CH714806A2 - Process for manufacturing watch components made of silicon - Google Patents

Abstract

The method according to the invention comprises the following steps: a) providing a substrate (1) comprising a first silicon layer (2), a second silicon layer (3) and, in between, an intermediate layer of silicon silicon oxide (4); b) etching the first silicon layer (2) to form the watch components therein; c) releasing from the substrate (1) a wafer (8) formed by at least all or part of the first etched silicon layer (2) and comprising the watch components; d) thermally oxidizing and deoxidizing the watch components; e) forming by thermal oxidation or depositing a layer of silicon oxide on the watch components; f) detach the watch components from the plate (8).

Description

CH 714 806 A2

Description: The present invention relates to a process for manufacturing watch components, such as hairsprings, anchors, wheels, needles, scales, levers, springs or pendulums, made of silicon.

Methods of manufacturing silicon watch components have been described in particular in documents EP 0 732 635, EP 1 422 436, EP 2 215 531 and EP 3 181 938.

The present invention aims to provide a method for manufacturing high quality silicon watch components.

To this end there is provided a method according to claim 1 or claim 2 and the claims dependent thereon.

The present invention further provides a support member which facilitates the implementation of this method and more generally the implementation of a heat treatment of a wafer. This support member is defined in claim 18 and the claims dependent thereon.

Other features and advantages of the present invention will appear on reading the following detailed description made with reference to the accompanying drawings in which:

fig. 1 to 11 schematically show successive stages of a method according to a particular embodiment of the invention; fig. 12 and 13 are respectively a perspective view and a profile view of a support member used in the method according to the particular embodiment of the invention for supporting a silicon wafer during a thermal oxidation treatment of the latter; fig. 14 and 15 schematically show a step in the method according to the particular embodiment of the invention, in which an etched silicon wafer is released from a composite substrate; fig. 16 shows a composite substrate from which a method according to another embodiment of the invention can be implemented.

A method of manufacturing silicon watch components, in particular for wristwatches, comprises, according to a particular embodiment of the invention, the successive steps illustrated in FIGS. 1 to 11.

In a first step (fig. 1), we provide a substrate 1 of silicon on insulator type known by the acronym SOI (Silicon-On-Insulator). The substrate 1 comprises an upper layer of silicon 2, a lower layer of silicon 3 and, between the two, an intermediate layer of silicon oxide 4. The silicon is monocrystalline, polycrystalline or amorphous. It can be doped or not. The thickness of the upper silicon layer 2 is chosen as a function of the thickness of the components that it is desired to produce. The lower silicon layer 3 is used to give the substrate 1 sufficient rigidity to facilitate its handling and the implementation of the operations which will be described below.

In a second step (FIG. 2), a layer of photosensitive lacquer 5 is deposited on the upper layer of silicon 2 and this layer 5 is structured by photolithography. More precisely, the photosensitive lacquer layer 5 is exposed to ultraviolet rays through a mask 6, typically made of glass or quartz, carrying a structure 7, typically made of chrome, to be transferred. Then the layer of photosensitive lacquer 5 is developed and baked (fig. 3). At the end of these operations, the photosensitive lacquer layer 5 has the same shape as the structure 7 and in turn constitutes a mask, said shape corresponding to that of a batch of watch components to be manufactured.

In a next step (fig. 4), the upper layer of silicon 2 is etched through the mask of photosensitive lacquer 5 by deep reactive ion etching known as DRIE (Deep Reactive Ion Etching) in order to form in this layer 2 the watch components. Etching is stopped by the intermediate layer of silicon oxide 4, thus making it possible to define a precise thickness for watch components. The etching parameters can be adjusted according to the components, to obtain particular characteristics in terms of, for example, roughness or angle of the flanks. The watch components formed in the upper silicon layer 2 are preferably identical, but they could alternatively be divided into several groups, each group corresponding to a type of component. Watch components include for example at least one of the following types of components: hairsprings, anchors, wheels, in particular escapement wheels, needles, rockers, levers, springs, pendulums, or parts of such components. The method according to the invention is particularly suitable for regulating component parts and more generally for timepiece movement components requiring a low mass and / or low inertia.

The photosensitive lacquer mask 5 is then removed by chemical etching or plasma etching (Fig. 5).

In a next step (Fig. 6), it releases from the substrate 1, in a manner which will be described later, a wafer 8 formed by at least all or part of the upper layer of silicon 2 etched. This plate 8 contains a basic structure and the watch components attached to the basic structure by bridges of material left during engraving.

CH 714 806 A2 Then the plate 8 is placed in an oxidation oven to be subjected to a heat treatment, typically between 600 ° C and 1300 ° C, oxidizing the entire outer surface of the watch components (fig. 7) . The silicon oxide layer (SiO ₂ ) 9 which then covers the wafer 8 and in particular the watch components is formed by consuming silicon from the wafer 8, which causes the interface between the silicon and the oxide to recede. silicon and attenuates silicon surface defects. By then eliminating the silicon oxide (FIG. 8), by wet etching, vapor phase etching or dry etching, watchmaking components are obtained having a good surface condition. In particular, the roughness of the sidewalls due to DRIE etching and the crystal surface defects are greatly reduced.

At this stage of the process, it is possible to measure the physical characteristics of the watch components or of some of them, in particular their dimensions. Thanks to the previous oxidation - deoxidation step, these physical characteristics are well defined and their measurement can therefore be precise, not being disturbed by surface defects. In the case of hairsprings, one can determine their stiffness. For a given hairspring, the stiffness can be determined by coupling the hairspring, while it is still attached to the wafer 8 or detached from the wafer 8, to a predetermined inertia balance, by measuring the frequency of the balance assembly -spiral and by deducing from this measurement, by calculation, the stiffness of the hairspring. One can more particularly implement the method described in patent application EP 3 181 938, namely determining the stiffness of the hairsprings, calculating a thickness of material to be removed from the hairsprings to obtain a desired stiffness, then removing this thickness of material in order to obtain spirals of the desired stiffness. To remove said thickness of material, it is possible to thermally oxidize the plate 8 and its watch components (fig. 9) and then deoxidize it (fig. 10), in the same manner as described previously with reference to fig. 7 and 8. The operations of determining the stiffness, of calculating the thickness to be removed and of removing this thickness by oxidation - deoxidation can be repeated if necessary to refine the dimensional accuracy of the hairsprings.

In yet another step of the process (fig. 11), a layer of silicon oxide (SiO ₂ ) 10 is formed on the wafer 8 and its watch components, for example by thermal oxidation or by chemical or physical deposition in vapor phase (CVD, PVD). This layer of silicon oxide 10 which coats the watch components reinforces their mechanical resistance. In the case of a hairspring, the silicon oxide layer 10 has a thickness which allows it to compensate for the variations as a function of the temperature of the elastic modulus of the silicon core as well as the variations as a function of the temperature of the moment of inertia of the balance that the balance spring is intended to equip, so that the frequency of the balance-spring oscillator is insensitive to temperature, as described in patents EP 1 422 436 and EP 2 215 531.

In a final step, the watch components are detached from the basic structure of the wafer 8.

During the oxidation steps (fig. 7 and 9 and, if necessary, fig. 11), the plate 8 is preferably supported horizontally by a support plate 11 as illustrated in fig. 12 and 13, which can be manipulated manually or by a robot. This support plate 11 is made of a material compatible with the oxidation treatment, for example quartz, silicon or silicon carbide. To allow homogeneous oxidation of the wafer 8, the latter is raised relative to the support wafer 11 by spacers 12 which support the wafer 8 in areas which do not contain components (in particular between the components). The plate 8 is prevented from moving horizontally by retaining elements 13 cooperating with the periphery of the plate 8. The spacers 12 and the retaining elements 13 are of generally cylindrical shape. They are integral with the support plate 11, for example fixed to the support plate 11 by bayonet type connections. They are made for example from quartz or from silicon carbide, and can be of the same material or in different materials. In a preferred embodiment, the support plate 11 is made of silicon and the spacers and retaining elements 12, 13 are made of quartz. Such a support plate 11 with its spacers 12 and retaining elements 13 can also be used during the step of FIG. 11 when this consists of a CVD or PVD deposit operation.

Preferably, during the oxidation treatment of FIG. 9, the plate 8 is placed on the support plate 11 in an inverted position relative to the oxidation treatment of FIG. 7. Likewise, during the oxidation or deposition treatment of FIG. 11, the plate 8 is placed on the support plate 11 in an inverted position relative to the oxidation treatment of FIG. 9. This makes it possible to prevent permanent deformation from occurring in watch components under the effect of gravity and heat, or at least to limit such deformation.

The step of releasing the wafer 8 from the substrate 1 (FIG. 6) can be implemented by removing all of the lower silicon layer 3 and of all of the intermediate silicon oxide layer 4 by chemical etching. or plasma etching. It is also possible to remove the lower layer of silicon 3 and the intermediate layer of silicon oxide 4 only on the back of the components or groups of components, the wafer 8 then retaining part of these layers 3, 4. However, these operations are long and expensive. In the present invention, preferably, the wafer 8 is formed by a part of the upper layer of silicon 2 and its release from the substrate 1 is implemented in the manner described below and illustrated in FIGS. 14 and 15.

The etched substrate 1 is fixed as shown in FIG. 5 against a heating element 14 in a closed chamber 15 (FIG. 14), the upper layer of silicon 2 being oriented downwards, the lower layer of silicon 3, therefore oriented upwards, being against the heating element 14. The method of fixing the substrate 1 against the heating element 14 can be electrostatic (by application of an electric field) or mechanical. A solution of hydrofluoric acid (HF) is added to the chamber 15, out of contact with the substrate 1. The vapors of hydrofluoric acid which then saturate the interior of the chamber 15 etch the intermediate layer of silicon oxide 4, without attacking the silicon. The heating element 14,

CH 714 806 A2 temperature controlled, prevents condensation of the water produced by the reaction between hydrofluoric acid and silicon oxide, condensation which would cause sticking between the part to be released and the rest of the substrate 1.

The part to be released, namely the wafer 8, is defined beforehand by a groove made during the etching of the upper layer of silicon 2 and which forms the periphery of the wafer 8. During this same etching of the upper layer of silicon 2, openings 16, for example in the form of hatching as shown in FIG. 15, are engraved in the plate 8 around a central area 17 comprising the components. These openings 16 allow the passage of hydrofluoric acid vapor.

[0022] FIG. 15 shows an example of a plate 8 having a shape made up of rectangular or square parts. Other shapes can of course be envisaged, for example the circular shape. In fig. 15 we can see the watch components 18 carried by the plate 8, here made of hairsprings. These watch components have been shown in reduced numbers compared to their real number, in order to facilitate the reading of the drawing.

The watch components manufactured by the process according to the invention can have very precise dimensions and good surface finishes which will improve the operating precision and the efficiency of the mechanisms which will use them.

Modifications to the method according to the invention as described above are of course possible.

For example, although the two stages of oxidation - deoxidation (fig. 7, 8 and fig. 9, 10) to respectively improve the surface condition of the watch components and adjust their stiffness (in the case of hairsprings ) are particularly advantageous, one could be provided with only one, at a time to improve the surface condition and adjust the stiffness, that would precede a step of determining the stiffness.

One could also start from a double or triple SOI substrate, or even more, that is to say from a substrate comprising more than two layers of silicon separated by intermediate layers of silicon oxide, such as substrate 20 shown in FIG. 16, and etching the watch components in a group of upper layers which would then be released from the substrate. The watch components would then have a composite structure comprising one or more intermediate layers of silicon oxide.

The photosensitive lacquer mask 5 which is used to structure the upper layer of silicon 2 (FIG. 3) could be replaced by a mask of silicon oxide. We could also associate a photosensitive lacquer mask and a silicon oxide mask to produce multilayer watch components by etching in the upper layer of silicon or in a group of upper layers.

In other variants, one could etch the substrate from its two faces.

Or the layers of silicon oxides used to stop the etching could be reinforced by one or more layers of parylene type.

Finally, the present invention also does not exclude the use of one or more metallic layers to stop etching.

claims

Claims (21)

1. Method for manufacturing watch components comprising the following steps: a) providing a substrate (1) comprising a first layer of silicon (2), a second layer of silicon (3) and, between the two, an intermediate layer of silicon oxide (4), b) etching the first layer of silicon (2) in order to form the watch components, c) releasing from the substrate (1) a wafer (8) formed by at least all or part of the first silicon layer (2) etched and comprising the horological components, d) thermally oxidize and then deoxidize watch components, e) forming by thermal oxidation or deposition a layer of silicon oxide (10) on the watch components, and f) detach the watch components from the plate (8). 2. Method for manufacturing watch components comprising the following steps: a) providing a substrate (20) comprising layers of silicon interspersed with layers of silicon oxide, b) etching a group of layers of the substrate in order to form the watch components, c) releasing from the substrate a wafer formed by at least all or part of the group of layers and comprising the horological components, d) thermally oxidize and then deoxidize watch components, e) forming, by thermal oxidation or deposition, a layer of silicon oxide on the watch components, and f) detach the watch components from the plate. 3. Method according to claim 1 or 2, wherein the etching in step b) comprises a deep reactive ion etching. 4. Method according to one of claims 1 to 3, comprising between steps d) and e) an additional step of thermally oxidizing and then deoxidizing the watch components. CH 714 806 A2 5. The method of claim 4, wherein step d) is used to improve the surface condition of the watch components and said additional step is used to adjust the stiffness of hairsprings constituting the watch components. 6. Method according to claim 4 or 5, wherein during the thermal oxidation operation of said additional step the wafer (8) is in an inverted position relative to the thermal oxidation operation of step d) . 7. Method according to one of claims 4 to 6, wherein during step e) the wafer (8) is in an inverted position relative to the thermal oxidation operation of said additional step. 8. Method according to one of claims 1 to 7, wherein during the thermal oxidation operation (s), the plate (8) is supported by a support member (11, 12, 13) comprising a support plate ( 11) and spacers (12) and retaining elements (13) carried by the support plate (11), the spacers (12) maintaining a spacing between the plate (8) and the support plate (11), the elements retainer (13) preventing the plate (8) from moving horizontally. 9. The method of claim 8, wherein the spacers (12) support the plate (8) in areas of the plate (8) not comprising a timepiece component. 10. The method of claim 8 or 9, wherein the support plate (11) is made of silicon, quartz or silicon carbide. 11. Method according to one of claims 8 to 10, in which the spacers (12) and the retaining elements (13) are made of quartz or silicon carbide. 12. Method according to one of claims 8 to 11, wherein the spacers (12) and the retaining elements (13) are fixed to the support plate (11) by bayonet type connections. 13. Method according to one of claims 1 and 3 to 12, wherein step c) comprises an operation of vapor phase etching of the intermediate layer of silicon oxide (4). 14. Method according to one of claims 1 and 3 to 13, wherein the wafer (8) released in step c) is formed by a portion of the first silicon layer (2) etched. 15. Method according to one of claims 1 and 3 to 14, wherein in step b) a groove is etched in the first silicon layer (2) to define the periphery of the wafer (8) to be released during step c). 16. Method according to one of claims 1 and 3 to 15, wherein in step b) openings (16) are etched in the first layer of silicon (2) around a central area (17) where are engraved watch components (18), these openings (16) allowing the passage of an etchant for the intermediate layer of silicon oxide (4) during step c). 17. Method according to one of claims 1 to 16, wherein the horological components comprise at least one of the following types of components: hairsprings (18), anchors, wheels, needles, scales, levers, springs, pendulums, or parts of such components. 18. Support member (11, 12, 13) intended to support a plate (8) during a heat treatment of this plate (8), this support member comprising a support plate (11) and spacers (12) and retaining elements (13) carried by the support plate (11), the spacers (12) serving to maintain a spacing between the support plate (11) and the plate (8), the retaining elements (13) serving to prevent the plate (8) from moving horizontally. 19. Support member (11) according to claim 18, wherein the support plate (11) is made of silicon, quartz or silicon carbide. 20. Support member (11) according to claim 18 or 19, wherein the spacers (12) and the retaining elements (13) are made of quartz or silicon carbide. 21. Support member (11) according to one of claims 18 to 20, in which the spacers (12) and the retaining elements (13) are fixed to the support plate (11) by bayonet type connections.