Device and method for evacuating a chamber and purifying the gas extracted from said chamber

Abstract

A device evacuates a chamber and purifies the gas extracted from said chamber of any foreign substances. The device comprises a dry-condensing vacuum pump having an input connected to the chamber to be evacuated and is suitable for maintaining the input pressure at a constant level at the output despite variable conditions. An intermediate line which connects to the output of the dry-condensing vacuum pump and a liquid ring vacuum pump, the input of which is connected to the intermediate line, are additionally provided. A corresponding method makes it possible to purify the gas of any foreign substances reliably and effectively.

Claims

1. A method for evacuating a vacuum coating processing chamber, said vacuum coating processing chamber having an atmosphere of a gas and solid substances dissolved in said gas, said method comprising: drawing the gas out of the vacuum coating processing chamber; increasing the pressure of the gas, with a first pump to a value below atmospheric pressure, the first pump having an inlet pressure and an outlet pressure, wherein the first pump is configured for keeping the inlet pressure constant even if the outlet pressure is variable, wherein an inlet and an outlet of the first pump are separated from one another by a plurality of sealing gaps in series, the inlet being connected to the vacuum coating processing chamber, and wherein an intermediate line connects to the outlet of the first pump; conducting the gas onward to a liquid ring vacuum pump which outputs the gas at atmospheric pressure, the liquid ring vacuum pump having an operating liquid and an inlet connected to the intermediate line, said liquid ring vacuum pump absorbing solid substances condensing from the gas into the operating liquid; and replacing the operating liquid with fresh operating liquid when the operating liquid has been enriched with absorbed solid substances during operation of the liquid ring vacuum pump.

2. The method of claim 1, wherein the first pump comprises a dry-compression vacuum pump.

3. The method of claim 1, wherein the first pump generates a pressure of between 1 mbar and 40 mbar at the inlet side.

4. The method of claim 1, wherein the first pump generates a pressure of between 80 mbar and 300 mbar in the intermediate line.

5. The method of claim 1, wherein an opening for a supply of scavenging gas is provided at the outlet of the first pump and/or in the intermediate line.

6. The method of claim 5, wherein the first pump has a housing characterized in that the opening is a gap that exists between a shaft and the housing of the first pump.

7. The method of claim 1, wherein the liquid ring vacuum pump has an operating liquid and is provided with an inlet and an outlet for the operating liquid, which inlet and outlet permit an inflow and outflow of the operating liquid during operation of the liquid ring vacuum pump.

8. The method of claim 1, wherein the operating liquid has a conductivity, characterized in that a sensor determines the conductivity of the operating liquid.

9. The method of claim 7, wherein the operating liquid has an inflow and an outflow and a concentration of foreign substances, characterized in that a control device adjusts the inflow and the outflow of the operating liquid as a function of the concentration of foreign substances in the operating liquid.

10. The method of claim 1, wherein the operating liquid has a concentration of foreign substances characterized in that the operating liquid of the liquid ring vacuum pump contains a solvent which is coordinated with the foreign substances contained in the gas.

11. The method of claim 1, wherein the operating liquid has a pH value, characterized in that a pH sensor determines the pH value of the operating liquid.

12. The method of claim 11, wherein the sensor determines measurement values, characterized in that a control device adjusts the pH value of the operating liquid as a function of the measurement values from the pH sensor.

13. The method of claim 1, wherein a combustion device is arranged in the intermediate line.

14. The method of claim 1, wherein the first pump generates a pressure of between 2 mbar and 30 mbar at the inlet side.

15. The method of claim 1, wherein the first pump generates a pressure of between 5 mbar and 20 mbar at the inlet side.

16. The method of claim 1, wherein the first pump generates a pressure of between 100 mbar and 150 mbar in the intermediate line.

17. The method of claim 3, wherein the first pump generates a pressure of between 100 mbar and 150 mbar in the intermediate line.

18. The method of claim 3, wherein an opening for a supply of scavenging gas is provided at the outlet of the first pump and/or in the intermediate line.

19. The method of claim 4, wherein an opening for a supply of scavenging gas is provided at the outlet of the first pump and/or in the intermediate line.

20. The method of claim 3, wherein the liquid ring vacuum pump has an operating liquid and is provided with an inlet and an outlet for the operating liquid, which inlet and outlet permit an inflow and outflow of the operating liquid during operation of the liquid ring vacuum pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described by way of example below with reference to the appended drawing and on the basis of advantageous embodiments. In the drawing:

(2) FIG. 1 shows an embodiment of the device.

DETAILED DESCRIPTION

(3) A process chamber of a CVD process forms the chamber 14 to be evacuated. The inlet 17 of a screw-type vacuum pump 15 is connected to the chamber 14 to be evacuated. A pressure reduction valve 16 is arranged in the line between the chamber 14 to be evacuated and the screw-type vacuum pump 15, by means of which pressure reduction valve the pressure in the chamber 14 can be set to be higher than the pressure at the inlet 17 of the screw-type vacuum pump 15. In the present example, a pressure of 80 mbar prevails in the chamber 14, and a pressure of 20 mbar prevails at the inlet 17 of the screw-type vacuum pump 15. The screw-type vacuum pump 15 has the task of keeping the pressure at the inlet 17 constant even if the conditions at the outlet 18 of the screw-type vacuum pump 15 vary. By means of the screw-type vacuum pump 15, the gas is compressed to a pressure of approximately 120 mbar and output via the outlet 18.

(4) The outlet 18 of the screw-type vacuum pump 15 is adjoined by an intermediate line 19 which leads to a liquid ring vacuum pump 20. The liquid ring vacuum pump 20 compresses the gas further such that it can be output at atmospheric pressure via the outlet 21.

(5) The screw-type vacuum pump 15 and the liquid ring vacuum pump 20 are coordinated with one another such that, in the intermediate line 19, the pressure of the gas is low enough, and the volume flow rate high enough, that no condensation of the foreign substances entrained by the gas takes place therein. Condensation occurs the first time as a result of the further pressure rise in the liquid ring vacuum pump 20. The foreign substances are then immediately absorbed by the operating liquid of the liquid ring vacuum pump 20 and consequently cannot be deposited on elements of the device.

(6) Also arranged in the intermediate line 19 is a valve 22 via which air from the environment can be admitted, as scavenging gas, into the intermediate line 19. By virtue of scavenging gas being admitted at this location, a small volume of scavenging gas is sufficient to considerably increase the volume flow rate in the intermediate line 19. The deposition of the foreign substances can thus be counteracted further by means of the scavenging gas.

(7) During the course of operation, the operating liquid is enriched with an ever-increasing amount of foreign substances. It is thus possible for new operating liquid to be fed to the liquid ring vacuum pump 20 and for old operating liquid to be discharged from the liquid ring vacuum pump, respectively, via an inlet 23 and an outlet 24 during operation. Here, a closed circuit for the operating liquid exists between the liquid ring vacuum pump 20 and a storage vessel 25 via a feed line 26 and a return line 27. Accordingly, during operation, operating liquid is continuously exchanged, whereby the material present in the storage vessel 25 is enriched with foreign substances to an ever greater extent.

(8) The conductivity of the operating liquid in the storage vessel 25 is continuously measured by means of a sensor 28. The content of foreign substances can be inferred from the conductivity, such that the operating liquid can cease to be used when a predefined threshold value is exceeded.

(9) The measurement values from the sensor 28 are fed to a control unit 30. If the threshold value is exceeded, the control unit 30 actuates a valve 31, such that some of the no longer usable operating liquid is extracted from the vessel 25. The vessel 25 is subsequently filled with a corresponding amount of fresh operating liquid. Furthermore, by means of the control unit 30, a pump 32 is actuated by means of which the operating liquid is fed to the liquid ring vacuum pump 20.

(10) The pH value of the operating liquid in the storage vessel 25 is measured by means of a further sensor 29. If, for example, acidic foreign substances are entrained in the gas, it may be advantageous, for the purification of the gas, for the operating liquid to be alkaline. The absorption of the acidic foreign substances has the effect that the pH value of the operating liquid falls until, at some point, the absorption of the acidic foreign substances is no longer ensured. This is determined by means of the sensor 29. When a corresponding measurement value is output by the sensor 29, the device 30 actuates a valve 33 by means of which additional alkaline solution is fed to the operating liquid. In this way, the operating liquid permanently maintains the desired alkaline characteristics.

(11) If the foreign substances entrained in the gas are alkaline, the procedure using the sensor 29, the control device 30 and the valve 33 is exactly reversed.

(12) Finally, a combustion device 34 is arranged in the intermediate line 19. Said combustion device is activated if foreign substances that can be absorbed by the operating liquid of the liquid ring vacuum pump 20 only after combustion are entrained in the gas.