Patent Application
20130336828
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-136799, filed on Jun. 18, 2012; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a roots pump and an exhaust method.
In a manufacturing process of a semiconductor device, a multi-stage roots pump is used as one means for causing a process room to become a vacuum state. The multi-stage roots pump has a configuration in which a gas is transferred by rotors respectively provided in a pair of rotary shafts, is compressed by pump chambers of which the volumes sequentially decrease, and is exhausted to the outside.
Since the gas is compressed in the respective pump chambers of the multi-stage roots pump, heat is generated. As a result, the temperature increases as it goes toward the exhaust-side pump chamber. The heat is transmitted to the rotor and the rotary shaft, so that the temperatures of the rotor and the rotary shaft increase and the temperature of the casing also increases. Since the outer surface of the casing contacts the external air, an increase in temperature thereof may be suppressed. One rotor and the rotary shaft are provided inside the pump chamber and the pressure of the pump chamber is lower than the atmospheric pressure. Accordingly, the heat radiation amount is smaller than that of the casing, and the temperature increasing degree is larger than that of the casing. Specifically, when the temperature increasing degree caused by the heat increases, a temperature difference between the casing and the portion including the rotor and the rotary shaft increases. As a result, the thermal expansion difference between the rotary shaft and the casing increases, and the rotary shaft becomes distorted by the heat, so that the rotor contacts the casing. Further, in a case where the multi-stage roots pump is used for the exhaust of the vacuum apparatus such as an etching apparatus using a corrosive gas, the exhaust side (high pressure side) rotor is corroded by the high-temperature gas, so that the surface state is degraded.
If the pump is stopped in a state where the temperature of the rotary shaft is high and the surface of the rotor is degraded, there is a problem in which the pump may not be operated due to the contact between the rotor and the casing even when an operator tries to activate the pump again.
In general, according to one embodiment, there is provided a roots pump including a first roots pump, a second roots pump, and a connection passage. The first roots pump includes a first casing which has therein a first pump chamber, a first gas transfer member which is disposed inside the first pump chamber and rotates so as to transfer a gas in a predetermined direction, and a first support member which supports the first gas transfer member. The second roots pump includes a second casing which has therein a second pump chamber, a second gas transfer member which is disposed inside the second pump chamber and rotates so as to transfer a gas in a predetermined direction, and a second support member which supports the second gas transfer member. The connection passage connects an exhaust hole which is provided in the first pump chamber to an intake hole which is provided in the second pump chamber.
Hereinafter, referring to the accompanying drawings, the roots pump and the exhaust method according to the embodiment will be described in detail. Furthermore, the invention is not limited to the embodiment.
In the description below, since the low pressure side roots pump 10L and the high pressure side roots pump 10H have the same structure, the description will be made by giving the same reference numerals to the same components.
Each of the low pressure side roots pump 10L and the high pressure side roots pump 10H includes an upstream side wall 11 and a downstream side wall 13 which are away from each other. The upstream side wall 11 is provided with a motor chamber 11a which accommodates a motor 23, and the upstream end of the motor chamber 11a in the gas transfer direction is covered by an upstream cover 12. A bearing 25 which rotatably supports a main shaft 21a is supported inside the motor chamber 11a.
At the downstream side of the downstream side wall 13 in the gas transfer direction, there are provided a gear 24 which is attached to the main shaft 21a, a gear (not illustrated) which is attached to a driven shaft 21b (
A partition wall constituting member 15 is disposed between the upstream side wall 11 and the downstream side wall 13. The partition wall constituting member 15 includes a plurality of partition walls 15a to 15d and an outer wall 15e which supports the partition walls 15a to 15d. A space which is surrounded by each of the partition walls 15a to 15d and the outer wall 15e becomes each of the first to third pump chambers 16a to 16c. Specifically, the space which is surrounded by the partition walls 15a and 15b and the outer wall 15e becomes the first pump chamber 16a, the space which is surrounded by the partition walls 15b and 15c and the outer wall 15e becomes the second pump chamber 16b, and the space which is surrounded by the partition walls 15c and 15d and the outer wall 15e becomes the third pump chamber 16c. Furthermore, the upstream side wall 11, the upstream cover 12, the downstream side wall 13, the downstream cover 14, and the partition wall constituting member 15 constitute the casing.
Inside the low pressure side roots pump 10L and the high pressure side roots pump 10H, an intake hole 31 is provided in the partition wall constituting member 15 constituting the first pump chamber 16a and an exhaust hole 33 is provided in the partition wall constituting member 15 constituting the third pump chamber 16c. Further, the partition wall 15b between the first pump chamber 16a and the second pump chamber 16b and the partition wall 15c between the second pump chamber 16b and the third pump chamber 16c are respectively provided with communication holes 32a and 32b. In this way, the intake hole 31 is connected to the exhaust hole 33 inside the same roots pump by the first pump chamber 16a, the communication hole 32a, the second pump chamber 16b, the communication hole 32b, and the third pump chamber 16c, and the direction from the intake hole 31 to the exhaust hole 33 becomes the gas transfer direction.
The volumes of the respective pump chambers 16a to 16c are formed so as to become smaller from the upstream side toward the downstream side in the gas transfer direction. Further, the volume of the first pump chamber 16a at the upstream side of the high pressure side roots pump 10H is formed so as to become smaller than the volume of the third pump chamber 16c at the downstream side of the low pressure side roots pump 10L.
As illustrated in
Rotors 22a to 22c which are respectively accommodated inside the first to third pump chambers 16a to 16c and have a plurality of teeth are fixed and supported by the main shaft 21a and the driven shaft 21b (hereinafter, both will be referred to as the rotary shaft 21 if both shafts are not particularly distinguished from each other). The respective rotors 22a to 22c rotate along with the rotary shaft 21, and the gas which is suctioned from the intake holes 31 or the upstream communication holes 32a or 32b of the first to third pump chambers 16a to 16c is transferred to the downstream communication holes 32a or 32b or the exhaust holes 33 during the rotation of the rotors. Here, the rotors 22a to 22c are arranged with a small gap therebetween and the rotors 22a to 22c and the casing inner wall surface are arranged with a small gap therebetween.
Furthermore, the main shaft 21a, the gear 24, the driven shaft 21b, and the gear attached to the driven shaft 21b constitute the support member. The support member is supported by the casing through the bearings 25 and 26. Further, the pairs of rotors 22a to 22c which are supported by the main shaft 21a and the driven shaft 21b inside the respective pump chambers 16a to 16c constitute the gas transfer member.
The exhaust hole 33 of the low pressure side roots pump 10L is connected to the intake hole 31 of the high pressure side roots pump 10H by the connection passage 41. It is desirable that the connection passage 41 is connected to a truncated conical tube so that the cross-sectional area perpendicular to the length direction decreases from the low pressure side roots pump 10L toward the high pressure side roots pump 10H. When the truncated conical tube is used, the flow rate of the gas increases and the temperature of the gas decreases due to the Venturi effect at the portion of which the cross-sectional area perpendicular to the length direction of the connection passage 41 is small, that is, the diameter of the cross-section is small. Since the pressure and the temperature are proportional to each other, the temperature of the gas decreases with a decrease in pressure. Further, since the outer periphery of the connection passage 41 contacts the external air, an increase in temperature may be suppressed. Furthermore, it is desirable that the connection passage 41 connect the low pressure side roots pump 10L to the high pressure side roots pump 10H at the shortest distance. Here, the shortest distance indicates a case where the connection passage 41 is disposed between the casing of the low pressure side roots pump 10L and the casing of the high pressure side roots pump 10H so that the length direction of the connection passage 41 is perpendicular to the rotary shaft 21, that is, the length direction is not deviated from the perpendicular direction.
As illustrated in
Meanwhile, as illustrated in
In this way, the temperature of the gas which is exhausted from the roots pumps when causing the gas to pass through the identical-stage pump chambers becomes lower in the roots pump 10 according to the embodiment compared to the roots pump of the related art. The reason is as below. The roots pump 10 according to the embodiment is formed as double stages with the low pressure side roots pump 10L and the high pressure side roots pump 10H, and the connection passage 41 which is formed as the truncated conical tube is provided therebetween. Accordingly, the temperature of the gas decreases at the connection passage 41 and the gas of which the temperature decreases is supplied again to the high pressure side roots pump 10H.
Since an increase in temperature at the downstream side is suppressed in the low pressure side roots pump 10L even by the number of stages of the pump chambers compared to the roots pump used in the related art, the corrosion caused by the corrosive gas is prevented by the suppressed degree. As a result, ductile cast iron or the like may be used in the casing, the rotary shaft 21, or the rotors 22a to 22c. Further, in the high pressure side roots pump 10H, ductile cast iron subjected to the Ni-plating may be used in the casing, the rotary shaft 21, or the rotors 22a to 22c so as to suppress the generation of the corrosion caused by the corrosive gas due to an increase in temperature at the downstream side. The thickness of the Ni-plating may be, for example, 15 to 30 μm.
Next, an operation of the roots pump with such a configuration will be described. When the main shafts 21a of the low pressure side roots pump 10L and the high pressure side roots pump 10H are respectively rotated by driving the motors 23, the rotors 22a to 22c supported by the main shaft 21a rotates, and the driven shaft 21b also rotates by the gear 24 connected thereto, so that the rotors supported by the driven shaft 21b also rotate. The rotation direction of the rotor which is supported by the driven shaft 21b becomes opposite to the rotation direction of the rotor which is supported by the main shaft 21a. By the rotation of the rotors 22a to 22c, the gas inside the first to third pump chambers 16a to 16c is transferred to the communication holes 32a and 32b or the exhaust hole 33 at the downstream side. Then, the transferred gas is compressed in response to the ratio between the volumes of the first to third pump chambers 16a to 16c.
Specifically, the gas inside the exhaust subject flows from the intake hole 31 of the low pressure side roots pump 10L into the first pump chamber 16a, and the gas is transferred to the second pump chamber 16b through the communication hole 32a by the rotation of the rotor 22a. Since the volume of the second pump chamber 16b is smaller than the volume of the first pump chamber 16a, the gas which is transferred to the second pump chamber 16b is compressed so that the temperature thereof increases. Further, the gas is further transferred to the third pump chamber 16c with the smaller volume by the rotation of the rotor 22b so that the temperature thereof increases. Subsequently, the gas is exhausted from the third pump chamber 16c to the truncated conical tube by the rotation of the rotor 22c. At this time, since the truncated conical tube becomes narrower toward the high pressure side roots pump 10H, the flow rate of the gas increases and the temperature of the gas decreases due to the Venturi effect. Further, since the periphery of the truncated conical tube contacts the atmosphere, the heat is also emitted into the atmosphere through the truncated conical tube, so that the temperature of the gas decreases. In a state where the temperature of the gas decreases as described above, the gas flows from the intake hole 31 of the high pressure side roots pump 10H into the first pump chamber 16a. Even in the high pressure side roots pump 10H, as in the case of the low pressure side roots pump 10L, the gas is transferred in a compressed state from the first pump chamber 16a to the third pump chamber 16c and is exhausted from the exhaust hole.
Furthermore, as for the capacities of the respective motors 23 of the low pressure side roots pump 10L and the high pressure side roots pump 10H, the capacity of the low pressure side roots pump 10L having a low pressure becomes small, and the capacity of the high pressure side roots pump 10H having a high pressure becomes large. Further, it is possible to decrease the capacities of the respective motors 23 of the low pressure side roots pump 10L and the high pressure side roots pump 10H compared to the capacity of the motor of the existing roots pump in which N number of pump chambers are connected in series to each other, and hence to decrease the capacity of the motor even in total compared to the capacity of the motor of the roots pump of the related art.
Further, in the description above, a case has been described in which both the low pressure side roots pump 10L and the high pressure side roots pump 10H are formed as triple stages of pump chambers, but the roots pump having a single stage or more of pump chambers may be used.
In the embodiment, as not in the roots pump (hereinafter, referred to as the existing roots pump) in which N number of stages (N is a natural number equal to or larger than 2) of the pump chambers are connected in series to each other, two roots pumps, that is, the low pressure side roots pump 10L and the high pressure side roots pump 10H each including the rotary shaft 21 are provided and both roots pumps are connected to each other through the connection passage 41 by forming N number of stages of the pump chambers so as to have the same number of pump chambers in total. As a result, the length of the rotary shaft 21 constituting each of the low pressure side roots pump 10L and the high pressure side roots pump 10H is shortened compared to the existing roots pump. As described above, since an increase in the temperature of each of the roots pumps 10L and 10H is also small compared to the existing roots pump, the deformation of the rotary shaft 21 is suppressed, and hence there is an effect that the contact between the rotors 22a to 22c and the casing may be prevented.
Further, in a case where the roots pump 10 is used for the exhaust of the corrosive gas, the deterioration occurs in the high pressure side roots pump 10H in which the temperature of the gas increases. At this time, since only the rotors 22a to 22c of the high pressure side roots pump 10H in which the corrosion actively occurs may be replaced, there is also an effect that the maintenance cost may be decreased compared to the existing roots pump in which all rotors need to be replaced.
In addition, since the exhaust hole 33 of the low pressure side roots pump 10L is connected to the intake hole 31 of the high pressure side roots pump 10H by the truncated conical tube of which the cross-sectional area decreases as it goes toward the high pressure side roots pump 10H, it is possible to decrease the temperature of the gas by the Venturi effect and the external cooling when the gas passes through the truncated conical tube. Accordingly, since the temperature of the gas at the final-stage pump chamber 16c of the high pressure side roots pump 10H may be lower than the temperature of the gas at the final-stage pump chamber of the existing roots pump, there is an effect that the corrosion of the rotor inside the first to third pump chambers 16a to 16c which increase in temperature and pressure may be suppressed compared to the related art.
Furthermore, in the embodiment, an example has been described in which two roots pumps, that is, the low pressure side roots pump 10L and the high pressure side roots pump 10H are used, but three or more roots pumps which are respectively connected to each other by the connection passage 41 may be used.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-136799 | Jun 2012 | JP | national |
