GB2407132A

GB2407132A - Multiple vacuum pump system with additional pump for exhaust flow

Info

Publication number: GB2407132A
Application number: GB0324067A
Authority: GB
Inventors: Derek Graeme Madgwick Savidge; Phillip North; Alan Lindsey Purvis; Nigel Paul Schofield; David Wong
Original assignee: BOC Group Ltd
Current assignee: BOC Group Ltd
Priority date: 2003-10-14
Filing date: 2003-10-14
Publication date: 2005-04-20
Also published as: TWM279740U; CN2767710Y; FR2860841A3; GB0324067D0; JP3108228U; FR2860841B3; DE202004015599U1; KR200372323Y1

Abstract

A vacuum pumping system comprises a plurality of vacuum pumps (P1 to P8), each for pumping fluid from a respective load lock chamber (C1 to C8). To reduce the fluid pressure at the pump outlets, and thus reduce the power consumption of the pumps, the fluid exhausted from the pumps is conveyed to an additional pump (Pexhaust), which pumps all of the exhaust fluid. To prevent overloading of the additional pump when a number of the chambers are being simultaneously evacuated, a blow-off valve (60) selectively diverts some of the exhaust fluid away from the additional pump.

Description

IMPROVEMENTS IN PUMPING EFFICIECY

This invention relates to improvements in pumping efficiency, and in particular to the reduction in power consumption of a vacuum pumping system having a plurality of pumps.

Vacuum processing is commonly used in the manufacture of semiconductor devices to deposit thin films on to substrates. Typically, a processing chamber is evacuated using a vacuum pump to a very low pressure, which, depending on the lo type of process, may be as low as 106mbar, and feed gases are introduced to the evacuated chamber to cause the desired material to be deposited on one or more substrates located in the chamber. Upon completion of the deposition, the substrate is removed from the chamber and another substrate is inserted for repetition of the deposition process.

Significant vacuum pumping time is required to evacuate the processing chamber to the required pressure. Therefore, in order to maintain the pressure in the chamber at or around the required level when changing substrates, transfer chambers and load lock chambers are typically used. The load lock chamber is connected to the transfer chamber by a first window or passageway that can be selectively opened to allow substrates to be inserted into and removed from the transfer chamber. The capacity of the load lock chamber can range from just a few litres to several thousand litres for some of the larger flat panel display tools.

The load lock also has a second window, which can be selectively opened to the 2.S atmosphere to allow substrates to be inserted into and removed from the load lock chamber. In use, the processing chamber is maintained at the desired vacuum by the processing chamber vacuum pump. With the first window closed, the second window is opened to the atmosphere to allow the substrate to be inserted into the load lock chamber. The second window is then closed, and, using a load lock So vacuum pump, the load lock chamber is evacuated until the load lock chamber is at substantially the same pressure as the transfer chamber. The first window is then opened to allow the substrate to be transferred to the transfer chamber. The - 2 transfer chamber is then evacuated to a pressure at substantially the same pressure as the processing chamber, whereupon the substrate is transferred to the processing chamber.

When vacuum processing has been completed, the processed substrate is transferred back to the load lock chamber. With the first window closed to maintain the vacuum in the processing chamber, the pressure in the load lock chamber is brought up to atmospheric pressure by allowing a nonreactive gas, such as air or nitrogen, to flow into the load lock chamber. When the pressure in lo the load lock chamber is at or near atmospheric pressure, the second window is opened to allow the processed substrate to be removed. Thus, for a load lock chamber, a repeating cycle of evacuation from atmosphere to a low or medium vacuum is required.

Load lock pumps are typically oil-free in their vacuum chambers, as any lubricants present in the vacuum chambers might cause contamination of the clean environment in which the vacuum processing is performed. Such "dry" vacuum pumps are commonly multi-stage positive displacement pumps employing inter-meshing rotors. The rotors may have the same type of profile in each stage so or the profile may change from stage to stage. An example of such a pump suitable for use as a load lock vacuum pump is one of the "iL" series of BOO Edwards dry vacuum pumps.

Factors that contribute towards the power drawn by a vacuum pump include power to overcome parasitic losses, power to compress the fluid to be pumped, and power losses due to motor inefficiencies. In order to reduce the power required to compress the pumped fluid, it is known to reduce the pump exhaust pressure. For example, the Ulvac Eco-Shock attachment provides an additional pump for pumping gases exhaust from a vacuum pump.

In a semiconductor processing plant, vacuum processing may be simultaneously performed in a number of reaction chambers, each having a respective load lock. - 3

_

To provide such an attachment for each load lock vacuum pump would significantly increase costs, and increase both the number of power supplies required for the pumping system and the overall foot-print of the pumping system.

In at least its preferred embodiment, the present invention seeks to solve these and other problems.

In a first aspect the present invention provides a vacuum pumping system comprising a plurality of vacuum pumps each for pumping fluid from a respective chamber, means for conveying fluid exhaust from the pumps to an additional lo pump for pumping the exhaust fluid, and, in fluid communication with said conveying means, means for selectively diverting exhaust fluid away from the additional pump.

By connecting two or more vacuum pumps to a common exhaust which conveys the fluid exhaust from the pumps to an additional pump which pumps the exhaust fluid, the fluid pressure at the pump outlets can be reduced from around 1000 mbar (atmospheric pressure) to a pressure in the range from, for example, 10 mbar to 100 mbar. Reducing the pressure difference between the pump inlet and the pump outlet by a factor of 10 or more can significantly reduce the power required to compress the fluid pumped from the chambers, and thus significantly reduce power consumption in each of the vacuum pumps.

Where the vacuum pumps comprise load lock pumps for evacuating a plurality of load lock chambers, the mass flow rate of exhaust fluid from the pump outlets will vary depending on the number of load lock chambers currently being evacuated from a relatively high pressure, for example, after substrates have been inserted in the chambers. As a result, the mass flow rate of the exhaust fluid from the pumps, and thus the pressure at the inlet to the additional pump, will typically vary significantly with time. In the event that the throughput of the load lock pumps so should exceed the throughput of the additional pump, when, say, four or more load lock chambers are simultaneously being evacuated from a relatively high pressure, "excess" exhaust fluid is diverted away from the pump in order to - 4 prevent the fluid pressure upstream from the additional pump from exceeding the fluid pressure downstream of the additional pump, and thus avoid overloading of the inlet stage of the additional pump and exhaust stage of the load lock pumps.

Thus, a single, relatively low capacity and low powered pump can be used as the pump for the exhaust fluid from all of the vacuum pumps. As a result, it is anticipated that the cost of providing and running this additional pump can be more than compensated for by the annual costs saved by reducing the power consumption of the vacuum pumps.

Preferably, the conveying means comprises a plurality of first conduits each for conveying exhaust fluid from a respective vacuum pump to a second conduit for receiving the exhaust fluid from each of the first conduits and conveying the exhaust fluid towards the additional pump.

Preferably, the diverting means comprises a valve. The valve may comprise a valve inlet for receiving the second stream of exhaust fluid, a valve outlet, and means permitting the second stream to flow from the valve inlet to the valve outlet when the pressure differential between the valve inlet and the valve outlet exceeds so a predetermined value, for example, around 50 mbar. Conveniently, the valve may be in the form of a ball valve, comprising a ball arranged to seat against a valve seat to prevent passage of fluid from the valve outlet to the valve inlet and being displaceable, in use, from the valve seat by pressurised exhaust fluid at the valve inlet end to permit passage of the exhaust fluid from the valve inlet to the as valve outlet. Preferably, the additional pump has an outlet in fluid communication with the valve outlet, so that the valve outlet and the pump outlet are at the same pressure.

Preferably, the conveying means comprises, upstream of the additional pump, so means for separating the fluid exhaust from the pumps into a first stream flowing towards the additional pump and a second stream flowing towards the valve. - 5

In one embodiment, the separating means may comprise a bifurcation for splitting the flow of exhaust fluid from the pumps into two streams. In another embodiment, the separating means also comprises a three-way valve, which comprises a valve inlet for receiving the fluid exhaust from the pumps, a first valve outlet for outputting received exhaust fluid towards the additional pump and a second valve outlet for outputting received exhaust fluid away from the additional pump. Means may be provided for selectively controlling the three-way valve either to output received exhaust fluid from the first valve outlet only or to output exhaust fluid from both the first valve outlet and the second valve outlet. For lo example, a sensor may be provided for sensing the pressure of the exhaust fluid at the valve inlet, the control means being arranged to control the three-way valve in dependence on an output from the sensor. This can enable the second valve outlet to be opened if the pressure at the valve inlet exceeds a predetermined level, for example, if, say, more than three chambers were being evacuated from a I5 relatively high pressure. The blow-off valve located downstream from the second valve outlet can provide a safety feature in the event of failure of the three-way valve to close the second valve outlet when the pressure falls below the predetermined level.

so Alternatively, or additionally, means may be provided for monitoring the power consumption of the vacuum pumps, the control means being arranged to control the additional valve in dependence on an output from the monitoring means.

This can enable the second valve outlet to be opened if the power consumption of the pumps increases above a predetermined level, which may also be indicative of the current evacuation from a relatively high pressure of a number of chambers by the pumps and thus a current, or anticipated, increase in the flow rate of the exhaust gases being conveyed to the additional pump. In another alternative, the monitoring means may monitor the opening and closing of valves located between the chambers and the pumps.

The system preferably comprises, in fluid communication with said conveying means, an additional chamber for pumping using the additional pump. Providing - 6 such a chamber can reduce the pressure increase at the inlet to the additional pump when one or more of the load lock chambers are evacuated from a relatively high pressure, which can assist in avoiding overload of the additional pump.

s The minimum pressure of the exhaust fluid may be controlled by the amount of a purge gas continuously pumped by the vacuum pumps. However, where no purge gas is used, then the exhaust fluid could be pumped down as low as the ultimate vacuum of the additional pump, which, depending on the nature of the additional pump, may be lower than 1 mbar. As pumping the exhaust fluid down lo lower than, say, 5 mbar, can reduce the overall efficiency of the pumping system, the system preferably comprises means for controlling the power consumption of the additional pump. The power consumption can then be reduced as and when required to prevent the additional pump from pulling a vacuum lower than, say 5 mbar.

In a second aspect, the present invention provides a method of vacuum pumping a plurality of chambers, comprising providing for each chamber a respective vacuum pump, driving the vacuum pumps to evacuate the chambers, conveying fluid exhaust from the vacuum pumps to an inlet of an additional pump for pumping the go fluid exhaust from the pumps, and selectively diverting exhaust fluid away from the additional pump to maintain the pressure of the exhaust fluid at the inlet below a predetermined level.

Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a vacuum pumping system; and Figure 2 illustrates the variation of power consumption with exhaust pressure for a so BOO Edwards iL600 pump. - 7

With reference to Figure 1, an embodiment of a vacuum pumping system 10 comprises a plurality (eight shown in Figure 1, although any suitable number of pumps could be provided) of vacuum pumps P1 to P8 each connected to a respective chamber C1 to C8 via respective valves V1 to V8. In this embodiment, each of the chambers C1 to C8 is a load lock chamber of a semiconductor processing system, and each of the vacuum pumps is a load lock pump.

Examples of suitable pumps for use as a load lock pump include the BOC Edwards iL70 and iL600 dry pumps.

lo The outlet of each of the load lock pumps C1 to C8 is connected to a respective conduit 20. The conduits 20 convey fluid exhaust from the load lock pumps to a common exhaust 30, which includes conduits 32, 34. A bifurcation N5 has an inlet 40 for receiving all of the fluid exhaust from the load lock pumps, a first outlet 42 for outputting exhaust fluid towards the inlet 50 of an exhaust pump Exhaust, and a second outlet 44 for outputting exhaust fluid towards the inlet 62 of a blow- off valve 60. The exhaust pump may also be in the form of a dry pump, such as a BOC Edwards iL70 pump. The exhaust pump has an outlet 52 connected via conduits 54 and 56 to the outlet 64 of the blow-off valve 60.

In use, the load lock chambers C1 to C8 are maintained at a low pressure, typically in the range from 10-2 to 103mbar, by the load lock pumps P1 to P8. The fluid exhaust from the load lock pumps is conveyed to the exhaust pump, which in turn exhausts the fluid to atmosphere. As indicated in Figure 1, a light purge gas, such as nitrogen, may be supplied to each of the load lock pumps at, for example, 4 sipm, and so, in the presence of such a purge gas, the amount of fluid exhaust from the load lock pumps and subsequently conveyed to the exhaust pump will be at least 32 sipm. At such a flow rate, the exhaust pump is able to reduce the fluid pressure at the outlets of the load lock pumps to less than 100 mbar, typically to around 12 mbar or less. With reference to Figure 2, reducing the exhaust so pressure of a load lock pump from 1000 mbar (atmospheric pressure) to around 12 mbar can significantly reduce the power consumption of that pump. For example, the average power saving for a single BOC Edwards iL600N pump - 8 operating at 60 Hz with an exhaust pressure at around 5 mbar is anticipated to be around 0.6kW, which could provide an annual cost saving of around $300. For an eight pump system as illustrated in Figure 1 comprising, say five iL70 pumps and three iL600 pumps, the annual cost saving is anticipated to be in excess of $1000.

In use, each of the load lock chambers C1 to C8 will be periodically pressurised back up to atmospheric pressure, for example, using a source of non-reactive gas such as air or nitrogen. Considering this pressurization for, for example, load lock chamber C1, firstly valve V1 is closed to isolate the load lock pump P1 from the lo chamber C1. Gas is then supplied to chamber C1 to bring the chamber back up to atmospheric pressure to enable a processed substrate to be removed from the chamber and a fresh substrate inserted for subsequent processing. Valve V1 is then opened to enable the chamber C1 to be evacuated by the load lock pump P1.

Is While the chamber is being evacuated, there will be an increase in the mass flow rate of fluid exhaust from the pump P1, which will increase the pressure of the exhaust fluid at the inlet 50 of the exhaust pump Pexhaus. Providing that the pressure at the inlet 50 of the exhaust pump does not exceed the pressure at the outlet 52 of the exhaust pump, the exhaust pump will be able to efficiently pump so the exhaust fluid. However, depending on the length of the process being conducted in each of the processing chambers (not shown) linked to the load lock chambers, it is possible that more than one of the load lock chambers may be being evacuated at the same time. By providing a blow-off valve 60 in fluid communication with the inlet 50 of the exhaust pump, it is possible to avoid a as situation where the rate of flow of fluid from the load lock pumps P1 to P8 is so great as to cause the exhaust pump to become overloaded. For example, if the pressure differential between the inlet 62 and outlet 64 of the blow-off valve 60 were to become greater than, say 50 mbar, the pressurised exhaust fluid would cause the ball 66 of the valve 60 to move away from the valve seat 68, enabling so exhaust fluid to by-pass the exhaust pump 50 and be discharged to the atmosphere. Once the pressure differential has fallen back to below 50 mbar, the - 9 - valve 60 closes, and all of the exhaust fluid is once again exhaust via the exhaust pump.

The minimum pressure of the exhaust fluid is controlled by the amount of purge gas continuously pumped by the vacuum pumps. However, where no purge gas is used, then the exhaust fluid could be pumped down as low as the ultimate vacuum of the exhaust pump, which could be lower than 1 mbar. As pumping the exhaust fluid down lower than, say, 5 mbar, can reduce the overall efficiency of the pumping system, a control system may be provided to control the power lo consumption of the exhaust pump. The power consumption can then be reduced as and when required to prevent the exhaust pump from pulling a vacuum lower than, say 5 mbar.

As shown in Figure 1, an additional chamber 70 may be provided downstream Is from the load lock pumps P1 to P8 for pumping using the exhaust pump.

Providing such a chamber 70 can reduce the pressure increase at the inlet to the exhaust pump when one or more of the load lock chambers C1 to C8 is evacuated, which can assist in avoiding overload of the inlet stage of the exhaust pump and the exhaust stage of the load lock pumps.

It is to be understood that the foregoing represents one embodiment of the invention, others of which will no doubt occur to the skilled addressee without departing from the true scope of the invention as defined by the claims appended hereto.

For example, instead of, or in addition to, the blow-off valve 60, a three-way valve may be provided at bifurcation N5. This valve can be controlled to direct exhaust fluid towards and/or away from the exhaust pump as required to avoid overloading of the exhaust pump. For instance, a sensor may be provided for sensing the so pressure of the exhaust fluid at the inlet 40. Depending on an output from the sensor, the valve can be controlled to direct fluid through outlet 44, that is, away from the exhaust pump, if the pressure at the inlet 40 exceeds a predetermined level, for example, if, say, more than three load lock chambers were being evacuated simultaneously. Alternatively, or additionally, the power consumption of the load lock pumps may be monitored, and the three-way valve controlled to open the second outlet 44 if the power consumption of the pumps increases above s a predetermined level, which may also be indicative of the current evacuation from a relatively high pressure of a number of chambers by the pumps, and thus a current, or anticipated, increase in the flow rate of the exhaust gases being conveyed to the exhaust pump. In another alternative, the three-way valve may be controlled by monitoring the status of the valves V1 to V8. A blow-off valve 60 lo located downstream from the outlet 44 can provide a safety feature in the event of failure of the three-way valve to close the second outlet 44 when the fluid pressure at the inlet 40 falls below the predetermined level.

In summary, a vacuum pumping system comprises a plurality of vacuum pumps, Is each for pumping fluid from a respective load lock chamber. To reduce the fluid pressure at the pump outlets, and thus reduce the power consumption of the pumps, the fluid exhausted from the pumps is conveyed to an additional pump, which pumps all of the exhaust fluid. To prevent overloading of the additional pump when a number of the chambers are being simultaneously evacuated, a so blow-off valve selectively diverts some of the exhaust fluid away from the additional pump. - 11

Claims

1. A vacuum pumping system comprising a plurality of vacuum pumps each for pumping fluid from a respective chamber, means for conveying fluid exhaust from the pumps to an additional pump for pumping the exhaust fluid, and, in fluid communication with said conveying means, means for selectively diverting exhaust fluid away from the additional pump.

lo

2. A system according to Claim 1, wherein the conveying means comprises a plurality of first conduits each for conveying exhaust fluid from a respective vacuum pump to a second conduit for receiving the exhaust fluid from each of the first conduits and conveying the exhaust fluid towards the additional pump.

3. A system according to Claim 1 or Claim 2, wherein the diverting means comprises a valve.

4. A system according to Claim 3, wherein the valve comprises a valve so inlet for receiving the second stream of exhaust fluid, a valve outlet, and means permitting the second stream to flow from the valve inlet to the valve outlet when the pressure differential between the valve inlet and the valve outlet exceeds a predetermined value.

as

5. A system according to Claim 4, wherein the valve comprises a ball arranged to seat against a valve seat to prevent passage of fluid from the valve outlet to the valve inlet and being displaceable, in use, from the valve seat by pressurised exhaust fluid at the valve inlet end to permit passage of the exhaust fluid from the valve inlet to the valve outlet. 12

6. A system according to Claim 4 or Claim 5, wherein the additional pump has an outlet in fluid communication with the valve outlet.

7. A system according to any preceding claim, wherein the conveying means comprises, upstream of the additional pump, means for separating the fluid exhaust from the pumps into a first stream flowing towards the additional pump and a second stream flowing towards the diverting means.

lo

8. A system according to Claim 7, wherein the separating means comprises a three-way valve comprising a valve inlet for receiving the fluid exhaust from the pumps, a first valve outlet for outputting received exhaust fluid towards the additional pump and a second valve outlet for outputting received exhaust fluid away from the additional pump.

9. A system according to Claim 8, comprising means for selectively controlling the three-way valve either to output received exhaust fluid from the first valve outlet only or to output exhaust fluid from both the first valve outlet and the second valve outlet.

10. A system according to Claim 9, comprising a sensor for sensing the pressure of the exhaust fluid at the valve inlet, the control means being arranged to control the three-way valve in dependence on an output from the sensor.

11. A system according to Claim 9 or Claim 10, comprising means for monitoring the power consumption of the vacuum pumps, the control means being arranged to control the three-way valve in dependence so on an output from the monitoring means.

-13 - , .

12. A system according to any preceding claim, comprising, in fluid communication with said conveying means, an additional chamber for pumping using the additional pump.

13. A system according to any preceding claim, comprising means for controlling the power consumption of the additional pump.

14. A system according to any preceding claim, wherein the vacuum pumps comprise a plurality of load lock vacuum pumps each for lo evacuating a respective load lock chamber.

15. A method of vacuum pumping a plurality of chambers, comprising providing for each chamber a respective vacuum pump, driving the vacuum pumps to evacuate the chambers, conveying fluid exhaust s from the vacuum pumps to an inlet of an additional pump for pumping the fluid exhaust from the pumps, and selectively diverting exhaust fluid away from the additional pump to maintain the pressure of the exhaust fluid at the inlet below a predetermined level.

so

16. A vacuum pumping system or a method of vacuum pumping substantially as herein described with reference to Figure 1 of the accompanying drawings.