Method for manufacturing silicon timepiece components

Abstract

The invention relates to a method for manufacturing a plurality of timepiece components (90) in an SOI-type manufacturing wafer (10), the method comprising the steps of: (a) forming the timepiece components (90) by etching patterns in a working layer (30) of the SOI wafer in order to obtain a structured working layer (30') and removed regions (130) of the working layer around the etched patterns in which the material of the working layer has been removed to expose the buried oxide layer (40) of the SOI wafer below; (b) optionally forming a silicon oxide layer (55) at least on the sidewall surfaces (95) of the timepiece components etched in step (a); (c) depositing a layer of masking material (160) at least on the structured working layer (30') and on the exposed portions of a buried oxide layer (40); (d) structuring the masking material (160) by removing at least a portion of the masking material deposited on the buried oxide layer (40); (e) removing the portions of the buried oxide layer (40) located below the resin removed in step (d) in order to obtain a perforated buried oxide layer (40') and removed regions (140) of the buried oxide layer (40) in which the material of the buried layer has been removed to expose the support layer (20) of the SOI wafer below; (f) etching the silicon in the support layer (20) through the removed regions (140) of the perforated buried oxide layer (40') in order to obtain an excavated support layer (20') having at least one cavity (125) formed below at least one timepiece component (90); and (g) removing the portions of the buried oxide layer (40) that remain between the at least one cavity (125) and the at least one timepiece component (90) arranged above the cavity (125) in order to obtain a structured buried oxide layer (40'') having remaining portions (42, 44) that still connect the excavated support layer (20') to the structured working layer (30').

Description

Manufacturing process for silicon watch components Domain EU

[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 etching of the layers of the wafer as well as manufacturing steps subsequent to the etching including the release of the components. State of the art

[0002] The manufacture of silicon watch components such as, but not limited to, hairsprings, cams, springs, pawls, 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 watch components 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. In addition, variations in the Young's modulus of a silicon watch component as a function of temperature can be compensated by adding a layer of SiOz oxide to the component. 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 (Dual Side Polished) wafers. 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 oxide layer of SiO? that is 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.

[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 bonding bridges that keep them attached to the remaining parts of the working layer, which notably allows the subsequent manufacturing steps to be carried out on the entire external surface of the components of the wafer. The subsequent steps may notably include oxidation and deoxidation steps for smoothing the surfaces of the components.Subsequent steps may also include oxidation and deoxidation steps to adjust 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 onto an SOI wafer can be achieved by various methods. One release approach is described in patent documents JP2017219520 and W02019180177. According to this approach, after the formation of the components by etching, a layer of oxide is grown. silicon on the surface of the silicon. This oxide layer serves as protection for the formed components. Subsequently, photolithography and etching are performed to expose the silicon of the support layer and etch the support layer by etching it from the side opposite the components, which removes the support layer below the components. To complete the release using this alternative, the buried layer of the SOI wafer below the components is removed as well as the protection layer on the components. This release approach is relatively time-consuming and expensive, as it requires patterning (or even photolithography and etching) through the thick support layer of the SOI wafer.

[0007] According to another approach 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 facilitated 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 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.

[0008] It would then be advantageous to have a method for manufacturing silicon watch components comprising component release steps that are shorter, more efficient and that allow the structural benefit of the support layer to be retained for subsequent manufacturing steps that take place on the components of the SOI wafer after their release. Furthermore, generally speaking, the manufacturing of silicon watch components comprises a significant number of steps, and it would then also be desirable to have a method for manufacturing such components having a reduced number of steps. Brief summary of the invention

[0009] An 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 drawbacks, or in any case to offer a better compromise between these drawbacks.

[0010] In particular, this aim is at least partially achieved by proposing a new method for manufacturing silicon watch components according to which the components are released without a long and costly etching of the support layer of the SOI wafer and according to which the structural benefit of the support layer can be retained for subsequent manufacturing steps carried out on the components of the SOI wafer after their release. Thus, according to one aspect, the present invention relates to a method for manufacturing a plurality of watch components having flank surfaces (or even lateral surfaces of the watch components, i.e. the surfaces of the watch components which are generally normal to the general plane of the wafer) in an SOI type manufacturing wafer, the SOI wafer comprising a silicon support layer, a silicon working layer,and a buried oxide layer of silicon oxide separating the support layer from the working layer, the method comprising the following steps: (a) forming the watch components by etching patterns in the working layer to obtain a structured working layer and regions removed from the working layer around the etched patterns (or even around the structure of the watch components), in which the material of the working layer has been removed to expose the buried oxide layer below; (b) optionally, forming a layer of silicon oxide on at least part, and preferably all,the flank surfaces of the watch components etched in step (a); (c) depositing a layer of mask material at least on the structured working layer and on the exposed parts of the buried oxide layer (and preferably also on the flank surfaces); (d) structuring the mask material by removing at least part of the mask material deposited on the buried oxide layer; (e) removing parts of the buried oxide layer lying below the mask material removed in step (d), in order to obtain an openwork buried oxide layer and removed regions of the buried oxide layer in which the material of the buried layer has been removed to expose the support layer below; (f) etching the, silicon in the support layer through the removed regions of the openwork buried oxide layer, in order to obtain an excavated support layer having at least one cavity formed below at least one, and preferably below each, watch component; and (g) removing the parts of the buried oxide layer remaining between said at least one, and preferably between each, cavity and said at least one, and preferably the watch component(s) arranged above said cavity, in order to obtain a structured buried oxide layer having remaining parts still bonding the excavated support layer to the structured working layer.

[0011] In one embodiment, the deoxidation of the SOI wafer - or even the elimination of the oxide layers on the SOI wafer - in step (g) makes it possible to achieve both the release of the watch components in the SOI wafer and a smoothing of the etched flank surfaces of these components.

[0012] Other advantageous and preferred characteristics of the manufacturing method are specified in the description and sub-claims below. Brief description of the figures

[0013] Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which: • Figures 1a-1q schematically illustrate a series of steps in manufacturing a silicon watch component in an SOI wafer according to one embodiment; Figures 2 and 2A are top views of the working layer of an SOI wafer after the steps of Figure 1 according to one embodiment; and Figure 3 is a sectional view along line III-III of Figure 2. embodiments 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] Figures 1a-1q illustrate a series of schematic manufacturing steps of 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 at the same time, but the views in Figure 1 are isolated on a single component for simplicity. The method begins with an SOI 10 wafer illustrated in Figure 1a, this SOI 10 wafer comprising a support layer 20 made of silicon, a working layer 30 made of silicon, and a buried oxide layer 40 separating the two silicon layers 20, 30 which is in particular made of silicon oxide (SiOz). The drawing is not to scale, but as an example, the support layer 20 may have a thickness of 500 pm, the working layer 30 may have a thickness of 120 pm, and the buried oxide layer 40 may have a thickness of 2 pm.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.

[0016] In Figure 1b, a lithography step begins with the formation of a silicon oxide layer 50 on the upper surface of the working layer 30. By “lithography” is meant all the operations making it possible to transfer an image or a pattern on or above the SOI 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 forms only on the upper surface of the support layer 20, as illustrated in FIG. 1b. Alternatively, if the oxide layer 50 is formed by thermal oxidation, it is noted that the oxide 50 can generally form at the same time on the surface of the support layer 20 (if the latter is not covered by a resist mask) or a second directional CVD or PVD type deposition can be carried out on the surface of the support layer 20. Generally speaking, the formation of the oxide layer 50 before the deposition of a resin layer (see FIG. 1c) 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 working layer 30.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.

[0017] In 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 may have a thickness of between 0.5 - 12 μm, purely for illustrative purposes. Subsequently, in Figure 1d, 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.

[0018] In Figure 1c, 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 1f, 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 working layer 30, 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 hydrofluoric acid (HF) vapor etching can also be used.

[0019] In the step illustrated in Figure 1g, the remaining portion of the resin layer 60 is removed and then, in the step of Figure 1h, patterns are etched into the working layer 30 through the structured layer 50 to form the timepiece component 90. In general, the etched patterns extend over 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 etching. In this way, the thickness of the timepiece 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 130 located around the structure of the component in which the material of the working layer 30 has been removed, thus exposing portions of the buried oxide layer 40 below these removed regions 130.

[0020] The etching in step 1h can be performed using a deep reactive ion etching (DRIE) technique. DRIE allows for machining deep holes and trenches in layer 30 with a high aspect ratio, which is well suited for micromechanical components such as watch components. Alternatively, the structuring of the support layer can be performed using other etching technologies such as an anisotropic wet / chemical etching operation, for example using a potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) bath. Structuring by 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 employed, the oxide layer 50 is normally not formed on the upper surface of the support layer 20 until the resist 60 is deposited on that surface.

[0021] It is also possible for the remaining part of the resin layer 60 to still be present during the etching step (DRIE or other) of the working layer 30. This remaining part of the resin layer can be removed after etching, and in this case the working layer 30 is etched through the two layers 50, 60 structured (or only through the structured 60 layer if an oxide 50 layer is not present). For example, a positive resist can be removed by solvents such as acetone or dimethyl sulfoxide (DMSO) or with an O2 plasma either before or after the etching step. For a negative resist such as SU-8, a CF4 / O2 plasma can be used for its removal.

[0022] Figures 11-12 illustrate the approach for releasing the watch components 90 according to one embodiment of the invention. In Figure 11, a silicon oxide layer 55 (SiC>2) is preferably formed on the flank surfaces 95 of the watch component and preferably on all of its flank surfaces. The oxide layer 55 can be formed by PVD, CVD, or ALD type deposition, but preferably it is formed by thermal oxidation. The oxide layer 55 is also formed on all the exposed silicon of the SOI wafer 10 including the support layer 20 as illustrated. The thickness of this oxide layer 55 can vary but preferably it is at least 0.05 μm. Furthermore, the oxide layer 55 joins the oxide layers 50 and 40 already present on the upper and lower surfaces of the component 90, and these latter layers can also become thicker if the deposition of this step is carried out by thermal oxidation.According to a variant, the oxide layer 50 can be removed after the etching step in figure 1h, and in this case the oxide layer 55 is also formed on the upper surface of the watch components 90 during the step in figure 11.

[0023] In the next step of Figure 1j, the exposed portions of the buried oxide layer 40 and the structured working layer 30' (which is already covered by the oxide layers 50, 55) are covered with a mask material, which is preferably a resist layer 160 but may alternatively comprise another material at least highly selective for the etchant such as a metal (e.g., aluminum, nickel, chromium, or platinum), an oxide (MgO, ZnO, TiCh, ZrCh, or AI2O3), or a nitride (AIN or SisN4). The resist 160 is preferably a positive-type photosensitive resist, and it may have a thickness of between 0.5 - 6 pm, for illustrative purposes. The deposition of the resin 160 is preferably carried out by spray coating but it can also be carried out by dip coating, spin coating, or vacuum deposition with powder.Alternatively, the formation of the oxide 55 in step 11 may also be. removed, and the resin 160 can be deposited directly on the structured working layer 30' (with or without the oxide layer 50) which results after the step of figure 1h.

[0024] Subsequently, in Figure 1k, the resin layer 160 is structured, preferably using a photolithography step with an ultraviolet light source 80 as well as, for example, an exposure mask 170 such as a photomask. A stepper and reticle system may also be used for the photolithography step or a direct writing system. In the illustrated example, the layer 160 comprises a positive-type photosensitive resin of which the portions 160E of the resin that are exposed to light become soluble in a developer and the unexposed portions remain insoluble. According to other embodiments, the resin may be structured by a laser or electron beam.

[0025] As illustrated in FIG. 1k, the exposed portions 160E of the resin 160 are located on the buried oxide layer 40 in the removed regions 130 of the structured working layer 30' between the structures of the timepiece component 90. Preferably, the exposed portions 160E of the resin 160 on the buried oxide layer 40 are located towards the middle of the removed regions 130 but do not extend towards the edges of these regions near the flank surfaces 95 of the timepiece components 90 in order to avoid shrinkage of the resin on these flank surfaces.

[0026] In Figure 11, the resist layer 160 is opened (or even structured) after being developed by a developer, in particular a solvent, which removes the exposed portions 160E of the resist on the buried oxide layer 40 by chemical means. Then, in Figure 1m, the portions of the buried oxide layer 40 which were below the exposed portions 160E of the resist are also removed from the upper surface of the support layer 20 of the SOI wafer 10, for example by using wet etching or hydrofluoric acid (HF) vapor etching. Alternatively, DRIE etching of the silicon oxide layer may be employed, and according to yet another alternative selective plasma etching, for example with CH4 / O2 or C4Fs / He / H2 gases, may be used to etch the buried oxide layer 40. After this step, an openwork buried oxide layer 40' is obtained with regions 140 in which the oxide of the buried layer has been removed, thereby exposing the support layer 20 below these removed regions 140.

[0027] The upper surface of the support layer 20 now being exposed below these eliminated regions 140, in the step of FIG. 1n (where three variants are presented) a step of etching the silicon of this layer is started to excavate a portion of the layer below the watch components 90. Three variants are illustrated in FIGS. 1ni, 1nii, and 1niii which respectively show etched regions 120i, 120ii, 120iii of the support layer below the eliminated regions 140. Preferably, anisotropic wet / chemical etching is used at this step, as in FIGS. 1ni and 1nii. Anisotropic etching makes it possible to remove silicon more quickly in the horizontal direction than in the vertical direction (in the direction of the figure) in each etched region 120i, 120ii of the support layer below the eliminated regions 140.The etched flank surfaces therefore form an angle as conceptually illustrated in the block diagram of Figure 11i with etched regions 120i, and in general this angle varies depending on different parameters including in particular the crystalline orientation of the silicon. Preferably, the anisotropic wet etching of this step uses a potassium hydroxide (KOH) bath where the etched regions 120ii of the support layer generally have the shape illustrated in Figure 11i. Alternatively, for example, a tetramethylammonium hydroxide (TMAH) bath can also be used for anisotropic wet etching.

[0028] A variant of the step of etching the silicon of the support layer below these eliminated regions 140 is illustrated in FIG. 1niii. According to this variant, an isotropic etching technique is used to attack the silicon of the support layer, for example a plasma etching based on xenon difluoride (XeF?). Such an isotropic etching removes the silicon more or less uniformly in all directions, thus creating etched regions 120iii of the support layer having the shape of semicircles below the eliminated regions 140.

[0029] Preferably, the etching step of Figure 1n continues so that the etched regions 120 in which the silicon of the support layer has been removed unite to form a cavity 125 extending below each watch component 90 as illustrated in Figure 10. A support layer is thus obtained excavated 20' comprising these cavities 125 on its upper surface. If the etching (anisotropic or isotropic) of the support layer is not strictly controlled, the cavities 125 typically do not have a uniform thickness, but preferably the maximum thickness of each cavity e cav is at most equal to 50% of the thickness e?o of the support layer, and it is even more preferred that the maximum thickness of each cavity e cav is at most equal to 25% of the thickness e?o of the support layer.

[0030] Since, in step 11, the oxide layer 55 has also been formed on the exposed silicon surfaces of the support layer 20, the etching attacks this layer only through the eliminated regions 140 of the perforated buried oxide layer 40', the other surfaces of the support layer 20 being protected by the oxide layer 55.

[0031] In the step illustrated in FIG. 1p, the remaining portion of the resin layer 160 is removed. Finally, to complete the release of the watch components, a deoxidation step is carried out in FIG. 1q, which removes the oxide layers 50 and 55 as well as the portions of the buried oxide layer 40 remaining between each cavity 125 and the watch component(s) 90 above this cavity. This deoxidation step can be carried out, for example, by wet etching or vapor phase etching based on hydrofluoric acid (HF). We therefore obtain a structured buried oxide layer 40'' of which a significant part of the layer has been eliminated, but which includes parts 42, 44 (see figure 3) still present outside the zones of the watch components 90. These remaining parts 42, 44 of the structured buried oxide layer 40'' maintain the connection between the structured working layer 30' and the excavated support layer 20'.

[0032] The watch components 90 are then released onto the SOI wafer allowing the subsequent manufacturing steps to be carried out, as will be described below, 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 (illustrated schematically by the line 35 in FIG. 1q; in reality the bridge extends over 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 FIG. 2 which is a top view of the SOI wafer 10 and in particular of the structured working layer 30' after the manufacturing steps of figures 1a-1q according to one embodiment. Note that in figure 2 the watch components 90 are located in areas of the layer which are simply illustrated by empty circles in order not to clutter the drawing, but figure 2A gives a magnified view of one of these areas showing as an example a hairspring like the watch component and its connecting bridge 35. Figure 3 is also a sectional view along line III-III of figure 2 showing a cavity 125 releasing each of the watch components 90 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 linked together by means of the remaining parts 42, 44 of the structured buried oxide layer 40''.As illustrated in Figures 2 and 3, 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.

[0033] In the above embodiment, each watch component 90 of the wafer has its own cavity 125, or even a cavity 125 dedicated to this component which extends only below this component. According to another embodiment, a single cavity 125 can extend below several components of the wafer, the structured buried oxide layer 40'' not having remaining parts 42 between the components located above the same cavity. It is even possible to have a single cavity 125 which extends below all the components of the wafer, and in this case it is only peripheral remaining parts 44 of the structured buried oxide layer 40'' which maintain the connection between the structured working layer 30' and the excavated support layer 20'.

[0034] After the step of etching the working layer to form the watch components 90 (see figure 1h), it is known that the flank surfaces 95 of the structured patterns of the components 90 have a relatively significant roughness. In the context of DRIE type etching, this roughness manifests itself in the form of a surface 95' with undulations often called "scallops" with peaks 96 as illustrated in the left part of figure 1h. In fact, during DRIE etching, a silicon etching phase alternates between a silicon etching phase and a passivation phase, which results in the undulated surface 95'. After DRIE etching or another type of etching, the roughness of the surfaces 95 can be reduced by a smoothing step, which reinforces these surfaces mechanically by limiting the initiation of fractures. This smoothing can in particular be carried out by a thermal oxidation step followed by a deoxidation step, consisting for example of wet etching or vapor phase etching based on hydrofluoric acid (HF). As is known, during thermal oxidation, the silicon at the surface 95 is consumed, and this consumption is generally faster towards the peaks 96, which results in a smoother silicon surface after deoxidation.

[0035] As mentioned above, the formation of the oxide 55 on the flank surfaces 95 of the component 90 in the step of FIG. 11 is preferably carried out by thermal oxidation. This makes it possible, unlike the manufacturing methods of the prior art where the smoothing is carried out after the release of the watch components 90, to carry out a smoothing of the flanks of the watch components during the release. More precisely, during the deoxidation step in FIG. 1q, not only the release of the watch components 90 in the SOI wafer is carried out but at the same time a smoothing of the flank surfaces 95 of these components on the wafer 10 is carried out. By carrying out the smoothing and the release with a single deoxidation step according to this embodiment of the present invention, the number of steps in the method of manufacturing the watch components 90 in the SOI wafer is favorably reduced.

[0036] After the release of the timepiece components 90, if desired, another thermal oxidation step followed by a deoxidation step may be performed to smooth at least once more. Other manufacturing steps subsequent to smoothing and release may also be performed. For example, another oxidation step may be performed followed by deoxidation to adjust the dimensions of the components, or a permanent silicon oxide (SiOz) layer may be formed on at least a portion of the entire outer surface of the timepiece components 90. In the context of a hairspring or other type of timepiece resonator, such a permanent oxide layer compensates for variations in the Young's modulus of the silicon core of the timepiece 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 mechanically strengthen these components. Other types of materials can also be formed on the watch components 90, for example by an ALD type deposition. It is also possible to carry out a pre-assembly or machining step of the. watch components 90 when they are still attached to the SOI 10 wafer, such as for example to assemble the component to an axis, a tigeron, a stud or a collet.

[0037] The various oxidation steps mentioned above can be carried out by placing the SOI wafer in an oven at a temperature between 800°C and 1200°C and in an oxidizing atmosphere comprising, for example, water vapor or dioxygen gas (O2). The thickness of the oxide layer formed depends in a known manner on the duration of the oxidation step.

[0038] Once the steps of manufacturing the watch components 90 on the SOI wafer 10 are completed, the watch components can be detached individually and subsequently assembled and mounted each in a timepiece, for example in an oscillator or in an escapement mechanism of a mechanical watch movement.

[0039] 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. Method for manufacturing a plurality of watch components (90) having flank surfaces (95) in an SOI type manufacturing wafer (10), the SOI wafer (10) comprising a support layer (20) made of silicon, a working layer (30) made of silicon, and a buried oxide layer (40) made of silicon oxide separating the support layer (20) from the working layer (30), the method comprising the following steps: (a) forming the timepiece components (90) by etching patterns into the working layer (30) to provide a structured working layer (30') and removed regions (130) of the working layer (30) around the etched patterns in which the working layer material has been removed to expose the buried oxide layer (40) below; (b) optionally, forming a layer of silicon oxide (55) at least on the flank surfaces (95) of the watch components engraved in step (a); (c) depositing a layer of a mask material (160) at least on the structured working layer (30') and on the exposed portions of the buried oxide layer (40); (d) structuring the mask material (160) by removing at least a portion of the mask material deposited on the buried oxide layer (40); (e) removing portions of the buried oxide layer (40) lying below the mask material removed in step (d), to obtain an openwork buried oxide layer (40') and removed regions (140) of the buried oxide layer (40), in which the material of the buried layer (40) has been removed to expose the support layer (20) thereunder; (f) etching the silicon in the support layer (20) through the eliminated regions (140) of the perforated buried oxide layer (40'), in order to obtain an excavated support layer (20') having at least a cavity (125) formed below at least one watch component (90); and (g) removing the parts of the buried oxide layer (40) remaining between said at least one cavity (125) and said at least one watch component (90) arranged above said cavity (125), in order to obtain a structured buried oxide layer (40'') having remaining parts (42, 44) still bonding the excavated support layer (20') to the structured working layer (30').

2. Method according to the preceding claim, in which step (a) of forming the watch components (90) is carried out by a deep reactive ion etching technique.

3. Method according to one of the preceding claims, in which step (a) of forming the watch components (90) comprises the formation of a structured oxide layer (50) on the upper surface of the working layer (30) before etching the patterns in the working layer (30), and in which step (g) also comprises the removal of the structured oxide layer (50) on the upper surface of the watch components (90).

4. Method according to one of the preceding claims, in which step (b) is carried out.

5. The method of claim 4, wherein step (b) also comprises forming a silicon oxide layer (55) on the support layer (20).

6. Method according to one of claims 4 or 5, in which the formation of the silicon oxide layer (55) in step (b) is carried out by thermal oxidation.

7. Method according to claim 6, in which the removal of the oxide layers in step (g) makes it possible to smooth the flank surfaces (95) of the watch components (90) and to release the watch components (90) in the SOI wafer (10), the released watch components (90) being structurally supported only by bonding bridges (35) in the structured working layer (30').

8. Method according to one of the preceding claims, in which the mask material (160) deposited in step (c) is a resin, preferably a positive-type photosensitive resin.

9. Method according to one of the preceding claims, wherein the deposition of the mask material (160) in step (c) is carried out by sputter coating.

10. Method according to one of the preceding claims, wherein step (d) comprises a step of removing the mask material (160) on the buried oxide layer (40) towards the middle of the removed regions (130) of the working layer (30) without removing the mask material (160) on the buried oxide layer (40) towards the edges of said removed regions (130) near the flank surfaces (95) of the watch components.

11. Method according to one of the preceding claims, in which said parts of the buried oxide layer (40) are removed in step (e) by wet etching or etching based on hydrofluoric acid (HF) vapor.

12. Method according to one of the preceding claims, in which said parts of the buried oxide layer (40) are removed in step (e) by DRIE etching.

13. Method according to one of the preceding claims, in which the etching in step (f) is an anisotropic etching.

14. Method according to the preceding claim, in which the anisotropic etching in step (f) uses a potassium hydroxide (KOH) bath or a tetramethylammonium hydroxide (TMAH) bath.

15. Method according to one of claims 1 to 12, in which the etching in step (f) is an isotropic etching.

16. Method according to the preceding claim, in which the isotropic etching in step (f) is a plasma etching based on xenon difluoride (XeFz).

1. Method according to one of the preceding claims, in which step (g) is carried out by wet or vapor phase etching based on hydrofluoric acid (HF).

18. Method according to one of the preceding claims, in which each watch component (90) of the SOI wafer (10) has its own cavity (125) which extends only below this watch component (90).

19. Method according to one of the preceding claims, in which the maximum thickness of each cavity (e cav ) is at most equal to 50% of the thickness (ezo) of the support layer (20), and preferably at most equal to 25% of the thickness (ezo) of the support layer (20).

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