Patent ID: 12228951

DETAILED DESCRIPTION

Below, examples of the present disclosure will be described.FIG.1shows a block view of a vacuum exhaust system of an example of the present disclosure.

InFIG.1, the process gas which has been used in a vacuum chamber5passes through a regulating valve7, and reaches a branch pipe29. The passage on the side indicated with A in the drawing of a branch pipe29is connected with an inlet port not shown of a second pump. On the other hand, the passage on the side indicated with B in the drawing of the branch pipe29is provided with a bypass valve23.

Then, the downstream of the outlet port not shown of the second pump and the downstream of the bypass valve23are connected with a first pump via a branch pipe27.

With such a configuration, as the first pump, for example, a volume transfer type vacuum pump of a root type, a screw type, a claw type, or the like is used. As the characteristics of the first pump, a pump with a high pumping speed in the medium vacuum region, and suitable for exhaust of a large flow rate gas is desirable. Then, in order to obtain a higher pumping speed, these may be configured in a multistage form. The first pump is large in pump size, and hence may be set outside a clean room.

On the other hand, as the second pump, for example, a momentum transfer type vacuum pump of a turbo-molecular pump, a molecular pump (a drag pump of a thread groove type, a Siegbahn type, a Gaede type, or the like), or the like is used. As the characteristics of the second pump, a pump with a high pumping speed in the high vacuum region, and with an ultimate pressure reaching high vacuum or a lower pressure than that is desirable. The momentum transfer type vacuum pump is operated at a high rotation rate so as to generally effectively apply a momentum to a gas molecule. For this reason, heat generation or a large electric power may be used for exhaust of a large flow rate gas in the medium vacuum region. Further, accordingly, the momentum transfer type vacuum pump is not suitable. According to the exhaust principle, in the medium vacuum region, the pumping speed is reduced.

Incidentally, the second pump is desirably set in the vicinity of the vacuum chamber5for acquiring a high vacuum performance.

Then, a description will be given to the effect of the example of the present disclosure.

InFIG.1, in the low and medium vacuum regions (at the time of large flow rate exhaust), the bypass valve23is opened. At this step, the gas is exhausted through both of the passage A including the second pump therethrough and the passage B. Then, when exhaust under medium and high vacuum conditions lower than that is performed, the bypass valve23is closed, and exhaust is performed through the passage A.

FIG.2shows an exhaust characteristic view of the vacuum exhaust system with the configuration ofFIG.1. The passage B ofFIG.1includes a pipe thinner than that in each case ofFIGS.3to5. For this reason, as indicated with a solid line inFIG.2, the height of the mountain shape of the exhaust characteristic of the passage B is lower than that of the characteristic of the first pump ofFIG.6. However, the gas is exhausted through both of the passage A and the passage B. For this reason, the pumping speed at a point C inFIG.1of the merging point between the passage A and the passage B becomes roughly the total pumping speed of the passage A and the passage B. Therefore, the exhaust characteristic in the low and medium vacuum regions at the point C has the shape having the same height as that of the characteristic of the exhaust gas flowing through the passage switching valve13in the case of each configuration ofFIGS.3to4as indicated with the mountain shape of a dotted line inFIG.2.

Thus, the gas is exhausted through both of the passage A and the passage B. For this reason, as the exhaust characteristic of the system, the exhaust characteristic in a mountain shape indicated with a dotted line inFIG.2in the low and medium vacuum regions, and the exhaust characteristic that while the effective pumping speed becomes flat in the high vacuum region while attenuating in the low and medium vacuum regions on the passage A side are synthesized as with the continuous transition portion indicated with “aa” inFIG.2.

Then, for transition from the operation in the low and medium vacuum regions to the operation in the medium and high vacuum at the position of “bb” inFIG.2, the bypass valve23is switched from open to close. As a result of this, the bypass valve23connected with the inlet/outlet port of the second pump is blocked, so that the compression performance in high vacuum possessed by the second pump is obtained.

If in the high vacuum region, the ultimate pressure of the first vacuum pump does not reach high vacuum, when the bypass valve23is opened, reverse flow is caused through the passage B. For this reason, the bypass valve23is desirably closed. Subsequently, the second pump allows transition at a constant effective pumping speed, leading to a high vacuum state.

Incidentally, desirably, the bypass valve23and a gas flow rate controller3are interlocked, so that the bypass valve23is opened at the time of large flow rate, and the bypass valve23is closed at the time of small flow rate (or a gas flow rate of zero) requiring high vacuum. Control of opening or closing the bypass valve23corresponds to the opening/closing control means.

From the description up to this point, the vacuum exhaust system enables vacuum exhaust making the best use of both the exhaust characteristics of the second pump and the first pump without increasing the size of the second pump.

Incidentally, the bypass valve23has been described as a valve only to be opened and closed. However, with the bypass valve23as the valve capable of controlling the degree of opening, the degree of opening may be regulated according to the gas flow rate and the pressure in the exhaust system, thereby smoothly performing switching. Control of the degree of opening of the bypass valve23corresponds to the opening degree control means. Herein, the flow rate is, for example, extracted from the gas flow rate controller3, and the pressure is extracted from the vacuum chamber5.

With this configuration, the pressure load applied to the pump is reduced, which enables the stable operation of the pump. In addition, it is possible to prevent a fluctuation in process conditions due to the pulsation of exhaust, or the misregistration due to fluctuations in pressure or vibration of the object to be processed in the vacuum chamber5.

From the description up to this point, the second pump, the bypass valve23, and the pipe diameter can be reduced in size. In addition, it becomes possible to perform highly efficient exhaust making the best use of the exhaust characteristics of the first and second pumps in from high vacuum to the large flow region.

Incidentally, with the present vacuum exhaust system, first, vacuum exhaust is performed with the first pump, and the second pump is driven after the pressure in the inside thereof satisfies the operable condition. Although not shown, the inlet/outlet port of the second pump may be provided with a valve for maintenance. Alternatively, although not shown, an exhaust path and a valve for roughly evacuating the vacuum chamber5from the atmosphere to a prescribed pressure may be set.

Incidentally, the present disclosure can be variously modified unless it departs from the spirit of the present disclosure. The examples and respective modified examples can be variously combined.