Turbomolecular vacuum pump

Abstract

A turbomolecular vacuum pump (1) comprising a stator (2), a rotor (3) configured to rotate within the stator (2), the rotor (3) comprising at least one stage of blades (9), an inner cylindrical skirt (14) and at least one outer cylindrical skirt (15), the inner and outer cylindrical skirts (14, 15) being coaxial and configured to rotate relative to the respective Holweck stators of the stator (2), characterized in that the inner cylindrical skirt (14) is made of a material with a thermal conductivity greater than that of the material forming at least one outer cylindrical skirt (15). Figure 1

Description

Title of the invention: Turbomolecular vacuum pump Technical field of the invention

[0001] The present invention relates to a turbomolecular vacuum pump. Technical background

[0002] The generation of a high vacuum in an enclosure requires the use of turbomolecular vacuum pumps composed of a stator in which a rotor is driven in rapid rotation, for example at a rotation of more than twenty thousand revolutions per minute.

[0003] Certain pumping applications require the pumping of high gas flow rates, particularly light gases. In the semiconductor industry, and especially in EUV lithography processes, cleaning processes for process chambers require the pumping of high hydrogen flow rates. This is also the case for certain battery manufacturing processes.

[0004] Pumping high hydrogen fluxes can be made possible, in particular, by using turbomolecular vacuum pumps with high compression ratios. For example, turbomolecular vacuum pumps with three Holweck stages are known, in which the gases to be pumped flow in series. These Holweck stages consist of Holweck stators interposed between two coaxial cylindrical skirts of the rotor, with the gases flowing alternately in opposite axial directions between the skirts and the Holweck stators.

[0005] However, in the case of rotors made of aluminum, the diameter of the outer skirt of the rotor is limited to avoid generating excessive mechanical stress due to the centrifugal forces exerted, in order to control the associated risk of scuffing. Another drawback stems from the difficulty of manufacturing the one-piece aluminum rotor due to the small gap between the two skirts. Furthermore, this rotor is relatively heavy, which can lead to significant energy consumption and a longer start-up time.

[0006] Rotors with cylindrical skirts made of composite material are also known. However, maintaining a low rotor temperature (around 50°C maximum, for example) at the turbomolecular stage is difficult because the heat generated by gas compression and friction is difficult to dissipate, firstly by conduction due to the low thermal conductivity of the skirts, and secondly by radiation at these temperatures. Furthermore, controlling the magnetic bearings is difficult for rotors with composite skirts because of their low weight, resulting in a high ratio between the polar and diametral moment of inertia (Ip / Id).

[0007] We therefore seek to produce a high-compression turbomolecular vacuum pump rotor with good mechanical strength and a rotor heating temperature that can be controlled to not exceed a few tens of degrees. We also seek to improve the control of the magnetic bearings, particularly to reduce the vibration level of the vacuum pump. Summary of the invention

[0008] One object of the present invention is therefore to propose a turbomolecular vacuum pump resolving at least partially the disadvantages of the prior art.

[0009] To this end, the invention relates to a turbomolecular vacuum pump comprising a stator, a rotor configured to rotate in the stator, the rotor comprising at least one stage of blades, an internal cylindrical skirt and at least one external cylindrical skirt, the internal and external cylindrical skirts being coaxial and configured to rotate in relation to the respective Holweck stators of the stator, characterized in that the internal cylindrical skirt is made of a material of thermal conductivity greater than that of the material forming the at least one external cylindrical skirt.

[0010] The material with the best thermal conductivity of the inner cylindrical skirt promotes heat exchange by conduction, convection, and radiation with the stator. This allows for better cooling of the rotor. The series arrangement of the Holweck stages thus makes it possible to achieve high compression ratios, particularly for pumping high hydrogen flow rates while maintaining a low rotor temperature.

[0011] The vacuum pump may further include one or more of the features described below, taken alone or in combination.

[0012] The thermal conductivity of the internal cylindrical skirt is, for example, at least ten times greater, such as at least fifty times greater, than the thermal conductivity of the material forming at least one external cylindrical skirt.

[0013] The internal cylindrical skirt can be metallic, such as made of aluminum.

[0014] At least one external cylindrical skirt can be made of composite material. The composite includes, for example, a thermosetting or thermoplastic matrix reinforced with glass or carbon fibers.

[0015] The thickness of the internal cylindrical skirt may be greater than the thickness of the skirt The outer cylindrical skirt must be at least twice as thick. A greater thickness of the inner cylindrical skirt promotes heat exchange with the stator, thus lowering the equilibrium temperature. The thickness of the inner cylindrical skirt can range from 5 mm to 10 mm. The thickness of the outer cylindrical skirt can range from 2 mm to 5 mm.

[0016] The density of the material with the highest thermal conductivity, such as Aluminum can have a higher density than materials with lower thermal conductivity, such as composites. With a higher density and / or greater thickness, the inner cylindrical skirt contributes more to increasing the diametral moment of inertia (Id) than the polar moment of inertia (Ip), thus decreasing the ratio between the polar and diametral moments of inertia (Ip / Id) of the rotor. The outer cylindrical skirt has the same effect on the ratio (being heavier on the outside), but this effect is minimized by the material's density. Therefore, using a material with lower density and / or thickness for the outer cylindrical skirt minimizes the increase in the ratio. The rotor's polar and diametral moments of inertia can thus be optimized, making the rotor more stable and reducing the vacuum pump's vibration level.

[0017] Furthermore, the external cylindrical skirt made of composite material can have a large diameter without risk of thinning and without a significant increase in weight. In addition, the rotor is less expensive than a rotor made entirely of aluminum.

[0018] According to one embodiment, the stator includes a dome extending under the internal cylindrical skirt, the vacuum pump including a cooling device configured to cool the stator, and in particular the dome of the stator.

[0019] According to one embodiment, the stator comprises an external sleeve and a coaxial internal sleeve, arranged inside the external sleeve, the Holweck stators being formed of first helical grooves formed in the external sleeve opposite an external face of the external cylindrical skirt, second helical grooves formed in the internal sleeve on an external face located opposite an internal face of the external cylindrical skirt and third helical grooves formed in the internal sleeve opposite the external face of the internal cylindrical skirt.

[0020] According to one embodiment, the rotor further features: - a hub, at least one stage of blades extending radially from the hub, and - a radial spacer extending from the top of the inner cylindrical skirt, the inner cylindrical skirt, at least one stage of blades, the hub and the annular spacer being made of a single piece.

[0021] The outer cylindrical skirt can be bonded to the periphery of the radial spacer.

[0022] The rotor can be guided laterally and axially by magnetic bearings. Brief description of the figures

[0023] Other advantages and features will become apparent upon reading the description of the invention, as well as the accompanying drawings in which:

[0024] [Fig-1] Fig. 1 shows a schematic axial cross-sectional view of an example of turbomolecular vacuum pump.

[0025] [Fig.2] Fig.2 shows a cross-sectional view of the rotor of the turbomo- vacuum pump lecular of the [Fig.l].

[0026] In these figures, identical elements bear the same reference numbers. Detailed description

[0027] 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.

[0028] The term "upstream" refers to an element that is placed before another with respect to the direction of flow of the gas to be pumped. Conversely, the term "downstream" refers to an element placed after another with respect to the direction of flow of the gas to be pumped.

[0029] The axial direction of the vacuum pump 1 is defined as the direction parallel to the axis of rotation II of the vacuum pump 1.

[0030] An element is considered to be located further outside than another element if it is further from the axis of rotation than the other element. An element is considered to be located further inside than another element if it is closer to the axis of rotation than the other element.

[0031] Fig. 1 illustrates an example of the realization of a turbomolecular vacuum pump.

[0032] The turbomolecular vacuum pump 1 comprises a stator 2 in which a rotor 3 is configured to rotate at high speed in axial rotation, for example a rotation at more than twenty thousand revolutions per minute, so as to drive gases to be pumped into a gas flow path interposed between the stator 2 and the rotor 3.

[0033] The vacuum pump 1 is for example intended to evacuate a process chamber in which large flows of hydrogen can be pumped, such as an EUV lithography process chamber in the semiconductor industry or a battery manufacturing process chamber.

[0034] The turbomolecular vacuum pump 1 is said to be hybrid: it comprises a turbomolecular stage 4 and a molecular drag stage 5 located downstream of the turbomolecular stage 4 in the direction of flow of the pumped gases (represented by the arrows Fl in [Fig. 1]). The pumped gases enter through the suction port 6, pass first through the turbomolecular stage 4, then through the molecular drag stage 5, and are then discharged to a discharge port 7 of the turbomolecular vacuum pump 1. During operation, the discharge port 7 is connected to a primary pump.

[0035] In the turbomolecular stage 4, the rotor 3 comprises at least one blade stage 9 and The stator 2 has at least one stage of fins 10. The stages of blades 9 and fins 10 follow each other axially along the axis of rotation II of the rotor 3 in the turbomolecular stage 4. The rotor 3 has, for example, more than four stages of blades 9, such as between four and fifteen stages of blades 9 (thirteen in the example illustrated in figures 1 and 2).

[0036] Each blade stage 9 of the rotor 3 comprises inclined blades extending in a substantially radial direction from a hub 11 of the rotor 3 fixed to a drive shaft 12 of the vacuum pump 1, for example by screwing. The blades are evenly distributed around the periphery of the hub 11.

[0037] Each stage of fins 10 of the stator 2 comprises a ring from which inclined fins extend in a substantially radial direction, evenly distributed around the inner circumference of the ring. The fins of a stage of fins 10 of the stator 2 engage between the blades of two successive stages of blades 9 of the rotor 3. The blades 9 of the rotor 3 and the fins 10 of the stator 2 are inclined to guide the pumped gas molecules towards the molecular stage 5.

[0038] The stator 2 includes a turbomolecular stator part 13 receiving the at least two stages of fins 10. This turbomolecular stator part 13 is open at one end to the suction port 6 of the vacuum pump 1. It may include an annular inlet flange 8 surrounding the suction port 6 for connecting the vacuum pump 1 to a chamber whose pressure is to be lowered.

[0039] In the molecular stage 5, and as more clearly seen in [Fig.2], the rotor 3 further comprises an internal cylindrical skirt 14 and at least one external cylindrical skirt 15, called Holweck skirts, the internal and external cylindrical skirts 14, 15 being coaxial, arranged downstream of at least two blade stages 9 and configured to rotate in relation to the respective Holweck stators of the stator 2.

[0040] Each skirt 14, 15 is formed by a smooth cylinder, which rotates opposite respective Holweck stators formed of helical grooves 16a, 16b, 16c ([Fig. 1]). The helical grooves 16a, 16b, 16c of each Holweck stator are arranged one above the other. The helical grooves 16a, 16b, 16c allow the pumped gases to be compressed and guided towards a discharge of the vacuum pump 1 provided in the stator 2 and opening through the discharge port 7.

[0041] According to one embodiment, the stator 2 comprises an external sleeve 18 and an internal sleeve 19 coaxial and arranged inside the external sleeve 18. The sleeves 18 and 19 are received in a molecular stator portion 17 to which they are fixed. The molecular stator portion 17 is fixed to the turbomolecular stator portion 13 and follows it axially along the axis of rotation II of the rotor 3.

[0042] The Holweck stators are formed by first helical grooves 16a formed in the external sleeve 18 opposite an external face of the external cylindrical skirt 15, second helical grooves 16b formed in the internal sleeve 19 on an external face located opposite an internal face of the external cylindrical skirt 15 and third helical grooves 16c formed in the internal sleeve 19 opposite the external face of the internal cylindrical skirt 14.

[0043] A first axial gap is formed between the annular end of the external cylindrical skirt 15 and the stator 2 at the bushings 18, 19 and a second axial gap is formed between the annular end of the internal bushing 19 and the rotor 3, between the two skirts 14, 15.

[0044] In operation, the gases flow in parallel directions in the succession of Holweck stages located between the smooth walls of the skirts 14, 15 and the helical grooves 16a, 16b, 16c of the bushings 18, 19, these Holweck stages being connected in series on one side, to the annular end of the external cylindrical skirt 15 and on the other side, to the annular end of the internal bushing 19.

[0045] The rotor 3 further comprises an internal bowl 20 ([Fig. 2]), coaxial with the axis of rotation II and arranged opposite a dome 21 of the stator 2, a base of which is fixed to the molecular stator portion 17, the dome 21 extending under the internal cylindrical skirt 14 and projecting under the rotor 3 ([Fig. 1]). In operation, the rotor 3 rotates within the stator 2 without contact between the internal bowl 20 and the dome 21.

[0046] The rotor 3 is driven in rotation in the stator 2 by a motor 22 of the vacuum pump 1. The motor 22 is for example arranged in the dome 21 of the stator 2, itself arranged under the internal bowl 20 of the rotor 3, the drive shaft 12 passing through the dome 21 of the stator 2.

[0047] The rotor 3 is guided laterally and axially by magnetic bearings 23a, 23b and backup mechanical bearings 24, supporting the drive shaft 12 of the rotor 3, located in the stator 2. For example, there are first radial magnetic bearings 23a supporting and guiding the drive shaft 12 in the dome 21 of the stator 2, second radial magnetic bearings 23a at the top of the dome 21 at a first end of the drive shaft 12, and axial magnetic bearings 23b located at a second end of the drive shaft 12. The active magnetic bearings 23a, 23b allow the rotor 3 to be kept levitating in the magnetic field created.

[0048] Other electrical or electronic components can be received in the dome 21 of the stator 2, such as position sensors.

[0049] The vacuum pump 1 may include a cooling device 25 for the stator 2, for example, a hydraulic circuit through which a coolant, such as water, flows, for example, at ambient temperature. The cooling device 25 is configured to cool the stator 2, and in particular the dome 21, by being arranged, for example, in the dome 21 or in an element in thermal contact with the dome 21 such as the molecular stator part 17 ([Fig.l]), in order to be able to continuously cool the elements it contains such as bearings 23a, 23b, 24, motor 22 and other electrical or electronic components to allow their operation.

[0050] The internal cylindrical skirt 14 is made of a material with a thermal conductivity greater than that of the material forming at least one external cylindrical skirt 15. The thermal conductivity of the internal cylindrical skirt 14 is, for example, at least ten times greater, or even at least fifty times greater, than the thermal conductivity of the material forming at least one external cylindrical skirt 15.

[0051] If the rotor 3 has an internal cylindrical skirt 14 and several coaxial external cylindrical skirts 15, the external cylindrical skirts 15 can all be made of a material with a lower thermal conductivity than the material forming the internal cylindrical skirt 14.

[0052] The internal cylindrical skirt 14 is, for example, metallic, such as made of aluminum. It is also possible to coat the internal cylindrical skirt 14, in particular the inner face, with a thermally conductive coating, such as a DLC (Diamond-Like Carbon) coating.

[0053] The outer cylindrical skirt 15 is, for example, made of a composite material (with an organic matrix). The composite comprises, for example, a thermosetting matrix, such as a resin, such as an epoxy resin (also called polyepoxide or epoxy polymer) or a thermoplastic matrix, reinforced with glass or carbon fibers. It is also possible to coat the outer cylindrical skirt 15, in particular the inner face, with a thermally conductive coating, such as a DLC (Diamond-Like Carbon) coating.

[0054] The rotor 3 comprises, for example, an inner cylindrical skirt 14 made of aluminum and an outer cylindrical skirt 15 made of a composite material of epoxy resin and carbon fibers. The thermal conductivity of aluminum (2.3 x 10⁵ OC*) is significantly higher than that of a composite material of epoxy resin and carbon fibers (2.0 x 10⁷ T1).

[0055] According to one embodiment, the hub 11, the at least one blade stage 9 extending radially from the hub 11, the inner cylindrical skirt 14, and a radial spacer 26 extending radially from the top of the inner cylindrical skirt 14, between the inner cylindrical skirt 14 and the at least one blade stage 9, are made of a single piece, for example, of a metallic material, such as aluminum. The outer cylindrical skirt 15 can be fixed to the periphery of the radial spacer 26, for example, by bonding.

[0056] The material with the best thermal conductivity of the internal cylindrical skirt 14 allows to promote thermal exchanges of conduction, convection and radiation with the cooled dome 21 located under the internal cylindrical skirt 14. The internal cylindrical skirt 14 but also the blade stages 9 of the rotor 3 can thus be better cooled.

[0057] The thickness of the inner cylindrical skirt 14 can be between 5 mm and 10 mm, such as 7 mm. The thickness of the outer cylindrical skirt 15 can be between 2 mm and 5 mm, such as 4 mm. For example, the thickness of the inner cylindrical skirt 14 is expected to be greater than the thickness of the outer cylindrical skirt 15, such that it is at least twice as thick. A greater thickness of the inner cylindrical skirt 14 promotes heat exchange with the stator 2 and thus lowers the equilibrium temperature. The thickness of the inner cylindrical skirt 14 can increase and the thickness of the cylindrical skirt 15 can decrease with a reduction in the diameter of the skirts 14 and 15 due to the reduction in mechanical stresses.

[0058] By their geometry, the turbomolecular vacuum pumps 1 have ratios between the polar and diametral moment of inertia (Ip / L) of the rotor 3 less than one and we seek to lower this ratio as much as possible in order to better control the active magnetic bearings (PMA) and the lowering of the vibration level of the vacuum pump 1.

[0059] The density of the material with the highest thermal conductivity, such as aluminium, may be higher than the density of the material with the lowest thermal conductivity, such as the composite.

[0060] With a higher density and / or greater thickness, the inner cylindrical skirt 14 contributes more to increasing the diametral inertia Id (because the mass is increased further from the center of gravity) than to increasing the polar inertia Ip (because of the small diameter), so that the ratio between the polar and diametral moments of inertia (Ip / Id) of the rotor 3 decreases. The outer cylindrical skirt 15 has the same effect on the ratio (being heavier on the outside), but this effect is minimized by the material's density; therefore, using a material of lower density and / or thickness for the outer cylindrical skirt 15 minimizes the increase in the ratio.

[0061] Furthermore, the external cylindrical skirt 15 made of composite material can have a large diameter without risk of thinning and without a significant increase in weight. In addition, the rotor 3 is less expensive than a rotor made entirely of aluminum.

[0062] The succession of Holweck stages in series thus makes it possible to achieve high compression ratios, in particular to allow the pumping of high hydrogen fluxes while maintaining a low temperature of the rotor 3. In addition, the polar and diametral moments of inertia of the rotor 3 are optimized, the rotor 3 becomes more stable which makes it possible to reduce the vibration level of the vacuum pump 1.

Claims

Demands

1. Turbomolecular vacuum pump (1) comprising a stator (2), a rotor (3) configured to rotate in the stator (2), the rotor (3) comprising at least one stage of blades (9), an inner cylindrical skirt (14) and at least one outer cylindrical skirt (15), the inner and outer cylindrical skirts (14, 15) being coaxial and configured to rotate in relation to respective Holweck stators of the stator (2), the inner cylindrical skirt (14) being made of a material of thermal conductivity greater than that of the material forming the at least one outer cylindrical skirt (15) characterized in that the thickness of the inner cylindrical skirt (14) is greater than the thickness of the outer cylindrical skirt (15).

2. Vacuum pump (1) according to claim 1, characterized in that the thermal conductivity of the inner cylindrical skirt (14) is at least ten times greater, such as at least fifty times greater, than the thermal conductivity of the material forming at least one outer cylindrical skirt (15).

3. Vacuum pump (1) according to any one of the preceding claims, characterized in that the internal cylindrical skirt (14) is metallic.

4. Vacuum pump (1) according to any one of the preceding claims, characterized in that the internal cylindrical skirt (14) is made of aluminum.

5. Vacuum pump (1) according to any one of the preceding claims, characterized in that at least one external cylindrical skirt (15) is made of composite material.

6. Vacuum pump (1) according to the preceding claim, characterized in that the composite comprises a thermosetting or thermoplastic matrix reinforced with glass or carbon fibers.

7. Vacuum pump (1) according to any one of the preceding claims, characterized in that the thickness of the inner cylindrical skirt (14) is at least twice the thickness of the outer cylindrical skirt (15).

8. Vacuum pump (1) according to any one of the preceding claims, characterized in that the thickness of the internal cylindrical skirt (14) is between 5mm and 10mm.

9. Vacuum pump (1) according to any one of the preceding claims, characterized in that the thickness of the external cylindrical skirt (15) is between 2mm and 5mm.

10. Vacuum pump (1) according to any one of the preceding claims, characterized in that the stator (2) comprises a dome (21) extending under the internal cylindrical skirt (14), the vacuum pump (1) comprising a cooling device (25) configured to cool the stator (2), and in particular the dome (21) of the stator (2).

11. Vacuum pump (1) according to any one of the preceding claims, characterized in that the stator (2) comprises an external sleeve (18) and a coaxial internal sleeve (19), arranged inside the external sleeve (18), the Holweck stators being formed of first helical grooves (16a) formed in the external sleeve (18) opposite an external face of the external cylindrical skirt (15), second helical grooves (16b) formed in the internal sleeve (19) on an external face located opposite an internal face of the external cylindrical skirt (15) and third helical grooves (16c) formed in the internal sleeve (19) opposite the external face of the internal cylindrical skirt (14).

12. Vacuum pump (1) according to any one of the preceding claims, characterized in that the rotor (3) further has: - a hub (11), the at least one stage of blades (9) extending radially from the hub (11), and - a radial spacer (26) extending from the top of the inner cylindrical skirt (14), the inner cylindrical skirt (14), the at least one stage of blades (9), the hub (11) and the annular spacer (26) being made of a single piece.

13. Vacuum pump (1) according to the preceding claim, characterized in that the external cylindrical skirt (15) is glued to the periphery of the radial spacer (26).

14. Vacuum pump (1) according to any one of the preceding claims, characterized in that the rotor (3) is guided laterally and axially by magnetic bearings (23a, 23b).

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