Patent Application
20200355190
The invention relates to pumps for evacuating a process chamber.
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.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.
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, C5F8, or O. generated from O2, O3 or H2O.
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 BCl3 or SiCl4 for generating said chloride radical.
BCl3 or SiCl4 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.
The Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detail Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:
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.
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 Sicl4, Bcl3, NF3, SF6, CSF8, 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.
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 BCl3 or SiCl4, 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. 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.
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 BCl3, which will react to form TiCl4 and BF3, or the reactive gas may be SiCl4, which will react to form TiCl4 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)+SiCl4=TiCl4+SiF4 is exothermic−161.6 kJ·mol−1 at 298K
3TiF4(s)+4BCl3=3TiCl4+4BF3 is exothermic−274 kJ·mol−1 at 298K
SiCl4 or BCl3 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 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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1721671.4 | Dec 2017 | GB | national |
This application is a Section 371 National Stage Application of International Application No. PCT/GB2018/053689, filed Dec. 19, 2018, and published as WO 2019/122873 A1 on Jun. 27, 2019, the content of which is hereby incorporated by reference in its entirety and which claims priority of British Application No. 1721671.4, filed Dec. 21, 2017.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2018/053689 | 12/19/2018 | WO | 00 |
