CH719668A2 - Process for manufacturing watch components. - Google Patents

Abstract

The present invention relates to a method for manufacturing watch components (110), in which, in a silicon-based wafer (100), watch components (110) are formed, according to target dimensions, as well as at least a specimen (120) of geometry different from that of the components (110), at least one characterization parameter of the specimen (120) representative of a characteristic of the components is determined, and from said parameter, said characteristic of the components and/or it is determined whether a dimensional correction should be applied to the components (110). The process can in particular be applied to the manufacture of watch hairsprings.

Description

Technical field of the invention

The present invention relates to the field of manufacturing watch components, such as watch balance springs, escape wheels, anchors, etc.

State of the art

[0002] A watch movement is made up of a plurality of components which interact closely with each other. These components include, for example, a pivoting balance wheel and a watchspring designed to produce a restoring torque on the balance wheel, which together determine the reference frequency from which the measurement of the passage of time is carried out.

[0003] To guarantee the precision of the movement, it is necessary to precisely control the characteristics of each of the components used. For example, the aforementioned reference frequency depends directly on the moment of inertia of the balance wheel and the stiffness of the hairspring, which must therefore be perfectly controlled.

[0004] A few years ago, we began to use new materials for the manufacture of watch components, resulting in new manufacturing techniques such as deep reactive ion engraving (also called DRIE engraving which is the acronym for Deep Reaction Ion Etching) could be used.

[0005] However, significant geometric dispersion was observed between identical components from the same substrate, and even greater dispersion between identical components from different substrates. This dispersion, if not controlled, can impact the precision of the watch movement.

[0006] By way of example, Figure 1 schematically illustrates the cross sections of the blades of three hairsprings S1, S2, S3 formed according to identical target dimensions, on different substrates P1, P2, P3.

The heights h1, h2, h3 of the hairspring blades (measured in the direction of the engraving) are identical. But their widths l1, l2, l3 are all different from the target width lc, and are, moreover, different from each other.

[0008] However, the stiffness Rs of a hairspring of constant section depends on its material and its dimensions, and is defined by formula [1] below:

[0009] With Rs= stiffness of the hairspring E= modulus of elasticity ls= width of the blade hs= height of the blade Ls= length of the blade

[0010] The dimensional differences between the hairsprings therefore also cause a dispersion of their stiffness. This emerges from Figure 2 which schematically represents, for each batch of hairsprings produced on each plate P1, P2, P3, the dispersion of stiffness R which follows a Gaussian distribution (curves C1, C2, C3).

[0011] Several methods have been developed in recent years with the aim of centering the average Gaussian distribution of hairsprings on a nominal stiffness value and reducing the standard deviation of the Gaussian.

[0012] Document EP 3181938 proposes for this purpose to form a hairspring with dimensions greater than the dimensions necessary to obtain a hairspring of a predetermined stiffness, by measuring the stiffness of this hairspring by coupling it with a balance wheel. equipped with a predetermined inertia, by calculating the thickness of material to be removed to obtain the dimensions necessary to obtain the desired stiffness, and by removing this thickness from the hairspring. This approach requires great precision in measuring the frequency of the hairspring to determine its stiffness. Furthermore, this frequency measurement constitutes a careful operation which requires a significant amount of time. It also poses a risk of pollution of the hairsprings.

[0013] Document EP 3 845 770 A1 proposes using a corrected mask for structuring by photolithography of a layer of photosensitive resin carried by a layer of the substrate. The mask comprises windows each defining the contour of a spiral, at least certain windows having different dimensions so as to compensate for the dispersion of stiffness within the spirals of the substrate. However, this process has not proven to be sufficiently effective for centering the Gaussian stiffness distributions of different substrates on the same nominal stiffness.

[0014] There is therefore still a need to improve the process for manufacturing such hairsprings, in particular batches of hairsprings from different substrates, with the aim of controlling their characteristics and in particular their stiffness, while avoiding the aforementioned drawbacks.

[0015] The problem arises in a similar manner for the manufacture of other watch components, in particular the balances mentioned above or the anchors or the escape wheels, which are subject to the same effects of dimensional dispersion during manufacture.

Summary of the invention

[0016] An aim of the present invention is to propose a process for manufacturing watch components making it possible to meet the aforementioned needs.

[0017] According to the invention, this goal is achieved thanks to a process for manufacturing watch components, in which: a) in a silicon-based wafer, watch components are formed according to target dimensions as well as at least one test piece with a target geometry different from that of the components, b) at least one characterization parameter of the test piece representative of a characteristic of the components is determined, c) from said parameter, said characteristic of the components is determined and/or it is determined whether a dimensional correction must be applied to the components.

[0018] In the context of the present invention, the components may be in particular (but not limited to) watch hairsprings or anchors or escape wheels for watch movements.

[0019] Watch components are generally manufactured in a substrate comprising a first layer based on silicon in which the components must be formed, a second layer called “support” also based on silicon and serving to stiffen the substrate and, between these two layers, an intermediate layer also called “stop layer”, made of silicon oxide.

The formation of watch components is typically carried out by deep ion reactive etching (DRIE) through a photosensitive resin mask formed by photolithography on the first layer of the substrate.

[0021] At the end of the forming process, the components were cut from a wafer comprising at least one useful portion of the first layer of the substrate, said useful portion being released from the support and from the barrier layer.

As explained previously, it is established that the illumination and development processes of the photosensitive resin such as DRIE etching result in dimensional dispersion between components from different substrates of the same series, which can influence the characteristics components.

The method makes it possible to deduce, from the characterization of a test structure (test specimen) formed on the same wafer as a plurality of components, at least one characteristic of these components. As an alternative or in addition, the method can also make it possible to identify a deviation between the target dimensions (those theoretically desired) and the effective dimensions of the components (obtained at the end of the engraving) of the same wafer, and the case possibly to quantify said deviation to allow subsequent correction.

The use of a test piece whose geometry and dimensions can be chosen and adapted according to needs makes it possible to systematize the characterization measurements, which can also be rapid and simple. The speed and reproducibility of the manufacturing process are improved, notwithstanding variations in the geometry of the components to be manufactured from one series to another.

[0025] Contact with the components to be manufactured is also avoided, eliminating the risk of pollution or damage to the latter.

[0026] By making it possible to better characterize the parts manufactured, the process also makes it possible, ultimately, to optimize the pairing between the different components of the watch movement and to improve the precision of the latter.

[0027] In the context of the present invention, a test piece is understood as any element, made in the same wafer as the components to be manufactured, and having a target geometry (i.e. reference geometry) different from the target geometry of said components.

[0028] By dimension(s) or respectively target geometry of a test piece or of a component, we mean here its dimension(s) or respectively its geometry seen in orthogonal projection in the general plane of the wafer (i.e. in projection according to the direction of the height or smallest dimension of the wafer) and as targeted during manufacturing. By dimension or geometry targeted during manufacturing, we mean a dimension or geometry that we wish to obtain after engraving, for said components, without taking into account possible minor divergences resulting from the manufacturing process and in particular from the engraving operation. .

[0029] Likewise, in the present application, and unless otherwise indicated, a shape of an element refers to said target geometry

Furthermore, in the present application, a width is always measured in projection in the plane of the wafer. A height is measured orthogonal to the general plane of the plate.

Finally, in the present application, a section of an element is a cross section of said element in a plane orthogonal to the general plane of the wafer.

[0032] In certain cases, the target geometry of the components can be deliberately chosen to be different from a theoretical geometry making it possible to obtain the desired final characteristics for said components. For example, the target dimensions, and in particular the target width, can be chosen greater than the theoretical dimensions, and in particular the theoretical width, making it possible to obtain the desired final characteristics for the components. For example, spirals can be formed on a plate by aiming for target dimensions greater than those theoretically allowing the desired final stiffness value to be obtained, to allow subsequent adjustment by removal of material.

[0033] The effective geometry at the end of the engraving generally diverges from this target geometry due to variations in the process.

[0034] For the rest, the test piece has a height identical to that of the components manufactured and is made of the same material. It can sometimes even have a section identical to that of the components, if its target width is the same.

[0035] A test piece used in the context of the present invention is a sacrificial element, which is used exclusively for the characterization of the components to be manufactured and is not intended to be used in a watch mechanism.

[0036] According to a first mode, the test piece does not have the same general shape as the components to be manufactured. In a case where the components to be manufactured are spirals, anchors or wheels, the specimen can for example have the shape of a straight beam or blade.

[0037] According to a second mode, the test piece can also have the same general shape as the components to be manufactured, but always with a target geometry different from that of said components. For example, in the case where the components to be manufactured are hairsprings, at least one test piece may be a reference hairspring with a target geometry different from the hairsprings to be manufactured.

[0038] A different geometry will for example be characterized by a different general/median line (for example a different curvature, a different number of turns, a different number of teeth, etc.) and/or different dimensions and/or a different external profile (for example a different sidewall profile).

[0039] A single test piece can be formed on the wafer. As an alternative, a plurality of test pieces can be formed in the wafer, and step b) can in this case comprise the calculation of an average of at least one parameter on the plurality of test pieces.

[0040] According to an advantageous example, at least one test piece may be a blade extending in a rectilinear direction, in particular between its two ends, at least one of which is fixed to the plate and the other may or may not be free. .

The blade may include at least one portion of constant section, and in particular it may be of constant section over its entire length. The blade may also include a portion of enlarged section at its distal end.

[0042] In step b), the specimen can be characterized directly on the wafer. In this case, the opening made in the plate around the test piece can advantageously be chosen sufficiently wide to allow it to be deformed in the plane of the plate.

[0043] As a less advantageous variant, the test piece can be characterized after having been previously detached from the wafer and fixed on a test support.

[0044] Step b) comprises for example the determination of a parameter for characterizing the test piece among: – a dimension of the test piece, in particular its width, – a deformation value of the test piece, – a speed or an acceleration of movement of the specimen, – a natural vibration frequency of the specimen, – one or more resonance frequency(s) of the specimen, – an effective stiffness of the specimen, or a plurality of these settings.

[0045] In the present application, the natural frequency of a system is the frequency at which this system oscillates when it is in free evolution, that is to say without an exciting force. A resonant frequency of a system subjected to an exciting force is a frequency at which a local maximum of displacement amplitude can be measured for a given point in the system.

A characterization parameter can be measured directly or can be obtained by deduction from another parameter measured previously.

[0047] Step b) may in particular comprise a measurement and/or determination of a frequency, in particular a natural frequency or one or more resonant frequencies, and/or an amplitude and/or a speed and/or an acceleration of movement of at least one point of the test piece.

[0048] Particularly advantageously, the specimen is defined in a base plane corresponding to the general plane of the wafer during its formation, and the movement is in a direction contained in said base plane. The plane of movement of the specimen during characterization then coincides with the plane of movement of the components in operation, which makes the characterization more precise and more direct. The characterization parameter expresses the particularly mechanical and/or geometric properties of the specimen and the components with the same weighting of the different value(s) taken into account.

According to one example, in step b), a vibratory excitation is applied to the specimen, and at least one vibrational characteristic of the specimen is determined during vibration.

[0050] By vibratory excitation we mean here any excitation enabling the test piece to vibrate.

[0051] According to one example, the vibrational excitation is maintained.

[0052] According to another example, the vibration excitation is punctual and not sustained.

Advantageously, the vibrational excitation is variable (or modified) over time. In other words, vibrational excitation includes the excitation of the specimen at different frequencies over time. For example, it is possible to carry out several successive excitation phases, the test piece being excited at a given frequency (sustained single-frequency excitation) during each excitation phase.

[0054] In this case we can identify at least one resonance characteristic of the test piece during vibration, for example a resonance frequency or a resonance peak.

Advantageously, the vibrational excitation covers a predetermined frequency range, preferably located in the vicinity of the resonance frequency.

The vibration excitation can be imposed by a source of acoustic vibrations, for example a piezoelectric source.

[0057] As an alternative, the excitation can be imposed by a mechanical excitation source.

[0058] According to one example, the vibratory excitation is an impulse excitation for example produced by a shock applied directly to the test piece or to an element integral with the test piece at the time of excitation, for example on the wafer when the The test piece is still attached to said plate. Such a pulse or shock can for example be induced using an excitation hammer.

[0059] According to another example, the test piece could be loaded by an end force to be deformed, then be released.

[0060] The vibratory characteristic of the test piece determined during excitation or after excitation can for example be a characteristic of a natural frequency or a resonance frequency of the test piece or it can be a speed or an acceleration or a displacement amplitude possibly making it possible to deduce a natural frequency or a characteristic of a resonance frequency of the test piece.

According to another example, in step b), a predetermined bending force is applied to the specimen and at least one amplitude of movement of the specimen is identified under the effect of said bending force.

According to yet another example of characterization, step b) comprises a measurement of at least one dimension of the test piece (for example its width), in particular an optical measurement, in particular a laser measurement.

[0063] According to yet another example, step b) comprises measuring the stiffness of at least one test piece in the form of a reference spiral.

[0064] A characteristic of the components that can be deduced from a characterization parameter of the test piece determined for example according to one of the aforementioned methods can be in particular: – a critical dimension of the components, or – a mechanical property of the components, for example a stiffness or an inertia, or – a characteristic linked to the future operation of the components, in other words a characteristic representative of the way in which said components will interact with other watch movement components in their movement, in particular an efficiency or a frequency or a range of movement (at iso parameters).

[0065] By critical dimension, we mean for example a dimension, an inclination (in particular an inclination of the sides), a radius of curvature.

[0066] The method makes it possible in particular to characterize dimensions that are difficult to measure optically, in particular dimensions that are difficult to access by optical measurement systems.

According to one example, in step c) it is determined whether a dimensional correction must be applied to the components. The method according to the invention makes it possible to detect the dimensional error linked to photolithography and DRIE etching using the test specimen(s) provided on each wafer.

[0068] For example, the method may include a step of comparing the characterization parameter of the test piece or the corresponding characteristic of the components with a reference value, to deduce the need for a dimensional correction.

[0069] A characteristic of the components and/or the need for a dimensional correction of the components can for example be deduced from the characterization parameter(s) of the test piece – by means of a predictive model, for example implementing an algorithm machine learning or a polynomial formula, and/or – through a lookup table.

[0070] According to an arrangement of the invention, in step c) a dimensional correction value to be applied to the components is further determined.

[0071] In other words, the method makes it possible not only to identify the dimensional error, but also to quantify the dimensional correction value to be applied.

[0072] The dimensional correction value typically corresponds to a thickness of material to be removed from the components to obtain the desired dimension. In this case, the components are initially manufactured to target dimensions, in particular a target width, wider than the theoretical dimensions, in particular the theoretical width, making it possible to obtain the desired stiffness.

[0073] The correction is usually - although not necessarily - applied to each side face of a component (for example to vary its width) and generally also to its upper and lower faces (to vary its height). Very often, the correction consists more generally of a reduction in the entire thickness of the wafer (on all of its surfaces), including the components and the test piece(s).

[0074] The dimensional correction value can also be determined by a predictive model, for example implementing an automatic learning algorithm or a polynomial formula.

[0075] As a variant, the determination of the dimensional correction value is carried out using a correspondence table.

[0076] According to one example, the method further comprises a step d) during which the dimensions of the components are actually corrected according to the correction value determined in step c).

[0077] Step d) advantageously comprises at least one oxidation step and a deoxidation step of the components.

[0078] According to a particular example, several or all of the watch components can be subjected to thermal oxidation prior to step b). In this case, the dimensional correction step d) may comprise at least one partial deoxidation step and a component reoxidation step.

[0079] According to a particular arrangement, step a) comprises at least the following sub-steps: a1) providing a substrate comprising a first layer based on silicon, a second layer based on silicon and an intermediate layer based on silicon oxide, a2) cover the first layer with a layer of photosensitive resin, a3) by photolithography, form openings in said layer of resin corresponding to the unattached contours of the watch components and at least one test piece, a4) engrave the first layer over its entire height under said openings to form the watch components and at least one test piece.

[0080] By contour excluding attachment of a part we mean here the contour of the part with the exception of a portion of its external contour intended to form an attachment holding it to the rest of the substrate/wafer.

[0081] Sub-step a3 may, in particular, comprise the following steps: a31) exposing the layer of photosensitive resin using a light source, through a photolithographic mask provided with windows defining the contours outside the attachment of the watch components and the test piece, a32) locally eliminate the photosensitive resin using a solvent to form the openings.

[0082] According to an advantageous arrangement, the photolithographic mask is a corrected mask, at least certain windows of the mask being of different dimensions so as to reduce the extent of dimensional dispersion between at least part of the watch components.

Brief description of the drawings

[0083] The particularities and advantages of the present invention will appear in more detail in the context of the description given below of exemplary embodiments given by way of illustration and not limitation with reference to the attached drawings in which: – Figure 1 illustrates the sections of the blades of three hairsprings formed, according to identical target dimensions, on different plates, – Figure 2 illustrates the dispersion of stiffnesses of hairsprings of the same series, formed on three different plates – Figure 3 represents a wafer in which a plurality of watch spirals and a test piece have been formed, – Figure 4 is an enlarged view of detail A of Figure 3, – Figures 5A to 5D are schematic and partial views illustrating the manufacturing process of the plate in Figure 3, – Figures 6 to 9 illustrate four other examples of test pieces that can be used in the process of the invention, – Figure 10 illustrates a method for characterizing a test piece, – Figure 11 illustrates a second method of characterizing a test piece, – Figure 12 illustrates a third method of characterizing a test piece, – Figure 13 illustrates a correspondence table that can be used to determine the dimensional correction value. – Figures 14A to 14C illustrate the dimensional correction of a spiral according to one mode of implementation of the invention, – Figure 15 illustrates a variant of cutting a test piece in a silicon substrate.

detailed description

[0084] The invention is illustrated below by examples relating to the manufacture of hairsprings. However, the same principles are applicable to any other type of watch components.

[0085] Figure 3 represents a top view of a silicon-based wafer 100 in which several watch hairsprings 110 have been formed with the same target geometry and in which a test specimen 120 forming a test structure has also been formed with a geometry target different from that of the components. The target geometry of the components is the geometry that we aim to obtain at the end of the engraving and before possible subsequent dimensional correction. It may be identical to or different from a theoretical geometry which would make it possible to achieve the desired characteristics for the hairsprings, in particular a determined stiffness. The effective geometry at the end of the engraving may be slightly different from this target geometry due to variations in the process and in particular the geometric dispersion within the wafer.

[0086] Such a wafer 100 can be produced by implementing the following process steps, illustrated in FIGS. 5A to 5D: A substrate 10 is provided, typically a silicon-on-insulator (SOI) type substrate, which comprises a first layer of silicon 11 in which the spirals must be formed, a second layer of silicon 12 and, between the two, an intermediate layer or stopping layer 13 of silicon oxide. The silicon of the first and/or second layers 11, 12 may be polycrystalline but it is preferably monocrystalline. It may not be doped or be doped, for example doped with phosphorus. Doped silicon, electrically conductive, is more dimensionally stable and has better mechanical strength. Preferably, the substrate 10 is made of silicon which has a {1,1,1} orientation and/or which is doped, advantageously so as to have a resistivity less than or equal to 0.1 Ω.cm-1, for example example a resistivity equal to 0.05 Ω.cm-1.

[0087] A layer of photosensitive resin 20 is deposited on the first layer 11 of the substrate 10.

[0088] Through a photolithographic mask 30 provided with windows 31 of shapes corresponding to the contours of the spirals 110 and the test piece 120, the resin layer 20 is exposed to light radiation R from a light source (not shown). The radiation R can in particular be radiation comprising UV, that is to say ultraviolet, or even consist of UV.

[0089] According to an advantageous arrangement, the photolithographic mask 30 is a mask corrected according to the teaching of document EP 3 845 770 A1, at least certain windows 31 of the mask being of different dimensions so as to aim for the same geometry for all the components target, by compensating for the stiffness dispersion within the substrate.

[0090] The irradiated photosensitive resin is then eliminated locally by solubilizing it in an appropriate chemical bath, to form openings 21 corresponding to the desired contours of the spirals and the test piece. We say that the resin is “developed”: in the case of a positive resin as illustrated, it is the portion of the resin exposed to the R radiation of the light source which is removed. The photosensitive resin which has not been irradiated and transformed by R radiation resists the chemical bath, thus remains in place on the substrate and forms a sacrificial mask.

[0091] In a variant of implementation with a so-called negative resin, the photosensitive resin is chosen so that its irradiation with radiation similar or identical to the R radiation renders this resin insoluble in an appropriate chemical bath, in which case the mask is transformed accordingly.

[0092] The silicon of the first layer 11, which is no longer protected, is then etched over its entire height through the openings 21 of the resin, in a direction perpendicular to the general plane of the substrate 10 (FIG. 5C). Several watch hairsprings 110 as well as the test piece(s) 120 are cut collectively, together and at the same time, all in the first layer 11.

[0093] The engraving is a deep reactive ion etching, also called DRIE engraving (acronym for “deep reaction ion etching”, which is the English designation for deep reactive ion etching) or engraving according to the Bosch process. Behind the mask, the first layer 11 is not engraved. Furthermore, the stopping layer 13 is less sensitive to etching which therefore does not affect it or to a very lesser extent.

[0094] The inclination of the engraving sides depends on the width of the engraved surface, it is preferable, to ensure a correspondence between the inclination of the sides of the specimen and that of the sides of the components, that the width of a engraving border around the test piece is substantially equal to the width of the engraving borders around the components. The width of the openings 21 of the resin are therefore configured accordingly.

[0095] According to one possible mode of implementation, it is possible, for each component as for the test piece, to engrave both an engraving border corresponding to the external profile of the element and a peripheral border around this external border. When releasing the plate, the portion located between the external border and the peripheral border is detached, freeing around the element an empty space 130 as illustrated in Figure 4, allowing the element to move around its tie to break it.

[0096] As a variant, one could also, as in Figure 15, engrave a single external engraving border 130' delimiting the test piece, said border having a width substantially identical to the width of the engraving borders delimiting the components.

[0097] In a new step, the support 12 and the stopping layer 13 are then removed locally, or completely removed, by chemical etching, so that the plate 100 carrying the watch hairsprings illustrated in Figure 1 is released (Figure 5D).

[0098] By wafer we generally mean in the present application any silicon-based structure comprising a useful portion (if applicable freed from the support and from the intermediate layer of the substrate from which it comes) from which the components to be manufactured are cut and at least one test piece with a target geometry different from that of the hairsprings.

[0099] The plate finally carries the watch hairsprings 110 and the test piece 120, so that they can easily be moved together and treated collectively and at the same time. As illustrated in Figure 3, the test piece 120 can for example be produced in the useful portion of the plate 100 where the spirals 110 are made and be surrounded by spirals. As a variant, the test piece 120 could however be placed indifferently anywhere on the plate 100.

[0100] The test piece 120 of Figure 3 appears in more detail in the enlarged view of Figure 4. In this example, the test piece 120 is connected to the rest of the plate 100 by a proximal end 121 and is free at its distal end 122. The opening 130 made in the plate 100 around the test piece 120 allows it to be deformed in the plane of the plate 100 if necessary.

[0101] In the example of Figure 3, the test piece 120 is a blade extending in a rectilinear manner, in a main direction Z, between the proximal end 121 and the distal end 122. Here, the blade has a constant rectangular section and in particular a constant width It, over its entire length Ltmeasured in its main direction Z. This embodiment is however not limiting and Figure 6 illustrates another example in which the blade 120 has a variable section the along its main rectilinear direction Z and ends, at its distal end 122, with a portion 123 of locally enlarged section forming a mass. According to yet another example illustrated in Figure 7, the test piece can be in the form of a blade, for example of constant section as in Figure 3, but fixed to the rest of the plate at its two ends. According to yet another example illustrated in Figure 8, the test piece 120 can be a spiral with a profile different from that of the spirals to be manufactured 110, of constant section or not over its entire length Ltmeasured between its proximal end 121 attached to the plate and its free distal end 122.

[0102] These examples are given for illustrative purposes and are not exhaustive. Any other suitable geometry, different from that of the spirals to be manufactured, can be considered for the test specimen(s).

[0103] The processes for illumination and development of the photosensitive resin, as well as DRIE etching, result in dimensional differences between the widths l of elements supposed to be identical on different wafers.

[0104] As explained previously, in the field of hairsprings we are interested in compensating for this dimensional dispersion to cause the average stiffness of the hairsprings of the same plate to tend towards a nominal value.

[0105] The method according to the invention makes it possible to detect the dimensional error linked to the engraving thanks to the characterization of the test piece(s) and to quantify the dimensional correction value to be applied to the hairsprings to achieve the desired average stiffness . In the context of hairsprings, the term dimensional correction value means the thickness e of material to be removed from each hairspring 110 to achieve this stiffness.

[0106] The characterization being carried out indirectly, via the test piece, the hairsprings are preserved. Furthermore, the test piece 120 can take very varied geometries as mentioned previously, the characterization methods can be very diverse, and some of them are described below by way of non-limiting examples.

[0107] In these examples, the test piece 120 is characterized directly on the plate 100. In other words, at least one parameter of the test piece 120, representative of the difference between the effective dimensions of the hairsprings and their target dimension or a dimension theoretical allowing the desired stiffness to be obtained, is determined while the specimen is still attached to the plate 100.

[0108] As an alternative, the test piece 120 can also be characterized after having been previously detached from the plate 100 and fixed on a test support. In this case, as illustrated in Figure 9, the test piece 120 is secured to the plate 100 via one or more detachment tabs 140. Such a detachment tab 140 advantageously has a junction portion of narrowed section 141 at its end located in the vicinity of the specimen 120. The junction portion 141, easily breakable, allows easy detachment of the specimen 120. When it must be characterized on a test support, the specimen 120 is advantageously linked, to at least one of its ends, to a fixing base 124, preferably of greater width than the test piece itself, for its fixing to the support. In this case, the fixing base 124 forms with the specimen an assembly 125 detachable from the plate. The fixing base 124 is preferably located between the detachment tab 140 and the test piece 120.

[0109] According to a first mode of characterization, the test piece 120 is subjected to vibrational excitation, and a vibration response of the test piece is measured to deduce a characterization parameter such as a resonance frequency.

[0110] In the example illustrated in Figure 10, a piezoelectric source 300 or any other source adapted to induce on the test piece 120 is used an acoustic excitation in an excitation frequency range chosen so as to include at least a resonance frequency of the test piece. By covering or sweeping a wide frequency range, multiple resonance peaks (or resonant frequencies) can be measured, which can provide greater accuracy.

[0111] For example, one or more frequencies are applied at a time, which are varied over time, in the vicinity of one or more resonance frequencies.

[0112] The excitation is preferably maintained for a sufficient duration to deduce the vibration spectra of the test piece.

[0113] During excitation, it is possible for example to record, via a suitable optical measuring means 310 such as a laser vibrometer by Doppler effect, an amplitude or a speed or an acceleration of movement or a frequency of movement of at least minus one point on test piece 120.

[0114] The test piece 120 is generally contained in a base plane of the plate 100. The displacement whose characteristics are measured is in a direction contained in this base plane or, alternatively, in a direction transverse to said base plane.

[0115] The signal thus obtained is then processed, generally by a computer program 320, to deduce whether and which dimensional correction is necessary.

[0116] Signal processing typically comprises a step of identifying the resonance frequency as a function of the amplitude or the speed or the acceleration measured, for example by frequency analysis by Fourier transform.

[0117] It may be noted that the method may or may not integrate an intermediate step of determining a stiffness of the specimen 120, then making it possible to calculate/deduce a level of dimensional correction to be applied to obtain the desired final stiffness.

[0118] The dimensional correction value of the hairsprings 110 is determined, from the determined resonance frequency or, where appropriate, from the calculated stiffness value, by a predictive model or by means of a correspondence table.

[0119] The predictive mathematical model implements, for example, an automatic learning algorithm, previously trained during test measurements, and capable of implementing a classification carried out by a neural network, or by partitioning.

[0120] As an alternative, the predictive model can implement a polynomial formula, for example by carrying out linear regression modeling.

[0121] As another alternative, a correspondence table can make it possible to determine more easily, although less precisely, the dimensional correction to be made.

[0122] Such a correspondence table can be obtained experimentally, for example by experimentally determining how much a shrinkage with a thickness of one micron over the entire surface of the wafer 100 causes the resonance frequency of the test piece 120 to vary. By proportionality, we can then determine the number of microns of thickness to be removed to obtain a predetermined resonance frequency, corresponding to a desired stiffness.

[0123] Alternatively, we can use a correspondence table making the direct link between a variation in material thickness and a variation in stiffness of the specimen.

[0124] The excitation can be maintained as in the aforementioned example, but it can also be punctual and not maintained.

[0125] According to one example, we could thus use an excitation hammer or any other source making it possible to induce pulsed vibratory excitation on the test piece.

[0126] Figure 11 illustrates an example of characterization in which the test piece 120 is loaded, near its distal end, by a force F directed substantially orthogonal to its main direction Z. Once the test piece is deformed, it is released (F=0) and then oscillates on either side of its equilibrium position. Its natural frequency can then be measured.

[0127] In this case, we could also advantageously use a test piece 120 as illustrated in Figure 6, in the form of a blade terminated at its distal end by an enlarged portion 123 forming a mass. This mass 123 makes it possible to amplify the movement and facilitate the measurement.

[0128] Whatever the mode of vibration excitation, the principle can remain the same as described previously, and consist of recording an amplitude or a speed or an acceleration of movement of the test piece, then processing the signal thus recorded to extract a natural frequency or one or more resonance frequencies from the test piece, to finally deduce the correction value to apply.

[0129] However, the vibration response to acoustic or mechanical excitation is only one parameter among others making it possible to characterize the test piece 120 in order to determine the need for a correction and, where appropriate, the level of dimensional correction. to be applied to the hairsprings 110 of the plate 100.

[0130] According to another characterization method illustrated in Figure 12, the test piece 120 can be subjected to a predetermined bending force F, and its amplitude of deformation (arrow f) can be measured by optical means such as mentioned above .

[0131] The test piece 120 then behaves like a free embedded beam. Its arrow f allows for example to deduce directly or indirectly the dimensional correction to be applied, by one or the other method mentioned previously.

[0132] Figure 13 illustrates an example of a correspondence table that can be created experimentally by measuring for a given deflection f of the test piece what is the average stiffness Rs of the hairsprings, and then carrying out several iterations of correction, for example by oxidation and deoxidation or by partial deoxidation and reoxidation in the case of an already oxidized hairspring.

[0133] The table is used as follows: Suppose that we measure an arrow f with a value corresponding to the value f1 and that we want a stiffness of value Rs5, we will apply a value to the plate of dimensional correction equal to the sum of the correction values e2, e3, e4 and e5. When the deflection and stiffness values are not shown exactly in the table, the dimensional correction value can be obtained by simple interpolation.

[0134] According to another characterization method, the test piece 120 could also simply be measured using a suitable optical device. The dimensional correction to be applied could in this case be determined from the dimension(s) thus measured.

[0135] According to yet another characterization method, in a case where the test piece 120 is a characterization spiral with a geometry different from that of the spirals to be manufactured 110, as illustrated for example in FIG. 8, the stiffness Rtde can be measured. this characterization hairspring 120, then by one or the other method mentioned previously, determine the dimensional correction to be applied to the hairsprings 110.

[0136] It is possible, for example, to carry out a so-called dynamic stiffness measurement as described for example in document EP 2 423 764, by coupling the characterization spring 120 to a reference balance wheel provided with a predetermined moment of inertia I, by measuring the frequency of the resonator formed by the balance/spring assembly and deducing the stiffness Rt of the characterization spiral 120 from the formula:

[0137] As a variant, it is also possible to carry out a so-called static measurement, as described for example in document EP 2 128 723, by coupling the characterization spiral to a reference spiral via an axis of a system of rotation, by applying a rotation to the reference hairspring thanks to the rotation system, the torque being transmitted to the characterization hairspring via the axis, by carrying out a differential measurement of the angle of rotation obtained on the hairspring of characterization and the angle imposed on the reference hairspring, and using this measurement to calculate the stiffness of the characterization hairspring using the formula below, in which Rtest the stiffness of the characterization hairspring, Rrest the stiffness of the reference hairspring, a is the angle of rotation of the reference hairspring and a' is the angle measured on the characterization hairspring.

[0138] The dimensional correction is typically carried out by removing material from the components.

[0139] In this case, the target dimensions of the components (in particular their width) are initially chosen larger than the theoretical dimensions making it possible to obtain the desired final stiffness for these components.

[0140] The dimensional correction can for example be carried out by oxidation then deoxidation of the hairsprings, as illustrated in Figures 14A to 14C.

[0141] Figure 14A illustrates the section of a blade of a hairspring 110 after its formation. Its height is haand its width is la. The dimensional correction value to be applied to the hairspring is here denoted e.

[0142] Figure 14B illustrates the same hairspring section after a layer of silicon dioxide has been formed on its external surface, consuming part of the silicon. The oxidation is carried out in the humid atmosphere of a thermal oxidation furnace heated to a temperature generally around 1000°C. In the figure, the reference 112 designates the unoxidized silicon and the reference designates the silicon dioxide 114 which has formed. The thickness e' of the layer of silicon dioxide resulting from the oxidation is greater than the thickness of the unoxidized silicon 112 whose oxidation led to this silicon dioxide 114.

[0143] A thickness of silicon dioxide, preferably all of the silicon dioxide, is then removed by etching, or by chemical attack, for example with hydrofluoric acid, to adjust the dimensions of the hairspring. Figure 14C represents the same section of the hairspring, free of silicon dioxide. It has a height hbless than the height haand a width Ibless than the width la.

[0144] As an alternative, several or all of the watch hairsprings may have been oxidized with an oxide thickness w after their formation. This oxide thickness w corresponds to the final thermocompensation thickness or to a chosen thickness. In this case, the dimensional correction step d) may include at least one partial or total deoxidation step and a reoxidation of the hairsprings to the value w.

[0145] The examples mentioned above illustrate the interest of the invention for the determination and/or control of mechanical properties of the manufactured components, in particular stiffness.

[0146] As an alternative or in addition, the characterization of test piece(s) according to the invention can also be used to obtain information on critical dimensions of the components, in particular dimensions that are difficult to measure using instruments. In particular, it is possible to simulate and optimize specimen shapes and geometries which make it possible to obtain a vibration signature, as mentioned in connection with Figure 10, allowing, by causal link, to go back to any dimension of the components. .

[0147] The characterization of the test piece 120 can also make it possible to trace the functional characteristics of the components, in other words to predict the manner in which said components will interact with other watch movement components in their movement. For example, the vibration signature of a test piece can make it possible to deduce an efficiency or a frequency or an amplitude of movement (at iso parameters), in operation.

Claims (20)

1. Process for manufacturing watch components (110), in which: a) in a wafer (100) based on silicon, watch components (110) are formed according to target dimensions as well as at least one test piece (120) of target geometry different from that of the components (110), b) at least one characterization parameter of the specimen (120) representative of a characteristic of the components is determined, c) from said parameter, said characteristic of the components is determined and/or it is determined whether a dimensional correction must be applied to the components (110). 2. Method according to claim 1, wherein in step b), a vibrational excitation is applied to the test piece, and at least one vibrational characteristic of the test piece is determined during vibration, for example at least one frequency. resonance or a natural frequency of vibration. 3. Manufacturing method according to claim 2, in which the vibratory excitation is variable over time, and at least one resonance characteristic of the test piece is identified during the vibration. 4. Manufacturing method according to claim 1, wherein in step b), a deformation value (f) of the specimen (120) is measured under the effect of a predetermined bending force (F). 5. Manufacturing method according to any one of claims 1 to 4, in which step b) comprises a measurement and/or a determination of a frequency and/or an amplitude and/or a speed and /or an acceleration of movement of at least one point of the test piece. 6. Manufacturing method according to claim 5, in which the specimen (120) is defined in a base plane corresponding to the general plane of the wafer (100) during its formation, and the movement is in a direction contained in said basic plan. 7. Manufacturing method according to any one of claims 1 to 6, wherein in step b), a dimension of the test piece is measured. 8. Manufacturing method according to any one of claims 1 to 7, wherein in step c) a dimensional correction value (e) to be applied to the components (110) is further determined. 9. Manufacturing method according to claim 8, further comprising a step d) during which the dimensions of the components (110) are corrected according to the correction value determined in step c). 10. Method according to claim 9, wherein step d) comprises at least one oxidation step and a deoxidation step of the components (110). 11. Manufacturing method according to any one of claims 1 to 10, in which the characteristic of the components and/or the need for a dimensional correction and/or a dimensional correction value (e) to be applied to the components (110) is determined by means of a predictive model, for example implementing a machine learning algorithm or a polynomial formula. 12. Manufacturing method according to any one of claims 1 to 11, in which the characteristic of the components and/or the need for a dimensional correction and/or a dimensional correction value (e) to be applied to the components (110) is determined using a correspondence table. 13. Manufacturing method according to any one of claims 1 to 12, in which the components (110) are watch hairsprings. 14. Manufacturing method according to any one of claims 1 to 13, in which at least one test piece (120) is a reference spiral, and in step b), the effective stiffness (Rt) of said spiral is measured. reference. 15. Manufacturing method according to any one of claims 1 to 14, in which at least one test piece (120) is a blade extending in a rectilinear direction (Z). 16. Method according to claim 15, in which the blade comprises at least one portion of constant section, preferably is of constant section over its entire length. 17. Method according to claim 15 or 16, in which the blade comprises a portion of enlarged section (123) at its distal end (122). 18. Method according to any one of claims 1 to 17, in which a plurality of test pieces (120) is formed in the wafer (100), and in step b) an average of the primary parameters resulting from the plurality of test pieces. 19. Method according to any one of claims 1 to 18, in which step a) comprises at least the following substeps: a1) providing a substrate (10) comprising a first layer (11) based on silicon, a second layer (12) based on silicon and an intermediate layer (13) based on silicon oxide, a2) covering the first layer (11) with a layer of photosensitive resin (20), a31) exposing the layer of photosensitive resin (20) using a light source, through a photolithographic mask (30) provided with windows (31) defining the contours outside the attachment of the watch components (110) and the at minus one test piece (120), a32) locally eliminate the photosensitive resin using a solvent to form openings (21) corresponding to the non-attached contours of the watch components (110) and the test piece (120), a4) engrave the first layer (11) over its entire height under said openings (21) to form the watch components (110) and at least one test piece (120). 20. Method according to claim 19, in which the photolithographic mask (30) is a corrected mask, at least certain windows (31) of the mask being of different dimensions so as to reduce the extent of a dimensional dispersion between at least one part of the watch components (110).