JP3992176B2 - Vacuum exhaust method and vacuum exhaust device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vacuum pump and a vacuum pump for reducing the power consumption of a vacuum pump for a semiconductor manufacturing apparatus such as a sputtering apparatus or a vacuum deposition apparatus, in particular, a dry vacuum pump.
[0002]
[Prior art]
Many oil rotary vacuum pumps were used as vacuum pumps for early semiconductor manufacturing equipment. This pump enhances the sealing effect in the rotor blade chamber by immersing the rotor blade in the vacuum pump oil and sucks the vacuum pump oil into the rotor blade chamber, while performing lubrication in the rotor blade chamber to achieve highly efficient exhaust. By doing so, a low ultimate pressure can be easily obtained.
[0003]
The oil rotary pump has an exhaust valve on the discharge port side, and the exhaust gas in the rotor blade chamber is compressed together with the vacuum pump oil in the rotor blade chamber and discharged from the exhaust valve. When the vacuum pump oil fills the space that becomes a dead volume in the rotor blade chamber, a small amount of gas is also entrained in the oil, compressed to a pressure higher than atmospheric pressure, and efficiently discharged from the exhaust valve. The exhaust valve allows the vacuum pump oil and the exhaust gas from the rotor blade chamber to pass through, but has a role of preventing the atmosphere side gas from entering the rotor blade chamber. The gas intrusion prevention effect by the exhaust valve here has realized an efficient pump with small power consumption, assuming that power loss due to the backflow gas, which is a drawback of the displacement moving vacuum pump described later, can be ignored.
[0004]
An oil rotary pump is a vacuum pump having a structure that generally consumes less power and can easily obtain a low ultimate pressure. However, when used in a semiconductor manufacturing apparatus, it is necessary to pay attention to the following points.
[0005]
(1) Most of the gases used in semiconductor manufacturing equipment are highly reactive gases, and reaction products are generated by reaction with vacuum pump oil, which can cause the pump to become unrotatable or cause pump oil to deteriorate. Inconvenient to cause poor lubrication.
[0006]
(2) The vapor of the vacuum pump oil diffuses into the vacuum vessel, causing contamination.
[0007]
(3) The used vacuum pump oil often contains toxic substances such as arsenic compounds and phosphorus compounds, which requires a large amount of processing costs for processing as industrial waste, and also requires management man-hours.
[0008]
For these reasons, in recent years, dry vacuum pumps that do not use vacuum pump oil are used instead of oil rotary pumps. The dry vacuum pump here is a mechanical vacuum pump (hereinafter the same) that can be evacuated from the atmospheric pressure and does not have seal oil (hydraulic oil) in the suction chamber, Roots type, claw type and screw type are often used. Each of these pumps has a biaxial structure, and a pair of rotors are evacuated by rotating in opposite directions while maintaining a slight gap between them, and since there is no contact portion, the life is long and the manufacturing apparatus The solid component contained in the gas flowing in from the gas can be exhausted, and the corrosion resistance can be easily given to the corrosive gas.
[0009]
As described above, vacuum pumps used in semiconductor manufacturing facilities have been replaced with dry vacuum pumps that do not use vacuum pump oil, but dry vacuum pumps have the problem of higher power consumption than oil rotary vacuum pumps. ing. In particular, there is a need to reduce the power consumption of the dry vacuum pump to 50% or less because it is necessary to reduce energy consumption due to environmental problems and cost reduction of semiconductor manufacturing is required.
[0010]
For example, a roots-type dry vacuum pump is provided with a rotating body having a plurality of rotors adjacent to each other along a rotation axis, and the rotors facing each other rotate in the opposite direction with a slight gap therebetween to suck gas. The exhaust chamber is composed of three to six pump chambers, and sequentially pumps in each pump chamber. In this pump, since the gas pressure increases as the exhaust gas moves from the front stage to the rear stage, the exhaust capacity may be smaller in the rear stage than in the front stage. In the case where multiple roots-type rotors are provided on the same shaft, the current outer shapes of the rotors are the same due to the ease of processing and the ease of synchronization between the rotors. Therefore, in order to reduce the exhaust capacity stepwise from the gas suction side to the discharge side, it is possible to reduce the rotor thickness stepwise.
[0011]
Here, the compression of the exhaust gas by the Roots type pump is such that the exhaust gas is once confined in the space constituted by the recess on the rotor surface and the casing, and this space is connected to the discharge side space by rotating the rotor. This is done by instantaneously flowing back the discharge side gas into the space. In the Roots-type pump, an ultimate pressure of about 1 to 10 Pa is obtained, and the pressure from the ultimate pressure to around 3 kPa is a normal pressure. The discharge port pressure is constant at atmospheric pressure. Therefore, in order to keep the suction side in a vacuum, it is necessary to push back the gas that has flowed back into the rotor chamber during the compression stroke, and in the final stage that receives back flow from atmospheric pressure, the entire pump needs to be pushed back. About 70% to 80% of the power is used.
[0012]
In the above-mentioned multi-stage roots type pump, the work of the final stage is reduced if the amount of gas to be pushed back is small. For this reason, as described above, the rotor thickness is reduced to reduce the exhaust capacity of the pump rear stage. In this way, by setting the exhaust capacity of the final stage to be small, the required power in the normal pressure range of the pump is suppressed, which is currently used for energy saving.
[0013]
The claw pump has the same exhaust principle as the root type except for the rotor shape. On the other hand, the screw-type pump transports gas by moving the space formed by the screw grooves of two screws along the axial direction, and the gas of the discharge part flows into the space formed by the screw grooves and is compressed. Is performed in the same manner as in the roots type. Since the thread groove is continuous, a structure is adopted in which the pitch of the thread groove is continuously reduced in order to reduce the exhaust capacity as desired, such as roots type or claw type. However, since there is a limit to changing the pitch of the thread groove, a contrivance has been made such as combining the rotors having different pitches in a block shape to reduce the exhaust capacity of the final stage.
[0014]
The setting of the exhaust capacity of the final stage differs depending on the use of the pump. For example, in a multi-stage Roots type pump, when the displacement of the final stage is set to about 50% with respect to the first stage, a large amount of compression heat is generated in the normal pressure range. That is, in the low pressure CVD apparatus and the etching apparatus of the semiconductor manufacturing apparatus, the gas generated in the course of the reaction includes one that precipitates as a solid when the concentration exceeds the saturated vapor pressure in the exhaust apparatus. In order to exhaust gas, it is necessary to prevent precipitation by raising the temperature of the dry pump to about 100 to 160 ° C. For this purpose, an exhaust speed ratio of about 50% that can efficiently heat the pump by compression heat is employed.
[0015]
On the other hand, in a sputtering apparatus or a vapor deposition apparatus, the exhausted gas is mainly an inert gas such as argon or helium, and it is not necessary to increase the pump temperature, so that a pump with as little power consumption as possible is required. In this case, the final stage exhaust capacity is set to about 20 to 25% with respect to the first stage. With this setting, the power consumption at the ultimate pressure can be reduced by 30 to 60% with respect to the pump whose final stage exhaust capacity is about 50% of the first stage exhaust capacity.
[0016]
By the way, in a dry pump for applications that do not require a high temperature pump, it is possible to further save energy by setting the final stage exhaust capacity to 20% or less of the first stage exhaust capacity. , Mechanical failure occurs. For example, when the final stage exhaust capacity is about 25% of the first stage, the maximum exhaust speed is 80 m. ^Three In the / Hr class pump, the thickness of the first stage rotor is often about 30 mm. In this case, the rotor thickness of the final stage is 7.5 mm, and the strength of the rotor itself is reduced. There is a problem that it is difficult to obtain a perpendicularity between the side surface and the shaft center, and it is difficult to maintain a gap between the rotor side surface and the partition wall from 0.1 mm to 0.2 mm.
[0017]
In addition, since the clearance between the rotor side surface and the partition wall is required to be 0.1 mm to 0.2 mm due to the processing accuracy and the limitation of fluctuation due to the difference in thermal expansion between the casing and the rotor shaft, the ratio of the clearance to the rotor width Increasing the thickness will increase the volume efficiency. On the other hand, there is a method in which the width of the rotor on the final stage is set to a mechanically stable width and the rotor diameter is reduced to determine the width of the front rotor, but this method increases the pump length and saves it. Inconvenient in terms of space.
[0018]
On the other hand, JP-A-6-129384 provides a check valve that allows only gas flow from the main pump side to the atmosphere side after the dry vacuum pump (hereinafter also referred to as main pump). By providing an auxiliary pump with a smaller exhaust capacity than the main pump on the discharge side of the main pump so as to bypass the check valve, the gas that exhausts the discharge side of the main pump below the atmospheric pressure and enters the final stage of the pump A technique for reducing the pushing back work is disclosed.
[0019]
According to this technique, since the discharge side of the main pump, which has been conventionally set to atmospheric pressure, is evacuated and maintained by the auxiliary pump at a predetermined vacuum level below atmospheric pressure, the backflow gas to the main pump is greatly reduced. Therefore, it is possible to surely reduce the power required for pushing back the backflow gas, and energy saving (hereinafter also referred to as energy saving) of the driving power of the main pump can be achieved.
[0020]
[Problems to be solved by the invention]
However, according to the above publication, it is possible to surely reduce the power consumption of the main pump, but it is always possible to achieve efficient energy saving when viewed from the whole vacuum exhaust system including the auxiliary pump. Not necessarily. In other words, even if the power consumption of the main pump is reduced, depending on the operating state of the auxiliary pump that contributes to lowering the power consumption of the main pump, the power consumption of the auxiliary pump increases and the overall vacuum exhaust system can save energy. It turns out that the effect is reduced.
[0021]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a vacuum exhaust method and a vacuum exhaust apparatus capable of obtaining a highly efficient energy saving effect of the entire vacuum exhaust system including the main pump and the auxiliary pump. .
[0022]
[Means for Solving the Problems]
In solving the above problems, the present invention provides: With an auxiliary pump operated with the main pump, The exhaust speed of the auxiliary pump when the suction pressure of the main pump is 400 Pa is set to 3% or less of the exhaust speed of the main pump. Thereby, the increase in the size of the auxiliary pump and the increase in power consumption thereof can be suppressed, the installation space of the entire vacuum exhaust system can be reduced, and efficient energy saving can be achieved.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, a vacuum exhaust apparatus for a vacuum processing chamber will be described as an example in a process (light process) in which exhaust gas does not contain a component that deposits and accumulates in a pump, such as sputtering and vapor deposition.
[0024]
FIG. 1 shows a schematic piping configuration of an evacuation apparatus according to an embodiment of the present invention. The vacuum processing chamber 1 communicates with a main pump 2 constituted by a single dry vacuum pump via an exhaust pipe 5. Pipes 6a and 6b communicating with the atmosphere are connected to the discharge side of the main pump 2, and a gas flow from the main pump 2 side to the atmosphere side is allowed between these pipes 6a and 6b and the opposite flow is allowed. A check valve 4 to be prohibited is provided. An auxiliary pump 3 that exhausts the discharge side of the main pump 2 is disposed between the bypass pipes 7 a and 7 b that bypass the check valve 4.
[0025]
Note that a main valve for communicating / blocking between the vacuum processing chamber 1 and the main pump 2 is arranged in the exhaust pipe 5 even if not shown, and a downstream side of the exhaust pipe 5 is connected to an exhaust gas treatment device. Yes. A high vacuum pump such as a turbo molecular pump may be connected to the upstream side of the main pump 2.
[0026]
The configuration of the main pump 2 will be described with reference to FIGS. The main pump 2 in the present embodiment is composed of a volume transfer type roots type dry vacuum pump, but of course not limited to this, other volume transfer type or volume transfer type dry vacuum pumps such as a claw type or a screw type may be used. It is also possible to use it.
[0027]
The roots type dry vacuum pump 2 as a main pump has a known configuration. That is, a pair of rotating shafts 21 and 22 supported by bearings 26 and 27 are accommodated in the housing 20 adjacent to each other, and each of the rotating shafts 21 and 22 has three shapes shown in FIG. A plurality of leaf rotors 21a, 21b are provided. A slight gap is formed between the rotors 21a and 21b in each stage, and the respective rotation shafts are synchronously rotated in the opposite directions by the DC brushless motor 25 via a timing gear 28 (only one side of a pair of gears is shown here). By doing so, the gas sucked from the suction port 23 to which the exhaust pipe 5 is connected is sequentially transferred from the rotor on the front stage side to the rotor on the rear stage side, and the transferred gas is sent out to the discharge port 24 to which the pipe 6a is connected. It has become. Thereby, the vacuum processing chamber 1 is evacuated to a predetermined degree of vacuum. Here the maximum exhaust speed is 150m ^Three A roots type dry vacuum pump is used which can achieve an ultimate pressure of 2 Pa at / Hr (3000 Pa).
[0028]
Here, in the present embodiment, the rotors 21a and 21b provided on the rotary shafts 21 and 22 are thinned stepwise from the front side to the rear side, thereby reducing the exhaust capacity from the gas suction side to the discharge side. The exhaust gas volume is set to be small in stages, and the final stage exhaust capacity is 25% of the first stage exhaust capacity.
[0029]
The auxiliary pump 3 requires an efficient pump with low power consumption. That is, the pump structure preferably has a structure in which the volume of exhaust gas is reduced during the compression stroke of the pump. Specifically, a rotary blade type (Gode type), a piston type, a diaphragm type (membrane type), and a scroll type are suitable.
[0030]
In the displacement type pumps such as the root type, claw type, and screw type used as the main pump, the space is moved to the discharge side by the rotation of the rotor against the gas confined in the space formed by the rotor and the housing. The compression is performed by the discharge-side gas flowing back into the space at the moment of opening. Therefore, in the positive displacement pump, the backflow gas cannot be reduced efficiently, and the energy saving rate is reduced.
[0031]
On the other hand, in a pump having a structure in which the volume of exhaust gas is reduced in the compression stroke as described above, the volume is reduced during the compression process and becomes equal to or higher than atmospheric pressure, so that the volume displacement pump Such a reverse flow does not occur basically. Further, since the piston-type and diaphragm-type reciprocating pumps must have a suction valve and a discharge valve from the principle of exhaust, there is no back flow from the discharge port to the pump chamber (inside the cylinder). In the rotary blade type, even if the compression is insufficient and the pressure does not exceed the atmospheric pressure at the stage of gas discharge, the volume released to the discharge port side of the rotor chamber at that time is small, so backflow The impact is small. In practice, an exhaust valve that opens when the rotor chamber is at or above atmospheric pressure can be provided, so that backflow is further suppressed.
[0032]
As is apparent from the above description, the vacuum pumping apparatus according to the present invention is obtained by using as the auxiliary pump 3 a vacuum pump having a structure such as a rotary blade type (Gode type), a piston type, a diaphragm type (membrane type), or a scroll type. High energy saving effect can be obtained.
[0033]
In addition, although illustration of the specific structure of the auxiliary pump 3 in the present embodiment is omitted, the maximum exhaust speed is 1.8 m in the present embodiment. ^Three A rotary blade type (Gode type) dry vacuum pump having an ultimate pressure of 20 kPa or less is used.
[0034]
On the other hand, as a pump of another principle and structure different from the above-described exhaustion principle and structure, for example, drag type, vortex type, and turbo type vacuum pumps using gas viscosity are low in pump efficiency. Is not appropriate. In addition, the gas or water ejector is not suitable as the auxiliary pump 3 because the total energy efficiency is low and there is a possibility that the working gas and the working fluid may contaminate the vacuum.
[0035]
Next, the structure of the check valve 4 will be described with reference to FIG.
[0036]
The check valve 4 is formed between a housing 40 composed of a cylindrical upper main body 41 located on the atmosphere side and a cylindrical lower main body 42 located on the main pump 2 side, and between the upper main body 41 and the lower main body 42. The valve chamber 44, the annular valve seat 45 formed at the lower body 42 side end of the valve chamber 44, the valve ball 46 that can be separated from the valve seat 45, and the valve chamber 44 on the upper body 41 side. And a stopper 47 for restricting the lift operation of the valve ball 46 beyond a predetermined value.
[0037]
An annular seal ring 48 is interposed on the joint surface between the upper main body 41 and the lower main body 42, and the upper main body 41 and the lower main body 42 are connected by a plurality of bolt members 43. Is integrated. The valve ball 46 is made of, for example, a hollow stainless steel ball, and the surface thereof is covered with a thin rubber film. In the present embodiment, the weight of the valve bulb 46 is about 50 g, and the pressure on the inlet side of the check valve 4 is about 700 Pa higher than the atmospheric pressure. FIG. Are lifted up (lifted). As shown in the figure, the stopper 47 is composed of four claws that protrude downward at an interval of 90 degrees along the circumferential direction of the cylindrical lower end portion of the upper body 41. Therefore, the gas that lifts the valve bulb 46 and flows into the valve chamber 44 flows out between the claws constituting the stopper 47 and flows out to the atmosphere side.
[0038]
The check valve 4 configured as described above has low fluid resistance and opens with a slight increase in pressure on the inlet side, so that it can follow fast pressure fluctuations. That is, in the positive displacement pump used as the main pump 2, the gas in the pump discharge section repeatedly moves back and forth in the rotor chamber and is pushed out of the rotor chamber. When the intake gas amount of the main pump 2 is reduced, the valve ball 46 repeats seating and separation with respect to the valve seat 45 due to the influence of the pulsation here. In this case, if the followability of the valve body with respect to pulsation is poor, there is no time for the valve body to be seated, and the suction side of the auxiliary pump remains open to the atmospheric pressure and the discharge part of the main pump is decompressed. Can not be. Therefore, in the present embodiment, the valve body (46) of the check valve 4 is formed into a spherical shape, and the check valve 4 is opened and closed only by its own weight, so that the followability to pulsation is improved.
[0039]
In addition, the structure of a general check valve often urges the valve body toward the valve seat with a spring or swings the valve body like a door, but these ones obtain a low opening pressure. There are many difficulties in securing the followability of the valve body against pulsation and eliminating leakage when it is closed, and it is suitable for use as a check valve in the vacuum exhaust apparatus according to the present invention. Absent.
[0040]
Next, the details of the present invention will be described together with the operation of the vacuum exhaust apparatus of the present embodiment configured as described above.
[0041]
The vacuum processing chamber 1 is roughly evacuated from the atmospheric pressure to a predetermined degree of vacuum by the main pump 2. The auxiliary pump 3 is always operated when the main pump 2 is operating. If the discharge amount of the main pump 2 is exhausted by the auxiliary pump 3 because the exhaust gas amount of the main pump 2 is large, the check valve 4 is opened and the exhaust gas is indicated by an arrow a in FIG. Drain in the direction shown. On the other hand, when the exhaust action of the vacuum processing chamber 1 proceeds, the suction pressure of the dry vacuum pump 2 decreases, and accordingly, the gas amount at the discharge port 24 of the main pump 2 decreases.
[0042]
When the discharge side of the main pump 2 reaches a gas flow rate that can be reduced to the atmospheric pressure or less by the exhaust action of the auxiliary pump 3, the check valve 4 is in a pulsating state that repeatedly opens and closes. In the present embodiment, as described above, the check valve 4 has a structure in which followability with respect to pulsation is improved, so that the vacuum exhaust apparatus of the present invention can be operated with high reliability.
[0043]
When the discharge side of the main pump 2 is below atmospheric pressure, the check valve 4 is completely closed, and thereafter the gas flow in the direction of arrow a in FIG. It becomes only. As a result, the discharge pressure of the main pump 2 begins to decrease, and the amount of backflow gas to the main pump 3 decreases, so the power consumption of the main pump 2 decreases.
[0044]
When the exhaust gas amount of the main pump 2 is large enough to open the check valve 4, the auxiliary pump 3 is not very useful, and the power consumption of the main pump 2 and the power consumption of the auxiliary pump 3 are combined. In addition, the power consumption of the entire vacuum evacuation device is larger than when the auxiliary pump 3 is not operated. However, in semiconductor manufacturing equipment, the volume of the vacuum processing chamber (vacuum vessel) is often less than 100 liters, and the time for the auxiliary pump 3 to reach a useful pressure is several minutes. Can do.
[0045]
FIG. 5 shows an exhaust speed of 150 m ^Three / Hr pump speed 1.8m after main pump 2 (discharge side) ^Three The graph shows the power consumption (main pump 2 + auxiliary pump 3) characteristics with respect to the suction pressure of the main pump 2 in the vacuum exhaust apparatus to which the / Hr auxiliary pump 3 is attached. As described above, the main pump 2 is an energy-saving type pump whose final stage exhaust capacity is set to 25% of the first stage exhaust capacity. In FIG. 5, the alternate long and short dash line indicates the case where the auxiliary pump 3 is not attached, and the solid line indicates the case where the auxiliary pump 3 and the check valve 4 are attached. The horizontal axis (suction pressure) is a logarithmic scale.
[0046]
As shown in FIG. 5, by attaching the auxiliary pump 3, the power consumption rapidly decreases in the pressure range of 1 kPa or less, and compared with the case where the auxiliary pump 3 is not attached, the power consumption is 1.35 kW at the ultimate pressure. Is 0.32 kW, and an energy saving rate (power consumption reduction rate) of about 76% is obtained. When the suction pressure of the main pump 2 is 400 Pa, the power consumption without the auxiliary pump is 1.4 kW, whereas the power consumption with the auxiliary pump 3 is 0.67 kW. 52%.
[0047]
When the exhaust speed of the auxiliary pump 3 is increased, the pressure at which the power consumption of the main pump 2 starts decreasing decreases from the vicinity of 1 kPa shown in the drawing to the right side in the drawing, that is, the pressure at which the suction pressure is higher, and the pressure at which energy saving becomes effective The range expands. However, when the exhaust speed of the auxiliary pump 3 is increased, the power consumption of the auxiliary pump is increased and the energy saving effect is reduced. In general, in an evacuation system used in a semiconductor manufacturing apparatus, a small amount of process gas is poured into the vacuum processing chamber 1 to perform processing such as film formation while maintaining a predetermined pressure. At this time, the suction pressure of the main pump 2 is about 1500 Pa even at a high level. Therefore, the object of the present invention can be achieved if an energy saving effect is obtained in the suction pressure range of about 3000 Pa or less.
[0048]
Next, FIG. 6 shows a pumping speed ratio when a main pump and an auxiliary pump having different pumping speeds are combined, assuming that a dry vacuum pump as a main pump is used as a downstream pump of a turbo molecular pump. And the power consumption ratio. The suction pressure of the main pump is 400 Pa.
Here, the pumping speed ratio is the ratio of the pumping speed of the auxiliary pump to the pumping speed of the main pump, and the power consumption ratio is the ratio of the power consumption when the auxiliary pump is used and the power consumption when the auxiliary pump is not used. Therefore, the power consumption ratio of 100% means that there is no energy saving effect. The power consumption when the auxiliary pump is used means the total power consumption of the main pump and the auxiliary pump, and the power consumption when the auxiliary pump is not used means the power consumption of the main pump.
[0049]
From FIG. 6, it can be seen that the power consumption ratio decreases as the exhaust speed ratio increases, and thus the energy saving effect increases. Moreover, it is recognized that the reduction rate of the power consumption ratio decreases when the exhaust speed ratio is close to 3%. The reason will be described later. From the above, when the suction pressure of the main pump is 400 Pa, energy saving can be efficiently achieved by using the auxiliary pump having an exhaust speed of 3% or less with respect to the exhaust speed of the main pump.
In the present embodiment, the exhaust speed ratio of the main pump 2 and the auxiliary pump 3 is 1.2%, so the above condition is satisfied.
[0050]
The suction pressure at which the energy saving effect of the main pump appears by increasing the pumping speed ratio of the auxiliary pump to the main pump shifts to the high pressure side as described above. However, the power consumption of the auxiliary pump increases, and the main pump and the auxiliary pump The combined power consumption becomes larger than the power consumption when the auxiliary pump is not used. This will be described with reference to FIGS.
[0051]
Here, FIG. 7 shows typical values of power consumption with respect to the pumping speed of a pump that can be used as an auxiliary pump. FIG. 8 shows 150 m as the main pump 2 in the present embodiment. ^Three FIG. 8 shows power consumption when the pumping speed ratio of the auxiliary pump having the characteristics shown in FIG. 7 is changed with respect to the pumping speed of the main pump suction pressure of 400 Pa, taking a dry vacuum pump with a pumping speed of / Hr as an example.
[0052]
In FIG. 8, the alternate long and short dash line is the power consumption of only the main pump 2, and the power consumption is drastically decreased by increasing the pumping speed ratio of the auxiliary pump. Converge to the value of. The broken line shows the power consumption of the auxiliary pump having the characteristics shown in FIG. 7 replaced with the relationship with the exhaust speed ratio. The solid line is the sum of these, and this is the power consumption of the vacuum exhaust device.
[0053]
From the result shown by the solid line in FIG. 8, it can be seen that an exhaust speed ratio of about 3% of the auxiliary pump with respect to the main pump 2 shows the lowest power consumption. Considering a case where an energy saving rate of 50% (see FIG. 5) is obtained at an intake pressure of 400 Pa of the main pump 2, the exhaust speed ratio may be either 1.2% or 9.4%. The auxiliary pump at 9.4% is larger than the 1.2% auxiliary pump (ie, auxiliary pump 3 in the present embodiment), which causes problems in comparison of installation space and energy for manufacturing the pump. become. Therefore, if an auxiliary pump with an exhaust speed ratio of 3% or less is selected, a vacuum exhaust system with a high energy saving rate can be obtained as a whole. On the other hand, an auxiliary pump with an exhaust speed ratio exceeding 3% has an energy saving effect. Can be seen to be diminished.
[0054]
On the other hand, as shown by the solid line in FIG. 5, the power consumption is almost horizontal in the suction pressure range of 10 Pa or less. This state is when the discharge pressure of the main pump 2 becomes low and the compression work in the pump chamber becomes so small that it can be ignored. The power consumption here is the bearings 26 and 27 of the main pump 2 and the DC motor 25. The mechanical loss of the timing gear etc. which transmits rotational drive force to each rotating shaft 21 and 22 (mechanical loss) is represented. When the suction pressure of the main pump 2 is gradually increased, the power consumption gradually increases. This indicates that the compression work (here, the work of pushing back the backflow gas) has become visible in the final stage of the main pump 2. Since the power consumption of the main pump 2 has a proportional relationship with the discharge section pressure, in order to obtain the low power consumption shown by the solid line in FIG. 5, the auxiliary pump has the ability to exhaust to the discharge pressure at the time of measurement here. Will have to be.
[0055]
Therefore, when various dry pumps having different exhaust speeds are used to set the intake gas amount in which the power consumption increases by 10% from the power consumption at the ultimate pressure, and the pressure of the auxiliary pump at this time is examined, 6.5 kPa A value of 20 kPa was obtained. This indicates that the power consumption equal to the mechanical loss of the main pump 2 cannot be obtained at the ultimate pressure unless a pump capable of exhausting to a pressure of 20 kPa or less is used as the auxiliary pump 3.
[0056]
Subsequently, the solid line in FIG. 9 shows the exhaust speed characteristics of the vacuum exhaust apparatus in the present embodiment in comparison with the exhaust speed characteristics in the case where there is no auxiliary pump indicated by a one-dot chain line. At a suction pressure of 1 kPa or less, the exhaust speed is increased by about 10% compared to the case without an auxiliary pump. Furthermore, the ultimate pressure is improved from 2 Pa to 1 Pa. This is because the volume of backflow gas is reduced and the volumetric efficiency is increased because the discharge port pressure of the main pump 2 is reduced. The addition of the auxiliary pump 3 is effective not only for reducing the power consumption but also for improving the exhaust speed and the ultimate pressure.
[0057]
As described above, according to the present embodiment, the power consumption of the main pump can be efficiently reduced with an auxiliary pump having a small exhaust capacity, so that the entire vacuum exhaust system can be efficiently saved. be able to.
For example, if approximately 300 dry vacuum pumps (main pumps) are used in a semiconductor factory that processes 10,000 wafers of φ200 mm per month, the dry process used in the light process that is the subject of the present invention. If the vacuum pumps account for 30% of the total, the number is 90 units. A dry vacuum pump without an auxiliary pump is used for these, and these are replaced with the dry vacuum pump with an auxiliary pump of the present invention, and the characteristics (pumping speed ratio) of the auxiliary pump 3 of the above embodiment as the auxiliary pump. By selecting a pump equipped with 1 kW, it is possible to reduce 1 kW of power per unit, so that the electricity bill per year can be saved 1,182 million yen per factory (calculated as 1 kW = 15 yen). Further, when the carbon dioxide emission amount is obtained, a reduction effect of 276 t can be obtained.
[0058]
On the other hand, the auxiliary pump 3 has a small installation space, and the bypass pipes 7a and 7b connected to the discharge pipe of the main pump 2 can be constituted by thin pipes of about 10 mm, and an electric control system is not required. The existing dry vacuum pump can be easily and inexpensively modified into the energy saving pump (evacuation apparatus) here. As a result, it is possible to greatly contribute to the reduction of the semiconductor manufacturing cost and the addition to the environment.
[0059]
The embodiment of the present invention has been described above. Of course, the present invention is not limited to this, and various modifications can be made based on the technical idea of the present invention.
[0060]
For example, in the above embodiments, a single dry vacuum pump has been described as the main pump 2. However, the present invention is not limited to this. For example, a composite pump constructed by connecting a plurality of roots type dry vacuum pumps in series. Can also be used as the main pump.
[0061]
Moreover, although the above embodiment demonstrated the structure which connects the auxiliary pump 3 to the discharge side of the single main pump 2, for example, as shown in FIG. 10, a plurality of units (three units in the figure) are arranged in parallel. The present invention is also applicable to a configuration in which the discharge side of the main pumps 2A to 2C is exhausted by a single auxiliary pump 3. In the illustrated example, check valves 4A to 4C are provided for the main pumps 2A to 2C, and on-off valves 11A to 11C are provided between the auxiliary pumps 3. The main pumps 2A to 2C are in communication with different vacuum processing chambers. In this case, since the amount of intake gas of the auxiliary pump 3 varies depending on the number of operating main pumps 2A to 2C, the pumping speed (rotation speed) of the auxiliary pump can be made variable according to the number of operating main pumps 2A to 2C. desirable.
[0062]
【The invention's effect】
As described above, according to the evacuation method and the evacuation apparatus of the present invention, the power consumption of the main pump can be efficiently reduced with an auxiliary pump having a small evacuation capacity. Efficient energy saving can be achieved. Moreover, since a small pump can be used as an auxiliary pump, the installation space of an auxiliary pump can be reduced.
[Brief description of the drawings]
FIG. 1 is a schematic piping configuration diagram of an evacuation apparatus according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a configuration of a main pump in the embodiment of the present invention.
3 is a cross-sectional view in the direction of line [3]-[3] in FIG. 2;
FIG. 4 is a cross-sectional view showing a configuration of a check valve in the embodiment of the present invention.
FIG. 5 is a diagram for explaining the operation of the vacuum exhaust apparatus according to the embodiment of the present invention, and shows the relationship between the main pump suction pressure and the power consumption of the entire apparatus.
FIG. 6 is a diagram for explaining the operation of the vacuum exhaust apparatus according to the embodiment of the present invention, and shows the relationship between the exhaust speed ratio of the auxiliary pump to the main pump and the power consumption ratio.
FIG. 7 is a diagram showing the relationship between the exhaust speed of a typical auxiliary pump and the power consumption.
FIG. 8 is a diagram showing power consumption characteristics of the vacuum exhaust device according to the embodiment of the present invention.
FIG. 9 is a diagram showing the relationship between the suction pressure and the exhaust speed of the vacuum exhaust apparatus in the embodiment of the present invention.
FIG. 10 is a schematic piping configuration diagram of an evacuation apparatus showing a modification of the embodiment of the present invention.
[Explanation of symbols]
1 Vacuum processing chamber
2 Main pump
3 Auxiliary pump
4 Check valve
21, 22 Rotating shaft
21a, 22a rotor
45 Valve seat
46 Ball

Claims (8)

A main pump that communicates with the vacuum processing chamber, a check valve that is connected to the discharge side of the main pump and allows only gas flow from the main pump to the atmosphere, and the check valve on the discharge side of the main pump A vacuum exhaust method for evacuating the vacuum processing chamber using a vacuum exhaust device that is connected in parallel to each other , has an exhaust capacity smaller than that of the main pump, and includes an auxiliary pump operated together with the main pump. There,
A vacuum evacuation method, wherein an exhaust speed of the auxiliary pump when the suction pressure of the main pump is 400 Pa is 3% or less of an exhaust speed of the main pump.   The vacuum exhaust method according to claim 1, wherein the ultimate pressure of the auxiliary pump is 20 kPa or less. A main pump that communicates with the vacuum processing chamber, a check valve that is connected to the discharge side of the main pump and allows only gas flow from the main pump to the atmosphere, and the check valve on the discharge side of the main pump are connected in parallel with respect to, the suction pressure of the main pump has a 3% of the exhaust speed of the exhaust gas velocity that put in 400 Pa, characterized in that it consists of an auxiliary pump which is operated together with the main pumping Vacuum exhaust device.   4. The vacuum exhaust apparatus according to claim 3, wherein the main pump is a displacement moving type dry vacuum pump or a composite pump in which the dry vacuum pumps are connected in series in a plurality of stages.   4. The vacuum exhaust apparatus according to claim 3, wherein a plurality of the main pumps are arranged in parallel, and the suction side of the auxiliary pump is connected to the discharge side of each main pump.   4. The vacuum exhaust apparatus according to claim 3, wherein the auxiliary pump is a vacuum pump having an ultimate pressure of 20 kPa or less.   The vacuum pumping apparatus according to claim 6, wherein the auxiliary pump is a rotary vane type (Gode type), piston type, diaphragm type (membrane type) or scroll type vacuum pump.   The vacuum exhaust apparatus according to claim 3, wherein the check valve has a spherical valve body that is seated on the valve seat by its own weight.

Images