JPH11241694A - Vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pump structure capable of venting to the atmosphere which can not be performed in a complex type vacuum pump or continuously operating in the vicinity of the atmosphere, in the vacuum pump used in a semiconductor facilities. SOLUTION: A complex pump is constituted of a first positive displacement pump part A transporting gas by a viscous flow area provided on the side of a discharge port 17 and a second positive displacement pump part B transporting gas by an intermediate flow area provided on the side of an inlet port 16 and pressure of the intermediate flow area or below. By providing a bypass 27 communicating a portion which is roughly located at the boundary of the first and second pump parts with the inlet port 16 and a bypass valve 28, load applied to a motor is remarkably reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vacuum pump used for semiconductor manufacturing equipment and the like.

[0002]

2. Description of the Related Art A vacuum pump for creating a vacuum environment is indispensable for a CVD apparatus, a dry etching apparatus, a sputtering apparatus and the like in a semiconductor manufacturing process. The demand for vacuum pumps has been increasing in recent years in order to respond to the high integration and miniaturization of semiconductor processes. The main contents are that high vacuum ultimate pressures can be obtained and cleanliness is required. , Maintenance is easy, small and compact.

An evacuation system mainly including a roughing pump is configured to evacuate a film forming chamber and a load lock chamber in a semiconductor facility. For example, in the case of a film forming chamber of a CVD device,
It is necessary to ensure the stability of the degree of vacuum during the reaction.
For example, the pressure condition at the time of film formation in the case of plasma CVD is 2 to 100 mtorr, and in the case of LP-CVD, it is 50 to 200 mtorr.
rr, and the fluctuation range of the set pressure at this time must be suppressed to ± 5 mtorr or less. Normally, a pressure regulating valve is used to maintain this set pressure. However, in a process such as CVD in which a large amount of reactive gas is flown, the exhausting ability is insufficient with only a roughing pump, and it is difficult to settle the pressure. Therefore, an exhaust system is provided in which an auxiliary pump having a high evacuation speed in the middle vacuum region or lower is provided upstream of the roughing pump.

[0004] An auxiliary pump is also used for evacuation of the load lock chamber in order to increase the production tact time or to reduce the background vacuum pressure. In the latter case, under the same tact condition, for example, if the background pressure of the preliminary chamber is changed from 100 mtorr to 10 mtorr, impurities (moisture etc.)
Can be suppressed low. As described above, in order to supplement the performance of the roughing pump and to create a high vacuum in the semiconductor equipment, a vacuum evacuation system comprising a combination of a roughing pump (a positive displacement vacuum pump) and an auxiliary pump (a high vacuum pump) is usually configured. I have.

[0005] The following describes the prior art and its problems [1]
In the case of a general exhaust system, [2] the case of a combined vacuum pump proposed by the present inventors will be described.

[1] In the case of a general exhaust system In a conventional general exhaust system, either a turbo molecular pump or a mechanical booster is used as an auxiliary pump depending on a process to be applied. Hereinafter, the structures of a roughing pump and a mechanical booster widely used as an auxiliary pump thereof will be described.

(1) Structure of Roughing Pump FIG. 8 shows a screw groove type (a type of screw type) dry vacuum pump which is a kind of a conventional roughing pump. In the figure, 101 is a housing, 102, 10
3 is a rotating shaft, 104 and 105 are rotating shafts 102, respectively.
A cylindrical rotor fastened to 103. On the outer periphery of each rotor 104 and 105, thread grooves 106 and 107 are provided.
Are formed. When the rotors 104 and 105 rotate, the closed space formed by the screw groove and the housing moves from the suction side to the discharge side with the rotation, and performs the suction action and the discharge action. Further, in the screw groove type vacuum pump shown in the figure, the synchronous rotation of the two rotors 104 and 105 is performed by the timing gears 110a and 110b. That is, the rotation of the motor 108
9a to the intermediate gear 109b,
The transmission is transmitted to one of the timing gears 110b provided on the shafts 4 and 105 and meshing with each other. Both rotors 10
The phases of the rotation angles of the gears 4 and 105 are adjusted by the engagement of the two timing gears 110a and 110b. An oil pump 111 is provided at an end of the driving gear 109b.
Is incorporated. Oil 112 for lubrication is sucked by the oil pump from an oil pan 113 at the lowermost part of the pump, and is supplied to the bearing and the gear via an oil filter.

(2) Structure of Mechanical Booster FIG. 9 shows a mechanical booster used as an auxiliary pump of the above-described roughing pump. 200 is a motor rotor, 201 is a motor stator, 202 and 203 are eyebrows, 204 is a suction port, 205 is a discharge port, 206 is a rotating shaft, 207, 208, and 209 are ball bearings that support the rotating shaft, and 210 is a timing. The gear 211 is a rotor casing. In the mechanical booster having the above-described configuration, the two eyebrow-shaped rotors rotate in opposite directions while maintaining a phase of 90 degrees without contacting each other by a set of timing gears provided at the shaft end. The gas is transported from the suction port to the discharge port by the movement of the closed space formed by the rotor and the casing.

However, with the recent incorporation of semiconductor processes, a so-called multi-chamber system, in which a plurality of vacuum chambers are independently evacuated and evacuated, has become the mainstream of semiconductor thin film processing equipment. To cope with the multi-chamber system, a vacuum pumping system comprising a combination of a roughing pump and an auxiliary pump (high vacuum pump) is required for each chamber. If it is configured for the chamber, there is a problem that the entire vacuum evacuation device becomes large and complicated.

[2] In the case of a combined vacuum pump As an alternative to the above-described vacuum evacuation system, the present inventors, on the same axis as the rotor constituting the positive displacement roughing pump,
A composite pump in which a pump portion for transporting a low-pressure gas in a middle vacuum (intermediate flow) region or lower is configured as a positive displacement type has already been proposed (
Hei 5-272478).

The composite vacuum pump shown in FIG. 10 has a first rotating shaft 302 and a second rotating shaft 303 in a housing 301.
Are housed vertically and rotatably, respectively. Cylindrical rotors 304 and 305 are fitted at the upper ends of the two rotating shafts. On the outer peripheral surface of the rotor, screw grooves (a kind of screw grooves) having different pitches and groove depths are formed at an upper portion (position B) and a lower portion (position A) so as to mesh with each other.

Reference numerals 304 and 305 denote lower screw grooves and a first pump part, and reference numerals 306 and 307 denote upper screw grooves and a second pump part. The closed space formed by these screw grooves and the housing 1 causes the rotation of both rotating shafts,
It moves from the intake port 310 side to the discharge port 311 side, and the movement of this space provides a suction / exhaust (discharge) action as a positive displacement pump.

The volume of the sealed space formed by the upper screw grooves 308 and 309 and the housing is equal to that of the lower screw grooves 306 and 309.
307 and the volume of the enclosed space formed by the housing. In other words, the lower thread groove (part A) is a roughing pump that transports gas at the pressure in the viscous flow region,
The upper thread groove (part B) covers the function as a mechanical booster that transports gas at an intermediate flow region and a pressure lower than the intermediate flow region.

An ultrahigh vacuum pump (third pump portion) of a momentum transfer type is formed on the upstream side (part C) of the rotor 305 on the same axis as the rotor 305 and away from the upper screw grooves 308 and 309. Rotating members 312, 313 and fixed members 314, 3
The gas molecules in the fifteen minute gaps are given rotational momentum by the high-speed rotation of the rotating member, and are transported to each of the positive displacement vacuum pump parts (part B → part A).

316 and 317 are AC servo motors,
The first rotating shaft 302 and the second rotating shaft 303 are driven by AC servomotors 316 and 317 provided on the respective shafts.
It rotates synchronously at a high speed of tens of thousands of rpm. The rotation signals of both shafts are detected by rotary encoders 318 and 319 provided at the lower ends of the respective rotation shafts on the side opposite to the intake port side.

With the above arrangement, the intermediate flow region (1 to 10 ^-3)
Since the exhaust performance of the gas in the molecular flow region below the torr) and the intermediate flow region can be significantly improved, the mechanical booster can be omitted, and the size and simplification of the vacuum exhaust system can be greatly reduced.

[0017]

However, when the above-mentioned composite vacuum pump is applied to a semiconductor process as an alternative to a vacuum pumping system composed of a roughing pump and an auxiliary pump (mechanical booster), the following problems occur. Occurred.

For example, in a load lock chamber, although it varies depending on the film formation rate, in a short one, the operation of repeating the opening to the atmosphere and the evacuation in a cycle of several seconds is continued. Atmospheric pressure is applied to the suction side of the vacuum pump connected to the load lock chamber when the air is released to the atmosphere. When the above-described combined vacuum pump was applied to this load lock chamber, the following became clear. The third pump portion (portion C), which is a momentum transport type, does not have a closed space and can pass gas relatively smoothly. However, the following problems occur when gas passes through the second and third pump sections of the positive displacement type. The exhaust volume of the second pump part (part B) having the function as the mechanical booster is much larger than the exhaust volume of the first pump part (part A) having the function of the roughing pump. Therefore, the transported gas that has passed through the second pump section is supplied to the inlet 3 of the first pump section.
At 20 the compression is large. That is, when the motor is opened to the atmosphere, a shock load torque is applied to the motor.

As a result, due to overload, the allowable torque limit of the motor is exceeded,
Emergency stop due to overcurrent error to prevent motor burn-in.

The abnormal compression heat causes the rotors 306-3
09 rises in temperature and the housing 301 or the rotors come into contact with each other to cause seizure. Troubles such as occurred.

When this combined vacuum pump is applied to a film forming chamber, if the evacuation is started only by the main valve without performing slow exhaust, the same problem as in the load lock chamber due to overload of the motor occurs immediately after the valve is opened. Occurred.
In addition, in a state where the thin film equipment is in a steady operation, normally, the film forming chamber does not change environmental conditions such as pressure except for cleaning the chamber, that is, the vacuum pressure is kept constant in principle. However, due to an operation error of the apparatus, for example, a large amount of gas purge may suddenly cause a high pressure in the film forming chamber. In this case, if the vacuum pump connected to the film forming chamber is stopped, a fatal trouble occurs during mass production.

The present invention has a large displacement on the intake side,
A vacuum pump with a smaller displacement on the exhaust side than on the intake side,
For example, the present invention provides a measure for solving the above-described problem when the combined vacuum pump that can cover a pressure range from the atmosphere to a pressure equal to or lower than a medium vacuum is opened to the atmosphere.

[0023]

In order to achieve the above object, a vacuum pump according to the present invention comprises a plurality of rotors housed in a housing and a plurality of shafts fastened to each of the rotors. A bearing for supporting the rotation of these shafts, a suction port and a discharge port for a fluid formed in the housing, and a sealed space formed by the rotor and the housing from the suction port side to the discharge port side. Utilizing movement, a first pump portion for transporting gas in the viscous flow region provided on the discharge port side, an intermediate flow region provided on the suction port side, and transporting gas at a pressure lower than the intermediate flow region A second pump portion, a relay port formed in the housing at a location roughly positioned at a boundary between the first pump portion and the second pump portion, and a relay port and the suction port side A bypass passage communicating, which is constituted of a vacuum pump with a bypass valve for opening and closing the bypass passage.

A relay port is formed at a location located at a boundary between the first pump portion having a small exhaust volume and the second pump portion having a large exhaust volume. A bypass path that connects the relay port and the suction port is formed, and a bypass valve that opens and closes the bypass path is provided. The bypass valve is opened on the basis of information from the detecting means for detecting that the suction side of the vacuum pump is open to the atmosphere or has reached a pressure equal to or higher than a set value.
The high-pressure gas compressed by the second pump passes through the bypass and returns to the suction side again, so that the pressure inside the pump is reduced and the problem related to overload torque of the motor is solved.

In the vacuum pump according to the present invention, even if the second pump corresponding to the auxiliary pump loses its function by opening the bypass valve, the first pump corresponding to the roughing pump does not lose its exhaust performance. . Therefore, if the pressure in the chamber is reduced by evacuation by only the first pump and the pressure difference across the valve is reduced to a predetermined set pressure, the valve is shut off, and the function of the second pump is quickly restored. . If a passive type, for example, a throttle valve that opens and closes by a pressure difference is used for the bypass valve, the configuration of the valve is greatly simplified.

When the present invention is applied to an electronically controlled synchronous control compound pump in which each rotor is driven by an independent motor, the following effects are obtained. For electronically controlled synchronous control,
A contact prevention gear for preventing contact between the rotors in consideration of an emergency synchronization shift is provided. For example, if the synchronous control of the two motors becomes unstable due to a sudden load change, the contact prevention gears first collide. As long as the unstable state continues, the two rotating shafts repeat the vibration caused by the collision. By applying the present invention, the instability factor relating to the load fluctuation is eliminated, and the reliability of the synchronization control is greatly improved.

[0027]

FIG. 1 shows an embodiment of a positive displacement vacuum pump (roughing pump) according to the present invention. The first rotary shaft 1 and the second rotary shaft 2 are provided in bearings 6a, 6b, 7a,
7b and housed in the vertical direction.
Above each rotating shaft, cylindrical upper rotors 8 and 9 are fitted to the rotating shaft, and lower rotors 10 and 11 are fitted to the rotating shaft below. Threads having different pitches and groove depths (a type of screw groove) are formed on the outer peripheral surface of each rotor so as to mesh with each other.

Numerals 12 and 13 are lower thread grooves and a first pump portion, and numerals 14 and 15 are upper thread grooves and constitute a second pump portion. These screw grooves and housings 3, 4
Is moved from the intake port 16 side to the discharge port 17 side with the rotation of both rotating shafts, and by the movement of this space, the suction / exhaust action as a positive displacement pump is obtained.

The volume of the closed space formed by the upper screw grooves 14 and 15 and the housing 3 is much larger than the volume of the closed space formed by the lower screw grooves 12 and 13 and the housing 4. In other words, the lower screw groove (part A) is a roughing pump that transports gas at a pressure in the viscous flow region, and the upper screw groove (part B) is a mechanical pump that transports gas at a pressure below the intermediate flow region and the intermediate flow region. Covers the function as a booster.

Reference numeral 18 denotes an upper cover having a suction port, and 19 denotes a lower case. Rotational position sensors 20 and 21 are provided at the lower ends of the respective rotation shafts, and are accommodated in the lower case which also serves as an oil tank.

Reference numerals 22a and 22b denote motor rotors on the rotating side of the AC servomotor, and reference numerals 23a and 23b denote motor stators on the fixed side. The first rotary shaft 1 and the second rotary shaft 2 are rotated at a high speed of tens of thousands rpm in the embodiment by the AC servomotor. The rotation signals of both shafts are detected by rotation position sensors 20 and 21.

Now, the two rotating shafts 1 and 2 in this embodiment are described.
The following method was used for the synchronization control. That is, the output pulses from the rotational position sensors 20 and 21 are compared with a set command pulse (target value) set assuming a virtual rotating rotor. The deviation between the target value and the output value (rotation speed, rotation angle) from each of the sensors 20 and 21 is processed by a phase difference counter, and the rotation of the servo motor of each axis is corrected so as to eliminate this deviation. Controlled. In the vacuum pump of the embodiment, contact preventing gears 24 and 25 for preventing contact between the rotors are provided in a form directly connected to lower ends of the rotors 10 and 11.

A space for a relay port 26 is provided below the second pump portion in the housing 3. A bypass 27 connecting the relay port 26 and the intake port 16 and a bypass valve for opening and closing the bypass are provided. 28 are provided.

In the vacuum pump having the above structure, the suction
No gas or no gas flows through the port 16
Pressure, the pressure in the relay port
10 ^-2-10^-3The pressure has been reduced to torr. At this time exhaust
Between the port 17 and the relay port 26, the exhaust operation of the first pump is performed.
Pressure is maintained approximately equal to atmospheric pressure
I have. On the other hand, the pressure between the relay port 26 and the intake port 16 is
The differential pressure is small because the absolute value of
It is rotating with almost no load. For motors
Such a load is also smaller than when only the first pump is configured.
It does not increase significantly.

However, here, the suction port 16 of the vacuum pump is used.
When the load lock chamber and the reaction chamber located upstream of the pump are at atmospheric pressure and the valve provided on the suction side is suddenly opened to the atmosphere, high-pressure, large-flow gas flows into the pump. Is assumed. At this time, since the amount of gas transported by the second pump is far greater than the amount of gas transportable by the first pump, the pressure of the relay port 26 rises above the pressure of the intake port 16 (atmospheric pressure), An excessive load is applied to the motor due to the differential pressure generated between the upstream and the downstream of the second pump. However, in the pump of the present invention, since the bypass path 27 connecting the relay port 26 and the intake port 16 is provided, if the pressure of the relay port 26 becomes higher than the pressure of the intake port 16, Occurs. In a normal operation state, the bypass valve 28 is provided and the bypass passage 27 is closed so that the exhaust efficiency of the bypass passage 27 does not decrease due to the backflow. Further, in the embodiment, a spring 29 is attached to the bypass valve 28 so that a force always acts in a direction to close the valve. The opening degree changes according to the pressure difference. By the backflow adjusting mechanism that works by the pressure difference, the pressure in the pump at the position of the relay port can be reduced as compared with the case where the bypass passage 27 and the bypass valve 28 are not provided. Therefore, the pressure difference between the intake pressure and the exhaust pressure of the second pump became small, and the load applied to the motor when it was opened to the atmosphere could be reduced.

FIG. 2 shows the motor load characteristics with respect to the intake pressure with and without the bypass. In this embodiment, if there is no bypass, when gas flows into the intake port at a pressure of approximately 200 torr, the motor will exceed its limit power of 3 kW, and the pump will stop.
When there was a bypass, the motor load did not reach 2 kW even if the air was continuously exhausted to the atmospheric pressure. FIG. 3 shows measured data comparing the exhaust capacity with and without a bypass as in FIG. When the bypass path and the bypass valve are provided, the evacuation capacity is slightly lowered near the atmospheric pressure, but it can be seen that the same performance as that without the bypass path can be maintained in a region of 10 torr or less required for vacuum evacuation equipment. In addition, it has an exhaust capability continuously up to the atmospheric pressure, and has a constant exhaust capability even at the atmospheric pressure.

The structure of the bypass valve is not limited to the passive type which is opened and closed by a pressure difference as shown in the embodiment, but may be an active type which is driven by an actuator based on information from a pressure sensor.

In the vacuum pump of the embodiment, a screw groove type which is a kind of a screw type having a screw groove on the outer peripheral portion of both the first pump part and the second pump part rotor is adopted. In the embodiment, the thread grooves of the first pump portion and the second pump portion are formed independently of each other. However, in the section from the first pump portion to the second pump portion, the pitch of the thread grooves ( Alternatively, the shape may be such that the groove depth continuously increases. In this case, in the present invention, the downstream side (discharge side) is the first pump portion with respect to the bypass relay port,
The upstream side (suction side) will be defined as the second pump section.

If the vacuum pump has a large exhaust volume on the intake side and a smaller exhaust volume on the exhaust side than the intake side, even a pump whose ultimate vacuum pressure can be reduced only to a viscous flow region, for example, when it is opened to the atmosphere. The problem is common, and the present invention can be applied.

The first and second pumps to which the present invention can be applied include a roots type (FIG. 4), a gear type (FIG. 5), a single-lobe type (FIG. 6 (a)), and a double-lobe type. (FIG. 6
(b)) and a screw type (FIG. 7). Also, the first and second pumps may be configured by combining these types of pumps.

[0041]

According to the present invention, the composite vacuum pump can be applied to a load lock chamber which repeatedly opens and evacuates to the atmosphere in a short cycle. As a result, the production tact time can be improved without losing the compact and space-saving features of the combined vacuum pump. Alternatively, the background vacuum pressure can be reduced by, for example, two digits or more under the same tact condition, so that higher quality process conditions can be obtained.

Even when the vacuum pump according to the present invention is applied to the vacuum evacuation of the film forming chamber, the problem relating to the overload of the motor immediately after the start of the vacuum evacuation is solved. That is, in a state where the pump is already operating normally, the intake side can be opened to the chamber side at a stretch. In addition, the function of evacuation is not lost even when the pressure conditions in the film formation chamber change.

In the vacuum pump according to the present invention, even if the second pump corresponding to the auxiliary pump loses its function by opening the bypass valve, the first pump corresponding to the roughing pump does not lose its exhaust performance. . Therefore, if the pressure in the chamber is reduced by evacuation by only the first pump and the pressure difference between the front and rear of the valve is reduced to a predetermined set pressure, the valve is shut off, and the function of the second pump is quickly restored. I do.

When the present invention is applied to a compound pump of an electronically controlled synchronous operation in which each rotor is driven by an independent motor, there is no instability factor (overload torque) that disturbs the synchronous control. It can be greatly improved. As a result, the electronically controlled pump can be used for a compound vacuum pump for a load lock chamber that repeatedly opens and evacuates the atmosphere in a short cycle. The present invention eliminates the weakness of the electronically controlled type that is vulnerable to shocking overload torque. As a result, since the AC servomotor can be selected without considering the overload torque, the size of the motor can be reduced and the drive driver can be simplified.

If the rotational speed of the positive displacement pump, which used to be limited to several thousand rpm in the past, is increased several times to, for example, 10,000 rpm or more by adopting the electronically controlled synchronous operation, the internal leakage during one stroke of the pump can be improved. Since the total volume is reduced, the basic performance of the pump is greatly improved. In particular, the effect of increasing the speed of the second pump corresponding to the auxiliary pump is remarkable, and a high pumping speed and a low vacuum ultimate pressure far exceeding the limits of the conventional mechanical booster can be obtained.

According to the present invention, the composite type empty pump can be widely applied to a film forming chamber, a load lock chamber, a spare chamber, and the like. As a result, significant space saving and simplification of the entire line composed of semiconductor thin film equipment is possible,
The effect is enormous.

[Brief description of the drawings]

FIG. 1 is a sectional view of a vacuum pump according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a bypass diameter and a motor load in the embodiment.

FIG. 3 is a diagram showing a relationship between a suction pressure and an exhaust speed in the embodiment.

FIG. 4 is a diagram showing a configuration of a roots pump according to another embodiment of the present invention.

FIG. 5 is a configuration diagram of a gear pump according to another embodiment.

FIG. 6 is a configuration diagram of a robe pump in another embodiment.

FIG. 7 is a configuration diagram of a screw pump according to another embodiment.

FIG. 8 is a sectional view of a conventional roughing pump.

FIG. 9 is a sectional view of a conventional mechanical booster pump.

FIG. 10 is a sectional view of a compound pump.

[Explanation of symbols]

 1, 2 axis 3 housing 5, 9, 10, 11 rotor 16 intake port 17 discharge port

Claims (7)

[Claims] A plurality of rotors housed in a housing, a plurality of shafts fastened to each of the rotors, a bearing for supporting the rotation of these shafts, and a fluid formed in the housing. Using a suction port and a discharge port, and using a movement of a sealed space formed by the rotor and the housing from the suction port side to the discharge port side, a positive displacement first provided on the discharge port side. A pump portion and a positive displacement type second pump portion provided on the suction port side, and a relay port formed in the housing at a position roughly located at a boundary between the first pump portion and the second pump portion, A vacuum pump, comprising: a bypass for connecting the relay port to the suction port; and a bypass valve for opening and closing the bypass. 2. The vacuum pump according to claim 1, wherein an exhaust volume of the second pump is larger than that of the first pump. 3. A pump comprising: a positive displacement first pump section for transporting gas in a viscous flow region; a positive displacement second pump portion for transporting gas at a pressure lower than the intermediate flow region and the intermediate flow region. 3. The vacuum pump according to claim 2, wherein: 4. The vacuum pump according to claim 1, wherein the bypass valve is configured to open and close by a pressure difference between an inlet side and an outlet side. 5. The vacuum pump according to claim 1, further comprising: a plurality of motors for independently rotating and driving the plurality of shafts; and means for synchronously controlling the plurality of motors. 6. The vacuum pump according to claim 1, wherein the first pump portion is a screw groove type or a screw type. 7. The vacuum pump according to claim 1, wherein the second pump portion is of a thread groove type or a screw type.