Cryopump

Abstract

A cryopump (10) includes a housing (12) having an inlet (16) to be connected to a vacuum chamber (18), a cold head (20) arranged in the housing (12) for generating a temperature for condensation of gases or vapors, a cold panel (30) connected to the cold head (20) and a non-evaporable getter (NEG) element (36) connected to the cold panel (30).

Description

[0001] CRYOPUMP

[0002] The present invention relates to a cryopump, or cryogenic pump, which generate a vacuum by the capture of gases and vapers through their condensation on cold surfaces.

[0003] Conventional cryopumps comprise a cold head extending into a housing of the cryopump. The housing comprises an inlet, wherein the inlet of the cryopump is connected to a vacuum chamber or vacuum apparatus. The cold head is usually cooled by liquid helium or liquid nitrogen. A cold panel is connected to the cold head in order to increase the surface area of the cold head for the cryo-conden- sation pumping process. The cold head cools down the cold panel to temperatures usually below 20 K for pumping N2, Ar, O2(other gases such as Xe, Kr, are CO are pumped at the cold panel at temperatures below 55K; H2O vapor, CO2, are usually pumped at around 65K).

[0004] Conventional cryopumps are usually combined with sorption pumps. In general, activated charcoal (AC) is used as a sorption material and coated on the cold panel located inside the pump and which is cooled by the cold head. Gases such as H2, He, and Ne are cryo-sorbed on the cooled AC.

[0005] AC can be easily irreversibly contaminated by hydrocarbons including methane. Therein, the contaminated AC cannot be cleaned or reactivated and must be replaced. Replacing AC is very complicated and expensive and requires the pump to be sent back to the manufacturer, thus halting operations for potentially long periods. In addition, usually the AC is glued to the cold panel by an epoxy resin. However, the epoxy resin can be degraded by radioactive materials such as tritium. Furthermore, common epoxy resins may contaminate the pumped environment. Replacing the commonly used epoxy resin for attaching the AC can be expensive. It is an object of the present invention to provide a cryopump with improved pump performance and reliable operation.

[0006] The problem is solved by a cryopump according to claim 1.

[0007] The cryopump according to the present invention comprises a housing having an inlet which is connectable to a vacuum chamber. A cold head is arranged in the housing. The cold head is preferably arranged to generate a temperature which is sufficiently low for the condensation of gas or vapour thereon. At least one cold panel is connected to the cold head. A non-evaporable getter element (NEG elements) is connected to the or each cold panel.

[0008] Thus, according to the present invention the activated charcoal (AC) used in the prior art is replaced by an NEG element. NEG elements have the advantage that they cannot be contaminated irreversibly with hydrocarbons. NEG elements can be reactivated by heating. Thus, a more reliable and stable operation of the cryopump is enabled. At the same time, it has been shown that NEG elements operating at reduced temperatures can have an increased pumping performance. Thus, the low temperature generated by the cold head can increase the pumping performance of the or each NEG element, and thus of the cryopump. In particular, compared to operating the NEG element at room temperature, an increase of the pumping capacity by a factor of more than 10, preferably more than 100, is feasible depending on the operating temperature.

[0009] Preferably, the cryopump comprises a plurality of cold panels, wherein to more than one and preferably each cold panel, an NEG element is connected. Thus, by providing a plurality of NEG elements a sufficient surface area of NEG material is provided for an efficient pumping of gas.

[0010] Preferably, the cold panels are formed as baffles or plates. An NEG element is preferably connected to a surface of the baffle which faces away from the inlet. Thus, the NEG elements are protected by the shape of the baffles and blocking of the NEG elements by condensed gases on the opposite surfaces of the baffles facing towards the inlet is prevented.

[0011] Preferably, the NEG elements are cooled to a temperature below 20 K and preferably below 10 K. At these temperatures cryo-condensation in the cryopump is possible. At the same time the pumping performance of the NEG elements is increased by a factor of more than 100 compared to their operation at room temperature.

[0012] Preferably, the or each NEG element comprises one of Zr, V, Ti, Fe, Al, Ta or a combination thereof.

[0013] Preferably, the cryopump comprises activated charcoal connected to one of the cold panels. Thus, the cryopump may comprise a combination of AC and NEG elements in order to combine their advantages. Alternatively, the cryopump may comprise no activated charcoal.

[0014] Preferably, the or each cold panel comprises a coating of NEG material. Thus, due to the direct coating of the NEG elements to the cold panels no additional adhesive or connection elements are required. Contamination of the NEG material due to any adhesive or degradation of the adhesive is prevented. Since the NEG elements can be reactivated, no replacement is necessary and permanent coating of the NEG elements on to the cold panels is feasible.

[0015] Alternatively, at least one NEG element, more preferably more than one NEG element and most preferably all of the NEG elements are glued to their respective cold panels, preferably by a radiation resistant epoxy resin.

[0016] As another alternative, at least one NEG element, more preferably more than one NEG element and most preferably all of the NEG elements are mechanically connected to their respective cold panels. This allows each NEG element to be built as a separate piece and clamped or otherwise mechanically connected to a cold panel. Thus, replacement of an NEG element is enabled if necessary.

[0017] Preferably, the NEG elements have a total surface area of 300 cm2or more, more preferably 500 cm2or more and most preferably 600 cm2or more, depending on the size of the cryopump in which the NEG elements are placed. Thus, the combined surface of all the NEG elements is sufficiently large in order to provide sufficient pumping speed and capacity.

[0018] Preferably, the pumping capacity of the NEG elements for H2 is larger than 1000 l / sec at room temperature, for a cryopump with a nominal N2pumping speed of 1500 l / s. The H2pumping speed of the NEG material below 20 K is improved by at least a factor of 10. Due to the combined effects of the large surface area and the low temperature increasing the pumping performance of the NEG elements, high pumping speeds can be achieved.

[0019] Preferably, a common heating element is provided in the cryopump to reactivate the cold panels and the NEG elements. The heating element may be connected to the cold head. By the heating element the temperature of the cold panels as well as the NEG elements can be increased. This allows condensate gases on the cold panels to be evaporated and removed and at the same time allows the NEG elements to be reactivated. Preferably, the heating element is arranged to heat the NEG elements to a temperature of above 100 °C, preferably more than 150 °C and most preferably above 250 °C in order to reactivate the NEG elements, preferably at a pressure below IE-5 mbar. NEG regeneration / reactivation may thus necessitate the use of a supporting, preferably demountable, pump such as a turbomolecular pump.

[0020] In the following the present invention is described in detail with reference to the accompanying figure. The figure shows a schematic cryopump according to the present invention.

[0021] The cryopump 10 comprises a housing 12 defining a pump chamber 14 and an inlet 16. The inlet 16 is connected to a vacuum chamber 18 in order to remove gases from the vacuum chamber 18 using the cryopump 10. The cryopump 10 comprises a cold head 20, which may be for example a two stage Gifford- McMahon refrigerator. Therein, the cold head 20 comprises a first stage 22 and a second stage 24. The cold head 20 may be cooled by liquid He. Therein, during use the first stage 22 may be at a temperature of around 80 Kelvin, and the second stage 24 may be at a temperature of less than 20 Kelvin and preferably less than 10 Kelvin. In particular, during operation the temperature of the second stage can be between 7 K and 9 K.

[0022] The cold head 20 is surrounded by a radiation shield 26 in order to reduce heat transfer by radiation to the cold head 20. The radiation shield 26 is complemented by an inlet baffle 28. During use, the baffle 28 and radiation shield 26 may be at a temperature of around 100 Kelvin. Gas compounds received from the vacuum chamber 18 which have a high condensation temperature will condense on the baffle. Similarly, those compounds will also condense on the inner surface of the radiation shield 26.

[0023] A plurality of cold panels 30 are connected to the second stage 24 of the cold head 20. Each of the cold panels 30 has a first surface 32 facing towards the inlet 16 and an opposing second surface 34 facing away from the inlet 16. In particular, the cold panels 30 may be shaped as baffles. During use, gas molecules may condense on the first surfaces 32. Thereby, during use the first surfaces 32 will become covered with frozen gases. NEG elements 36 are attached to the second surfaces 34 of the cold panels 30. Attachment of the NEG elements 36 to the cold panels 30 may be performed by either coating NEG material onto the second surfaces 34. This is possible since replacement of the NEG elements 36 is not necessary. Alternatively, the NEG elements 36 may be glued or otherwise mechanically connected to the cold panels 30. Due to the shape of the cold panels 30 coverage of the NEG elements 36 by frozen or condensed gas compounds is minimized, maintaining the pumping action of the NEG elements 36 over a longer period of operation.

[0024] Due to the connection of the NEG elements 36 to the cold head 20, the NEG elements 36 are maintained at the same low temperature as the cold panels 30. Due to this low temperature, it has been surprisingly shown that the pumping performance of the NEG elements 36 is increased by a factor of more than 10 and in particular, more than 100 compared to their operation at room temperature. At the same time, compared to the prior art use of activated charcoal (AC) there is no contamination of the NEG elements by hydrocarbons such as methane. Degradation of any adhesive used to attach the AC to the cold panels in the prior art can be avoided through directly coating the NEG elements onto the second surfaces 34 of the cold panels 30.

[0025] Since it has been found that the pumping performance of NEG materials increases at low temperatures, beneficial combination of a cryopump with at least one NEG element is provided by the present invention, thereby avoiding the disadvantages of using activated charcoal in the prior art. Thus, the cryopump can be operated over a longer time, having an increased pumping performance. Afterwards, reactivation of the NEG elements 36 is possible without requiring their replacement.

[0026] Reference List:

[0027] 10 cryopump

[0028] 12 housing

[0029] 14 pump chamber

[0030] 16 inlet

[0031] 18 vacuum chamber

[0032] 20 cold head

[0033] 22 first stage

[0034] 24 second stage

[0035] 26 radiation shield

[0036] 28 baffle

[0037] 30 cold panels

[0038] 32 first surface

[0039] 34 second surface

[0040] 36 NEG element

Claims

CLAIMS1. Cryopump comprising: a housing having an inlet which is connectable to a vacuum chamber, a cold head arranged in the housing, at least one cold panel connected to the cold head and one or more non-evaporable getter, NEG, elements connected to said at least one cold panel.

2. Cryopump according to claim 1, comprising a plurality of cold panels, wherein a respective NEG element is connected to each cold panel.

3. Cryopump according to claim 1 or 2, comprising a common heating element for re-activating the cold panels and their respective NEG elements.

4. Cryopump according to any preceding claim, wherein the or each cold panel is in the form of a baffle having an NEG element connected to a surface thereof which faces away from the inlet.

5. Cryopump according to any preceding claim, wherein the cold panel is arranged to cool the or each NEG element to a temperature below 20K, preferably below 10K.

6. Cryopump according to any preceding claim, wherein the or each NEG element comprises one of Zr, V, Ti, Fe, Al, Ta or a combination thereof.

7. Cryopump according to any preceding claim, wherein activated charcoal is connected to the or each cold panel.

8. Cryopump according to any preceding claim, wherein said at least one cold panel is coated with NEG material.

9. Cryopump according to any of claims 1 to 7, wherein a respective NEG element is glued or mechanically connected to the or each cold panel.

10. Cryopump according to any preceding claim, wherein said one or more NEG elements have a surface area of at least 300 cm2, preferably at least 500 cm2and more preferably at least 600 cm2.

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