GB2569633A

GB2569633A - A vacuum pumping arrangement and method of cleaning the vacuum pumping arrangement

Info

Publication number: GB2569633A
Application number: GB1721671.4A
Authority: GB
Inventors: Bailey Christopher; Paul Schofield Nigel
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2017-12-21
Filing date: 2017-12-21
Publication date: 2019-06-26
Also published as: US20200355190A1; EP3728858A1; WO2019122873A1; JP2021507172A; GB201721671D0

Abstract

A vacuum pumping arrangement for evacuating a process chamber comprises at least one turbomolecular pumping stage, at least one further pumping stage downstream of said turbomolecular pumping stage and at least one inlet located downstream of said turbomolecular pumping stage and upstream of said at least one further pumping stage. The further pumping stages may comprise at least one regenerative and at least one drag pumping stage. The arrangement may comprise a single multistage pump with each of the pumping stages being mounted on the same shaft. A method of cleaning a vacuum pumping arrangement comprising a process chamber in fluid communication with said turbomolecular pumping stage comprises generating radicals and inputting said radicals at said inlet. The radicals preferably comprise at least one of fluorine and oxygen radicals and may be generated using a plasma source. The process chamber may be for semiconductor fabrication. Inputting of said radicals may be performed in response to an indication that the process chamber is commencing a cleaning cycle or that a wafer in said process chamber is being changed.

Description

A VACUUM PUMPING ARRANGEMENT AND METHOD OF CLEANING THE VACUUM PUMPING ARRANGEMENT

FIELD OF THE INVENTION

The invention relates to pumps for evacuating a process chamber and methods of cleaning these pumps.

BACKGROUND

Evacuation of gases from a process chamber via turbo, drag and regenerative pumping stages can lead to deposition in the pumps due to condensation of process by-products. This problem is particularly acute in the later higher pressure stages of the pumps. Increasing the temperature of the pumps could be used to address this, but the temperature of operation of a turbomolecular pump is limited. In this regard, turbo stages are generally made of aluminium to provide low mass leading to low hoop stresses. Unfortunately, aluminium is not suitable for high temperature operation. Other materials such as steel are able to handle higher temperatures, but owing to a turbo pump’s high speed of rotation these materials are too dense for use in most turbo stages.

It would be desirable to be able to prevent or at least reduce the deposition of materials due to the condensation of process by-products in a multi-stage pump for evacuating a process chamber.

SUMMARY

A first aspect provides a vacuum pumping arrangement comprising multiple pumping stages for evacuating a process chamber, said vacuum pumping arrangement comprising: at least one turbomolecular pumping stage; at least one further pumping stage downstream of said turbomolecular pumping stage; at least one inlet for admitting radicals into said vacuum pumping arrangement, said

-2at least one inlet being located downstream of said turbomolecular stage and upstream of at least one of said at least one further pumping stage.

The inventors of the present invention recognised much of the deposition in multiple stage vacuum pumps occurs in the higher pressure stages of the pumps. They also recognised that the introduction of radicals into a pump inlet to clean the pump can lead to problems of contamination of any process chamber being evacuated and also to the radicals no longer being reactive when they reach the higher pressure regions of the pump where they are perhaps most needed.

They have addressed this by adding the radicals into the pump downstream of the turbomolecular stage but upstream of at least one of the other stages, such that the radicals are input at a point, or at least close to a point, where they are most needed. Thus, they are still reactive and have not recombined when they reach the higher pressure end of the pump where most of the deposition occurs. Furthermore, contamination of the process chamber by these radicals is much reduced as they are introduced in the viscous flow region of the pump and at a point remote from the process chamber.

In some embodiments, said vacuum pumping arrangement comprises a single shaft multistage pump, each of said multiple stages being mounted on a same shaft and said at least one inlet comprising an inter-stage inlet between said stages.

In some embodiments, at least one of said at least one inlet comprises an inlet between said turbomolecular stage and a pumping stage immediately downstream of said turbomolecular pumping stage.

Although the inlet may be between any of the different stages and there may be more than one inlet for admitting the radicals, it may be advantageous if at least

-3one of the inlets for admitting the radicals is immediately downstream of the turbomolecular pumping stage. Deposition may start to become a problem at this point and the radicals will travel to further higher pressure regions with the gas flow, while reverse upstream flow is resisted as the inlet is at a point where the fluid is entering a viscous flow region.

In other embodiments, said multiple pumping stages comprise a plurality of pumps, said plurality of pumps comprising a turbomolecular pump and at least one further pump located downstream of said turbomolecular pump; said at least one inlet being arranged to introduce said radicals between said turbomolecular pump and said at least one further pump.

Where the different pumping stages are decoupled and formed as a plurality of pumps the turbomolecular pump being separate from at least one further pump located downstream of it, then this can provide more flexibility in how the pumping system is arranged. The pumps may for example be located in a side by side arrangement thereby reducing the overall height of the pumping package which may make it easier to accommodate in the confined space of a clean room. Furthermore, having separate pumps makes it easier to heat the higher pressure downstream stages to higher temperatures without unduly affecting the temperature of the turbomolecular pump. It also provides greater flexibility in choice of material of the later pumping stages as the rotor of these stages are no longer formed integrally with the turbomolecular stage. Thus, they can be formed of materials that can operate effectively at higher temperatures.

The input of the radicals may also be more easily and conveniently achieved where the available input space is between pumps rather than between stages of a single pump, as there generally more available space for such an inlet, it can for example be located on the connecting conduit between the pumps.

-4Thus, although there is a technical prejudice against providing the multiple stages of the pumping arrangement as separate pumps with the additional shaft and motor requirements that this entails, there are many attendant advantages to such a system. One further advantage is that as the later higher pressure stages of the pump may be configured to be suitable for operation at a higher temperature, they can also be operated to a higher exhaust pressure while still resisting condensation of by-products. This allows the forelines connecting these pumps to pumps and abatements systems outside of the clean room to be smaller than in conventional systems. This has a saving both in materials and in heating costs as these pipes need to be heated to avoid condensation.

In some embodiments, said at least one further pump comprises a multistage pump comprising a plurality of said further pumping stages.

Separating the turbomolecular pumping stage from the downstream stages has advantages as set out above. For the further pumping stages a multi-stage pump may be used which shares a motor and shaft.

In some embodiments, the pumping arrangement further comprises a radical source connected to said at least one inlet.

In some embodiments the radical source comprises a plasma source.

The radicals may be generated by high temperature or they may be generated from a plasma source. The radical source may be separate to the pump and connected to it during operation, or it may be part of the pumping system. In this regard, plasma sources may be used for the cleaning of process chambers and these sources are often large and may not be suitable for attaching to the pumping system. However, smaller remote plasma sources are available and the use of such a source provides an effective and compact arrangement.

-5In some embodiments, said at least one further pumping stage comprise at least one drag pumping stage.

Although the further pumping stages may be a number of things, in some embodiments they comprise at least one drag stage while in other embodiments they may comprise at least one regenerative pumping stage and at least one drag pumping stage. Where there is only a drag stage then in some embodiments the pump may rely on a regenerative booster.

In some embodiments, said vacuum pumping arrangement comprises control circuitry, said control circuitry being configured to control input of said radicals via said inlet.

The input of the radicals to help clear debris from the pump may be performed manually when it is determined that the pump needs cleaning or more advantageously it may be performed under the control of control circuitry. In some cases the control of the cleaning may be combined with the control of the pump itself and there may also be a link to the control system of the process chamber which the pump is evacuating such that data is shared between the two control systems.

In this regard, where the control circuitry is also controlling the process chamber or at least has a link to this control system then it can coordinate operation of the pump and the process chamber and in particular, can trigger cleaning of the pump at appropriate moments.

For example, the control circuitry may control input of said radicals via said inlet in response to an indication that a process in said process chamber is not active

-6for example a wafer may be being changed and/ or in response to receipt of a signal indicating said process chamber is commencing a cleaning cycle.

It may be advantageous to clean the pump when the process chamber is not active and/or is itself performing a cleaning cycle as this reduces the likelihood of contamination of the process from the radicals or their by-products due to backflow.

Where a process has just completed and a wafer is being changed for example, then deposition in the pump may be an issue and cleaning may be advantageous to remove any debris during a time when contamination of the process chamber is less critical.

In some embodiments, said inlet comprises a valve, said control circuitry being operable to control input of said radicals via said inlet by controlling said valve.

One way of controlling the input of the radicals is to control a valve at the inlet which can be opened and closed by signals from the control circuitry.

In some embodiments, said control circuitry is configured to control a motor driving at least one rotor of said multiple pumping stages. Where there are multiple motors then the control circuitry may be configured to drive the rotors to control the driving of the rotors of the multiple pumps.

In some embodiments, said inlet is arranged such that said radicals are injected into said pumping arrangement in a region having viscous fluid flow and downstream of a region having molecular fluid flow.

Turbomolecular pumps provide molecular fluid flow and in molecular fluid flow there are always some molecules travelling in the upstream direction. Thus,

-7inputting the radicals into the molecular flow region may result in some contamination of the process chamber. Inputting the radicals downstream of the molecular flow region and in a viscous flow region considerably reduces the chance of any backflow of the cleaning products or the reactants thereof.

Although the radicals may be formed from a number of different chemicals and comprise a number of different species in some embodiments said radicals comprise at least one of: F, generated thermally from F2 or by a plasma source from NF3, SFe, CsFs, or 0' generated from O2, O3 or H2O.

A second aspect provides a method of cleaning a vacuum pumping arrangement comprising multiple pumping stages for evacuating a process chamber, said vacuum pumping arrangement comprising: at least one turbomolecular pumping stage in fluid communication with said process chamber; at least one further pumping stage downstream of said turbomolecular pumping stage, said method comprising: generating radicals for cleaning said vacuum pumping arrangement; and inputting said radicals into said vacuum pumping arrangement at a point downstream of said turbomolecular stage and upstream of at least one of said at least one further pumping stage.

In some embodiments, said step of generating said radicals comprises using a plasma source to generate said radicals.

In some embodiments, said step of generating said radicals comprises using a high temperature to generate said radicals.

In some embodiments, said radical comprises a fluorine radical generated by heating elemental fluorine.

-8ln some embodiments, said multiple pumping stages comprise a plurality of pumps; said plurality of pumps comprising a turbomolecular pump and at least one further pump located downstream of said turbomolecular pump; and said step of inputting said radicals comprising inputting said radicals into a conduit connecting said turbomolecular pump and said at least one further pump.

In some embodiments, said step of inputting said radicals via said inlet is performed in response to an indication that a process in said process chamber is not active.

In some embodiments, said step of inputting said radicals via said inlet is performed in response to an indication that said process chamber is commencing a cleaning cycle.

In some embodiments, said step of inputting said radicals via said inlet is performed in response to an indication that a wafer in said process chamber is being changed.

In some embodiments, said step of inputting said radicals comprises controlling a valve at an inlet for inputting said radicals.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

-9Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 shows a vapour curve illustrating how deposition is dependent on pressure and temperature and varies through a multiple stage pumping system; Figure 2 illustrates a pumping arrangement according to an embodiment;

Figure 3 illustrates a different configuration of a pumping arrangement according to an embodiment; and

Figure 4 illustrates a further embodiment of a pumping arrangement pumping a process chamber and including control circuitry.

DESCRIPTION OF THE EMBODIMENTS

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

The application relates to pumping systems for process chambers, particularly semiconductor fabrication process chambers and to reducing deposition in such pumping systems due to the condensation of by-products of the process. Deposition in the pumping system and potential blockages of the pumping system are reduced by injecting radicals created in some cases by a remote plasma source into the pumping system downstream of the turbo stage, such that they are available at or close to the point where they are most effective, where pressure is higher and deposition is more likely to occur. Furthermore, any process chamber being evacuated by the pumping system is protected from the radicals and from products of the radical reactions by the upstream turbo stage.

- 10The injection of the radicals may occur periodically, preferably when the process in the process chamber is not active, for example during chamber clean or during wafer change cycles. Injection of the radicals may be controlled by control circuitry which may receive signals from the process control circuitry and/or from sensors in the pumping system. The control circuitry may also control the motor(s) of the pumping system and the abatement system.

In some embodiments, the pumping system is a single shaft pumping system with different stages, the radicals being injected between the stages.

In other embodiments, the pumping system is a two or more shaft pumping system with the turbo pump having one shaft and the drag and regenerative stages having another shaft. This allows the two pumps to be made of different material, be operated at different temperatures and provides more flexibility in the physical configuration of the pumping system.

Figure 1 shows a vapour pressure curve, illustrating how deposition is more likely to occur at lower temperatures and higher pressures. The operating pressures and temperatures of a multiple stage pump are also shown, and this illustrates how the turbine or tubromolecular stage of the pump is generally operating at pressures and temperatures in the gaseous phase of the substance being pumped such that deposition is not a significant problem. However, as the pump progresses to higher pressures at the drag stage the vapour curve is crossed and some substances being pumped start to condense and deposition becomes a problem.

Figure 2 shows a pumping system according to an embodiment. In this embodiment the drag/regenerative stage is decoupled from the turbo stage. This reduces the height of the overall pump package and also provides improved thermal isolation between the drag/regenerative stage and turbo stage. It also allows the drag/regenerative stage to be formed of different material to the turbo

- 11 stage and to operate at higher temperatures, in some embodiments at temperatures above 180°C.

The conduit linking the two turbo and drag/regenerative stages of the pumping system comprises an inlet for admitting radicals. These radicals are generated in this embodiment by a plasma source. The inlet may also be used for admitting a purge gas to purge the radicals and reactants formed therefrom following a cleaning cycle. The radicals used may comprise either fluorine or oxygen, both being effective cleaning products which do not generally cause unsuitable contamination. In this regard, the chemical from which they are generated by the plasma source should also be selected to be one which is not corrosive and does not contaminate in an unacceptable manner. In this regard suitable chemicals include NF3, SF6, CsFs, or 0' generated from O2, O3 or H2O.

The conduits linking the two pumping stages are heated to reduce condensation occurring.

In summary, a pumping system where the turbo stage is formed as a separate pump to the drag and regenerative stage provides a system where the height envelope of the pump is reduced and increased flexibility of where the different pumping stages and control systems can be located is provided. The separation of the pumping stages allows the drag/regenerative stage to operate at a higher temperature and therefore up to a higher pressure while still controlling deposition. Deposition is further controlled by the input of radicals to the higher pressure stages periodically. The higher pressure operation of the later stages also reduces the size required for the foreline and valve linking this pumping system to the pumping system outside of the clean room or fab (semiconductor fabrication plant). This in turn reduces the cost of heating this foreline and may eliminate the need for a roots pump in the sub-fab.

- 12Figure 3 shows an alternative embodiment with the drag stage located in a different position. One advantage of separating the drag and turbo stages is the flexibility that it provides in the pump design allowing the different stages to be arranged in different configurations depending on the arrangement of the process chamber they are evacuating.

Figure 4 schematically shows a further embodiment with control circuitry 30 for controlling the input of the radicals, the purging of the system and the rotation of the motors of the different pumps and abatement units.

Control circuitry 30 controls both the generation of the radicals and their admission to the pump. Valve 1 on the inlet to the pumping system from the radical source is controlled by the control circuitry 30 to control the input of the radicals and also in this embodiment purge gas to the pump.

The control circuitry 30 is configured to share data with the process chamber control. In some embodiments, the control circuitry 30 is also operable to receive sensor data from sensors (not shown) within the turbo and drag stages. These sensors may comprise temperature and/or pressure sensors, and they may comprise species detectors operable to determine the nature of the gases being pumped and where particular process by-products are present. The control circuitry 30 responds to these sensors and to data from the process chamber 20 indicating the current status of the process to initiate cleaning cycles of the pump with the radicals. The control circuitry 30 may also control the abatement unit and dry pump in the sub fab such that a system with coordinated control of the different pumping systems and cleaning cycles is provided and blocking of the pumping system due to condensation of by-products of the process is avoided or at least reduced.

- 13Although 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 5 from the scope of the invention as defined by the appended claims and their equivalents.

-14REFERENCE SIGNS valve process chamber control circuitry

Claims

1. A vacuum pumping arrangement comprising multiple pumping stages for evacuating a process chamber, said vacuum pumping arrangement comprising:

at least one turbomolecular pumping stage;

at least one further pumping stage downstream of said turbomolecular pumping stage; and at least one inlet for admitting radicals into said vacuum pumping arrangement, said at least one inlet being located downstream of said turbomolecular stage and upstream of at least one of said at least one further pumping stage.

2. A vacuum pumping arrangement according to claim 1, said vacuum pumping arrangement comprising a single shaft multistage pump, each of said multiple stages being mounted on a same shaft and said at least one inlet comprising an inter-stage inlet between said stages.

3. A vacuum pumping arrangement according to claim 2, wherein at least one of said at least one inlets comprises an inlet between said turbomolecular stage and a pumping stage immediately downstream of said turbomolecular pumping stage.

4. A vacuum pumping arrangement according to claim 1, said multiple pumping stages comprising a plurality of pumps;

said plurality of pumps comprising a turbomolecular pump and at least one further pump located downstream of said turbomolecular pump;

said at least one inlet being arranged to introduce said radicals between said turbomolecular pump and said at least one further pump.

5. A vacuum pumping arrangement according to claim 4, said at least one inlet being arranged to introduce said radicals into a conduit connecting said turbomolecular pump and said at least one further pump.

6. A vacuum pumping arrangement according to claims 4 or 5, wherein said at least one further pump comprises a multistage pump comprising a plurality of said further pumping stages.

7. A vacuum pumping arrangement according to any one of claims 4 to 6, wherein said turbomolecular pump is located adjacent to said at least one further pump.

8. A vacuum pumping arrangement according to any preceding claim, said vacuum pumping arrangement further comprising a radical source for generating said radicals connected to said at least one inlet.

9. A vacuum pumping arrangement according to claim 8, wherein said radical source comprises a plasma source for generating a plasma.

10. A vacuum pumping arrangement according to any preceding claim, wherein said at least one further pumping stage comprise at least one drag pumping stage.

11. A vacuum pumping arrangement according to any preceding claim, wherein said at least one further pumping stage comprise a plurality of further pumping stages, said plurality of further pumping stages comprising at least one regenerative pumping stage and at least one drag pumping stage.

12. A vacuum pumping arrangement according to any preceding claim, said vacuum pumping arrangement comprising control circuitry, said control circuitry being configured to control input of said radicals via said inlet.

13. A vacuum pumping arrangement according to any preceding claim, said vacuum pumping arrangement comprising control circuitry, said control circuitry being configured to control input of said radicals via said inlet in response to an indication that a process in said process chamber is not active.

14. A vacuum pumping arrangement according to claim 12 or 13, said control circuitry comprising an input for receiving signals from a controller of said process chamber, said control circuitry being configured to control input of said radicals via said inlet in response to receipt of a signal indicating said process chamber is commencing a cleaning cycle.

15. A vacuum pumping arrangement according to claim 12 or 13, said control circuitry comprising an input for receiving signals from a controller of said process chamber, said control circuitry being configured to control input of said radicals via said inlet in response to receipt of a signal indicating a wafer in said process chamber is being changed.

16. A vacuum pumping arrangement according to any one of claims 12 to 15, said inlet comprising a valve, said control circuitry being operable to control input of said radicals via said inlet by controlling said valve.

17. A vacuum pumping arrangement according to any one of claims 12 to 16, said control circuitry being configured to control a motor driving at least one rotor of said multiple pumping stages.

18. A vacuum pumping arrangement according to any one of claims 12 to 17 when dependent on claim 4, said control circuitry being configured to control multiple motors driving rotors of said multiple pumps.

19. A vacuum pumping arrangement according to any preceding claim, said inlet being arranged such that said radicals are injected into said pumping arrangement in a region having viscous fluid flow and downstream of a region having molecular fluid flow.

20. A vacuum pumping arrangement according to any preceding claim, wherein said radicals comprise at least one of: F, generated from F2 thermally of generated by a plasma source from NF3, SF6, CsFs, or 0' generated from O2, O3 or H2O.

21. A method of cleaning a vacuum pumping arrangement comprising multiple pumping stages for evacuating a process chamber, said vacuum pumping arrangement comprising: at least one turbomolecular pumping stage in fluid communication with said process chamber; at least one further pumping stage downstream of said turbomolecular pumping stage, said method comprising:

generating radicals for cleaning said pump; and inputting radicals into said vacuum pumping arrangement at a point downstream of said turbomolecular stage and upstream of at least one of said at least one further pumping stage.

22. A method of cleaning a vacuum pumping arrangement according to claim 21, wherein said step of generating said radicals comprises using a plasma source to generate said radicals.

23. A method of cleaning a vacuum pumping arrangement according to claim 21, wherein said step of generating said radicals comprises using a high temperature to generate said radicals.

24. A method of cleaning a vacuum pumping arrangement according to any one of claims 21 to 23, wherein said multiple pumping stages comprising a plurality of pumps; said plurality of pumps comprising a turbomolecular pump and at least one further pump located downstream of said turbomolecular pump; and said step of inputting said radicals comprising inputting said radicals into a conduit connecting said turbomolecular pump and said at least one further pump.

25. A method of cleaning a vacuum pumping arrangement according to any one of claims 21 to 24, wherein said step of inputting said radicals via said inlet is performed in response to an indication that a process in said process chamber is not active.

26. A method of cleaning a vacuum pumping arrangement according to any one of claims 21 to 25, wherein said step of inputting said radicals via said inlet is performed in response to an indication that said process chamber is commencing a cleaning cycle.

27. A method of cleaning a vacuum pumping arrangement according to any one of claims 21 to 26, wherein said step of inputting said radicals via said inlet is performed in response to an indication that a process in said process chamber is not active.

28. A method of cleaning a vacuum pumping arrangement according to any one of claims 21 to 27, wherein said step of inputting said radicals via said inlet is performed in response to an indication that a wafer in said process chamber is being changed.

29. A method of cleaning a vacuum pumping arrangement according to any one of claims 21 to 28, wherein said step of inputting said radicals comprises controlling a valve at an inlet for inputting said radicals.