CH714806B1 - Process for manufacturing silicon watch components. - Google Patents

Abstract

The method according to the invention comprises 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 therein; c) releasing from the substrate (1) a wafer (8) formed by at least all or part of the etched first silicon layer (2) and comprising the timepiece 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; f) detaching the watch components from the plate (8).

Description

The present invention relates to a process for manufacturing watch components, such as hairsprings, anchors, wheels, hands, levers, levers, springs or pendulums, in silicon.

[0002] Processes for manufacturing silicon watch components have been described in particular in documents EP 0732635, EP 1422436, EP 2215531 and EP 3181938.

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.

Other characteristics and advantages of the present invention will appear on reading the following detailed description given with reference to the appended drawings in which: FIGS. 1 to 11 schematically show successive steps of a method according to a particular embodiment of the invention; FIGS. 12 and 13 are respectively a perspective view and a side view of a support member used in the method according to the particular embodiment of the invention to support a silicon wafer during a thermal oxidation treatment of the latter; FIGS. 14 and 15 schematically show a step of 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.

[0006] A process for manufacturing watch components in silicon, in particular for wristwatches, comprises, according to a particular embodiment of the invention, the successive steps illustrated in FIGS. 1 to 11.

At a first step (Figure 1), it is provided with a substrate 1 of the silicon-on-insulator type known by the acronym SOI (Silicon-On-Insulator). 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. Silicon is monocrystalline, polycrystalline or amorphous. It can be doped or not. The thickness of the upper layer of silicon 2 is chosen according to the thickness of the components which it is desired to produce. The lower layer of silicon 3 serves 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 (Figure 2), is deposited on the upper layer of silicon 2 a layer of photoresist 5 and this layer 5 is structured by photolithography. More specifically, the layer of photosensitive lacquer 5 is exposed to ultraviolet rays through a mask 6, typically made of glass or quartz, carrying a structure 7, typically made of chromium, to be transferred. Then the layer of photosensitive lacquer 5 is developed and baked (FIG. 3). At the end of these operations, the layer of photosensitive lacquer 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 (Figure 4), the upper silicon layer 2 is etched through the photosensitive lacquer mask 5 by deep reactive ion etching called DRIE (Deep Reactive Ion Etching) in order to form in this layer 2 the components watchmakers. The etching is stopped by the intermediate layer of silicon oxide 4, thus making it possible to define a precise thickness for the watch components. The etching parameters can be adjusted according to the components, to obtain particular characteristics in terms for example of roughness or angle of the flanks. The timepiece components formed in the upper layer of silicon 2 are preferably identical but they could alternatively be divided into several groups, each group corresponding to a type of component. The horological components comprise for example at least one of the following types of components: hairsprings, levers, wheels, in particular escapement wheels, hands, rockers, levers, springs, balances, or parts of such components. The method according to the invention is particularly suitable for regulating member components and more generally for watch movement components requiring low mass and/or low inertia.

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

At a next step (Figure 6), is released 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 wafer 8 contains a base structure and the timepiece components attached to the base structure by bridges of material left during the engraving.

[0012] Then the wafer 8 is placed in an oxidation furnace 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 layer of silicon oxide (Si02) 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 silicon oxide to recede. and attenuates silicon surface defects. By then eliminating the silicon oxide (FIG. 8), by wet etching, vapor phase etching or dry etching, watch components with a good surface condition are obtained. In particular, the roughness of the flanks due to the DRIE etching and the surface crystalline defects are greatly reduced.

[0013] 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, their stiffness can be determined. 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 balance wheel of predetermined inertia, by measuring the frequency of the balance wheel assembly -hairspring and deducing from this measurement, by calculation, the stiffness of the hairspring. It is more particularly possible to implement the method described in patent application EP 3181938, namely to determine the stiffness of the hairsprings, calculate a thickness of material to be removed from the hairsprings to obtain a desired stiffness, then remove this thickness of material in order to obtain hairsprings of the desired stiffness. To remove said thickness of material, the wafer 8 and its timepiece components can be thermally oxidized (FIG. 9) then deoxidized (FIG. 10), in the same way as previously described with reference to FIGS. 7 and 8. the stiffness, calculation of the thickness to be removed and removal of this thickness by oxidation - deoxidation can be repeated if necessary to refine the dimensional precision of the hairsprings.

At yet another step of the process (FIG. 11), a layer of silicon oxide (SiO2) 10 is formed on the wafer 8 and its timepiece components, for example by thermal oxidation or by chemical or physical phase deposition. steam (CVD, PVD). This layer of silicon oxide 10 which coats the timepiece components reinforces their mechanical strength. In the case of a hairspring, the layer of silicon oxide 10 has a thickness which enables it to compensate for the variations as a function of temperature of the modulus of elasticity 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 hairspring is intended to equip, so that the frequency of the balance-hairspring oscillator is insensitive to temperature, as described in patents EP 1422436 and EP 2215531.

[0015] In a final step, the watch components are detached from the basic structure of the wafer 8.

During the oxidation steps (Figures 7 and 9 and, where appropriate, Figure 11), the wafer 8 is preferably supported horizontally by a support plate 11 as shown in Figures 12 and 13, which can be handled manually or by a robot. This support plate 11 is in 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 that do not contain components (in particular between the components). Plate 8 is prevented from moving horizontally by retaining elements 13 cooperating with the periphery of plate 8. Spacers 12 and retaining elements 13 are generally cylindrical in 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, of quartz or of silicon carbide, and may be of the same material or of different materials. In a preferred exemplary 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 the latter consists of a CVD or PVD deposition operation.

Preferably, during the oxidation treatment of Figure 9, the wafer 8 is placed on the support plate 11 in an inverted position relative to the oxidation treatment of Figure 7. Similarly, during the treatment oxidation or deposition of Figure 11, the wafer 8 is placed on the support plate 11 in an inverted position with respect to the oxidation treatment of Figure 9. This prevents permanent deformations from occurring in watch components under the effect of gravity and heat, or to at least limit these deformations.

The step of releasing the wafer 8 from the substrate 1 (FIG. 6) can be implemented by eliminating all of the lower layer of silicon 3 and all of the intermediate layer of silicon oxide 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 keeping part of these layers 3, 4. However, these operations are long and expensive. In the present invention, the wafer 8 is preferably formed by a part of the upper layer of silicon 2 and its release from the substrate 1 is implemented in the manner set out below and illustrated in FIGS. 14 and 15.

[0019] The substrate 1 etched as shown in FIG. 5 is fixed 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 hydrofluoric acid (HF) solution is added to chamber 15, out of contact with substrate 1. The hydrofluoric acid vapors which then saturate the interior of chamber 15 etch the intermediate layer of silicon oxide 4, without attacking the silicon. The heating element 14, regulated in temperature, prevents the condensation of the water produced by the reaction between the hydrofluoric acid and the 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 represented in FIG. 15, are etched in the wafer 8 around a central zone 17 comprising the components. These openings 16 allow the passage of hydrofluoric acid vapor.

Figure 15 shows an example of plate 8 having a shape consisting of rectangular or square parts. Other shapes can of course be envisaged, for example the circular shape. In FIG. 15 one can see the timepiece components 18 carried by the wafer 8, here made up of hairsprings. These timepiece components have been represented in reduced numbers compared to their real number, in order to facilitate reading of the drawing.

[0022] The watch components manufactured by the process according to the invention can have very precise dimensions and good surface states which will improve the operating precision and the efficiency of the mechanisms which will use them.

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

[0024] For example, although the two oxidation-deoxidation steps (FIGS. 7, 8 and FIGS. 9, 10) to respectively improve the surface condition of watch components and adjust their stiffness (in the case of hairsprings) are particularly advantageous, only one could be provided, both to improve the surface condition and to adjust the stiffness, which would be preceded by a step of determining the stiffness.

One could also start from a double or triple SOI substrate, or even more, that is to say a substrate comprising more than two layers of silicon separated by intermediate layers of silicon oxide, such as substrate 20 shown in Figure 16, and etch the timepiece 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 serves to structure the upper silicon layer 2 (FIG. 3) could be replaced by a silicon oxide mask. It would also be possible to combine a mask of photosensitive lacquer and a mask of silicon oxide to produce, by etching in the upper layer of silicon or in a group of upper layers, multilevel timepiece components.

In other variants, the substrate could be etched from both sides.

[0028] The silicon oxide layer(s) serving to stop etching could be reinforced by one or more parylene-type layers.

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

Claims (17)

1. Process 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 therein, c) releasing from the substrate (1) a wafer (8) formed by at least all or part of the etched first silicon layer (2) and comprising the timepiece components, d) thermally oxidize then deoxidize the watch components, e) forming by thermal oxidation or deposition a layer of silicon oxide (10) on the watch components, and f) detaching the watch components from the plate (8). 2. Process for manufacturing watch components comprising the following steps: a) providing a substrate (20) comprising layers of silicon intercalated 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 timepiece components, d) thermally oxidize then deoxidize the watch components, e) forming by thermal oxidation or deposition a layer of silicon oxide on the watch components, and f) detaching the watch components from the wafer. 3. Process according to claim 1 or 2, in which the etching in step b) comprises deep reactive ion etching. 4. Method according to one of claims 1 to 3, comprising between steps d) and e) an additional step consisting in thermally oxidizing then deoxidizing the timepiece components. 5. Method according to claim 4, in which step d) serves to improve the surface condition of the timepiece components and said additional step serves to adjust the stiffness of hairsprings constituting the timepiece 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 with respect 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 with respect 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 or operations, the wafer (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 distance between the wafer (8) and the support plate (11), the elements retainer (13) preventing the pad (8) from moving horizontally. 9. Method according to claim 8, in which the spacers (12) support the wafer (8) in areas of the wafer (8) not comprising any timepiece component. 10. Method according to claim 8 or 9, in which the support plate (11) is made of silicon, quartz or silicon carbide. 11. Method according to one of claims 8 to 10, wherein 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, in which step c) comprises a vapor phase etching operation 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 part of the first etched silicon layer (2). 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 silicon layer (2) around a central zone (17) where engraved the watch components (18), these openings (16) allowing the passage of an etching agent for the intermediate layer of silicon oxide (4) during step c). 17. Method according to one of claims 1 to 16, in which the timepiece components comprise at least one of the following types of components: hairsprings (18), anchors, wheels, hands, levers, levers, springs, balances, or parts of such components.