Classifications

• • G—PHYSICS
  • G04—HOROLOGY
  • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
  • G04B17/00—Mechanisms for stabilising frequency
  • G04B17/04—Oscillators acting by spring tension
  • G04B17/06—Oscillators with hairsprings, e.g. balance
  • G04B17/066—Manufacture of the spiral spring
• • G—PHYSICS
  • G04—HOROLOGY
  • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
  • G04B17/00—Mechanisms for stabilising frequency
  • G04B17/04—Oscillators acting by spring tension
  • G04B17/045—Oscillators acting by spring tension with oscillating blade springs
• • G—PHYSICS
  • G04—HOROLOGY
  • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
  • G04B17/00—Mechanisms for stabilising frequency
  • G04B17/20—Compensation of mechanisms for stabilising frequency
  • G04B17/22—Compensation of mechanisms for stabilising frequency for the effect of variations of temperature
  • G04B17/227—Compensation of mechanisms for stabilising frequency for the effect of variations of temperature composition and manufacture of the material used
• • G—PHYSICS
  • G04—HOROLOGY
  • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
  • G04B31/00—Bearings; Point suspensions or counter-point suspensions; Pivot bearings; Single parts therefor
• • G—PHYSICS
  • G04—HOROLOGY
  • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
  • G04B31/00—Bearings; Point suspensions or counter-point suspensions; Pivot bearings; Single parts therefor
  • G04B31/06—Manufacture or mounting processes

Definitions

• the invention relates to a method of manufacturing a watch component, in particular a spiral spring for an oscillator. It also relates to a horological component as such, as well as to a timepiece movement and a timepiece as such which include such a horological component.
• a watch component must meet many properties, among which it should preferably be non-magnetic, be endowed with reliable and high-performance mechanical properties, durable over time, independent of external conditions and including temperature, while being as simple as possible to manufacture to allow commercial use.
• Existing solutions are often based on trade-offs, and the resulting components are not optimized in terms of performance.
• the manufacturing processes for watch components are often very complex to implement.
• the regulation of mechanical watches is based on at least one mechanical oscillator, which generally comprises a flywheel, called a balance, and a spring wound in the form of a spiral, called a spiral spring or more simply a spiral.
• the hairspring can be fixed by one end to the balance axis and by the other end to a fixed part of the timepiece, such as a bridge, called a cock, on which the balance axis pivots.
• the spiral spring equipping mechanical watch movements of the prior art is in the form of an elastic metal blade or of a silicon blade of rectangular section, most of which is wound around itself in a spiral. of Archimedes.
• the sprung balance oscillates around its equilibrium position (or neutral). When the balance leaves this position, it arms the hairspring.
• document EP1422436 describes a solution based on a silicon hairspring comprising a layer of silicon dioxide intended to thermocompensate an oscillator.
• This solution requires a thick oxide layer. Its manufacture requires treating the hairspring for a long time at very high temperature, which is a drawback.
• document EP3159746 proposes to use a highly doped silicon. However, it is difficult to achieve the high doping rates required for thermo compensation.
• the precision of mechanical watches also depends on the stability over time of the natural frequency of the oscillator formed by the balance and the hairspring.
• the existence of phenomena of drift in the frequency of a sprung balance oscillator as a function of time is well known to watchmakers.
• an oscillator provided with a hairspring made of raw ferromagnetic alloy can see its frequency progressively increase to reach a rate variation of the order of 10 s / d after one year.
• heat treatments called parboiling treatments, which reduce the drift in the first years to below 1 s / d, which is acceptable, taking into account other disturbances caused by wearing the watch, such as shocks.
• a ferromagnetic alloy is more susceptible to adverse external magnetic influences which can manifest as an operating drift.
• an existing horological oscillator hairspring like any other horological component, has drawbacks which do not allow optimized operation of a timepiece to be achieved.
• the aim of the invention is to provide a new solution for a watch component, in particular a spiral spring, which allows its optimization, by achieving both optimum performance, suitable for thermocompensation of a functional assembly, and sufficiently simple manufacture. and robust.
• the invention seeks a solution for manufacturing on a large scale a watch component whose performance is optimized, that is to say that its intrinsic mechanical properties guarantee high performance in its operation, while being as stable as possible. , remaining little or not sensitive to external aggressions such as magnetic fields and temperature variations.
• the invention is based on a method of manufacturing a watch component capable of thermocompensating a functional assembly comprising the watch component, characterized in that it comprises at least the following steps: a. Use a semiconductor or metallic material substrate; b. Deposit a polycrystalline or monocrystalline silicon layer on the substrate; vs. Release the clock component from the substrate.
• the invention also relates to a horological component for a timepiece totally or partially in polysilicon, characterized in that it comprises a part in polysilicon comprising a homogeneous doping over its entire thickness, or in that it comprises a polycrystalline silicon part comprising a doped layer on the surface.
• the invention also relates to an oscillator for a timepiece and a timepiece as such.
• FIGS 1 to 4 schematically show steps of a method of manufacturing a watch component according to one embodiment of the invention.
• Figures 5 to 7 schematically represent a technique that can be used for a complementary doping step in an alternative embodiment of the method of manufacturing a watch component according to the embodiment of the invention.
• FIGS 8 and 9 show different possible embodiments of watch components according to the embodiment of the invention.
• the invention will be described in the context of a hairspring of a balance-spring assembly forming an oscillator for a timepiece.
• the hairspring is in the form of an elastic blade of rectangular section, wound on itself in an Archimedean spiral.
• the hairspring could have another basic geometry, such as a non-rectangular section, which may or may not be constant over the length of the hairspring.
• the invention will naturally be transposable to manufacture of other horological components than a balance spring, including a component of a flexible guided oscillator or a component of an arrangement of flexible geometries forming an elastic virtual pivot.
• the balance can be made of a copper-berrylium alloy, in a known manner. Alternatively, other materials can be used for the balance.
• the invention according to this embodiment does not relate to this balance as such.
• the hairspring is designed with a view to being able to thermocompensate the functional unit forming an oscillator, made up of the association of the hairspring with a certain given balance.
• This method comprises in particular a first step E1 consisting in providing a substrate 1, which is a single crystal silicon wafer in this embodiment (often referred to by its English term of “wafer”).
• a simple wafer is sufficient, it is not necessary to use a silicon-on-insulator wafer (known by its English name of SOI for “Silicon on Insulator”), unlike most of the existing methods. , even if such a silicon-on-insulator wafer remains compatible with the invention.
• the substrate can be metallic, or of silicon carbide, or of tungsten carbide, or of quartz.
• a first advantage of the invention is to allow the use as a substrate of a wafer that is simpler and less expensive than those used in the solutions of the state of the art.
• this first step E1 comprises optional additional steps for preparing the wafer. So this wafer can be polished and cleaned. It can also be covered with an oxidation layer 2, as shown in Figure 1. For example, its surface can be oxidized to form a layer of the order of 2 ⁇ m thick of silicon dioxide S1O2 on the surface.
• the method then comprises a second step E2 illustrated by FIG. 2 consisting in depositing a layer of silicon 5, polycrystalline or monocrystalline, on the surface of the substrate 1 (that is to say optionally on the surface of the oxidation layer 2 when there is one).
• the polycrystalline or monocrystalline silicon can be deposited in a CVD reactor at high temperature with a flow of gas containing silane and hydrogen.
• the growth takes place epitaxially.
• the starting surface is made from an already polycristaline silicon layer such as those deposited in a low temperature LPCVD reactor (seed layer). This growth forms a layer that rises in a direction perpendicular to the surface of substrate 1.
• polycrystalline silicon could be deposited by any other process.
• the silicon deposition can consist of a deposition of the silicon by a CVD (for “Chemical Vapor Deposition”) or PVD (for “Physical Vapor Deposition”) method.
• the silicon deposition is continued until a height of approximately 120 miti is reached, which will determine the thickness of the future watch component as will be specified.
• an optional intermediate step is advantageously implemented, consisting in polishing the silicon layer 5 thus formed, to guarantee a satisfactory surface condition of its upper surface and a homogeneous height of the layer.
• This polishing can be a polishing known by its acronym CMP (coming from its English name of “Chemical Mechanical Polishing”).
• the method then implements a third etching step E3 of the silicon layer 5, the result of which is illustrated in FIG. 3.
• An etched silicon layer 6 is obtained.
• This etching is carried out by known methods, such as for example by deep reactive ionic etching (known by its acronym DRIE for “Deep Reactive Ion Etching”).
• DRIE deep reactive ionic etching
• Such a method uses a resin forming a mask, making it possible to delimit the areas to be etched according to a predefined pattern, corresponding to the watch component (the hairspring) to be manufactured in this embodiment, before the final removal of the resin.
• This method is well known and will not be described in detail.
• this etching can be carried out using a laser or by any other method known from the state of the art.
• the result of this step is an etched silicon layer 6 arranged on the substrate 1.
• the method comprises a fourth step E4 of freeing the etched silicon layer 6 from the substrate 1, as illustrated in FIG. 4, which makes it possible to obtain the timepiece component 10.
• the substrate 1 therefore serves only for the manufacture of the timepiece component, is not intended to belong to the timepiece component 10.
• the latter therefore has a thickness corresponding to the height of the silicon layer 5 formed by the silicon deposition step E2, optionally treated.
• This method advantageously makes it possible to simultaneously manufacture several watch components on the same substrate 1.
• the fourth release step E4 consists in such a case in the release of all these watch components.
• the release is carried out according to one of the techniques known in the state of the art, for example by etching the substrate 1 by its lower surface in order to create laces facilitating access to the oxidation layer 2 in order to dissolve it by hydrofluoric acid or by perforating the unetched parts of the upper part of the SOI wafer.
• monocrystalline silicon exhibits anisotropy of its elastic properties since its elastic modulus depends on crystal orientation. This elastic modulus anisotropy was measured to be of the order of ⁇ 15% around its mean value. This technical characteristic is reflected by constraints during the manufacture of a component in monocrystalline silicon, since such a design must take this phenomenon into account in order to achieve a watch component whose performance suffers little or little from this anisotropy.
• the variant embodiment using a polycrystalline silicon thus has an advantage of making it possible to obtain a watch component with isotropic elastic properties, which simplifies the overall design of the watch component, of the balance spring in this embodiment.
• the watch component 10 obtained by the embodiment results from a single silicon deposition step, which makes it possible to obtain a watch component that is in a single piece, integral, homogeneous, monobloc, monolithic. It is not formed by the union of several distinct parts, nor even by a succession of layers resulting from distinct growths.
• the watch component thus formed is intended for association with one or more other components for the implementation of a certain horological functionality: this is the case when this watch component is a balance spring, which is intended for a hairspring. association with a balance to form a watch movement oscillator, as explained above.
• the two separate watch components, the hairspring and the balance are thus intended to cooperate in order to fulfill their common oscillator functionality.
• a given horological component is intended to belong to a larger functional unit.
• a strong doping of the silicon of a balance-spring makes it possible to improve the performance of the oscillator obtained with respect to temperature variations. It is in fact observed that depending on the material used for the balance, for example titanium or a titanium alloy, this single highly doped silicon of the balance spring may be sufficient to obtain thermocompensation of the oscillator resulting from the cooperation of the balance spring with the pendulum.
• an n-type silicon doping is for example obtained by using at least one element from: antimony Sb, arsenic As, or phosphorus P. We mean by doping one of the solutions mentioned above or an equivalent solution. .
• the invention has another advantage of making it easier to obtain a doped silicon component, as will be detailed below.
• doping of the so-called “in-situ” silicon is implemented, that is to say directly during the step of depositing the silicon E2, simultaneously with this deposit, in particular with n-type dopants such as phosphorus.
• n-type dopants such as phosphorus.
• This first variant embodiment has the advantage of obtaining a watch component comprising a doping of silicon over its entire thickness (over the entire height of the deposited silicon layer 5). Such doping can even be substantially uniform, homogeneous, throughout the volume of the silicon.
• a doping step is implemented after the end of the step E2 of depositing the silicon layer 5.
• the doping step can be implemented before or after. etching of the silicon layer 5, in the case of the embodiment described above. It is preferably implemented before the E4 release step of the timepiece component, but as a variant, it could even be implemented after the E4 release step, therefore on the timepiece component separated from the substrate.
• Such a doping step is a doping step by diffusion or ion implantation, allowing the dopant to diffuse into the clock component, forming a doped layer in part of the thickness of the clock component.
• Such doping does not result in uniform doping in said doped layer, the doping decreasing as one moves away from the surface through which the diffusion is carried out. It is notable that such diffusion is faster in polysilicon than in monocrystalline silicon, thanks to the presence of grain boundaries in polysilicon.
• FIGS. 5 to 7 illustrate for this purpose a method of doping a component 11 made of silicon, represented by FIG. 5, which can be used for the second variant embodiment described above.
• This component 11 is first coated with a layer 12 of 110 nanometers of POCI3, as shown in FIG. 6.
• a first diffusion of phosphorus within the polycrystalline silicon is then carried out via at least one annealing of 60 minutes under an atmosphere of. nitrogen (for example a first annealing of 60 minutes at 900 ° C, followed by another annealing of 60 minutes at 1000 ° C).
• the POCI3 layer is then removed by immersion in buffered hydrofluoric acid. The result obtained is illustrated in FIG. 7.
• Such a method makes it possible to form a doped layer 14 at a high rate, greater than or equal to 10 21 at / cm 3 .
• a second phosphorus diffusion test within the polysilicon was carried out via a 4 hour annealing.
• PSG phosphosilicate glass
• the two doping variants described above can be combined, a posteriori doping thus completing a first doping carried out in situ during the growth of the polysilicon layer.
• a doped polycrystalline silicon watch component has the advantage of retaining an isotropic thermal coefficient (CTE), which makes the design of a watch component unconstrained. Indeed, the fact of implementing the invention with polycrystalline silicon has the advantage of great freedom for the design of a watch component, while being able to achieve great insensitivity to temperature variations. In addition, it should be noted that the doping of polysilicon is easier to obtain compared to the doping of monocrystalline silicon.
• CTE isotropic thermal coefficient
• the doping methods described above are compatible with different silicon doping rates, even high rates making it possible to achieve thermal compensation of a watch component such as an oscillator.
• heavily doped silicon can be used.
• heavily doped it is understood that silicon exhibits doping with an ionic density greater than or equal to 10 18 at / cm 3 , or even greater than or equal to 10 19 at / cm 3 , or even greater than or equal to 10 2 ° at / cm 3 .
• this layer of silicon oxide may not be an external layer, but for example an internal layer, for example sandwiched in the structure of the component.
• the timepiece component can more generally comprise a portion made of silicon oxide. The fact of carrying out a doping has the advantage in all cases of making it possible to reduce the layer or portion of oxide which would be necessary in a solution without doping.
• the process can optionally comprise an additional oxidation step.
• the oxidation layer or portion used may have a low thickness, which has the advantage of allowing it to be produced at a low oxidation temperature.
• this small thickness of the oxidation layer or portion also allows its production using oxygen as a precursor, instead of the water vapor used for thicker oxidation layers, thus making it possible to form a high quality oxidation layer or portion while minimizing its growth time.
• the invention advantageously makes it possible to achieve a zero thermal coefficient (CTE) value for a sprung balance, the oscillations of which thus become independent or almost independent of temperature.
• the hairspring of the invention advantageously makes it possible to be adapted to the cancellation of the thermal coefficient (CTE) of a balance-spring oscillator forming a functional unit.
• the method of manufacturing a watch component of the invention is simplified and less expensive than the existing methods, as described above, while offering great flexibility since several variants.
• implementation make it possible to greatly improve the performance of the watch component in a simple manner, in particular by making it possible to respond to the problem of thermocompensation.
• the method of the invention proposes the manufacture of a watch component capable of thermocompensating a larger functional assembly comprising several components including said watch component, these several components together fulfilling a certain horological functionality, such as that of an oscillator, as described previously.
• a finishing step can consist of smoothing the surface of the silicon as described by document EP2277822.
• This document describes the performance of a step of forming an oxide layer and then dissolving it, making it possible to remove the surface layer of silicon, which may contain defects and / or the initiation of cracks. Such a step thus makes it possible to round off the roughness and strengthen the component.
• This solution ultimately consists of smoothing the surface of the polysilicon.
• the invention also relates to a watch component in polycrystalline silicon obtained by the method described above.
• a watch component advantageously comprises a single-piece part, integrally formed, originating from a single polysilicon growth step. It can also include doping, possibly strong, of polysilicon.
• the invention is particularly suitable for forming a hairspring, as described above, but also other horological components illustrated in FIGS. 8 and 9 such as a component of a flexible guided oscillator, a component of an arrangement of flexible geometries forming a elastic virtual pivot.
• the invention also relates to a timepiece oscillator, a timepiece movement, and a timepiece, such as a watch, for example a wristwatch, comprising at least one horological component as described above.

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• Metallurgy (AREA)
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• 2021
  • 2021-02-18 US US17/800,467 patent/US20230136065A1/en active Pending
  • 2021-02-18 JP JP2022550858A patent/JP2023514445A/ja active Pending
  • 2021-02-18 WO PCT/EP2021/053950 patent/WO2021170473A1/fr unknown
  • 2021-02-18 EP EP21704834.7A patent/EP4111264A1/de active Pending
  • 2021-02-18 CN CN202180016517.8A patent/CN115176206A/zh active Pending

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