VACUUM EXHAUST APPARATUS AND VACUUM PUMP USED THEREIN

A vacuum exhaust apparatus capable of accurately and rapidly adjusting the pressure in an exhaust chamber and a vacuum pump used therein are provided. A vacuum pump includes a rotor that rotates to exhaust an exhaust chamber and a casing having an inlet port. A valve is located between the inlet port of the vacuum pump and an outlet port of the exhaust chamber. A controller performs control such that the pressure in the exhaust chamber matches a target value. The controller adjusts the opening degree of the valve when the absolute value of the difference between the pressure in the exhaust chamber and the target value is greater than a predetermined value, and adjusts the rotational speed of the rotor of the vacuum pump when the absolute value of the difference between the pressure in the exhaust chamber and the target value is less than the predetermined value.

TECHNICAL FIELD

The present disclosure relates to a vacuum exhaust apparatus for controlling the pressure in an exhaust chamber and a vacuum pump used therein.

BACKGROUND

An apparatus that manufactures semiconductors, liquid crystals, solar cells, light emitting diodes (LEDs), and the like (hereinafter referred to as “semiconductors and the like) has a vacuum chamber that is an exhaust chamber to be exhausted and into which process gas is introduced for processes, such as thin film formation and etching, on objects to be processed placed in the vacuum chamber.

For example, Japanese Patent Application Publication No. 2014-148703 discloses a technique to perform control to set the pressure in such a vacuum chamber to a desired pressure by vacuum exhausting the vacuum chamber while changing the opening degree of a valve connected to the outlet port of the vacuum chamber and the rotational speed of the rotor of a turbomolecular pump, which is a vacuum pump connected to the downstream side of the valve.

SUMMARY

However, with the above-mentioned vacuum exhaust technique, a change in the opening degree of the valve results in a relatively large change in the pressure in the vacuum chamber, whereas a change in the rotational speed of the rotor of the turbomolecular pump results in a relatively small change in the pressure in the vacuum chamber. Accordingly, it is difficult to set the pressure in the vacuum chamber to a desired pressure.

In view of the above, it is an objective of the present disclosure to provide a vacuum exhaust apparatus capable of accurately and rapidly adjusting the pressure in an exhaust chamber and a vacuum pump used therein.

In order to achieve the above objective, a vacuum exhaust apparatus according to the first aspect of the present disclosure includes:

a vacuum pump including a rotor configured to rotate to exhaust an exhaust chamber, and a casing having an inlet port;

a valve located between the inlet port of the vacuum pump and an outlet port of the exhaust chamber; and

a controller configured to perform control such that a pressure in the exhaust chamber matches a target value, wherein

the controller is configured to control the pressure by adjusting an opening degree of the valve when an absolute value of a difference between the target value and the pressure is greater than a predetermined value, and by adjusting a rotational speed of the rotor when the absolute value of the difference is less than the predetermined value.

In the above vacuum exhaust apparatus, the controller may be configured to perform control such that the rotational speed of the rotor is constant when the absolute value of the difference is greater than the predetermined value, and that the opening degree of the valve is constant when the absolute value of the difference is less than the predetermined value.

In the above vacuum exhaust apparatus, the controller may be configured to increase a gain of a transfer function GVrepresented by equation (1):

when the absolute value of the difference is greater than the predetermined value, and increase a gain of a transfer function GMrepresented by equation (2):

when the absolute value of the difference is less than the predetermined value,

in equation (1), OVis a Laplace transform where an initial value of the opening degree of the valve is 0, in equation (2), ΩMis a Laplace transform where an initial value of the rotational speed of the rotor is 0, and in equations (1) and (2), δPis a Laplace transform where an initial value of the difference is 0.

In the above vacuum exhaust apparatus, the controller may be configured to reduce the gain of the transfer function GMwhen the absolute value of the difference is greater than the predetermined value, and reduce the gain of the transfer function GVwhen the absolute value of the difference is less than the predetermined value.

In the above vacuum exhaust apparatus,

the vacuum pump may include a magnetic bearing configured to levitate and support the rotor, and

the controller may be configured to change the opening degree of the valve when the rotational speed of the rotor matches a natural frequency of displacement of the rotor or an absolute value of a difference between the rotational speed and the natural frequency is less than or equal to a predetermined value while the pressure matches the target value, and control the rotational speed of the rotor such that the pressure matches the target value again.

In the above vacuum exhaust apparatus, the predetermined value may be changed while the rotor is rotated according to at least one of the opening degree of the valve and a type and an amount of gas that is introduced into the exhaust chamber and exhausted by the vacuum pump.

To achieve the above objective, a vacuum pump according to the second aspect of the present disclosure is a vacuum pump to be used in a vacuum exhaust apparatus including a valve and a controller configured to perform control such that a pressure in an exhaust chamber matches a target value, the vacuum pump including:

a rotor configured to rotate to exhaust the exhaust chamber; and

a casing having an inlet port that allows the valve to be located between the inlet port and an outlet port of the exhaust chamber,

wherein the controller is configured to control the pressure by adjusting an opening degree of the valve when an absolute value of a difference between the target value and the pressure is greater than a predetermined value, and by adjusting a rotational speed of the rotor when the absolute value of the difference is less than the predetermined value.

In the above vacuum pump, the controller may be configured to perform control such that the rotational speed of the rotor is constant when the absolute value of the difference is greater than the predetermined value, and that the opening degree of the valve is constant when the absolute value of the difference is less than the predetermined value.

In the above vacuum pump, the controller may be configured to increase a gain of a transfer function GVrepresented by equation (1):

when the absolute value of the difference is greater than the predetermined value, and increase a gain of a transfer function GMrepresented by equation (2):

when the absolute value of the difference is less than the predetermined value, in equation (1), OVis a Laplace transform where an initial value of the opening degree of the valve is 0, in equation (2), ΩMis a Laplace transform where an initial value of the rotational speed of the rotor is 0, and in equations (1) and (2), δPis a Laplace transform where an initial value of the difference is 0.

In the above vacuum pump, the controller may be configured to reduce the gain of the transfer function GVwhen the absolute value of the difference is greater than the predetermined value, and reduce the gain of the transfer function GMwhen the absolute value of the difference is less than the predetermined value.

The above vacuum pump may further include a magnetic bearing configured to levitate and support the rotor.

The controller may be configured to change the opening degree of the valve when the rotational speed of the rotor matches a natural frequency of displacement of the rotor or an absolute value of a difference between the rotational speed and the natural frequency is less than or equal to a predetermined value while the pressure matches the target value, and control the rotational speed of the rotor such that the pressure matches the target value again.

In the above vacuum pump, the predetermined value may be changed while the rotor is rotated according to at least one of the opening degree of the valve and a type and an amount of gas that is introduced into the exhaust chamber and exhausted by the vacuum pump.

According to the present disclosure, a vacuum exhaust apparatus capable of accurately and rapidly adjusting the pressure in an exhaust chamber and a vacuum pump used therein are provided.

DETAILED DESCRIPTION

A vacuum exhaust apparatus according to an example of the present disclosure is now described with reference to the drawings. As shown inFIG.1, a vacuum exhaust apparatus10is an apparatus included in a vacuum apparatus D used for processes, such as thin film forming process and etching process, in a semiconductor manufacturing apparatus, for example. The vacuum exhaust apparatus10vacuum exhausts an exhaust chamber to be exhausted (vacuum chamber)4, in which objects to be processed are placed, so that the pressure in the exhaust chamber becomes a desired pressure.

The vacuum exhaust apparatus10includes a vacuum pump1, which exhausts the process gas introduced in the exhaust chamber4, a valve2, which is located between an outlet port (not shown) of the exhaust chamber4and an inlet port11a(FIG.2) of the vacuum pump1to open and close the gas flow passage, and a controller3for performing control such that the pressure in the exhaust chamber4matches a target value.

As shown inFIG.2, the vacuum pump1, which is a turbomolecular pump, includes an outer cylinder portion11, a base portion12fixed to the outer cylinder portion11, and a rotor20, which is rotatably housed in a casing13formed by the outer cylinder portion11and the base portion12. The upper side as viewed inFIG.2of the outer cylinder portion11is opened to form a gas inlet port11a, and a gas outlet port12ais formed in the side surface of the base portion12. The outer cylinder portion11has a flange11bat the side including the inlet port11a, and the lower end surface of a valve main body2a(FIG.6) of the valve2is fixed to this flange11b.

The rotor20has a rotor main body20a, a rotating shaft30, and a washer70. The rotating shaft30is rotatably supported in the casing13to rotate the rotor20. A plurality of rotor blades21inclined at a predetermined angle is integrally formed on the outer circumferential surface of an upper part, as viewed inFIG.2, of the rotor main body20a. The rotor blades21are arranged radially with respect to the axis of the rotating shaft30of the rotor20and in multiple stages in the axial direction of the rotating shaft30of the rotor20. Stator blades40are located between the stages of the rotor blades21. The rotor blades21and the stator blades40alternate in the axial direction of the rotating shaft30of the rotor20. The plurality of stator blades40is also inclined at a predetermined angle. The outer circumference ends of the stator blades40are held between multiple ring-shaped stator blade spacers50arranged in stages in the outer cylinder portion11, so that the stator blades40are arranged radially and in multiple stages between the rotor blades21.

A threaded spacer60is provided between the base portion12and the stator blade spacer50that is the closest to the downstream side. The threaded spacer60is cylindrical and has a spiral thread groove60ain its inner circumference surface. A cylindrical portion22is formed under the rotor main body20aas viewed inFIG.2(on the downstream side in the gas flow direction) and about the axis of the rotating shaft30. The outer circumferential surface of the cylindrical portion22is adjacent to and faces the inner circumference surface including the thread groove60aof the threaded spacer60. The space defined by the outer circumferential surface of the cylindrical portion22and the thread groove60aof the threaded spacer60communicates with the outlet port12a.

The disc-shaped washer70is formed about the axis of the rotating shaft30. Bolts71are fastened to the rotating shaft30through the rotor main body20aand the washer70, fixing the rotor main body20aand the washer70to the rotating shaft30.

In the vacuum pump1, when the rotor20is rotated at high speed, the rotor blades21strike the gas molecules sucked through the inlet port11atoward the downstream side. The struck gas molecules collide against the stator blades40, which are alternately arranged, move downward, and are then struck by the rotor blades21of the next stage and thus moved to the downstream side. This action is sequentially repeated to the lowermost stages of the rotor blades21and the stator blades40. The gas thus sent to threaded spacer60is guided by the thread groove60ato the outlet port12aand exhausted from the outlet port12a. In this procedure, the pressure in the gas exhaust chamber4can be adjusted to a desired pressure by adjusting the rotational speed of the rotor20. As shown inFIG.1, the vacuum pump1has a rotational speed detector1afor detecting the rotational speed of the rotor20. The detection value of the rotational speed of the rotor20detected by the rotational speed detector1ais output to the controller3.

Protective bearings31are arranged near the upper side and the lower side as viewed inFIG.2(the upstream side and downstream side in the gas flow direction) of the rotating shaft30. The protective bearings31prevent damage of the vacuum pump1, which would otherwise occur if an abnormality renders radial magnetic bearings33or axial magnetic bearing34, which will be described below, uncontrollable, causing the vacuum pump1to be in contact with and support the rotating shaft30.

The rotating shaft30is driven by a brushless DC pump motor32to rotate. Two radial magnetic bearings33support the rotating shaft30in the radial direction, and an axial magnetic bearing34supports the rotating shaft30in the axial direction. The two radial magnetic bearings33are on opposite sides of the pump motor32. The rotating shaft30is levitated and supported by these radial magnetic bearings33and the axial magnetic bearing34.

The two radial magnetic bearings33each have four electromagnets33a, which exert magnetic attraction force on the rotating shaft30. Two of the four electromagnets33aare located across the rotating shaft30on one of two coordinate axes that are perpendicular to the axis of the rotating shaft30and also perpendicular to each other. The other two electromagnets33aare located on the other coordinate axis. The two radial magnetic bearings33each have four position sensors33b, which may be inductance or eddy current sensors, for detecting the radial position of the rotating shaft30. Two of the four position sensors33bare located across the rotating shaft30on one of two coordinate axes that are perpendicular to the axis of the rotating shaft30, parallel to the above-mentioned coordinate axes, and perpendicular to each other. The other two position sensors33bare located on the other coordinate axis.

The rotating shaft30has a magnetic disc (hereinafter referred to as “armature disc”)80located about the axis of the rotating shaft30. The axial magnetic bearing34has two electromagnets34athat exert magnetic attraction force on the armature disc80. The two electromagnets34aare on opposite sides of the armature disc80. The axial magnetic bearing34has a position sensor34b, which may be an inductance or eddy current sensor, for detecting the axial position of the rotating shaft30. The inductance or eddy current position sensors33bof the radial magnetic bearings33and the inductance or eddy current position sensor34bof the axial magnetic bearing34have the same structure as an electromagnet, and their cores, on which conductor coils are wound, face the rotating shaft30.

A stator90extends upright from the base portion12to protect the radial magnetic bearings33, the axial magnetic bearing34, the pump motor32, and the like from the sucked gas.

The vacuum pump1has a pump controller (not shown), which is integral with or connected via a cable to the vacuum pump1. The pump controller supplies power to the radial magnetic bearings33, the axial magnetic bearing34, and the pump motor32and transmits and receives signals to and from the position sensors33band34b. The pump controller supplies a high-frequency alternating voltage having a predetermined amplitude to the conductor coils of the position sensors33band34bof the radial magnetic bearings33and the axial magnetic bearing34. The inductance of the conductor coil wound around the core of each position sensor33b,34bvaries according to the distance between the core and the rotating shaft30. This variation in the inductance results in variation in the amplitude of the voltage applied to the conductor coil. The pump controller detects this variation in the amplitude value, thereby detecting the position of the rotating shaft30. As shown inFIG.3, this amplitude value (position sensor detection value EO) has nonlinearity and increases or decreases in a curve according to the variation in the position of the rotating shaft30. The sum EO1+EO2(or the difference depending on how the positive and negative signs are set) of the amplitude values of the two position sensors33bfacing each other across the rotating shaft30on each of the above-mentioned coordinate axes has quasi-linearity with respect to the variation in the position of the rotating shaft30. Thus, the pump controller calculates this sum (or difference) and uses the value as a detection signal of the position sensors33bin order to apply the linear control theory. This allows the position of the rotating shaft30to be controlled based on this theory. The pump controller places the rotating shaft30at the target position by performing feedback control that adjusts the values of current flowing through the electromagnets33abased on the sum (or difference) of the detection signals of the two position sensors33bon each coordinate axis.

As shown inFIG.4, the magnetic attraction force f exerted by each electromagnet33aof the radial magnetic bearings33on the rotating shaft30also has nonlinearity and increases or decreases in a curve according to the variation in the current flowing through the electromagnet33a. As such, when the rotating shaft30is deviated from the target position, one of the two electromagnets33afacing each other across the rotating shaft30on each coordinate axis that has a greater distance to the rotating shaft30receives a current of a current value (I0+i1) obtained by adding a current value i1to a predetermined DC current value I0(hereinafter referred to as “bias current value”). The other of the two electromagnets33athat has a smaller distance to the rotating shaft30receives a current of a current value (I0−i1) obtained by subtracting the current value i1from the bias current value I0. The current values are thus controlled. In this manner, the sum of the magnetic attraction forces fhx1+(−fhx2) exerted by two electromagnets33ais used as the magnetic attraction force acting on the rotating shaft30. Accordingly, the magnetic attraction force has quasi-linearity with respect to the variation in the current value, allowing for the application of the above-mentioned linear control theory.

The configuration of the axial magnetic bearing34is basically the same as the configuration of the radial magnetic bearings33. However, for purposes such as reducing the required space, instead of arranging two position sensors on opposite sides of the armature disc80in the axial direction of the rotating shaft30, only one position sensor34bmay be placed, and the other position sensor may be replaced by a coil that is placed on a circuit substrate in the controller and has a predetermined inductance. In this case, the inductance of the coil provided on the circuit substrate is a predetermined value, and the amplitude value of the alternating voltage is a predetermined value. This lowers the accuracy of the linearization of the sum (or difference) of the two position sensors with respect to the variation in the position of the rotating shaft30. Nevertheless, this technique is useful when the vacuum pump1operates normally.

The bearing force for the rotor20, which is supported and levitated by the radial magnetic bearings33and axial magnetic bearing34, includes a component of force proportional to the variation in the position of the rotor20, that is, a component corresponding to elastic force. The rotor20therefore has a natural frequency according to its mass or moment of inertia. The levitated rotor20has six degrees of freedom in total, including three degrees of freedom in the directions of the coordinate axes of a three-dimensional rectangular coordinate system having one coordinate axis (hereinafter referred to as “z-axis”) aligned with the axis of the rotating shaft30, and three degrees of freedom about these axes. The angle of rotation of the degree of freedom about the z-axis is controlled by the pump motor32. The other five degrees of freedom are affected by the bearing forces of the radial magnetic bearings33and the axial magnetic bearing34and thus have natural frequencies according to the bearing forces of the radial magnetic bearings33and the axial magnetic bearing34. In particular, each of the equations of motion of the rotor20of the two degrees of freedom about the two axes perpendicular to the z-axis and perpendicular to each other (hereinafter referred to as “x-axis” and “y-axis”) includes a term that is proportional to the rotational speed about the axis of the other of these degrees of freedom (hereinafter referred to as an “interaction term”), as shown in equation (3) of the equation of motion about the x-axis and equation (4) of the equation of motion about the y-axis below. The magnitudes of these interaction terms are proportional to the rotational speed of the rotating shaft30rotated by the pump motor32.

In equations (3) and (4), J is the moment of inertia about the x-axis or y-axis of the rotor20, Jzis the moment of inertia about the z-axis of the rotor20, C is the viscous resistance coefficient about the x-axis or y-axis, θxis the angle of rotation of the rotor20about the x-axis, θyis the angle of rotation of the rotor20about the y-axis, and Oz is the angle of rotation of the rotor20about the z-axis. In equation (3), Dxis the disturbance moment acting about the x-axis, and Gxis the spring constant of the moment about the x-axis produced by the bearing force of the radial magnetic bearings33. In equation (4), Dyis the disturbance moment acting about the y-axis, and Gyis the spring constant of the moment about the y-axis produced by the bearing force of the radial magnetic bearings33. Dxand Dyare caused by factors such as the imbalance of the rotor20and the exhaust load of the vacuum pump1. Gxand Gyactually have frequency characteristics according to the control design of the radial magnetic bearings33. Specifically, since the rotor20has the rotor main body20a, the rotating shaft30, and the washer70as described above, the moment of inertia Jzand the moment of inertia J are the sum of the moments of inertia of the rotor main body20a, the rotating shaft30, and the washer70.

Normally, an equation for obtaining the natural frequency of each degree of freedom can be derived from the equation of motion of the degree of freedom. However, as for the degrees of freedom about the x-axis and y-axis of the radial magnetic bearings33, it is difficult to derive the equations for obtaining the natural frequencies for reasons such as the presence of the interaction terms in the equations of motion of these degrees of freedom as described above. For this reason, a conventional technique designs a specific magnetic bearing and relies on trial experiments or computer simulation using the finite element method or the like to obtain values of the natural frequencies of the specific magnetic bearing.

However, even though this technique can determine the natural frequency for each specific magnetic bearing, qualitative analyses of natural frequency, such as an analysis on how the natural frequency changes when the design value is changed, cannot be conducted. The natural frequency of a specific magnetic bearing is obtained after its design is completed, and if the design is changed for some reason, the natural frequency is obtained again after completing the design change. The design needs to be changed again in case of any problem. As a result, a significant amount of time is required to design a magnetic bearing and a turbomolecular pump.

In the present disclosure, in light of the fact that the radial magnetic bearings33of the vacuum pump1, which is a turbomolecular pump, are used in a vacuum, the viscous resistance coefficient C is taken as 0, and equations (5) and (6) that give two natural frequencies ω1and ω2of the rotor20that are present about each of the x-axis and the y-axis are derived from equations (3) and (4) above. Two natural frequencies given by equations (5) and (6) are present for each of the degrees of freedom about the x-axis and y-axis.

As shown inFIG.5, as the

increases after the rotating shaft30starts to rotate, the natural frequency ω1of the rotor20decreases while the natural frequency ω2increases. As the rotation frequency Ωzincreases, the natural frequency ω2approaches the rotation frequency Ωz, matches the rotation frequency Ωz, and then departs from the rotation frequency Ωz.

When the natural frequencies ω1and ω2are equal or close to the rotation frequency Ωzof the rotating shaft30, resonance of the rotor20is induced, making it difficult for the radial magnetic bearings33and the axial magnetic bearing34to levitate and support the rotor20and also causing fatigue failure due to the continuous vibration of the rotor blades21and the repeated stress fluctuation. As such, the controller3changes the opening degree of the valve2when the rotational speed (rotation frequency Ωz) of the rotor20matches the natural frequency ω1, ω2of displacement, or when the absolute value of the difference between the rotational speed of the rotor20and the natural frequency ω1, ω2is less than or equal to a predetermined value while the pressure in the exhaust chamber4matches the target value, and controls the rotational speed of the rotor20such that the pressure in the exhaust chamber4matches the target value again.

As shown inFIG.6, the valve2includes a valve main body2a, a valve body2cfixed to a shaft2b, a valve motor2dthat drives and rotates the shaft2bto pivot the valve body2c, and an opening2e, which is opened and closed by the valve body2c. The valve2is provided between the outlet port (not shown) of the exhaust chamber4and the inlet port11aof the vacuum pump1. The opening2eof the valve2is connected to and communicates with the outlet port of the exhaust chamber4and the inlet port11aof the vacuum pump1.

The valve2uses the valve motor2dto pivot the valve body2cto place it at a desired position overlapping the opening2e. The opening area of the opening2eis thus adjusted to adjust the opening degree. By adjusting the opening degree of the valve2, the pressure in the exhaust chamber4can be adjusted to a desired pressure. As shown inFIG.1, the valve2has an opening degree detector2f, such as an encoder, that detects the opening degree. The detection value of the opening degree of the valve2detected by the opening degree detector2fis output to the controller3.

The controller3performs control such that the pressure in the exhaust chamber4matches a target value by adjusting the opening degree of the valve2or the rotational speed of the rotor20of the vacuum pump1under predetermined conditions. The controller3has portions including a control portion, which may include a central processing unit (CPU) (not shown), and a storage portion, which may include a random-access memory (RAM), read-only memory (ROM), and flash memory. The storage portion stores various data such as programs to be executed by the control portion, fixed data, and detection data. The storage portion also functions as working memory for the control portion. The control portion controls the pressure in the exhaust chamber4by executing a program stored in the storage portion.

When the opening degree of the valve2is changed, a change in the opening degree results in a relatively large change in the pressure in the exhaust chamber4. For example, when the pressure in the exhaust chamber4needs to be increased only minimally, even a minimal decrease in the opening degree of the valve2increases the pressure significantly. When the pressure needs to be lowered only minimally, even a minimal increase in the opening degree of the valve2reduces the pressure significantly. Furthermore, factors such as the backlash of the gear that transmits the rotation of the valve motor2dto the valve body2cor the elastic slippage or movement slippage of the belt may cause an error in the position of the valve body2cmoved by a rotation of the valve motor2d. This may prevent the accurate setting of the desired opening degree. An attempt to achieve accurate control by increasing the gain of a change in the opening degree of the valve2with respect to a change in pressure and reducing the steady-state deviation of the pressure with respect to the desired pressure would cause, in the worst case, the oscillatory phenomenon of the opening degree of valve2. As such, the desired pressure cannot be achieved accurately.

In contrast, when the rotational speed of the rotor20of the vacuum pump1is changed, a change in the rotational speed results in a relatively small change in the pressure in the exhaust chamber4. Thus, when the pressure in the exhaust chamber4needs to be changed significantly, a significant change is required in the rotational speed of the rotor20. However, when the vacuum pump1is a turbomolecular pump, the rotor20needs to be rotated at high speed to provide a desired exhaust performance and is thus made of a high-strength metal, such as an aluminum alloy, that resists damage when receiving a large centrifugal force. Accordingly, the rotor20has a large moment of inertia. It is therefore difficult to significantly change the rotational speed of the rotor20within a short time, or rapidly.

It may also be contemplated to use a motor capable of generating high torque as the pump motor32for rotating the rotor20to increase the acceleration/deceleration torque. However, when a brushless DC motor, which is relatively inexpensive to manufacture, is used, a greater torque constant increases the induced voltage constant. This in turn increases the counter-electromotive force during high-speed operation, which may prevent a current from flowing sufficiently to generate acceleration/deceleration torque. As a result, a significant rapid change in the rotational speed cannot be achieved. Inability to achieve a significant rapid change in the rotational speed of the rotor20lengthens the time required for a semiconductor manufacturing apparatus to treat wafer surfaces, for example, hindering an increase in the quantity of manufactured semiconductors.

The controller3solves the above problem by adjusting the opening degree of the valve2when the absolute value of the difference between the pressure in the exhaust chamber4and the target value is greater than a predetermined value, and adjusting the rotational speed of the rotor20of the vacuum pump1when the absolute value of the difference between the pressure in the exhaust chamber4and the target value is less than the predetermined value.

A method is now described that vacuum exhausts the exhaust chamber4using the controller3so that the pressure in the exhaust chamber4becomes a desired pressure. As shown inFIG.1, a pressure gauge5is provided in the exhaust chamber4, into which process gas flows, and the pressure gauge5measures the pressure in the exhaust chamber4. The pressure measurement value measured by the pressure gauge5is output to the controller3and is compared with the pressure target value by the controller3.

When the absolute value of the difference between the pressure target value and the pressure measurement value is greater than a predetermined value, the controller3transmits a drive signal having a value corresponding to the value of difference to the valve motor2dof the valve2to adjust the opening degree of the valve2. At this time, the controller3may use the control system shown inFIG.7to increase the gain |GV| of a transfer function GVrepresented by equation (1) below as shown inFIG.8A. Alternatively, the controller3may use the control system inFIG.7to reduce the gain |GM| of a transfer function GMrepresented by equation (2) below as shown inFIG.8B. Additionally, the controller3may perform control to maintain the rotational speed of the rotor20detected by the rotational speed detector1aconstant.

In equation (1), OVis a Laplace transform where the initial value of the opening degree of the valve2is 0. In equation (2), ΩMis a Laplace transform where the initial value of the rotational speed of the rotor20is 0. In equations (1) and (2), δPis a Laplace transform where the initial value of the difference between the pressure target value and the pressure measurement value is 0.

Here, increasing the gain refers to increasing the gain by 3 dB or more with respect to the gain when the frequency is 0, that is, the direct current gain. Reducing the gain refers to reducing the gain by 3 dB or more with respect to the gain when the frequency is 0, that is, the direct current. Alternatively, increasing or reducing the gain refers to setting the average value of gains for the range of absolute values between the pressure target value and pressure measurement values that is less than a predetermined value to be greater than or less than the average value of gains for the range that is greater than the predetermined value. Alternatively, increasing or reducing the gain refers to setting the average value of gains for the range of absolute values between the pressure target value and pressure measurement values that is greater than the predetermined value to be greater than or less than the average value of gains for the range that is less than the predetermined value.

When the absolute value of the difference between the pressure target value and the pressure measurement value is smaller than the predetermined value, the controller3transmits a drive signal having a value corresponding to the value of difference to the pump motor32of the vacuum pump1to adjust the rotational speed of the rotor20. In this case, the controller3may increase the gain |GM| of the rotational speed of the rotor20with respect to the absolute value of the difference between the pressure target value and the pressure measurement value. Conversely, the controller3may reduce the gain |GV| of the opening degree of the valve2with respect to the absolute value of the difference between the pressure target value and the pressure measurement value. Additionally, the controller3may perform control to maintain the opening degree of the valve2detected by the opening degree detector2fconstant. Accordingly, the pressure in the exhaust chamber4can be adjusted more accurately and rapidly.

A method is now described that solves the problem of induced resonance of the rotor20of the vacuum pump1described above and in which the controller3controls to vacuum exhaust the exhaust chamber4so that the pressure in the exhaust chamber4becomes a desired pressure. The controller3compares the rotational speed of the rotor20detected by the rotational speed detector1awith the natural frequencies ω1and ω2of the rotor20. When the rotational speed of the rotor20matches the natural frequency ω1, ω2or the absolute value of the difference between the rotational speed and the natural frequency is less than or equal to a predetermined value while the pressure measurement value measured by the pressure gauge5matches the pressure target value, the controller3sends an opening degree change command signal to the valve motor2dto change the opening degree of the valve2by a specific amount. Then, a drive signal having a value corresponding to the difference between the pressure target value and the pressure measurement value measured by the pressure gauge5is transmitted to the pump motor32to adjust the rotational speed of the rotor20so that the pressure measurement value matches the pressure target value.

According to the example, the controller3adjusts the opening degree of the valve2when the absolute value of the difference between the pressure in the exhaust chamber4and the target value is greater than a predetermined value, and adjusts the rotational speed of the rotor20of the vacuum pump1when the absolute value of the difference between the pressure in the exhaust chamber4and the target value is less than the predetermined value. As a result, the problem caused by changing the opening degree of the valve2and the problem caused by changing the rotational speed of the rotor20are avoided, and the pressure in the exhaust chamber4can be accurately adjusted to a desired pressure in a short time, or rapidly.

The present disclosure is described above with reference to examples, but the present disclosure is not limited to the above examples and can be modified in various manners. For example, the above examples are examples in which the valve motor2dpivots the valve body2cto place it at a desired position overlapping the opening2e, thereby adjusting the opening area of the opening2eto adjust the opening degree. However, the mechanism of the valve is not limited to this, and the valve may have any mechanism as long as it can open and close the gas flow passage. For example, the valve2may be a butterfly valve or a flap valve. Also, instead of the valve motor2d, gears, belts, or the like, a valve may be used that drives the valve body2cby means of the pressurized air generated by a compressor or the like.

According to the present disclosure, the method for controlling the pressure in the exhaust chamber4is changed depending on whether the absolute value of the difference between the pressure target value and the pressure measurement value is greater or less than the predetermined value. This predetermined value is appropriately selected according to factors including the type of the vacuum apparatus D, such as a semiconductor manufacturing apparatus, an electronic microscope, a surface analyzer, or a micromachining apparatus, that uses the vacuum exhaust apparatus10, the condition and situation in which the vacuum exhaust apparatus10is used, and the mechanisms and types of the vacuum pump1and the valve2.

Furthermore, this predetermined value may be appropriately changed while the rotor20is rotated according to the opening degree of the valve2, the type and amount of process gas introduced into the exhaust chamber4and exhausted by the vacuum pump1, and the like. In this case, the storage portion of the controller3may store a plurality of predetermined values, and the predetermined value may be appropriately changed to a value selected or calculated from these values.