WO2019122873A1

WO2019122873A1 - A vacuum pumping arrangement

Info

Publication number: WO2019122873A1
Application number: PCT/GB2018/053689
Authority: WO
Inventors: Christopher Mark Bailey; Nigel Paul Schofield; Michael Colin GRAHAM; Andrew Seeley
Original assignee: Edwards Limited
Priority date: 2017-12-21
Filing date: 2018-12-19
Publication date: 2019-06-27
Also published as: GB201721671D0; US20200355190A1; JP2021507172A; EP3728858A1; GB2569633A

Abstract

A vacuum pumping arrangement comprising multiple pumping stages for evacuating a process chamber and a method of cleaning the vacuum pumping arrangement is discussed. The vacuum pumping arrangement comprises: at least one turbomolecular pumping stage; at least one further pumping stage downstream of the turbomolecular pumping stage; and at least one inlet for admitting radicals into the vacuum pumping arrangement, the at least one inlet being located downstream of the turbomolecular stage and upstream of at least one of the at least one further pumping stage.

Description

A VACUUM PUMPING ARRANGEMENT

FIELD OF THE INVENTION

The invention relates to pumps for evacuating a process chamber.

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 of said at least one further pumping stage comprising a drag pumping stage; and at least one inlet configured to admit radicals into said vacuum pumping arrangement, said at least one inlet being located

downstream of said turbomolecular stage and upstream of said drag stage; wherein 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. 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.

It may be advantageous if at least one 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 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.

Although the further pumping stages may be a number of things, in some embodiments they comprise at least one regenerative pumping stage and at least one drag pumping stage. Where there is only a drag stage and no regenerative 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 for 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 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, inputting 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: Cl generated from a chloride, F , generated thermally from F2 or by a plasma source from NF3, SF6, CsFs, or O generated from O2,

O3 or FI2O.

In some embodiments, said vacuum pump arrangement further comprises a radical source for generating said radicals prior to injection via said inlet, said radical source comprising a source of BCh or SiCUfor generating said chloride radical.

BCh or SiCU will react exothermically with some solid fluorides, such as TiF₄, which may be deposited in vacuum pumps pumping process chambers to generate gaseous chlorides which can then be evacuated. This reduces the amount of deposit and increases the lifetime of the pump.

The vacuum pump system disclosed can be used in a method of cleaning the vacuum pumping arrangement of embodiments by generating radicals for cleaning said vacuum pumping arrangement exterior to the pump; 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.

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.

Where 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; and Figure 3 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.

The 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.

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

Figure 1 shows a vapour pressure curve, illustrating how deposition is more likely to occur at lower temperatures and higher pressures. Operating above the vapour curve being in the solid region and liable to cause deposition, while operating below the vapour curve being in the gaseous region. The operating pressures and temperatures of a multiple stage pump from the inlet 40 to the outlet 46 are also shown, and this illustrates how the turbine or turbomolecular stage 42 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 44 the vapour curve 48 is crossed and some substances being pumped start to condense and deposition becomes a problem. If the

substances liable to solidify can be decomposed prior to crossing the vapour curve then this can mitigate the problem.

Figure 2 shows a pumping system according to an embodiment. In this embodiment the drag/regenerative stage 44 is formed on the same shaft as the turbo stage 42.

There is an inlet 50 for admitting radicals from a radical source. These radicals are generated in this embodiment by a plasma source 52. The inlet 50 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, a chloride or oxygen, each 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 SicU, Bch, NF3, SF₆, C5F8, or O generated from O2, O3 or H2O.

In summary, a pumping system where deposition is controlled by the input of radicals to the higher pressure stages periodically is disclosed. 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 70 outside of the clean room or fab (semiconductor fabrication plant) 72. This in turn reduces the cost of heating this foreline and may eliminate the need for a roots pump in the sub-fab. There is a valve 10 on the foreline. Figure 3 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 60. Control circuitry 30 controls both the generation of the radicals and their admission to the pump. Valve 51 on the inlet 50 to the pumping system from the radical source 52 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 20 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 70 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.

In summary a gas in some embodiments, a halogen-containing gas is injected into a turbopump in order to remove, prevent or at least reduce the formation of, a solid deposit that could cause the pump to slow down or seize.

The gas is injected between the turbine blade stage and the drag or Holweck stage of the turbopump.

Where the process chamber being pumped is such that the deposited solid is a non-volatile fluoride, the reactive gas may be a chloride such as BCh or SiCU, that will react exothermically with the solid fluoride to form a volatile chloride.

The reactive gas is passed through a plasma before injection to create more reactive species. In some techniques the reactive gas may be heated electrically before injection to increase its reactivity.

Embodiments seek to address the problems of pump failure due to

accumulation of solids in the drag stage that arise with turbopumps utilizing molecular drag stages, particularly those used on some etch or deposition processes.

If the deposited material is volatile at temperatures within the range of operation of the pump (typically up to 150°C), then heating of the turbopump can reduce accumulation of solids. Flowever in some cases the deposited material is not volatile. For example in some cases a deposit of titanium tetrafluoride (TiF4) is formed and this requires temperature above 377°C to volatilise, well beyond the operating range of the pump. TiF4 solid is formed by the reaction of TiCI4 gas (which is a reaction product of etching titanium-containing layers from a semiconductor wafer), with HF gas, in the process by-product gas stream which enters the turbopump.

In some embodiments, a plasma to decompose NF3 and create fluorine radicals is used to address deposition problems.

Where the deposited solid in the turbopump is a non-volatile fluoride, and the corresponding chloride is volatile at a temperature achievable within the turbopump, the reactive gas is preferably a chloride that will react

exothermically with the solid fluoride to form a volatile chloride. For example, if the solid deposit is TiF₄, the reactive gas may be BC , which will react to form TiCU and BF3, or the reactive gas may be SiCU, which will react to form TiCU and SiF₄. These products are volatile and will flow out of the turbopump as gases, this reducing the amount of deposit and increasing the lifetime of the pump.

TiF₄(s) + SiCU = TiCU + SiF₄ is exothermic -161 .6 kJ.moM at 298K

3TiF₄(s) + 4BC = 3TiCU + 4BF3 is exothermic -274 kJ.mol-1 at 298K SiCU or BC will react preferentially with HF, which will help prevent the formation of TiF₄ solids in the turbopump, again reducing the amount of deposit and increasing the lifetime of the pump.

The gas may preferably be injected between the turbine blade stage and the Flolweck stage of the turbopump, to prevent contamination of the process chamber by the injected gas. The turbine blade stage prevents or at least reduces the injected gas flowing towards the process chamber and potentially contaminating the process.

In some embodiments the turbopump or parts within it may use materials or coatings (such as nickel) to increase the corrosion resistance to the radicals being injected, particularly where these are halogens.

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.

REFERENCE SIGNS

10 valve

20 process chamber 30 control circuitry

40 inlet

42 turbo-stage

44 drag stage

46 outlet

48 vapour curve

50 radical inlet

51 valve

52 plasma source

60 abatement system 70 sub-fab pumping system 72 clean room

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, at least one of said at least one further pumping stages comprising a drag pumping stage; and

at least one inlet configured to admit radicals into said vacuum pumping arrangement, said at least one inlet being located downstream of said turbomolecular stage and upstream of said drag pumping stage; wherein

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.

2. A vacuum pumping arrangement according to claim 1 , 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.

3. 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 said at least one drag pumping stage.

4. A vacuum pumping arrangement according to any preceding claim, wherein said drag stage is adjacent to said at least one turbomolecular stage and said inlet is located between said at least one turbomolecular stage and said drag stage.

5. 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.

6. A vacuum pumping arrangement according to claim 5, wherein said radical source comprises a plasma source for generating a plasma.

7. 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.

8. 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.

9. A vacuum pumping arrangement according to claim 7 or 8, 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.

10. A vacuum pumping arrangement according to claim 7 or 8, 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.

11. A vacuum pumping arrangement according to any one of claims 7 to 10, said inlet comprising a valve, said control circuitry being operable to control input of said radicals via said inlet by controlling said valve.

12. A vacuum pumping arrangement according to any one of claims 7 to 11 , said control circuitry being configured to control a motor driving said rotor of said multiple pumping stages.

13. 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.

14. A vacuum pumping arrangement according to any preceding claim, wherein said radicals comprise at least one of: Cl generated from a chloride, F , generated from F2 thermally or generated by a plasma source from NF3, SF₆, C5F8, or O ^' generated from O2, O3 or FI2O.

15. A vacuum pumping arrangement according to claim 13, said vacuum pump arrangement further comprising a radical source for generating said radicals prior to injection via said inlet, said radical source comprising a source of BC or SiCUfor generating said chloride radicals.