Method for treating a silicon component

Abstract

The present invention relates to a plate (10) for supporting at least one individual silicon watch component (1) or a wafer carrying a plurality of silicon watch components, and a thermal oxidation treatment method using this plate (10). A useful face (10a) of the plate (10) forms, on at least one receiving area (11), a receiving surface (20) for said watch component (1) or said wafer, with said receiving surface (20) being made of a nitride-based material and having a roughness Ra greater than 50 nm, more preferably greater than 200 nm, more preferably greater than 1 micron.

Description

Technical field of the invention

[0001] The present invention relates to the processing of silicon components, in particular watch components such as balance springs, anchors, escape wheels, gear wheels, plates, hands, balance wheels. State of the art

[0002] Silicon watch components are typically manufactured using a substrate - also called a wafer - of the silicon-on-insulator type known by the acronym SOI (silicon on insulator) and comprising a first layer of silicon in which the components are to be formed, a second layer, typically of silicon, used to stiffen the substrate and, between these two layers of silicon, an intermediate layer of oxide serving as a stop layer for the etching operations of the useful layer.

[0003] According to a known process, the first layer of silicon is etched to form the components, and then a wafer formed from at least part of this first layer bearing the components is "released," that is, detached from the substrate for processing, particularly by thermal oxidation. Oxidation aims to improve the surface finish of the components and / or adjust their dimensions, notably to regulate their stiffness (in the case of spirals), before they are finally detached from the wafer.

[0004] A primary advantage of treating a wafer rather than individual components is that it avoids the laborious handling of small, individual components, which would otherwise have to be deposited one by one onto a substrate for oxidation. This also allows for oxidation of the components on all sides, something impossible with a substrate. However, a disadvantage is that the wafer can deform during treatment under its own weight, potentially rendering the components unusable.

[0005] In some cases, it may also be impossible to provide fasteners connecting the components to a wafer. This is particularly true when manufacturing small components. In this case, the components are necessarily released from the substrate as individual elements, which are then deposited onto a support for processing, with the drawbacks mentioned previously. Summary of the invention

[0006] One aim of the present invention is therefore to propose an optimized process for the treatment of watch components by thermal oxidation, making it possible in particular to provide a solution to the aforementioned disadvantages of the prior art.

[0007] According to the invention, this objective is achieved through the subject matter of the independent claims. More specific aspects are defined in the dependent claims as well as in the description.

[0008] More specifically, one objective of the invention is achieved through a thermal oxidation treatment process for at least one silicon-based watch component, in which: a support platform is provided, delimited in a transverse direction by a useful face forming, on at least one receiving area, a receiving surface for said watch component or a plate bearing said watch component, the watch component or the plate bearing the component is placed on the receiving surface of the support platform, and the watch component or the plate placed on said receiving surface is subjected to at least one thermal oxidation step. According to the invention, the receiving surface of the support plate is made of a nitride-based material and has a roughness Ra greater than 50 nm, more preferably greater than 200 nm, more preferably greater than 1 micron.

[0009] The process according to the invention is particularly suitable for processing watch components in the form of individual elements, that is, elements with finite contours. Such elements are obtained by etching without a tether in a silicon substrate (for example, but not limited to, a silicon dioxide substrate of the type mentioned above). The individual components are then placed one by one on the surface of the support platform. They can also be obtained by detaching components from their wafer, components that were initially etched with a tether attaching them to the wafer.

[0010] However, the process is also suitable for watch components still attached to the same plate. The plate carrying the components is then placed on the support plate.

[0011] Examples of components to be treated include balance springs, anchors, escape wheels, gear wheels, platters, hands, and balance wheels.

[0012] They include at least one silicon core, possibly totally or partially re-coated with silicon dioxide.

[0013] The invention also relates to a support plate adapted for supporting at least one individual silicon watch component or a wafer carrying a plurality of silicon watch components during a thermal oxidation treatment, typically for implementing the process according to the invention.

[0014] The support plate according to the invention comprises a useful face which forms, on at least one receiving area, a receiving surface for a watch component or a plate bearing said component, said receiving surface being made of a nitride-based material and having a roughness Ra greater than 50 nm, more preferably greater than 200 nm, more preferably greater than 1 micron.

[0015] Throughout this application, each component, whether individual or mounted on a plate, is defined as having a parallel upper and lower face, the lower face being the one intended to come into direct contact with the support plate during the oxidation process. These upper and lower faces are connected by one or more lateral surfaces.

[0016] The process according to the invention allows individual components, or components still attached to their wafer, to be oxidized on their supported underside during the oxidation step. It has been observed that if components placed on a substrate made of a nitride-based material with sufficient roughness are thermally oxidized, these components are also oxidized at their interface with the substrate and can then be easily removed from this surface once the oxidation is complete.

[0017] The use of a rough-surfaced tray made of nitride-based material allows silicon components to be oxidized on all their lower, upper and lateral faces, including when these components are not bonded to a wafer.

[0018] Similarly, in the case of wafers, these can advantageously be supported on all or part of their lower surface without impacting the oxidation process. This easily prevents their deformation while simultaneously ensuring good final component quality.

[0019] The invention therefore makes it possible to carry out, in the same way and with the same result, the thermal oxidation of individual components and of wafers bearing components.

[0020] According to an advantageous provision, the nitride-based material can be silicon nitride (Si3N4).

[0021] The roughness Ra of the receiving surface is defined according to the ISO 4287 standard.

[0022] It is preferably less than 50 microns, and even more preferably less than 20 microns.

[0023] The support plate is obviously a separate element from the component and the substrate from which the component originates. The component, or a wafer bearing this component, is actively placed on the receiving surface of this support plate, which is generally positioned approximately horizontally and oriented upwards.

[0024] The transverse direction of the support platform should be understood as a direction generally orthogonal to the receiving surface and therefore oriented substantially vertically during the platform's use. Unless otherwise specified, the heights and thicknesses defined below are measured in this transverse direction.

[0025] A lateral direction is orthogonal to said transverse direction.

[0026] To ensure good rigidity and therefore good support of the component(s), the support plate typically has a total thickness of at least 300µm to 800µm (measured in the transverse direction).

[0027] The support platform can be a monolithic or composite element.

[0028] For example, the support platform may include a core in the form of a plate and a coating made of a nitride-based material on at least one face of said plate and forming the receiving surface.

[0029] According to an advantageous arrangement, the nitride-based coating typically has a thickness between 100nm and 500nm.

[0030] According to an advantageous arrangement, the plate is a silicon plate or wafer.

[0031] According to an advantageous arrangement, the plate is entirely covered with a nitride-based coating.

[0032] According to one example, the receiving surface is globally flat, that is to say a maximum height (measured in the transverse direction of the plateau) between a peak and a trough of this surface is less than 100 microns.

[0033] According to a particularly advantageous arrangement, at least on the receiving area, the useful face can be textured with one or more cavities, for example forming a network and / or a regular pattern, the height of which is at least 2 times greater than the roughness value Ra of the receiving surface, preferably at least 5 times greater than this roughness value Ra.

[0034] According to one example, the cavities are grooves forming a grid, the receiving surface then being formed by the upper surface of pillars delimited by said grooves and of typically square, rectangular or circular section.

[0035] With such an arrangement, each component placed on the platform is supported by a plurality of pillars. During thermal oxidation, oxygen penetrates more easily under the component through the cavities and then through the passages resulting from the irregularities (roughness) of the receiving surface.

[0036] As an alternative or in addition, the usable surface can also be equipped with receiving openings, including blind openings. In this case, when the watch component or the plate bearing the component is placed on the receiving surface, at least a protruding part of the watch component is positioned in one of these receiving openings.

[0037] Such openings allow components with non-planar faces to be stored "flat", thus avoiding possible local over-stresses that could damage the edges of these components and hinder their final functionality.

[0038] According to one example, the support platform may further include at least one lateral retaining surface configured to retain the component or pad in a lateral direction orthogonal to the transverse direction.

[0039] The retention surface can also be made of a nitride-based material with a roughness Ra greater than 50 nm, preferably greater than 200 nm, preferably greater than 1 micron.

[0040] To create such a retaining surface, one can, for example, engrave a central part of the plate corresponding to the receiving area. The plate then has a recess whose base forms the receiving surface and whose edge, oriented towards the inside of the plate, forms the retaining surface.

[0041] Alternatively, the lateral retaining surface can also be oriented outwards from the plate. This case is particularly suitable for holding a plate with at least one peripheral part, advantageously a frame, extending transversely and designed to engage around the retaining surface.

[0042] This retaining surface helps to prevent or limit the movement of the components or the wafer in a lateral direction orthogonal to the transverse direction, during handling and / or oxidation.

[0043] According to another aspect, the invention relates to a method for manufacturing at least one watch component, comprising at least one processing step as defined above. Brief description of the drawings

[0044] The features and advantages of the present invention will become apparent in more detail in the following description of several illustrative and non-limiting embodiments, with reference to the accompanying figures in which: THE figures 1 to 3 schematically represent different successive stages of the treatment process according to an implementation method of the invention. Figures 4A and 4B are cross-sectional views according to IV of the figure 2 , respectively before and after oxidation, The figure 5 is an enlarged view of detail V of the figure 1 , There figure 6 illustrates a support platform according to another embodiment of the invention, in which the usable face is textured, The figure 7 illustrates a support platform according to yet another embodiment of the invention, in which the usable face is provided with receiving openings intended to receive protruding parts of watch components arranged on the receiving surface, The figure 8 illustrates a support platform according to yet another embodiment of the invention, in which the receiving surface is tiered, The figure 9 illustrates a support platform according to yet another embodiment of the invention, comprising a lateral retaining surface preventing lateral slippage of the components during use. Figure 10 illustrates a support platform according to yet another embodiment of the invention, in which the lateral retaining surface is oriented towards the outside of the platform. Detailed description

[0045] There figure 1illustrates an example of a support plate 10 according to the invention, which can be used for the thermal oxidation of one or preferably a plurality of silicon-based watch components 1, for example balance springs, anchors, escape wheels, gear wheels, plates, hands and / or balance wheels.

[0046] The support plate 10 is delimited, in a transverse direction Z, by a lower face 10b and a top or useful face 10a.

[0047] In this example, the thickness e1 of the tray, measured in the transverse direction Z, must be sufficient to give it a certain rigidity and is typically between 300 µm and 800 µm. The dimensions and shape of the tray 10 orthogonally to this transverse direction Z can vary according to the requirements of the process, but can, for example, correspond to those of the substrates or wafers commonly used in the manufacture of watch components or semiconductors, so as to be compatible with existing placement systems in thermal oxidation furnaces.

[0048] As described below, the useful face 10a of the tray includes, on a receiving area 11, a receiving surface 20 intended to receive the components, and which is made of a nitride-based material.

[0049] The roughness Ra of this receiving surface is greater than 50 nm, preferably greater than 200 nm, even more preferably greater than 1 micron, and preferably less than 50 microns, even more preferably less than 20 microns, obtained for example by etching.

[0050] But as schematically illustrated on the figure 5 which is an enlarged view of detail V of the figure 1 Apart from the aforementioned roughness, the receiving surface extends substantially orthogonally to the transverse direction and is generally flat. According to a particular arrangement, the maximum height between a peak and a trough of this surface can advantageously be less than 100 microns, preferably less than 50 microns.

[0051] The support platform 10 can for example be obtained by coating a plate 14, advantageously made of a relatively rigid material, in particular silicon, and forming a stiffening core for the platform.

[0052] The plate 14 typically comprises a first and a second main face 14a, 14b, generally parallel, connected by an edge (not shown). It may, for example, be a solid silicon substrate of the type used in the manufacture of watch components or semiconductors.

[0053] The first main face 14a of the plate 14 exhibits, at least locally, a certain roughness Ra that can correspond substantially to that desired for the receiving surface, and which is therefore greater than 50 nm, preferably greater than 200 nm, even more preferably greater than 1 micron, and preferably less than 50 microns, even more preferably less than 20 microns. This roughness can notably be obtained, during a preparation step, by etching, for example by wet etching with potassium hydroxide (KOH) or HNO3 / HF or by deep reactive ion etching (DRIE) or reactive ion etching (RIE).

[0054] At least part of this first rough main face 14a, and preferably the entire perimeter of the plate 14 (as illustrated), is covered with a coating 16 made of a nitride-based material, typically silicon nitride. The thickness e2 of the coating is, for example, between 100 nm and 500 nm and is advantageously constant, to facilitate proper adjustment of the final roughness of the receiving surface (the roughness of the receiving surface 20 then corresponding to that of the first main face 14a of the plate 14).

[0055] The coating (nitriding) of the plate 14 is preferably a low pressure chemical vapor deposition (LPCVD) of silicon nitride (ideally stoichiometric) Si3N4, generally carried out in a furnace.

[0056] The first main face 14a of the plate 14, coated, forms the upper face 10a or useful face of the support tray 10, and the receiving surface 20 is formed by this upper face 10a.

[0057] The illustrated example is not, however, limiting. As indicated above, the plate 14 could, for example, be coated only on its first main face 14a. Or the support plate 10 could be formed entirely from a nitride-based material. Other embodiments will be described later with reference to Figures 5 to 10 .

[0058] The process for treating components 1 by thermal oxidation will now be described in relation to the figures 1 to 3 And 4A, 4B .

[0059] After the support tray 10 is provided, the watch components 1 are placed on the receiving surface 20, as illustrated in the figure 1. The platform 10 is therefore positioned substantially horizontally, with its transverse direction Z substantially vertical and its upper face 10a (and therefore the reception surface 20) oriented upwards.

[0060] In the example, each component 1 is a unit element and the components 1 are placed one by one on the surface 20.

[0061] This example is not limiting to the invention and one could also place on the receiving surface 20 a plate bearing a plurality of watch components 1 held by fasteners.

[0062] In a second step of the process illustrated on the figure 2The tray 10, bearing the components 1, is placed, either manually or automatically, in a thermal oxidation furnace (not shown). As explained previously, the tray advantageously has the same standard dimensions as the wafers used in prior art processes, so no special mounting is required.

[0063] The oven is heated to a temperature generally between 900 and 1200 degrees, allowing the oxidation of components 1.

[0064] As the oxidation reaction progresses, and as illustrated by the difference between the Figures 4A and 4B , part of the silicon S is gradually consumed and transformed into silicon dioxide D. The interface between the silicon and the new layer of silicon dioxide gradually recedes: The dimensions of the silicon S core decrease, and the thickness of silicon dioxide D on the surface increases.

[0065] The implementation of a rough receiving surface 20, in a nitride-based material, allows oxidation to also take place on the lower face 2b of the components 1 in contact with this surface 20. Also, the nitride-based material prevents the components 1 from sticking to the platform 10, at the end of the thermal oxidation step.

[0066] As illustrated on the figure 3 , components 1 can thus easily be removed from the support plate 10 after their thermal oxidation.

[0067] There figure 6 illustrates a support platform according to another embodiment of the invention.

[0068] Here, the useful or upper face 10a of the plate 10 is textured, at least on its receiving area 11, with one or more cavities 30 for example forming a network or a regular pattern, in particular a grid or a succession of parallel lines.

[0069] In this case, the receiving surface 20 is formed by the residual part(s) of the useful face 10a located between the cavities 30.

[0070] The height H1 of these cavities 30 is typically at least twice greater than the roughness value Ra of the receiving surface, preferably at least 5 times greater than this value.

[0071] This texturing helps to limit the points of contact between components 1 and the platform 10. It promotes the uniformity of oxidation by increasing the surface area in contact with oxygen during this step.

[0072] Texturing can in particular be obtained by etching, in particular wet etching or deep reactive ion etching (DRIE), of the first main face 14a of the stiffening plate 14 before its coating.

[0073] There figure 7illustrates a support platform 10 according to yet another embodiment of the invention, in which the useful face is further provided with receiving openings 40, in particular blind openings, intended to receive protruding parts 3 of watch components arranged on the receiving surface 20.

[0074] The height H2 of the opening 40 is at least equal to, preferably strictly greater than, the height of the protrusion 3 of the component 1 to be received.

[0075] This height H2 is also typically at least twice greater than the roughness value Ra of the receiving surface, preferably at least 5 times greater than this value.

[0076] In the particular example shown, and although it is only optional, the useful face 10a is further textured according to arrangements similar to those described previously in connection with the figure 6 .

[0077] In connection with the methods of implementation of Figures 6 and 7 It should be noted that the edges or bottom of the cavities 30 or openings 40, resulting from etching, may not have a roughness Ra identical to that of the receiving surface 20. However, this has no influence on the effectiveness of thermal oxidation since these edges and bottoms are not in contact with the components 1 during this operation.

[0078] There figure 8 illustrates a support platform 10 according to yet another embodiment of the invention, in which the receiving surface 20 is this time not globally flat but tiered, so as to receive respectively different levels of multilevel components 1.

[0079] In the particular example shown, and although it is only optional, the useful face 10a is further textured according to arrangements similar to those described previously in connection with the figure 6

[0080] There figure 9illustrates a support platform 10 according to yet another embodiment of the invention.

[0081] This includes here, near the receiving area 11, a lateral retaining surface 19 for the components 1 or, as illustrated, a plate 50 carrying the components 1, preventing their lateral sliding during use.

[0082] Preferably, this retention surface 19 is also made of a nitride-based material and has a roughness Ra similar to that of the receiving surface 20, in other words a roughness Ra greater than 50 nm, more preferably greater than 200 nm, more preferably greater than 1 micron.

[0083] It can in particular be obtained by engraving a recess in the silicon plate 14 forming the core of the plate 10, before coating said plate 14 with a nitride-based material.

[0084] There Figure 10illustrates a support platform 10 according to yet another embodiment of the invention.

[0085] Here, the lateral retaining surface 18 is oriented outwards from the tray 10. This case is more particularly suited to holding a wafer 50 comprising a first silicon layer 52 in which the components 1 are formed, an intermediate layer 54 typically of silicon oxide and a part of a stiffening layer 56, typically also of silicon, forming a peripheral frame or ring, where the intermediate layer 54 is interposed transversely between the first layer 52 and the stiffening layer 56. Here, the wafer frame can be engaged around the retaining surface 18, for its laterally held position.

Claims

1. A method for thermally oxidizing at least one silicon-based watch component (1), wherein: - a support platform (10) is provided, delimited in a transverse direction (Z) by a useful face (10a) forming, on at least one receiving area (11), a receiving surface (20) for said watch component (1) or a wafer (50) bearing said component (1), - the watch component (1) or the wafer (50) bearing the component (1) is placed on the receiving surface (20) of the support platform (10), and - the watch component (1) or the wafer placed on said receiving surface (20) is subjected to at least one thermal oxidation step, characterized in that the receiving surface (20) of the support plate (10) is made of a nitride-based material and has a roughness Ra greater than 50 nm, more preferably greater than 200 nm, more preferably greater than 1 micron.

2. Processing method according to claim 1, wherein the or each watch component (1) is a unit element with finite contours.

3. Processing method according to claim 1 or 2, wherein the useful face (10a) of the support plate (10) is provided with receiving openings (40), in particular blind openings, and by placing the watch component (1) or the plate (50) carrying the component (1) on the receiving surface (20), at least one protruding part (3) of the watch component (1) is placed in one of said receiving openings (40).

4. Method for manufacturing at least one watch component (1), comprising at least one processing step according to any one of claims 1 to 3.

5. Support platform (10), in particular for implementing the method of any one of the preceding claims, said platform (10) being delimited in a transverse direction (Z) by a useful face (10a) forming, on at least one receiving area (11), a receiving surface (20) for a watch component (1) or a plate (50) carrying said component (1), characterized in that the receiving surface (20) is made of a nitride-based material and has a roughness Ra greater than 50 nm, more preferably greater than 200 nm, more preferably greater than 1 micron.

6. Support plate (10) according to claim 5, wherein the roughness Ra of the receiving surface (20) is less than 50 microns, preferably less than 20 microns.

7. Support tray (10) according to claim 5 or 6, wherein the nitride-based material is silicon nitride.

8. Support plate (10) according to any one of claims 5 to 7, comprising a core in the form of a plate (14) and a coating (16) made of a nitride-based material on at least one face (14a) of said plate and forming the receiving surface (20).

9. Support plate (10) according to any one of claims 5 to 8, wherein, at least on the receiving area (11), the useful face (10a) is textured with one or more cavities (30), for example forming a network and / or a regular pattern, the height (H1) of which is at least 2 times greater than the roughness value Ra of the receiving surface, preferably at least 5 times greater than this roughness value Ra.

10. Support platform (10) according to any one of claims 5 to 9, in which the useful face (10a) is provided with receiving openings (40), in particular blind openings, intended to receive protruding parts (3) of watch components (1) arranged on the receiving surface (20).

11. Support platform (10) according to any one of claims 5 to 10, wherein the receiving surface (20) is generally flat.

12. Support plate (10) according to any one of claims 5 to 11, further comprising at least one lateral retaining surface (18, 19) configured to retain the component (1) or the plate (50) in a lateral direction substantially orthogonal to the transverse direction (Z).

13. Support plate (10) according to claim 12, wherein the retention surface (18, 19) is made of a nitride-based material and has a roughness Ra greater than 50 nm, more preferably greater than 200 nm, more preferably greater than 1 micron.

14. Support plate (10) according to claim 12 or 13, wherein the lateral retaining surface (19) is oriented towards the inside of the plate.

15. Support plate (10) according to claim 12 or 13, wherein the lateral retaining surface (18) is oriented towards the outside of the plate.

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