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EP-4741946-A1 - METHOD FOR MANUFACTURING SILICON CLOCK COMPONENTS

EP4741946A1EP 4741946 A1EP4741946 A1EP 4741946A1EP-4741946-A1

Abstract

A method for manufacturing watch components (90) in an SOI-type wafer comprises the steps of: (a) forming a structured silicon oxide layer (50) on the upper surface of the working layer (30) of the wafer; (b) forming the components (90) by etching, through this structured layer (50), patterns in the working layer (30) to obtain removed regions (35) which expose the buried oxide layer (40) below; (c) forming a protective layer (55, 155) at least on the flank surfaces (95) of the components etched in step (b); (d) perform a directional etch, without using a mask, of the buried oxide layer (40) to the point where regions (45) of the buried oxide layer (40) are removed to obtain a perforated buried oxide layer (40'), (e) perform a silicon etch in the support layer (20) through the removed regions (45) of the perforated buried oxide layer (40'), to obtain an excavated support layer (20') having at least one cavity (24) formed below at least one of the watch components (90); and (f) remove the portions of the buried oxide layer (40) remaining between the at least one cavity (24) and the at least one component (90) arranged above the cavity (24).

Inventors

  • Chabart, Mickaël
  • DEMOLON, Pierre

Assignees

  • Richemont International SA

Dates

Publication Date
20260513
Application Date
20251017

Claims (18)

  1. A method for manufacturing, in an SOI-type wafer (10), a plurality of watch components (90) having flanks (95) having surfaces, the SOI wafer (10) comprising a silicon support layer (20), a silicon working layer (30), and an embedded silicon oxide oxide layer (40) having a thickness (e 40 ) and separating the support layer (20) from the working layer (30), the method comprising the following steps: (a) form a structured silicon oxide layer (50, 150) on the upper surface of the working layer (30); (b) forming the watch components (90) by engraving, through the structured silicon oxide layer (50, 150), patterns in the working layer (30) in order to obtain a structured working layer (30'), the structured working layer (30') comprising removed regions (35) around the engraved patterns in which the material of the working layer has been removed to expose the buried oxide layer (40) below; (c) form a protective layer (55, 155) at least on the surfaces of the flanks (95) of the watch components engraved in step (b); (d) either after or before step (c), perform a directional etch, without using a mask, of the buried oxide layer (40) to the point where regions (45) of the buried oxide layer (40) below the removed regions (35) of the working layer are removed to obtain a perforated buried oxide layer (40'), the structured silicon oxide layer (50', 150) still being present on the upper surface of the structured working layer (30') after this step; (e) etch the silicon into the support layer (20) through the removed regions (45) of the perforated buried oxide layer (40'), in order to obtain an excavated support layer (20') having at least one cavity (24) formed beneath at least one of the watch components (90); and (f) remove the remaining portions of the buried oxide layer (40) between said at least one cavity (24) and said at least one watch component (90) arranged above said cavity (24), in order to obtain a structured buried oxide layer (40") having remaining portions (42, 44) still linking the excavated support layer (20') to the structured working layer (30').
  2. Method according to the preceding claim, wherein step (f) also includes the removal of the structured silicon oxide layer (50', 150) on the upper surface of the structured working layer (30').
  3. A method according to any one of the preceding claims, wherein the formation of the structured silicon oxide layer (50, 150) in step (a) comprises: the formation of an unstructured silicon oxide layer on the upper surface of the working layer (30), the formation of a resin layer (60) on the unstructured silicon oxide layer, the removal of a portion of the resin layer (60), and the structuring of the structured silicon oxide layer (50, 150) through the remaining portion of the resin layer (60).
  4. A method according to the preceding claim, wherein the formation of the protective layer (55) in step (c) is carried out by thermal oxidation, the protective layer (55) being made of silicon oxide and also forming on exposed silicon surfaces of the support layer (20), and the remaining part of the resin layer (60) being removed before said formation of the protective layer (55) by thermal oxidation.
  5. A method according to claim 3 or 4, wherein: - before the formation of the protective layer (55) in step (c), a first directional etching step, without using a mask, of the buried oxide layer (40) located below the removed regions (35) of the working layer, the remaining part of the resin layer (60) still being present on the structured silicon oxide layer (150) during this first directional etching step; and - after the formation of the protective layer (55) in step (c), a second directional etching step, without using a mask, of the silicon oxide (40, 55) located below the removed regions (35) of the working layer.
  6. A method according to any one of claims 1 to 4, wherein the structured silicon oxide layer (50) formed in step (a) has a thickness (e 50 ) greater than the thickness (e 40 ) of the buried oxide layer (40), in step (d) the structured silicon oxide layer (50) is also etched onto the upper surface of the structured working layer (30'), and a thinned structured silicon oxide layer (50') is still present on the upper surface of the structured working layer (30') after the etching in this step (d).
  7. A method according to any one of claims 1 to 4 or 6, wherein the formation of the protective layer (55) in step (c) is carried out before the directional etching in step (d).
  8. A method according to any one of the preceding claims, wherein the directional etching of step (d) is a DRIE or ICP-RIE type etching.
  9. A method according to the preceding claim, wherein the directional etching of step (d) uses at least one fluorinated gas such as CHF 3 , C 4 F 8 , and/or SF 6 in combination with at least one of the gases He and/or H 2 .
  10. A method according to any one of the preceding claims, wherein the etching of the support layer (20) in step (e) comprises an anisotropic etching.
  11. A method according to any one of claims 1 to 10, wherein the etching of the support layer (20) in step (e) comprises an isotropic etching.
  12. A method according to the preceding claim, wherein the etching in step (e) is a vapor phase etching based on xenon difluoride ( XeF2 ).
  13. A method according to claim 11, wherein the etching in step (e) uses a sulfur hexafluoride ( SF6 ) based plasma.
  14. A method according to any one of the preceding claims, wherein each watch component (90) of the SOI plate (10) has its own cavity (24) which extends only below that watch component (90).
  15. A method according to any one of the preceding claims, wherein a maximum thickness of each cavity (e cav ) is at most equal to 50% of the thickness (e 20 ) of the support layer (20), and preferably at most equal to 25% of the thickness (e 20 ) of the support layer (20).
  16. A method according to any one of the preceding claims, wherein step (b) of forming the watch components (90) is carried out by a DRIE type engraving technique.
  17. A method according to the preceding claim, wherein during the DRIE type engraving carried out in step (b) a fluoropolymer layer forms on the surfaces of the flanks (95) of the engraved watch components, and the protective layer of step (c) comprises this fluoropolymer layer.
  18. A process according to any one of the preceding claims, the process comprising, after step (f), a thermal oxidation step followed by a deoxidation step to smooth the watch components (90) or to adjust the dimensions of the watch components and/or a step to form a permanent silicon oxide layer on at least a part of the external surface of the watch components (90).

Description

technical field The invention relates to a method for manufacturing silicon watch components on a silicon-on-insulator (SOI) wafer. Such a manufacturing process generally comprises microfabrication steps including lithography and etching of the wafer layers, as well as post-etching manufacturing steps including component release. State of the art The fabrication of silicon watch components, such as balance springs, cams, springs, pawls, wheels, and pallet forks, using microfabrication processes is well established. Advantageously, several hundred watch components can be manufactured on a single wafer using these technologies. For example, it is known to produce a multitude of silicon resonators with very high precision using photolithography and etching processes on a silicon wafer. The processes for manufacturing these watch components generally use monocrystalline silicon wafers, but polycrystalline or amorphous silicon wafers are also suitable. Silicon is a diamagnetic material, and its use in the manufacture of watch components, particularly for the regulating organ components of a mechanical watch movement, is advantageous because no remanent effect is observed after exposure of this material to magnetic fields. Furthermore, variations in the Young's modulus of a silicon watch component with temperature can be compensated for by adding a layer of SiO₂ oxide to the component. When watch components are made from a single-crystal silicon wafer, any one of the three crystal orientations <100>, <110>, or <111> can be used. Silicon wafers are offered in single-sided wafer form, for example SSP (Single Side Polished) or DSP (Digital Single Side Polished) wafers. (Dual Side Polished in English). The document EP3495894 This document describes a process for manufacturing silicon watch components using a wafer comprising a single silicon layer without a support layer. According to this document, the single wafer has a thickness substantially equal to the maximum thickness of the watch components to be manufactured. To form the watch components, an etching step is performed through the entire thickness of the wafer, thus utilizing all the component material present in the wafer to form the watch components, without any support function within the wafer. After formation, the watch components are structurally supported only by thin bonding bridges that hold them attached to the remaining portions of the single silicon layer. Subsequent manufacturing steps can be performed on almost the entire external surface of the components without the need for a prior component release step. However, in the manufacturing process described in this document EP3495894 The engraving stage is delicate because it takes place in a relatively thin, and therefore fragile, wafer without any support. Alternatively, silicon-on-insulator (SOI) wafers are often used for manufacturing watch components. An SOI wafer comprises a silicon working layer (the "device" layer) in which the watch components are fabricated, a silicon support layer that serves as a substrate or support during component fabrication (the "handle" layer), and a buried SiO₂ oxide layer located between the two silicon layers (the "buried oxide layer" or BOX layer). The surface of the working layer and possibly the surface of the support layer can also be polished to facilitate lithography steps on these layers. After the lithography and etching steps to initially form the watch components in the working layer of an SOI wafer, the components are normally freed from the support layer and the buried oxide layer of the SOI wafer to facilitate subsequent manufacturing steps. In this way, after freeing, the watch components are structurally supported only by thin bonding bridges that hold them attached to the remaining portions of the working layer, which notably allows for the following: Subsequent manufacturing steps are performed on virtually the entire external surface of the wafer components. These subsequent steps may include oxidation and deoxidation processes to smooth the component surfaces. They may also include oxidation and deoxidation processes to adjust component dimensions (for example, to correct stiffness when the components are balance springs or resonators) and/or oxidation processes to form an external silicon oxide layer on the components for thermal compensation and/or mechanical reinforcement. After these subsequent steps, the watch components can be detached from the wafer and mounted in, for example, the movement of a timepiece. The release of watch components on a SOI wafer can be achieved using various methods. One release approach is described in the patent documents. JP2017219520 And WO2019180177 According to this approach, after the components are formed by etching, a silicon oxide layer is grown on the surface of the silicon. This oxide layer serves as a protective layer for the formed components. Subsequently, photolithography and etching are perfo