GB2437968A

GB2437968A - Vacuum pumping arrangement for evacuating a plurality of process chambers

Info

Publication number: GB2437968A
Application number: GB0609413A
Authority: GB
Inventors: Michael S Boger; Masaharu Miki; Alan Lindsey Purvis; Andrew John Harpham
Original assignee: BOC Group Ltd; Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2006-05-12
Filing date: 2006-05-12
Publication date: 2007-11-14
Also published as: GB0609413D0

Abstract

The pumping arrangement comprises a plurality of molecular vacuum pumps 30, 31, 32 each for evacuating a respective process chamber 25, 26, 27. Downstream of the molecular vacuum pumps is located a booster pumping means 35, 36, 37 configured to provide a plurality of isolated fluid flow paths within stator means of the booster pumping means. The booster pumping means 35, 36, 37 comprises stator means which defines a plurality of swept volumes each having a respective inlet connected to an outlet of a respective molecular pump, and a respective outlet. Means for delivering a barrier gas to ports 40, 41, 42 in the vicinity of each outlet of the booster pumping means 35, 36, 37 are provided together with a manifold 45 having a plurality of inlets each connected to a respective outlet of the booster pumping means. The booster pumping means may have pumping mechanisms 150, 151, 152 of the Rootes, Holweck or Northey type driven by pair of drive shafts 135, (136) passing through all the swept volumes 130, 131, 132.

Description

VACUUM PUMP AND VACUUM PUMPING ARRANGEMENT

This invention relates to the field of vacuum pumping.

Physical vapour deposition (PVD) is a vaporisation coating technique involving transfer of material on an atomic level. One example of a PVD technique used in semiconductor manufacture is sputter coating, in which atoms in a solid target material located within an evacuated process chamber are ejected into the gas phase due to the bombardment of the material with energetic ions. These atoms are deposited on a substrate located within the process chamber to form a thin film on the substrate.

: ** The presence of contaminants in the residual gas of the process S...

* *.. chamber can be detrimental to the quality of the film or layer formed on the * S..

substrate. The dominant residual pas is usually water but may also be ::::. oxygen or hydrogen. Impurities within the generated layer can result in one or *s 15 more of low density, low stress film, intrinsic stress in the film, an increase in * the electrical resistivity of the film and a reduction in the positive temperature 5: coefficient of the resistance of the film. Hydrogen, being a light gas can be 5SS*SS * 0 particularly intrusive and can lead to hydrogen embrittlement of the generated layer. In PVD processes the avoidance of contamination by hydrogen is, therefore, of particular importance.

Conventional PVD process systems use a process tool 1 having a configuration as depicted in Figure 1. The tool I comprises a plurality of process chambers 5. Each process chamber 5 is evacuated by a respective molecular vacuum pump 10, e.g. cryogenic pump, or a combination of a turbomolecular pump and a water pump. Each molecular pump 10 is connected to a respective backing pump 20 via a dedicated conduit 15. The backing pumps 20 are typically located remotely from the process tool 1, for example in the basement of the building.

Since the volumes of fluid flow are not particularly large in PVD techniques, space is at a premium and cost reductions are always being sought, it is desirable to reduce the number of backing pumps 20 that are MO6BI 34GB/KCR necessary for a system of the type represented in Figure 1. However, using a manifold to link the outlets of the turbomolecular pumps 10 to a single backing pump 20 is likely to lead to backward migration of gas, particularly a light gas.

such as hydrogen, being evacuated from one process chamber into one of the other process chambers, resulting in chamber contamination.

It is, therefore, desirable to provide a pumping arrangement suitable for use in a PVD process that reduces the number of backing pumps required whilst maintaining reliable separation of gas evacuated from a number of process chambers.

In a first aspect, the present invention provides a pumping arrangement, for evacuating a plurality of process chambers, the pumping arrangement comprising: a plurality of molecular vacuum pumps each for evacuating a * ** respective process chamber; * : : 15 booster pumping means comprising stator means defining a plurality of S. * swept volumes each having a respective inlet connected to an outlet of a . : respective molecular pump and a respective outlet to provide a plurality of * : *.: isolated fluid flow paths within the stator means; means for delivering a barrier gas to each outlet of the booster pumping means; and a manifold having a plurality of inlets each connected to a respective outlet of the booster pumping means.

By providing a gas barrier between the outlet of each molecular vacuum pump and the point where the gases drawn from the process chambers merge into a single fluid stream, backward migration through one molecular pump of a gas drawn from a process chamber by another molecular pump can be inhibited. In order to enable effective delivery of this barrier gas, the flow regime in the gas stream at the point of delivery must be viscous, and so the booster pumping means is provided downstream of the plurality of molecular pumps to further compress, and therefore raise the pressure of, the gas stream so that a viscous flow regime is achieved.

MO6BI 34GB/KCR The pumping arrangement may further comprise a backing pump having an inlet connected to an outlet of the manifold.

Each molecular vacuum pump may comprise a turbomolecular vacuum pump or a water pump. A series combination of a turbomolecular pump and a water pump may be used to evacuate a process chamber.

The booster pumping means may comprise a plurality of separate booster pumps. Alternatively the booster pumping means may comprise a parallel booster pump comprising a single stator defining a plurality of swept volumes each having a respective inlet and a respective outlet to provide a plurality of isolated fluid flow paths within the stator.

: ** The pumping arrangement is particularly suitable for evacuating the S...

*::::* process chambers of a PVD tool. However, the parallel booster pump mentioned above may be used in applications other than physical vapour ::5:. deposition processes, for example in circumstances where the compactness * . 15 of the booster pumping means, reduced capital and running costs, and * efficiency of a reduced loss machine are desirable. Accordingly, in a second :.: aspect there is provided a vacuum pump comprising: * S** S I * a stator defining a plurality of swept volumes each having a respective inlet and a respective outlet to provide a plurality of isolated fluid flow paths within the stator; a pumping mechanism located within each swept volume; and a drive mechanism extending through the swept volumes for driving the pumping mechanisms.

Each pumping mechanism may be one of the group of a screw mechanism, a Roots mechanism, a Holweck mechanism and a Northey mechanism. Each pumping mechanism may comprise a single rotor, the rotors being mounted on a drive shaft of the drive mechanism. Alternatively, each pumping mechanism may comprise a pair of cooperating rotors, the drive mechanism comprising a pair of drive shafts extending through the swept volumes and upon which the rotors are mounted.

MO6BI 34GB/KCR The pumping mechanism of each swept volume may be configured to accommodate a predetermined pumping capacity. The axial length of each rotor may be selected to accommodate a predetermined pumping capacity, and/or the axial length of a rotor located in one swept volume may differ from that of a rotor located in another swept volume. Alternatively, or in addition, the diameter of each rotor may be selected to accommodate a predetermined pumping capacity, and/or the diameter of a rotor located in one swept volume may differ from that located in another swept volume.

Each swept volume may comprise a plurality of chambers in fluid communication with one another, each chamber representing a separate stage of the respective swept volume. Each pumping mechanism may * ** comprise a plurality of rotors or a plurality of pairs of cooperating rotors, each rotor or pair of cooperating rotors being located in a respective chamber. S...

* The outlets from one or more swept volumes may be in fluid communication.

* At least one swept volume may house a means for detecting pressure.

:.: At least one inlet may comprise means for controlling gas flow therein S.....

* dependent on the pressure detected in a swept volume.

The invention is described below in greater detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a conventional pumping arrangement for a physical vapour deposition process tool; Figure 2 illustrates a first embodiment of a pumping arrangement for isolating exhaust fluids from a number of process chambers; Figure 3 illustrates a second embodiment of a pumping arrangement for isolating exhaust fluids from a number of process chambers Figure 4 illustrates a longitudinal cross section through the parallel booster pump of Figure 3 illustrated in more detail; Figure 5 illustrates an axial cross section through the parallel booster pump of Figure 3; Figure 6 illustrates a portion of a multi-stage parallel booster pump; and MO6BI 34GB/KCR Figure 7 illustrates a third embodiment of a pumping arrangement for isolating exhaust fluids from a number of process chambers.

Figure 2 illustrates a number of process chambers 25, 26, 27 within which, for example, a solid material is bombarded by a high energy source in order to generate reactive species which are subsequently transported to and deposited on a substrate located within the chamber. The outlet of each process chamber 25, 26, 27 is connected to an inlet of a respective turbomolecular pump 30, 31, 32 so that operation of each pump results in evacuation of the respective process chamber. In order to achieve an improved vacuum in each process chamber, the pressure at the exhaust of each turbomolecular pump is further reduced by connecting the exhaust to a * ** backing pump 50. The backing pump 50 is typically located remotely from the :: process tool, for example in a basement of the building housing the tool. A * manifold or other conduit system 45 is provided to connect the outlet of each :..15 turbomolecular pump 30, 31, 32 to the backing pump. * I..

* To inhibit fluid flow from one outlet, say that of pump 31, towards the outlet of another turbomolecular pump, say either pump 30 or pump 32 and * :.: thereby prevent any backward migration of gas through that turbomolecular pump into the process chamber to which it is connected, ports 40, 41, 42 are provided for delivering a barrier gas, such as nitrogen, to each of the fluid streams exhausted from the turbomolecular pumps to provide a net flow of fluid away from the process chambers. For the introduction of the barrier gas to be effective it is necessary to deliver the gas into a region having a viscous flow regime with a net downstream flow. In this example, ports 40, 41, 42 are provided within the conduit that serves as the manifold 45.

The pressure experienced at the inlet of any turbomolecular pump is generally quite insensitive to pressure fluctuations at the outlet unless the outlet pressure approaches a predetermined "critical backing pressure" of the turbomolecular pump. If the conditions at the outlet of the turbomolecular pump 30, 31, 32 were forced to be in the viscous regime, either to ensure satisfactory introduction of barrier gas or by virtue of the introduction of a higher pressure barrier gas, then the pressures associated with that regime MO6B1 34GB/KCR approach those that define the critical backing pressure. Consequently, the pressure at the inlet of the turbomolecular pump 30, 31, 32 can fluctuate significantly, potentially adversely affecting the process being carried out in the process chamber 25, 26, 27. It is therefore desirable to maintain a reduced outlet pressure of each turbomolecular pump 30, 31, 32.

In view of this, a booster pump 35, 36, 37 is introduced downstream of each turbomolecular pump 30, 31, 32 in order to address the conflicting requirements of providing a low outlet pressure for the turbomolecular pump whilst providing a viscous regime in which to introduce the barrier gas. In this example, the ports 40, 41, 42 are located within conduits of the manifold 45 which are connected to respective outlets of the booster pumps 35, 36, 37.

* ** However, the ports could readily be located within an outlet of each booster pump 35, 36, 37. I..

* By introducing the booster pump 35, 36, 37 downstream of the *::.is turbomolecular pump 30, 31, 32, an increased pressure environment is *: achieved prior to any merging of the exhaust fluids from the different process chambers 25, 26, 27. Consequently, barrier gas can be introduced into the * : fluid stream to prevent backward transmission into one process chamber from a different process chamber.

Figure 3 illustrates an alternative embodiment of a pumping arrangement wherein the process chambers 105, 106, 107 are each connected to a respective pair of molecular pumps each pair connected in series. Each pair of pumps comprises a water pump 110, 111, 112 and a turbomolecular pump 115, 116, 117. Each of these types of pumps function in the molecular regime and therefore may be referred to here collectively as molecular pumps. The outlets of the turbomolecular pumps 115, 116, 117 are connected to booster pumping means 120. In this example the booster pumping means 120 is provided by a parallel booster pump, described in more detail below with reference to Figures 4 and 5.

The parallel booster pump 120 comprises a housing, which also serves as a stator 125 for the pump. The stator 125 defines a number of MO6B1 34GB/KCR independent swept volumes 130, 131, 132 through which a common drive mechanism extends. The drive mechanism comprises a pair of drive shafts 135, 136 driven by a motor 137. The stator 125 defines for each swept volume a respective inlet 140, 141, 142 and a respective outlet 145, 146, 147.

In this way a plurality of isolated fluid flow paths are provided within the stator.

A pumping mechanism 150, 151, 152 is located within each swept volume 130, 131, 132. In the illustrated example the pump 120 is provided with a Roots rotor assembly, and so each pumping mechanism 150, 151, 152 comprises a pair of cooperating Roots rotors 151a, 151b (more clearly depicted in Figure 5) mounted on respective drive shafts 135, 136. In operation, the drive shafts counter-rotate to effect displacement of fluid along the isolated fluid flow paths through cooperation between the pumping : .. mechanisms and the stator 125. a.. S...

es** Each pumping mechanism 150, 151, 152 may alternatively be provided : ..15 by a screw rotor mechanism or a Northey rotor mechanism in which case, as S...

in the present example the drive mechanism comprises a pair of drive shafts.

Alternatively, each pumping mechanism 150, 151, 152 may be a Holweck mechanism, in which case the drive mechanism comprises a single drive shaft driven by motor 137. Different pumping mechanisms could be provided in different swept volumes in order to accommodate pressure and flow requirements of different chambers 105, 106, 107.

Returning now to Figure 3, ports 160, 161, 162 for delivering a barrier gas to the vicinity of each outlet 145, 146, 147 of the booster pump 120 and are provided downstream of the booster pump and within a manifold 165. The manifold 165 serves to connect each outlet 145, 146, 147 of the booster pump 120 to one or more backing pumps 170.

In operation, each process chamber 105, 106, 107 is evacuated by the molecular pump combination comprising the water pump and turbomolecular pump. Once again, in order to raise the pressure into the viscous flow regime the exhaust flow streams are each further compressed by the booster pump 120. The flows experienced in physical vapour deposition techniques are not particularly large and so to provide separate booster pumps as shown MO6BI 34GB/KCR in Figure 2 could be regarded as excessive. By providing a single parallel booster pump as described above in relation to Figure 4, several fluid streams can be isolated irom one another whilst achieving the benefits associatedwith reduced capital expenditure, reduced running costs and a compact foot print.

Barrier gas is introduced downstream of the parallel booster pump 120 in a similar manner as that described in relation to Figure 2 to prevent backward migration through the molecular pumps of any exhaust fluid originating from a non-associated process chamber. Ultimately, the exhaust fluids from each process chamber, 105, 106, 107 all merge together within manifold 165 and are routed through backing pump 170, which may be located remotely from the process tool, for example in a basement of the : * building.

S... . The pumping mechanisms 150, 151, 152 located in each swept volume * 130, 131, 132 of the parallel booster pump 120 illustrted in Figure 4 each * 15 comprise a single stage, i.e. a single pair of contra-rotating rotors. In an S..

* alternative configuration, as represented in Figure 6, a multi-stage pumping : * mechanism is used. In this example, the swept volume 231 is divided into :;:.:: three chambers 231a, 231b, 231c positioned in series and in fluid communication with one another to provide a convoluted flow path thereth rough. Three pairs of cooperating, contra-rotating rotors 251, 252, 253 are located within the swept volume 231, each pair being located within a respective chamber 231a, 231b, 231c. In operation, fluid is transported through the swept volume 231 from an inlet 241 to an outlet 246 via each chamber in turn. The additional complexity of a multi-stage apparatus as depicted in Figure 6 results in a greater level of compression of the pumped fluid than that achieved in a single stage apparatus of the type depicted in Figure 4.

Each pumping mechanism, in either a single stage device or a multi-stage device, can be tailored to accommodate particular pumping capacity requirements of the booster means. For example the axial length of the, or each, rotor can be varied, the number of lobes on the, or each, Roots rotor can be varied and/or the overall diameter of the, or each, rotor can be varied.

MO6BI 34GB/KCR In circumstances where there is less sensitivity to backward contamination of exhaust fluids from different process chambers it may still be beneficial to achieve the advantages associated with a parallel booster pump as described above, in particular the reduced capital and running costs and the compact footprint. For example in some pump down applications the proximity of an on-tool booster may be important as it is more efficient to convey a higher pressure bulk fluid to the backing pump situated remotely from the process tool e.g. a hydrogen based application where compression is particularly important. As illustrated in Figure 7 the process chambers 305, 306, 307 are directly connected to the parallel booster pump 320 which is, in turn, connected to a backing pump 370 via manifold 365.

Furthermore, flow control means can be introduced upstream or in combination with the inlet of each swept volume, in order to restrict the volume of fluid passing therethrough. For example a gate valve could be : *.15 provided in or near the inlet and actuated by a controller. One or more * S. pressure sensors, located within one or more swept volumes or outlets, may be used in combination with the controller to determine when the fluid flow through the swept volume is to be restricted by actuating the fluid control means. The ability to restrict fluid flow in this way can be used to lessen the impact of a fault in the system. For example if one of the fluid sources providing process fluid to the process chamber delivers excessive fluid, perhaps due to a faulty valve mechanism, the flow control means can inhibit escalation of the problem.

Claims

MO6BI 34GB/KCR

CLAIMS

1. A vacuum pump comprising: a stator defining a plurality of swept volumes each having a respective inlet and a respective outlet to provide a plurality of isolated fluid flow paths within the stator; a pumping mechanism located within each swept volume; and a drive mechanism extending through the swept volumes for driving the pumping mechanisms.
2. A pump according to Claim 1, wherein each pumping mechanism is one of the group of a screw mechanism, a Roots mechanism, a Hoiweck ::. mechanism and a Northey mechanism. S... * S

S... . . .
3. A pump according to Claim 1 or Claim 2, wherein each pumping mechanism comprises a single rotor, the rotors being mounted on a drive *:. 15 shaft of the drive mechanism, the drive shaft extending through the swept volumes.

4. A pump according to Claim 1 or Claim 2, wherein each pumping mechanism comprises a pair of cooperating rotors, the drive mechanism comprising a pair of drive shafts extending through the swept volumes and upon which the rotors of the pumping mechanisms are mounted.

5. A pump according to Claim I or Claim 2, wherein each swept volume comprises a plurality of chambers in fluid communication with one another, each chamber representing a separate stage of the respective swept volume.

6. A pump according to Claim 5, wherein each pumping mechanism comprises a plurality of rotors or a plurality of pairs of cooperating rotors, each rotor or pair of cooperating rotors being located in a respective chamber.

7. A pump according to any preceding claim, wherein the outlets from one or more swept volumes are in fluid communication.

MO6BI 34GB/KCR 8. A pump according to any preceding claim, wherein at least one swept volume houses a means for detecting pressure.

9. A pump according to Claim 8, wherein at least one inlet comprises means for controlling gas flow therein dependent on the pressure detected in asweptvolume.

10. A pump according to any preceding claim, wherein the pumping mechanism of each swept volume is configured to accommodate a predetermined pumping capacity.

II. A pump according to Claim 10, wherein the axial length of each rotor is selected to accommodate a predetermined pumping capacity.

12. A pump according to Claim 11, wherein the axial length of a rotor located in one swept volume differs from that located in another swept volume.

13. A pump according to any of Claims 10 to 12, wherein the diameter of each rotor is selected to accommodate a predetermined pumping capacity.

:.:.15 14. A pump according to Claim 13, wherein the diameter of a rotor located in one swept volume differs from that located in another swept volume.

15. A pumping arrangement, for evacuating a plurality of process chambers, the pumping arrangement comprising: a plurality of molecular vacuum pumps each for evacuating a respective process chamber; booster pumping means comprising stator means defining a plurality of swept volumes each having a respective inlet connected to an outlet of a respective molecular pump and a respective outlet to provide a plurality of isolated fluid flow paths within the stator means; means for delivering a barrier gas to each outlet of the booster pumping means; and a manifold having a plurality of inlets each connected to a respective outlet of the booster pumping means.

MO6B1 34GB/KCR 16. A pumping arrangement according to Claim 15, wherein the pumping arrangement comprises a backing pump having an inlet connected to an outlet of the manifold.

17. A pumping arrangement according to Claim 15 or 16, wherein each molecular vacuum pump comprises a turbomolecular vacuum pump.

18. A pumping arrangement according to any of Claims 15 to 17, wherein each molecular vacuum pump comprises a water pump.

19. A pumping arrangement according to any of Claims 15 to 18, wherein the booster pumping means comprises a plurality of separate booster pumps.

20. A pumping arrangement according to any of Claims 15 to 18, wherein the booster pumping means comprises a vacuum pump according to any of Claims Ito 14. * S.

SI S ***

S *.* * * * * * S *.. .

S

S.....

S S