JP2000045976A - Screw type vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provided a screw type vacuum pump with high exhaust speed and compact construction. SOLUTION: A screw type vacuum pump 1 has a pair of screw rotors 5, 6. At shaft ends on intake side of respective screw rotors 5, 6 are mounted rotor extension portions 7, 8 in a coaxial manner. The sectional shapes of the rotor extension portions 7, 8 are almost the same as the extension of the sectional shape of the shaft end perpendicular to the axis. The rotor extension portions 7, 8 have a larger gas intake capacity than a screw rotor. Accordingly, it is possible to increase exhaust speed without having to make the pump a multi-stage pump.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw-type vacuum pump used in a semiconductor manufacturing apparatus or the like to evacuate a reaction chamber and discharge generated reaction by-products.

[0002]

2. Description of the Related Art As a screw type vacuum pump, for example, one having a structure shown in FIG. 4 is known. The screw vacuum pump 300 is an example of a dry vacuum pump that does not use a sealing liquid in a pump working chamber used in a semiconductor manufacturing process or the like. Further, in order to maintain the cleanliness of the vacuum, the screw rotor is supported by a single-sided shaft support structure without bearings requiring oil lubrication or the like on the vacuum side.

That is, the screw type vacuum pump 3
In 00, a pair of screw rotors 304 and 305 are disposed in parallel in a vertically installed state in a pump action chamber 303 in which an intake port 301 and an exhaust port 302 are formed.
Right-handed screws 307 and left-handed screws 308 are formed on the outer peripheral surfaces of the screw rotors 304 and 305 with equal leads, and mesh with each other. The lower ends of the screw rotors 304 and 305 project into the gear chamber 310 and are rotatably supported by bearings 311 and 312.

[0004] These screw rotors 304,
Reference numeral 305 is connected to the motor 320 via timing gears 313 and 314, an idle gear 315, and a drive gear 316. When the pair of screw rotors 304 and 305 are rotated relative to each other by the motor 320, a pump action of transferring the gas sucked from the intake port 301 while compressing the gas toward the exhaust side occurs.

Here, in order to form a clean vacuum space, no sealing liquid is used in the pump working chamber 303, so that the suction gas passing through the gap between the screw rotors 304, 305 and the pump casing 330 is reversed. High flow rate. Therefore, generally, the number of turns of the screw is increased to increase the number of partitions.

Further, reaction by-products (powder and the like) generated in each step of the semiconductor manufacturing process such as etching and CVD are deposited inside the screw type vacuum pump 300,
In order to prevent the screw rotors 304 and 305 from sticking to the screw rotors 304 and 305, the screw rotors 304 and 305 are arranged vertically, and reaction by-products that have entered through the intake port 301 located at the upper end are located at the lower end of the rotor. A large gap is provided between the lower ends of the screw rotors 304 and 305 and the inner end surface of the pump casing 330 facing the lower end of the screw rotors 304 and 305 so as not to be fixed.

[0007]

In order to increase the pumping speed of the screw type vacuum pump of this construction, a method of increasing the number of revolutions of the screw rotor, a method of increasing the volume of the spiral groove defined by the screw, and the like. An increase method is conceivable.

However, increasing the rotation speed of the screw rotor is not preferable because problems such as shortening of the life of the bearing mechanism occur.

Further, as a method of increasing the volume of the spiral groove, a method of increasing the lead angle of the screw, increasing the rotor diameter, increasing the depth of the groove, or the like is conceivable. But,
Increasing the screw lead angle significantly increases the overall length of the screw rotor, which makes it mechanically difficult to adopt a single-sided shaft support structure for the screw rotor. In addition, an increase in the rotor diameter causes an increase in the thrust acting on the screw rotor.

The method of increasing the depth of the groove has a limitation that the depth of the groove is limited when the outer diameter of the rotor is limited, and a desired groove volume cannot be obtained. In addition to this,
When the thread of the equal lead is formed as in the example shown in the figure, the volume of the groove on the exhaust side also increases, so that there is a problem that the required power increases accordingly.
In order to avoid this problem, it is conceivable to use an unequal lead in which the lead angle of the screw is increased on the intake side and reduced toward the discharge side. However, screws with unequal leads cause a problem that the processing is complicated and time-consuming.

On the other hand, in order to increase the pumping speed, a multi-stage vacuum pump as shown in FIG. 5 is used.
Pump elements 402 and 403 having a large suction volume such as a roots rotor and a short rotor length are provided via a partition wall 401.
May be added to the coaxial state.

However, the multi-stage vacuum pump 400 having this structure has a problem that the structure is complicated by the number of stages. Also, a pump element 4 such as a roots rotor
There is also a problem that reaction by-products are likely to adhere to the partition wall 401 at the lower end of the first and the second 402.

[0013] The object of the present invention is to solve the above problems.
An object of the present invention is to realize a small screw-type vacuum pump capable of increasing the pumping speed without having a complicated structure.

[0014]

In order to solve the above-mentioned problems, the present invention comprises a pair of screw rotors each having a right-handed screw and a left-handed screw which can be engaged with each other formed on an outer peripheral surface thereof. In a screw-type vacuum pump that performs an exhaust operation by rotating the screw rotors relative to each other, at the shaft end on the suction side of each screw rotor,
The rotor extension is integrally formed or attached coaxially. In addition, the rotor extension has a cross section perpendicular to the axis substantially the same as the cross section perpendicular to the axis at the shaft end on the suction side of the screw rotor. Furthermore, the rotor extension and the shaft end on the suction side of the screw rotor are joined to each other in a state in which both end face shapes match.

In the screw type vacuum pump according to the present invention, since the rotor extension having a large suction capacity is formed on the suction side of the screw rotor, the pumping speed can be increased. Also, the structure does not become complicated. Furthermore, since the joint surface between the rotor extension and the screw rotor has the same end surface shape, the gas sucked by the rotor extension is smoothly introduced into the screw groove side of the screw rotor. No adverse effects such as gas leakage occur.

If powder or the like adheres between the outer peripheral surface of each rotor extension located on the pump suction side and the inner peripheral surface of the pump casing, a sliding area between them is reduced. It is desirable to determine the contour of the rotor extension, in other words, its cross-sectional shape perpendicular to the axis, as follows.

That is, the cross-section perpendicular to the axis of each rotor extension is radially inward from the outer diameter of the screw rotor that defines the cross-section perpendicular to the axis at the shaft end on the suction side of the screw rotor. What is necessary is just to include the part which receded, and the part which protruded outward in the radial direction from the said screw rotor thread root diameter line.

Next, in a case where the rotor extension is fastened and fixed to a shaft end on the suction side of the screw rotor by a fastener, the rotor extension and the suction side of the screw rotor on the suction side are screwed. By inserting the shim plate between the shaft ends, the gap between the shaft end on the suction side of the rotor extension and the pump casing can be easily adjusted. As a result, a desired assembled state can be formed without increasing the precision of parts of the screw rotor and the rotor extension.

On the other hand, the screw rotor is arranged vertically so that the suction side is located on the upper side,
It is desirable to support the shaft only at the lower exhaust side. With this configuration, there is no bearing that requires oil lubrication on the suction side of the pump, so that it is suitable for maintaining the cleanliness of the vacuum atmosphere on the side to be evacuated. In addition, since the screw rotor is arranged vertically, when used in processes where powdery reaction by-products are generated, such as etching and CVD processes, the reaction by-products that have entered the pump are screwed. It can be dropped to the lower end in the pump without being fixed to the rotor or the like. For this reason, it can be stably used for the purpose of sucking a gas containing a powdery reaction by-product.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a screw type vacuum pump to which the present invention is applied will be described below with reference to the drawings.

FIG. 1A is a schematic longitudinal sectional view of the screw type vacuum pump of the present embodiment. The basic configuration of the screw vacuum pump 1 is a screw vacuum pump 30 shown in FIG.
0, and has a pump casing 4 in which an intake port 2 and an exhaust port 3 are formed. Inside the pump casing 4, a pair of screw rotors 5 and 6 are arranged in parallel in a vertically installed state.

The screw rotors 5 and 6 are
a, 6a, rotor shafts 5b, 6b attached so as to penetrate the centers thereof, and right-hand screws 5c and left-hand screws 6c formed on the outer peripheral surfaces of the rotor bodies 5a, 6a, respectively. The right-hand thread 5c and the left-hand thread 6c are in a positional relationship where they are engaged with each other with a slight gap therebetween. The right-hand thread 5c and the left-hand thread 6c in the present example are equal-lead square threads.

The shaft ends 5d, 6d on the suction side of the screw rotors 5, 6 are coaxially mounted on the rotor extensions 7, 8 respectively.
Are fastened and fixed by fastening bolts 9. These rotor extensions 7 and 8 have an axial perpendicular cross-sectional shape obtained by extending the axial perpendicular cross-sectional shapes of the shaft ends 5d and 6d on the suction side of the screw rotors 5 and 6 substantially in the axial direction.

In general, as shown in FIG. 1 (B), one is a large diameter semicircular portion 7a, 8a, and the other is a small diameter semicircular portion 7b, 8b. The contours of the large-diameter semicircular portions 7a and 8a substantially coincide with the outer diameter lines of the screw rotors 5 and 6,
The contours of the small diameter semicircular portions 7b, 8b substantially coincide with the thread root diameters of the screw rotors 5, 6.

Here, FIG. 2 shows an example of a specific contour shape of each of the rotor extensions 7 and 8. As shown in this figure, the large-diameter semicircular portions 7a and 8a have portions that are slightly receded inward in the radial direction with respect to the outer diameter line of the screw rotor indicated by a dashed line. On the other hand, the small-diameter semicircular portions 7b and 8b have portions slightly protruding outward in the radial direction with respect to the screw rotor thread root diameter line indicated by the chain line. The reason for this is that when powder or the like adheres to the outer peripheral surface of the rotor extension or the inner peripheral surface of the pump casing opposed thereto, the sliding area between them is reduced.

Referring back to FIG. 1, the exhaust-side shaft ends of the shafts 5b and 6b of the screw rotors 5 and 6 are connected to the pump casing bottom wall 4a where the pump discharge port is formed. It is rotatably supported by bearings 11 and 12, and penetrates through the bottom wall 4a to protrude into the gear box 11 attached to the bottom surface of the pump casing. The lower ends of the lower end protrusions 51, 61 of these rotor shafts are also mounted on the bearings 13, 1
4 rotatably supported. Thus, the support structure of the screw rotors 5, 6 is a one-sided shaft support structure in which only the lower end portion on the exhaust side is rotatably supported.

Inside the gear box 11, timing gears 21 and 22 attached to the lower end protrusions 51 and 61 of the rotor shaft and meshing with each other, and a pinion gear integrally formed coaxially with one of the timing gears 22. 23, an idle gear 24 meshing with the pinion gear 23, and a drive gear 25 meshing with the idle gear are housed. The drive gear 25 is fixed to an output shaft 31 of a motor 30 which is vertically arranged at a position adjacent to the pump casing 4 in a downward posture.

In the screw type vacuum pump 1 of this configuration, screw rotors 5 and 6 having rotor extensions 7 and 8 attached to the upper end are arranged inside the pump casing 4. A pump working chamber is defined by the rotor and the inner surface of the pump casing 4. When the motor 30 is driven, the rotation of the motor is transmitted to each of the screw rotors 5 and 6 via the gear train having the above-described configuration, and the screw rotors 5 and 6 rotate in opposite directions to perform a pump operation.

FIG. 3 shows the exhaust principle of the rotor extensions 7 and 8 of the screw type vacuum pump 1 of this embodiment. To explain the rotor extension 8 on one side, first, FIG.
As shown in (a) and (b), the space formed between the small-diameter portion 8b of the rotor extension 8 and the inner peripheral surface of the pump casing 4 is caused by the rotation of the rotor extension 8 in the direction of the arrow. The gas is sucked from the intake port 2 with this increase.

The small diameter portion 8b of the rotor extension 8 is
(FIG. 3 (c)), the intake operation ends.

Next, as shown in FIG. 3D, when the leading portion in the rotation direction of the small-diameter portion of the rotor extension 8 that has sucked the gas reaches the position facing the other rotor extension 7, The compression operation of the sucked gas starts,
With the rotation of the rotor extension, the gas is compressed while
It is transferred into the screw grooves of the screw rotors 5 and 6. When the rear end portion of the small-diameter portion 8b of the rotor extension portion 8 in the rotational direction rotates to a position facing the outer peripheral surface of the other rotor extension portion 7, the transfer of gas into the screw grooves of the screw rotors 5, 6 ends. .

In this manner, the pair of rotor extension portions 7,
By 8, the gas is sucked from the intake port 2 and transferred to the pair of screw rotors 5 and 6 while being compressed.

In the screw-type vacuum pump 1 of the present embodiment having the above-described configuration, the shaft end on the suction side of the screw rotors 5 and 6 is formed by extending the shaft right-angle cross-sectional shape as it is in the axial direction. The configuration in which the rotor extension portions 7 and 8 having a shape are attached is adopted. This rotor extension 7,
Since the suction capacity of 8 is larger than that of the screw rotors 5 and 6, the pumping speed of the pump can be increased.

Here, in a constant pressure region where a screw vacuum pump is commonly used, the power required by the pump is substantially determined by a screw rotor that compresses gas to atmospheric pressure. Therefore, the problem that the required power increases even if the suction volume on the vacuum side is increased as in this example does not occur.

The gas discharged from the rotor extensions 7 and 8 as described above flows directly into the screw grooves of the screw rotors 5 and 6. Therefore, there is no need to provide a partition between the rotor extensions 7 and 8 and the screw rotors 5 and 6 to form a flow path connecting the two. For this reason, a single-stage pump is possible, and the structure can be simplified. In addition, there is no adverse effect such as powdery reaction by-products contained in the suction gas sticking to the partition wall or the like.

Further, the screw type vacuum pump 1 of this embodiment
Adopts a structure in which the screw rotors 5 and 6 having the rotor extensions 7 and 8 attached to the upper end are arranged vertically, and only the lower end portion on the exhaust side is supported by the shaft. As a result, since there is no bearing portion on the suction side that requires oil lubrication, there is no adverse effect that oil or the like enters the vacuum side space and the cleanliness is reduced. In addition, since it is installed vertically, the powdery reaction product that has entered from the intake port located at the upper end is easy to fall on the bottom wall of the pump casing, so it adheres to the inner peripheral side surface of the screw rotor or the pump casing or Deposition is suppressed.

The rotor extensions 7 and 8 of this embodiment are fastened and fixed to the suction-side shaft ends of the screw rotors 5 and 6 by fastening bolts. The distal ends of 5a and 6a may be extended to form a large diameter portion and a small diameter portion integrally therewith.

Further, it is possible to attach a lead to the rotor extensions 7 and 8.

[0039]

As described above, the screw-type vacuum pump of the present invention has a pair of screw rotors each having a suction-side shaft end provided with a shaft right-angle cross-sectional shape obtained by extending the shaft right-angle cross-sectional shape as it is. In this case, the rotor extension is formed or attached.

Since such a rotor extension has a larger gas suction capacity than the screw rotor, the pumping speed can be increased. Further, since the rotor extension has a cross-sectional shape obtained by directly extending the cross-sectional shape perpendicular to the axis of the shaft end on the suction side of the screw rotor, the gas sucked by the rotor extension can be smoothly removed without causing leakage or the like. There is an advantage that it can be transferred to the rotor side. Furthermore, the structure can be simplified as compared with a multi-stage vacuum pump having a pump element partitioned by a partition wall, and the accumulation and adhesion of powdery reaction by-products sucked together with gas can be suppressed. There is also an advantage.

Further, in the present invention, since the split rotor having a structure in which the rotor extension is fastened and fixed by the fastening bolt is used at the shaft end on the suction side of the screw rotor, the screw rotor and the rotor extension are separately processed. Therefore, there is an advantage that processing can be simplified. In addition, by interposing a shim plate or the like between these divided portions, the axial length of the divided rotor can be adjusted, so that there is an advantage that it is not necessary to increase the precision of the components of each rotor so much.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a screw type vacuum pump to which the present invention is applied, and an end view of a rotor extension thereof.

FIG. 2 is an explanatory view showing a shape of a rotor extension of the pump of FIG. 1;

3 is an operation explanatory diagram for explaining gas suction, compression and transfer operations by a rotor extension of the pump of FIG. 1;

FIG. 4 is a schematic longitudinal sectional view of a general screw type vacuum pump and an end view of a screw rotor thereof.

FIG. 5 is a schematic longitudinal sectional view of a multistage vacuum pump and an end view showing a shape of a roots rotor thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Screw-type vacuum pump 2 Intake port 3 Discharge port 4 Pump casing 4a Casing bottom wall 5, 6 Screw rotor 5a, 6a Rotor body 5b, 6b Rotor shaft 5c, 6c Screw 5d, 6d Suction end of screw rotor 51, 61 Shaft end protruding part 7, 8 Rotor extension part 7a, 8a Large diameter semicircular part 7b, 8b Small diameter semicircular part 11-14 Bearing

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[Procedure amendment]

[Submission date] September 2, 1998 (1998.9.2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

Returning again to FIG. 1, the exhaust-side shaft ends of the shafts 5b and 6b of the screw rotors 5 and 6 are connected to the pump casing bottom wall 4a where the pump discharge port is formed. The gear box is rotatably supported by bearings 11 and 12 and penetrates through the bottom wall 4a and is attached to the bottom surface of the pump casing.
Projecting into the box 10 . The lower ends of the lower end protrusions 51, 61 of these rotor shafts are also mounted on the bearings 13, 1
4 rotatably supported. Thus, the support structure of the screw rotors 5, 6 is a one-sided shaft support structure in which only the lower end portion on the exhaust side is rotatably supported.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0027

[Correction method] Change

[Correction contents]

Inside the gear box 10 , timing gears 21 and 22 attached to the lower end projections 51 and 61 of the rotor shaft and meshing with each other, and a pinion gear integrally formed coaxially with one of the timing gears 22. 23, an idle gear 24 meshing with the pinion gear 23, and a drive gear 25 meshing with the idle gear are housed. The drive gear 25 is fixed to an output shaft 31 of a motor 30 which is vertically arranged at a position adjacent to the pump casing 4 in a downward posture.

[Procedure amendment 3]

[Document name to be amended] Drawing

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

FIG.

Claims (4)

[Claims] A screw-type vacuum pump comprising a pair of screw rotors each having a right-hand screw and a left-hand screw that can mesh with each other formed on an outer peripheral surface, and performing an exhaust operation by rotating these screw rotors relative to each other. At the suction-side shaft end of each screw rotor, a rotor extension is integrally formed or attached coaxially, and each rotor extension has a cross section perpendicular to the axis at the suction-side shaft end of the screw rotor. A screw having substantially the same cross-sectional shape perpendicular to the axis, wherein each rotor extension and the shaft end on the suction side of the screw rotor are connected to each other in a state where both end surface shapes are substantially the same. Type vacuum pump. 2. The screw rotor outer diameter line according to claim 1, wherein a cross-section perpendicular to the axis of each rotor extension is defined at a suction-side shaft end of the screw rotor. A screw-type vacuum pump comprising: a radially inwardly receding portion; and a portion protruding radially outward from the screw rotor thread root diameter line. 3. The rotor extension according to claim 1, wherein the rotor extension is fixedly fastened to a shaft end on a suction side of the screw rotor by a fastener, and the rotor extension and the suction side of the screw rotor. A screw-type vacuum pump characterized in that a gap between a pump end and a shaft end on the suction side of the rotor extension can be adjusted by inserting a shim plate between the shaft ends. 4. The exhaust-side portion according to claim 1, wherein the screw rotor is disposed vertically so that a suction side thereof is located on an upper side, and a lower portion is located on an exhaust side. A screw type vacuum pump which is supported only by a shaft.