Micromechanical timepiece part and method for manufacturing same

Abstract

A watchmaking micromechanical component (1) based on silicon, comprising an upper face (11), a lower face opposite the upper face (11) and side walls (12) connecting the upper face (11) to the lower face, the side walls (12) forming the contour of the watchmaking micromechanical component (1), the contour comprising an upper edge at the intersection between the side walls (12) and the upper face (11) and a lower edge at the intersection between the side walls (12) and the lower face, the contour comprising at least one chamfered portion (121) in which the upper edge has a chamfer, and at least one right-angled portion (122) in which the upper edge is at a right angle.

Description

[0001] The present invention relates to a silicon-based micromechanical watch component and its manufacturing process. In particular, the present invention relates to a silicon-based micromechanical watch component formed by reactive ion etching of a silicon-based substrate.

[0002] It is known to produce micromechanical watch parts by micromachining a mono- or polycrystalline silicon substrate. For example, patent document EP 0 732 635 A1 describes the fabrication of a silicon escapement anchor. Silicon micromachining largely consists of etching operations. To give the parts the desired shape, an etching mask, previously formed and structured on the surface of the silicon wafer, is generally used.

[0003] The most widespread etching technique is called deep reactive ion etching (DRIE), which involves subjecting a silicon-based substrate to an etching phase followed by a passivation phase. This sequence is repeated until an anisotropic, or essentially vertical, etch is obtained from the mask pattern in a top layer of the substrate. The sequence of an etching phase followed by a passivation phase is repeated many times until an opening is obtained that vertically penetrates the top layer of the substrate, which is on the order of a hundred to a few hundred micrometers thick.

[0004] Such a process is described, for example, in US patent 5,501,893 in the name of Robert Bosch GmbH, which proposes etching profiles with nearly vertical flanks into a silicon substrate by alternating the steps of depositing an inert passivation layer and plasma etching. Both the passivation layer deposition and etching steps use fluorinated compounds, thus taking place in the same chemical environment. Each step lasts a few seconds; the passivation layer is formed over the entire surface of the substrate, protecting it against any subsequent etching. During the following etching step, bombardment by vertically accelerated ions disintegrates the portion of the passivation layer located at the bottom of the profiles, but not the portion covering their flanks. The bottom of the profiles is thus very quickly exposed to reactive etching.

[0005] One disadvantage of vertical engraving using the DRIE process is that the right-angled edges of the parts produced in this way are susceptible to chipping, for example when driving the part onto an axis.

[0006] Another drawback is the semi-finished appearance of the parts, whose edges are not chamfered, unlike what is customary for micromechanical watch parts.

[0007] One aim of the present invention is to provide a silicon-based micromechanical part whose level of finish meets the requirements of the watchmaking industry.

[0008] Another objective of the present invention is to propose a manufacturing process for producing silicon-based micromechanical watch parts with partially chamfered edges.

[0009] These goals and other advantages are achieved using a silicon-based micromechanical watch part comprising a top face, a bottom face opposite the top face and side walls connecting the top face to the bottom face, the side walls forming the contour of the micromechanical watch part, the contour comprising a top edge at the intersection between the side walls and the top face and a bottom edge at the intersection between the side walls and the bottom face, the contour comprising at least one chamfered portion in which the top edge has a chamfer, and at least one right-angled portion in which the top edge is at a right angle.

[0010] The fact that the top edge of the micromechanical component is partially chamfered allows the upper surface of the component—which is generally the visible side when integrated into a watch movement—to achieve a level of finish never before attained for silicon micromechanical components, which are difficult to machine. This also protects certain sensitive areas of the top edge from wear, for example, due to mechanical stresses on the component. Another advantage of at least partially chamfering the visible edges of the micromechanical component is that it prevents the formation of paint ridges on the edges when the silicon component is painted after its fabrication.Indeed, the capillary action phenomenon tends to retain the paint on the edges of the silicon part, creating a visual bead effect which is reduced, or even eliminated, when the edge is chamfered.

[0011] Preferably, the upper and lower faces of the watch micromechanical component are essentially flat. Preferably also, the side walls are essentially vertical and the angle of the chamfer of the chamfered portion(s) relative to the vertical is between 10 degrees and 45 degrees, more preferably between 30 degrees and 45 degrees.

[0012] The height of the chamfer of the chamfered portion(s) measured in the direction of the height of the corresponding side wall, i.e. in a direction perpendicular to the plane of the top face of the part, is for example between 20 micrometers and 50 micrometers.

[0013] The thickness of the micromechanical watch part is, for example, between 80 micrometers and 300 micrometers, for example 150 micrometers.

[0014] Optionally, the lower edge of the part has a chamfer with an angle of between 5 and 12 degrees relative to the vertical. This allows for easier mounting of the part on an axis, for example.

[0015] The micromechanical watchmaking component belongs, for example, to the group comprising a jumper, in particular a jumper with negative stiffness, an anchor, a hand and a wheel.

[0016] The aforementioned goals and other advantages are further achieved using a reactive ion etching manufacturing process for such a watch micromechanical component. The process includes providing a silicon-based substrate, forming a first mask on the upper surface of the substrate. This first mask includes initial perforations to expose the areas on the upper surface of the substrate corresponding to the chamfered portion(s) to be etched. A second mask is then formed on the upper surface of the substrate. This second mask includes further perforations to expose the areas on the upper surface of the substrate corresponding to the entire contour of the watch micromechanical component to be etched. The substrate is then etched through these initial perforations to engrave the chamfer of the chamfered portion(s), and the first mask is removed.a second step of etching the substrate through the second perforations to form the side walls, removal of the second mask, detachment of the micromechanical part from the substrate.

[0017] According to one embodiment of the process of the invention, the formation of the second mask is carried out after the first etching step and the removal of the first mask. The first and second masks are then both formed, for example, from silicon dioxide. Alternatively, the first mask is formed, for example, from photosensitive resin and the second mask is formed, for example, from silicon dioxide.

[0018] According to another embodiment of the process of the invention, the formation of the second mask is carried out before the formation of the first mask and before the first and second etching steps. The first mask is formed, for example, from photosensitive resin, and the second mask is formed, for example, from silicon dioxide.

[0019] The present invention will be better understood upon reading the following description illustrated by the figures, where: there figure 1 shows a detail of a micromechanical watch component according to the invention; the figure 2 schematically illustrates a substrate for manufacturing a micromechanical watchmaking component according to the invention; the figures 3 to 8 schematically illustrate the manufacturing steps of a micromechanical watch component according to a preferred embodiment of the invention; Figures 9 and 10 schematically illustrate the manufacturing steps of a micromechanical watch part according to another embodiment of the invention.

[0020] With reference to the figure 1The watchmaking micromechanical component 1 of the invention, only a part of which is shown, is a silicon-based component manufactured by reactive ion etching from a silicon-based substrate, for example, from a silicon-on-insulator (SOI) substrate. The watchmaking micromechanical component 1 is essentially flat with a top face 11 corresponding to the top face of the substrate from which the watchmaking micromechanical component 1 was cut, and a bottom face opposite the top face, not visible in the illustration. figure 1One or more lateral walls 12, preferably essentially vertical, connect the upper face 11 to the lower face and thus form the contour of the part. The contour of the micro-mechanical watch part 1 as defined in this application includes the outer contour of the part as well as any inner contours bordering any functional and / or aesthetic openings 13 of the micro-mechanical watch part 1. According to the invention, the contour of the micro-mechanical watch part 1 comprises one or more chamfered portions 121 in which the upper edge, which is at the intersection of the corresponding wall 12 and the upper face 11, is chamfered, and one or more right-angled portions 122 in which the upper edge is at a right angle.

[0021] Typically, the thickness of the micromechanical component 1 is between 80 and 300 micrometers; the thickness of the component is, for example, 150 micrometers. However, other thicknesses are possible for the micromechanical component 1 within the scope of the invention, in particular thicknesses greater than 150 micrometers, for example, due to technical and / or mechanical constraints related to the use of the micromechanical component 1. The chamfer of the chamfered portion(s) 121 is preferably straight, or even slightly concave or slightly convex. The average angle formed by the chamfer with the vertical, i.e., with the rest of the side wall 12, is between 10 degrees and 45 degrees, preferably between 30 degrees and 45 degrees. The height of the chamfer measured vertically, i.e. in a direction perpendicular to the upper face 11, is preferably between 20 micrometers and 30 micrometers.

[0022] The micromechanical part of the invention is, for example, a jumper, for example a jumper with negative stiffness, an anchor, a hand, a wheel, or any other watchmaking micromechanical part.

[0023] Preferably, several identical micromechanical parts 1 are etched simultaneously onto the same substrate wafer. For the sake of simplicity, the manufacturing process according to the invention is described below in relation to a single micromechanical part. However, those skilled in the art will understand that it applies simultaneously and in the same way to all parts manufactured from the same wafer.

[0024] Silicon-based substrate 2, schematically illustrated in the figure 2This includes, for example, monocrystalline silicon, doped monocrystalline silicon, polycrystalline silicon, doped polycrystalline silicon, porous silicon, silicon oxide, quartz, silica, silicon nitride, or silicon carbide. When in its crystalline phase, silicon can have any crystal orientation. The silicon-based substrate 2 is, for example, SOI comprising a top layer 21 of silicon, an intermediate layer 22 of silicon oxide, and a bottom layer 23 of silicon. According to other embodiments not shown, the silicon-based substrate comprises a silicon layer on a base of a different material, for example, a metal.

[0025] According to the process of the invention, the substrate undergoes two successive etching steps: a first etching step to form the chamfers of the chamfered portion(s) of the micromechanical part, and a second step to form the side walls of the part. During the first etching step, the substrate is covered with a first mask comprising initial perforations to expose to etching only the areas of the upper surface of the substrate 2 corresponding to the portions of the part's contour to be chamfered. During the second etching step, the substrate is covered with a second mask comprising further perforations to expose the entire contour to etching. After the second etching step, the micromechanical part thus formed is detached from the wafer in a known manner.

[0026] According to a preferred embodiment of the process of the invention, schematically illustrated by the figures 3 to 8The first mask 31 is formed in a known manner on the substrate 2 from a material capable of withstanding etching. The first mask 31, comprising the first perforations 310, is, for example, formed from silicon dioxide or photosensitive resin on the upper part of the top silicon layer 21. According to the invention, the first mask 31 exposes only the locations corresponding to the chamfered portions 121 of the part to be manufactured, the locations corresponding to the right-angled portions 122 of the part to be manufactured being covered by the first mask 31.

[0027] Once the first mask 31 is formed on the surface of the substrate 2, the first etching step, which involves engraving oblique walls into a portion of the substrate 2's thickness from the first perforations 310, is carried out in an etching chamber. The oblique walls thus engraved will form the chamfer(s) of the micromechanical part.

[0028] The first etching step is essentially isotropic, forming depressions in the areas of the upper layer 21 of the substrate 2 exposed to etching through the first perforations 310. These depressions have walls that extend slightly below the first mask 31 at an open angle and are preferably oriented in a nearly rectilinear fashion. The shape and angle of these oblique walls determine the shape and angle of the chamfers of the micromechanical part to be manufactured. This first etching step is preferably carried out by mixing etching gas, for example sulfur hexafluoride (SF6), and passivation gas, for example octafluorocyclobutane (C4F8), in the etching chamber. The ratio of etching gas to passivation gas determines the angle of the resulting oblique walls.Preferably, the angle of the oblique walls relative to the vertical is between 10° and 45°, and even more preferably between 35° and 45°. The method of introducing the gases into the etching chamber, typically in a pulsed manner, allows control of the etching direction and thus defines the shape of the oblique walls, for example straight, or slightly convex or concave.

[0029] Following the first etching step, the first mask is preferably removed in a known manner from substrate 2 ( figure 5 ).

[0030] Before the second etching step 32, a second etching mask comprising second perforations 320 is formed preferably in a known manner on the substrate from a material capable of resisting etching ( figure 6). The second mask 32 is, for example, formed from silicon dioxide on the upper part of the upper silicon layer 21 of the substrate 2. According to the invention, the second mask 32 exposes all the locations corresponding to the contours of the part to be manufactured, thus exposing the locations corresponding to the chamfered portions 121 and the locations corresponding to the right-angled portions 122. The second mask 32 covers the locations on the upper surface of the substrate 2 that correspond to the upper face of the part to be manufactured.

[0031] According to this embodiment of the process of the invention, the removal of the first mask and the formation of the second mask 32 are preferably carried out outside the engraving chamber.

[0032] Once the second mask 32 is formed on the surface of the substrate 2, the second etching step, which etches vertical walls from the second perforations 230 through the entire thickness of the upper silicon layer 21 of the substrate 2, is carried out in an etching chamber. This second etching step thus forms the contour of the micromechanical part. For example, the second etching step is performed in the same etching chamber as the first etching step.

[0033] With reference to the figure 7 , the second etching step is essentially anisotropic and thus allows the formation of substantially vertical walls 12 from the second perforations 320 of the second mask 32, preferably in a known manner by alternating etching phases during which the substrate 2 is exposed to the etching gas, and passivation phases during which the substrate 2 is exposed to the passivation gas.

[0034] The second engraving stage is optionally completed with a slightly longer engraving phase than the previous ones in order to accentuate the engraving in the lower part of the side walls and thus form a slightly oblique lower edge, schematically illustrated in the figure 8Such a slightly oblique lower edge, preferably with an angle between 5° and 10° from the vertical, is advantageous, for example, if the micromechanical part thus manufactured must be driven onto an axis, to avoid chipping the lower edge during driving. The formation of this slightly oblique lower edge by extending the last engraving step is commonly called notching. Alternatively, the second engraving step is optionally completed with an isotropic engraving phase similar to the first engraving step in order to also create a chamfer on the lower edges of the part, as described above in relation to the chamfered portions.

[0035] Following the second etching step, the watch micromechanical component 1 is preferably freed from the second mask and substrate 2 in a known manner. A deoxidation step is performed, for example, to remove the second silicon oxide mask and, possibly, part of the intermediate silicon oxide layer 22. Then, a step to free the substrate 2 from the micromechanical component is carried out, for example, using a selective chemical etch to disintegrate the intermediate layer 22.

[0036] According to the process of the invention, the first etching stage and the second etching stage can be carried out in the same etching chamber using the same etching and passivation gases, but according to different protocols, for example different exposure times to each gas, different gas mixtures, etc. in order to obtain a different result at each etching stage.

[0037] According to the embodiment of the method of the invention described above, between the first and second engraving steps, the first mask, exposing only the chamfered portions of the workpiece contour, is removed, and the second mask, exposing the complete contour of the workpiece, is formed on the substrate. The substrate is thus removed from the engraving chamber after the first engraving step and reintroduced into the engraving chamber(s) after the formation of the second mask.

[0038] According to another embodiment of the process of the invention, schematically illustrated by the Figures 9 and 10The first mask 31 and the second mask 32 are both formed on the substrate 2 before the first etching step. The second mask 32 is formed in a known manner on the substrate 2 from a material capable of withstanding the etching steps of the process. The second mask 32 is, for example, formed from silicon dioxide. The second mask 32 is formed on the upper surface of the substrate 2. According to the invention, the second mask 32 exposes all the locations in the upper silicon layer 21 corresponding to the contour of the part to be manufactured, thus exposing the locations corresponding to the chamfered portion(s) 121 and the locations corresponding to the right-angled portion(s) 122.

[0039] The first mask 31 is then formed on the upper surface of the substrate 2, which already bears the second mask 32. The first mask 31 is therefore at least partially formed on the second mask 32. The first mask 31 is formed on the substrate 2 from a material capable of withstanding the etching steps of the process, but which can be removed in the etching chamber without damaging the second mask 32. The first mask 31 is, for example, formed from a photosensitive resin. According to the invention, the first mask 31 includes the first perforations 310, which allow only the areas corresponding to the chamfered portion(s) 121 of the contour of the part to be manufactured to be exposed to etching, the areas corresponding to the right-angled portion(s) 122 of the contour of the part to be manufactured being covered by the first mask 31.

[0040] Once the second mask 32 and the first mask 31 have been formed on the surface of the substrate 2, the first essentially isotropic etching step to etch oblique walls is carried out in an etching chamber in order to form the chamfered edges of the micromechanical part, as explained above.

[0041] Following the first etching step, the first mask 31 is removed from the etching chamber, for example using oxygen plasma. Oxygen is introduced into the etching chamber, which will dissolve the first mask in photoresistible resin.

[0042] Once the first mask 31 has been removed from substrate 2 ( Figure 10The second etching step, which engraves the vertical walls 12 from the second perforations 320 of the second mask 32, is carried out in the etching chamber, thus forming the contour of the micromechanical part, as explained above. Since the second etching step is essentially anisotropic, the oblique walls formed during the first etching step, which are at least partially covered by the second mask 32, are practically unaffected by the second etching step.

[0043] As explained previously, the second engraving stage is optionally completed with a notching phase: a slightly longer engraving phase than the previous ones, designed to create a gently angled lower edge. Alternatively, the second engraving stage is optionally completed with an isotropic engraving phase similar to the first engraving stage, in order to also create a chamfer on the lower edges of the part, as described above in relation to the chamfered sections.

[0044] Following the second etching step, the micromechanical part is preferably freed from the second mask and substrate using a known method. For example, a deoxidation step is performed to remove the second silicon dioxide mask and, possibly, part of the intermediate silicon oxide layer. Then, a substrate liberation step is carried out, for example, using a selective chemical etch to disintegrate the intermediate layer.

[0045] As is known, the silicon-based watchmaking micromechanical part 1 of the invention can be subjected to finishing operations, for example surface treatments, to improve its physical resistance and / or its aesthetic appearance.

[0046] The manufacturing process according to the invention makes it possible to produce a watch micromechanical component whose aesthetic appearance meets the criteria of the watchmaking industry, in that its upper surface exhibits a level of finish superior to that of prior art silicon-based watch micromechanical components. The combination of the first step of essentially isotropic etching through the first mask, and the second step of essentially anisotropic etching through the second mask with perforations different from those of the first mask, makes it possible to obtain a component whose upper edge is partially chamfered, thus highlighting, and also protecting from scratches, certain selected portions of the component.This partial chamfering of the upper edge of the silicon micromechanical part thus produced also helps to reduce, or even completely avoid, the formation of paint ridges, at least on the chamfered portions, when the part is painted after its manufacture.

Claims

1. Micromechanical timepiece part (1) which is silicon-based, comprising an upper face (11), a lower face opposite to the upper face (11) and side walls (12) connecting the upper face (11) to the lower face, the side walls (12) forming the contour of the micromechanical timepiece part (1), the contour comprising an upper edge at the intersection between the side walls (12) and the upper face (11) and a lower edge at the intersection between the side walls (12) and the lower face, characterised in that the contour comprises at least one chamfered portion (121), wherein the upper edge comprises a chamfer, and at least one right-angle portion (122), wherein the upper edge is at a right angle.

2. Micromechanical timepiece part (1) as claimed in the preceding claim, in which the upper face (11) and the lower face are essentially planar.

3. Micromechanical timepiece part (1) as claimed in any one of claims 1 and 2, in which the side walls (12) are essentially vertical and in which the angle of the chamfer of the at least one chamfered portion with respect to the vertical is between 10 degrees and 45 degrees, more preferably between 30 degrees and 45 degrees.

4. Micromechanical timepiece part (1) as claimed in any one of claims 1 to 3, in which the height of the chamfer of the at least one chamfered portion (121) measured in the direction of the height of the corresponding side wall (12) is between 20 micrometres and 50 micrometres.

5. Micromechanical timepiece part (1) as claimed in any one of claims 1 to 4, in which the thickness of the micromechanical timepiece part (1) is between 80 micrometres and 300 micrometres.

6. Micromechanical timepiece part (1) as claimed in claim 5, in which the thickness of the micromechanical timepiece part (1) is 150 micrometres.

7. Micromechanical timepiece part (1) as claimed in any one of claims 1 to 6, in which the micromechanical timepiece part (1) belongs to the group comprising a jumper, a pallet, a hand and a wheel.

8. Method of producing by reactive-ion etching a micromechanical timepiece part (1) as claimed in any one of claims 1 to 6, comprising: - the provision of a silicon-based substrate (2); - the formation of a first mask (31) on an upper surface of the substrate (2), the first mask (31) comprising first cut-outs (310) to expose to etching the locations of the upper surface of the substrate (2) corresponding to the at least one chamfered portion (121); - the formation of a second mask (32) on the upper surface of the substrate (2), the second mask (32) comprising second cut-outs (320) to expose to etching the locations of the upper surface of the substrate (2) corresponding to the whole of the contour of the micromechanical timepiece part (1); - a first step of etching the substrate (2) through the first cut-outs (310) in order to etch the chamfer of the at least one chamfered portion (121); - the removal of the first mask (31); - a second step of etching the substrate (2) through the second cut-outs (320) in order to form the side walls (12); - the removal of the second mask (32); - the detachment of the micromechanical part (1) from the substrate (2).

9. Method as claimed in claim 8, in which the formation of the second mask (32) is carried out after the first etching step and the removal of the first mask (31).

10. Method as claimed in claim 9, in which the first mask (31) and the second mask (32) are formed of silicon dioxide.

11. Method as claimed in claim 8, in which the formation of the second mask (32) is carried out before the formation of the first mask (31) and before the first and second etching steps.

12. Method as claimed in any one of claims 9 or 11, in which the first mask (31) is formed of photosensitive resin and the second mask (32) is formed of silicon dioxide.

Images