Vacuum Pumping System

Abstract

To provide a vacuum exhaust system capable of reducing sizes of a pump and a valve, and a diameter of piping, and performing exhausting with high efficiency by making use of exhaust characteristics of a pump from a high vacuum region to a large flow rate region.SOLUTION: A process gas used in a vacuum chamber 5 passes through a regulating valve 7 and reaches branch piping 29. A flow channel at a side shown by A in a drawing of the branch piping 29 is connected to a suction port of a second pump. On the other hand, a flow channel at a side shown by B in the drawing of the branch piping 29 is provided with a bypass valve 23. A first pump is connected to the downstream of an exhaust port of the second pump and the downstream of the bypass valve 23 through the branch pipe 27. In a low / intermediate vacuum region (at exhausting at large flow rate), the bypass valve 23 is opened. Here, the gas is exhausted from both of the flow channel A and the flow channel B through the second pump. In a case of performing the exhausting under the intermediate / high vacuum condition lower than the above, the bypass valve 23 is closed and the exhausting is performed by the flow channel A. Thus, the piping of the flow channel B can be thinned.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a vacuum exhaust system, and more particularly to a vacuum exhaust system that enables miniaturization of pumps and valves, narrowing of piping diameters, and highly efficient exhaust from high vacuum to large flow rates by making use of the pump's exhaust characteristics. [Background technology]

[0002] With the recent development of electronics, the demand for semiconductors such as memory and integrated circuits is rapidly increasing. These semiconductors are manufactured by doping extremely pure semiconductor substrates with impurities to give them electrical properties, or by forming fine circuit patterns on semiconductor substrates and stacking them. These operations must be carried out in a vacuum chamber under high vacuum conditions to avoid the effects of dust in the air, etc. To evacuate this vacuum chamber, a vacuum evacuation system using a pump device generally consisting of a positive displacement vacuum pump or a momentum displacement vacuum pump is used.

[0003] Furthermore, in the semiconductor manufacturing process, there are many steps in which various process gases are applied to the semiconductor substrate, and vacuum pumping systems are used not only to create a vacuum inside the vacuum chamber, but also to evacuate these process gases from the vacuum chamber (see, for example, Patent Document 1). Furthermore, in equipment such as electron microscopes, vacuum pumping systems are also used to create a high degree of vacuum in the vacuum chamber of the electron microscope or the like in order to prevent refraction of the electron beam due to the presence of dust or the like. A configuration diagram of this conventional vacuum pumping system is shown in Figure 3.

[0004] In Fig. 3, the process gas supplied from a gas cylinder 1 has its flow rate adjusted by a gas flow rate controller 3 and is then introduced into a vacuum chamber 5. Thereafter, the process gas that has been used in the vacuum chamber 5 is discharged from the vacuum chamber 5 and passes through an adjustment valve 7 that adjusts the gas flow rate to reach a branch pipe 9. The flow path on the side indicated by A in the figure of the branch pipe 9 is connected to an intake port (not shown) of a second pump via a flow path switching valve 11. Meanwhile, a flow path switching valve 13 is provided in the flow path on the side indicated by B in the figure of the branch pipe 9.

[0005] A flow path switching valve 15 is provided at an exhaust port (not shown) of the second pump, and the first pump is connected downstream of this flow path switching valve 15 and downstream of the flow path switching valve 13 via branch piping 17.

[0006] In such a configuration, a case will be described in which the process conditions performed in the vacuum chamber 5 require both a process in a low to medium vacuum range with a high gas flow rate and a process in a medium to high vacuum range requiring lower pressure conditions.

[0007] In this case, conventionally, in a process in the low to medium vacuum range where the gas flow rate is high, flow path switching valve 11 and flow path switching valve 15 are closed, and flow path switching valve 13 is opened to perform exhaust through flow path B. On the other hand, in a process in the medium to high vacuum range where a lower pressure condition is required, flow path switching valve 13 is closed, flow path switching valve 11 and flow path switching valve 15 are switched to be open, and exhaust is performed through flow path A. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 8-74737 Summary of the Invention [Problem to be solved by the invention]

[0009] Incidentally, in this vacuum exhaust system, in order to reduce the pressure in the vacuum chamber 5 during high flow rate exhaust, it is necessary to increase the diameter of the piping of the flow path B and the flow path switching valve 13. This may result in a large vacuum exhaust system, making it difficult to secure the installation space and increasing costs.

[0010] In addition, when the process gas flowing from the vacuum chamber 5 is at a high flow rate, a bypass pipe 21 may be connected directly to the vacuum chamber 5 as shown in Fig. 4, but as described above, the vacuum exhaust system becomes larger, which may make it difficult to secure the installation space and increase the cost. In Fig. 4, the same elements as those in Fig. 3 are given the same reference numerals and the explanation will be omitted (the same applies below).

[0011] Furthermore, FIG. 5 shows an example in which a second pump is connected in series with the first pump, where the second pump is also capable of operating in the medium vacuum range. However, in this case, the pumping efficiency of the second pump may decrease in the medium vacuum region, causing a risk of a decrease in the pumping performance of the system. Figure 6 shows how the pumping characteristics of the second pump decrease in this medium vacuum region. That is, in the medium vacuum region where the pressure is higher than 0.1 [Pa], the effective pumping speed of the second pump gradually decreases as the pressure increases.

[0012] To compensate for this, it would be necessary to increase the size of the second pump and the size of the piping and valves, which would result in a larger vacuum pumping system. As a result, as mentioned above, there was a risk that it would be difficult to secure the installation space and that costs would increase. The present invention has been made in consideration of the above-mentioned problems in the conventional art, and has as its object to provide a vacuum exhaust system which enables miniaturization of pumps and valves and narrowing of piping diameters, while also enabling highly efficient exhaust by making use of the exhaust characteristics of the pump from high vacuum to large flow rate ranges. [Means for solving the problem]

[0013] Therefore, the present invention (claim 1) provides a vacuum exhaust system including a first pump for performing vacuum exhaust from atmospheric pressure to a medium vacuum range, a second pump connected in series to the first pump and having an ultimate pressure lower than that of the first pump, and a bypass valve arranged in parallel to the second pump via a pipe communicating with an intake port and an exhaust port of the second pump, The bypass valve is switched from open to closed when the operation is shifted from a low-medium vacuum region of the atmospheric pressure to a medium-high vacuum region having an ultimate pressure lower than that of the low-medium vacuum region, By exhausting exhaust gas from the vacuum chamber through both the flow path of the second pump and the flow path of the bypass valve while the first pump is in operation, the effective exhaust speed is not reduced in the medium vacuum region and the low vacuum region compared to when only the first pump and the second pump are in operation.

[0014] In addition to the suction of the first pump, exhaust gas from the vacuum chamber is exhausted through both the flow path of the second pump and the flow path of the bypass valve. As a result, compared to when suction is performed by switching between the flow path of the second pump and the flow path of the bypass valve, or when suction is performed by connecting the first pump and the second pump in series, this vacuum exhaust system makes it possible to perform vacuum exhaust by utilizing the exhaust characteristics of both the second pump and the first pump without increasing the size of the second pump. The bypass valve and piping diameters can also be made small.

[0015] In addition, the present invention (claim 2) is The above In a low to medium vacuum region, the first pump and the second pump are operated while the bypass valve is opened; The above In the medium to high vacuum region, the first pump and the second pump are operated while the bypass valve is closed.

[0016] This allows the second pump, bypass valve, and piping diameter to be reduced in size, and enables highly efficient evacuation from high vacuum to large flow rates by taking advantage of the evacuation characteristics of the first and second pumps.

[0017] Furthermore, the present invention (claim 3) further comprises a flow rate measuring means for measuring a flow rate of the exhaust gas flowing through the vacuum chamber, and a bypass valve based on the magnitude of the flow rate measured by the flow rate measuring means. The above Open or The above The device is configured with an opening / closing control means for closing the door.

[0018] The bypass valve is opened or closed based on the magnitude of the flow rate measured by the flow rate measuring means, thereby enabling efficient control by switching between a high flow rate of exhaust gas flowing through the vacuum chamber and a low flow rate (or zero gas flow rate) that requires a high vacuum in the vacuum chamber.

[0019] Furthermore, the present invention (claim 4) is characterized in that it comprises an aperture control means for controlling the aperture of the bypass valve, and the aperture control means controls the aperture in response to at least one of the flow rate of the exhaust gas flowing through the vacuum chamber and the pressure in the exhaust system.

[0020] By controlling the opening of the bypass valve, the pressure load on the pump can be reduced, allowing the pump to operate stably. It also prevents fluctuations in process conditions due to exhaust pulsation, and prevents the position of the object to be processed in the vacuum chamber from shifting due to pressure fluctuations or vibrations.

[0021] Furthermore, the present invention (claim 5) is characterized in that the first pump is a positive displacement vacuum pump having a high pumping speed in a medium vacuum range.

[0022] Furthermore, the present invention (claim 6) is characterized in that the second pump is configured as a momentum transfer vacuum pump having a high exhaust speed in a high vacuum region and an ultimate pressure that reaches high vacuum or a pressure lower than that. Effect of the Invention

[0023] As described above, according to the present invention, in addition to the suction of the first pump, exhaust gas from the vacuum chamber is exhausted through both the flow path of the second pump and the flow path of the bypass valve, so that this vacuum exhaust system makes it possible to perform vacuum exhaust by utilizing the exhaust characteristics of both the second pump and the first pump without increasing the size of the second pump. The bypass valve and piping diameters can also be made small. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a block diagram of a vacuum exhaust system according to an embodiment of the present invention. [Diagram 2] Pumping characteristics of the vacuum pumping system in the configuration shown in Figure 1 [Diagram 3] Diagram of a conventional vacuum pumping system (part 1) [Figure 4] Diagram of a conventional vacuum pumping system (part 2) [Diagram 5] Diagram of a conventional vacuum pumping system (part 3) [Figure 6] FIG. 13 is a diagram showing how the pumping characteristics of the second pump decrease in the medium vacuum region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described. A configuration diagram of a vacuum pumping system according to an embodiment of the present invention is shown in FIG. In Fig. 1, the process gas used in the vacuum chamber 5 passes through the regulating valve 7 and reaches the branch pipe 29. The flow path of the branch pipe 29 on the side indicated by A in the figure is connected to an intake port (not shown) of a second pump. On the other hand, a bypass valve 23 is provided in the flow path of the branch pipe 29 on the side indicated by B in the figure.

[0026] A first pump is connected via a branch pipe 27 to the downstream of an exhaust port (not shown) of the second pump and the downstream of the bypass valve 23 . In this configuration, a positive displacement vacuum pump such as a Roots type, screw type, or claw type is used as the first pump. The first pump preferably has a high pumping speed in the medium vacuum range and is suitable for pumping a large amount of gas. To achieve a higher pumping speed, these pumps may be multi-staged. Since the first pump is large in size, it may be installed outside the clean room.

[0027] On the other hand, the second pump is a momentum transfer type vacuum pump such as a turbomolecular pump or a molecular pump (a drag pump such as a screw groove type, Siegbahn type, or Gaede type). The second pump should have a high pumping speed in the high vacuum region and a final pressure that can reach high vacuum or lower. Momentum transfer type vacuum pumps are generally operated at high rotation speeds so that momentum can be effectively imparted to gas molecules, so they are not suitable for pumping large amounts of gas in the medium vacuum region because they generate heat and require large amounts of electricity. In addition, the pumping speed decreases in the medium vacuum region due to the pumping principle. It is preferable that the second pump is installed near the vacuum chamber 5 in order to obtain high vacuum performance.

[0028] Next, the operation of the embodiment of the present invention will be described. 1, in the low to medium vacuum range (high flow rate exhaust), the bypass valve 23 is opened. At this time, gas is exhausted through both flow path A and flow path B via the second pump. When exhausting under lower medium to high vacuum conditions, the bypass valve 23 is closed and exhaust is performed through flow path A.

[0029] FIG. 2 shows the pumping characteristics of the vacuum pumping system in the configuration of FIG. 1. Flow path B in FIG. 1 is configured with thinner piping than those in the cases of FIGS. 3 to 5. For this reason, as shown by the solid line in FIG. 2, the height of the peak shape of the pumping characteristics of flow path B is lower than that of the peak shape of the first pump in FIG. 6. However, since gas is exhausted from both flow paths A and B, the pumping speed at point C in FIG. 1, which is the confluence of flow paths A and B, is approximately the sum of the pumping speeds of flow paths A and B. Therefore, the pumping characteristics of the low and medium vacuum region at point C, as shown by the dotted peak shape in FIG. 2, have the same height as the pumping characteristics of the flow path switching valve 13 in the configurations of FIGS. 3 to 4.

[0030] Because gas is exhausted from both flow path A and flow path B in this way, the system's exhaust characteristics are a combination of the mountain-shaped exhaust characteristics shown by the dotted line in Figure 2 in the low and medium vacuum region, and the exhaust characteristics in which the effective pumping speed decreases in the low and medium vacuum region on the flow path A side but becomes flat in the high vacuum region, as shown by the continuous transition portion shown by "I" in Figure 2.

[0031] 2, in order to shift from low-medium vacuum operation to medium-high vacuum operation, the bypass valve 23 is switched from open to closed. This blocks the bypass valve 23 connected to the intake and exhaust ports of the second pump, and the second pump's compression performance at high vacuum is obtained. If the ultimate pressure of the first vacuum pump does not reach high vacuum in the high vacuum region, it is desirable to close the bypass valve 23 since opening the bypass valve 23 would cause backflow through flow path B. After that, the second pump maintains a constant effective pumping speed and reaches a high vacuum state.

[0032] It is preferable to link the bypass valve 23 with the gas flow controller 3 so that the bypass valve 23 opens at high flow rates and closes at low flow rates (or zero gas flow rates) that require a high vacuum. The control of opening or closing the bypass valve 23 corresponds to an opening / closing control means. As a result, in this vacuum pumping system, vacuum pumping is possible by making use of the pumping characteristics of both the second pump and the first pump, without increasing the size of the second pump.

[0033] Although the bypass valve 23 has been described as a valve that only opens and closes, the bypass valve 23 may be a valve whose opening can be controlled, and the opening can be adjusted according to the gas flow rate and the pressure in the exhaust system to perform smooth switching. The control for adjusting the opening of the bypass valve 23 corresponds to the opening control means. Here, the flow rate is extracted from the gas flow rate controller 3, for example, and the pressure is extracted from the vacuum chamber 5.

[0034] This configuration reduces the pressure load on the pump, allowing it to operate stably, and also prevents fluctuations in process conditions due to exhaust pulsations and displacement of the object to be processed in the vacuum chamber 5 due to pressure fluctuations or vibrations. As a result, the second pump, the bypass valve 23, and the piping diameter can be reduced in size, and highly efficient evacuation is possible from high vacuum to large flow rates by taking advantage of the evacuation characteristics of the first and second pumps.

[0035] In this vacuum exhaust system, the first pump performs vacuum exhaust first, and the second pump starts after the internal pressure reaches an operable condition. Although not shown, a maintenance valve may be provided at the intake and exhaust port of the second pump. Also, although not shown, an exhaust path and a valve may be provided to roughly exhaust the vacuum chamber 5 from the atmosphere to a predetermined pressure. The present invention can be modified in various ways without departing from the spirit of the present invention, and the above-described embodiments and modifications can be combined in various ways. [Explanation of symbols]

[0036] 1 gas cylinder 3 Gas Flow Controller 5. Vacuum Chamber 7. Regulating valve 9, 17, 27, 29 Branch piping 11, 13, 15 Flow path switching valve 23 Bypass valve

Claims

1. A first pump that performs evacuation from atmospheric pressure to a medium vacuum range; a second pump connected in series to the first pump and having an ultimate pressure lower than that of the first pump; a bypass valve disposed in parallel with the second pump via a pipe communicating with an intake port and an exhaust port of the second pump, The bypass valve is switched from open to closed when the operation is shifted from a low-medium vacuum region of the atmospheric pressure to a medium-high vacuum region having an ultimate pressure lower than that of the low-medium vacuum region, a flow passage of the second pump and a flow passage of the bypass valve, and thereby, in a medium vacuum region and a low vacuum region, an effective pumping speed is not reduced compared to when only the first pump and the second pump are operating.

2. A vacuum exhaust system as described in claim 1, characterized in that in the low / medium vacuum region, the first pump and the second pump are operated while the bypass valve is opened, and in the medium / high vacuum region, the first pump and the second pump are operated while the bypass valve is closed.

3. a flow rate measuring means for measuring a flow rate of the exhaust gas flowing through the vacuum chamber; 3. The vacuum exhaust system according to claim 1, further comprising an opening / closing control means for opening or closing said bypass valve based on the magnitude of the flow rate measured by said flow rate measuring means.

4. an opening control means for controlling an opening of the bypass valve, 3. The vacuum exhaust system according to claim 1, wherein the opening control means controls the opening in response to at least one of the flow rate of the exhaust gas flowing through the vacuum chamber and the pressure in an exhaust system.

5. 5. The vacuum evacuation system according to claim 1, wherein the first pump is a positive displacement vacuum pump having a high evacuation speed in a medium vacuum range.

6. 6. The vacuum exhaust system according to claim 1, wherein the second pump is a momentum transfer vacuum pump having a high exhaust speed in a high vacuum region and an ultimate pressure that reaches a high vacuum or a pressure lower than that.

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