REDUNDANT PUMPING SYSTEM AND PUMPING METHOD BY MEANS OF THIS PUMPING SYSTEM

Abstract

The present invention relates to a redundant vacuum pumping system (300) and a pumping method using this system, comprising a primary roots pump (302), a first pumping sub-system (310) and a second pumping sub-system (320), wherein the first pumping sub-system (310) and the second pumping sub-system (320) are arranged to pump in parallel the gas evacuated by the primary roots pump (302), the first pumping sub-system (310) comprising a first secondary roots pump (311) and a first positive displacement pump (312) and a first valve (313) positioned between the gas discharge outlet (302b) of the primary roots pump (302) and the gas suction inlet (311a) of the first secondary roots pump (311), and the second pumping sub-system (320) comprising a second secondary roots pump (311) and a second positive displacement pump (312) and a second valve (323) positioned between the gas discharge outlet (302b) of the primary roots pump (302) and the gas suction inlet (321a) of the second secondary roots pump (321). According to the invention, the first pumping sub-system (310) and the second pumping sub-system (320) are configured to pump at a same flow rate, and the primary roots pump (302) is configured to be able to pump at a flow rate F equal to the pumping flow rate of the primary pumping sub-system (310) plus the pumping flow rate of the secondary pumping sub-system (320).

Claims

1. Redundant vacuum pumping system, comprising a primary roots pump having a gas suction inlet connectable to a process chamber and a gas discharge outlet connected to a first pumping sub-system and a second pumping sub-system, wherein the first pumping sub-system and the second pumping sub-system are arranged to pump in parallel gas evacuated by the primary roots pump, the first pumping sub-system comprising a first secondary roots pump, a first positive displacement pump and a first valve positioned between the gas discharge outlet of the primary roots pump and a gas suction inlet of the first secondary roots pump, and the second pumping sub-system comprising a second secondary roots pump, a second positive displacement pump and a second valve positioned between the gas discharge outlet of the primary roots pump and a gas suction inlet of the second secondary roots pump, wherein the first pumping sub-system and the second pumping sub-system are configured to pump at a same flow rate, and the primary roots pump is configured to be able to pump at a flow rate F equal to a pumping flow rate of the primary pumping sub-system plus a pumping flow rate of the secondary pumping sub-system.

2. Redundant vacuum pumping system according to claim 1, wherein the first positive displacement pump and/or the second positive displacement pump is a dry screw pump.

3. Redundant vacuum pumping system according to claim 1, wherein the first positive displacement pump and/or the second positive displacement pump is a dry claw pump.

4. Redundant vacuum pumping system according to claim 1, wherein the first positive displacement pump and/or the second positive displacement pump is a scroll pump.

5. Redundant vacuum pumping system according to claim 1, wherein the first positive displacement pump and/or the second positive displacement pump is a diaphragm pump.

6. Redundant vacuum pumping system according to claim 1, comprising a bypass duct with a third valve arranged in parallel to the primary roots pump.

7. Redundant vacuum pumping system according to claim 1, wherein the first positive displacement pump and the second positive displacement pump are connected to waste gas treatment installations, advantageously scrubbers.

8. Redundant vacuum pumping system according to claim 1, wherein the pumping flow rate of the primary roots pumps is from 5,000 l/min to 100,000 l/min, advantageously between 10,000 l/min and 70,000 l/min, preferably between 25,000 l/min and 55,000 l/min.

9. Redundant vacuum pumping system according to claim 1, comprising failure detecting means for detecting a failure of any of the primary roots pump, the first secondary roots pump, the second secondary roots pump, of the first positive displacement pump or the second positive displacement pump.

10. Redundant vacuum pumping system according to claim 9, wherein the failure detecting means are configured to be able actuate the first valve, the second valve, and/or the third valve in case of a detected failure.

11. Pumping method by means of the redundant vacuum pumping system according to claim 1, wherein the primary roots pump is driven all the time at a nominal flow rate equal to a sum of the pumping flow rate of the first pumping sub-system and of the pumping flow rate of the second pumping sub-system.

12. Pumping method according to claim 11, wherein the pumping system comprises a bypass duct with a third valve and wherein the third valve is switched to its open position when a failure of the primary roots pump is detected by a failure detecting means.

13. Pumping method according to claim 11, wherein a failure detecting means close the first valve when a failure of the first secondary roots pump or of the first positive displacement pump is detected.

14. Pumping method according to claim 11, wherein a failure detecting means close the second valve when a failure of the second secondary roots pump or of the second positive displacement pump is detected.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The specific embodiments and advantages of the present invention will become apparent from the attached Figures that show:

[0024] FIG. 1 is a schematic illustration of a first redundant pumping system known from the prior art;

[0025] FIG. 2 is a schematic illustration of a second redundant pumping system known from the prior art; and

[0026] FIG. 3 is a schematic illustration of a preferred embodiment of a redundant pumping system according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0027] FIG. 1 schematically illustrates a first redundant pumping system 100 known from the prior art. The known redundant pumping system 100 comprises two pumping sub-systems 110 and 120 arranged in parallel for pumping the process chamber 101. As mentioned above, redundant pumping systems are provided in situation in which it must absolutely be ensured that the pressure level in the chamber 101 is maintained at all time during certain manufacturing processes, especially in the semiconductor industry.

[0028] The pumping system 100 must be configured not only to be able to reach a predetermined end-pressure but to handle a large flow of gases F. This is in particular important where chemical vapor etching processes or chemical vapor deposition are involved. These processes require that a constant flow of process gases is fed into the chamber 101, these gases and the residues of the processes having to be pumped away by the pumping system 100. In order to reach a sufficiently low end-pressure and to be able to pump a large flow of gases, the known pumping systems typically used in the semiconductor industry employ a combination of a positive displacement pump, advantageously a dry screw pump, and a roots pump, known also as booster pump. Thanks to the dry screw pump with its high compression ratio, a low end-pressure can be reached, while with the roots pump a very large flow of gases can efficiently be handled.

[0029] Referring back to FIG. 1, each of the two pumping sub-systems 110, 120 comprise therefore a roots pump 111, 121 and a dry screw pump 112, 122. As mentioned above, the two sub-systems are arranged in parallel and are connected to the process chamber 101 by means of two valves 113, 123. The pumping system 100 is redundant in the sense that, during normal operation, the valve 113 is open and the valve 123 is closed. The flow of gases F pumped out of the process chamber 101 is therefore, during normal operation, pumped by the sub-system 110 alone. Only in case of failure of either pump of this sub-system, the valve 113 is closed and the valve 123 opened such that the chamber 101 is evacuated by the sub-system 120 alone.

[0030] Redundant pumping system, like system 100 of FIG. 1, has however many drawbacks. First, it suffers from severe pressure hunting when the system must switch from sub-system 110 to sub-system 120. This pressure hunting leads to contamination in the process chamber 101 which are unacceptable in many applications. Furthermore, during a certain amount of time after the detection of the failure of sub-system 110, the pressure will raise in the process chamber 101 eventually leading to wafer damaging kept in the chamber 101. Finally, since during normal operation pumps 121 and 122 of sub-system 120 are running all the time, the pressure between the inlet of roots pump 121 and valve 123 is kept at the end-pressure of sub-system 120. This implies that, when valve 123 is suddenly opened in reaction to a failure detection of sub-system 110, the pressure in the process chamber will be affected. Such pressure changes make impossible to guarantee high-quality process conditions in the process chamber.

[0031] FIG. 2 schematically illustrates a second redundant pumping system 200 known from the prior art. The system 200 differs from system 100 in that the two pumping sub-systems 210, 220 comprise each only a positive displacement pump 212, 222, such as a dry screw pump. In order to handle an important flow of gas F, the system 200 comprises a roots pump 202, which is “mutual” to both sub-systems 210 and 220. During normal operation, valve 213 is open and valve 223 is closed. The entire flow of gas F is therefore pumped solely by the roots pump 202 and the dry screw pump 212. In case of failure of the dry screw pump 212, the valve 213 is closed and the valve 223 is opened such that the flow of gas F can be evacuated by the combination of the roots pump 202 and the dry screw pump 222.

[0032] While the redundant system 200, in comparison to the redundant system 100, has improved performances in terms of being able to maintain a constant pressure in the process chamber 201 in case of failure of the dry screw pump 212, it has the major drawback that a failure of the roots pump 202 results in an unacceptable and constant raise of pressure in the process chamber 201.

[0033] FIG. 3 schematically illustrates a redundant pumping system 300 according to a preferred embodiment of the present invention. The pumping system 300 comprises a primary roots pump 302, connectable to a process chamber 301, and two pumping sub-systems 310 and 320, each of them comprising a secondary roots pump 311, respectively 321, and a positive displacement pump 312, respectively 322, such as dry screw pumps. During normal operation, the valve 313 and the valve 323 are always open, half of the gas flow F evacuated from the process chamber 301 being pumped by the sub-system 310, and the other half being pumped by the sub-system 320. Essential for the proper implementation of this invention is that the primary roots pump 302 is drivable at the same pumping speed as the total pumping speed of the sub-systems 310 and 320. In other terms, during normal operation, the primary roots pump 302 is not participating in the pumping effort and the pressure P1 at its inlet 302a is the same as the pressure P2 at its outlet 302b, i.e. the compression ratio of the primary roots pump 302 in normal operation is equal to 1. This can be achieved by having a primary roots pump whose pumping speed can be adapted or by having a primary roots pump whose maximal pumping speed is equal to the pumping speed of the sub-systems 310 and 320.

[0034] The idea beyond the present invention is better explained with a concrete implementation example. For this example, let us assume that the flow rate of gas F required to be evacuated from the process chamber is equal to 20′000 l/min. As mentioned above, the inventive redundant pumping system 300 is configured such that the primary roots pump 302 can be driven with a pumping speed equal to F and such that each sub-system 310 and 320 has a pumping speed equal to F/2, in this example equal to 10′000 l/min. Since the entering and existing flow rates of the primary roots pump 302 are equal, the compression ratio of the primary roots pump 302 during normal operation K.sub.normal is equal to 1.

[0035] This means that during normal operation, the performances of the pumping system 300 in terms of pumping speed and end-pressure are the same as if the primary roots pump 302 would not be present, would be switched off or would fail (as long as it does not represent an obstacle to the evacuation). During normal operation, the end pressure of the complete system 300 is given by the end pressure of each of the sub-systems 310, respectively 320, divided by K.sub.0, the compression ratio at zero flow rate and at its outlet pressure. Typically, sub-systems 310, respectively, 320, have an end-pressure of the order of 0.1 mbar. Primary roots pumps have in this pressure range a compression ratio K.sub.0 of the order of 50. The end pressure of the whole system 300 is consequently of the order of 2*10.sup.−4 mbar.

[0036] If now the sub-system 320 would fail, the valve 323 will be closed and the whole flow F would need to be accommodated by the combination of the primary roots pump 302 and the sub-system 310. Since the flow rate of the sub-system 310 is fixed and equal to F/2, the primary roots pump 302 must compress the gas evacuated from the process chamber with a factor 2. This happens automatically as soon as the flow rate beyond the primary roots pumps 302 drops from F down to F/2 due to the failure of the sub-system 320. Naturally, the pressure P3 at the inlet of the sub-system 311a becomes two times higher than during normal operation, but since the primary roots pump 302 now participates in the pumping effort by compressing the gas evacuated from the processing chamber 301 by a factor 2, the end-pressure as well as the pumping speed are not affected by the failure of sub-system 320 and the pressure in the process chamber can be maintained constant even in that case.

[0037] Furthermore, as mentioned above, in case of failure of the primary roots pump 302, the performances of the system 300 are not affected at all as long as the two sub-systems 310 and 320 are running normally. As it is extremely improbable that the primary roots pump 302 and one of the sub-systems 310 or 320 would fail at the same time, the redundant pumping system 300 according to the present invention allows for circumventing the drawbacks of the redundant systems known from the prior art.

[0038] Moreover, it is possible to provide in addition for a bypass duct 303 with a valve 304 in the pumping system 300. With the additional bypass duct 303 it is possible to evacuate the process chamber 301 with the two sub-systems 310 and 320 and to maintain a constant pressure in the chamber 301 even if the primary roots pump 302 becomes a pumping resistance du to failure. In such a case, the flow F is deviated through the bypass duct 304 and directed in the two sub-systems 310 and 320.

[0039] Furthermore, it is advantageous to connect the gas discharge outlet of both positive displacement pumps 312 and 322 to at least one waste gas treatment installation, advantageously scrubbers.

[0040] Finally, it should be pointed out that the foregoing has outlined one pertinent non-limiting embodiment. It will be clear to those skilled in the art that modifications to the disclosed non-limiting embodiment can be effected without departing from the spirit and scope thereof. As such, the described non-limiting embodiment ought to be considered merely illustrative of some of the more prominent features and applications. Other beneficial results can be realized by applying the non-limiting embodiments in a different manner or modifying them in ways known to those familiar with the art.