Method for manufacturing silicon clock components

Abstract

A method for manufacturing watch components (90) in an SOI-type wafer comprises the steps of: (a) forming a structured silicon oxide layer (50) on the upper surface of the working layer (30) of the wafer; (b) forming the components (90) by etching, through this structured layer (50), patterns in the working layer (30) to obtain removed regions (35) which expose the buried oxide layer (40) below; (c) forming a protective layer (55, 155) at least on the flank surfaces (95) of the components etched in step (b);(d) perform a directional etch, without using a mask, of the buried oxide layer (40) to the point where regions (45) of the buried oxide layer (40) are removed in order to obtain a perforated buried oxide layer (40'), (e) perform a silicon etch in the support layer (20) through the removed regions (45) of the perforated buried oxide layer (40'), in order to obtain an excavated support layer (20') having at least one cavity (24) formed below at least one of the watch components (90); and (f) remove the portions of the buried oxide layer (40) remaining between the at least one cavity (24) and the at least one component (90) arranged above the cavity (24).

Description

Domaine technique

[0001] The invention relates to a method for manufacturing silicon watch components on a silicon-on-insulator (SOI) wafer. Such a manufacturing process generally comprises microfabrication steps including lithography and etching of the wafer layers, as well as post-etching manufacturing steps including component release. Etat de la technique

[0002] The fabrication of silicon watch components, such as balance springs, cams, springs, pawls, wheels, and pallet forks, using microfabrication processes is well established. Advantageously, several hundred watch components can be manufactured on a single wafer using these technologies. For example, it is known to produce a plurality of silicon resonators with very high precision using photolithography and etching processes on a silicon wafer. The processes for manufacturing these watch components generally use monocrystalline silicon wafers, but polycrystalline or amorphous silicon wafers are also suitable.

[0003] Silicon is a diamagnetic material, and its use in the manufacture of watch components, particularly for the regulating organ components of a mechanical watch movement, is advantageous because no remanent effect is observed after exposing this material to magnetic fields. Furthermore, variations in the Young's modulus of a silicon watch component with temperature can be compensated for by adding a layer of SiO₂ oxide to the component. When watch components are made from a single-crystal silicon wafer, any one of the three crystal orientations <100> , <110> Or <111> can be used.

[0004] Silicon wafers are available in single-sided wafer form, such as SSP (Single Side Polished) or DSP (Dual Side Polished) wafers. Document EP3495894 describes a process for manufacturing silicon watch components using such a wafer, which comprises a single silicon layer without a support layer. According to this document, the single wafer has a thickness approximately equal to the maximum thickness of the watch components to be manufactured. To form the watch components, an etching step is performed through the entire thickness of the wafer, thus utilizing all the component material present in the wafer to form the watch components, without any support function within the wafer.After their formation, the watch components are structurally supported only by thin bonding bridges that hold them attached to the remaining portions of the single silicon layer, and subsequent manufacturing steps can be performed on almost the entire external surface of the components without the need for a prior component release step. However, in the manufacturing process described in document EP3495894, the etching step is delicate because it takes place on a relatively thin, and therefore fragile, wafer without any support.

[0005] Alternatively, silicon-on-insulator (SOI) wafers are often used for manufacturing 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 component manufacturing (the "handle" layer), and a buried SiO₂ oxide layer located 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.

[0006] After the lithography and etching steps initially form the watch components in the working layer of a SOI wafer, the components are typically freed 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 bonding bridges that hold them attached to the remaining portions of the working layer. This allows subsequent manufacturing steps to be performed on virtually the entire external surface of the wafer components. These subsequent steps may include oxidation and deoxidation steps to smooth the component surfaces.Subsequent steps may also include oxidation and deoxidation to adjust the dimensions of the components (for example, to correct stiffness when the components are balance springs or resonators) and / or oxidation steps to form an outer layer of silicon oxide on the components for thermal compensation and / or mechanical reinforcement. After these subsequent steps, the watch components can be detached from the wafer and mounted in, for example, the movement of a timepiece.

[0007] The release of watch components from a silicon dioxide (SOI) wafer can be achieved using various methods. One such release approach is described in patent documents JP2017219520 and WO2019180177. According to this approach, after the components are formed by etching, a silicon oxide layer is grown on the surface of the silicon. This oxide layer serves as a protective layer for the formed components. Subsequently, photolithography and etching are performed to expose the silicon in the support layer. The support layer is then etched from the side opposite the components, removing the support layer beneath them. To complete the release process using this alternative, the buried layer of the SOI wafer beneath the components, as well as the protective layer on the components, is removed.This release approach is relatively long and expensive, as it requires structuring (or even photolithography and etching steps) through the thick support layer of the SOI wafer.

[0008] According to another approach described in document WO2019180596, after component formation, the working layer (or a portion of it containing the components) is separated from the support layer. This separation can be facilitated by etching a groove around 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 portion of the working layer defined by the groove is separated from the support layer of the SOI wafer. In this release approach, because the working layer is much thinner and more fragile than the support layer, subsequent manufacturing steps are more delicate and risky because they are performed without the benefit of the support layer, even if it is partially removed.

[0009] It would therefore be advantageous to have a manufacturing process for silicon watch components that includes shorter, more efficient component release steps, preserving the benefit of structural support for subsequent manufacturing steps performed on the components after release. Furthermore, the manufacturing of silicon watch components generally involves a significant number of steps, and it would therefore also be desirable to have a manufacturing process for such components with a reduced number of steps. Bref résumé de l'invention

[0010] One aim of the present invention is to propose a method for manufacturing a plurality of watch components on an SOI wafer, which makes it possible to avoid or overcome the above disadvantages, or at least to offer a better compromise between these disadvantages.

[0011] In particular, this goal is at least partially achieved by proposing a new manufacturing process for silicon watch components in which the components are released without a long and costly etching of a support layer and in which the benefit of structural support can be retained for subsequent manufacturing steps carried out on the components after their release.

[0012] Thus, according to one aspect, the present invention relates to a method for manufacturing, in a silicon dioxide (SOI) wafer, a plurality of watch components having flanks having surfaces, the SOI wafer comprising a silicon support layer, a silicon working layer, and an embedded silicon dioxide oxide layer having a thickness and separating the support layer from the working layer. The method comprises the following steps: (a) forming a structured silicon dioxide layer on the upper surface of the working layer;(b) form the watch components (with their flanks), or at least a rough draft of the watch components, by engraving, through the structured silicon oxide layer, patterns in the working layer in order to obtain a structured working layer, the structured working layer comprising regions removed around the engraved patterns in which the material of the working layer has been removed to expose the oxide layer buried below; (c) form a protective layer at least on the surfaces of the flanks of the watch components engraved in step (b);(d) either after or before step (c), perform a directional etch, without using a mask, of the buried oxide layer to the point where regions of the buried oxide layer below the removed regions of the working layer are removed to obtain an open-work buried oxide layer, the structured silicon oxide layer still being present on the upper surface of the structured working layer after this step; (e) perform a silicon etch in the support layer from or through the removed regions of the open-work buried oxide layer, to obtain an excavated support layer having at least one cavity formed below at least one of the watch components and / or below the buried layer opposite said at least one of the watch components;and (f) remove the remaining portions of the buried oxide layer between said at least one cavity and said at least one watch component arranged above said cavity, in order to obtain a structured buried oxide layer having remaining portions still linking the excavated support layer to the structured working layer.

[0013] The directional etching of step (d) is preferably a DRIE or ICP-RIE type etching and may use at least one fluorinated gas such as CHF 3, C 4 F 8, and / or SF 6 in combination with at least one of the gases He and / or H 2.

[0014] Other advantageous and preferred features of the manufacturing process are detailed in the description and sub-claims below. Brève description des figures

[0015] Examples of implementation of the invention are given in the description illustrated by the accompanying figures, in which: THE figures 1a-1m schematically illustrate a series of manufacturing steps for a silicon watch component in a SOI wafer according to one embodiment; figures 2a-2k schematically illustrate a series of manufacturing steps for a silicon watch component in a SOI wafer according to another embodiment; The figures 3h et 3i schematically illustrate two manufacturing steps of a silicon watch component in an SOI wafer according to another embodiment which is a variant of the embodiment of the figure 2 ; THE figures 4 et 4A These are top views of the working layer of a SOI wafer after the manufacturing steps of the figure 1 , 2 Or 3 according to one embodiment; and The figure 5 is a section view along the VV line of the figure 4 . Exemples de mode de réalisation de l'invention

[0016] Throughout what follows, "orientations" refers to the orientations of the figures. In particular, terms such as "upper," "lower," "left," "right," "above," "below," "horizontal," "vertical," "forward," and "backward" are generally understood in relation to the direction in which the figures are represented. The figures are schematic and may exhibit proportions and / or aspects that differ from reality, even within the same figure, but they at least illustrate the sequence and / or steps of the processes described.

[0017] THE figures 1a-1m illustrate a series of schematic manufacturing steps for a watch component in an SOI 10 wafer according to an embodiment of the invention. Of course, several watch components can be manufactured in the SOI 10 wafer simultaneously, but the views of the figure 1 are isolated onto a single component for simplicity. The process begins with an SOI 10 wafer illustrated in the figure 1a This SOI 10 wafer comprises a silicon support layer 20, a silicon working layer 30, and a buried oxide layer 40 separating the two silicon layers 20 and 30, which is primarily composed of silicon dioxide (SiO₂). The drawing is not to scale, but as an example, the support layer 20 can be up to 500 µm thick, the working layer 30 can be 120 µm thick, and the buried oxide layer 40 can be 0.5–2 µm thick. The support and working layers can be of the same type of silicon or different types—for example, monocrystalline silicon with any crystal orientation, polycrystalline silicon, or amorphous silicon. Silicon layers 20, 30 (and in particular the working layer 30) can be N-type or P-type doped.For example, the use of heavily doped silicon can be advantageous for the manufacture of resonators because, for example, less deformation of the doped material is observed during thermal oxidation under certain conditions.

[0018] The thickness of the working layer 30 generally corresponds to the maximum thickness e 90 of watch components. The SOI wafer 10 includes a lower side 10A (or the support layer side 20), and it is from this side that the wafer 10 normally rests on equipment during the various microfabrication stages. The wafer 10 also includes an upper side 10B (or the working layer side 30), and it is from this side that the microfabrication stages for forming the watch components are generally carried out.

[0019] In the figure 1b A lithography step begins with the formation of a silicon oxide layer 50 on the upper surface of the working layer 30. "Lithography" refers to all the operations involved in transferring an image or pattern onto or above the SOI wafer 10. In this embodiment, the oxide layer 50 has a thickness e50 greater than the thickness e40 of the buried oxide layer 40, for example, a thickness of 1–6 µm. The oxide layer 50 can be formed by thermal oxidation or alternatively by PVD, CVD, or ALD deposition. If the oxide layer 50 is formed by a directional deposition process such as CVD or PVD, the oxide forms only on the upper surface of the support layer 20, as illustrated in Figure 1. figure 1b Alternatively, if the oxide layer 50 is formed by thermal oxidation, it is noted that the oxide 50 can generally form simultaneously on the surface of the support layer 20 (if the latter is not covered by a mask), or a second directional deposition of the CVD or PVD type can be carried out on the surface of the support layer 20. Generally, the formation of the oxide layer 50 before the deposition of a resin layer (see the figure 1c ) allows for the deposition of a relatively thin and uniform layer of resin with good surface homogeneity, thus optimizing the subsequent engraving of fine and deep patterns in the working layer 30.

[0020] To the figure 1c The oxide layer 50 is covered with a resin layer 60, which is typically a positive or negative type photosensitive resin. This resin layer can have a thickness of between 0.5 and 12 µm, purely for illustrative purposes. Subsequently, in the figure 1d The resin layer 60 is preferably structured using a photolithography step with an ultraviolet light source 80 and, for example, an exposure mask 70 such as a photomask. A stepper and reticle system can also be used for the photolithography step, or alternatively, a direct writing system (i.e., without a photomask) such as a laser or electron beam lithography system (e-beam lithography). In the illustrated example, the layer 60 comprises a positive-type photosensitive resin, the parts of which 60E that are exposed to light become soluble in a developer, while the unexposed parts remain insoluble.

[0021] In the figure 1e The resin layer 60 is opened after being developed by a developer, specifically a solvent that chemically removes the exposed 60E parts of the resin. Then, at the figure 1f The portions of the oxide layer 50 that were located beneath the exposed portions 60E of the resin are also removed from the surface of the working layer 30, and the oxide layer 50 is thus structured on the surface of the working layer. This step can be carried out, for example, using directional selective plasma etching with one or more fluorinated gases (such as CHF 3, C 4 F 8, and / or SF 6) in combination with at least one of the gases He and / or H 2, depending on the desired selectivities and etching speeds. The use of a directional etching technique is generally preferred in this step because it is more precise, but alternatively, etching with hydrofluoric acid (HF) vapor or with a liquid buffer solution such as BHF can also be used.

[0022] At the stage illustrated in the figure 1g The remaining portion of the resin layer 60 can be removed, for example using a dioxygen (O2) plasma, but optionally, the remaining portion of this layer can be retained as a mask in addition to the oxide layer 50. The steps of figures 1a - 1g These elements are then used to form a structured silicon oxide layer 50 on the upper surface of the working layer 30, this layer having a thickness e50 greater than the thickness e40 of the buried oxide layer 40 according to this embodiment. In alternative configurations, the structured silicon oxide layer can be formed by other means.

[0023] Next, at the stage of the figure 1h Patterns are engraved into the working layer 30 through the structured silicon oxide layer 50, and optionally the remaining resin layer 60, to form the watch component 90 (or at least a rough version of the component). Generally, the engraved patterns extend across the entire thickness of the working layer 30 as illustrated, and for this purpose the buried oxide layer 40 can act as a stop during the engraving. In this way, the thickness of the watch components 90 corresponds to the thickness of the working layer 30. As illustrated, at the end of this step, a structured working layer 30' is obtained with regions 35 surrounding the component structure where material from the working layer 30 has been removed, thus exposing parts of the buried oxide layer 40 beneath these removed regions 35.

[0024] The engraving at the stage of figure 1h This can be achieved, in particular, by a deep reactive ion etching (DRIE) technique, for example, by using SF6 as the reactive gas to etch the silicon of the device layer and periodically using C4F8 as a passivation gas to protect the surfaces of the sidewalls 95 of the watch component. DRIE etching allows for the formation of deep holes and trenches in the layer 30 with a high width-to-height ratio, which is well-suited for micromechanical components such as watch components. The use of C4F8 as a passivation gas is known to produce a fluoropolymer layer on the sidewall surfaces 95. Such a layer, which typically has a thickness of 0.1–5 µm, can be removed from the sidewalls by a suitable technique, for example, using a dioxygen (O2) plasma.Alternatively, the working layer can be structured using other etching technologies such as anisotropic wet / chemical etching, for example, using a potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) bath. However, the dimensional resolution of the etched structures is generally lower with wet / chemical etching than with deep reactive ion etching.

[0025] As mentioned above, it is also possible for the remaining portion of the resin layer 60 to still be present during the deep etching step (DRIE or other) of the working layer 30. This remaining portion of the resin layer can be removed after etching, and in this case, the working layer 30 is etched through the two structured layers 50 and 60. For example, a positive resin can be removed with solvents such as acetone or dimethyl sulfoxide (DMSO) or with an O₂ plasma, 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.

[0026] THE figures 1i-1m illustrate the approach to releasing 90 watch components according to this embodiment of the invention. At the figure 1i A silicon dioxide (SiO₂) oxide layer 55 is preferably formed on all exposed surfaces of the wafer 10, including the flank surfaces 95 of the watch component. Preferably, this oxide layer 55 is formed by thermal oxidation and thus also forms on all exposed silicon of the SOI wafer 10, including the lower surface of the support layer 20, as illustrated. The oxide layer 55 joins the oxide layers 50 and 40 already present on the upper and lower (underside) surfaces of the watch component 90, and these latter layers may become slightly thicker during thermal oxidation, at least where the buried oxide layer 40 is exposed below the regions 35. The thickness of the oxide layer 55 may vary but is preferably between 0.05 and 2 µm.

[0027] The formation of the oxide layer 55 serves, in particular, to protect the flank surfaces 95 of the watch components 90, as well as other areas of the wafer where silicon is exposed, during subsequent manufacturing steps of the process. Alternatively, a protective layer of silicon oxide (SiO2) or of another material (e.g., a resin, a polymer, or another oxide such as Al2O3) can be selectively formed on these surfaces, and in particular on the flank surfaces 95. Such selective deposition can be achieved, for example, by an ALD (atomic layer deposition) technique as described in the document by Taguhi Yeghoyan, Vincent Pesce, Moustapha Jaffal, Gauthier Lefevre, Rémy Gassilloud, Nicolas Posseme, Marceline Bonvalot, and Christophe Vallée; Low temperature Topographically Selective Deposition by Plasma Enhanced Atomic Layer Deposition with ion bombardment assistance. J. Vac. Sci. Technol.A 1 May 2021; 39 (3): 032416 or the document A. Chaker, C. Vallee, V. Pesce, S. Belahcen, R. Vallat, R. Gassilloud, N. Posseme, M. Bonvalot, A. Bsiesy; Topographically selective deposition. Appl. Phys. Lett. 28 January 2019; 114 (4): 043101. Other selective deposition techniques could also be used. Selective deposition of a protective layer can also be carried out subsequently, after a directional etching step described below in association with the . figure 1j However, selective deposition is generally more complicated to achieve on the vertical surfaces of the flanks 95 of watch components, and for this reason the formation of the oxide layer 55 by thermal oxidation remains preferred.

[0028] As described above, if a DRIE etching using a fluorinated gas such as C4F8 was employed in the step of the figure 1h A fluoropolymer layer typically forms on the surfaces of the lateral flanks 95. According to one variant, this fluoropolymer layer can be retained and not removed after the DRIE etching of this step of the figure 1h and this fluoropolymer layer can subsequently serve as a protective layer for these flanks in the following steps. Such a protective layer can be advantageously used, for example, when a subsequent etching of the support layer 20 (as described below in connection with the figures 1k And 1l ) is achieved by xenon difluoride (XeF2) vapor etching, as a fluoropolymer layer is typically highly selective with respect to this etching agent.

[0029] Next, at the figure 1j A directional etch, particularly of the DRIE or ICP-RIE type (Inductively Coupled Plasma-Reactive Ion Etching), is performed to etch the oxide layers 40 and 50 of the wafer until the regions 45 of the buried oxide layer 40 located below the regions 35 are eliminated. This directional etch takes place in the vertical direction of the wafer 10 from its side 10b as illustrated by the arrows in the figure 1j and acts on all surfaces perpendicular to the etching flow. Since the thickness of the oxide layer 50 is greater than the thickness of the buried oxide layer 40 in this embodiment, by controlling the parameters and duration of the etching, a thinned oxide layer 50' (with a lower thickness than the initial layer 50) is always present on the upper surface of the structured working layer 30' at the end of this etching step. As the etching is directional, the oxide layers 55 on the vertical surfaces of the structured working layer 30', and in particular on the flank surfaces 95 of the watch components, are only slightly exposed to reactive ions during etching and are therefore only slightly, if at all, etched, the directional etching acting mainly on the oxide layers 40, 50 which are arranged horizontally on the wafer 10.For this reason, the presence of a protective layer on the surfaces of the 95 sidewalls is not essential during directional engraving, although it is preferred.

[0030] A directional selective plasma etching using at least one fluorinated gas (such as CHF 3, C 4 F 8, and / or SF 6) in combination with at least one of the gases He and / or H 2 can be used during the step of the figure 1j depending on the desired selectivity and etching speeds. Advantageously, this directional etching step is performed without a mask, and in particular without a protective mask (such as a resin mask), making this step relatively fast and economical. At the end of this step, a buried oxide layer 40' is obtained, with openwork regions 45 (located below regions 35) in which the oxide of the buried layer has been removed, exposing the upper surface of the support layer 20.

[0031] If a protective layer has not been formed on the surfaces of the flanks 95 of the watch components 90 before the directional etching of the oxide layers 40, 50, such a protective layer can be selectively deposited on these flanks after this directional etching of the oxide layers 40, 50. In this case, it is important that the selective deposition does not cover the exposed regions of the support layer 20 below the removed regions 45 of the buried oxide layer.

[0032] To the figure 1k A silicon etching step is initiated on the support layer 20 to excavate a portion of the support layer 20 beneath the watch components 90. More specifically, the support layer 20 is etched where it is exposed below the removed regions 45 of the buried oxide layer. According to the illustrated variant, anisotropic wet / chemical etching is used in this step to form etched regions 22 in the support layer 20. Anisotropic etching allows for faster silicon removal in certain directions within each etched region 22, depending on the crystalline orientations of the wafer. The flank surfaces in the etched regions 22 therefore form an angle, and this angle generally varies according to several parameters, including the crystalline orientation of the silicon.Preferably, a potassium hydroxide (KOH) bath can be used for this anisotropic etching, but alternatively, a tetramethylammonium hydroxide (TMAH) bath can also be used. According to another variant for the step of the... figure 1k An isotropic etching technique can be used to attack the silicon in the support layer 20, for example, a vapor-phase etch using xenon difluoride (XeF2). Such an isotropic etch removes the silicon more or less uniformly in all directions, thus creating etched regions 22 of the support layer having the shape (in cross-section) of semicircles below the removed regions of the buried oxide layer.

[0033] According to yet another particularly advantageous variant for attacking the silicon of the support layer 20 at the stage of the figure 1k An isotropic etching technique using a sulfur hexafluoride (SF6) plasma can be employed. In this case, the reaction rate during etching is very fast, and the etched surfaces are relatively clean and smooth. Furthermore, this step can be performed in the same chamber as the DRIE etching step used to form watch components (see the step of the figure 1h ), particularly when an SF6 plasma is also used for this last step. Furthermore, during the etching of the silicon in support layer 20, cracks can appear in the protective layers (made of SiO2 or another material) on watch components, especially on the edges of these components. However, by using an SF6-based plasma, the fluorine radicals created by the plasma are largely blocked before they can penetrate these cracks, thus preventing any etching of the protective layers during the etching step. figure 1k .

[0034] Preferably, the engraving step of the figure 1k continues so that the etched regions 22 in which the silicon of the support layer has been removed unite to form a cavity 24 extending below each watch component 90, as illustrated in the figure 1l We thus obtain an excavated support layer 20' comprising these cavities 24 on its upper surface. If the etching (anisotropic or isotropic) of the support layer is not strictly controlled, the cavities 24 typically do not have a uniform thickness, but preferably the maximum thickness of each cavity ecav is at most equal to 50% of the thickness e20 of the support layer, and it is even more preferable that the maximum thickness of each cavity ecav is at most equal to 25% of the thickness e20 of the support layer. However, the maximum thickness of each cavity ecav can also be greater, and it is even possible for the cavity 24 to penetrate the entire thickness of the support layer 20 (i.e., ecav is equal to e20).

[0035] According to the preferred embodiment in which the oxide layer 55 is produced during the step of the figure 1i is by thermal oxidation, the etching of silicon in the stages of figures 1k And 1l attacks the support layer 20 only through the eliminated regions of the openwork buried oxide layer 40', the other surfaces of this layer being protected by the oxide layer 55, particularly the oxide layer on the back face (or even on the 10A side of the wafer).

[0036] Finally, to complete the release of the watch components, the following steps are performed: figure 1m a deoxidation step, which removes the oxide layers 50' and 55 as well as the portions of the perforated buried oxide layer 40' remaining between each cavity 24 and the watch component(s) 90 above that cavity. This deoxidation step can be carried out, for example, by wet etching or etching in the vapor or gas phase, for example, using hydrofluoric acid (HF) or anhydrous HF gas. A structured buried oxide layer 40' is thus obtained, a significant portion of which has been removed, but which includes parts 42, 44 (see the figure 5 ) always present outside the watch component areas 90. These remaining parts 42, 44 of the structured buried oxide layer 40" maintain the link between the structured working layer 30' and the excavated support layer 20'.

[0037] If the protective layer on the sidewall surfaces 95 comprises a material other than silicon dioxide (SiO2), this protective layer could be removed or eliminated before or after the step of the figure 1m by an appropriate technique. For example, in the case of a resin or fluoropolymer coating, a dioxygen (O2) plasma can be used to remove such a protective layer.

[0038] THE figures 2a-2k illustrate a series of schematic manufacturing steps for a watch component in the SOI 10 wafer according to a second embodiment of the invention (these views are not to scale and are still isolated on a single component for simplicity). The steps of figures 2a-2f are generally identical to the steps of figures 1a-1f described above except that, at the figure 2b , on the upper surface of the working layer 30 a layer of silicon oxide (SiO 2 ) 150 is formed which has a thickness e 150 which is not necessarily greater than the thickness e 40 of the buried oxide layer 40. In other words, the thickness e 150 can be greater than, less than, or even equal to the thickness e 40 in this embodiment.

[0039] Furthermore, in this embodiment, the remaining part of the resin layer 60 is kept as a mask in addition to the oxide layer 150 during the etching of the watch components 90 during the step illustrated in the figure 2g Subsequently, before protecting the surfaces of the watch components' flanks, a directional selective plasma etching, specifically of the DRIE or ICP-RIE type (as described above), is performed at the stage of the figure 2h in order to remove, or at least reduce in thickness, the parts of the buried oxide layer 40 located below the regions 35. As indicated above, this directional selective plasma etching step is advantageously carried out without a mask, and in particular without a protective mask.

[0040] Since the etching at this stage is directional and primarily attacks silicon oxide, a protective layer on the flank surfaces of the watch components is not necessary. Alternatively, if a DRIE etch using a fluorinated gas such as C4F8 was employed in the step of the figure 2g A fluoropolymer layer typically forms on the surfaces of the lateral flanks 95, and this fluoropolymer layer can be retained to serve as a protective layer for these flanks during the directional etching of the figure 2h .

[0041] Since the resin layer 60 is always present during this directional etching step, the oxide layer 150 on the upper surface of the structured working layer 30' is generally not etched during the directional etching. According to this embodiment, the remaining portion of the resin layer 60 is removed after this directional etching step, as illustrated in the figure 2i Next, a thermal oxidation step is carried out at the figure 2j to form a silicon dioxide (SiO2) oxide layer 55 on all exposed silicon surfaces of the wafer 10, including the bottom of the regions 35 and on the flank surfaces 95 of the watch component 90. If present, the fluoropolymer layer on the flank surfaces can be removed before this thermal oxidation step. The oxide layer 150 on the upper surface of the structured working layer 30' can also become slightly thicker during this thermal oxidation step. The thickness of the oxide layer 55 can vary but is preferably between 0.05 and 1 µm. As in the first embodiment, the oxide layer 55 can be formed by a method other than thermal oxidation in the step of figure 2j , for example by ALD or CVD filing.

[0042] The oxide layer 55 at the bottom of the regions 35 is subsequently removed during a second directional selective plasma etching step in the figure 2k Advantageously, this directional selective plasma etching step is still performed without a mask, and in particular without a protective mask, and it can be a DRIE or ICP-RIE type etch (as described above). The thickness of the oxide layer 55 located below the regions 35 that must be removed during this second directional selective plasma etching step is generally less than the oxide below these regions in the embodiment of the figure 1 As illustrated, the oxide layer 150 on the upper surface of the structured working layer 30' is partially etched during the directional etching step of the figure 2j but a reduced-thickness 150' oxide layer is still present at the end of this second directional selective plasma etching step. By ensuring that the 55' thickness of the oxide layer formed in the step of the figure 2j is less important than the thickness of the oxide layer 150 formed in the step of the figure 2b , this reduced-thickness 150' silicon oxide layer will still be present on the upper surface of the structured working layer (30') after the second directional selective plasma etching step.

[0043] Subsequently, the manufacturing process according to this second embodiment can continue by carrying out the steps described above in connection with the figures 1k-1m of the first embodiment which will not be repeated here.

[0044] According to a third embodiment, which is a variant of the second embodiment, instead of the steps of figures 2h-2k and of the two directional selective plasma etching steps described above, a single directional selective plasma etching step can be performed as illustrated in the steps of figures 3h et 3i using a protective layer 155 that is not formed by thermal oxidation. More specifically, the blanks of the watch components 90 are formed as described above in connection with the figures 2a - 2g , and always keeping the remaining part of the 60 resin layer to protect the 150 oxide layer on the upper surface of the 30 structured working layer.

[0045] In this variant, at the step of the figure 3h A protective layer 155 of silicon dioxide (SiO2) or another material (e.g., a resin, a polymer, or another oxide such as Al2O3) is formed on the flank surfaces 95 of the watch components. For example, this layer 155 can be formed by selective deposition using a technique based on ALD, PVD (physical vapor deposition), or sol-gel. Forming the protective layer 155 by thermal oxidation is not suitable at this stage, as the resin 60 would burn due to the associated high temperatures. With the remaining portion of the resin layer 60 still protecting the oxide layer 150 on the upper surface of the structured working layer 30', a directional selective plasma etching step is performed. figure 3i (still without using a protective mask). This directional etching can still be of the DRIE or ICP-RIE type, and it removes the portions of the oxide layer 40 located at the bottom of the regions 35. The oxide layer 150 is generally not etched during this directional etching, as it is protected by the resin layer 60. Subsequently, the remaining portion of the resin layer 60 can be removed, and the manufacturing process can proceed according to the embodiment of the figure 3 can continue by carrying out the steps described above in connection with the figures 1k-1m of the first embodiment, with layer 155 protecting the surfaces of the flanks 95 of the watch components.

[0046] After the manufacturing steps according to one of the embodiments described above, the watch components 90 are released onto the SOI plate, allowing the subsequent manufacturing steps, as described below, to be carried out over almost the entire external surface of these components. To this end, after release, the watch components 90 are structurally supported only by connecting bridges (schematically illustrated by line 32 in the figure 1m (In reality, the bridge extends across the entire thickness of the component) in the structured working layer 30'. In this way, the components 90 remain attached to the remaining parts of the structured working layer 30'. This is illustrated in the figure 4 which is a top view of the SOI 10 plate and in particular of the structured 30' working layer after the manufacturing steps of figures 1a-1m according to one embodiment. Note that in the figure 4 The 90 watch components are located in areas of the layer that are simply illustrated by empty circles so as not to clutter the drawing, but the figure 4A gives a magnified view of one of these areas, showing as an example a spiral as the watch component and its connecting bridge 32. figure 5 is also a sectional view along the VV line of the figure 4 showing a cavity 24 releasing each of the 90 watch components from below. Despite this release, the structured working layer 30' is still supported by the excavated support layer 20' of the SOI wafer, these two layers being bonded together by means of the remaining portions 42, 44 of the structured buried oxide layer 40". As illustrated in the figure 5 , the remaining parts 44 located at the periphery of the plate 10 preferably have a greater width than the remaining parts 42 located between the watch components 90.

[0047] In the above embodiments, each watch component 90 of the wafer has its own cavity 24, or even a cavity 24 dedicated to that component which extends only below that component. According to another embodiment, a single cavity 24 can extend below several components of the wafer, the structured buried oxide layer 40" not having any remaining portions 42 between components located above the same cavity. It is even possible to have a single cavity 24 which extends below all the components of the wafer, and in this case only the remaining peripheral portions 44 of the structured buried oxide layer 40" maintain the bond between the structured working layer 30' and the excavated support layer 20'.

[0048] After the etching stage of the working layer to form the 90 watch components (see the figure 1h Or 2g), it is known that the surfaces of the flanks 95 of the structured patterns of the components 90 possess a relatively high roughness. In the context of a DRIE-type etching, this roughness manifests itself in the form of a surface 95' with undulations often called "scallops" with peaks 96 as illustrated on the left side of the figure 1h (Or 2gIn fact, during DRIE etching, a silicon etching phase alternates with a passivation phase, resulting in the wavy surface 95'. After DRIE etching or another type of etching, the surface roughness of the flanks 95 can be reduced by a smoothing step, which mechanically strengthens these surfaces by limiting the initiation of fractures. This smoothing can be achieved, in particular, by a thermal oxidation step followed by a deoxidation step, consisting, for example, of wet or vapor etching, for example, using hydrofluoric acid (HF) or anhydrous HF gas. As is known, during thermal oxidation, the silicon on the surface of the flanks 95 is consumed, and this consumption is generally faster towards the peaks 96, resulting in a smoother silicon surface after deoxidation.

[0049] As mentioned above, preferably at the stage of the figure 1i (Or 2j) The oxide layer 55 is formed on the flank surfaces 95 of component 90 by thermal oxidation. This allows, unlike prior art manufacturing processes where smoothing is carried out after the release of the watch components 90, for smoothing of the flanks of the watch components during release. More precisely, during the deoxidation step at the figure 1m , not only is the liberation of the watch components 90 in the SOI wafer achieved, but at the same time the surfaces of the flanks 95 of these components on the wafer 10 are smoothed. By achieving the smoothing and liberation with a single deoxidation step according to this embodiment of the present invention, the number of steps in the manufacturing process of the watch components 90 in the SOI wafer is favorably reduced.

[0050] After the release of the watch components 90 as described above, another thermal oxidation step followed by a deoxidation step can be performed to achieve smoothing at least once more, if desired. Other manufacturing steps subsequent to smoothing and release can also be carried out. For example, another oxidation step followed by deoxidation can be performed to adjust the dimensions of the components, or a permanent silicon oxide (SiO2) layer can be formed on at least part of the external surface of the watch components 90. In the context of a balance spring or other type of watch resonator, such a permanent oxide layer compensates for variations in the Young's modulus of the silicon balance spring core of the watch component as a function of temperature.Furthermore, the formation of such an outer layer of silicon oxide on watch components of any type can also serve to mechanically strengthen these components. Other types of materials can also be formed on watch components 90, for example by an ALD-type coating. It is also possible to perform a pre-assembly or machining step on the watch components 90 while they are still attached to the plate 10, for example to assemble the component to a shaft, stud, pin, or ferrule.

[0051] The various oxidation steps mentioned above can be carried out by placing the wafer 10 in a furnace at a temperature between 800°C and 1200°C and in an oxidizing atmosphere including, for example, water vapor or dioxygen gas (O2). The thickness of the oxide layer formed depends, as is known, on the duration of the oxidation step.

[0052] Once the manufacturing steps of the watch components 90 on the plate 10 are completed, the watch components can be individually detached (in particular by breaking the bridges 32) and subsequently assembled and mounted each in a watch part, for example in an oscillator or in an escapement mechanism of a mechanical watch movement.

[0053] The present invention is not limited to the embodiments and variations shown, and other embodiments and variations will be obvious to those skilled in the art. Thus, the above embodiments are examples. Although the description refers to one or more embodiments and their variations, 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. Simple features of different embodiments and their variations can also be combined and / or interchanged to provide other embodiments.

Claims

1. A method for manufacturing, in an SOI-type wafer (10), a plurality of watch components (90) having flanks (95) having surfaces, the SOI wafer (10) comprising a silicon support layer (20), a silicon working layer (30), and an embedded silicon oxide oxide layer (40) having a thickness (e 40) and separating the support layer (20) from the working layer (30), the process comprising the following steps: (a) forming a structured silicon oxide layer (50, 150) on the upper surface of the working layer (30); (b) forming the watch components (90) by engraving, through the structured silicon oxide layer (50, 150), patterns in the working layer (30) to obtain a structured working layer (30'), the structured working layer (30') comprising removed regions (35) around the engraved patterns in which the material of the working layer has been removed to expose the buried oxide layer (40) below; (c) forming a protective layer (55, 155) at least on the flank surfaces (95) of the watch components engraved in step (b);(d) either after or before step (c), perform a directional etch, without using a mask, of the buried oxide layer (40) to the point where regions (45) of the buried oxide layer (40) lying below the removed regions (35) of the working layer are removed in order to obtain a perforated buried oxide layer (40'), the structured silicon oxide layer (50', 150) still being present on the upper surface of the structured working layer (30') after this step; (e) perform a silicon etch in the support layer (20) through the removed regions (45) of the perforated buried oxide layer (40'), in order to obtain an excavated support layer (20') having at least one cavity (24) formed below at least one of the watch components (90);and (f) eliminate the remaining portions of the buried oxide layer (40) between said at least one cavity (24) and said at least one watch component (90) arranged above said cavity (24), in order to obtain a structured buried oxide layer (40") having remaining portions (42, 44) still linking the excavated support layer (20') to the structured working layer (30').

2. Method according to the preceding claim, wherein step (f) also includes the removal of the structured silicon oxide layer (50', 150) on the upper surface of the structured working layer (30').

3. A method according to any one of the preceding claims, wherein the formation of the structured silicon oxide layer (50, 150) in step (a) comprises: the formation of an unstructured silicon oxide layer on the upper surface of the working layer (30), the formation of a resin layer (60) on the unstructured silicon oxide layer, the removal of a portion of the resin layer (60), and the structuring of the structured silicon oxide layer (50, 150) through the remaining portion of the resin layer (60).

4. A method according to the preceding claim, wherein the formation of the protective layer (55) in step (c) is carried out by thermal oxidation, the protective layer (55) being made of silicon oxide and also forming on exposed silicon surfaces of the support layer (20), and the remaining part of the resin layer (60) being removed before said formation of the protective layer (55) by thermal oxidation.

5. A method according to any one of claims 3 or 4, wherein the following are carried out: - before the formation of the protective layer (55) in step (c), a first directional etching step, without using a mask, of the buried oxide layer (40) located below the removed regions (35) of the working layer, the remaining part of the resin layer (60) still being present on the structured silicon oxide layer (150) during this first directional etching step; and - after the formation of the protective layer (55) in step (c), a second directional etching step, without using a mask, of the silicon oxide (40, 55) located below the removed regions (35) of the working layer.

6. A method according to any one of claims 1 to 4, wherein the structured silicon oxide layer (50) formed in step (a) has a thickness (e 50 ) greater than the thickness (e 40) of the buried oxide layer (40), in step (d) the structured silicon oxide layer (50) is also etched onto the upper surface of the structured working layer (30'), and a thinned structured silicon oxide layer (50') is still present on the upper surface of the structured working layer (30') after the etching of this step (d).

7. A method according to any one of claims 1 to 4 or 6, wherein the formation of the protective layer (55) in step (c) is carried out before the directional etching in step (d).

8. A method according to any one of the preceding claims, wherein the directional engraving of step (d) is a DRIE or ICP-RIE type engraving.

9. A method according to the preceding claim, wherein the directional etching of step (d) uses at least one fluorinated gas such as CHF3, C4F8, and / or SF6 in combination with at least one of the gases He and / or H2.

10. A method according to any one of the preceding claims, wherein the etching of the support layer (20) in step (e) comprises an anisotropic etching.

11. A method according to any one of claims 1 to 10, wherein the etching of the support layer (20) in step (e) comprises an isotropic etching.

12. A method according to the preceding claim, wherein the etching in step (e) is a vapor-phase etching based on xenon difluoride (XeF2).

13. Method according to claim 11, wherein the etching in step (e) uses a sulfur hexafluoride (SF6) based plasma.

14. A method according to any one of the preceding claims, wherein each watch component (90) of the SOI plate (10) has its own cavity (24) which extends only below that watch component (90).

15. A method according to any one of the preceding claims, wherein a maximum thickness of each cavity (e cav) is at most equal to 50% of the thickness (e 20 ) of the support layer (20), and preferably not more than 25% of the thickness (e 20 ) of the support layer (20).

16. A method according to any one of the preceding claims, wherein step (b) of forming the watch components (90) is carried out by a DRIE type engraving technique.

17. Method according to the preceding claim, wherein during the DRIE type engraving carried out in step (b) a fluoropolymer layer forms on the surfaces of the flanks (95) of the engraved watch components, and the protective layer of step (c) comprises this fluoropolymer layer.

18. A method according to any one of the preceding claims, the method comprising, after step (f), a thermal oxidation step followed by a deoxidation step to smooth the watch components (90) or to adjust the dimensions of the watch components and / or a step to form a permanent silicon oxide layer on at least a part of the external surface of the watch components (90).

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