Methods for manufacturing silicon watch components

Abstract

According to the present invention, a method for manufacturing a watch component includes the following steps: a) providing a wafer comprising a first silicon layer, a second silicon layer, and an intermediate silicon oxide layer (9) between the first silicon layer and the second silicon layer; b) etching the first silicon layer to form a first portion (1a) of the watch component therein, and etching the second silicon layer to form a second portion (1b) of the watch component therein; c) removing the intermediate silicon oxide layer (9) between the element (4) of the first portion (1a) and the element (5) of the second portion (1b); d) thermally oxidizing the elements (4, 5) without bringing them into contact with each other, and then deoxidizing the elements (4, 5); e) repeating step d) once or more until a predetermined distance between the elements (4, 5) is obtained.

Description

Technical Field

[0001] This invention relates to a method for manufacturing silicon watch components. Background Technology

[0002] The silicon clock component to be manufactured includes two elements, such as two intersecting elastic blades or two overlapping teeth of a flexible guide member, which are separated by a certain overhead space along the height direction of the component.

[0003] Patent application EP 2911012 describes such a component, more specifically a watch oscillator obtained integrally by deep etching, wherein two elements, in this case, are two intersecting elastic blades that guide the rotation of the balance wheel of the oscillator, are separated by only a few micrometers. As proposed in the patent application, if the oscillator is coated with a silicon oxide thermal compensation layer, the distance separating the two elements is further reduced.

[0004] With such a small gap between the two components, the latter component may come into contact with the former component during operation, especially during movement while wearing the watch, thus reducing the watch's accuracy. The two components may also collide and be damaged when the watch is subjected to an impact.

[0005] Patent application WO 2015 / 033238 describes a watch wheel assembly with backlash compensation, comprising a first gear ring rigidly connected to a hub and a second gear ring connected to the hub via a resilient arm. The assembly is manufactured by etching both sides of a silicon-on-insulator (SOI) wafer and removing an intermediate silicon oxide layer (except at the hub) to separate the second rim and the resilient arm from the first rim. In this assembly, the two elements formed by the gear rings are spaced apart by a distance corresponding to the height of the intermediate silicon oxide layer, i.e., at most 3 μm. Therefore, they may collide and be damaged during a shock to the watch.

[0006] In the case of a completely rigid silicon clock component, for example, two toothed elements or other interacting elements are spaced apart at a height, the close proximity of these elements necessitates placing the corresponding parts that cooperate with them very close together, which complicates the assembly process.

[0007] To avoid the aforementioned problems, the spacing between the two components can be increased using under-etching techniques, but this compromises the geometric and dimensional quality of the components. Alternatively, the component can be manufactured as two glued or welded parts, separated by a spacer maintaining sufficient distance between the two components. However, this loses the advantages of integral manufacturing and makes it difficult to achieve ideal alignment of the glued or welded parts.

[0008] Therefore, there is a need for a method for manufacturing silicon clock components that can increase the height spacing between the two elements of the silicon clock component as needed without adversely affecting manufacturing accuracy. Summary of the Invention

[0009] This requires a method for manufacturing watch components, which includes the following steps:

[0010] a) Provide a wafer comprising a first silicon layer, a second silicon layer and an intermediate silicon oxide layer located between the first silicon layer and the second silicon layer;

[0011] b) Etch a first silicon layer to form a first portion of a watch component therein, and etch a second silicon layer to form a second portion of a watch assembly therein;

[0012] c) Remove the intermediate silicon oxide layer between the components in the first part and the components in the second part;

[0013] Furthermore, this method is characterized by including the following additional steps:

[0014] d) Thermally oxidize the elements without bringing them into contact with each other, and then deoxidize the elements;

[0015] e) Repeat step d) once or more until the predetermined distance between the elements is obtained.

[0016] When a silicon part or assembly is thermally oxidized, the silicon oxide layer that appears on its surface is formed by consuming silicon with a depth equivalent to 44% of its thickness. Therefore, after removing the silicon oxide layer, a smaller silicon part or assembly remains. In this invention, the spacing between the two elements of a watch component is increased by reducing their size. Furthermore, by performing the oxidation-deoxidation operation without allowing the two elements to contact each other during oxidation—that is, without the oxide layers around the first element and the second element bonding together during growth—the two elements are prevented from fusing during the deoxidation process, thus avoiding rendering the component unusable.

[0017] Several methods for implementing oxidation-deoxidation sequences are known in the prior art (see EP 3181938, WO 2019 / 166922, WO 2019 / 180596, EP 3416001), but these methods are always intended to adjust the stiffness of the hairspring or the frequency of the oscillator, while oxidation-deoxidation sequences are never intended to increase the spacing between two elements of a watch component. Attached Figure Description

[0018] Other features and advantages of the invention will become apparent upon reading the following detailed description with reference to the accompanying drawings, in which:

[0019] - Figure 1This is a perspective view of a clock oscillator with a flexible guiding device manufactured by the method according to the present invention;

[0020] - Figures 2 to 7 The sequential steps of the manufacturing method according to the present invention are illustrated schematically. Detailed Implementation

[0021] exist Figure 1 The diagram shows a watch oscillator with a flexible guide device 1, comprising a balance wheel 2 suspended from a support 3 by two intersecting elastic blades 4 and 5. The blades 4 and 5 extend in two different planes P1 and P2 parallel to the plane of the balance wheel 2, and thus intersect at a distance from each other. The intersection of the blades 4 and 5 defines a virtual axis of rotation of the balance wheel 2 relative to the support 3.

[0022] exist Figures 2 to 7 The method according to the present invention is shown, which can produce a clock oscillator with sufficient distance between blades 4 and 5 and high manufacturing precision.

[0023] First, a wafer 6 of the insulator-on-substrate type is provided, which includes an upper silicon layer 7 and a lower silicon layer 8, the upper silicon layer 7 and the lower silicon layer 8 being separated by an intermediate silicon oxide (SiO2) layer 9. Figure 2 Silicon can be monocrystalline silicon regardless of its crystal orientation, or it can be polycrystalline or amorphous silicon. It can be doped or undoped. The thickness of the intermediate silicon oxide layer 9 is typically 3 μm.

[0024] Then, etch continuously or simultaneously on both sides of wafer 6. Figure 3 The first portion 1a of the oscillator 1 is formed in the upper silicon layer 7, and the second portion 1b of the oscillator 1 is formed in the lower silicon layer 8. Each portion 1a, 1b can be single-layered or multi-layered, as shown in the figure.

[0025] The first part 1a of the oscillator 1 is one of the two intersecting elastic blades, blade 4, as well as the upper part of the balance wheel 2 and the support 3. The second part 1b of the oscillator 1 is the other blade 5 of the two intersecting elastic blades, as well as the lower part of the balance wheel 2 and the support 3.

[0026] At this stage, the two parts 1a and 1b of oscillator 1 are used to separate the intermediate silicon oxide layer 9 for stopping the etching. The etching is typically a deep reactive ion etching known as DRIE.

[0027] Then, for example, by chemical etching with hydrofluoric acid, certain areas—particularly the area between the two blades 4 and 5—are removed, and only the intermediate silicon oxide layer 9 is retained in the area where the first part 1a and the second part 1b of the oscillator 1 must remain together, namely the intermediate silicon oxide layer 9 at the balance wheel 2 and the support 3. Figure 4 This step separates blades 4 and 5, allowing them to deform relative to each other.

[0028] In the next step ( Figure 5 In this process, the oscillator 1 is thermally oxidized to form a silicon oxide layer 10 around the oscillator 1, particularly around blades 4 and 5. The formation of this silicon oxide layer 10 damages the silicon, causing its surface to retract. Oxidation is typically carried out at temperatures between 800 and 1200°C in an oxidizing environment using steam or hydrogen peroxide. Oxidation can be localized, for example, by using a mask such as a nitride mask, to oxidize only blades 4 and 5.

[0029] The growth of the silica layer 10 on leaves 4 and 5 stops oxidation before leaves 4 and 5 come into contact with each other. Therefore, after oxidation, leaves 4 and 5 are still separated by a distance d1.

[0030] The oscillator is then deoxidized by, for example, removing the silicon oxide layer 10 through chemical etching with hydrofluoric acid. Figure 6 Then, the dimensions of blades 4 and 5 decrease, so the distance d2 separating them is relative to... Figure 4 Increase.

[0031] Then, Figure 5 and Figure 6 The oxidation-deoxidation process shown is repeated N times to obtain a predetermined distance d2 between leaves 4 and 5. This number N is typically at least 2, preferably at least 3, preferably at least 4, preferably at least 5, preferably at least 6, and preferably at least 7. At the end of all oxidation-deoxidation processes, the distance d2 is typically at least 7 μm, preferably at least 9 μm, preferably at least 11 μm, preferably at least 13 μm, and preferably at least 15 μm. During each oxidation-deoxidation cycle, the distance d2 increases by, for example, a value between 1 μm and 3 μm.

[0032] Oxidation parameters can vary from one oxidation-deoxidation process to the next. For example, oscillator 1 can be oxidized for a longer time in the final process than in the earlier processes because there is more space between blades 4 and 5 available for silica growth.

[0033] Each oxidation step stops before leaves 4 and 5 come into contact with each other. Figure 5 In this way, the risk of leaves 4 and 5 attracting and fusing to each other during the removal of oxide layer 10 is reduced.

[0034] After the complete oxidation-deoxidation process, the final silicon oxide layer 11 can be formed on the entire oscillator 1 or at least on the blades 4 and 5 by thermal oxidation or deposition. Figure 7This increases the mechanical resistance of the oscillator 1 and makes its frequency less sensitive to thermal changes. Preferably, after the final layer 11 is formed, the distance d3 between the blades 4 and 5 is at least 5 μm, preferably at least 7 μm, preferably at least 9 μm, preferably at least 11 μm, and preferably at least 13 μm.

[0035] Preferably, the oxidation-deoxidation process and the formation of the final silicon oxide layer 11 are performed while the oscillator 1 is still connected to the wafer 6 via silicon material bridges left during the etching process. Then, the final step of the method involves separating the oscillator 1 from the wafer 6 by disconnecting or removing the material bridges. It should be noted that separating the oscillator 1 by disconnecting the material bridges is facilitated by the preceding oxidation-deoxidation process, and this eliminates most of the defects generated by the etching plasma in the silicon lattice.

[0036] Oscillator 1 may be part of a batch of identical oscillators manufactured simultaneously in wafer 6.

[0037] This invention is not limited to the manufacture of balance wheel oscillators. It can be applied in the same manner to other types of watch components, such as levers, rockers, anchors, rakes, fingers, wheels, or motor components. As with oscillators, the two elements used to increase their spacing can be intersecting elastic blades of the moving parts used to guide the components. These two elements can also be elements that interact with other components, such as the forks and darts of an anchor, two overlapping teeth of a wheel or rake, two overlapping protrusions of a finger, etc. This invention is particularly applicable to the backlash compensation wheel described in patent application WO 2015 / 033238 or the motor component described in patent application WO 2018 / 146639.

[0038] Furthermore, the wafer on which the watch component according to the invention is formed can be a multi-substrate on an insulator, i.e., comprising more than two silicon layers separated by an intermediate silicon oxide layer. In this case, the number of elements requiring increased spacing may be greater than two.

Claims

1. A method of manufacturing a watch component, comprising the steps of: a) providing a wafer (6) comprising a first silicon layer (7), a second silicon layer (8) and an intermediate silicon oxide layer (9) between the first silicon layer (7) and the second silicon layer (8); b) etching the first silicon layer (7) to form a first part (la) of the watch component therein and etching the second silicon layer (8) to form a second part (lb) of the watch component therein; c) removing the intermediate silicon oxide layer (9) between elements of the first part (la) and elements of the second part (lb); characterized in that it comprises the additional steps of: d) thermally oxidizing the elements of the first part (la) and the elements of the second part (lb) without bringing the elements of the first part (la) and the elements of the second part (lb) into contact with each other, and then deoxidizing the elements of the first part (la) and the elements of the second part (lb); e) repeating step d) one or more times until a predetermined distance d2 between the elements of the first part (la) and the elements of the second part (lb) is obtained.

2. The method of claim 1, wherein, The predetermined distance d2 is at least 7 pm.

3. The method according to claim 1 or 2, characterized in that, Step e) comprises repeating step d) at least twice.

4. The method according to claim 1 or 2, characterized in that, Step d) comprises thermally oxidizing the entire watch component and then deoxidizing the entire watch component.

5. The method according to claim 1 or 2, characterized in that, After step e), the method comprises the step of: f) forming a silicon oxide layer (11) on the elements of the first part (la) and the elements of the second part (lb).

6. The method of claim 5, wherein, In step f), the silicon oxide layer (11) is formed on the entire watch component.

7. The method of claim 5, wherein, At the end of step f), the distance d3 between the elements of the first part (la) and the elements of the second part (lb) is at least 5 pm.

8. The method of claim 1 or 2, wherein, The elements of the first part (la) and the elements of the second part (lb) are two intersecting resilient blades.

9. The method of claim 1 or 2, wherein, The watch component is an oscillator, a bar, an anchor, a rake, a finger, a wheel or an electric machine component.

10. A watch component manufactured according to the method of claim 1.

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