Vacuum pumping system and method

Abstract

A vacuum pump system and method for evacuating a process chamber comprising is disclosed. The system has two vacuum pumps (20, 30) each having a required pumping performance and being arranged in parallel. There is a valve system comprising respective first and second valves (V1, V2) for controlling a rate of flow of fluid into the respective two vacuum pumps. There is also control circuitry (40) configured: to control the first and second valves (V1, V2) during a first period of operation, such that each of the valves is partially open and a cumulative pumping performance of the two vacuum pumps (20, 30) provides the required pumping performance. In response to determining that one of the two vacuum pumps is to be shut down, the control circuitry (40) closes one of the first and second valves and to fully opens the other of the first and second valves, such that the pumping performance of the pump with the open valve provides the required pumping performance.

Description

[0001] VACUUM PUMPING SYSTEM AND METHOD

[0002] FIELD OF THE INVENTION

[0003] The field of the invention relates to a vacuum pumping system and method.

[0004] BACKGROUND

[0005] Some pumping systems such as those used for providing and maintaining a vacuum in a semiconductor processing chamber are configured with redundancy to enable the vacuum in the chamber to be maintained in the event of a pump failure.

[0006] Semiconductor processing equipment is costly and the wafers are valuable thus, a pumping system with some backup capability is desirable to reduce shut down times of such systems and any associated loss of wafers. A conventional system may provide a backup vacuum pump arranged in parallel with an operating vacuum pump, with a valve system configured to connect the backup pump to the process chamber, while isolating the operating pump in the event of pump shutdown. Although this allows pumping to continue the process chamber may see a pressure spike during the valve switching procedure. Some processes are very sensitive to pressure spikes and it would be desirable if any spike in pressure when a pump is shut down could be reduced.

[0007] SUMMARY

[0008] A first aspect provides a vacuum pump system for evacuating a process chamber comprising: a first and a second vacuum pump arranged in parallel and each comprising respective first and second valves for controlling a rate of flow of fluid into said respective first and second vacuum pumps; control circuitry configured: to control said first and second valves and first and second vacuum pumps during a first period of operation, such that each of said valves is partially open and a cumulative pumping performance of said first and second vacuum pumps comprises a first pumping performance; and in response to determining that one of said first and second pumps is to be shut down, to close one of said first and second valves and to more fully open the other of said first and second valves, such that the pumping performance of said pump with said more fully open valve comprises said first pumping performance.

[0009] As mentioned earlier, vacuum pumping systems configured with a backup pump may introduce pressure spikes into the process chamber when switching from the operational to the backup pump. Furthermore, where the backup pump has not been pumping a gas flow it will initially be relatively cold and not at optimum temperature and this can result in process gas condensation in the pump and damage to the pump.

[0010] These problems have been addressed in embodiments by providing for the pumping load of the chamber to be shared between two pumps with partially open valves restricting each pump’s performance. In this way were a pump to shut down, the partially open valve to that pump could be closed and the partially open valve to the other pump opened and with appropriate design the overall pump performance or flow rate could be retained and provided by a single pump rather than by two pumps in parallel. This leads to significantly reduced pressure variations in the process chamber when compared to switching between an operational and backup pump. It has the additional advantage that the first and second pump are both operating at the same optimal or close to optimal temperature thereby avoiding or at least reducing the risk of process gas condensation when one pump switches to providing the full pumping performance on its own. A further advantage of having valves default as partially open during extended use on process is that the valves will less likely become clogged / jammed shut by condensate, powder or corrosion e.g., compared to if the valves needed to cycle between closed and open during extended use on process. This may ensure longer valve operational lifetime and reduce maintenance requirements and operational downtime. In some embodiments, said control circuitry is configured during said first period of operation to control each of said first and second valves to be open enough to allow a respective pump to pump at least 40% of said first pumping performance.

[0011] In some embodiments, said control circuitry is configured to control said first and second valves to be partially open by different amounts such that one of said vacuum pumps pumps a greater proportion of said first pumping performance than the other. The pumping performance or flow rate through the pumps may not be shared completely equally between the pumps. This may be advantageous as this means that one pump, the one with the greater load, is likely to fail earlier than the other pump and the chances of having pump failure at or about the same time is reduced. Although it may be advantageous to have the pumps fail at different times, there are advantages to them pumping at approximately the same flow rate or performance as this makes the change between partially open and fully open valves smaller. A ratio of up to 40 and 60% still provides an effective reduction in the pressure spike, the closer to 40 and 60 % the lower the chances of the two pumps failing at about the same time.

[0012] In other embodiments, said control circuitry is configured to control said first and second valves to be partially open such that each pump pumps substantially 50% of said first pumping performance. Substantially the same pumping performance may be within 5% preferably 2% of each other.

[0013] In some embodiments, said first and second vacuum pumps and valves are arranged on parallel first and second process lines, said first and second process lines connecting to a further process line providing fluid communication with a process chamber.

[0014] This arrangement is particularly effective at providing redundancy and parallel pumping possibilities for semiconductor chambers. In some embodiments, said further process line comprises a valve for selectively isolating a process chamber from said vacuum pumping system.

[0015] In some embodiments, said further process line comprises a booster pump and said first and second vacuum pumps comprise backing pumps.

[0016] Booster pumps may be less likely to fail, and thus, in some cases it may be advantageous to have the redundancy in the backing pumps and only have a single booster pump.

[0017] In some embodiments, said first and second vacuum pumps each comprise a plurality of vacuum pumps arranged in series. These vacuum pumps may be booster and backing pumps for example.

[0018] In some embodiments, said control circuitry comprises determining circuitry configured to determine when a pump starts to fail and to select said pump to be shut down.

[0019] In some embodiments, said determining circuitry comprises monitoring circuitry configured to monitor performance of said pumps.

[0020] The monitoring circuitry may be connected to sensors configured to monitor pressure, temperature or vibration fluctuations or fluctuations in power used by the pump motor. Changes in these values may be indications of changes in performance of the pump and in some cases by, for example comparing them with thresholds, these changes may be used to provide an indication of a pump starting to fail.

[0021] In some embodiments, said determining circuitry comprises predictive circuitry configured to predict a failure of said pumps. Predictive circuitry, which may have some machine learning element in it, may be used to predict a failure of the pumps and this may be used in conjunction with the sensor measurements mentioned above. A more complex analysis may be performed with predictive circuitry where several sensor measurements and their variation over time may be considered. These variations may be used to provide a prediction of when pump failure might be expected to occur, and the predictions may be improved over time where a machine learning element is used.

[0022] A second aspect provides a method of evacuating a process chamber using a first and a second vacuum pump arranged in parallel process lines, said parallel process lines providing parallel flow paths to said process chamber, wherein flow through each of said pumps is controlled by respective valves; said method comprising: operating said first and second vacuum pumps at a first and second speed, respectively; controlling said respective valves such that each of said valves is partially open and process gas is pumped by both pumps, a cumulative pumping performance of said first and second vacuum pumps comprising a first pumping performance; determining that one of said pumps is to be shut down, and in response: closing the respective valve of said pump to be shut down such that said pump is isolated from said process chamber and more fully opening the other valve, such that the pumping performance through said pump that is not isolated comprises said first pumping performance.

[0023] In some embodiments, said step of controlling said respective valves such that each of said valves is partially open comprises controlling said respective valves such that each is open by a different amount such that each pump provides a minimum of 40% of said pumping performance.

[0024] In some embodiments, said step of controlling said respective valves comprises controlling said first and second valves to be partially open by different amounts such that one of said vacuum pumps pumps a greater proportion of said first pumping performance than the other. In some embodiments, said step of controlling said respective valves such that each of said valves is partially open comprises controlling said respective valves such that each is open by substantially a same amount, such that each pump provides substantially 50% of said pumping performance.

[0025] In some embodiments, said step of determining that one of said pumps is to be shut down comprises monitoring at least one of a temperature, pressure, vibrations, current or power consumed by said pumps for changes indicative of an imminent pump shut down.

[0026] In some embodiments, said step of determining that one of said pumps is to be shut down comprises using predictive circuitry to predict a failure of one of said pumps.

[0027] 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.

[0028] 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.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0031] Figure 1 schematically shows a vacuum pumping system according to an embodiment;

[0032] Figure 2 schematically shows a vacuum pumping system according to a further embodiment; and Figure 3 shows a flow chart illustrating steps in a method according to an embodiment.

[0033] DESCRIPTION OF THE EMBODIMENTS

[0034] Before discussing the embodiments in any more detail, first an overview will be provided.

[0035] The application describes a vacuum pumping system and a method for evacuating a process chamber with some redundancy to provide a backup capability. The vacuum pumping system has vacuum pumps arranged in parallel, each having a predetermined pumping performance. There is a valve system with respective first and second valves for controlling a rate of flow of fluid into the respective vacuum pumps. There is also control circuitry configured: to control the first and second valves during normal operation such that each of the valves is partially open and the pumping is shared between the two pumps, a cumulative pumping performance of the two pumps providing the required predetermined pumping performance. If shutdown or failure of a pump is determined or predicted the control circuity closes the valve corresponding to the pump due to be shut down and more fully opens the other valve such that the pumping performance of the pump with the more fully open valve provides the required predetermined pumping performance and the vacuum chamber sees little change in pumping performance and any pressure spike is small.

[0036] In effect, having two substantially identical, but performance-restricted, vacuum pumps connected to a single process foreline, has the potential to minimise or at least reduce foreline pressure changes when a single process pump fails unexpectedly.

[0037] Furthermore, having two substantially identical, but performance-restricted, vacuum pumps connected to a single process foreline has the benefit of sharing the process load between two pumps, which should extend individual pump lifetime. Additionally, having two substantially identical, but performance-restricted, vacuum pumps connected to a single process foreline has the benefit of both pumps operating at optimum temperature due to each having a process gas load, thus eliminating or at least reducing the possibility of process by-product condensation inside the pump.

[0038] Traditional vacuum pump backup arrangements have one main pump connected to the process foreline while a second backup pump is running off-line (valved off) ready for when needed. If the main pump fails, valves switch the process foreline from the main pump to the backup pump. This usually results in a pressure dip as a consequence of closing the main pump inlet valve and opening the backup pump inlet valve. This can cause problems in the process chamber if the chamber pressure control valve isn’t able to compensate for the pressure change, potentially resulting in wafer loss. Ideally, there would be zero pressure fluctuation in the process chamber when switching from main to backup pump, to allow wafer processing to continue as normal. Additionally, the backup pump is typically not operating at optimal temperature due to receive zero gas load while at standby.

[0039] By having two pumps, in some embodiments two identical pumps, connected to the process foreline at the same time and with inlet valves partially open (restricting the vacuum pumping performance of each pump), it is possible to achieve a similar pumping performance from the two pumps as would be achieved by a single, unrestricted pump. Should either pump start to fail, the failing pump inlet valve can be closed at the same time as the second pump’s inlet valve is more fully or fully opened, thus maintaining the foreline pressure. Since both pumps share the process gas load under normal conditions, both pumps will be operating at or close to optimal temperature.

[0040] In an alternative arrangement there may be a single booster pump backed by two, valved backing pumps. The two valved backing pumps would function in the same way as described above. This would have the advantage of saving the cost of one booster pump, however the disadvantage would be that the single booster would not have a backup should it fail.

[0041] The backup system could be linked to a predictive monitoring system such that the backup sequence could be triggered pro-actively, ahead of a pump failing.

[0042] Figure 1 schematically illustrates a vacuum pumping system 5 according to an embodiment. Vacuum pumping system 5 comprises a plurality of vacuum pumps 20, 30 connected by respective valves V1 and V2 to a process line 12 that is connected via valve V3 to a process chamber 10. Valves V1 and V2 and pumps 20 and 30 are controlled by control circuity 40.

[0043] Valves V1 and V2 can be any suitable valve that can be controlled between closed and fully open to be partially opened at different percentages. Such valves are well known and can include proportional valves, servo controlled valves, pendulum valves, poppet valves, solenoid valves and the like.

[0044] The pumping system 5 is a pumping system configured for fail-safe operation such that there is redundancy to reduce the probability of a pump failing leading to vacuum loss in the process chamber 10.

[0045] In this embodiment during normal operation both pumps are operational and both pumps are connected to the process chamber via partially open valves V1 and V2 and open valve V3. In this way valves V1 and V2 restrict the pumping performance of the respective pumps 20, 30 and the degree of partial opening is selected so that the cumulative pumping performance is substantially equal to the pumping performance of one of the pumps without such a restriction. In this way, the pumping performance is similar to the process chamber being pumped by a single pump, but both pumps are contributing to the pumping and thus, both pumps are operating at or close to optimal temperature. Furthermore, as the flow rate through the pumps is restricted, the lifetime of the pumps is increased and the time period between pump failures is reduced.

[0046] The degree of partial opening may be selected to be substantially equal for both pumps, so that both pumps contribute substantially the same amount to the overall pumping performance. Alternatively, one valve may be selected to be open to a greater extent (i.e. , more fully open) than the other which may lead the pump pumping the larger amount of gas to fail earlier than the other one. Staggering failure of the pumps in this way may help reduce the likelihood of both failing at around the same time. The degree of opening may be set so that one contributes between 40 and 45% of the pumping performance and the other between 60 and 55% of the pumping performance.

[0047] If control circuitry 40 determines that one of the pumps 20 or 30 may be about to fail or is failing, then it will act to fully close the respective valve V1 or V2, shutting down flow into the failing pump, and fully open the other valve. In this way, any pumping performance change in the pumping system is limited and although there may be a small pressure spike during the valves fully opening and closing this is considerably less than would occur were the valves to go from one being fully open and the other being fully closed to the one being fully closed and the other being fully open. Furthermore, as both pumps are pumping process gas they are both at or closer to optimal temperature and the risk of condensate of process gas in a cold pump is reduced. Moreover, opening valves to a greater or lesser extent (i.e., more fully opening and closing valves) allows a quicker reaction to maintain pumping performance compared to speeding up or slowing down a vacuum pump alone (e.g., from a standby condition or otherwise).

[0048] In some embodiments, the vacuum pumps 20 and 30 are a set of vacuum pumps such as booster and a backing pump.

[0049] In some embodiments, the pumping system may comprise monitoring circuitry 42 which may monitor the performance of the pump and determine when the pump is starting to fail. In this regard, it may monitor the power consumed by the pump motor, the temperature, pressure, vibration or other factors indicative of pump health. In some embodiments, the monitoring circuitry 42 may be predictive monitoring circuitry configured to predict potential failure and it may use a machine learning technique to improve its predictions over time. The monitoring circuitry 42 may be part of the pump’s control circuitry 40 or it may be a separate monitoring system.

[0050] Where failure of a pump is predicted or detected, then the pump is isolated from the process chamber and repaired, replaced or serviced. Once it is operational again then the two valves V1 and V2 may be returned to their partially open states and the two pumps will again each contribute to the pumping of the process chamber.

[0051] Figure 2 shows an alternative embodiment, where redundancy is provided in the backing pumps 20, 30 and there is a single booster pump 22 in process foreline 12. Booster pumps may be more reliable than backing pumps and thus, it may in some circumstances be preferable to provide the redundancy only in the backing pumps.

[0052] Figure 3 shows a flow chart illustrating steps in a method according to an embodiment. In an initial step pump 1 and pump 2 that are each configured with a predetermined pumping performance are arranged in parallel and connected to a process chamber via respective valves.

[0053] At step S20 each pump is operated at full speed while the respective valves are partially opened so that the pumping performance of the pumps is restricted and a cumulative pumping performance equal to the predetermined pumping performance of a single pump is provided. However, in other embodiments, each pump may be operated at a first and second speed respectively that is lower than the pump’s full speed. For example, between 50%-100% full speed. In one such example, pumping performance may be maintained by utilising higher flow rate / bigger pumps operating at reduced speeds compared to lower flow rate / smaller pumps operating at full speed. In further embodiments, the speed of each pump may be varied below full speed or between a particular percentage of their full speed and the amount of opening of each valve varied as appropriate to meet different process requirements. It will be appreciated that reducing and varying pump speed in this manner can maintain required pumping performance whilst providing power and energy cost savings. This may also improve pump endurance, as pump motors are operated under reduced load.

[0054] At step D5 it is determined if one of the pumps is to be shut down. This may be determined in response to a manual indication indicating a pump is to be replaced for some reason, or it may be determined in response to detection of a potential fault condition by the monitoring circuitry 42 of Figure 1 or the pump’s control system itself. If there is an indication that one of the pumps is to be shut down then at step S30 the valve linking that pump to the process chamber is closed and the valve linking the other pump to the process chamber is fully opened so that the other pump provides the predetermined pumping performance by itself. In this way the process chamber sees very little variation in pumping performance and any pressure spike is very small. At step D15 it is determined if the shut down pump has been replaced, serviced or repaired and when it has step S40 is performed and the pump is turned on and operates at full speed and the respective valves are set to the partially open position again.

[0055] In some embodiments, the partially open position may be at 50% such that each pump pumps approximately the same amount of gas. In other embodiments one may be set to pump slightly more gas than the other and this may make it less likely that the pumps fail at a similar time. In further embodiments, the first and second pumps may be operated at differential speeds (i.e. , a first and second speed respectively - with one speed lower than the other) with corresponding differential partial openings of the respective valves to still maintain cumulative pumping performance. Both these strategies can be used alone or in combination to allow one pump to operate at reduced load compared to the other to maintain pumping performance with a lower risk of both pumps failing at a similar time. This means one pump can be reliably replaced whilst the other is still running, to ensure processes can be continued (e.g., compared to having to take both pumps offline or schedule overly short maintenance windows to ensure they are replaced before one of them fails).

[0056] 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.

[0057] REFERENCE SIGNS

[0058] 5 pumping system

[0059] 10 process chamber

[0060] 12 process foreline 20, 30 vacuum pumps, or sets of vacuum pumps

[0061] 22 booster vacuum pump

[0062] 40 control circuitry

[0063] 42 monitoring or predictive monitoring circuitry

Claims

CLAIMS1 . A vacuum pump system for evacuating a process chamber comprising: a first and a second vacuum pump arranged in parallel and each comprising respective first and second valves for controlling a rate of flow of fluid into said respective first and second vacuum pumps; control circuitry configured: to control said first and second valves and first and second vacuum pumps during a first period of operation, such that each of said valves is partially open and a cumulative pumping performance of said first and second vacuum pumps comprises a first pumping performance; and in response to determining that one of said first and second pumps is to be shut down, to close one of said first and second valves and to more fully open the other of said first and second valves, such that the pumping performance of said pump with said more fully open valve comprises said first pumping performance.

2. A vacuum pump system according to claim 1 , wherein said control circuitry is configured during said first period of operation to control each of said first and second valves to be open enough to allow a respective pump to pump at least 40% of said first pumping performance.

3. A vacuum pump system according to claim 2, wherein said control circuitry is configured to control said first and second valves to be partially open by different amounts such that one of said vacuum pumps pumps a greater proportion of said first pumping performance than the other.

4. A vacuum pump system according to claim 1 or 2, wherein said control circuitry is configured to control said first and second valves to be partially open such that each pump pumps substantially 50% of said first pumping performance.

5. A vacuum pump system according to any preceding claim wherein said first and second vacuum pumps and valves are arranged on parallel first andsecond process lines, said first and second process lines connecting to a further process line providing fluid communication with a process chamber.

6. A vacuum pump system according to any preceding claim, wherein said further process line comprises a booster pump and said first and second vacuum pumps comprise backing pumps.

7. A vacuum pump system according to any preceding claim, wherein said first and second vacuum pumps each comprise a plurality of vacuum pumps arranged in series.

8. A vacuum pump system according to any preceding claim, said control circuitry comprising determining circuitry configured to determine when a pump starts to fail and to select said pump as said pump to be shut down.

9. A vacuum pump system according to claim 8, wherein said determining circuitry comprises monitoring circuitry configured to monitor performance of said pumps.

10. A vacuum pump system according to claim 8 or 9, wherein said determining circuitry comprises predictive circuitry configured to predict a failure of said pumps.

11. A method of evacuating a process chamber using a first and a second vacuum pump arranged in parallel process lines, said parallel process lines providing parallel flow paths to said process chamber, wherein flow through each of said pumps is controlled by respective valves; said method comprising: operating said first and second vacuum pumps at a first and second speed respectively; controlling said respective valves such that each of said valves is partially open and process gas is pumped by both pumps, a cumulative pumpingperformance of said first and second vacuum pumps comprising a first pumping performance; determining that one of said pumps is to be shut down, and in response: closing the respective valve of said pump to be shut down such that said pump is isolated from said process chamber and more fully opening the other valve, such that the pumping performance through said pump that is not isolated comprises said first pumping performance.

12. A method according to claim 11 , wherein said step of controlling said respective valves such that each of said valves is partially open comprises controlling said respective valves such that each is open by a different amount such that each pump provides a minimum of 40% of said pumping performance.

13. A method according to claim 11 , wherein said step of controlling said respective valves such that each of said valves is partially open comprises controlling said respective valves such that each is open by substantially a same amount such that each pump provides substantially 50% of said pumping performance.

14. A method according to any one of claims 11 to 13, wherein said step of determining that one of said pumps is to be shut down comprises monitoring at least one of a temperature, pressure, vibrations, current or power consumed by said pumps for changes indicative of an imminent pump shut down.

15. A method according to any one of claims 11 to 14 wherein said step of determining that one of said pumps is to be shut down comprises using predictive circuitry to predict a failure of one of said pumps.

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