FR2860841A3 - IMPROVEMENTS IN THE EFFICIENCY OF A PUMPING SYSTEM - Google Patents

Abstract

The pumping system for evacuating comprises a plurality of vacuum pumps (P1 to P8) each for pumping fluid from a respective loading chamber (C1 to C8). In order to reduce the pressure of the fluid at the discharge outlets of the pumps and thereby reduce the energy consumption of the pumps, the fluid discharged from the pumps is conveyed to an additional pump (exhaust) which pumps all the fluid discharged. To prevent an additional pump surface when multiple loading locks are simultaneously being evacuated, a purge valve (60) selectively deflects a portion of the fluid removed from the supplemental pump.

Description

2860841 1

  The present invention relates to improvements made to the pumping efficiency, and in particular to the reduction of the energy consumption of a pumping system for evacuating a pump. plurality of pumps.

  Vacuum treatment is commonly used in the manufacture of semiconductor devices for the deposition of thin films on substrates. Typically, a treatment chamber is evacuated to very low pressure using a vacuum pump, which pressure, depending on the type of process, can go down to 10-6 mbar, and feed gases are introduced into the evacuated chamber to deposit the desired material on one or more substrates placed in the chamber. Once deposition is complete, the substrate is removed from the chamber and another substrate is inserted for repetition of the deposition process.

  A large pumping time is required to evacuate the treatment chamber to the required pressure. Therefore, in order to maintain the pressure in the chamber at or near the required level when changing the substrates, transfer chambers and loading chambers are usually used. The lock chamber is connected to the transfer chamber by a first porthole or passage that can be selectively opened to allow the substrates to be inserted and removed from the transfer chamber. The capacity of the cargo lock can range from a few liters up to several thousand liters for some of the largest flat billboard tools. The loading chamber also has a second porthole that can be selectively opened to the atmosphere to allow the insertion and removal of the cargo from the cargo lock. In use, the treatment chamber is maintained under the desired vacuum by the vacuum pump of the treatment chamber. The first porthole being closed, the second porthole is open to the atmosphere to allow insertion of the substrate in the loading chamber. The second window is then closed and, using a vacuum pump for the loading chamber, the loading chamber is evacuated until it is essentially at the same pressure as the transfer chamber. The first porthole is then opened to allow the transfer of the substrate into the transfer chamber. The transfusion chamber is then evacuated to a pressure which is essentially the same as the treatment chamber, whereupon the substrate is transferred to the treatment chamber.

  When the vacuum treatment is finished, the substrate after treatment is again transferred to the loading chamber. While the first porthole is closed to maintain the vacuum in the process chamber, the pressure in the loading chamber is brought to atmospheric pressure by allowing a non-reactive gas, such as, for example, air or gas. nitrogen, to enter the loading chamber. When the pressure in the loading chamber is at or near atmospheric pressure, the second porthole is opened to allow removal of the prepared substrate. Thus, for a loading chamber, a repetitive evacuation cycle which starts from atmospheric pressure and goes to a primary or medium vacuum is necessary.

  The airlock pumps are typically oil-free in their vacuum chambers because any lubricant present in the vacuum chambers could cause contamination of the clean environment in which the vacuum treatment is performed. These "dry" vacuum pumps are often multi-stage volumetric pumps using meshing rotors. The rotors can have the same type of profile for each floor or the profile can change from one floor to another. An example of such a pump suitable for use as a loading lock pump is one of the "iL" pumps of BOC Edwards dry vacuum pumps.

  The factors contributing to the power demanded by a vacuum pump include the power to overcome parasitic losses, the power to compress the fluid to be sucked, and the power losses due to engine failure. To reduce the power required to compress the aspirated fluid, it is known to reduce the discharge pressure of the pump. The Ulvac EcoShock auxiliary device provides, for example, an additional pump for pumping the exhaust gases from a vacuum pump.

  In a semiconductor manufacturing facility, the vacuum treatment can be carried out simultaneously in several reaction chambers, each equipped with a respective loading chamber. The presence of such an auxiliary device for each vacuum pump for a loading chamber would considerably increase the costs and increase both the number of energy sources claimed for the pumping system and the total footprint of the pumping system. . In its preferred embodiment at least, the present invention solves these and other problems.

  The present invention provides a vacuum pumping system comprising a plurality of vacuum pumps, each for pumping a fluid from a respective chamber, means for conveying the fluid discharged from the pumps to an additional pump for pumping the pump. fluid evacuated, and in fluid communication with said conveying means, means for selectively diverting the evacuated fluid from the additional pump.

  2860841 3 By connecting two or more vacuum pumps to a common drain which conveys the fluid discharged from the pumps to an additional pump that pumps the discharged fluid, the pressure of the fluid at the discharge ports of the pumps can be reduced by about 1000 mbar. (atmospheric pressure) to a pressure of the order of, for example, 10 mbar to 100 mbar. Reducing the pressure difference between the suction port of the pumps and the discharge port of the pumps by a factor of 10 or more can significantly reduce the power required to compress the fluid drawn from the chambers and thereby reduce importantly the energy consumption in each of the vacuum pumps.

  When the vacuum pumps comprise loading lock pumps for evacuating a plurality of loading locks, the mass flow rate of the fluid discharged from the pump backs will vary according to the number of loading locks being evacuated from a relatively high pressure, for example after substrates have been inserted into the chambers. As a result, the mass flow rate of the fluid discharged from the pumps, and thus the inlet pressure of the additional pump, will typically vary significantly over time. In the case where the flow rate of the loading lock pumps exceeds the flow rate of the additional pump, as when, for example, four or more loading chambers are discharged simultaneously from a relatively high pressure, the fluid discharged "in excess "is diverted from the pump so as to prevent the fluid pressure upstream of the additional pump from exceeding the fluid pressure downstream of the additional pump and thus to avoid overloading the inlet stage of the pump. the additional pump and the discharge stage of the pumps of the loading chamber.

  Thus, a single pump of relatively low power and capacity can be used as a pump for the fluid discharged from all vacuum pumps. As a result, it can be anticipated that the cost of supply and operation of this additional pump may be more than offset by the annual expenses saved by reducing the energy consumption of the vacuum pumps.

  Preferably, the conveying means comprise a plurality of first conduits each serving to convey a fluid discharged from a respective vacuum pump to a second conduit intended to receive the fluid discharged from each of the first conduits and to convey the fluid discharged to the additional pump.

  Preferably, the diverting means (or diversion) comprise a valve. The valve may include a valve inlet for receiving an evacuated fluid, a valve outlet, and means for allowing the evacuated fluid to flow from the valve inlet to the valve outlet when the pressure difference between the valve and the valve outlet. the valve inlet and the valve outlet exceeds a predetermined value, for example about 50 mbar. Conveniently, the valve may be in the form of a ball valve comprising a ball 2860841 4 positioned to abut a valve seat to prevent passage of fluid between the valve outlet and the valve. valve inlet, and which, in use, is movable from the valve seat by the fluid discharged under pressure at the inlet end of the valve to allow the passage of the fluid discharged from the inlet of the valve until the exit of the valve.

  Preferably, the additional pump has a discharge outlet in fluid communication with the outlet of the valve, so that the valve outlet and the pump outlet are at the same pressure.

  Preferably, the conveying means comprise, upstream of the additional pump, means for separating the fluid discharged from the pumps in a first stream flowing towards the additional pump and a second stream flowing towards the valve. .

  In one embodiment, the separation means may comprise a bifurcation to divide the flow of fluid discharged from the pumps into two streams. In another embodiment, the separating means may also comprise a three-way valve, which has a valve inlet for receiving the fluid discharged from the pumps, a first valve outlet for sending to the additional pump the evacuated fluid. received and a second valve outlet for diverting the discharged fluid received from the additional pump. Means may be provided for selectively controlling the three-way valve either to send the discharged fluid received only from the first outlet of the valve, or to send the fluid discharged from both the first outlet of the valve and the second output of the valve. A sensor may for example be provided to detect the pressure of the fluid discharged at the inlet of the valve, the control means being arranged to control the three-way valve in dependence on an output of the sensor. This may allow the second valve outlet to be opened if the pressure at the valve inlet exceeds a predetermined level, for example if more than three chambers have been evacuated from a relatively high pressure. The purge valve located downstream of the second valve outlet can provide a safety element in the event of a failure of the three-way valve by closing the second valve outlet when the pressure drops below the predetermined level .

  Alternatively, or in addition, means may be provided for monitoring the energy consumption of the vacuum pumps, the control means being provided for controlling the additional valve in dependence on an output quantity of the monitoring means. This may allow the second valve outlet to be open if the energy consumption of the pumps increases beyond a predetermined level, which may also be indicative of the current evacuation, from a relatively high pressure. , several rooms by the pumps and, thus, a current or anticipated increase in the flow of exhaust gases that are routed to the additional pump. In another variant, the monitoring means can control the opening and closing of the 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. The presence of this chamber can reduce the pressure increase at the inlet of the additional pump when one or more of the loading locks are evacuated from a relatively high pressure, which can help to avoid an overload of the additional pump.

  The minimum pressure of the evacuated fluid can be controlled by the amount of a purge gas pumped continuously by the vacuum pumps. However, when no purge gas is used, the evacuated fluid can then be pumped to a value as low as the limit vacuum of the additional pump which, depending on the nature of the additional pump, may be less than 1 mbar. Since pumping the evacuated fluid to less than 5 mbar, for example, may decrease the overall efficiency of the pumping system, the system preferably includes means for controlling the energy consumption of the supplemental pump. The power consumption can then be decreased as and when it is necessary to prevent the additional pump from producing a vacuum less than, for example, 5 mbar.

  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 pumping system for evacuating; and Figure 2 illustrates the variation in power consumption versus discharge pressure for a BOC Edwards iL600 pump.

  Referring to FIG. 1, one embodiment of a vacuum pumping system 10 includes a plurality (eight shown in FIG. 1, although any suitable number of pumps may be provided) of pump pumps. vacuum, P1 to P8, each connected to a respective chamber, C1 to C8, through respective valves, V1 to V8. In this embodiment, each of the chambers C1 to C8 is a load lock of a semiconductor manufacturing system, and each of the vacuum pumps is a loading lock pump. Examples of suitable pumps for use as a loading dock pump are the BOC Edwards iL70 and iL600 dry pumps.

  The discharge outlet of each of the pumps P 1 to P 8 of the loading chamber is connected to a corresponding conduit 20. The conduits 20 convey the fluid discharged from the pumps for loading lock to a common evacuation 30 which comprises conduits 32, 34. An N5 bifurcation has an inlet 40 for receiving all of the fluid evacuated from the loading lock pumps, a first outlet 42 for sending the discharged fluid to the inlet 50 of a pump for the exhaust and a second exhaust pipe 2860841. outlet 44 for sending the evacuated fluid to the inlet 62 of a purge valve 60. The pump for the exhaust may also be in the form of a dry pump, such as the BOC Edwards iL70 pump. The pump for the exhaust has an outlet 52 connected via the conduits 54 and 56 to the outlet 64 of the purge valve 60.

  In use, the loading locks C 1 to C 8 are maintained at low pressure, typically in a range of 10 -2 to 10 -3 mbar, by the pumps P 1 to P 8 of the loading chamber The fluid evacuated from the pumps Loading locks are routed to the exhaust pump which, in turn, discharges the fluid into the atmosphere As shown in Figure 1, a light purge gas, for example nitrogen, can be supplied. at each of the loading chamber pumps at, for example, 4 slpm (standard liters per minute), and thus, in the presence of this purge gas, the quantity of fluid discharged from the pumps of the loading chamber and then sent to the pump for the exhaust shall be at least 32 slpm At such a rate, the pump for the exhaust is capable of lowering the pressure of the fluid at the discharge outlets of the pumps of the loading chamber to less than 100 mbar, and typically up to about 12 mbar or less, with reference to Figure 2, the reductio n the discharge pressure of a loading lock pump of 1000 mbar (atmospheric pressure) up to about 12 mbar can considerably reduce the energy consumption of this pump. For example, the average energy saving expected for an individual BOC Edwards iL600N pump operating at 60 Hz with a delivery pressure of around 5 mbar will be around 0.6 kW, which could result in savings. annual cost of about $ 300. For an eight-pump system as illustrated in Figure 1 including, for example, five iL70 pumps and three iL 600 pumps, an annual cost saving of more than $ 1000 can be expected.

  In use, each of the loading chambers C 1 to C 8 will periodically be brought back to atmospheric pressure, for example by using a source of non-reactive gas such as air or nitrogen. By studying this pressurization for, for example, the air-lock C1, the valve V1 is first closed to isolate the pump P 1 of the lock-sas-ment of the lock C1. Gas is then supplied to the Cl lock to bring the airlock back to atmospheric pressure to allow a transformed substrate to be removed from the chamber and a new substrate to be inserted for further processing. The valve V1 is then open to allow the evacuation of the airlock by the pump P 1 of the lock.

  During evacuation of the chamber, there will be an increase in the mass flow rate of the fluid discharged from the pump P1, which will increase the pressure of the fluid discharged to the suction inlet 50 of the pump for the exhaust. ensuring that the pressure at the inlet 50 of the pump for the exhaust does not exceed the pressure at the discharge outlet 52 of the pump for the exhaust, the pump for the exhaust will be able to pump effectively the evacuated fluid. However, depending on the duration of the process performed in each of the processing chambers (not shown) connected to the loading lock, it is possible that several locks can be evacuated at the same time. The presence of a purge valve 60 in fluid communication with the suction inlet 50 of the pump for the exhaust, it is possible to avoid a situation where the flow of fluid from the pumps P1 to P8 of the airlock loading would be so important that it would result in an overload of the pump for the exhaust. If, for example, the pressure difference between the inlet 62 and the outlet 64 of the purge valve 60 becomes greater than 50 mbar, for example, the fluid discharged under pressure would cause the ball to leave the seat 68 of the valve, allowing the evacuated fluid to avoid the pump for the exhaust and to be discharged into the atmosphere. Once the pressure difference has fallen below 50 mbar, the valve 60 closes and all the evacuated fluid is once again evacuated via the pump for the exhaust.

  The minimum pressure of the evacuated fluid is controlled by the amount of purge gas pumped continuously by the vacuum pumps. However, when no purge gas is used, the evacuated fluid can be lowered to the vacuum limit of the pump for the exhaust, which may be less than 1 mbar. Since pumping the evacuated fluid down to less than 5 mbar, for example, can reduce the overall efficiency of the pumping system, a control system can be provided to regulate the energy consumption of the pump for the pump. exhaust. The energy consumption can then be decreased when and where it is necessary to prevent the pump for the exhaust from producing a depression lower than, for example, 5 mbar.

  As shown in FIG. 1, an additional chamber 70 may be provided downstream of the pumps P1 to P8 of the loading chamber for pumping using the pump for the exhaust. The presence of such a chamber 70 can reduce the pressure increase at the suction inlet of the pump for the exhaust when one or more load chambers C1 to C8 is evacuated This can help to avoid overloading the pump inlet stage for the exhaust and the pump discharge stage for the load locks.

  It will be understood that the foregoing represents only one embodiment of the invention, of which others of these will not fail to come to the mind of those skilled in the art without departing from the real scope of the invention.

  By way of example, instead of or in addition to the purge valve 60, a three-way valve can be placed at the N5 bifurcation. This valve can be controlled to direct the evacuated fluid to and / or away from the pump for the exhaust, as needed to avoid overloading the pump for the exhaust. For example, a sensor may be provided for detecting the pressure of the fluid discharged at the inlet 40. In dependence on an output quantity of the sensor, the valve may be controlled to send the fluid into the outlet 44; that is, diverting it from the pump for the exhaust, if the pressure at the inlet 40 exceeds a predetermined level, for example if more than three loading chambers 2860841 are evacuated simultaneously. Alternatively, or in addition, the energy consumption of the loading lock pumps can be monitored, and the three-way valve controlled to open the second outlet 44 if the energy consumption of the pumps increases above a predetermined level, which may also be indicative of an evacuation in progress, from a relatively high pressure, of several of the loading locks by the pumps, and therefore of a current or anticipated increase in the flow of the evacuated gases which are conveyed to the pump for the exhaust. In another variant, the three-way valve can be controlled by monitoring the status of the valves V1 to V8. A purge valve 60 located downstream of the outlet 44 may provide a safety element in the event of a failure of the three-way valve to close the second outlet 44 when the inlet fluid pressure 40 drops below the predetermined level.

  In summary, a pumping system for evacuating comprises a plurality of vacuum pumps, each for pumping the fluid from a respective loading chamber. To reduce the fluid pressure at the discharge outlets of the pumps and thus reduce the energy consumption of the pumps, the fluid discharged from the pumps is routed to an additional pump that pumps all the fluid discharged. To prevent over-charging of the additional pump, when more than one of the chambers are discharged simultaneously, a purge valve selectively deflects a portion of the fluid removed from the additional pump.

Claims (1)

9 CLAIMS   A vacuum pumping system comprising a plurality of vacuum pumps (P1-P8) each for pumping fluid from a respective chamber (C 1 -C 8), means (20, 30) for conveying the fluid discharged from the pumps to an additional pump (exhaust) for pumping the evacuated fluid, and, in fluid communication with said conveying means (20, 30), means (60) for selectively diverting the fluid from the additional pump; evacuated.   The system of Claim 1, wherein the conveying means comprises a plurality of first conduits (20) each for conveying the fluid discharged from a respective vacuum pump to a second conduit (30) for receiving the fluid discharged from each of the first conduits and to convey the fluid discharged to the additional pump.   A system as claimed in Claim 1 or Claim 2, wherein the diverting means comprises a valve (60).   The system of Claim 3, wherein the valve comprises a valve inlet (62) for receiving an evacuated fluid, a valve outlet (64), and means (66) for evacuating fluid to flow. from the valve inlet to the valve outlet when the pressure difference between the valve inlet and the valve outlet exceeds a predetermined value.   The system of Claim 4, wherein the valve comprises a ball (66) positioned to abut a valve seat (68) to prevent passage of fluid between the valve outlet (64) and the valve the inlet (62) of the valve, which in use is movable from the valve seat by the pressurized fluid at the inlet end of the valve to allow passage of the fluid discharged from the valve seat; inlet of the valve to the outlet of the valve.   The system of Claim 4 or Claim 5, wherein the supplemental pump has a discharge outlet (52) in fluid communication with the outlet (64) of the valve.   7. System according to any one of the preceding claims, wherein the conveying means comprise, upstream of the additional pump, means (N5) for separating the fluid discharged from the pumps in a first stream flowing to the pump. additional (exhaust,) and a second stream flowing to the diverting means (60).   The system of Claim 7, wherein the separating means comprises a three-way valve, which has a valve inlet (40) for receiving fluid discharged from the pumps, a first valve outlet (42) for sending to the An additional pump 2860841 10 fluid received and a second valve outlet (44) to divert the additional pump received fluid received.   9. A system as claimed in Claim 8, comprising means for selectively controlling the three-way valve to either send the discharged fluid received only from the first outlet of the valve, or to send the evacuated fluid from both the first outlet of the valve and the second outlet of the valve.   10. System according to claim 9, comprising a sensor for detecting the pressure of the fluid discharged at the inlet of the valve, the control means being arranged to control the three-way valve in dependence on an output of the sensor.   System according to Claim 9 or Claim 10, comprising means for monitoring the energy consumption of the vacuum pumps, the control means being provided for controlling the additional valve in dependence on an output quantity of the monitoring means. .   A system as claimed in any one of the preceding claims comprising, in fluid communication with said conveying means, an additional chamber (70) for pumping using the additional pump.   System according to any one of the preceding claims, comprising means for monitoring the energy consumption of the additional pump.   System according to any one of the preceding claims, wherein the vacuum pumps comprise a plurality of vacuum pumps (P1P8) for loading locks, each serving to evacuate a respective loading chamber (C1-C8).