Method for manufacturing a silicon clock part

Abstract

The method for manufacturing a watch component according to the present invention comprises the steps of: a) providing a wafer comprising a first silicon layer, a second silicon layer and an intermediate silicon oxide layer (9) therebetween; b) etching the first silicon layer to form therein a first part (1a) of the watch component and etching the second silicon layer to form therein a second part (1b) of the watch component; c) removing the intermediate silicon oxide layer (9) between the elements (4) of the first part (1a) and the elements (5) of the second part (1b); d) thermally oxidizing the elements (4, 5) without them being in contact with each other, and then deoxidizing the elements (4, 5); and e) repeating step d) one or more times until a predetermined distance (d2) between the elements (4, 5) is obtained.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing silicon watch parts.

Background Art

[0002] The manufactured silicon watch parts include two elements, for example, two intersecting elastic blades of a flexible guide member or two overlapping teeth, and are separated by a gap in the height direction of the parts.

[0003] European Patent No. 2911012 describes such parts, more specifically, a watch oscillator integrally obtained by deep etching. In this case, two elements (in this case, two intersecting elastic blades that guide the rotation of the oscillator template) are separated by only a few microns. As proposed in European Patent No. 2911012, when the oscillator is coated with a thermal compensation layer of silicon oxide, the distance separating the two elements becomes even smaller.

[0004] When the distance between the two elements is thus small, there is a possibility that the two elements may come into contact with each other during the operation of the part, specifically during the operation when worn, and the accuracy of the watch may be reduced. Also, they may collide and be damaged when the watch is subjected to an impact.

[0005] International Publication No. 2015 / 033238 describes a backlash-compensated watch wheel assembly including a first toothed rim rigidly coupled to a hub and a second toothed rim coupled to the hub by an elastic arm. This part is manufactured by etching two surfaces of a silicon-on-insulator (SOI) type wafer and removing the intermediate silicon oxide layer except for the hub to separate the second rim and the elastic arm from the first rim. In this part, the two elements constituted by the toothed rims are separated by a distance corresponding to the height of the intermediate silicon oxide layer, that is, up to 3 μm at most. Therefore, they may collide and break when an impact is applied to the watch.

[0006] In the case of a silicon clock part that is rigid as a whole, for example, with respect to two elements of a tooth profile that are spaced apart in height or other interacting elements, it is necessary to arrange the respective cooperating parts very close to each other so that the two elements are in close proximity, which makes the assembly complicated.

[0007] To avoid the above problems, the distance between the two elements can be increased by an underetching technique, but in that case, the geometric and dimensional quality of the elements is no longer guaranteed. It is also possible to manufacture the part with two bonded or welded elements separated by a spacer that maintains a sufficient distance between the two elements. However, in this case, the advantages of integral manufacturing are lost, and it is difficult to achieve perfect alignment of the bonded or welded elements.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] Therefore, there is a need for a method of manufacturing a silicon clock part that can widen the height interval between two elements as desired without adversely affecting the manufacturing accuracy.

Means for Solving the Problems

[0010] This need is met by a method of manufacturing a clock part, which method a) providing a wafer including a first silicon layer, a second silicon layer, and an intermediate silicon oxide layer therebetween; b) etching the first silicon layer to form a first part of the clock component therein, and etching the second silicon layer to form a second part of the clock component therein; c) removing the intermediate silicon oxide layer between the elements of the first part and the elements of the second part; which includes, further, d) thermally oxidizing the elements without contacting them with each other, and then deoxidizing the elements; e) repeating step d) one or more times until a predetermined distance between the elements is obtained. The method further includes additional steps.

[0011] When a silicon element or component is thermally oxidized, the silicon oxide layer that appears on its surface is formed by silicon being consumed at a depth corresponding to 44% of its thickness. Therefore, after removing the silicon oxide layer, a silicon element or component with a reduced size remains. In the present invention, by reducing the size of two elements of the clock component, the distance between them is increased. Further, by performing the oxidation-deoxidation operation such that the two elements do not contact each other during oxidation, that is, the oxide layers around the first element and the oxide layers around the second element do not join during growth, it is avoided that the two elements merge during deoxidation and render the component inoperable.

[0012] Methods of performing multiple oxidation-deoxidation sequences are known in the prior art (see European Patent No. 3181938, International Publication No. 2019 / 166922, International Publication No. 2019 / 180596, European Patent No. 3416001), but these are always methods intended to adjust the rigidity of the hairspring or the frequency of the oscillator, and it is not intended that the oxidation-deoxidation sequence increases the distance between two elements of the clock component.

[0013] Other features and advantages of the present invention should become apparent by reading the following detailed description given with reference to the accompanying drawings.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

DETAILED DESCRIPTION OF THE INVENTION

[0015] FIG. 1 shows a clock oscillator 1 including a flexible guide member, comprising a template 2 suspended from a support 3 by two intersecting elastic blades 4, 5. The blades 4, 5 extend in two different planes P1, P2 parallel to the plane of the template 2 and intersect each other at a predetermined distance. The intersection point of the blades 4, 5 defines a virtual axis of rotation of the template 2 with respect to the support 3.

[0016] FIGS. 2 to 7 show a method that enables manufacturing this clock oscillator with a sufficient distance between the blades 4, 5 and high manufacturing precision according to the present invention.

[0017] First, a wafer 6 of the substrate-on-insulator type is provided, which includes an upper silicon layer 7 and a lower silicon layer 8 separated by an intermediate silicon oxide layer 9 (FIG. 2). The silicon can be a single crystal, polycrystalline regardless of its crystal orientation, or amorphous. This may or may not be doped. The thickness of the intermediate silicon oxide layer 9 is typically 3 μm.

[0018] Next, the wafer 6 is etched continuously or simultaneously from both sides (Fig. 3) to form the first part 1a of the oscillator 1 in the upper silicon layer 7 and the second part 1b of the oscillator 1 in the lower silicon layer 8. Each of the parts 1a, 1b can be single-level or multi-level as shown in the figure.

[0019] In the first part 1a of the oscillator 1, there is one of the two intersecting elastic blades (4), as well as the upper parts of the template 2 and the support 3. In the second part 1b of the oscillator 1, there is the other of the two intersecting elastic blades (5), as well as the lower parts of the template 2 and the support 3.

[0020] At this stage, the two parts 1a, 1b of the oscillator 1 are separated by an intermediate silicon oxide layer 9 which serves to stop the etching. The etching is typically deep reactive ion etching called DRIE.

[0021] Next, the intermediate silicon oxide layer 9 is removed, for example, by chemical attack with hydrofluoric acid in a specific zone, specifically between the two blades 4, 5, i.e., the zone where the first and second parts 1a, 1b of the oscillator 1 need to remain together, so that only the template 2 and the support 3 remain (Fig. 4). This step separates the blades 4, 5 so that they can deform relative to each other.

[0022] In the next step (Fig. 5), the oscillator 1 is thermally oxidized to form a silicon oxide layer 10 around it, specifically around the blades 4, 5. This silicon oxide layer 10 is formed so as to damage the silicon and its surface recedes. The oxidation is usually carried out at a temperature between 800 and 1200 °C in an oxidizing atmosphere using water vapor or dioxygen gas. It can also be carried out locally, for example, only on the blades 4, 5, using a mask such as a nitride-based mask.

[0023] The oxidation stops before the growth of the silicon oxide layer 10 on the blades 4, 5 brings the blades 4, 5 into contact with each other. Thus, after oxidation, the distance d1 still separates the blades 4, 5.

[0024] Next, the oscillator is deoxidized by removing the silicon oxide layer 10, for example, by chemical attack with hydrofluoric acid (Fig. 6). As a result, the sizes of the blades 4 and 5 become smaller, so the distance d2 separating them increases relative to Fig. 4.

[0025] Next, in order to obtain a predetermined distance d2 between the blades 4 and 5, the oxidation-oxidation sequence shown in Figs. 5 and 6 is repeated N times. N is typically equal to at least 2, preferably equal to at least 3, preferably equal to at least 4, preferably equal to at least 5, preferably equal to at least 6, preferably equal to at least 7. The distance d2 at the end of all oxidation-deoxidation sequences is typically at least 7 μm, preferably at least 9 μm, preferably at least 11 μm, preferably at least 13 μm, preferably at least 15 μm. In each oxidation-deoxidation, the distance d2 increases by a value, for example, between 1 μm and 3 μm.

[0026] The oxidation parameters can vary from one oxidation-deoxidation sequence to the next. For example, since a larger space is obtained between the blades 4 and 5 for the growth of the silicon oxide, the oscillator 1 can be oxidized for a longer time in the last sequence than in the first sequence.

[0027] Each oxidation step stops before the blades 4 and 5 come into contact with each other (Fig. 5). In this way, the risk that the blades 4 and 5 are attracted to each other and combined during the removal of the oxide layer 10 is suppressed.

[0028] After all the oxidation - deoxidation sequences, the final silicon oxide layer 11 is formed, by thermal oxidation or deposition, over the whole of the oscillator 1 or at least over the blades 4, 5 (Figure 7), which can increase its mechanical resistance and make its frequency independent of thermal fluctuations. Preferably, the distance d3 between the blades 4, 5 after the formation of this final layer 11 is at least 5 μm, preferably at least 7 μm, preferably at least 9 μm, preferably at least 11 μm, preferably at least 13 μm.

[0029] Preferably, the oxidation - deoxidation sequence and the formation of the final silicon oxide layer 11 are carried out while the oscillator 1 is still attached to the wafer 6 by the silicon - material bridges left during etching. The last step of this method is to remove the oscillator 1 from the wafer 6 by breaking or removing the material bridges. It should be noted that the removal of the oscillator 1 by breaking the material bridges is facilitated by the prior oxidation - deoxidation, which removed most of the defects created in the silicon crystal lattice by the etching plasma.

[0030] The oscillator 1 can be part of a batch of identical oscillators manufactured simultaneously on the wafer 6.

[0031] The present invention is not limited to the manufacture of template oscillators. The present invention can equally well be applied to other types of watch parts, such as levers, rockers, ankles, rakes, fingers, wheels or motor members. As in the case of oscillators, the two elements whose spacing is increased can be crossed elastic blades for guiding the movable parts of the component. Also, the two elements can be elements that interact with other components, such as, for example, the fork and the dirt of an ankle, two overlapping teeth of a wheel or a rake, two overlapping protrusions of a finger. The present invention can be applied in particular to the backlash - compensating wheel described in WO 2015 / 033238 or to the motor member described in WO 2018 / 146639.

[0032] Furthermore, the wafer on which the clock parts according to the present invention are manufactured can be composed of a multi-substrate on an insulator, that is, three or more silicon layers separated by an intermediate silicon oxide layer. In this case, the number of elements with an increased interval may be greater than two.

Claims

1. A method for manufacturing a timepiece part (1), a) providing a wafer (6) comprising a first silicon layer (7), a second silicon layer (8), and an intermediate silicon oxide layer (9) therebetween; b) etching the first silicon layer (7) to form a first part (1a) of the timepiece part (1) therein, and etching the second silicon layer (8) to form a second part (1b) of the timepiece part (1) therein; c) removing the intermediate silicon oxide layer (9) between an element (4) of the first part (1a) and an element (5) of the second part (1b); comprising, further, 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) one or more times until a predetermined distance (d2) between the elements (4, 5) is obtained; and further comprising the additional steps of

2. The method according to claim 1, wherein the predetermined distance (d2) is at least 7 μm.

3. The method according to claim 1 or 2, wherein step e) repeats step d) at least twice.

4. The method according to any one of claims 1 to 3, wherein step d) thermally oxidizes the entire timepiece part (1) and then deoxidizes it.

5. After step e), f) forming a silicon oxide layer (11) on the elements (4, 5), the method according to any one of claims 1 to 4.

6. The method according to claim 5, wherein step f) forms the silicon oxide layer (11) over the entire timepiece part (1).

7. The method according to claim 5 or 6, wherein the distance (d3) between the elements (4, 5) before the end of step f) is at least 5 µm. **Claim 8** The method according to any one of claims 1 to 7, wherein the elements (4, 5) are two intersecting elastic blades. **Claim 9** The method according to any one of claims 1 to 8, wherein the timepiece component is an oscillator (1), a lever, a rocker, an anchor, a rake, a finger, a wheel, or a motor member.

Images