Drag pump and a set of vacuum pumps including a drag pump

Abstract

A drag pump for pumping gas and a set of vacuum pumps including the drag pump are disclosed. The drag pump comprises: a rotor configured to rotate within a stator component and to drive a gas to be pumped from a gas inlet to a gas outlet; magnetic bearings for rotatably mounting the rotor within the pump; wherein at least a portion of the rotor and stator component configured to contact the gas to be pumped are configured for operation at temperatures above 130° C.

Claims

1. A drag pump for pumping gas, said drag pump comprising: a rotor configured to rotate within a stator component and to drive a gas to be pumped from a gas inlet to a gas outlet; magnetic bearings for rotatably mounting said rotor using magnetic levitation within said pump; and at least one thermal break between a drive shaft and said rotor mounted thereon; wherein at least the portion of said rotor and stator component configured to contact said gas to be pumped are configured for operation at temperatures above 130° C. and said rotor is fabricated at least partially from steel.

2. The drag pump according to claim 1, wherein the portion of said rotor and stator component configured to contact said gas to be pumped are configured for operation at temperatures above 150° C.

3. The drag pump according to claim 1, wherein said drag pump comprises a heater configured to heat said drag pump such that said rotor and stator component configured to contact said gas to be pumped are maintained at a temperature above 130° C. during operation.

4. The drag pump according to claim 1, wherein said drag pump comprises at least one drag stage and at least one regenerative stage.

5. The drag pump according to claim 4, wherein a rotor of said regenerative stage is formed at least partially from steel.

6. The drag pump according to claim 4, wherein said at least one drag stage comprises at least one of a Holweck pump stage and a Siegbahn pump stage.

7. The drag pump according to claim 4, wherein said at least one regenerative stage and said at least one drag stage are mounted on a same drive shaft.

8. The drag pump according to claim 4, comprising at least two drag stages arranged in series.

9. The drag pump according to claim 1, wherein said drag pump comprises at least two drag stages arranged in parallel, each operable to receive gas from a respective gas input and/or wherein the drag pump comprises a rotor blade adjacent to said gas inlet, said rotor blade comprising a turbomolecular pump stage, having blades angled to push gas into said pump and/or wherein said drag pump is configured for operation between 0.1-0.5 mbars at an inlet and 0.5-3 mbars at an outlet and/or wherein said drag pump comprises an inlet configured to connect to a pipe of a diameter between 80 and 160 mm.

10. The drag pump according to claim 1, wherein said drag pump comprises an exhaust outlet configured to connect to a pipe of a diameter between 30 to 60 mm.

11. The drag pump according to claim 1, wherein said drag pump is configured for operation as a backing pump for at least one high vacuum turbomolecular pump.

12. A set of pumps for providing a high vacuum within a semiconductor processing chamber, said set of pumps comprising: at least one high vacuum turbomolecular pump for evacuating a process chamber; and a drag pump comprising: a rotor configured to rotate within a stator component and to drive a gas to be pumped from a gas inlet to a gas outlet; magnetic bearings for rotatably mounting said rotor using magnetic levitation within said pump, said drag pump being connected to an exhaust of said at least one turbomolecular pump via at least one first pipe; wherein said set of pumps comprising valve means configured to selectively connect or isolate an inlet of said drag pump with said vacuum chamber via at least one further pipe and to isolate or connect said inlet of said drag pump with said exhaust of said turbomolecular pump.

13. The set of pumps according to claim 12, wherein said drag pump is configured for operation as a backing pump for at least one high vacuum turbomolecular pump and said drag pump comprises: wherein at least the portion of said rotor and stator component configured to contact said gas to be pumped are configured for operation at temperatures above 130° C. and said rotor is fabricated at least partially from steel.

14. The set of pumps according to claim 12, further comprising: a backing pump connected to an exhaust of said drag pump by a second pipe; wherein said at least one first pipe is shorter and has a larger diameter than said second pipe.

15. The set of pumps according to claim 12, wherein said at least one high vacuum turbomolecular pump is configured to operate at lower temperatures than said drag pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

(2) FIG. 1 illustrates a drag pump according to an embodiment;

(3) FIG. 2a illustrates a set of vacuum pumps for evacuating a high vacuum semiconductor process chamber according to the prior art;

(4) FIG. 2b illustrates a set of vacuum pumps for evacuating a high vacuum semiconductor process chamber according to an embodiment; and

(5) FIG. 3 schematically shows a set of vacuum pumps according to a further embodiment.

DETAILED DESCRIPTION

(6) Before discussing the embodiments in any more detail, first an overview will be provided.

(7) Embodiments provide a drag pump for use in a system of vacuum pumps to enable the pumping of process gas streams that contain condensable products. This is achieved by heating the different pumps to temperatures sufficiently high to avoid condensation. A new high temperature drag pump with a regenerative exhaust stage is used to back a turbo pump. The new pump may use a rotor with a steel construction to withstand higher temperatures and stress.

(8) Embodiments also provide a set of pumps comprising a separate drag pump and turbomolecular pump for use in generating and maintaining a vacuum in a vacuum chamber of a semiconductor processing system.

(9) In embodiments a turbo pump is used with no integrated drag stage. This turbo pump can be operated up to a temperature of 130° C. and does not suffer from condensation. Above this temperature aluminium loses its strength. A second pump, of a new design, is mounted in close proximity to the turbo pump, and in some embodiments has both drag stages and regenerative stages. This pump has a rotor fabricated from steel sections to withstand a higher operating temperature, typically 150° C. to 180° C.

(10) To enable the pump to be operated effectively at high temperatures there may be an arrangement of thermal breaks to reduce the heat flow to the motor and bearing components. One thermal insulating member may be located at the top of the drive spindle to limit heat flow from the top flange of the rotor to the drive spindle. A second thermal insulating member may be located between the hot pump stator and the cooler base and drive column. A heat shield may be used to reduce heat transfer from the rotor to the central drive column.

(11) When used in a vacuum system for a semiconductor process chamber, a long pipe connects this pump to a dry backing pump. The roots blower used in such conventional backing pump systems is not required as the exhaust pressure of the new drag/regenerative pump is sufficiently high not to need the booster. The pipe can be of a relatively small diameter compared to that conventionally used, say 40 to 50 trim diameter as opposed to 100 mm diameter. This saves cost and heating power.

(12) This pump could be used to back two or more turbo pumps in applications with a low flow.

(13) The turbo pump can be made more compact due to the lack of drag stage.

(14) The On Tool Booster or drag pump is a magnetically levitated machine, with a similar magnetic bearing system to the turbo pumps used in semiconductor processing.

(15) The rotor construction is from high strength steel components. A typical design would use a cylinder to support a range of Siegbahn or Holweck drag stages and one or more regenerative stages at the exhaust. The cylinder itself is supported on a top flange that connects to the central drive shaft. The top flange may be used to provide a dual inlet Siegbahn disk.

(16) One or more steel turbo stages could be added to the inlet to increase speed at low pressure and help with gas admission, however it is considered that a separate turbo pump would generally be used and extra inlet turbo stages would not be required.

(17) In a typical pump the tip speeds would be less than for a pump made from aluminium due to the reduced ratio of strength to weight of steel compared to aluminium. To counter this the inlet drag stage can be 2 or more parallel stages, such as 2. Siegbahn stages as shown in FIG. 1. This would be followed by further Siegbahn or Holweck stages in series. Finally a regenerative section, consisting typically of 2 stages is provided.

(18) FIG. 1 shows a drag pump according to an embodiment. The drag pump has an inlet 6 for admitting gas which has been output from a turbomolecular pump. The gas flows into two parallel Siegbahn stages 8. Siegbahn stages 8 comprise helical paths arranged around a disk, a rotor 31 pushing gas along these helical paths. In this embodiment there are two parallel Siegbahn stages in that there are two sets of helical paths above and below the rotor and the rotation of the rotor pushes the gas along each of them. Thus the gas is input into two inputs 10, 12 one above the other and the helical paths in the stators 20 and 22 form paths for the gas to be pushed along by the rotating rotor 31.

(19) The gas then passes into the subsequent stage which is a Holweck stage. The Holweck stage has helical paths on stator component 30 and the gas is driven by the vertical portion of die rotor 32 along these paths towards an outlet of this stage 34 and into the regenerative stages of the pump.

(20) The inlet to the regenerative stages 37 is on a side wall of these stages and is not shown. Rotation of the blades 36 extending from the rotor 31, 32 drives the gas around the circular passage of the outer regenerative stage and into the inner regenerative stage and then out through an exhaust.

(21) Drive shaft 54 mounts the rotor and is itself mounted on magnetic bearings 56 such that it is magnetically levitated during operation and does not require oil lubrication and produces very few vibrations.

(22) There is a heater 58 for heating the pump and this provides heat to the stator and rotor components which contact the pumped gas and maintains them at temperatures greater than 130° C. so as to avoid, or at least reduce condensation of process by-products. There are thermal breaks 50, 52 between the base of the pump and the stator and between the drive shaft and rotor respectively. These help maintain the drive shaft and other motor components at temperatures below the temperature of the rotor and stator. There is also a heat shield 53 protecting the drive shaft and motor from the stator and rotor.

(23) In this embodiment, the Holweck stage is a single stage, in some embodiments it may be multiple stages perhaps two on either side of the vertical rotor cylinder such that there are two helical stator components through which gas is directed by rotation of the rotor. Cooling 55 is provided to the magnetic bearing assembly 56.

(24) FIG. 2 shows the arrangement of this pump within a set of pumps for evacuating a semiconductor chamber in a fabrication plant. FIG. 2a shows a prior art set of pumps where the drag pump is integral with the turbomolecular pump 60 and operates at the lower temperature of operation of this pump and has a low exhaust pressure to avoid condensation of by-products. This set of pumps has a long and wide diameter pipe 62 to exhaust the low pressure gases towards the booster roots blower pump 64 and dry primary pump 66 located remotely from the clean room.

(25) FIG. 2b shows a different arrangement comprising a drag pump 61 according to an embodiment. In this arrangement the drag pump 61 which comprises both drag pump stages and one or more regenerative stages is configured as a separate pump to the turbomolecular pump 60a. It is configured with magnetic bearings and as such can be located within the clean room and thus requires a shorter pipe between it and the turbomolecular pump. Furthermore, as it is a separate pump it can be configured of a different material to the turbomolecular pump 60a allowing it to operate at higher temperatures and therefore at a higher pressure. The exhaust gas output by the drag pump is therefore at a significantly higher temperature and pressure than that output by the turbo/drag pump of the prior art. Thus, a smaller diameter pipe with fewer heating requirements can be used to connect this pump to the further backing pumps. Furthermore, owing to the higher pressure at the output of the separate drag pump the roots blower pump used in the conventional system may be dispensed with.

(26) Thus, although it might be considered to add costs to provide the drag stage as a separate pump as it requires an additional motor and magnetic bearings, it allows a higher temperature and therefore pressure of operation and thus, it allows for smaller diameter connecting pipes with lower heat requirements. Furthermore, in some embodiments it may allow for one or more of the backing pumps such as the roots blower pump of the conventional backing pump system to be dispensed with.

(27) FIG. 3 shows a set of pumps for a further embodiment. In this embodiment there is a turbomolecular pump 60a configured to evacuate vacuum chamber 90. There is also a drag pump 61 that is connected via a conduit and valve 80 to the exhaust of the turbomolecular pump 60a and via a further conduit and valve 80 to the vacuum chamber 90. There is a valve 80 between the vacuum chamber 90 and turbomolecular pump 60a.

(28) The valves may be set such that the drag pump is connected to the vacuum chamber and the turbomolecular pump is isolated from it. The valves may also be set so that the chamber is isolated from direct connection with the drag pump but is connected with the turbomolecular pump and the turbomolecular pump exhaust is connected to the drag pump so that it is backed by the drag pump.

(29) In effect by providing the drag pump 61 as a pump that is separate from the turbomolecular pump 60a the drag pump can be used to evacuate the chamber independently from the turbomolecular pump. Thus, it can be used to evacuate the chamber when it is at higher pressures than would be the case were the turbo pump acting alone. When the chamber pressure falls to a certain value, the valves can be switched and the turbo pump 60a backed by drag pump 61 can be used to create and maintain a higher vacuum.

(30) Although the drag pump may be made of a different material to the turbo pump and one resistant to higher temperatures, in embodiments of the set of pumps may be formed of a similar material to the turbo pump.

(31) Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

(32) Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

(33) Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.