Method for manufacturing silicon timepiece components on an soi wafer

Abstract

A method for manufacturing a plurality of timepiece components (90) in an SOI-type manufacturing wafer (10) is disclosed. The SOI wafer (10) comprises a support layer (20), a working layer (30), and a buried layer (40). The method comprises the steps of: (a) structuring the support layer (20) by removing part of said support layer (20); (b) forming the timepiece components (90) in the working layer (30), the structured support layer (20') acting as support during this formation; (c) releasing the timepiece components (90) formed in step (b) by removing at least those parts of the buried layer (40) which are beneath the timepiece components (90); and (d) performing at least one subsequent manufacturing step on the released timepiece components (90).

Description

Process for manufacturing silicon watch components on an SOI wafer Technical field

[0001] The invention relates to a method for manufacturing silicon watch components on a silicon-on-insulator (SOI) wafer, such a wafer comprising a silicon support layer, a silicon working layer in which the components are manufactured, and a silicon oxide layer separating these two layers. Such a manufacturing method generally comprises microfabrication steps including lithography and dry or wet etching of the layers of the wafer. State of the art

[0002] The manufacture of silicon watch components such as balance springs, wheels and anchors using microfabrication processes is well known. Advantageously, several hundred watch components can be manufactured on a single wafer using these technologies. It is, for example, known to produce a plurality of silicon resonators with very high precision using photolithography and etching machining processes in a silicon wafer. The methods for producing these mechanical resonators generally use monocrystalline silicon wafers, but polycrystalline or amorphous silicon wafers can also be used.

[0003] Silicon is a diamagnetic material, and its use in the manufacture of watch components, and in particular for the components of the regulating organ of a mechanical watch movement, is advantageous because no residual effect is observed after exposure of this material to magnetic fields. When watch components are made from a monocrystalline silicon wafer, any one of the three crystal orientations <100> , <110> Or <111> can be used.

[0004] Silicon wafers are available in single wafer form, for example SSP (Single Side Polished) or DSP wafers. ("Dual Side Polished"). However, SOI (silicon-on-insulator) wafers are most often used for the manufacture of watch components. An SOI wafer comprises a silicon working layer (the "device" layer) in which the watch components are manufactured, a silicon support layer that serves as a substrate or support during the manufacture of the components (the "handle" layer), and a buried silicon oxide (SiO2) layer that lies between the two silicon layers (the "buried oxide layer" or BOX layer). The surface of the working layer and possibly the surface of the support layer can also be polished to facilitate lithography steps on these layers.

[0005] After the lithography and etching steps to initially form the watch components in the working layer, the latter are normally released from the support layer and the buried oxide layer of the SOI wafer to facilitate subsequent manufacturing steps. In this way, after release, the watch components are structurally supported only by thin bridges that keep them attached to the remaining parts of the working layer, which notably allows subsequent manufacturing steps to be carried out on almost the entire external surface of the components on the wafer.Subsequent steps may include oxidation and deoxidation steps, either for smoothing the surfaces of the components or for adjusting the dimensions of the components (e.g. to correct stiffness when the components are hairsprings or resonators) and / or oxidation steps to form an outer layer of silicon oxide on the components for the purpose of thermal compensation and / or mechanical strengthening. After these subsequent steps, the watch components may be detached from the wafer and mounted in, for example, the movement of a timepiece.

[0006] The release of watch components on an SOI wafer can be achieved by different methods. In an example illustrated by document W02021053501, before release, the components are first protected by an oxide layer, for example silicon oxide, deposited by a CVD (chemical vapor deposition), ALD (atomic layer deposition) or PVD (physical vapor deposition) type deposition or formed by an oxidation step. Subsequently, the components are released, or even separated and disengaged, of the support layer first by opening the oxide layer by plasma etching or by using selective etching based on hydrofluoric acid (also called hydrofluoric acid or HF) which can be anhydrous or in aqueous solution, and subsequently by exposing the entire wafer to a potassium hydroxide (KOH) bath to carry out anisotropic etching of the silicon below the protected components and over a certain thickness of the support layer. In this way, pockets are formed below the components to create space to better manage and facilitate subsequent manufacturing steps on the components.

[0007] An alternative to the above release approach is described in patent documents JP2017219520 and W02019180177. In this case too, after forming the components by etching, a silicon oxide layer is grown on the surface of the silicon. This oxide layer serves as protection for the formed components and if formed by thermal oxidation it also forms on the support layer. Subsequently, photolithography and etching are performed to expose the silicon of the support layer and the support layer is etched by etching it from the side opposite the components, which removes the support layer below the components. To complete the release according to this alternative, the buried layer of the SOI wafer below the components and the protective layer on the components are removed.

[0008] According to yet another release alternative described in WO2019180596, after the formation of the components, the working layer (or a part of this layer including the components) is separated from the support layer. This separation can be implemented by etching a kerf surrounding the components as well as openings in the working layer. Subsequently, the buried oxide layer is etched with hydrofluoric acid (HF) vapor passing through the openings in the working layer, and the part of the working layer defined by the kerf is separated from the support layer of the SOI wafer. In this latter release approach, since the working layer is much thinner and more fragile than the support layer, performing subsequent fabrication steps is more delicate and risky because they are performed without the benefit of the support layer, even for the case where it is partially removed.

[0009] With all the previous release steps described above, there is a risk of unexpectedly damaging or altering the watch components already formed in the working layer before release. This is the case despite the use of a layer deposited around the formed components in order to protect them. In addition, such a protective layer also involves additional steps for its formation and removal, which makes release more time-consuming and complex. Brief summary of the invention

[0010] An aim of the present invention is to propose a method for manufacturing a plurality of mechanical resonators on an SOI wafer, which makes it possible to avoid or overcome the above drawbacks, or in any case to offer a better compromise between these drawbacks.

[0011] In particular, this aim is at least partially achieved by proposing a novel manufacturing method according to which a portion of the support layer of the SOI wafer required for release is removed before the formation of the watch components in the working layer. Thus, according to one aspect, the present invention relates to a method for manufacturing a plurality of watch components in an SOI-type manufacturing wafer, the SOI wafer comprising a silicon support layer, a silicon working layer, and a buried silicon oxide layer separating the two silicon layers, i.e. the buried layer separates the silicon support layer from the silicon working layer.The method comprises the steps of: (a) structuring the support layer by removing a portion of said layer to obtain a modified SOI wafer comprising a structured support layer, the structured support layer comprising structures which are intact at locations on the wafer where the material of the support layer has not been removed, said structures defining between them regions in which the material of the support layer has been removed to expose the oxide layer buried in these regions; (b) forming the components in the working layer of the modified SOI wafer, the structured support layer acting as a support during this formation, the components being located in areas of the working layer which are aligned at least in part with removed regions of the structured support layer; (c) releasing the. components formed in step (b) by removing at least those parts of the buried oxide layer which are located below the watch components; and (d) carrying out at least one subsequent manufacturing step on the released components.

[0012] Advantageously, step (c) of releasing the components can be performed without re-structuring the structured support layer, and the at least one subsequent manufacturing step of step (d) can be performed while the released components are still attached to the resulting SOI wafer of step (b). Other advantageous and preferred features of the manufacturing method are specified in the description and subclaims below. Brief description of the figures

[0013] Examples of implementation of the invention are given in the description illustrated by the accompanying figures, in which: Figures 1a-11 schematically illustrate a first series of manufacturing steps on a support layer of an SOI wafer according to an embodiment of the invention; • Figure 2 is a top view of the support layer after the steps of Figure 1 according to one embodiment of the invention; • Figures 2a-2h illustrate different variants for the embodiment of Figure 2; • Figure 3 is a top view of the support layer after the steps of Figure 1 according to another embodiment of the invention; • Figure 4 is a top view of the support layer after the steps of Figure 1 according to another embodiment of the invention; • Figure 5 is a top view of the support layer after the steps of Figure 1 according to another embodiment of the invention; Figures 6a-6i schematically illustrate a second series of manufacturing steps on a working layer of an SOI wafer according to an embodiment of the invention; and • Figure 7 is a sectional view of an SOI wafer where watch components have been released after the steps of Figures 1 and 6 according to an embodiment of the invention.

[0014] In all that follows, the orientations are the orientations of the figures. In particular, terms such as "upper", "lower", "left", "right", "above", "below", "forward" and "backward" are generally understood to refer to the direction in which the figures are represented. The figures are schematic and may have proportions and / or aspects that differ from reality even within the same figure, but at the very least illustrate the sequence and / or steps of the processes described.

[0015] According to the manufacturing method of the present invention, the watch components are formed in a working layer of an SOI wafer in a known manner. However, to facilitate the release of these watch components from the support layer of the SOI wafer according to the invention, a portion of the support layer necessary for the release is eliminated before the formation of the watch components in the working layer. Consequently, it is avoided that the release steps may affect or worsen the watch components already formed. Furthermore and preferably, when carrying out the subsequent manufacturing steps of the watch components after their initial formation, the structural advantage of the presence of the partially eliminated support layer can still be obtained.

[0016] Figures 1a-11 illustrate a first series of schematic manufacturing steps on a support layer of an SOI wafer according to an embodiment of the invention. The method begins with an SOI wafer 10 illustrated in Figure 1a, this wafer comprising a support layer 20 made of silicon, a working layer 30 made of silicon, and a buried layer 40 separating the two silicon layers 20, 30 made of silicon oxide (in particular SiO2). The drawing is not to be scale, but for example, the support layer 20 may have a thickness of 500 μm, the working layer 30 may have a thickness of 120 μm, and the oxide layer 40 may have a thickness of 2 μm. The support and working layers may be of the same type of silicon or of different types - for example, monocrystalline silicon with any crystal orientation, polycrystalline silicon, or amorphous silicon. The silicon layers 20, 30 and in particular the working layer 30 may be N-type or P-type doped. For example, the use of heavily doped silicon may be advantageous for the manufacture of resonators because, for example, less deformation of the doped material is observed during thermal oxidation under certain conditions.

[0017] Unlike prior watch component manufacturing processes, the process does not begin with manufacturing steps performed on the working layer 30, but with manufacturing steps performed on the support layer 20. To enable this, in Figure 1b the wafer 10 is turned over so that the working layer 30 constitutes the support when the wafer 10 is installed in or on lithography and etching equipment with the support layer 20 now in the top position.

[0018] In Figure 1c, a lithography step begins with the formation of a silicon oxide layer 50 on the surface of the support layer 20. By "lithography" is meant all the operations making it possible to transfer an image or a pattern on or above the wafer 10 to the latter. The oxide layer 50 may for example have a thickness of between 0.4 - 6 μm, and it may be formed by thermal oxidation or alternatively by a PVD, CVD, or ALD type deposition. If the oxide layer 50 is formed by a directional deposition process such as CVD or PVD, the oxide is formed only on the upper surface of the support layer, as illustrated in Figure 1c.Alternatively, if the oxide layer 50 is formed by thermal oxidation, it is noted that the oxide 50 generally forms at the same time on the surface of the working layer 30 (if the latter is not covered by a saving mask) or else a second directional deposition of CVD or PVD type can be carried out on the surface of the working layer 30. In general, the formation of the oxide layer 50 before the deposition of a resin layer (see figure 1d) makes it possible to deposit a relatively thin and uniform resin layer with good surface homogeneity and thus. to optimize the subsequent etching of fine and deep patterns in the support layer 20. However, in other embodiments, it is also possible to carry out a lithography step without the oxide layer, in particular by using a thicker photosensitive resin.

[0019] In Figure 1d, the oxide layer 50 is covered with a resin layer 60, which is typically a positive or negative type photosensitive resin. This resin layer may have a thickness of between 0.5 - 12 μm, purely for illustrative purposes. Subsequently in Figure 1c, the resin layer 60 is preferably structured using a photolithography step with an ultraviolet light source 80 as well as, for example, an exposure mask 70 such as a photomask. A stepper and reticle system may also be used for the photolithography step. In the illustrated example, the layer 60 comprises a positive type photosensitive resin of which the parts 60E of the resin that are exposed to light become soluble in a developer and the unexposed parts remain insoluble. According to other embodiments, the resin may be structured by a laser or electron beam.

[0020] In Figure 1f, the resin layer 60 is opened after being developed by a developer, in particular a solvent which removes the exposed portions 60E of the resin chemically. Then, in Figure 1g, the portions of the oxide layer 50 which were located below the exposed portions 60E of the resin are also removed from the surface of the support layer 20, for example by using selective plasma etching with CH4 / O2 gases. The use of a directional etching technique is generally preferred during this step because it is more precise, but alternatively an etching based on hydrofluoric acid (HF) vapor can also be used.

[0021] In the step illustrated in Figure 1h, after removing or eliminating the remaining portion of the resin layer 60, the support layer 20 is etched through the structured layer 50 to form a structured support layer 20'. The etching in the step of Figure 1h may in particular be carried out by a deep reactive ion etching technique (also known by the acronym DRIE for "Deep Reactive Ion Etching" in English). Alternatively, the structuring of the support layer may be carried out by an anisotropic wet / chemical etching operation, for example, using a potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) bath. In particular, wet / chemical etching can be faster than deep reactive ion etching, but the dimensional resolution of the etched structures is generally lower. If an anisotropic wet / chemical etching operation is used, the oxide layer 50 is normally not formed on the surface of the support layer 20 before the deposition of the resist 60 on this surface. Since DRIE etching generates significant heat, a flow of a cooling element (such as helium) can be infiltrated under the SOI wafer to lower its temperature during this step.

[0022] It is also possible for the remaining portion of the resin layer 60 to still be present during the etching step (DRIE or other) of the support layer 20. This remaining portion of the resin layer can be removed after etching, and in this case the support layer 20 is etched through the two structured layers 50, 60. For example, a positive resin can be removed by solvents such as acetone or dimethyl sulfoxide (DMSO) either before or after the etching step. For a negative resin such as SU-8, a CF4 / O2 plasma can be used for its removal.

[0023] After the step of etching the support layer, a modified SOI wafer 10' results, comprising the structured support layer 20', as illustrated in FIG. 11. On this modified wafer 10', after the removal of the remaining resin 60, the oxide layer 50 which is still on the main surface of the remaining parts of the structured support layer 20' (in the case of deep reactive ion etching) is preferably kept for the following operations related to the manufacture of the watch components.

[0024] Generally, the structured support layer 20' comprises structures that are intact at locations on the wafer where the support layer material has not been removed. These structures define between them regions in which the support layer material has been removed, thereby exposing the buried oxide layer 40 of the wafer in these regions. This structuring cannot damage watch components that are not yet formed, but the structured support layer 20' will facilitate the release of watch components that will be formed later in the working layer 30, because the positions of the future watch components are aligned (in the vertical direction in the views of Figure 1) at least in part with regions in which the material of the structured support layer 20' has been removed. As described below, the structured support layer 20' can take different forms, but in all cases the modified SOI wafer 10' comprising this structured support layer 20' is much better suited for the subsequent release of the watch components after their formation. In addition, after the release of the watch components, the structural support benefit of the structured support layer 20' can be retained for the manufacturing steps that will take place after this release.

[0025] Referring to the embodiments of Figures 2-5, the structured support layer 20' may include structures 22 that are intact where the support layer material has not been removed and are generally located at peripheral and internal locations of the wafer. The internal structures are located inwardly relative to the peripheral structures. These structures 22 define between them the regions 24 in which the support layer material has been removed. The buried oxide layer 40 of the wafer is therefore exposed in these regions 24. In the illustrated embodiments, the peripheral structures 22 form a single-piece annular assembly, but these structures may also be distributed non-continuously along the circular periphery of the structured support layer 20' without being connected together.

[0026] According to one embodiment, Figure 2 is a top view (along the direction of arrow F in Figure 11) of the structured support layer 20' of the modified SOI wafer 10', after the steps of Figure 1 have been carried out. Areas 25 correspond to the future positions of the watch components that will be formed in the working layer 30. These areas 25 are aligned (in the vertical direction in the views of Figure 1), at least in part, with regions 24 in the structured support layer 20'. As illustrated, each area 25 may have a circular (cross-sectional) shape that is delimited by the structures 22 of the structured support layer 20', but other shapes are of course possible for the areas. For example, the shape of each area 25 may correspond to the external periphery of the future watch component.Notwithstanding its shape, it can be considered that the surface area of ​​the zones 25 is substantially equal, slightly less than or slightly greater than the surface area of ​​the overall footprint of the future watch components in the layer of. work 30 of the wafer. For example, the areas 25 may have an area that is between 80%-120%, and preferably between 90-110%, of the area of ​​the overall footprint of the future components in the work layer 30.

[0027] Figures 2a-2c show three possible variants for the structured support layer 20' in areas 25a-25c, or even illustrate how the part of the support layer that is aligned with an area 25 is structured. In the variant illustrated in Figure 2a, all the material of the support layer has been removed in an area 25a, the buried oxide layer 40 being exposed throughout this area. In this case, the area 25 then only comprises a region 24 in which the material of the support layer has been removed. In the area 25b illustrated in Figure 2b, the structured support layer 20' comprises, in a central or internal part of this area, fine structures 22 composed of the material of the still intact support layer.By a “thin” structure is meant a structure 22 having a thickness (i.e. its smallest dimension in a plane parallel to the plane of the support layer) of a value similar to the smallest dimension of the components, for example a thickness which is less than or equal to 100 μm and preferably less than or equal to 60 μm. These thin structures form a mesh in the central part of the zone 25b, for example in a honeycomb pattern. In this example, even if the buried oxide layer 40 is exposed in the vast majority of the zone 25b, the structures 22 within this zone still provide a certain level of support for the layers 30, 40 located above, but without hindering the subsequent release of the watch components. The structures 22 can of course be arranged otherwise, for example in the shape of any mesh.In the area 25c illustrated in Figure 2c the structured support layer 20' also comprises at least one structure 22 within the area, but in this case the structures 22 in the area 25c substantially repeat the negative shape of one of the watch components that will be subsequently manufactured in the working layer 30. In the example of Figure 2c, a simple wheel is used to schematically represent the watch component with a structure 22 in the center of the area 25c, but it is understood that the geometric shape of the component would normally be more elaborate in practice. Optionally, as illustrated in Figure 2c, thin structures 22 may bond the structure 22 in the center of the area 25c to the rest of the structured support layer 20' for stabilization.

[0028] Figure 2d illustrates another embodiment for structuring the support layer in a region 25d of a watch component. In this example, the structuring is essentially a mirror image of the structuring in the variant of Figure 2b above, where the regions 24 in which the support layer material has been removed define a plurality of structures 22' within the region 25d. According to this variant, these structures 22' remain attached to the modified SOI wafer 10' during the subsequent fabrication of the watch components, but they are detached from the SOI wafer after the fabrication of these components and before any subsequent manufacturing step is performed on the released components.This detachment may in particular take place during a release step (described below in connection with FIG. 6i) during which the parts of the buried oxide layer 40 which are located above the structures 22' are eliminated, allowing their detachment. Optionally, the structures 22' inside the area 25d may be linked by bridges to each other or to other remaining parts of the structured support layer 20'. This makes the structures 22' more stable, in particular during the manufacture of the watch components. In this case, these bridges may be mechanically broken after the release step to complete their detachment from the wafer. Similarly, a single monobloc detachable structure may be formed inside the area 25d and detached after a release step where the part of the buried oxide layer 40 which is located above this structure is eliminated.

[0029] Like the variant of Figure 2c, Figures 2e-2g illustrate still other embodiments for areas 25e, 25f and 25g in which structures of the structured support layer 20' substantially take the negative shape of a watch hairspring. Unlike the examples of Figures 2a-2d, the views of Figures 2e-2g are from the side of the working layer 30 of the SOI wafer after the hairspring has been manufactured in this layer. 2e-2g then shows a structured working layer 30' in which the hairspring has been formed by an etching step which removes the material of the working layer in regions 34 of this layer (as described below in association with Figure 6). As illustrated, the hairspring remains attached to another surviving or intact portion of the structured working layer 30' by a bridge 35 which serves to hold the hairspring to the plate even after its release.For each of Figures 2e-2g, only the regions 24 in which. the material of the support layer has been removed are referenced so as not to overload the drawing.

[0030] In each of the examples of Figures 2e-2g, the regions in which the support layer material has been removed include holes 24' that are formed around areas 25e, 25f and 25g in the structured support layer 20'. Since these holes 24' extend throughout the thickness of the support layer to reach the buried oxide layer 40, they allow an etchant (such as HF acid) to more quickly attack the buried oxide layer 40 when releasing the watch components, while reducing the period during which these components are in contact with the etchant. For this same purpose, similar holes can also be formed in the working layer 30 during the formation of the components, but such holes can at the same time weaken the working layer 30 if the latter is relatively thin.

[0031] In the examples of Figures 2e and 2f, a region 24 in which the material of the support layer has been removed generally follows the wound shape of the hairspring but, for reasons explained below, this region 24 preferably has a width less than the width of the turns of the hairspring. In this way, the structures of the structured support layer 20' which are intact in areas 25e and 25f substantially take up the negative shape of the hairspring, i.e. of the watch component. In Figure 2f, another region in which the material of the support layer has been removed has the shape of a groove 24'' surrounding area 25f of the hairspring. The groove 24'' then allows this negative shape of the hairspring to be detached in the structured support layer 20' after release, similar to the detachment described above in connection with the variant of Figure 2d.Such a bleed can have other shapes and it can alternatively surround the areas of several or even all of the watch components on the SOI wafer.

[0032] The variant of Figure 2g is similar to the example of Figure 2f, but instead of a continuous region 24 following the coil shape of the hairspring, several discrete holes 24' are formed in the structured support layer along this coil in the area 25g. Again, the width of these holes 24' is preferably less than the width of the coils of the hairspring for reasons explained below.

[0033] It has been observed that, in the zones 25 of watch components, the size and positioning of the regions 24, 24' in which the support layer material has been removed (i.e., the size and positioning of the openings in this layer) can affect the thermal conductivity of the SOI wafer (and therefore its cooling capacity) during the subsequent etching of the watch components in the working layer, particularly when the buried oxide layer 40 is relatively thin. If cooling is compromised, the etching of the watch components may not be optimal. Firstly, it can be advantageous if the regions 24, 24' in which the support layer material has been removed are not very wide in the zones 25.For example, it has been observed that wafer cooling remains sufficiently effective if these regions and holes have a width (e.g., a diameter within a circular hole) of 100 pm or less, but cooling may be less efficient if these regions have larger widths. However, in other embodiments (e.g., those in Figures 3-5), the size of the regions 24, 24' in which the support layer material has been removed can be larger.

[0034] Second, if the regions 24, 24' are formed below the portions of the working layer 30 that remain intact after the formation of the components, this makes it possible to better avoid possible leakage of the coolant. Such leakage can occur when regions 24, 24' in which the material of the support layer has been removed and openings in the working layer 30 are at least partially aligned in the vertical direction of FIG. 1. In this case, the flow of the cooling element can rupture the thin buried oxide layer 40 where these openings are vertically aligned (at least in part) and the buried layer 40 is exposed on both sides. For this reason, in some embodiments, the regions 24, 24' in which the material of the support layer has been removed are not vertically aligned with the openings 34 in the structured working layer 30', at least in the areas 25.This vertical non-alignment of the openings in the vertical direction of the SOI wafer (or even the direction of the thickness of the wafer in the views of FIG. 1) is illustrated in FIG. 2h where the arrow V indicates the vertical direction of the SOI wafer. Furthermore, as illustrated in FIGS. 2fd and 2h, preferably, a gap d of at least 5 μm is maintained, in the horizontal direction in the views of FIG. 1 (see the arrow H of FIG. 2h), between the openings in the support layer 20 and the openings in the working layer 30 to better avoid. the occurrence of leaks during wafer cooling. It is also preferable that the gap d between these openings is less than or equal to 40 pm in order to limit the extent of under-etching of the buried oxide layer 40 during the release step.

[0035] In other embodiments (e.g., those of Figures 3-5), the regions 24, 24' in which the support layer material has been removed may be vertically aligned with the openings 34 in the structured working layer 30' including in the areas 25.

[0036] Figure 3 shows a top view (along the direction of arrow F in Figure 11) of the structured support layer 20' of the modified SOI wafer 10' according to another embodiment. In this case, the structured support layer still comprises the peripheral structures 22 as in the previous embodiment, but the internal structures 22 form a honeycomb mesh over the remainder of the layer 20'. Between the mesh of the structures are the regions 24 in which the material of the support layer has been removed, exposing the buried oxide layer 40.As in the previous embodiment and as shown in Figure 3, these regions 24 can be directly aligned (vertically in the views of Figure 1) with the areas 25 corresponding to the positions of the future watch components, but this is not necessary; it suffices that the areas 25 be partially aligned with the removed regions 24 of the structured support layer 20'. Nevertheless, preferably in this embodiment, the internal structures 22 do not overlap, or only slightly overlap, with these areas 25 so as not to affect the subsequent release of the watch components. However, if the internal structures 22 are thin, this is not essential. The internal structures 22 can also be arranged differently, for example, in the form of any mesh.

[0037] Another embodiment of the structured support layer 20' is illustrated in Figure 4, which again shows a top view in the direction of the arrow F in Figure 11. Here, internal structures 22 are arranged in the form of wheel spokes connecting a central internal structure 22, taking a shape similar to that of a hub, to peripheral structures 22 which are similar to the previous embodiments. Again, between the structures 22, there are regions 24 in which the material of the support layer has been removed, exposing the buried oxide layer 40. Preferably in this embodiment, the internal structures 22 do not overlap or barely overlap with the areas 25 (some being drawn in dotted lines in the figure) corresponding to the positions of the future watch components so as not to affect their subsequent release, but if the internal structures 22 are thin, this is not essential.

[0038] Figure 5 illustrates yet another embodiment (in top view along the direction of arrow F in Figure 11) of the structured support layer 20'. In this example, there are still peripheral structures 22 which are similar to the previous embodiments, but the internal structures 22 are arranged in the form of concentric rings around the center of the wafer. Regions 24, also annular in shape, are located between the structures 22 and in these regions, the material of the support layer has been removed to expose the buried oxide layer 40. Again, preferably in this embodiment, the internal structures 22 do not overlap or barely overlap with the areas 25 (some of them being drawn in dotted lines in the figure) corresponding to the positions of the future watch components so as not to affect their subsequent release, but if the internal structures 22 are thin, this is not essential.

[0039] Of course, other shapes of the structured support layer 20' are possible. For example, the embodiments described above may be adapted to eliminate the peripheral structures 22, at least in part, along the circular periphery of the structured support layer 20'. According to another example, the structured support layer 20' may comprise only peripheral structures 22, its entire inner part having been eliminated. The different shapes of structures 22 of the above embodiments may also be combined together. For example, by introducing a mesh of thin structures 22 between the thicker structures of Figures 4 or 5. As in the variant of Figure 2d, one or more structures 22 may also be formed which extend below the areas 25 of several future watch components (or even all future watch components) and which remain attached to the modified SOI wafer 10' during the subsequent manufacture of the watch components. This or these structures would be detached after the manufacture of the watch components when the parts of the buried oxide layer 40 which are located above this or these structures are eliminated during the release step (described below in connection with figure 6i), optionally, after mechanically breaking any attachment bridges.

[0040] What is important is that the eliminated regions 24 of the structured support layer 20' facilitate the subsequent release of the watch components. Moreover, during the manufacturing steps that will take place after this release, the working layer comprising the components can still remain attached (or bonded) to the structured support layer 20' so that the remaining structures 22 of this layer still serve as structural support.

[0041] After the formation of the structured support layer, the manufacturing method of the present invention continues with the formation of watch components in the working layer 30. According to an embodiment of the invention, Figures 6a-6i schematically illustrate a second series of manufacturing steps on the working layer 30 of a modified SOI wafer 10'.

[0042] To begin, in Figure 6a, the modified SOI wafer 10' of Figure 11 is turned over so that the structured support layer 20' constitutes and acts as a support when the modified wafer 10 is installed in or on lithography and etching equipment. The working layer 30 is then once again in the top position. Subsequently, in Figure 6b, a silicon oxide layer 55 is formed on the surface of the working layer 30 as well as on the surfaces of the flanks of the structures 22 of the structured support layer 20'. The oxide 55 that is formed on these flanks can fuse with the oxide 50 already present on the main surface of the structures 22 of the structured support layer 20'. Preferably, the oxide layer 55 is formed by thermal oxidation, but it can also be formed by PVD, CVD, or ALD deposition. The oxide layer 55 may for example have a thickness of between 0.4 - 6 pm.As indicated above, the formation of the oxide layer 55 before the deposition of a resist layer (see Figure 6c) makes it possible to deposit a relatively thin and uniform resist layer with good surface homogeneity and thus to optimize the subsequent etching of fine and deep patterns in the working layer 30 (but it is also possible to carry out a lithography step without the oxide layer, in particular by using a thicker photosensitive resist). In addition, the oxide layers 50, 55 serve to protect the structured support layer 20' during the formation of the components. watchmakers in the working layer 30. On the other hand, if an oxide layer has already been formed on the working layer 30 according to a variant of the step of figure 1e below, this step of figure 6b becomes superfluous.

[0043] In Figure 6c, the oxide layer 55 is coated with a resin layer 65, which is typically a positive or negative type photosensitive resin. This resin layer can have a thickness of 0.5–12 µm, for illustrative purposes. Subsequently, in Figure 6d, the resin layer 65 is structured preferably using a photolithography step comprising an ultraviolet light source 80 and, for example, an exposure mask 75 such as a photomask. A stepper and cross-link system can also be used for the photolithography step. In the illustrated example, the layer 65 comprises a positive type photosensitive resin, the light-exposed portions of which 65E become soluble in a developer, while the unexposed portions remain insoluble. According to other embodiments, the resin 65 can be structured by a laser or electron beam.

[0044] In Figure 6e, the resin layer 65 is opened after being developed with a developer, specifically a solvent that chemically removes the exposed portions 65E of the resin. Then, in Figure 6f, the portions of the oxide layer 55 that were beneath the exposed portions 65E of the resin are also removed from the surface of the working layer 30, for example, by using selective plasma etching with CH4 / O2 gases. Directional etching is generally preferred for this step because it is more precise, but alternatively, hydrofluoric acid (HF) vapor etching can also be used.

[0045] In the step illustrated in Figure 6g, after removing or stripping away the remaining portion of the resin layer 65, the working layer 30 is etched through the structured oxide layer 55 to form the patterns of the watch components in the structured working layer 30' by removing the material of the working layer in regions 34. The resulting SOI wafer 10'' then comprises the structured support layer 20' and the structured working layer 30' with the components formed therein. The etching in the step of Figure 6g is preferably performed by a deep reactive ion etching (DRIE) technique. Alternatively, the Structuring of the working layer can be achieved by an anisotropic wet / chemical etching operation, for example using a potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) bath, but as noted above, the dimensional resolution of the etched structures is typically lower with wet / chemical etching. If an anisotropic wet / chemical etching operation is used, the oxide layer 55 is not normally formed on the main surface of the working layer 30 before the resin 65 is deposited on this surface. Since DRIE etching in particular generates significant heat, a flow of a cooling element (such as helium) can be introduced under the SOI wafer to lower its temperature during this step.

[0046] It is also possible to keep the remaining part of the resin layer 65 during the etching step (DRIE or other) of the working layer 30 and to remove it after the etching, and in this case the working layer 30 is etched through the two structured layers 55, 65. For example, if the resin is of the positive type it can be removed by solvents of the acetone or dimethyl sulfoxide (DMSO) type either before or after the etching step. For a negative type resin such as SU-8, a CF4 / O2 plasma can be used for its removal.

[0047] After the step of etching the structured working layer 30', the resulting SOI wafer 10" with the watch components 90 formed in the structured working layer 30' is obtained in Figure 6h. Subsequently, at least the parts of the buried oxide layer 40 that are located below the components 90, as well as the remaining oxide layers 50, 55 on the wafer are removed in order to release the watch components 90, as illustrated in step 6i. Again, these different oxide layers can be removed by using hydrofluoric acid (HF) vapor-based etching in a known manner. Alternatively, the different oxide layers can be removed by plasma etching. Advantageously, this release step can be carried out without re-structuring the structured support layer 20'.

[0048] Alternatively, the release of the watch components 90 can be achieved by a complete separation of the structured working layer 30' (or a part of this layer comprising the watch components) and the resulting SOI wafer 10'' as in document WO2019180596. However, preferably, The structured working layer 30' remains attached to the SOI wafer 10" so that the structured support layer 20' continues to serve as structural support during subsequent manufacturing steps performed on the released components. In this case, it is sufficient to remove the portions of the buried oxide layer 40 located beneath the components 90. Given the prior structuring of the support layer, this step of releasing the watch components 90 by removing the oxide is straightforward and does not require a step of depositing a protective layer on these components after their formation, as the structured support layer 20' already has the necessary shape for release and does not need to be restructured.In general, the watch components 90 remain attached to the structured working layer 30' by at least one bridge 35 after their formation (illustrated schematically by line 35 in figure 6i; in reality the bridge extends over the entire thickness of the component), so that they are still held and supported by the remaining part of this layer after their release.

[0049] According to one embodiment, Figure 7 is a sectional view to better illustrate the released watch components 90 as part of a structured working layer 30' still attached to the resulting SOI wafer 10” after the steps of Figures 1 and 6. In this example, the watch components 90 may be watch hairsprings, and the structured support layer 20' corresponds to the embodiment of Figure 2a described above for simplicity. Thus, below each watch component 90, areas 25a are seen in which all the material of the support layer and all the material of the buried oxide layer 40 have been removed. In this way, the watch components 90 are structurally supported only by thin bridges (not shown) that keep them attached to the remaining portions of the structured working layer 30'.It is also noted that in other regions of the wafer, the structured working layer 30' remains attached to the structures 22 of the structured support layer 20' by means of a remaining portion of the buried oxide layer 40. In reality, a portion of the oxide layer 40 above the structures 22 may be removed during the release step of FIG. 6i, but a sufficient portion generally remains to maintain the bonding of the silicon layers 20', 30' at these locations. After this release, at least one subsequent manufacturing step may be carried out on almost the entire external surface of the watch components 90.

[0050] For example, a subsequent manufacturing step may include a smoothing step in which the etched surfaces of the watch components on the resulting 10” wafer are smoothed, thereby mechanically strengthening them. This smoothing may in particular be carried out by a thermal oxidation step followed by a deoxidation step, consisting for example of wet etching using hydrofluoric acid (HF). Such smoothing may be repeated at least once to improve the surface properties of the watch components.

[0051] When the watch components 90 are hairsprings or another type of watch resonator, it is of course important to manufacture them with the desired elastic properties. However, the microfabrication steps, and more specifically etching, employed in the manufacture of hairsprings on a wafer typically result in variations between the dimensions of the components on the wafer. This results in a significant dispersion between the stiffnesses of the components, notwithstanding that the etching pattern is the same for each component. To overcome this problem, it is known to oversize the components initially formed on the resulting 10” silicon wafer and finely adjust their dimensions (and therefore their elastic properties) by performing a thermal oxidation step (during which the silicon material is precisely removed) followed by a deoxidation step.These operations therefore constitute another example of a subsequent manufacturing step.

[0052] Yet another possible subsequent manufacturing step on the resulting silicon wafer 10” concerns the formation of a layer of silicon oxide, preferably around the entire external surface of the watch components 90. This external layer of silicon oxide may have a thickness of between 2-5 μm. In the context of a hairspring or another type of watch resonator, such a layer compensates for variations in the Young's modulus of the silicon core of the watch component as a function of temperature. Furthermore, the formation of such an external layer of silicon oxide on watch components of any type can also serve to strengthen these components mechanically.

[0053] Other types of materials may also be formed on the watch components 90, for example by ALD-type deposition, during a subsequent manufacturing step.

[0054] These subsequent manufacturing steps and / or others can be easily performed on the resulting 10" silicon wafer, which advantageously always includes the structured support layer 20' as a structural substrate. At the same time, the pre-structuring of the structured support layer 20' before component formation facilitates simple and reliable release. In particular, with the manufacturing process of the present invention, the release steps do not pose a risk of unexpectedly damaging or altering the watch components after their formation, and furthermore, the formation of a protective layer around the formed watch components is no longer necessary.

[0055] Once the manufacturing step(s) are completed, the watch components can be detached from the resulting 10” SOI wafer by breaking the bridge(s) connecting them to the structured working layer (30').

[0056] The present invention is not limited to the embodiments and variations presented and other embodiments and variations will become apparent to those skilled in the art. Thus, the above embodiments are examples. Although the description refers to one or more embodiments and variations thereof, this does not necessarily mean that each reference relates to the same embodiment or variation, or that the features apply only to a single embodiment or variation. Single features of different embodiments and variations thereof may also be combined and / or interchanged to provide other embodiments.

Claims

Claims 1. A method of manufacturing a plurality of watch components (90) in an SOI type manufacturing wafer (10), the SOI wafer (10) comprising a support layer (20) of silicon, a working layer (30) of silicon, and a buried layer (40) of silicon oxide separating the support layer (20) from the working layer (30), the method comprising the steps of: (a) structuring the support layer (20) by removing a portion of said layer to obtain a modified SOI wafer (10) comprising a structured support layer (20'), the structured support layer (20') comprising structures (22) which are intact at locations on the wafer where the material of the support layer has not been removed, said structures (22) defining therebetween regions (24) in which the material of the support layer has been removed to expose the buried oxide layer (40) in these regions; (b) forming the clock components (90) in the working layer (30) of the modified SOI wafer (10'), the structured support layer (20') acting as a support during this formation, the clock components (90) being located in areas (25) of the working layer (30) which are aligned at least in part with eliminated regions (24) of the structured support layer (20'); (c) releasing the watch components (90) formed in step (b) by removing at least the parts of the buried oxide layer (40) which are located below the watch components (90); and (d) performing at least one subsequent manufacturing step on the released components (90).

2. Method according to the preceding claim, characterized in that each zone (25) has a surface area substantially equal to, slightly less than or slightly greater than the surface area of ​​an overall imprint of one of the watch components (90) in the working layer (30).

3. Method according to claim 2, characterized in that each zone (25) has a circular shape.

4. Method according to claim 2, characterized in that each zone (25) has a shape corresponding to an external periphery of one of the watch components (90).

5. Method according to one of the preceding claims, characterized in that the material of the support layer is completely removed in the areas (25).

6. Method according to one of claims 1 to 4, characterized in that, in the areas (25), the structured support layer (20') comprises structures (22) which are still intact.

7. Method according to claim 6, characterized in that the structures (22) inside the zones (25) form a mesh, for example a honeycomb.

8. Method according to claim 6, characterized in that the structures (22) inside the zones (25) substantially take on the negative shape of one of the watch components (90).

9. Method according to one of claims 6 to 8, characterized in that the structures (22) inside the zones (25) are detached after the release step (c) before carrying out the at least one subsequent manufacturing step.

10. Method according to one of claims 6 to 9, characterized in that the removed regions (24) of the structured support layer (20') are not aligned, in the vertical direction of the SOI wafer (10), with openings in the working layer (30), at least in the areas (25).

11. Method according to one of the preceding claims, characterized in that the intact structures (22) of the structured support layer (20') comprise peripheral structures extending, at least in part, along a circular periphery of the structured support layer (20').

12. Method according to one of the preceding claims, characterized in that the intact structures (22) of the structured support layer (20') comprise internal structures which are located inwards relative to the periphery of the support layer and which form a mesh, for example a honeycomb.

13. Method according to one of the preceding claims, characterized in that step (a) of structuring the support layer (20) is carried out by a deep reactive ion etching technique.

14. Method according to one of claims 1 to 10, characterized in that step (a) of structuring the support layer (20) is carried out by an anisotropic wet / chemical etching operation, preferably using a potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) bath.

15. Method according to one of the preceding claims, characterized in that, before the formation of the components in step (b), the method also comprises at least one step of forming an oxide layer (50, 55) on the structured support layer (20').

16. Method according to one of the preceding claims, characterized in that step (c) of releasing the watch components (90) is carried out without re-structuring the structured support layer (20').

17. Method according to one of the preceding claims, characterized in that the at least one subsequent manufacturing step of step (d) is carried out when the released watch components (90) are still attached to the resulting SOI wafer from step (b).

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