flanges with a “dropping” profile can effectively reduce joint defects. Figure 2c shows the residue 1' after the three steps described above have been applied, with the peripheral zone 13 being the average plane of the central portion 12. F This shows an advantageous configuration of the grinding step where the maximum height M' is less than or equal to the height of [the specified value].

[0035] Simply reducing the maximum height M' of the surrounding zone relative to the height at the completion of the second step, even if that height is the average plane F It should be noted that even if the height remains higher than the specified height, it may be sufficient to suppress the increase in the occurrence of joint defects as recycling progresses. Therefore, in most cases, this third grinding step attempts to shape the peripheral zone into a predetermined profile.

[0036] To enable the peripheral zone 13 to be corrected with the required precision, this step is advantageously carried out by non-mechanical action (more specifically, without any abrasive contact with external tools), for example, by chemical etching, or preferably by ion beam trimming or ion etching.

[0037] According to this method, ions or clusters of ions are projected with sufficient energy onto the surrounding zone 13 of the residue 1', depending on the properties of the constituent material of the residue 1', and gradually erode the surface thickness of this zone (at the atomic level). The ions are preferably heavy ions such as argon, neon, or krypton ions.

[0038] Therefore, the ion beam is directed towards the peripheral zone 13, gradually and very precisely shaping this zone into a determined profile. The ion beam can also be projected onto only a portion of the peripheral zone 13, and by moving the beam relative to the residue, the entire zone can be treated gradually, with the time the beam passes through a portion of the zone determining the amount of material removed. Of course, it is also possible to pass the beam through multiple times.

[0039] To avoid degrading the characteristics of the central zone 12 during the application of the third grinding step, a resin mask, for example, can be placed outside the peripheral zone 13.

[0040] To record the height profiles of the peripheral zone 13 and the central zone 12, one or more steps may be provided before, during, and / or after the third grinding step to inspect the residue 1'. In this way, the parameters of the ion etching (or more generally, the third grinding step) can be adjusted to effectively control and reproduce the determined height profile on the residue 1'.

[0041] The substrate shown in Figure 2c, obtained upon completion of the third grinding step, forms a reconditioned residue 1' according to the present invention, which can therefore be used as a donor substrate 1 in further applications of the method for removing and transferring thin layers.

[0042] Application examples This particular example is generally intended to form a hybrid substrate 9, which is created by a thin ferromagnetic layer 3 transferred onto a silicon final support 7. This is shown in Figure 3.

[0043] First, a composite donor substrate 1 (step 3A in Figure 3) is produced, which is formed by a silicon intermediate support 1b in the form of a circular wafer with a diameter of 150 mm and a thick layer 1a of a ferroelectric material which may have a thickness in the range of 5 to 400 microns. The ferroelectric material forming the thick layer 1a is monodomain and is formed of, for example, LiTaO3, LiNbO3, LiAlO3, BaTiO3, PbZrTiO3, KNbO3, BaZrO3, CaTiO3, PbTiO3, or KTaO3. The crystal orientation of this material is selected depending on the intended application. For example, if the properties of the transferred thin layer 3 are intended to be used to form a SAW filter, an orientation in the range of 30° to 60°RY or 40° to 50°RY is usually selected. However, the present invention is by no means limited to a specific crystal orientation.

[0044] In this example, the thick layer 1a is circular in shape and substantially the same size as the intermediate support, so the donor substrate 1 also has a circular shape with a diameter of 150 mm. The specific manufacturing of this donor substrate 1 can be carried out according to the teachings provided in U.S. Patent Application Publication No. 2020 / 0186117, which is cited at the beginning of this application.

[0045] Therefore, according to the first method, the thick layer 1a is assembled onto a silicon wafer forming an intermediate support 1b by molecular adhesion. Alternatively, a layer (e.g., silicon oxide or silicon nitride) that facilitates this adhesion can be inserted between the silicon wafer 1b and the thick layer 1a.

[0046] In another method, a thick ferromagnetic layer 1a is held on the silicon wafer 1b by a layer of adhesive material such as polymer.

[0047] As proposed in the third step of grinding off the residue 1', the height profile of the free surface of the thick ferromagnetic layer can be ground to provide the donor substrate with a predetermined profile, such as the "falling" edge flange described above. In this way, bonding quality is ensured during the first iteration of the layer removal method.

[0048] Regardless of the method chosen for assembling a thick ferromagnetic layer onto a silicon wafer, the composite donor substrate 1 is used as a donor substrate for a method of implementing SmartCut™ technology. For this purpose, a certain dose of light seeds is introduced on the main surface side of the composite substrate 1 (the exposed surface of the thick ferromagnetic layer 1a), resulting in the formation of an embedded vulnerable surface 2 in the thick layer 1a. This surface, along with the main surface of the donor substrate, defines the thin ferromagnetic layer 3 to be removed. The properties of the injected seeds, the dose, and the injection energy are selected according to the thickness of the thin layer to be transferred and the physicochemical properties of the thick layer 1a of the donor substrate 1. For a thick layer made of LiTaO3, the energy range is 30-250 keV with an injection rate of 1E16-5E17 at / cm². 2 By injecting hydrogen in doses within this range, a thin layer 3 of approximately 200-1,500 nm can be defined.

[0049] In step 3C of the removal method, the main surface of the thick layer 1a is assembled by molecular adhesion to the exposed surface of a 150 mm diameter silicon wafer, and this silicon wafer is similar to the wafer that forms the intermediate support of the donor substrate 1. This wafer forms the final support 7 of the thin layer 3. As already stated at the beginning of this application, the donor substrate 1 can have a convex shape, and the apex of the outward-facing convex surface is located on the side of the thick ferromagnetic layer. The deflection of this convex surface can be about 200 microns, taking a 150 mm wafer as an example. As a result, the donor substrate can have an apex that is substantially located in the center of the substrate.

[0050] During the assembly step, the vertex of the donor substrate 1 is brought into contact with the final support 7. Then, a force is applied to the edge of one of the substrates to bring them closer together, thereby initiating bonding. This application of force causes bonding waves to propagate substantially concentrically from the vertex of the donor substrate 1 in contact with the final substrate toward the periphery of that substrate. These waves deform the two substrates 1 and 7 so that their surfaces are in close contact with each other.

[0051] In the subsequent step 3D, the assembly formed by the donor substrate and the final support 7 is subjected to thermal and / or mechanical processing, the donor substrate is fractured at the fragile surface 2, the thin layer 1 is peeled off and removed, and transferred to the final support 7.

[0052] Thus, on the one hand, a first hybrid substrate 9 is obtained, formed from the thin ferromagnetic layer 3 removed from the thick layer 1a and the silicon wafer forming the final support 7. On the other hand, a residue 1' matching that of Figure 1 is also obtained.

[0053] This residue 1' is prepared according to the steps described in the general description above. In this particular example, the peripheral ring 11 is first removed by grinding during the first removal step so that the height of the peripheral zone 13 containing this ring 11 becomes the height of the average surface of the central portion 12. Next, the entire main surface 10 of the residue, i.e., the central portion 12 and the peripheral zone 13, is treated by chemical mechanical polishing to remove up to 1 micron from the surface layer, reducing the surface roughness to less than 0.3 nm as the root mean square value. Finally, a third grinding step is applied to the peripheral zone, in this case the peripheral portion 1 cm from the edge of the wafer, by projecting an argon ion beam to reduce the height of this peripheral portion.

[0054] Once these steps are complete, the residue 1' is completely readjusted. In addition to a surface roughness suitable for the molecular bonding assembly steps, the residue has a "downward" edge flange, i.e., the maximum height in the peripheral zone 13 is within or below the average height plane of the central portion 12.

[0055] In subsequent cycles using this reconditioned substrate, the aforementioned removal-reconditioned cycle is applied again to provide multiple hybrid substrates 9, each containing a thin ferromagnetic layer 3 placed on a silicon wafer 7. The number of cycles is limited by the remaining thickness of the thick layer 1a of the composite donor substrate 1, and if the thick layer 1a is initially sufficiently thick, for example, approximately 400 microns, then 10 cycles can be reached, and even more.

[0056] It can be seen that the defect level of the sequentially obtained hybrid substrates 9 (particularly due to adhesive defects at the edges of the substrate) does not necessarily increase with the number of cycles, i.e., with the degree of recycling of the composite donor substrate.

[0057] Of course, the present invention is not limited to the embodiments and examples described, and alternative embodiments can be used without departing from the scope of the invention as defined by the claims.

[0058] Therefore, the present invention is applicable to any type of donor substrate in which a layer has been removed by delamination at a fragile surface formed by the introduction of a light seed. This donor substrate does not need to be a "composite" type formed by a thick layer placed on an intermediate substrate.

[0059] This donor substrate can also exhibit any properties suitable for this type of layer removal. In particular, this donor substrate can be made of any semiconductor material, such as silicon, silicon carbide, germanium, etc.

[0060] In general, the substrate can take any suitable form, and the present invention is by no means limited to a circular wafer, as has been used as an example.

Claims

1. A method for preparing a residue (1') of a donor substrate (1), wherein a thin layer (3) is removed from the donor substrate (1) by peeling off a fragile surface (2) formed by the introduction of a light seed, and the residue (1') includes a peripheral ring (11) on the peripheral zone (13) of the main surface (10) corresponding to the unremoved portion of the donor substrate (1), and the method is A first step of removing at least a portion of the peripheral ring (11), A second step involves treating the main surface (10) of the residue (1') with the aim of removing the surface layer (4), A third step, following the second step, involves ion etching grinding the peripheral zone (13) of the main surface (10) of the residue (1'), the purpose of which is to reduce the height of the peripheral zone (13), Methods that include...

2. The method according to claim 1, wherein the second step is after the first step.

3. The method according to claim 1 or 2, wherein the first step is performed by grinding the peripheral ring (11).

4. The method according to any one of claims 1 to 3, wherein the second step is carried out by chemical mechanical polishing of the main surface (10).

5. The method according to any one of claims 1 to 4, wherein the thickness of the removed surface layer (4) is less than 5 microns.

6. The method according to any one of claims 1 to 5, wherein the ion etching grinding is performed using argon ions.

7. The method according to any one of claims 1 to 6, wherein the third step is to shape the peripheral zone (13) into a predetermined profile.

8. The method according to any one of claims 1 to 7, wherein the peripheral zone (13) has a maximum height (M') that is less than or equal to the height of the average height plane (F) of the central portion (12) of the main surface (10) upon completion of the third step.

9. The method according to any one of claims 1 to 8, wherein the residue (1') includes a thick layer (1a) of material disposed on the intermediate support (1b).

10. The method according to claim 9, wherein the material of the thick layer (1a) is a ferroelectric material.

11. The method according to claim 9 or 10, wherein the thick layer (1a) is assembled onto the intermediate support by a layer of adhesive material.

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