A timepiece component including a substrate made of glass that is transparent to visible light and has improved tensile strength

Abstract

The present invention relates to a timepiece component (10) having improved tensile strength, comprising a substrate (20) made of glass that is transparent to visible light and has a lateral dimension on the order of a few centimeters or less and a thickness on the order of 5 millimeters or less. The substrate (20) is coated with a passivation layer (30) having a thickness of less than 1000 nm and in direct contact with the surface (25) of the substrate (20). The passivation layer (30) comprises a heat-resistant ceramic containing at least 1 atomic % hydrogen. The present invention also relates to a method for manufacturing this component.

Description

Technical Field

[0001] The present invention relates to a timepiece component including a glass substrate that is transparent to visible light and has improved damage resistance, and a method for manufacturing the component.

Background Art

[0002] Amorphous fused silica or quartz glass (SiO2) has the theoretical potential to achieve very high mechanical performance defined by the Si - O interaction strength (fracture strength potential calculated at 17 GPa). In practice, the mechanical performance of quartz glass is reduced by the presence of defects (such as scratches, microcracks, microporosities, inclusions, etc.). These defects are often caused during the shaping of quartz glass components. These defects are generally the cause of slow crack growth. Slow crack growth can be likened to stress corrosion caused by the presence of OH ions in ambient humidity, accelerating crack propagation and being the microscopic cause of brittle material failure. Downsizing of components reduces the possibility of millimeter-sized defects (scratches, microcracks) because smaller components statistically have fewer defects. Thus, the use of quartz glass is more interesting for the manufacture of small components, such as millimeter or sub-centimeter components, as in the case of micro-mechanical and timepiece manufacturing components.

[0003] Despite the beneficial possibility of reducing the size of mechanical components to utilize the performance of vitreous silica, the inevitable increase in surface-to-volume ratio and the effect of slow crack propagation require the implementation of solutions that can reduce the surface density of defects and prevent (or at least reduce) the ingress of ambient moisture (especially OH ions) into the components.

[0004] Furthermore, passivation layers have been developed for electronic devices in single-crystalline materials commonly used in optoelectronic applications (especially silicon, GaAs, etc.), and their main technical characteristic is the integrity of the single-crystalline lattice, which is essential to ensure optimal device operation. In these fields of use, the current device performance is limited by the presence of defects (usually atomic) on the surface or at the interface.

[0005] In the field of single-crystalline silicon-based electronic components (transistors) and photovoltaic (PV) devices, it is well known that atomic defects on the surface and / or at the crystal interface are the determining factors when the component size decreases or when the density of bulk defects in the material is low, as in PV applications.

[0006] Various passivation solutions developed in the field of single-crystalline silicon-based electronics and the PV sector consist of coating the surface of the active volume with a thin, usually amorphous phase composed of amorphous silicon (a-Si:H), silicon oxide (SiO2), silicon carbide (SiC), silicon nitride (Si3N4), or mixtures thereof (e.g., oxynitrides, oxicarbides of silicon), or combinations thereof (e.g., SiO2+Si3N4) or their laminated structures (e.g., oxynitrides, oxicarbides of silicon), or combinations thereof (e.g., SiO2+Si3N4) or their laminated structures.

[0007] To limit the ingress of ambient humidity, glass components can be coated with a kerosene layer or a polymer coating (parylene, ORMOCER, etc.). However, these types of coatings are not suitable for the tribological stresses to which the component surface must respond in micro-mechanical and watchmaking applications.

[0008] It is also possible to use types of glass that are more resistant to slow crack propagation than fused silica, such as aluminosilicate glass and borosilicate glass.

Summary of the Invention

Problems to be Solved by the Invention

[0009] One object of the present invention is the use of an electronic industry grade passivation layer to improve the mechanical properties of visible light transmissive glass in components ranging from millimeters to sub - centimeters. Here, the term "glass" refers to an amorphous or nanocrystalline material. The expression "transmissive to visible light" means being transmissive in a sufficient region of the wavelength range between 0.38 mm and 0.78 mm so that the human eye can perceive the presence of the background. Glass that is transmissive to visible light is simply referred to as "glass" in the remainder of this disclosure. Such glass is of interest in the watchmaking field for the design of aesthetic components having particularly high rigidity and environmental stability.

[0010] Another object of the present invention is to improve the mechanical properties, such as fracture strength, of transmissive glass for use in micro - components sized from millimeters to sub - millimeters, such as watch components.

Means for Solving the Problems

[0011] According to the present invention, these objects are achieved in particular by a passivation layer that reduces the surface density of point defects (such as irregular or low - regularity bonds) and separates the components from moisture (OH ions) of atmospheric origin that is involved in accelerating the propagation of cracks leading to breakage.

[0012] More particularly, the present invention relates to a watch component having improved fracture resistance, including a glass substrate having a lateral dimension on the order of centimeters or less and a thickness on the order of millimeters or less. The substrate is coated with a passivation layer that is in direct contact with the substrate surface and has a thickness of less than 1000 nm, preferably less than 600 nm, or more preferably less than 400 nm. The passivation layer includes a heat-resistant ceramic containing at least 1% atomic hydrogen.

[0013] The thin thickness of the passivation layer enables high dimensional accuracy of the component. This is particularly advantageous in micro-mechanical applications and watchmaking applications.

[0014] Brief Description Embodiments of the present invention are illustrated in the description shown by the accompanying drawings:

Brief Description of the Drawings

[0015] FIG. 1 schematically shows a micro-mechanical component comprising a substrate having a passivation layer, according to one embodiment; FIG. 2 shows a schematic cross-sectional view of a substrate surface, according to one embodiment; FIG. 3 shows a flexural strength test of a glass disc performed by the B3B test. FIG. 4 shows a mesoscale three-point flexural strength test performed in a micro-test.

[0016] Detailed Description FIG. 1 schematically shows a watch component 10 comprising a glass substrate 20 that is transparent to visible light and has a lateral dimension on the order of several centimeters or less and a thickness on the order of 1 millimeter or less. The substrate 20 is coated with a passivation layer 30 that is in direct contact with the surface 25 of the substrate 20.

[0017] The glass may include fused silica or a glass containing fused silica.

[0018] In one embodiment, the passivation layer 30 has a thickness of less than 1000 nm, preferably less than 600 nm, or more preferably less than 400 nm.

[0019] The passivation layer 30 includes a heat-resistant ceramic containing at least 1 atomic % hydrogen.

[0020] The passivation layer 30 reduces the defect density of the substrate 20 and, in particular, improves the impact resistance. The passivation layer also isolates the substrate 20 (and thus the component 10) from the ambient humidity and thus from the OH ions present in the atmosphere, which are involved in crack propagation leading to failure. Depending on the choice of its chemical composition, the passivation layer 30 can also be used to maintain the aesthetic appearance (invisibility, transparency) of the initial component 10 machined on the substrate 20.

[0021] The choice of one or the other of the chemical compositions of the passivation layer 30, as well as its thickness, can also depend on the properties required for the coating, such as resistance on the substrate, suitability for charge transport, transparency, qualification, deposition temperature, hardness, chemical barrier to ion migration, tribological behavior, chemical compatibility with lubricants, etc.

[0022] In one embodiment, the heat-resistant ceramic includes one of the following: silicon oxynitride hydride (SiON:H), silicon oxycarbide hydride (SiOxCy:H), silicon carbide hydride (SiC:H), silicon nitride hydride (Si3N4:H), or a combination thereof.

[0023] A heat-resistant ceramic passivation layer 30 containing SiON:H, SiOxCy:H, SiC:H or Si3N4:H ceramic, or a combination of these ceramics, ensures the visual transparency of the layer and is sealed against the transport of ions, in particular OH ions, to the substrate 20.

[0024] A hydrogen content on the order of atomic percent saturates defects formed by unsaturated atomic bonds on the surface 25 of the substrate 20. For example, on the surface 25 of a single crystal silicon substrate, hydrogen reduces the density of dangling bonds. The importance and effects of hydrogen passivation are utilized in the semiconductor electronics industry and photovoltaic applications. In the present invention, a passivation layer 30 including a heat-resistant ceramic containing at least 1 atomic % of hydrogen improves the fracture toughness of the component 10.

[0025] In the case of a brittle material such as glass constituting the substrate 20, the resistance to fracture is potentially inversely proportional to the density of defects at the origin of microcracks (the propagation of microcracks leads to the breakage of the component 10).

[0026] A passivation layer including a heat-resistant ceramic containing at least 1 atomic % of hydrogen reduces the surface density of defects on the surface 25 of the substrate 20. The decrease in the surface density of defects increases the mechanical strength of the component 10, particularly the fracture resistance.

[0027] A thickness of less than 1000 nm, less than 600 nm or less than 400 nm enables the passivation layer 30 to act as a barrier against the penetration of impurities, such as OH ions, in the quartz silica substrate 20 that catalyze or accelerate the propagation of microcracks.

[0028] The performance of the passivation layer 30, particularly the reduction of the surface defect density of the substrate 20 and the separation of the substrate 20 from the ambient humidity, depends on the surface state 25 of the substrate 20. For example, the surface 25 of the substrate 20 should not be affected by machining. Therefore, defects such as scratches and microcracks on the surface 25 of the substrate 20 should be avoided or at least minimized.

[0029] In one embodiment, the surface 25 of the substrate 20 on which the passivation layer 30 is formed is smoothed or polished to a roughness Ra of less than 100 nm. FIG. 2 shows a schematic cross-sectional view of the surface 25. Preferably, the surface 25 is flattened such that the surface 25 of the substrate 20 has a surface topology including irregularities 27 or rounded depressions having a radius of curvature greater than 500 nm, preferably greater than 4 μm. The flattened surface 25 does not have facets or sharp corners that can introduce the possibility of stress concentration during mechanical loading.

[0030] Preferably, the surface 25 of the substrate 20 should also be clean, i.e., have a controlled surface chemical state. Such a controlled surface chemical state may mean that the surface 25 of the substrate 20 is substantially free of particle contamination, native oxides (due to moisture and oxygen in the air), organic substances, coating residues, inorganic bases or inorganic acids, or other metal contaminants. In other words, the chemical composition at the surface 25 is as close as possible to the overall chemical composition of the substrate 20.

[0031] A bending strength test was conducted on a glass disc with a diameter of 10 mm and a thickness of 0.2 mm. Examples of the glass used include aluminosilicate glass, borosilicate glass, and quartz glass. Both sides of the disc were polished by optical quality polishing that results in a roughness Ra of less than 1 nm. Discs with a 400 nm thick SiON:H passivation layer 30 and discs without the passivation layer 30 were measured. The bending strength test was performed using the "Ball on three balls" (B3B) test. The results of these tests performed on 30 discs in air are shown in FIG. 3.

[0032] In FIG. 3, the arrow indicates the effect of the passivation layer on the distribution of the bending strength B3B for a quartz glass disc having a SiON:H passivation layer and a thickness of 400 nm.

[0033] In addition, a mesoscale three-point bending fracture test was conducted on a microtube with a 0.2 mm rectangular cross-section. The microtube was machined from an SiO2 wafer using a technique that preferably includes a chemical dissolution etching step. This mechanism is essential for obtaining a machined surface of sufficient quality from the perspective of defects and residual machining stress. The results of the mesoscale three-point bending test are shown in Fig. 4.

[0034] In Fig. 4, the fracture toughness distribution of microtubes machined using the spark-assisted chemical engraving (SACE) method is plotted. Mechanical stress is applied to the unpassivated specimens using paraffin coating (SACE-paraffin). The passivated specimens (SACE passivation) are characterized by a 400 nm SiON:H passivation layer and are loaded in air. Mechanical stress is applied to the machined surface. The passivation layer is considered functional when the mechanical properties measured in air on the passivated specimens are at least equal to those measured on the paraffin-coated specimens. The beneficial effect of passivation on mechanical properties can also be seen in the narrowing of the fracture strength distribution.

[0035] The results in Figs. 3 and 4 show that the passivation layer 30 improves the mechanical properties for both initial surface states of fused silica, i.e., the optically polished surface 25 with Ra < 1 nm for the B3B test and the machined surface 25 for the mesoscale test.

[0036] In particular, the minimum strength of the specimens is improved. The statistical analysis of the B3B results (Fig. 3) shows a 25% improvement in the average fracture toughness of the double-side polished passivated fused silica disks. The results also show a narrower distribution of the fracture toughness of the specimens.

[0037] In the case of the bending test performed on the disc in the B3B configuration, two thicknesses of the passivation layer 30 were evaluated. Analysis of these results indicates that the thickness of the passivation layer 30 should preferably be 400 nm or less.

[0038] The study of the qualification of the growth of the passivation layer 30 (coating of the same layer thickness on protruding or recessed elements in the component) shows that all surfaces of the component 10 gathering characteristic watchmaking elements (for example, escapement teeth, holes (diameter from 3 mm to 0.2 mm), elongated beams, tongues, points and recessed elements) are satisfactorily coated by the passivation layer 30.

[0039] The substrate 20 can be coated with the passivation layer 30 on one, some or all of its surfaces 25. Preferably, the passivation layer 30 can be formed on the entire surface 25 of the substrate 20. Even more preferably, the three-dimensional component 10 has a passivation layer 30 of substantially uniform thickness on all of its surfaces 25.

[0040] In one embodiment, the watch component can include a display component or an external component.

[0041] In one embodiment, a method for manufacturing the watch component 10 includes the following steps: machining glass to form a substrate 20 having lateral dimensions on the order of centimeters or less and a thickness on the order of millimeters or less; and forming a passivation layer 30 on the surface 25 of the substrate 20, the passivation layer 30 including a heat-resistant ceramic having a thickness of less than 1000 nm and containing at least 1 atomic % hydrogen.

[0042] The passivation layer 30 can be formed by a chemical vapor deposition process. In particular, the passivation layer 30 can be formed by a plasma-assisted chemical vapor deposition (PECVD) process dedicated to a uniform three-dimensional coating of the component 10. For example, the passivation layer 30 can be formed in a reactor that includes rotation / mixing / reverse means to promote the uniform deposition of the passivation layer 30 onto one or more three-dimensional components 10, as described in the Swiss patent application CH715599. To ensure that the deposition of the passivation layer 30 does not cause additional defects on the surface 25, a low-temperature and gentle coating process, such as thermal growth or PECVD layer deposition, is preferred.

[0043] In one embodiment, the method can further include a step of chemical vapor or liquid phase dissolution of the surface 25 of the substrate 20 before the step of forming the passivation layer 30.

[0044] The step of machining the substrate 20 can include selectively chemically dissolving the substrate 20 and releasing the machined component 10.

[0045] According to one embodiment, the machining step can include one of the following processes: deep reactive-ion etching (DRIE), spark assisted chemical engraving (SACE), or ultrashort pulse laser marking (from femtoseconds to picoseconds). Optionally, after the machining step, selective chemical dissolution (or selective laser engraving) of the marked volume can be continued.

[0046] Other machining methods, such as light induced deep etching (LIDE) or selective laser etching (SLE), which all include a chemical dissolution step to release the machined component 10, can also be used within the scope of the present invention.

[0047] In one embodiment, the process includes smoothing and / or flattening the surface 25 of the substrate 20 to obtain rounded irregularities or depressions having a radius of curvature greater than 500 nm, preferably greater than 4 μm. The smoothing and / or flattening step can also include polishing the surface 25 that will receive the passivation layer 30. Preferably, the polishing is carried out with optical quality resulting in a roughness Ra of less than 1 nm. The step of smoothing and / or flattening the surface 25 is carried out before the formation of the passivation layer 30.

[0048] In one embodiment, the method includes a surface cleaning step carried out before the formation of the passivation layer 30 to achieve a controlled chemical state of the surface, i.e., the surface 25 is substantially free of contamination by particles, native oxides (due to humidity and oxygen in the air), organic substances, layer residues, inorganic bases or inorganic acids, or other metal contaminants. The surface cleaning step is carried out before the passivation layer 30 is formed.

[0049] Reference numerals used in the figures 10 Component 20 Substrate 25 Surface 27 Roughness 30 Passivation layer

Claims

1. A watch component (10) having improved breakage resistance, comprising a glass substrate (20) that is transparent to visible light and has a lateral dimension on the order of a few centimeters or less and a thickness on the order of a few millimeters or less, wherein the substrate (20) is coated with a passivation layer (30) that is in direct contact with the surface (25) of the substrate (20) and has a thickness of less than 1000 nm, and the passivation layer (30) comprises a heat-resistant ceramic containing at least 1% atomic hydrogen, said watch component (10).

2. The component according to claim 1, wherein the passivation layer (30) has a thickness of less than 600 nm, preferably less than 400 nm.

3. The component according to claim 1 or 2, wherein the heat-resistant ceramic comprises silicon oxynitride hydride (SiON:H), silicon oxycarbide hydride (SiOxCy:H), silicon carbide hydride (SiC:H), silicon nitride hydride (Si3N4:H), or a combination of these ceramics and their laminates.

4. The component according to any one of claims 1 to 3, wherein the surface (25) of the substrate (20) has a roughness Ra of less than 100 nm.

5. The component according to claim 4, wherein the surface (25) of the substrate (20) includes irregularities having a radius of curvature greater than 4 µm.

6. The component according to any one of claims 1 to 5, wherein the glass comprises fused silica or a glass containing fused silica.

7. The component according to any one of claims 1 to 6, including a mechanically stressed component.

8. The component according to any one of claims 1 to 7, including a component of a display device or a watch exterior part.

9. A method for manufacturing a watch component according to any one of claims 1 to 8, comprising the following steps: machining glass to form a substrate (20) having a lateral dimension on the order of a few centimeters or less and a thickness on the order of a few millimeters or less; forming a passivation layer (30) on the surface of the substrate (20), said passivation layer (30) having a thickness of less than 1000 nm and comprising at least one heat-resistant ceramic containing at least 1% atomic hydrogen.

10. The method according to claim 9, wherein the passivation layer (30) is formed by a chemical vapor deposition process.

11. The method according to claim 10, wherein the passivation layer (30) is formed by a plasma-enhanced chemical vapor deposition (PECVD) process.

12. The method according to any one of claims 9 to 11, comprising the step of smoothing and / or flattening the surface (25) of the substrate (20) so as to obtain a surface topology comprising unevenness (27) having a radius of curvature greater than 500 nm, preferably greater than 4 µm.

13. The method according to any one of claims 9 to 12, further comprising the step of chemically dissolving the surface of the substrate (20) in the gas phase or the liquid phase before the step of forming the passivation layer (30).

14. The method according to any one of claims 9 to 13, wherein the step of machining the substrate (20) comprises selectively chemically dissolving the substrate (20) and releasing the machined component (10).

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