VACUUM PUMPING ARRANGEMENT

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.

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. The 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. The vacuum pumping arrangement according to claim 1, 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. The vacuum pumping arrangement according to claim 1, 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. The vacuum pumping arrangement according to claim 1, said vacuum pumping arrangement further comprising a radical source for generating said radicals connected to said at least one inlet.

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

7. The vacuum pumping arrangement according to claim 1, said vacuum pumping arrangement comprising control circuitry, said control circuitry being configured to control input of said radicals via said inlet.

8. The vacuum pumping arrangement according to claim 1, 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. The vacuum pumping arrangement according to claim 7, 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. The vacuum pumping arrangement according to claim 7, 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. The vacuum pumping arrangement according to claim 7, said inlet comprising a valve, said control circuitry being operable to control input of said radicals via said inlet by controlling said valve.

12. The vacuum pumping arrangement according to claim 7, said control circuitry being configured to control a motor driving said rotor of said multiple pumping stages.

13. The vacuum pumping arrangement according to claim 1, 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. The vacuum pumping arrangement according to claim 1, 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 H2O.

15. The 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 BCl3 or SiCl4 for generating said chloride radicals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0032] FIG. 1 shows a vapour curve illustrating how deposition is dependent on pressure and temperature and varies through a multiple stage pumping system;

[0033] FIG. 2 illustrates a pumping arrangement according to an embodiment; and

[0034] FIG. 3 illustrates a further embodiment of a pumping arrangement pumping a process chamber and including control circuitry.

DETAILED DESCRIPTION

[0035] Before discussing the embodiments in any more detail, first an overview will be provided.

[0036] 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.

[0037] 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.

[0038] The pumping system is a single shaft pumping system with different stages, the radicals being injected between the stages.

[0039] FIG. 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.

[0040] FIG. 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.

[0041] 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 Sicl.sub.4, Bcl.sub.3, NF.sub.3, SF.sub.6, CSF.sub.8, or O. generated from O.sub.2, O.sub.3 or H.sub.2O.

[0042] 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.

[0043] FIG. 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The gas is injected between the turbine blade stage and the drag or Holweck stage of the turbopump.

[0048] 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 BCl.sub.3 or SiCl.sub.4, that will react exothermically with the solid fluoride to form a volatile chloride.

[0049] The reactive gas is passed through a plasma before injection to create more reactive species.

[0050] In some techniques the reactive gas may be heated electrically before injection to increase its reactivity.

[0051] 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.

[0052] 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. However 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 TiCl4 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.

[0053] In some embodiments, a plasma to decompose NF.sub.3 and create fluorine radicals is used to address deposition problems.

[0054] 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 TiF.sub.4, the reactive gas may be BCl.sub.3, which will react to form TiCl.sub.4 and BF.sub.3, or the reactive gas may be SiCl.sub.4, which will react to form TiCl.sub.4 and SiF.sub.4. 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.

TiF.sub.4(s)+SiCl.sub.4=TiCl.sub.4+SiF.sub.4 is exothermic161.6 kJ.Math.mol1 at 298K

3TiF.sub.4(s)+4BCl.sub.3=3TiCl.sub.4+4BF.sub.3 is exothermic274 kJ.Math.mol1 at 298K

[0055] SiCl.sub.4 or BCl.sub.3 will react preferentially with HF, which will help prevent the formation of TiF.sub.4 solids in the turbopump, again reducing the amount of deposit and increasing the lifetime of the pump.

[0056] The gas may preferably be injected between the turbine blade stage and the Holweck 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.