Method for preparing escape wheel by etching
By using thermally conductive liquid bonding and dry etching in the processing of silicon-based escapement wheels, the difficulties in the processing of silicon-based escapement wheels have been solved, and high-precision, low-cost fabrication has been achieved, which is suitable for mechanical timing devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-04-21
AI Technical Summary
Existing technologies for processing silicon-based escape wheels face challenges such as high material brittleness, high processing precision, complex surface treatment, and complex etching processes. These challenges result in high processing difficulty and numerous defects, limiting their production and application.
Using a liquid with good thermal conductivity, such as perfluoropolyether, as an intermediate layer, a thin silicon wafer is bonded to a substrate. The escapement wheel structure is formed by dry etching, and the liquid is dissolved and removed after etching. This simplifies the process and avoids the defects caused by heat accumulation and traditional bonding.
It achieves controllability of the etching process and integrity of the parts, reduces process costs, improves processing accuracy and yield, is suitable for mass production, simplifies the operation process, and avoids the complexity and defects of traditional processes.
Smart Images
Figure CN121900126A_ABST
Abstract
Description
Technical Field
[0001] This application relates to a method for etching and fabricating an escapement wheel, belonging to the field of micro-nano fabrication technology. Background Technology
[0002] As the core component of the escapement mechanism, the escape wheel is the "soul hub" for mechanical timekeeping devices (such as mechanical watches, clocks, and pocket watches) to achieve accurate timekeeping. Its importance runs through the three core aspects of power transmission, rhythm control, and energy compensation, and directly determines the accuracy, stability, and reliability of the timekeeping device.
[0003] The main difficulties in processing silicon-based escapement wheels are reflected in material properties and processing technology, as follows: (1) High material brittleness: Silicon material has the disadvantages of high brittleness and insufficient toughness, and it is easy to break during processing. This puts forward extremely high requirements for processing technology and operation accuracy; (2) High processing accuracy: The processing accuracy of silicon escapement wheels usually needs to reach the micron level. Its shape needs to be finely adjusted to reduce mass and inertia. This requires the use of extremely complex photolithography process and deep reactive ion etching (DRIE) technology to project the image of the escapement wheel onto the silicon wafer for processing. The process is difficult and the requirements for equipment and technicians are very high; (3) High surface treatment requirements: Although silicon has natural anti-friction properties and does not need to lubricate the outer surface of the escapement wheel, some surface treatment may be required to further improve its performance and wear resistance. This also increases the complexity and difficulty of processing; (4) Complex etching process: When processing silicon escapement wheels using etching methods such as DRIE, sharp edges will be left, and wavy plate-shaped defects, called "fan-shaped", will be generated on the side of the part. These defects can affect the performance and lifespan of silicon escape wheels, and need to be minimized or eliminated through special processes and treatment methods.
[0004] Existing technologies face significant limitations in etching precision and defect elimination, severely restricting the production and application of silicon-based escapement wheels. Summary of the Invention
[0005] To address at least one of the problems in existing technologies for etching and fabricating escapement wheels, namely, high precision requirements and difficulty in eliminating defects, this application provides a technical solution for etching and fabricating escapement wheels. First, a silicon wafer is thinned to the required thickness, followed by photolithography patterning. The resulting silicon wafer is then attached to another silicon wafer using a liquid with good thermal conductivity, such as perfluoropolyether, to facilitate good thermal conductivity. The flexible liquid interlayer also facilitates the collection of the etched escapement wheel components.
[0006] The technical solution adopted in this application is as follows: According to a first aspect of this application, a method for etching an escapement wheel is provided, comprising: A thin silicon wafer of a target thickness is provided, and a soft mask is fabricated on one side of the thin silicon wafer; The side of the thin silicon wafer facing away from the soft mask is bonded to the substrate using a thermally conductive liquid to obtain an adhesive sheet; Etching is performed on one side of the soft mask on the adhesive sheet to etch through the thin silicon wafer to form an escapement structure; The thermally conductive liquid on the adhesive sheet is dissolved and removed to obtain a free escape wheel.
[0007] Optionally, the target thickness is 80 μm to 300 μm.
[0008] Optionally, before fabricating a soft mask on one side of the thin silicon wafer, the process further includes: The thin silicon wafer is polished.
[0009] Optionally, the heat-conducting liquid is selected from at least one of perfluoropolyether, perfluorocarbon compound, polydimethylsiloxane, alkylbenzene, and mineral oil.
[0010] Optionally, the substrate is made of a material with high thermal conductivity.
[0011] Optionally, the high thermal conductivity material is selected from silicon, diamond, and silicon nitride.
[0012] Optionally, the thin silicon wafer is obtained by thinning a silicon wafer or silicon wafer.
[0013] Optionally, the fabrication of a soft mask on one side of the thin silicon wafer includes: Photoresist is coated on one side of the thin silicon wafer; After selective exposure and development of the photoresist, a soft mask with an escapement wheel pattern is obtained.
[0014] Optionally, the thickness of the photoresist coating is 0.6µm to 5µm; And / or, the exposure dose is 60 mJ / cm 2 ~200mJ / cm 2 .
[0015] Optionally, the etching method for one side of the soft mask on the adhesive sheet is dry etching.
[0016] The beneficial effects of this application include: (1) By coating the target wafer and the substrate wafer with a thermally conductive liquid, this application effectively avoids the uneven etching caused by heat accumulation in dry etching, thus achieving controllable etching process.
[0017] (2) This application utilizes the viscosity of the thermally conductive liquid on the substrate to ensure that the escape wheel parts fall onto the intermediate layer after being etched through, and will not slide between the wafers or fly out of the cavity, thus ensuring the integrity of the parts and providing an excellent solution for the mass production of escape wheels with high yield.
[0018] (3) This application replaces the bonding after coating resin with simple adhesive bonding, which requires high equipment. The operation is simpler, the requirements for silicon wafer raw materials are lower, the process cost is reduced, and the risk of resin, bonding glue and other materials being difficult to remove is avoided.
[0019] (4) This application provides a highly compatible preparation method that effectively provides a preparation method for the same type of parts on different substrates, and has wide applicability. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the wafer fabrication process using thermally conductive liquid bonding for dry etching, as described in this application. Figure 2 This is a process flow diagram of the method for releasing the escape wheel after deep silicon etching in this application; Figure 3 This is a schematic diagram of the process for preparing escapement wheel parts using the glue-filled key method in the comparative example. Detailed Implementation
[0021] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.
[0022] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.
[0023] Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.
[0024] The precision issues and defects in existing escapement wheel etching technologies greatly limit the production and application of silicon-based escapement wheels. Existing technologies mainly include photolithography etching and silicon wafer thinning with filler.
[0025] Photolithography is currently the mainstream process for fabricating silicon escapement devices. It's a MEMS (Micro-Electro-Mechanical Systems) based processing technology, primarily consisting of two steps. First, photolithography is the fundamental step in silicon escapement fabrication. It first creates a mask for the escapement's design pattern, then transfers this pattern onto photoresist on the silicon wafer surface using photolithography. This causes a photochemical reaction in the photoresist, forming a microstructure on the silicon wafer that matches the design pattern, providing a precise pattern template for subsequent etching processes. The subsequent etching process, particularly deep reactive ion etching (DRIE), is crucial for silicon escapement fabrication. After photolithography, DRIE etches the silicon wafer, using ions in plasma to chemically react with and physically bombard the silicon material, precisely etching the three-dimensional structure of the silicon escapement according to the photoresist pattern. This technology can achieve high aspect ratio etching, producing extremely precise escapement tooth profiles and other structures, with a processing accuracy reaching 1 micrometer. However, since the escape wheel itself is not particularly thick, heat buildup and sticking are likely to occur during deep reactive ion etching, or over-etching and damage to the pattern may occur due to in-plane non-uniformity of the etching.
[0026] The silicon wafer thinning method involves etching an escapement wheel structure on one side of a monocrystalline silicon wafer using photolithography and deep reactive ion etching. The escapement wheel structure is then bonded to a hard material layer using a cured resin. The side of the monocrystalline silicon wafer facing away from the escapement wheel structure is thinned until the escapement wheel structure is exposed. Finally, the cured resin is removed to obtain a free escapement wheel component. However, this technology also faces some technical challenges and limitations. The main problems include: (1) the complexity and difficulty of the bonding process. When bonding the escapement wheel structure to a hard material layer using a cured resin, it is necessary to precisely control parameters such as the amount of resin applied, the curing temperature, and the time. If the resin coating is uneven or the curing conditions are not suitable, the bonding strength may be insufficient. In subsequent processes, the escape wheel may easily separate from the hard material layer, affecting product quality. During the bonding process, bubbles or impurities may be generated. These defects will affect the bonding quality between the escape wheel and the hard material layer, thus affecting the performance and stability of the escape wheel. (2) The thinning process is difficult. When thinning the bonded sheet, it is very difficult to accurately control the thickness and uniformity of the thinning. Excessive thinning may result in insufficient support of the escape wheel structure, affecting its mechanical properties. Uneven thinning will cause the escape wheel to generate uneven stress distribution during vibration, affecting its timekeeping accuracy. In addition, if the filling process is uneven, it will lead to unbalanced force during thinning, which may cause the device to fly out or crack during the thinning process, which is not conducive to the maintenance of the thinning machine. (3) Potential risks of the de-curing process. When removing the cured resin, the organic solvents or plasma treatment methods used may corrode the escape wheel, reducing the mechanical strength and reliability of the escape wheel.
[0027] To address these issues, researchers are working to improve the precision of photolithography etching equipment, enhance the detection capabilities of etching equipment, and develop new fabrication processes. They are also implementing strict quality control and real-time monitoring to address reliability and stability concerns.
[0028] This application provides an extremely simple processing method. First, the silicon wafer is thinned to the required thickness, then patterned using photolithography. The resulting silicon wafer is then bonded to another silicon wafer using a liquid with good thermal conductivity, such as perfluoropolyether, to facilitate good thermal conductivity. The flexible liquid interlayer also facilitates the collection of the escapement wheel components after etching. This avoids the difficult-to-remove adhesive residue that can result from bonding methods, and reduces the sticking phenomenon caused by poor thermal conductivity due to etching through the parts. This provides a solution for the mass production of high-yield escapement wheel devices.
[0029] According to one embodiment of this application, a method for etching an escapement wheel includes: A thin silicon wafer of a target thickness is provided, and a soft mask is fabricated on one side of the thin silicon wafer; The side of the thin silicon wafer facing away from the soft mask is bonded to the substrate using a thermally conductive liquid to obtain an adhesive sheet; Etching is performed on one side of the soft mask on the adhesive sheet to etch through the thin silicon wafer to form an escapement structure; The thermally conductive liquid on the adhesive sheet is dissolved and removed to obtain a free escape wheel.
[0030] In one embodiment, the target thickness is 80 μm to 300 μm. The target thickness is determined by the escapement wheel component, and this range represents the typical thickness requirement for escapement wheel devices. If the thickness is less than 80 μm, the escapement wheel structure may be too fragile and lack sufficient mechanical strength; if the thickness is greater than 300 μm, it will significantly increase the difficulty and time of subsequent etching processes, potentially leading to an excessively large aspect ratio, affecting the uniformity and accuracy of etching, and even causing heat accumulation problems. Including this range in the claims clarifies the key dimensions applicable to the process, ensuring that the final product has sufficient structural strength and suitable machinability. The target thickness is preferably 100 μm to 200 μm.
[0031] In one embodiment, prior to fabricating the soft mask on one side of the thin silicon wafer, the thin silicon wafer is further polished. The polishing step aims to obtain a smooth, flat, and undamaged silicon wafer surface. A high-quality starting surface is fundamental to the success of subsequent photolithography processes; it ensures uniform photoresist coating, reduces defects, and thus guarantees the transfer accuracy and edge sharpness of the mask pattern. This directly improves the dimensional accuracy and surface quality of the final escapement wheel's fine structure.
[0032] In one embodiment, the thermally conductive liquid is selected from at least one of perfluoropolyether (PFPE), perfluorocarbon (PFC), polydimethylsiloxane (PDMS), alkylbenzene, and mineral oil. These liquids are chosen primarily because they possess good thermal conductivity, chemical stability, and suitable viscosity. The thermally conductive liquid can rapidly conduct heat generated during etching from the thin silicon wafer to the substrate, effectively preventing problems such as "smearing" or uneven etching rates caused by localized overheating ("heat buildup"). It is also less prone to reaction in etching environments (especially plasma environments), thus avoiding contamination of the process chamber or damage to the device. Furthermore, these thermally conductive liquids provide sufficient adhesion to fix the silicon wafer and collect etched parts, while being relatively easy to dissolve and remove after the process, avoiding the risk of residue from traditional bonding adhesives.
[0033] In one embodiment, the substrate is made of a material with high thermal conductivity. Using a material with high thermal conductivity as the substrate allows it to work synergistically with the thermally conductive liquid to form an efficient heat dissipation path. This enables the heat generated by the etching heat source to be dissipated more quickly, further improving the heat dissipation efficiency of the entire system and fundamentally suppressing process instability and structural defects caused by heat accumulation.
[0034] In one embodiment, the high thermal conductivity material is selected from silicon, diamond, and silicon nitride. Silicon has good compatibility with the workpiece and is relatively inexpensive; diamond is one of the materials with the highest known thermal conductivity, providing excellent heat dissipation; silicon nitride combines good thermal conductivity with excellent mechanical strength. These materials are common and reliable substrate choices in the prior art, providing a specific, easy-to-implement, and optimized solution, with silicon being the preferred high thermal conductivity material.
[0035] In one embodiment, the thin silicon wafer is obtained by thinning a silicon wafer or silicon wafer. Obtaining a thin silicon wafer of the target thickness is a mature process route. That is, first use silicon wafers or silicon wafers of standard thickness, and then process them to the required thickness through thinning techniques such as grinding and polishing. The high feasibility of the process allows the method of this application to be well integrated with the existing silicon wafer processing industry chain.
[0036] In one embodiment, the process of preparing the thin silicon wafer includes cleaning, drying, and then thinning the silicon wafer or diaphragm.
[0037] In one embodiment, the fabrication of a soft mask on one side of the thin silicon wafer includes: Photoresist is coated on one side of the thin silicon wafer; After selective exposure and development of the photoresist, a soft mask with an escapement wheel pattern is obtained.
[0038] In one embodiment, the thickness of the photoresist coating is 0.6µm to 5µm; this thickness range ensures that the photoresist has sufficient etching resistance (as a mask layer) in subsequent dry etching (such as DRIE) to protect the underlying silicon material until the etching is complete. If the photoresist is too thin, it may be etched through prematurely and lose its protective function, while if the photoresist is too thick, it will affect the pattern resolution and increase the process difficulty. The thickness of the photoresist coating is preferably 1µm to 2µm. And / or, the exposure dose is 60 mJ / cm 2 ~200mJ / cm 2 This range of exposure doses is an optimized setting designed to ensure steep and dimensionally precise pattern boundaries after photoresist development, thereby achieving the best photolithographic pattern quality and forming a high-quality mask. The preferred exposure dose is 110 mJ / cm². 2 ~130 mJ / cm 2 .
[0039] In one embodiment, the etching method for one side of the soft mask on the adhesive sheet is dry etching. Dry etching (especially deep reactive ion etching, DRIE) is the mainstream and best technology for achieving high aspect ratio and high verticality silicon microstructures. It can precisely perform anisotropic etching along the pattern defined by the soft mask, thereby creating the precise tooth profile and three-dimensional structure required for the escapement wheel. The use of a "thermally conductive liquid" scheme combined with dry etching in this application can retain the advantages of dry etching while avoiding the etching non-uniformity caused by heat accumulation in dry etching.
[0040] In one embodiment, the method for etching to prepare the escapement wheel includes: Step 1: Cleaning. Take one single-polished silicon wafer and another material with high thermal conductivity (such as silicon wafer, diamond, silicon carbide, etc.) and ultrasonically clean them in acetone, isopropanol and deionized water respectively. Then dry them with nitrogen and bake them. Step 2: Thinning. One silicon wafer is thinned to a target thickness determined by the escapement wheel components, and then polished. The other silicon wafer serves as the subsequent substrate and requires no further processing.
[0041] Step 3: Photolithography. For example... Figure 1 As shown, PR photoresist is coated on the surface of a clean silicon wafer. In some embodiments, exposure is then performed, followed by development, to complete the photolithography step of the escapement wheel.
[0042] Step 4: Substrate bonding. (e.g.) Figure 1As shown, a silicon wafer that has undergone photolithography and another ordinary silicon wafer are bonded together using a thermally conductive liquid. The photolithographic surface is the front side. The thermally conductive liquid can be selected from perfluoropolyether (PFPE), perfluorocarbon compound (PFC), polydimethylsiloxane (PDMS), alkylbenzene, mineral oil, etc., preferably perfluoropolyether (PFPE) or perfluorocarbon compound (PFC), to obtain a bonding sheet for subsequent processes.
[0043] Step 5: Etching. For example... Figure 2 As shown, the adhesive sheet was dry-etched, with the etching depth determined by the thickness of the photomask, etching until it penetrated through. The etched escape wheel component successfully landed on the heat-conducting liquid, and due to its high viscosity, the component did not slip. After etching, the heat-conducting liquid was dissolved in acetone to obtain a single escape wheel component.
[0044] In one embodiment, the thermally conductive liquid and its corresponding thermal conductivity and kinematic viscosity are shown in Table 1; Table 1
[0045] In one embodiment, the thermal conductivity of the commonly used substrate is shown in Table 2; Table 2
[0046] Example 1 Step 1: Cleaning. Take two single-sided polished silicon wafers and ultrasonically clean them successively in acetone, isopropanol, and deionized water, then dry them with nitrogen and bake them.
[0047] Step 2: Thinning. One silicon wafer is thinned to a target thickness of 120 μm and then polished. The other silicon wafer serves as the subsequent substrate and requires no further processing.
[0048] Step 3: Photolithography. A PR photoresist layer with a thickness of 1.5 μm is coated onto the surface of a clean silicon wafer. Exposure is then performed at a dose of 120 mJ / cm². 2 Then development is performed to complete the photolithography step of the escapement wheel.
[0049] Step 4: Substrate bonding. The photolithographically etched silicon wafer and another ordinary silicon wafer are bonded together using a thermally conductive liquid, with the photolithographic side facing up and perfluoropolyether (PFPE) as the thermally conductive liquid, to obtain a bonded sheet for subsequent processes.
[0050] Step 5: Etching. Dry etching is performed on the bonding sheet, with the etching depth determined by the thickness of the photoresist, etching until the entire sheet is etched through. The etched escape wheel component then successfully lands on the thermally conductive liquid, and due to its high viscosity, the component does not slip. After etching, the thermally conductive liquid and photoresist are dissolved in acetone to obtain a single escape wheel component.
[0051] Comparative Example 1 Step 1: Cleaning. Take one single-polished silicon wafer and one double-polished silicon wafer and ultrasonically clean them successively in acetone, isopropanol and deionized water, then dry them with nitrogen and bake them. Step 2: Photolithography. A PR photoresist layer with a thickness of 1.5 μm is coated onto the surface of a clean silicon wafer. Exposure is then performed at a dose of 120 mJ / cm². 2 Then development is performed to complete the photolithography step of the escapement wheel.
[0052] Step 3: Etching. Dry etching is performed on the photomask to a depth of 150 μm. After etching, the resist is removed.
[0053] Step 4: Epoxy Bonding. A layer of epoxy resin is first spin-coated onto the etched wafer surface to fill the gaps in the pattern and ensure the flatness of the wafer surface. Bonding then occurs, with the epoxy-coated side bonded to the polished surface of another silicon wafer.
[0054] Step 5: Thinning. Thin the back side coated with epoxy resin until the front pattern is visible, then stop thinning.
[0055] Step 6: Release the part. The bonded sheet is heated and soaked in NMP (N-methylpyrrolidone), which dissolves the epoxy resin between the gaps in the escape wheel pattern, resulting in the released free escape wheel part.
[0056] In summary, this application represents a fundamental technological breakthrough compared to the typical traditional "etch-fill-bond-thinning-release" process. Its core innovation lies in simplifying the process flow to "pre-thinning-photolithography-liquid bonding-one-time etching and release." This restructuring directly addresses three major pain points of existing technologies: First, by pre-thinning the silicon wafer to the target thickness and bonding it to a high thermal conductivity substrate using liquids such as perfluoropolyether, a highly efficient heat dissipation channel is formed, completely solving the heat accumulation problem in deep reactive ion etching and avoiding paste formation and pattern distortion caused by uneven temperature. Second, the viscosity of the liquid layer enables in-situ flexible capture of the escape wheel at the moment of etching, allowing the component to fall directly into the liquid layer instead of splashing within the cavity, perfectly avoiding the damage risks that inevitably occur during subsequent bonding and thinning of fragile structures in traditional processes. Finally, this solution completely eliminates the difficult fill-bonding and precision thinning steps, not only simplifying the operation but also eradicating defects such as bubbles, impurities, weak bonding, and wafer cracking. Ultimately, only a mild solvent is needed to dissolve the liquid layer to complete the release, posing no risk of corroding the silicon material. This solution transforms a complex process into a combination of several standard modules, significantly improving process stability, repeatability, and yield, and providing a practical industrialization path for the mass production, low-cost, and high-reliability manufacturing of silicon escape wheels.
[0057] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.
Claims
1. A method for etching an escapement wheel, characterized in that, include: A thin silicon wafer of a target thickness is provided, and a soft mask is fabricated on one side of the thin silicon wafer; The side of the thin silicon wafer facing away from the soft mask is bonded to the substrate using a thermally conductive liquid to obtain an adhesive sheet; Etching is performed on one side of the soft mask on the adhesive sheet to etch through the thin silicon wafer to form an escapement structure; The thermally conductive liquid on the adhesive sheet is dissolved and removed to obtain a free escape wheel.
2. The method for preparing an escapement wheel by etching according to claim 1, characterized in that, The target thickness is 80 μm to 300 μm.
3. The method for preparing an escapement wheel by etching according to claim 1, characterized in that, Before fabricating the soft mask on one side of the thin silicon wafer, the process further includes: The thin silicon wafer is polished.
4. The method for preparing an escapement wheel by etching according to claim 1, characterized in that, The heat-conducting liquid is selected from at least one of perfluoropolyether, perfluorocarbon compound, polydimethylsiloxane, alkylbenzene, and mineral oil.
5. The method for etching and preparing an escapement wheel according to claim 1, characterized in that, The substrate is made of a material with high thermal conductivity.
6. The method for preparing an escapement wheel by etching according to claim 5, characterized in that, The high thermal conductivity material is selected from one of silicon, diamond, and silicon nitride.
7. The method for preparing an escapement wheel by etching according to claim 1, characterized in that, The thin silicon wafer is obtained by thinning a silicon wafer or silicon wafer.
8. The method for preparing an escapement wheel by etching according to claim 1, characterized in that, The process of fabricating a soft mask on one side of the thin silicon wafer includes: Photoresist is coated on one side of the thin silicon wafer; After selective exposure and development of the photoresist, a soft mask with an escapement wheel pattern is obtained.
9. The method for preparing an escapement wheel by etching according to claim 8, characterized in that, The thickness of the photoresist coating is 0.6µm to 5µm; And / or, the exposure dose is 60 mJ / cm 2 ~200mJ / cm 2 .
10. The method for preparing an escapement wheel by etching according to claim 1, characterized in that, The etching method used to etch one side of the soft mask on the adhesive sheet is dry etching.