Turbomolecular vacuum pump

Abstract

The invention relates to a 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 facing respective Holweck stators of the stator (2), the inner cylindrical skirt (14) being made of a material with a thermal conductivity that is higher than that of the material forming the at least one outer cylindrical skirt (15), characterised in that the thickness of the inner cylindrical skirt (14) is greater than the thickness of the outer cylindrical skirt (15).

Description

Description Title: Turbomolecular vacuum pump Technical field of the invention

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

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

[0003] Some pumping applications require the pumping of high gas flows, particularly light gases. In the semiconductor industry, particularly in EUV lithography processes, process chamber cleaning processes require the pumping of high hydrogen flows. This is also the case in some battery manufacturing processes.

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

[0005] However, in the case of rotors made of aluminum material, the diameter of the external skirt of the rotor is limited in order not to generate too many mechanical constraints due to the centrifugal forces exerted to control the associated risks of creep. Another disadvantage comes from the difficulty of producing the single-piece aluminum rotor due to the small gap separating the two skirts. Also, this rotor is relatively heavy, which can lead to significant energy consumption and a longer start-up time.

[0006] We also know rotors whose cylindrical skirts are made of composite material. However, it is difficult to maintain a low rotor temperature (around 50°C maximum for example) at the turbomolecular stage because the heat generated by the compression and friction of the gases is difficult to evacuate on the one hand, by conduction due to the low thermal conductivity of the skirts and on the other hand, by radiation at these temperatures. In addition, the control of magnetic bearings is difficult to achieve for rotors with skirts made of composite material due to their low weight resulting in a ratio between the polar and diametrical moment of inertia (l p / Id) high.

[0007] We are therefore seeking to produce a turbomolecular vacuum pump rotor with a high compression ratio, with good mechanical strength and whose rotor heating temperature can be controlled so as not to exceed a few dozen degrees. We are also seeking to improve the control of the magnetic bearings, in particular to lower the vibration level of the vacuum pump. Summary of the invention

[0008] An aim of the present invention is therefore to propose a turbomolecular vacuum pump which at least partially resolves the drawbacks of the state of the 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 opposite respective Holweck stators of the stator, characterized in that the internal cylindrical skirt is made of a material with a thermal conductivity greater than that of the material forming the at least one external cylindrical skirt.

[0010] The better thermal conductivity material of the inner cylindrical skirt promotes conduction, convection and radiation heat exchanges with the stator. This allows the rotor to be better cooled. The series of Holweck stages thus makes it possible to achieve high compression ratios, in particular to allow the pumping of strong hydrogen flows 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 inner 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 the at least one outer cylindrical skirt.

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

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

[0015] The thickness of the inner cylindrical skirt may be greater than the thickness of the outer cylindrical skirt, such as at least twice as much. A greater thickness of the inner cylindrical skirt promotes heat exchange with the stator and therefore lowers the equilibrium temperature. The thickness of the inner cylindrical skirt may be between 5mm and 10mm. The thickness of the outer cylindrical skirt may be between 2mm and 5mm.

[0016] The density of the material with higher thermal conductivity, such as aluminum, may be higher than the density of the material with lower thermal conductivity, such as the composite. With a higher density and / or greater thickness, the internal cylindrical skirt contributes more to the increase in diametrical inertia Id than to that of the polar inertia l p so that the ratio between the polar and diametrical moment of inertia (l p / Id) of the rotor decreases. The external cylindrical skirt has the same effect on the ratio (less heavy on the outside) but minimized by the density of the material, so using a material of lower density and / or thickness for the external cylindrical skirt minimizes the increase in the ratio. The polar and diametrical moments of inertia of the rotor can therefore be optimized, the rotor becomes more stable which reduces the vibration level of the vacuum pump.

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

[0018] According to an exemplary embodiment, the stator comprises a dome extending under the internal cylindrical skirt, the vacuum pump comprising a cooling device configured to cool the stator, and in particular the dome of the stator.

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

[0020] According to an exemplary embodiment, the rotor further has: - a hub, the 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, the at least one stage of blades, the hub and the annular spacer being made in one piece.

[0021] The outer cylindrical skirt can be glued 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 characteristics will appear on reading the description of the invention, as well as the attached drawings in which:

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

[0025] [Fig.2] Figure 2 shows a sectional view of the rotor of the turbomolecular vacuum pump of Figure 1.

[0026] In these figures, identical elements have 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. Single features of different embodiments may also be combined or interchanged to provide other embodiments, without departing from the scope of the invention, as defined by the claims.

[0028] "Upstream" means an element that is placed before another in relation to the direction of flow of the gas to be pumped. Conversely, "downstream" means an element placed after another in relation to the direction of flow of the gas to be pumped.

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

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

[0031] Figure 1 illustrates an exemplary embodiment 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 rotation at more than twenty thousand revolutions per minute, so as to drive gases to be pumped in 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 into 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 called hybrid: it comprises a turbomolecular stage 4 and a molecular stage 5 (“molecular drag stage” in English) located downstream of the turbomolecular stage 4 in the direction of circulation of the pumped gases (represented by the arrows F1 in Figure 1). The pumped gases enter through the suction port 6, first pass through the turbomolecular stage 4, then the molecular stage 5, to then be evacuated towards a discharge port 7 of the turbomolecular vacuum pump 1. In operation, the discharge port 7 is connected to a primary pump.

[0035] In the turbomolecular stage 4, the rotor 3 comprises at least one stage of blades 9 and the stator 2 comprises at least one stage of fins 10. The stages of blades 9 and fins 10 follow one another axially along the axis of rotation 11 of the rotor 3 in the turbomolecular stage 4. The rotor 3 comprises, 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 FIGS. 1 and 2).

[0036] Each stage of blades 9 of the rotor 3 comprises inclined blades which extend 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 distributed regularly around the periphery of the hub 11.

[0037] Each stage of fins 10 of the stator 2 comprises a crown from which extend, in a substantially radial direction, inclined fins, distributed regularly around the inner periphery of the crown. 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 comprises 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 orifice 6 of the vacuum pump 1. It may comprise an annular inlet flange 8 surrounding the suction orifice 6 to connect the vacuum pump 1 to an enclosure whose pressure is to be lowered.

[0039] In the molecular stage 5, and as best seen in Figure 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 the at least two blade stages 9 and configured to rotate opposite 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 (figure 1). The helical grooves 16a, 16b, 16c of each Holweck stator are arranged one above the other. The helical grooves 16a, 16b, 16c make it possible to compress and guide the pumped gases towards a discharge of the vacuum pump 1 formed in the stator 2 and opening through the discharge orifice 7.

[0041] According to an exemplary embodiment, the stator 2 comprises an outer sleeve 18 and an inner sleeve 19 coaxial and arranged inside the outer sleeve 18. The sleeves 18, 19 are received in a molecular stator part 17 to which they are fixed. The molecular stator part 17 is fixed to the turbomolecular stator part 13 and follows it axially along the axis of rotation 11 of the rotor 3.

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

[0043] A first axial gap is formed between the annular end of the outer cylindrical skirt 15 and the stator 2 at the level of the sleeves 18, 19 and a second axial gap is formed between the annular end of the inner sleeve 19 and the rotor 3, between the two skirts 14, 15.

[0044] In operation, the gases circulate 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 sleeves 18, 19, these Holweck stages being connected in series on the one hand, to the annular end of the external cylindrical skirt 15 and on the other hand, to the annular end of the internal sleeve 19.

[0045] The rotor 3 further comprises an internal bowl 20 (figure 2), coaxial with the axis of rotation 11 and arranged opposite a dome 21 of the stator 2, a base of which is fixed to the molecular stator part 17, the dome 21 extending under the internal cylindrical skirt 14 and projecting under the rotor 3 (figure 1). In operation, the rotor 3 rotates in 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 emergency mechanical bearings 24, supporting the drive shaft 12 of the rotor 3, located in the stator 2. There are for example 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 as well as axial magnetic bearings 23b located at a second end of the drive shaft 12. The active magnetic bearings 23a, 23b make it possible to maintain a rotor 3 in levitation in the magnetic field created.

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

[0049] The vacuum pump 1 may comprise a device 25 for cooling the stator 2, for example produced by a hydraulic circuit, traversed by a cooling liquid, such as water, for example at ambient temperature. The cooling device 25 is configured to cool the stator 2, and in particular the dome 21, in 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 (figure 1), in order to be able to continuously cool the elements which it contains such as in particular the bearings 23a, 23b, 24, the motor 22 and other electrical or electronic components to enable their operation.

[0050] The internal cylindrical skirt 14 is made of a material with a thermal conductivity greater than that of the material forming the 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 the at least one external cylindrical skirt 15.

[0051] If the rotor 3 comprises 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 thermal conductivity lower than that of 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 internal face, with a thermally conductive coating, such as a DLC (for “Diamond Like Carbon” in English) 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 coating (for “Diamond Like Carbon” in English).

[0054] The rotor 3 comprises, for example, an internal cylindrical skirt 14 made of aluminum and an external cylindrical skirt 15 made of a composite material made of epoxy resin and carbon fibers. The thermal conductivity of aluminum (2.3 x 10' 5 °C' 1 ) is significantly higher than that of an epoxy resin and carbon fiber composite material (2.0 x 10- 7 O It 1 ).

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

[0056] The better thermal conductivity material of the internal cylindrical skirt 14 makes it possible 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 may be between 5mm and 10mm, such as 7mm. The thickness of the outer cylindrical skirt 15 may be between 2mm and 5mm, such as 4mm. For example, the thickness of the inner cylindrical skirt 14 is provided to be greater than the thickness of the outer cylindrical skirt 15, such as at least twice as much. A greater thickness of the inner cylindrical skirt 14 makes it possible to promote heat exchanges with the stator 2 and therefore makes it possible to lower the equilibrium temperature. The thickness of the inner cylindrical skirt 14 may increase and the thickness of the cylindrical skirt 15 may decrease with the reduction in the diameter of the skirts 14, 15 due to the reduction in mechanical stresses.

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

[0059] The density of the higher thermal conductivity material, such as aluminum, may be higher than the density of the lower thermal conductivity material, such as composite.

[0060] With a higher density and / or a greater thickness, the internal cylindrical skirt 14 contributes more to the increase in the diametrical inertia Id (because the mass is increased far from the center of gravity) than to that of the polar inertia l p (because small diameter) so that the ratio between the polar and diametrical moment of inertia (l p / Id) of rotor 3 decreases. The external cylindrical skirt 15 has the same effect on the ratio (less heavy on the outside) but minimized by the density of the material, therefore the use of a material of lower density and / or thickness for the external cylindrical skirt 15 makes it possible to minimize the increase in the ratio.

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

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

Claims

CLAIMS

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 internal cylindrical skirt (14) and at least one external cylindrical skirt (15), the internal and external cylindrical skirts (14, 15) being coaxial and configured to rotate opposite respective Holweck stators of the stator (2), the internal cylindrical skirt (14) being made of a material with a thermal conductivity greater than that of the material forming the at least one external cylindrical skirt (15) characterized in that the thickness of the internal cylindrical skirt (14) is greater than the thickness of the external cylindrical skirt (15).

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

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

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

5. Vacuum pump (1) according to one of the preceding claims, characterized in that the 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 one of the preceding claims, characterized in that the thickness of the internal cylindrical skirt (14) is at least twice the thickness of the external cylindrical skirt (15).

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

12. Vacuum pump (1) according to 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 internal cylindrical skirt (14), the internal cylindrical skirt (14), the at least one stage of blades (9), the hub (11) and the annular spacer (26) being made in one 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 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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