Vacuum pump rotor, vacuum pump and manufacturing method

Abstract

Vacuum pump rotor (20; 30) wholly or partly made of a composite material (11) comprising an organic matrix (12) and carbon fibres (13), characterised in that the carbon fibres (13) of the composite material (11) are coated with a nickel layer and in that a nickel-based coating (14) covers the composite material (11), the interface between the coated carbon fibres (13) and the nickel-based coating (14) being free of organic matrix (12).

Description

Vacuum pump rotor, vacuum pump and manufacturing process Technical field of the invention

[0001] The present invention relates to a vacuum pump rotor. The invention also relates to a vacuum pump and a method for manufacturing a vacuum pump rotor. Technical background

[0002] Turbomolecular vacuum pumps used in semiconductor manufacturing processes are subject to increasing mechanical, thermal and chemical stresses with the increase in the fineness of the etching steps and the materials of electronic circuits requiring the use of highly corrosive gases (Cl2, HBr, F2, Iodine).

[0003] The turbomolecular pumps used to pump these gases are generally made of aluminum coated with a layer of nickel to resist corrosion. However, the increasing stresses of high-temperature operation required to prevent solid deposits on the internal surfaces of the turbomolecular pumps, as well as the high rotational speeds necessary for pumping performance, promote creep phenomena in the aluminum alloys over time. Furthermore, the levels of kinetic energy stored by the turbine become critical in the event of a mechanical failure.

[0004] Some turbomolecular vacuum pump designs now incorporate carbon fiber composite components to achieve higher rotational speeds, improved performance at higher temperatures, and reduced kinetic energy. However, the resistance of carbon fiber composite materials to chemical attack is very low, particularly against fluorinated gases.

[0005] Furthermore, depositing a nickel layer onto a carbon / graphite composite substrate is difficult because the latter is not a catalyst. In fact, initiating the nickel layer deposition on this type of substrate is challenging, if not impossible.

[0006] Primary or Roots vacuum pumps can also be used to evacuate corrosive gases such as halogenated gases or particularly aggressive particles, notably those originating from reaction byproducts of certain manufacturing processes. Corrosion layers can form on the surface of vacuum pump components, which can reduce the operating clearances between the rotors and stator and alter the performance of the vacuum pumps. Nickel plating or Teflon-type polymer coatings are generally used to protect the cast iron from corrosion.

[0007] One aim of the present invention is to provide a vacuum pump that at least partially resolves the drawbacks of the prior art, in particular by featuring a rotor made of nickel-coated composite material.

[0008] To this end, the invention relates to a vacuum pump rotor made entirely or partly of composite material, the composite material comprising an organic matrix and carbon fibers characterized in that the carbon fibers of the composite material are coated with a layer of nickel and in that a nickel-based coating covers the composite material, the interface between the coated carbon fibers and the nickel-based coating being devoid of organic matrix.

[0009] The nickel-based coating applied to the carbon fibers, which are coated with a layer of nickel without an organic matrix between them, provides the coating with an optimal adhesion surface to the composite material. The resulting coating is resistant to mechanical pull-off, thermal stress, and the penetration of corrosive elements such as Cl2, F2, and O2, which are harmful to carbon fibers. This improved resistance to thermal and mechanical stress stems from the fact that the composite material and the coating share the same mechanical and physical properties.

[0010] Vacuum pump rotors then offer improved resistance to corrosive agents and can feature a more compact design for the same pumping performance due to a higher rotor speed resulting from the low weight of the composite material. Maintenance intervals can be extended in corrosive pumping applications.

[0011] The rotor may also include one or more of the characteristics described below, taken alone or in combination.

[0012] The organic matrix is, for example, a thermoset or a thermoplastic, such as an epoxy resin.

[0013] Coated carbon fibers can be grouped into twisted bundles of a plurality of carbon fibers.

[0014] Carbon fibers, for example, have a diameter greater than 5 µm.

[0015] The nickel layer, for example, has a thickness greater than 50 nm.

[0016] The nickel layer, for example, contains more than 99% nickel.

[0017] Carbon fibers can be made from polyacrylonitrile (PAN) [-CH2-CH(CN)-].

[0018] Coated carbon fibers, for example, exhibit a tensile strength greater than 3600 MPa, for example less than 5000 MPa, and can exhibit a Young's tensile modulus between 238 GPa and 280 GPa.

[0019] Nickel-based coatings may contain between 10% and 13% phosphorus by mass.

[0020] The nickel-based coating can have a thickness greater than 5 µm.

[0021] According to one example of an embodiment, the rotor has at least one stage of blades.

[0022] According to one embodiment, the rotor includes at least one cylindrical skirt, at least one cylindrical skirt being made at least partly of composite material.

[0023] The invention also relates to a vacuum pump characterized in that it comprises a rotor as described above.

[0024] The invention further relates to a vacuum pump characterized in that it comprises two rotors as described above, in particular Roots or Claw or screw, configured to rotate in opposite directions in a pumping chamber.

[0025] The invention also relates to a method for manufacturing a vacuum pump rotor, characterized in that it comprises: - a shaping step in which at least a part of the rotor is formed from composite material, the composite material comprising an organic matrix and carbon fibers coated with a layer of nickel, - a removal step in which an outer layer of organic matrix is ​​removed from the composite material so as to expose the nickel layers of the underlying carbon fibers, - a deposition step in which a nickel-based coating is deposited on the etched outer surface of the composite material.

[0026] Once the outer layer of organic matrix has been stripped, the exposed nickel surfaces of the carbon fibers allow for the deposition of the nickel-based coating, particularly through autocatalytic nickel deposition. Indeed, the nickel layers of the carbon fibers provide the desired catalytic properties, enabling coating initiation. Furthermore, the cleaned outer surface of the composite material contains very few foreign elements that could potentially disrupt the initiation of the autocatalytic nickel deposition.

[0027] According to one embodiment, the removal of the outer layer of organic matrix of the composite material is carried out chemically such as by oxygen plasma or mechanically such as by polishing, sandblasting or laser beam or by bathing in a resin solvent.

[0028] According to one example of implementation, the deposition is carried out by autocatalytic nickel deposition. Brief description of the figures

[0029] Other advantages and features will become apparent upon reading the description of the invention, as well as the accompanying drawings, which show:

[0030] Lamontre a flowchart outlining the different stages of a manufacturing process for a vacuum pump rotor.

[0031] Lamontre is a composite material.

[0032] Lamontre the composite material at the end of the removal stage of the manufacturing process.

[0033] Lamontre the composite material sample at the end of the deposition stage of the manufacturing process.

[0034] Lamontre a rotor of a turbomolecular vacuum pump whose cylindrical skirt was obtained by the manufacturing process.

[0035] Lamontre a cross-sectional view of a pumping chamber of a vacuum pump whose rotors were obtained by the manufacturing process.

[0036] In these figures, identical elements bear the same reference numbers. Detailed description

[0037] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features of different embodiments can also be combined or interchanged to provide other embodiments, without departing from the scope of the invention as defined by the claims.

[0038] The term "upstream" refers to an element that is placed before another element in relation to the direction of flow of the gas being pumped. Conversely, the term "downstream" refers to an element placed after another element in relation to the direction of flow of the gas being pumped.

[0039] Lamontre describes a manufacturing process 100 for a vacuum pump rotor. All or part of the rotor can be manufactured according to this process. Two examples will be described later with reference to Figures 5 and 6.

[0040] The manufacturing process 100 includes a shaping step 101, followed by a shrinkage step 102 and a deposition step 103.

[0041] During shaping step 101, at least part of a rotor is formed from composite material 11. The rotor may be hollow in whole or in part.

[0042] As can be seen in the illustrative diagram, the composite material 11 comprises an organic matrix 12 and carbon fibers 13. Each carbon fiber 13 is coated with a layer of nickel, the coated carbon fibers 13 being embedded in the organic matrix 12.

[0043] Carbon fibers 13, for example, are made from polyacrylonitrile (PAN) [-CH2-CH(CN)-] in order to exhibit good mechanical properties and good resistance to high temperatures.

[0044] Carbon fibers 13 (also called NCCF (for "Nickel Coated Carbon Fiber")) are individually coated with a layer of nickel, for example by a chemical vapor deposition (CVD) process based on the high-temperature decomposition of nickel.

[0045] The nickel layer, for example, has a thickness greater than 50 nm and / or less than 150 nm, such as 80 nm. The nickel layer contains, for example, more than 99% nickel, such as 99.97%. The nickel layer represents, for example, 22% of the total weight of the coated carbon fiber 13.

[0046] Preferably, these coated carbon 13 fibers exhibit a tensile strength greater than 3600 MPa but less than 5000 MPa, and a Young's tensile modulus (also called the modulus of elasticity) between 238 GPa and 280 GPa. Tensile strength is the amount of load per unit area that the material can withstand before it breaks, and the tensile modulus defines the stress levels at maximum load within a material's yield strength.

[0047] Preferably, the composite material 11 can be a woven textile composite (the fibers are ordered / organized). The orientation of the layers relative to each other allows for control of the specific mechanical properties required for the shape and depending on the final part to be obtained, such as a rotor (or part) of a vacuum pump. To obtain a composite material 11 with fibrous textile reinforcements, the coated carbon fibers 13 are impregnated with the organic matrix 12, which can be deposited during the winding and weaving of the fiber bundles 13.

[0048] In particular, coated carbon fibers 13 can be twisted in bundles of a plurality of carbon fibers to give them greater mechanical strength. Specifically, coated carbon fibers 13 can be twisted in bundles of twelve, each bundle containing one thousand carbon fibers.

[0049] Carbon fibers 13, for example, have a diameter greater than 5 µm, for example less than 10 µm, such as between 6 µm and 8 µm.

[0050] The organic matrix 12 can be a thermoset or a thermoplastic, such as an epoxy resin (also called polyepoxide or epoxy polymer comprising a base, a hardener, an accelerator and additives) which exhibits good mechanical characteristics over a wide temperature range, high hardness, resistance to abrasion, gases, chemicals and moisture, a high glass transition and good dielectric properties.

[0051] The shaping of the rotor in composite material 11 can be carried out for example by (hot) molding or by injection.

[0052] Then, during the removal step 102 of the manufacturing process 100, the outer layer of organic matrix 12 of the composite material 11 is removed so as to expose the nickel layers of the underlying carbon fibers 13 ().

[0053] An organic matrix layer 12 less than 60 µm thick, such that between 2 µm and 50 µm, can be removed from the external surface of the composite material 11.

[0054] The removal of the outer organic matrix layer 12 can be achieved chemically, such as by oxygen plasma. Oxygen plasma cleans the outer surface of the composite material 11 to expose the nickel-plated surface of the underlying carbon fibers 13. In other embodiments, the outer organic matrix layer is removed mechanically (polishing or sandblasting) or by laser beam or immersion in a resin solvent bath.

[0055] Then, during the deposition step 103, a nickel-based coating 14 is deposited on the etched external surface of the composite material 11, revealing the nickel layers of the coated carbon fibers 13.

[0056] Nickel-based coating 14 may contain phosphorus. Nickel-phosphorus coating 14 is particularly corrosion-resistant because it does not exhibit cracking in its layer. Nickel-phosphorus coating 14, for example, contains between 10% and 13% phosphorus by mass ("high phosphorus"). This coating 14 can be produced without heat treatment for hardening, resulting in high corrosion resistance. Furthermore, the coating 14 has a thickness, for example, greater than 5 µm, or less than 25 µm, such as 20 µm.

[0057] The coating can be applied by electroless (autocatalytic) nickel deposition. This method uses a bath containing metal ions and chemicals that reduce them to metal through redox reactions. The reaction is autocatalytic, allowing the new metal to be deposited onto the coating as it forms. This solution offers good adhesion and coating uniformity.

[0058] Alternatively, the coating can be applied by electrolytic nickel plating (electroplating). Electroplating nickel plating is performed by immersing the rotor or the portion of the rotor of the composite material 11 to be coated in an electrolytic solution, with the immersed rotor or portion of the rotor serving as the cathode. The nickel anode dissolves in the electrolyte, forming nickel ions (Ni). 2+ ). The ions pass through the solution and are deposited on the cathode.

[0059] Other examples include chemical immersion deposition (CID), sputtering, physical vapor deposition (PVD), and chemical vapor deposition (CVD). Sputtering uses an electron beam or plasma to eject microscopic metal particles onto the substrate under vacuum. PVD transfers the metal to the substrate through evaporation. CVD uses a gas containing a volatile compound of the metal, which is deposited onto the substrate through a chemical reaction.

[0060] Once the outer layer of organic matrix 12 has been stripped, the exposed nickel surfaces of the carbon fibers 13 allow the nickel-based coating 14 to be deposited, particularly by autocatalytic nickel deposition. Indeed, the nickel layers of the carbon fibers 13 provide the desired catalytic properties, enabling layer initiation. Furthermore, the cleaned outer surface of the composite material 11 contains very few foreign elements that could interfere with the initiation of the autocatalytic nickel deposition.

[0061] The coating 14 thus formed has an optimal adhesion surface to the external surface of the composite material. The coating 14 is highly resistant to mechanical pull-off, thermal stress, and penetration by corrosive elements such as Cl2, F2, and O2, which are harmful to carbon fibers. This superior resistance to thermal and mechanical stress stems from the fact that the composite material 11 and the coating 14 share the same mechanical and physical properties.

[0062] The vacuum pump rotor thus obtained is then made entirely or partly of composite material 11, the composite material 11 comprising an organic matrix 12 and carbon fibers 13 coated with a layer of nickel, a nickel-based coating 14 covering the composite material 11, the coating 14 being deposited on coated carbon fibers 13 on the external surface of the composite material 11, the interface between the coated carbon fibers 13 and the nickel-based coating 14 being devoid of organic matrix 12.

[0063] Vacuum pump rotors then exhibit better resistance to corrosive agents, can have a more compact architecture for the same pumping performance due to a higher rotational speed possible due to the low weight of the composite material 11. Maintenance intervals on corrosive pumping applications can be increased.

[0064] Laillustre an example of the realization of a 20 rotor of a turbomolecular vacuum pump.

[0065] The rotor 20 is configured to rotate at high speed in axial rotation, for example a rotation at more than twenty thousand revolutions per minute in a turbomolecular vacuum pump stator, for gas pumping.

[0066] The vacuum pump is, for example, intended to create a vacuum in a process chamber, such as an EUV lithography process chamber in the semiconductor industry.

[0067] The turbomolecular vacuum pump includes a turbomolecular stage and here a molecular drag stage located downstream of the turbomolecular stage in the direction of circulation of the pumped gases.

[0068] In the turbomolecular stage, the rotor 20 has at least one stage of blades 21 and the stator has at least one stage of vanes. The stages of blades 21 and vanes are arranged axially along the axis of rotation of the rotor 20 in the turbomolecular stage. The rotor 20 may, for example, have more than four stages of blades 21, such as between four and fifteen stages of blades 21 (thirteen in the illustrated example).

[0069] Each stage of the rotor 20 comprises inclined blades 21 extending in a substantially radial direction from a hub 22 of the rotor 20, which is fixed to a drive shaft of the vacuum pump. The blades 21 are evenly distributed around the periphery of the hub 22. The rotor blades 21 and the stator vanes are inclined to guide the pumped gas molecules towards the molecular stage.

[0070] In the molecular stage, the rotor 20 includes at least one cylindrical skirt, here an internal cylindrical skirt 23 and an external cylindrical skirt 24, called Holweck skirts, the cylindrical skirts 23, 24 being coaxial, arranged downstream of at least one blade stage 21 and configured to rotate in relation to the respective Holweck stators of the stator.

[0071] Each skirt 23, 24 is formed by a smooth cylinder, which rotates in relation to respective Holweck stators formed of helical grooves allowing to compress and guide the pumped gases towards a discharge of the vacuum pump provided in the stator.

[0072] The rotor 20 further comprises an internal bowl 25, coaxial with the axis of rotation and arranged opposite a stator dome extending under the internal cylindrical skirt 23. In operation, the rotor 20 rotates within the stator without contact between the internal bowl 25 and the dome.

[0073] According to one embodiment, the hub 22, the blade stage(s) 21 extending radially from the hub 22, the internal cylindrical skirt 23 and a radial spacer 26 extending radially from the top of the internal cylindrical skirt 23, between the internal cylindrical skirt 23 and at least one blade stage 21, are made of a single piece, for example of metallic material, such as aluminium.

[0074] The external cylindrical skirt 24 can be fixed to the periphery of the radial spacer 26 for example by gluing.

[0075] The external cylindrical skirt 24 is for example made of composite material 11 comprising an organic matrix 12 and carbon fibers 13 coated with a layer of nickel, a nickel-based coating 14 covering the composite material 11, the interface between the coated carbon fibers 13 and the nickel-based coating 14 being devoid of organic matrix 12.

[0076] It is thus possible to fabricate one or more skirts 24 of turbomolecular vacuum pumps from composite material with a nickel-based coating 14 to make them resistant to the aggressive chemistries that may be encountered in semiconductor manufacturing, particularly in etching. These fabrications also allow turbomolecular vacuum pumps equipped with a composite skirt 24 to have a nickel-based coating 14, minimizing contamination and outgassing problems on the surfaces of composite materials. The nickel-based coating 14 on the external surfaces of the composite materials reduces the absorption of gaseous substances at the surface or by diffusion, which is essential in certain microelectronic sectors such as lithography, which require high levels of cleanliness and low levels of material outgassing.

[0077] The external cylindrical skirt 24, made of composite material, can have a large diameter without risk of creep and with a moderate weight. The safety of people and property is improved due to the reduction of kinetic energy.

[0078] Laillustre an example of implementation for a primary or Roots vacuum pump.

[0079] A primary vacuum pump is defined as a positive displacement vacuum pump configured to draw in, transfer, and then discharge the gas to be pumped at atmospheric pressure using two rotor shafts. The rotors 30 may have lobes with identical profiles, such as a two-lobe Roots rotor, a Roots rotor with more than two lobes, a Claw rotor, or a similar positive displacement vacuum pump design. The rotors 30 are supported by two shafts 31 driven by a primary vacuum pump motor. A primary vacuum pump is also configured to be able to operate at atmospheric pressure.

[0080] A Roots vacuum pump (also called a "Blower" in English, Roots compressor, or "Booster" in English) is defined as a positive displacement vacuum pump configured to draw in, transfer, and then discharge a gas using two Roots rotors 30. The Roots vacuum pump is mounted upstream and in series with a primary vacuum pump. The rotors 30 are supported by two shafts 31 driven by a motor of the Roots vacuum pump.

[0081] The rotors 30 are configured to rotate in opposite directions in a pumping chamber 32 to drive a gas to be pumped between a suction port 33 and a discharge port 34.

[0082] The rotors 30 are made entirely or in part of composite material 11 comprising an organic matrix 12 and carbon fibers 13 coated with a layer of nickel and a nickel-based coating 14 covers the composite material 11, the interface between the coated carbon fibers 13 and the nickel-based coating 14 being devoid of organic matrix 12.

[0083] The properties of composite material 11 such as lightness, mechanical and thermal resistance can thus be associated with resistance to aggressive (potentially corrosive and abrasive) chemistries, allowing the manufacture of much more compact and lightweight primary or Roots vacuum pumps that can operate at very high rotational speeds.

Claims

Vacuum pump rotor (20; 30) entirely or partly made of composite material (11) comprising an organic matrix (12) and carbon fibers (13) characterized in that the carbon fibers (13) of the composite material (11) are coated with a layer of nickel and in that a nickel-based coating (14) covers the composite material (11), the interface between the coated carbon fibers (13) and the nickel-based coating (14) being devoid of organic matrix (12). Vacuum pump rotor (20; 30) according to the preceding claim, characterized in that the organic matrix (12) is a thermoset or a thermoplastic, such as an epoxy resin. Rotor (20; 30) according to any one of the preceding claims, characterized in that the coated carbon fibers (13) are grouped into twisted bundles of a plurality of carbon fibers (13). Rotor (20; 30) according to any one of the preceding claims, characterized in that the carbon fibers (13) have a diameter greater than 5 µm, the nickel layer has a thickness greater than 50 nm and more than 99% nickel. Rotor (20; 30) according to any one of the preceding claims, characterized in that the carbon fibers (13) are made from polyacrylonitrile (PAN) [-CH2-CH(CN)-]. Rotor (20; 30) according to any one of the preceding claims, characterized in that the coated carbon fibers (13) have a tensile stress strength greater than 3600 MPa, less than 5000 MPa and a Young's tensile modulus between 238 GPa and 280 GPa. Rotor (20; 30) according to any one of the preceding claims, characterized in that the nickel-based coating (14) comprises between 10% and 13% by mass of phosphorus and a thickness greater than 5 µm. Rotor (20) according to any one of the preceding claims, characterized in that it comprises at least one stage of blades (21). Rotor (20) according to the preceding claim, characterized in that it comprises at least one cylindrical skirt (23, 24), at least one cylindrical skirt (24) being made at least partly of composite material. Vacuum pump characterized in that it comprises a rotor (20) according to one of claims 8 or 9. Vacuum pump characterized in that it comprises two rotors (30) according to any one of claims 1 to 7, such as Roots or Claw or screw, configured to rotate in opposite directions in a pumping chamber. A manufacturing method (100) for a vacuum pump rotor (20; 30), characterized in that it comprises: - a shaping step (101) in which at least a part of the rotor (20; 30) is formed from composite material (11), the composite material (11) comprising an organic matrix (12) and carbon fibers (13) coated with a layer of nickel, - a shrinkage step (102) in which an outer layer of organic matrix (12) is removed from the composite material (11) so as to expose the nickel layers of the underlying carbon fibers (13), - a deposition step (103) in which a nickel-based coating (14) is deposited on the etched outer surface of the composite material (11). Manufacturing method (100) according to claim 12, characterized in that the removal of the outer layer of organic matrix (12) of the composite material (11) is carried out by chemical means such as by oxygen plasma or by mechanical means such as by polishing, sandblasting or by laser beam or by bath in a resin solvent. Manufacturing process (100) according to any one of claims 12 or 13, characterized in that the deposition is carried out by autocatalytic nickel deposition.

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