Method for manufacturing a timepiece component

Abstract

The present invention relates to a method for manufacturing a watch component, in which a useful layer (10) of silicon is etched on at least one main area (A) and at least one secondary area (B), with at least one etchable retarding layer (60) initially covering said at least one secondary area (B) such that said retarding layer (60) is etched simultaneously with said main area (A) in a first etching phase and such that said secondary area (B) is etched simultaneously with at least one main area (A) in a second etching phase, once said retarding layer (60) has been removed.

Description

Technical field of the invention

[0001] The present invention relates to the field of watchmaking. More specifically, it concerns a method for manufacturing a watch component, in particular a silicon watch component. State of the art

[0002] In the field of watchmaking, some applications require the use of complex or multi-level components.

[0003] These components are typically obtained by assembling several separately manufactured elements. This is the case, for example, with anchors, in which the tang is assembled onto the fork intended to cooperate with a regulating organ of a watch mechanism.

[0004] In the past, this assembly was carried out using a technique called "driving," which consists of forcing an axle of one element to be assembled into a hole in the other element.

[0005] A few years ago, we also started using new materials for the manufacture of watch components, including silicon.

[0006] Silicon is a brittle material, making it difficult to use the previously mentioned press-fit assembly method, or at the very least, poorly suited to industrial production due to the high losses associated with breakage. Therefore, researchers sought new techniques for manufacturing complex silicon components.

[0007] A method for manufacturing multilevel watch components by etching in a monolithic silicon wafer has, for example, been described in patent application EP 4 283 408. According to this method, the wafer is etched on one of its sides, then the etched side is covered with an etching stop layer and then the wafer is etched on its second side, at least locally down to said stop layer.

[0008] But this process remains relatively complex. Summary of the invention

[0009] The present invention proposes a new process for the manufacture of multilevel silicon components, which is an alternative to the known process of the prior art and which is in particular simpler to implement.

[0010] The invention relates to a method for manufacturing at least one watch component, the method comprising at least the following steps: a) a substrate is provided extending between a first side and a second side in a transverse direction, and comprising a useful silicon layer, f) at least a part of the watch component is formed by etching said useful layer, from the first side, on at least one main area and at least one secondary area, with at least one etch-removable retarding layer initially covering said at least one secondary area such that said retarding layer is etched simultaneously with said main area in a first etching phase and such that said secondary area is etched simultaneously with at least one main area in a second etching phase, once said retarding layer has been removed.

[0011] Steps a) and f) are typically carried out in this order, with possible interposition of other complementary steps.

[0012] The process according to the invention therefore allows the manufacture of a watch component with at least two levels, in other words a component comprising an upper face, a lower face and at least one intermediate surface between said upper and lower faces, the upper face, the lower face and the intermediate surface being orthogonal or substantially orthogonal to a transverse direction corresponding to the transverse direction of the substrate from which the component is derived and therefore to the direction of the engraving which made it possible to obtain it.

[0013] At the end of the etching step f), an intermediate surface of the component is formed on the or each secondary area, with this intermediate surface delimiting a part of the component of thickness equal to the difference between the total thickness of the useful layer and the thickness etched on said area.

[0014] A component obtained through this process may, for example, have one or more blind cavities of the same or different dimensions. The bottom surface of a cavity is an intermediate surface, as defined previously, forming the junction between two levels of the component.

[0015] The components obtained using the process according to the invention are monolithic silicon components. A monolithic component is understood here to be a solid block made of a single material.

[0016] The process according to the invention can in particular, but not limited to, be implemented for the manufacture of anchors, wheels, balance wheels, plates, hands, dials, spirals or even elements with flexible blade(s).

[0017] It can also be used for the simultaneous manufacture, on the same substrate, of a plurality of watch components of the same type or of different types, and of the same shape or of different shapes.

[0018] The process according to the invention makes it possible to form different levels of the component during the same step f) of etching.

[0019] Step f) of the etching process allows for the formation of all or part of the watch component. In other words, at the end of step f), the component(s) may be fully formed, with its at least two levels, or the process may include additional etching steps, before or after step f), intended to complete the formation of the component.

[0020] A primary zone typically defines at least one first level of the watch component. A secondary zone typically defines at least one second level of the watch component.

[0021] The primary and secondary zones may be disjoint or at least one primary zone and one secondary zone may be contiguous.

[0022] In one example, at least one principal area defines an outer edge of the watch component. For instance, such a principal area might form a continuous groove defining a closed contour. In this case, the component has a finite contour; that is, in a direction orthogonal to the transverse direction, each watch component is externally bounded by a lateral face forming a continuous, closed contour. In another case, this area might correspond to the outer edge of the component, except for an unetched portion called a lug, which connects the component to the rest of the working layer. This case corresponds to the desired outcome of obtaining a plate carrying the watch component(s) rather than one or more individual components.

[0023] According to one example, at least one main area can also define a through hole in the component.

[0024] Applying at least one retarder layer over each secondary zone results in a time lag between the etching of the primary zone(s) and that of the secondary zones thus covered. Ultimately, the primary zones are etched for a longer duration and consequently to a greater thickness than the secondary zones. The etching lag between the primary and secondary zones depends on the time required to remove the retarder layer over the secondary zone, and therefore on the thickness and nature of this layer. Each material has a different etching rate. The etching speed can therefore vary considerably depending on the material being etched. The shape of the etched zone also influences this speed.All of these parameters must therefore be taken into account when determining the thickness of the retarder layer(s) and the total etching time to achieve the desired component dimensions. It is also possible, by adjusting the thickness of the retarder layer associated with several secondary zones, to create a component with more than two layers.

[0025] According to an example, in step f), the useful layer is etched onto the primary and secondary areas in a single continuous etching step.

[0026] According to one example, the etching is a deep reactive ion etching also called DRIE for Deep Reactive Ion Etching.

[0027] According to one example, in step f), at least one main area is etched over the full thickness of the useful layer and at least one secondary area is etched over a predetermined intermediate thickness, less than the full thickness of the useful layer.

[0028] In practice, either the progress of the engraving is controlled in real time and the engraving is stopped as soon as the secondary zone is engraved to the predetermined intermediate thickness, or a duration t2 of engraving is determined beforehand - empirically or by calculation - for which the intermediate thickness must be obtained, and the engraving is stopped after this duration t2. These two control methods can also be combined.

[0029] The thickness of at least one retarder layer is also chosen so that the etching of the secondary zone on the predetermined intermediate thickness coincides with the etching of the primary zone on the full thickness of the active layer. In other words, the thickness of at least one retarder layer is chosen so that at a time t2 when the secondary zone is etched on a predetermined intermediate thickness, the primary zone is etched on its full thickness. The etching of the primary zone on the full thickness of the active layer may, however, occur before or precisely at this time t2.

[0030] Each secondary zone can be covered with a single retardant layer or with at least two superimposed retardant layers. The retardant layers applied to the same zone or to different zones can be made of similar or different materials.

[0031] A retarder layer can, for example, be a layer of photosensitive resin. It can also be a layer of oxide or any other suitable material that can be removed by etching. The thickness of the retarder layer can be adjusted according to the etching rate of the material constituting the layer, which can vary depending on the material.

[0032] The substrate in step a) can be a bulk substrate, in the form of a single monolithic silicon layer (useful layer).

[0033] As an advantageous alternative, the substrate in step a) can comprise the silicon work layer, an intermediate oxide layer, and a stiffening layer, superimposed in that order in the transverse direction between the first and second sides. This type of substrate, known as a Silicon-on-Insulation (SOI) substrate, has the advantage that the etching arrest layer is directly integrated within it. This eliminates the need for the step of creating such an arrest layer, which is present in the earlier process described in EP 4 283 408. In an SOI substrate, the work layer is also called the "device" layer. Its thickness is, for example, between 50 microns and 500 microns. The stiffening layer is also called the "handle" layer and can, for example, be made of silicon. The intermediate layer, which forms the arrest layer, can, in particular, be made of silicon dioxide.

[0034] The substrate, whether solid or SOI type, is generally a thin and flat element, its transverse direction corresponding to the direction of its thickness and the direction in which it is engraved during the process.

[0035] According to one example, the process includes, before step f), a step c) in which at least one secondary mask is made on the first side of the substrate for etching at least one secondary area and a step e) in which a main mask is made on the same first side for etching at least one main area.

[0036] According to one example, the process includes, before step c), a step b) in which an oxide layer is formed on the first side of the substrate and in step c), the secondary mask is made by etching said oxide layer to form openings covering and / or delimiting at least one secondary area.

[0037] According to one example, the process includes, after step c) and before step e), a step d) in which the secondary mask is covered with at least one retarder layer.

[0038] For example, in step e), the main mask is created in at least one retardation layer. In other words, openings are formed in said retardation layer, delimiting at least one primary zone.

[0039] The process may further include, after step f), a step g) for releasing the fabricated component. For this purpose, in the case of a SOI substrate, the intermediate layer of the substrate is removed at least opposite the component. The release step is carried out, for example, by vapor-phase etching, in particular by hydrofluoric acid vapor etching. In the case of a bulk substrate, the stop layer used for etching the component is removed at least opposite the component. Step g) results in the release of either an individual component when it has been etched without a support, or a wafer carrying the component when it has been etched with a support.

[0040] According to an example, at the end of step f), or where applicable step g), a step h) is carried out at least once, comprising oxidation and deoxidation of the component.

[0041] According to one example, the process further includes, at the end of step f), and where applicable step g) and / or h), a final oxidation step i) of the component.

[0042] When a wafer has been released in step g), the process may further include a final step of detaching the components from said wafer. Brief description of the drawings

[0043] The features and advantages of the present invention will become apparent in more detail in the following description, with an illustrative and non-limiting example given by reference to the accompanying figures, in which: THE Figure 1A has 1L illustrate a first method of implementing the process according to the invention, The figure 2 illustrates an example of a watch component that can be manufactured using the process of the invention. Detailed description

[0044] The process according to the invention allows the manufacture of a component 1 or a plurality of components 1 in silicon at least two levels I, II in a substrate 100 comprising a silicon layer called the useful layer 10.

[0045] There figure 2 This represents, as an example, a two-level anchor 1 that can be manufactured using this process. This example is not limiting, however, and the process can be applied in an equivalent or similar manner to any other type of watch component, for example wheels, balance wheels, plates, hands, balance springs, or elements with flexible blade(s).

[0046] An anchor 1 as illustrated on the figure 2is intended to equip an escapement of a watch movement (not shown). The anchor 1 is a monolithic silicon element. It has a parallel upper face 1a and lower face 1b, with the distance between these two faces corresponding to the total thickness e of the anchor, measured in a transverse direction Z'. This total thickness e corresponds to the thickness of the useful layer 10 from which the anchor 1 is formed.

[0047] The anchor 1 here has an overall T-shape with a central stem 2 and, at one end of this stem 2, a head 3 with a through hole 4 for receiving a pivot pin (not shown). The anchor 1 also includes two pallets 5a, 5b formed respectively at one end of the head 3 and, at the end of the stem 2 opposite the head 3, a fork 6 for cooperating with a regulating organ (not shown) of the movement, for example, a balance wheel and hairspring. The fork 6 has two horns 7a, 7b defining between them a thin dart 8, which is further defined in the transverse direction Z' by an intermediate surface 9 located between the two main faces 1a, 1b of the anchor.

[0048] The intermediate surface 9 of the dart forms a junction surface between the two levels I, II of the anchor 1, superimposed along the transverse direction Z'.

[0049] The first level I has a height H1. The second level II has a height H2.

[0050] The substrate 100 in which the component is formed is illustrated on the Figure 1A It is generally thin and flat, and delimited, in the direction of its thickness or transverse direction Z, between a first side 101 and a second side 102. As will be shown later, the transverse direction Z' of the components 1 which will be formed there will be parallel to this transverse direction Z.

[0051] In the illustrated example, the substrate 100 is a Silicon On Insulation (SOI) substrate which, in addition to its active layer 10, comprises a second layer or stiffening layer 20 and an intermediate oxide layer 30 interposed between the active layer 10 and the stiffening layer 20 in the transverse Z direction. The use of such a substrate 100, known as a Silicon On Insulation (SOI) substrate, is advantageous for several reasons: the etching arrest layer 30 is integrated into the substrate, thus eliminating the need for an additional step of preparing a dedicated arrest layer. Furthermore, the stiffening layer 20 prevents deformations of the substrate 100 that could adversely affect the shape and strength of the formed watch components 1.

[0052] The use of an SOI substrate is not limiting, however, and the substrate could also be a bulk substrate in the form of a monolithic silicon wafer.

[0053] The thickness e1 of the useful layer 10 of the substrate 100 determines the total thickness e of component 1 (in particular, e can be equal to e1 in the absence of thermal oxidation operations as described below). The thickness e1 can, for example, be between 50 and 500 µm.

[0054] The stiffening layer 20 is generally thicker than the useful layer.

[0055] The intermediate layer 30 forms a bonding layer between the active layer 10 and the stiffening layer 20, and also serves as a stop layer during deep reactive ion etching (DRIE) operations, which will be described in more detail later. It is typically made of silicon dioxide (SiO2, also commonly called silicon oxide).

[0056] As illustrated on the figures 1I to 1L The process according to the invention includes an etching step, preferably continuous, during which respectively primary A and secondary B zones of the useful layer 10 are attacked by ion bombardment from the first side 101 of the substrate 101. The etching is typically a deep reactive ion etching also called DRIE etching.

[0057] The main areas A are areas intended to be engraved over the total thickness of the useful layer 10. These areas are typically grooves externally delimiting the components 1 or correspond to through holes such as hole 4, formed in the components 1. They define at least the edges of the first level I.

[0058] Secondary zones B are areas intended to be engraved to a thickness e' less than the total thickness of the useful layer 10. These zones define the edges of the second level II.

[0059] As an illustration, we will subsequently consider the section plane V of the figure 2 To form this part of the anchor 1, a secondary zone B, intended to form the dart 8, will be engraved on an intermediate thickness e' corresponding to the height H2 of the second level II. A first main zone A1 intended to form the through hole 4 and a second main zone A2, adjoining the secondary zone B and intended to form the external contour of the dart, will also be engraved on the total thickness of the useful layer 10.

[0060] There figure 1 illustrates schematically, in relation to this section plane V, different stages of the process according to a first method of implementing the invention.

[0061] For the sake of brevity and clarity, this description will focus on the fabrication of a single component. However, even though it is theoretically possible to manufacture only one component at a time, it is generally desirable to simultaneously manufacture multiple watch components on the same substrate. These components may be of the same type or different types, the same shape or different shapes.

[0062] In a step a) of the process, a substrate 100 is therefore provided comprising a useful layer 10 of silicon.

[0063] In step b) illustrated on the figure 1B , an oxide layer 40 is formed at least on the first side 101 of the substrate 100, for example by thermal oxidation, generally in a furnace heated to a temperature typically around 1000°C. The thickness of the oxide layer 40 formed around the substrate is typically between 0.5 and 4 microns.

[0064] Note that thermal oxidation slightly reduces the silicon thickness of the useful layer 10, as silicon dioxide is formed at the expense of silicon (the thickness of the useful layer decreases from e1 to e, as can be seen in the Figures 1A and 1B ).

[0065] This oxide layer 40 is used to prepare a sub-mask or secondary mask 44 which will later be used for etching secondary areas B: In a step c1) illustrated on the figure 1C The oxide layer 40 is covered with a layer of photosensitive resin 50 and, by photolithography using a mask M1, at least one aperture 52 is formed in the resin layer 50. In a step c2) illustrated in the figure 1D , the oxide layer 40 is etched through said opening 52 to form openings 42 in the oxide 40. Then the resin layer 50 is removed ( figure 1E ).

[0066] The openings 42 of the secondary mask 44 delimit or at least cover the secondary area B but can also, in addition, cover or partially delimit a main area (here A2).

[0067] In step d) illustrated on the figure 1F The secondary mask 44 thus created is covered with a layer of photosensitive resin 60. This photosensitive resin 60 therefore covers the aforementioned secondary zone B and forms an etching retardant layer for this zone B. The thickness of the layer 60 is chosen beforehand according to the etching rate of the resin, the desired height H1, H2 for levels I, II of component 1, and the shape of the secondary zone B to be etched.

[0068] In step e), a primary etching mask 64 is then prepared for etching the main areas A1, A2. In step e1) illustrated in the figure 1G, openings 62 delimiting the main zones A1, A2 are made in the resin 60, by photolithography using a mask M2. Then in a step e2) illustrated on the figure 1H , the underlying oxide of the oxide layer 40 is etched - if necessary - through these openings 62.

[0069] Finally, in step f) illustrated on the figures 1I to 1L , the main areas A1, A2 and secondary B are etched by deep reactive ion etching (also called DRIE for Deep Reactive Ion Etching).

[0070] According to the invention, when the etching starts at time t0, the secondary zone B is covered with the retarder layer 60 which therefore shifts the time when this zone B is etched relative to the unprotected main zones A1, A2.

[0071] During the initial engraving phase ( figures 1I, 1J), the main zones A1, A2 are attacked while the secondary zone B remains temporarily protected by the retardant layer 60, which is nevertheless also attacked and therefore progressively eliminated. At time t1 ( figure 1K ), the retarder layer 60 is completely removed, revealing the secondary zone B. At this instant t1, each main zone A1, A2 has already been etched to a certain thickness which corresponds to the height H1 of the first level I.

[0072] In a second etching phase, the secondary zone B also begins to be etched while the etching of the main zones A1 and A2 continues. The etching operation is finally stopped at time t2, at which point each main zone A1 and A2 has been etched to the full thickness e of the useful layer 10, while the secondary zone B has only been etched to an intermediate thickness e' less than this full thickness e.

[0073] It is easy to understand that the thickness of the retarder layer influences the offset between the etchings of the main areas A1, A2 and secondary areas B and thus allows the thickness of levels I, II of component 1 to be adjusted.

[0074] In order to obtain a component with more than two levels, it is also possible to provide a different thickness of the retarder layer on different secondary areas B so as to etch at least one secondary area B on a first intermediate thickness e1', at least one secondary area B on a second intermediate thickness e2', etc.

[0075] In a step g) not shown, the component is released. In the example of the SOI substrate shown, it is typically deoxidized with acid, in particular hydrofluoric acid, in the vapor phase, so as to remove its intermediate layer 30 at least opposite the watch component 1.

[0076] In the case of a solid substrate, the stop layer, typically made of parylene, prepared for etching on the second side 102 of the substrate 100, would then be removed.

[0077] In the case of etched components 1 with attachment, deoxidation leads to the release of a wafer, comprising all or part of the useful layer 10 and carrying the components.

[0078] In the case of components 1 etched without attachment, deoxidation leads to the release of individual components.

[0079] In addition, the process may include at least one sequence h) of thermal oxidation followed by deoxidation of the wafer or of the component(s) 1.

[0080] The process may further include, at the end of step g), and where appropriate step h), a final oxidation step i) of the component(s) 1 (where appropriate on their wafer).

[0081] And finally, in the case of a wafer, the process may include a step j) in which the components 1 are detached from their wafer.

Claims

1. Method for manufacturing at least one watch component (1), the method comprising at least the following steps: a) a substrate (100) extending between a first side (101) and a second side (102) in a transverse direction (Z), and comprising a useful layer (10) of silicon, f) at least a part of said watch component (1) is formed by etching said useful layer (10), from the first side, on at least one main area (A) and at least one secondary area (B), with at least one etch-removable retarding layer (60) initially covering said at least one secondary area (B) such that said retarding layer (60) is etched simultaneously with said main area (A) in a first etching phase and such that said secondary area (B) is etched simultaneously with at least one main area (A) in a second etching phase, once said retarding layer (60) has been removed.

2. A method according to claim 1, wherein the useful layer (10) is etched by deep reactive ion etching.

3. Method according to claim 1 or 2, wherein in step f), the useful layer (10) is etched onto the main area(s) (A) and secondary area(s) (B) in a single continuous etching step.

4. A method according to any one of claims 1 to 3, wherein in step f), the main area (A) is etched over the total thickness (e) of the useful layer (10) and the secondary area (B) is etched over a predetermined intermediate thickness (e') less than the total thickness (e) of the useful layer (10).

5. A method according to any one of claims 1 to 4, wherein the retarding layer (60) is a photosensitive resin layer.

6. A method according to any one of claims 1 to 5, comprising, before step f), a step c) in which at least one secondary mask (44) is made on the first side (101) of the substrate (100) for etching at least one secondary area (B) and a step e) in which a main mask (64) is made on the same first side (101) for etching at least one main area (A).

7. Method according to claim 6, further comprising, before step c), a step b) in which an oxide layer (40) is formed on the first side of the substrate and in step c), the secondary mask (44) is made by engraving said oxide layer (40) to form openings (42) covering and / or delimiting at least one secondary zone (B).

8. Method according to claim 6 or 7, comprising, after step c) and before step e), a step d) in which the secondary mask (44) is covered with the retarder layer (60).

9. Method according to claim 8, wherein in step e), the main mask (64) is made in the retarder layer (80).

10. A method according to any one of claims 1 to 9, wherein the substrate (100) of step a) comprises the useful silicon layer (10), an intermediate oxide layer (30) and a stiffening layer (20) superimposed in that order in the transverse direction between the first side (101) and the second side (102).

11. Method according to claim 10, further comprising, after step f), a step g) in which the intermediate layer (30) of the substrate (100) is removed at least with respect to said watch component (1).

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