CH717409B1 - Silicon part for watchmaking and process for manufacturing such a part. - Google Patents

Abstract

The present invention relates to a silicon part (1) for watchmaking, comprising a surface (18), at least a portion of the surface (18) comprising a forest of peaks (11), the density of the peaks (11) being at least 10 peaks (11) per 100 µm 2 of the surface (18), the peaks having a height of between 1 µm and 15 µm, so as to make said surface (18) anti-reflective. The silicon part (1) according to the invention has a color which does not depend on the viewing angle of the user, in particular for a viewing angle of at least 100° or more. It can therefore be used in a place which is visible to the user, for example in a dial.

Description

Technical area

[0001] The present invention relates to a silicon part for watchmaking and a method of manufacturing such a part. This invention also finds application in the field of silicon parts for MEMS and in the general field of microtechnology, in particular if the silicon part is visible to a user during operation of the MEMS or microtechnical system.

State of the art

[0002] Watch brands, particularly high-end ones, are increasingly using silicon components to equip their watches. They thus take advantage of the exceptional characteristics presented by this material, both from the point of view of its physical characteristics and the precision of its machining.

Silicon is generally monocrystalline or polycrystalline. The parts are generally obtained by etching, in particular by deep etching (“Deep Reactive Ion Etching” - DRIE), from a silicon wafer.

[0004] Silicon, however, has a dark, changing color, not very defined. Its mirror-polished surface presents a lot of unwanted or parasitic reflections.

[0005] The surface of the silicon can be covered with different layers (oxide, metal, dielectric, etc.) in order to improve its aesthetics or its mechanical performance, or to allow the addition of decorative elements to the surface. If, for example, it is covered with a metal, we will only see the color of the metal if we look perpendicular to this surface, otherwise we only see darkness or reflections.

[0006] In addition, the engraving sides are extremely steep and the contours obtained are extremely sharp. Bevelling, so popular in watchmaking, is almost impossible here. The pieces produced in this way are most often cold and a little aggressive.

[0007] Although they do not appreciate this aesthetic, watchmakers use these parts because most often they are functional parts, barely visible and inside the movement.

[0008] The use of a silicon part in a location which is visible to the user currently poses a certain number of problems: parasitic reflections disturb the user, and do not make it possible to read any indications carried by the room. This is very important for example if the part in question is a display system or an animated dial, such as those described for example in documents EP3291024, EP3435362, EP3579059, EP3588204 in the name of the applicant.

[0009] Certain watch brands attempt to soften the appearance of a silicon part covered with a metallic layer by an operation on the finished part, therefore retrospectively, for example by micro-sandblasting the metallic layer. However, it is a long, delicate, piece-by-piece operation which can severely damage the physical properties of the finer parts of the part, such as bending blades for example.

Brief summary of the invention

[0010] An aim of the present invention is to propose a silicon part for watchmaking free from the limitations of known silicon parts.

[0011] Another aim of the present invention is to provide a silicon part for watchmaking visible to the user when it is mounted in a timepiece such as a wristwatch, which has a color which does not depend on the user's viewing angle.

[0012] Another aim of the present invention is to provide a silicon part for watchmaking visible to the user when it is mounted in a timepiece such as a wristwatch, which allows reading without difficulties of the indications carried by the silicon part.

[0013] Another aim of the present invention is to propose a process for manufacturing a silicon part for watchmaking which is less time-consuming and/or less delicate than known processes.

[0014] Another aim of the present invention is to propose a process for manufacturing a silicon part for watchmaking which does not damage the physical properties of the part, in particular its finest parts, such as blades. bending for example.

[0015] According to the invention, these goals are achieved in particular by means of a silicon part for watchmaking according to claim 1 and by means of a method of manufacturing a silicon part for watchmaking according to claim 1. claim 13.

The silicon part according to the invention comprises a surface, at least a portion of the surface comprising a forest of peaks.

[0017] In this context, the term “forest” indicates a dense, or even very dense, set of peaks. According to the invention, the density of the peaks is at least 10 peaks per 100 µm<2> of the surface of the silicon part.

[0018] In a preferred variant, the peaks are distributed irregularly over the surface. In a preferred variant, the peaks are not arranged so as to form a matrix comprising rows and columns, the lines being perpendicular to the columns. In a preferred variant, the peaks are contiguous.

[0019] According to the invention, the peaks have a height of between 1 µm and 15 µm, for example between 2 µm and 3 µm. This, in combination with their density, makes the surface comprising the forest of spikes anti-reflective.

[0020] In this context, the term "peak" indicates a pointed protuberance, namely a protuberance defined between two ends, in which one end (the base) is larger than the other end (the free end or tip). .

[0021] A peak can have the shape of a pyramid, a cone, a truncated pyramid, or a truncated cone, etc.

[0022] In a variant, the height of the peaks is irregular.

[0023] In a variant, the width of the peaks at the base, or in general, the largest dimension of the base of the peaks is between 1 μm and 10 μm.

[0024] The silicon part according to the invention is not limited to the field of watchmaking, but also finds application in the field of silicon parts for MEMS and the general field of microtechnology, particularly if the silicon part is visible to a user during operation of the MEMS or microtechnical system.

[0025] In a variant, the peaks are separated by hollows, namely openings, defined by surfaces, in particular by at least two surfaces. In a variant, these surfaces are lateral surfaces of two contiguous peaks. In this variant, the peaks are contiguous.

The peaks are not necessarily periodic, that is to say regularly spaced, and can have different sections, for example and without limitation sections in the shape of an inverted V, inverted U, etc. The silicon part may include peaks of different shapes.

[0027] In a variant, the bottom of the recesses is located at a substantially constant depth of the silicon part. However, hollows of varying depth can also be considered.

[0028] In a preferred embodiment, the silicon part is a wafer, namely a part comprising at least one flat surface (or base) and having a small thickness, for example less than 2 mm, for example less than 500 µm . In a preferred variant, the forest of peaks belongs to the surface opposite the flat surface. The surface comprising the forest of peaks can be called “matte surface” or “satin surface”.

[0029] Due to the presence of the woodpecker forest, it is an anti-reflective surface. In this context, the expression "anti-reflective surface" indicates that on this surface unwanted reflections are significantly reduced (i.e., reduced by more than 65%) or even completely eliminated, compared to the same surface without the woodpecker forest.

The silicon part according to the invention therefore has a color which does not depend on the viewing angle of the user, in particular for a viewing angle of at least 100° or more. It can therefore be used in a place which is visible to the user, for example in a dial. The silicon part according to the invention can itself constitute a watch dial.

[0031] The silicon part according to the invention also makes it possible to read without difficulty any indications carried by the part.

The silicon part according to the invention is therefore a matte part, that is to say a part which has no shine, which does not shine, which does not reflect light. This also helps soften the appearance.

[0033] The silicon part according to the invention is therefore a “satin” part, because it has a surface with a forest of peaks and which is beautiful to see.

[0034] In a preferred variant, the silicon part is a one-piece part, that is to say made from a single block.

[0035] In a preferred variant, the silicon part, in particular its surface comprising the forest of peaks, comprises a layer of silicon oxide having a thickness between 0.25 µm and 4 µm, for example a thickness of 1 µm, obtained by thermal, anodic or plasma oxidation of the silicon part. This oxidation, by consuming silicon from the part, makes it possible to eliminate any facets still present in the surface structuring, by rounding them, which provides a perfectly anisotropic unity of appearance over a wide field of viewing angles, for example a field of viewing angles of more than 100°.

[0036] In a preferred variant, the silicon part, in particular its surface comprising the forest of peaks, comprises a metallic or dielectric layer, for example a gold layer, for example having a thickness of less than 1 µm, for example of 0.2 µm.

[0037] In a preferred variant, the silicon part is an analog display module (or system), such as that described in documents EP3291024, EP3435362, EP3579059, EP3588204 in the name of the applicant.

[0038] In a variant, the display portions of this system comprise a colored varnish coating layer.

[0039] In a preferred variant, the silicon part is a dial, animated or not animated.

[0040] In a preferred variant, the silicon part is a decorative element of a dial background.

[0041] In a preferred variant, the silicon part is a balance wheel and/or a hairspring; an exhaust; an anchor ; a power source such as a barrel; or a mobile; etc.

[0042] In a preferred variant, a timepiece, such as a watch or a wristwatch for example, comprises the silicon part according to the invention.

[0043] The present invention also relates to a method of manufacturing a (matte) silicon part for watchmaking, comprising: – production from a silicon wafer of a forest of peaks in at least one portion of 'a surface of the silicon wafer, the density of the peaks being at least 10 peaks per 100 µm<2> of the surface of the silicon part, the peaks having a height of between 1 µm and 15 µm; – cutting the wafer, for example by engraving, to obtain the part.

The process according to the invention takes less time than known processes. In addition, it does not damage the physical properties of the part, and can be used successfully, particularly for parts including thin parts, such as bending blades.

The step of producing the forest of peaks from a silicon wafer can be carried out mechanically, for example with grinding (used in the semiconductor industry) or micro-sandblasting ( used in the watch industry).

[0046] In addition or as an alternative, the step of producing the forest of peaks from a silicon wafer can be carried out chemically, for example with an (anisotropic) silicon etching process known in the photovoltaic cell industry.

[0047] In a preferred embodiment, the method comprises a step of oxidation (thermal or anodic or plasma) of the silicon part, in particular of the surface comprising the forest of peaks, the oxide thus obtained having a thickness between 0.25 µm and 4 µm, in particular 1 µm.

[0048] In coating a preferred embodiment, the method comprises a step of coating the (possibly oxidized) silicon part with a metallic or dielectric layer (or coating): the color of the part thus coated will not depend on the user's viewing angle.

Brief description of the figures

[0049] Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which: Figure 1 illustrates a perspective view of an embodiment of a silicon part according to the invention . Figure 2 illustrates a portion of a sectional diagram along the line A-A of Figure 1 of the silicon part of Figure 1. Figure 3 illustrates the sectional diagram of Figure 2, in which certain peaks have been removed . Figure 4 illustrates a sectional diagram of another embodiment of a silicon part according to the invention. Figure 5 illustrates two microscope views with two different enlargements, of an embodiment of a silicon part according to the invention, in which the forest of peaks has been produced by micro-sandblasting. Figure 6 illustrates a view from above of an embodiment of a silicon part according to the invention, in which the forest of peaks has been produced by grinding, partially covered with a layer of gold and placed on a polished wafer coated with gold. Figure 7 illustrates a sectional view of an embodiment of a silicon part according to the invention, in which the forest of peaks has been produced by chemical etching. Figure 8 illustrates two microscope views with two different magnifications, of the silicon part of Figure 8, after thermal oxidation which created a layer of silicon oxide with a thickness of 1 µm. Figure 9 illustrates a sectional diagram of one embodiment of a silicon part according to the invention, comprising the oxide layer. Figure 10 illustrates a microscope view of an embodiment of a silicon part according to the invention, constituting an animated dial. Figure 11 illustrates a perspective view of an embodiment of a silicon part according to the invention (bottom part) placed on a just satin-finished wafer (top part). Figures 12A to 12F illustrate views from above of a known polished silicon part placed in the vicinity of the same part produced with the method according to the invention, for six different viewing angles. Figures 13A and 13B represent a view of one embodiment of a silicon part according to the invention, constituting a display module.

Example(s) of mode(s) of carrying out the invention

[0050] Figure 1 illustrates a perspective view of an embodiment of a silicon part 1 according to the invention. The shape of the part is not restrictive. Part 1 of Figure 1 comprises a first surface 18, and a second surface 16, opposite the first surface 18. In the illustrated embodiment, the second surface 16 is parallel to the first surface 18. In the embodiment of Figure 1, the silicon part 1 is in one piece. The silicon part in Figure 1 is a wafer, that is to say it comprises at least one flat surface or base 16, and has a small thickness, for example less than 2 mm, in particular less than 500 µm .

[0051] According to the invention, at least a portion of the first surface 18 (in the embodiment of Figure 1, the entire first surface 18) comprises a forest of peaks. According to the invention, the density of the peaks is at least 10 peaks per 100 µm<2> of the surface 18 of the silicon part 1.

[0052] Figure 2 illustrates a portion of a sectional diagram along the line A-A of Figure 1 of the silicon part of Figure 1.

[0053] In the embodiment of Figure 2, the peaks 11 are distributed irregularly on the surface. In other words, the peaks 11 are not arranged so as to form a matrix comprising rows and columns perpendicular to each other. In the embodiment of Figure 2, the peaks are contiguous.

[0054] In the embodiment of Figure 2, the peaks 11 have a pyramid shape, but this shape is not at all limiting. In this context, the term “peak” indicates a pointed protrusion, i.e. a defined protrusion between two ends, in which one end (the base) is larger than the other end (the free end or tip).

[0055] In the embodiment of Figure 2, the height of the peaks 11 is irregular.

[0056] Figure 3 illustrates the sectional diagram of Figure 2, in which certain peaks 11 have been deleted for reasons of clarity.

[0057] According to the invention, the peaks have a height e3 of between 1 µm and 15 µm, for example between 2 µm and 3 µm. This, in combination with their density, makes surface 18 anti-reflective. Due to the presence of the forest of these peaks 11, the surface 18 becomes matte, or satin.

[0058] In Figure 3, the peaks 11 are contiguous and are separated by hollows 10, which in the example illustrated are V-shaped. The surface 18 of Figure 3 therefore comprises an alternation of peaks 11 and hollows 10. Each hollow 10 is defined by a first surface 102 and a second surface 104. The first surface 102 forms a first angle α with a direction h parallel to that of the base surface 16, the second surface 104 forms a second angle β with management h. In the variant illustrated, the first angle α has a value substantially equal to that of the second angle β. In another variant (not illustrated), the first angle α has a value different from that of the second angle β.

[0059] In a variant, the angles α and β are approximately 55°. This is the case for example when the forest of peaks is obtained thanks to an anisotropic attack on a monocrystalline silicon part. In this case, the attack can stop on the <111> planes of the monocrystalline silicon, planes which then constitute the surfaces 102 and 104.

[0060] In a variant, the peaks only comprise <111> planes of monocrystalline silicon, this not necessarily being linked to an anisotropic attack on the silicon. In this variant, the width d of the base of the peaks is approximately 1.2 times the height: for example we have a base of 6 µm for a height of 5 µm.

[0061] Although in the variant illustrated in Figure 3, the area of the first surface 102 is substantially equal to that of the second surface 104, this is not limiting. In another variant, the area of the first surface 102 is significantly different from that of the second surface 104.

[0062] In the variant of Figure 3, neither the first nor the second surface are parallel to the planar base 16.

[0063] In another variant (not illustrated), the recesses 10 have a U shape and are also defined by a third surface between the first and the second, this third surface being able to be parallel to the planar base 16. In another variant again (not illustrated), between the first and second surfaces there are two or more other surfaces.

[0064] Advantageously, the part 1 comprises an alternating succession of upper edges 12 and lower edges 14. In the variant illustrated, all the lower edges 14 are substantially at the same second distance e2 from the planar base 16 and the upper edges 12 are not all at the same second distance e1 from the planar base 16, because they have different heights e3 (=e1- e2).

However, other embodiments are also possible, such as that illustrated in Figure 4, where the upper edges 12 and/or lower 14 are placed at different distances from the base 16.

The solidity of the piece of one-piece silicon part is guaranteed by the minimum value of its thickness e2, chosen during the production of the forest of peaks 11 and by the dimension of the silicon part 1.

[0067] In particular, the dimension e3 is small, even very small (that is to say more than 100 times smaller) compared to the dimension e1, so that the mechanical properties of the part 1 according to the The invention does not change compared to a room without the forest of woodpeckers.

[0068] In the embodiment of Figure 3, the surfaces 102, 104 defining the peaks 11 and the hollows 10 are planar, but they can also be cone portions.

[0069] Part 1 according to the invention therefore comprises a surface having a “sawtooth” profile.

[0070] In a variant, the width of the peaks at the base, or in general, the largest dimension d of the base of the peaks is between 1 μm and 10 μm.

[0071] In a preferred variant, the thickness e1 is less than 400 μm.

[0072] Figure 5 illustrates two microscope views with two different enlargements, of an embodiment of a silicon part according to the invention, in which the forest of peaks 11 has been produced by micro-sandblasting, namely by projecting a jet of fine sand onto the silicon part 1. The diameter of the sand is for example in the range 10 µm - 40 µm. As visible in Figure 5, only certain areas of the surface 18 of the part 1 present the forest of peaks 11. In the example illustrated in particular, there remains approximately 20-25% of the initial surface of the part 1, which is devoid of peaks, which leads to a reflectivity which is still quite high.

[0073] In a preferred variant, only a portion equal to or less than 3% of the surface 18 of the part 1 is devoid of peaks, which significantly reduces the reflectivity.

[0074] Figure 6 illustrates a top view of a silicon part according to one embodiment of the invention, partially covered with metal 2 placed on a smooth silicon substrate (namely, devoid of the forest of peaks 11 ) covered with the same metal. In this variant, the forest of picks was produced by grinding, namely by friction of the part on a grinding wheel, for example a rotating grinding wheel.

[0075] The metallized part 2 of the part 1 according to the invention illustrated in Figure 6 has a pretty golden yellow color, a color which remains the same depending on the viewing angle, which is not the case with the piece in polished silicon covered with gold 3, whose color does not appear yellow, but rather black with a large parasitic reflection of light. In this example, the height of the peaks is between 3 µm and 6 µm.

[0076] Figure 7 illustrates a sectional view of an embodiment of a silicon part according to the invention, in which the forest of peaks 11 has been produced with a chemical attack, for example with an anisotropic attack of the silicon. In other variants, isotropic attacks are also possible. In a preferred variant, the attack is carried out without using masks. In other variants, one or more masks are used in order to have a selective attack. In a preferred variant, solutions based on potassium hydroxide are used as products to carry out the attack. An example of a chemical attack to produce the forest of peaks 11 is described in the document “Highly-efficient low cost anisotropic wet etching of silicon wafers for solar cells application” by Sami Iqbal et al., published for AIP Advances.

[0077] In a variant, the chemical attack is carried out using a wet method. In other variants, the chemical attack is dry (for example “Plasma Deep Reactive Ion Etching”).

[0078] In the example of Figure 7, the height of the peaks 11 is between 2 µm and 3 µm. In the example of Figure 7, the peaks 11 are small pyramids.

[0079] Figure 8 illustrates two microscope views with two different enlargements, of the silicon part of Figure 7, after thermal oxidation which created a layer of silicon oxide with a thickness of 1 μm.

[0080] Oxidation tends to reduce the topology and round off the pyramids, in particular the upper stops 12', by making their facets disappear. This does not degrade the optical properties of the surface 18', since the reflectivity further decreases.

[0081] Figure 9 illustrates a sectional diagram of an embodiment of a silicon part 1 according to the invention, comprising the oxide layer 4. In this variant, the peaks have the same height. This is not necessarily linked to the presence of oxide layer 4.

[0082] Figure 10 illustrates a microscope view of an embodiment of a silicon part 1 according to the invention, constituting an animated dial.

[0083] Figure 11 illustrates a perspective view of an embodiment of a silicon part 1 according to the invention (bottom part), having the surface 18' identical to that of Figure 8, placed on a part (wafer) in silicon 5 just satined (part at the top).

[0084] Figures 12A to 12F illustrate views from above of a known polished silicon part 5 placed in the vicinity of part 1 produced with the method according to the invention and having the same shape, not yet detached from the substrate, for six different viewing angles. Both parts are covered with the same 1 µm thick thermal oxide.

[0085] It is possible to note the fairly radical changes in appearance of the known part 5, compared to that 1 according to the invention, and the appearance remains constant.

[0086] Figures 13A and 13B represent a view of an embodiment of a silicon part according to the invention, constituting a display module.

[0087] As shown in Figures 13A and 13B, a display module 1 consists of a digital display module of a pattern M such as a digit or a number comprising a fixed frame 20 to which at least two display members, in this case five display members 31, 32, 33, 34, 35 to form the number “12” (Figure 13B). The display members 31, 32, 33, 34, 35 are integral with the frame 20 and each comprise a display portion of the pattern M, these display portions being complementary to each other so as to form the pattern M in at least one display position as shown in Figure 13B.

[0088] For this purpose, at least some of the display members 31, 32, 33, 34, 35 are movable relative to the frame 20 via at least one deformable connection 40 formed by at least one flexible blade 41 between a first rest position, shown in Figure 13A, in which the display portions of the display members 31, 32, 33, 34, 35 are spaced from each other and said display position, shown in Figure 13B, in which said display portions are counterposed to each other to form and display the pattern M.

[0089] The movement of the movable display members around their deformable connection 4 between the rest and display positions results from the movement of an actuation pusher 50 also secured to the frame 20 by a structure 8 for guiding in translation linear with flexible blades 81. The pusher 50 comprises at its lower end a contact member adapted to cooperate with actuating device 6, such as a cam 61 movable in rotation around an axis A. At its upper end the pusher 5 comprises a plate 51 to which are secured two flexible “butterfly” pivots 42 connected to the base of deformable actuation rockers B1, B2 to the upper end of which the display members 32, 33, 34 are attached. display are thus mobile around the deformable links.

[0090] The frame 20 of the display module 1 can be fixed on a dial, a disk or directly on the middle of a watch case for a skeleton watch by any appropriate means and in particular gluing or welding. As an actuating device 6, one comprising one or more cams 61, is kinematically linked to the hour barrel and pivots around the axis A, for example centered on the dial of the watch as in a conventional needle display.

[0091] During the rotation of the ring 6 under the driving action of the hour wheel of the train of a watch movement, the cam 61 pushes the free end of the actuating pusher 50 (Figure 13B) which acts as a follower contact, and causes a translation movement of the actuating pusher 50 along its longitudinal axis by deformation of the guide structure 8. This translation induces a rise of the plate 51 and the deformation of the butterfly pivots 42, causing the rotation of the two rockers B1 and B2. The display members 32, 33, 34 connected to the upper ends of said flip-flops B1, B2 then adjust into the display position with respect to the other display portions 31, 35 to form the pattern M. After the passage of the cam 61 the follower contact of the actuating pusher 5 comes back to rest on the ring 6. The display members 32, 33, 34 then move away to return to the rest position (figure 13A) and the pattern is no longer visible.

[0092] An animated display system is thus produced comprising mobile display portions following a determined period to generate a visual animation effect within the display.

[0093] A dial can be formed of twelve elementary modules each animating an hour as presented in Figs. 11A and 11B, or even be formed on a monolithic form comprising the twelve modules linked together in a unitary part.

[0094] In a variant, the display members 31-34 comprise a colored varnish coating layer.

Reference numbers used in the figures

[0095] 1 Silicon part 2 Metal layer 3 Polished silicon part covered with metal 4 Silicon oxide layer 5 Polished silicon part 6 Actuation device 8 Guide structure 10, 10' Hollow 11 Pic 12, 12 ' Upper edge 14 Lower edge 16 Flat surface (base) 18 Matte or satin surface 18' Matte or satin surface, oxidized 20 Frame 31-34 Display elements 41 Flexible blade 42 Flexible pivot 50 Actuation pusher 51 Plate 81 Flexible blade of the guide structure 8 102 First surface 104 Second surface α First angle β Second angle d Largest dimension of the base of a peak 11 e1First distance or thickness e2Second distance or thickness e3Height of a peak 11 h Line having a parallel direction at the flat base B1, B2 Rocker A1 Rising profile of the pusher 50 A2 High point of the pusher 50 A3 Downward profile of the pusher 50

Claims (18)

1. Silicon part (1) for watchmaking, comprising a surface (18), at least a portion of the surface (18) comprising a forest of peaks (11), the density of the peaks (11) being at least least 10 peaks (11) per 100 µm<2> of the surface (18), the peaks having a height e3 of between 1 µm and 15 µm, so as to make said surface (18) anti-reflective. 2. Silicon part (1) according to claim 1, being in one piece. 3. Silicon part (1) according to one of claims 1 and 2, the peaks (1) being contiguous and/or distributed irregularly on the surface (18). 4. Silicon part (1) according to one of claims 1 to 3, the height e3 of the peaks (11) being irregular 5. Silicon part (1) according to one of claims 1 to 4, the height e3 of the peaks (11) being between 2 µm and 3 µm. 6. Silicon part (1) according to one of claims 1 to 5, said portion of the surface (18) comprising a forest of peaks (11) comprising a layer of silicon oxide (4) having a thickness between 0 .25 µm and 4 µm, so that this portion has an anisotropic appearance unit. 7. Silicon part (1) according to one of claims 1 to 6, said portion of the surface (18) comprising a forest of peaks (11) comprising a metallic or dielectric layer (2), so that the color of said portion thus coated is independent of a user's viewing angle. 8. Silicon part (1) according to one of claims 1 to 7, being an analog display module 9. Silicon part (1) according to claim 8, the display module comprising display members (31-34) comprising a colored varnish coating layer. 10. Silicon part (1) according to one of claims 1 to 7, being a dial or a portion of a dial. 11. Silicon part (1) according to one of claims 1 to 7, being a balance, a balance spring, an escapement, an anchor and/or a mobile. 12. Timepiece comprising the silicon part according to one of claims 1 to 11. 13. Process for manufacturing the silicon part (1) for watchmaking according to claim 1, comprising: – production from a silicon wafer of a forest of peaks (11) in at least a portion of a surface of the silicon wafer, the density of the peaks being at least 10 peaks (11) per 100 µm<2> of the surface (18) of the silicon part, the peaks (11) having a height e3 of between 1 µm and 15 µm, so as to make said surface (18) anti-reflective; – cutting the pancake to obtain said part (1). 14. Manufacturing method according to claim 13, the step of producing the forest of peaks (11) from a silicon wafer being carried out by micro-sandblasting the wafer. 15. Manufacturing method according to claim 13, the step of producing from a silicon wafer the forest of peaks (11) being carried out by grinding the wafer. 16. Manufacturing method according to claim 13, the step of producing the forest of peaks (11) from a silicon wafer being carried out by chemical attack on the wafer. 17. Manufacturing method according to one of claims 13 to 16, comprising a step of oxidizing said portion of the surface (18) comprising a forest of peaks (11), in order to create a layer of silicon oxide ( 4) having a thickness between 0.25 µm and 4 µm, so that this portion has an anisotropic appearance unit. 18. Manufacturing method according to one of claims 13 to 17, comprising a step of coating with a metallic or dielectric layer of said portion of the surface (18) comprising a forest of peaks (11), so that the color of said portion thus coated is independent of a user's viewing angle.