U.S. patent application number 16/955444 was filed with the patent office on 2020-11-12 for vacuum pumping arrangement.
The applicant listed for this patent is Edwards Limited. Invention is credited to Christopher Mark Bailey, Michael Colin Graham, Nigel Paul Schofield, Andrew Seeley.
Application Number | 20200355190 16/955444 |
Document ID | / |
Family ID | 1000004990516 |
Filed Date | 2020-11-12 |
United States Patent
Application |
20200355190 |
Kind Code |
A1 |
Bailey; Christopher Mark ;
et al. |
November 12, 2020 |
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.
Inventors: |
Bailey; Christopher Mark;
(Burgess Hill, Sussex, GB) ; Schofield; Nigel Paul;
(Burgess Hill, Sussex, GB) ; Graham; Michael Colin;
(Burgess Hill, Sussex, GB) ; Seeley; Andrew;
(Burgess Hill, Sussex, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Edwards Limited |
Burgess Hill, West Sussex |
|
GB |
|
|
Family ID: |
1000004990516 |
Appl. No.: |
16/955444 |
Filed: |
December 19, 2018 |
PCT Filed: |
December 19, 2018 |
PCT NO: |
PCT/GB2018/053689 |
371 Date: |
June 18, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F04D 19/042 20130101;
F04D 19/046 20130101; F04D 19/044 20130101; F16C 2360/45 20130101;
F04D 23/008 20130101 |
International
Class: |
F04D 19/04 20060101
F04D019/04 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2017 |
GB |
1721671.4 |
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
CROSS-REFERENCE OF RELATED APPLICATION
[0001] 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.
FIELD
[0002] The invention relates to pumps for evacuating a process
chamber.
BACKGROUND
[0003] 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.
[0004] 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.
[0005] 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.
SUMMARY
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] In some embodiments, the pumping arrangement further
comprises a radical source connected to said at least one
inlet.
[0011] In some embodiments the radical source comprises a plasma
source.
[0012] 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.
[0013] 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.
[0014] In some embodiments, said vacuum pumping arrangement
comprises control circuitry, said control circuitry being
configured to control input of said radicals via said inlet.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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 F.sub.2 or
by a plasma source from NF.sub.3, SF.sub.6, C.sub.5F.sub.8, or O.
generated from O.sub.2, O.sub.3 or H.sub.2O.
[0025] 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 BCl.sub.3 or SiCl.sub.4 for generating said chloride
radical.
[0026] BCl.sub.3 or SiCl.sub.4 will react exothermically with some
solid fluorides, such as TiF.sub.4, 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
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.degree.
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.degree. 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 exothermic-161.6
kJmol-1 at 298K
3TiF.sub.4(s)+4BCl.sub.3=3TiCl.sub.4+4BF.sub.3 is exothermic-274
kJmol-1 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.
* * * * *