JPS63192987A - Centrifugal high vacuum pump - Google Patents

Abstract

PURPOSE:To obtain a high vacuum by generating difference in molecular density between the rotation center and the peripheral part of rotation of a rotary disk by means of a centrifugal force, effectively taking out said molecular density difference, and forming it in multiple stages. CONSTITUTION:The front face of the disk of each rotor 16 is in close vicinity to the back of each partition wall 12 or the inner face of a casing front wall 24, whereas, the rear face of the disk is separated by a defined distance from the front face of the partition wall 12 or the inner wall of a casing rear wall 26. Thereby, the difference in molecular density which is generated between the center part of the rotor 16 and its peripheral part through the ventilation passage of the rotor 16 is effectively maintained during the rotation of the rotor 16. And, the chambers 14 of a casing 10 which are adjacent to each other are mutually connected by a flow passage via a ventilation port 32 formed on the center part of each of the partition walls 12, thereby, carrying out a multistage exhaust. And, the difference in the number of molecules is gradually increased between the suction port 28 of the casing 10 and each chamber 14, and the exhaust gas is discharged out of the outlet 30 of the casing 10 into the atmospheric pressure, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high vacuum pump used when it is necessary to evacuate the inside of a chamber to a high vacuum in semiconductor manufacturing equipment, various analysis equipment, testing equipment, etc. In particular, it relates to centrifugal high vacuum pumps that utilize centrifugal action.

[Conventional technology]

Commonly used vacuum pumps include those that mechanically exhaust air such as oil rotary pumps, mechanical booster pumps, and turbomolecular pumps, and those that pump jets of vapor such as oil and mercury such as diffusion pumps and ejector pumps. There are various types, including those that utilize getter adsorption, such as ion pumps and cryopumps.

By the way, the vacuum pump used to evacuate the inside of the reaction chamber to a high vacuum in the semiconductor manufacturing process is designed not only to obtain a high vacuum but also to prevent back diffusion of oil into the evacuation system. The temperature of the exhaust gas exhausted from the reaction chamber is high, so it must be oil-free, and the exhaust gas may contain reaction products, so it must be oil-free. It is required that conditions such as no biting or dissolution in oil occur. A turbo-molecular pump is a high vacuum pump that relatively satisfies these conditions. This turbo molecular pump.

A rotor having a large number of blades around the outer periphery of a disk that is inclined in the direction opposite to the axial direction, and a stator having a large number of blades around the outer periphery of a disk that are inclined in the opposite direction to the above-mentioned blades in the axial direction. By installing the rotors in parallel and rotating the rotor at high speed, the molecular density on the intake side is gradually made smaller than the molecular density on the exhaust side, thereby achieving a high vacuum.

However, the above-mentioned turbo molecular pump has a back pressure of about 0.1~
Conventionally, for high vacuum evacuation in semiconductor manufacturing processes, an oil rotary pump was installed behind this turbomolecular pump, and these two Vacuum evacuation systems are used in combination with different types of pumps.

[Problem that the invention seeks to solve]

However, turbomolecular pumps have a structure in which a rotor and a stator are arranged side by side, each with a large number of blades arranged around the outer periphery of a disk at an angle to the axial direction. Difficult to adjust.

There are manufacturing issues. Since it has to be used in combination with an oil rotary pump, the characteristics of the entire vacuum evacuation system are greatly influenced by the characteristics of the oil rotary pump.For example, the dissolution of particles in the oil of the oil rotary pump is This may require maintenance such as replacing the oil, or at least a particle trap on the front side of the oil rotary pump to reduce particles in the exhaust gas, a gas cooler to lower the temperature of the exhaust gas, etc. Furthermore, it is necessary to provide an oil trap to prevent back diffusion of oil, which reduces the advantages of turbomolecular pumps.

Additionally, since turbomolecular pumps and oil rotary pumps are of completely different types and structures, they cannot be formed as a single unit, and must be manufactured and installed separately. Therefore, there is also the problem that it requires a large installation space.

This invention has been made to solve all of the above-mentioned problems in the prior art at once.

It is relatively easy to manufacture, satisfies all the above-mentioned requirements for vacuum pumps used in semiconductor manufacturing processes, is maintenance-free, does not require various ancillary equipment on the front side of the pump, and has a single pump body. It is an object of the present invention to provide a high-vacuum pump that can evacuate from atmospheric pressure to high vacuum and, in some cases, can be formed as an integral part with a turbo-molecular pump or the like.

[Means for solving problems]

As a technical means for achieving the above-mentioned object, this invention creates a molecular density difference between the rotational center and the rotational periphery of a rotating disk by centrifugal force, and effectively extracts the molecular density difference. The high vacuum pump was constructed based on an operating principle completely different from that of conventional vacuum pumps.

That is, the present invention includes a cylindrical casing having an intake port and an exhaust port, a vent hole vertically provided on the inner circumferential wall surface of the casing, and a vent hole formed in the center of each of the casings. A plurality of partition walls defining a plurality of chambers communicating with each other through ventilation holes, and a plurality of ventilation passages extending from the center toward the circumference in the centrifugal direction are formed on the front side of the disc, and the Each chamber of the casing is provided with a steel membrane in which the front surface of the disk and the back surface of the partition wall or the inner surface of the front wall of the casing are brought close to each other, and the rear surface of the disk and the front surface of the partition wall or the inner surface of the rear wall of the casing are spaced apart by a predetermined distance. a plurality of rotors, a rotary drive shaft fixed to each rotation center of these rotors and holding the rotors coaxially;
The gist of the present invention is a centrifugal high vacuum pump comprising a rotary drive source connected to the rotary drive shaft.

[For production]

In the centrifugal high vacuum pump of the present invention configured as described above, when the rotary drive shaft connected to the rotational drive source rotates, each rotor enclosed in each chamber defined by the partition wall inside the casing is rotated. The centrifugal force generated by the rotation of the rotor rearranges gas molecules from the center of rotation of the rotor in the centrifugal direction through multiple ventilation channels formed on the front side of the rotor, causing the rotation of the rotor. A density distribution of gas molecules occurs between the center and the periphery, with the center of rotation being lower. This point will be explained in more detail below.

The distribution of the number of molecules due to the difference in potential energy E is
According to the Maxwell-Boltzmann statistics, it is expressed by the following formula.

In this formula, N = N, e-, No means that the potential energy is E0 =
is the number of molecules at the reference position set to 0, N is the number of molecules at the position where the potential energy is E, k is the Boltzmann constant, and T is the absolute temperature of the gas. The distribution expressed by the above equation is called the Boltzmann distribution. , which is generally well known. In the above formula, 1For example, if E = mgh (m: mass of gas molecules, g: acceleration of gravity, h: height from the earth's surface), No indicates the number of molecules on the earth's surface, and N-20- = =N, e The expression kT shows the distribution of the number of molecules in the earth's atmosphere under the influence of 1 gravity. Here, potential energy E includes everything based on mechanical force.

Let us consider the case where centrifugal force is applied to gas molecules by the rotation of a rotor. In this case, No is the circumference of the rotor, i.e. the radius r.

is the number of gas molecules at the position, and the potential energy at this position is E0=0.

Then, the centrifugal force F acting on a gas molecule of mass m at a position of arbitrary radius r is.

(However, V: peripheral speed at rotation radius r.

n: rotational speed of the rotor) When this centrifugal force is acting, the energy U required to move a gas molecule from a position with radius r to a position with radius r is u = S' Fd r=J'-4
i”n”mrd r= 2 x” n”m (r” −
Therefore, the potential energy E at the position of radius r is E = −u = 2 x” n”m (r,” −r
”), and the number of molecules N at the position of radius r is.

,=,. . -t=,. . - rotation speed and radius of the rotor, which can be obtained relatively easily industrially, are: n = 60° r, p, s, , r, = 15
Substituting the value of cn into the above equation, calculate the number of molecules N at the position of the rotation center of the rotor, r=o.

In other words, the number of molecules at the center of rotation of the rotor is 0.145 times that at the periphery. Therefore,
If this operation is repeated, for example, 10 times and then exhausted to atmospheric pressure, the theory is 760TorrX (0,1
45)" = 3.12X10-'Torr vacuum will be obtained.

Here, in the high vacuum pump according to the present invention, the front surface of the disk of the rotor and the back surface of the partition wall or the inner surface of the front wall of the casing are close to each other, and the rear surface of the disk and the front surface of the partition wall or the inner surface of the rear wall of the casing are close to each other. Because they are separated by a predetermined distance.

The molecular density difference created between the center of the rotor and its periphery through the rotor's ventilation channels is effectively maintained during rotor rotation. Adjacent chambers of the casing communicate with each other via a vent hole formed in the center of the partition wall, so multi-stage exhaust is performed, and the number of molecules is increased between the inlet of the casing and each chamber. As the difference gradually increases, the exhaust gas is exhausted to atmospheric pressure from the exhaust port of the casing.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

1 and 2 show one embodiment of the present invention, FIG. 1 is a side sectional view of a centrifugal high vacuum pump, and FIG.
-u' is a front sectional view.

As shown in these figures, this centrifugal high vacuum pump
A casing 10, a plurality of partition walls 12 vertically disposed on the inner circumferential wall surface of the casing 10, a plurality of rotors 16 each conjunctivatized in a plurality of chambers 14 formed by defining the inside of the casing 10 by these partition walls 12, A rotary drive shaft 18 fixed to each rotation center of these rotors 16 and holding each rotor 16 coaxially, and this rotary drive shaft 18
The rotary drive source 20 is connected to the rotary drive source 20. The casing 10 has a cylindrical peripheral wall 22, a front wall 24, and a rear wall 26.
An air intake port 28 is formed in the center of the front wall 24 and is connected to a vacuum chamber or the like (none of which is shown) via a conduit.

An exhaust port 30 is formed near the rear wall 26.

The partition walls 12 are arranged parallel to each other at equal intervals in the axial direction of the casing 10. A ventilation hole 32 is formed in the center of each partition wall 12, and the adjacent partition walls 12 are connected through the ventilation hole 32. The 14 matching chambers communicate with each other through channels. The rotor 16 has a circular recess 36 formed in the center of one side of a circular thick plate 34, and a plurality of grooves 38 extending from the circumferential surface of the recess 36 to the peripheral edge of the thick plate 34, which are equally distributed in the circumferential direction. It is composed of disks. The grooves 38 have a parabolic shape extending from the center of the disk toward the centrifugal direction, and are carved with a constant depth and a constant width, and these grooves 38 serve as ventilation paths. Each rotor 16 has one disk in each chamber 14, with the front surface of the disk being close to the back surface of the partition wall 12 (or the inner surface of the casing front wall 24), and the rear disk surface being close to the front surface of the partition wall 12 (or the inner surface of the casing rear wall 26). ) and are spaced apart from each other by a predetermined distance. That is, as shown in a partially enlarged view in FIG. 3, the gap a between the front surface of the rotor 16 and the back surface of the partition wall 12 is significantly smaller than the gap between the rear surface of the rotor 16 and the front surface of the partition wall 12. This suppresses backflow of exhaust gas between the chambers 14. In addition, in order to suppress backflow of exhaust gas, a large number of guide vanes 40 are disposed in the circumferential direction, facing and close to the outer peripheral edge of the rotor 16, and inclined with respect to the normal direction. A bearing portion 42 of the 0-rotation drive shaft 18 fixed to the back surface of the partition wall 12 is provided with a seal portion 44 for sealing with the rotational drive source 20. Since this seal portion 44 is provided on the exhaust side where the relative pressure is high (atmospheric pressure in some cases), there is no need to use a special rotary shaft seal as a sealing means, and there is no need to use a screw seal or a purge gas seal. A sealing means such as a seal by injection can be used, and the pump body can be made oil-free if the above-described constituent members of the pump body are molded from ceramic materials.

Both corrosion resistance and heat resistance in high vacuum pumps can be satisfied. As the one-rotation drive source 20, a high frequency motor, a turbine, etc. are used.

Next, when the rotary drive shaft 18 connected thereto is rotated by the 0-rotation drive source 20 to explain the operation of the centrifugal high vacuum pump having the above configuration, the rotary drive shaft 18
All rotors 16 fixed to rotate clockwise at the same speed. As each rotor 16 rotates, centrifugal force acts on the gas molecules within the grooves (air passages) 38 of the rotor 16.

There is a density distribution of gas molecules in the centrifugal direction from the center of rotation of the rotor 16 to its periphery, and from the above, the pressure in the recess 36 of the rotor 16 in each chamber 14 is equal to the pressure in the outer periphery of the rotor 16. The pressure is reduced by comparison. Then, the exhaust gas once discharged from the outer end of the groove (air passage) 38 due to centrifugal force is transferred to the front surface of the rotor 16 and the rear surface of the partition wall 12 (or the inner surface of the casing front wall 24) by the action of the guide vane plate 40. ) are extremely close to each other (a<b in FIG. 3), so that backflow is suppressed while the rotor 16 is rotating. The outer periphery of the rotor 16 is connected to a recess 3 of the rotor 16 which is stored in the next chamber 14 via the rear part of the rotor 16 and the ventilation hole 32 of the partition wall 12.
6 and is in communication with the groove (air passage) 38 of the primary rotor 16.
A similar distribution of molecular density occurs in . By repeating this process, the vacuum is gradually evacuated,
Finally, the intake port 28. Therefore, a high vacuum can be obtained in a vacuum chamber or the like connected to the flow path. still.

The exhaust gas is exhausted from the exhaust port 30 to atmospheric pressure or the like.

4 and 5 show another embodiment of the present invention, and FIG.
The figure is a front view of the rotor of the centrifugal high vacuum pump, and Fig. 5 is a cross-sectional view taken along the line ■-■'' in Fig. 4, together with parts of the casing and bulkhead.The rotor of this high vacuum pump 16' is a thin plate 46 on one side of the circular thin plate 46.
It is composed of a circular plate in which a plurality of vanes 48 are vertically arranged and arranged evenly in the circumferential direction from the center to the periphery. The blade 48 has a constant thickness and a shape extending parabolically from the center of the disk toward the centrifugal direction.

A space 50 sandwiched between adjacent vanes 48 becomes a ventilation path. The height of the vane 48 from the surface of the thin plate 46 is gradually lowered from the center toward the periphery so that the cross-sectional area of the space (air passage) 50 is always constant regardless of the radial position of the rotor 16''. That is, as shown in FIG.

If the height of the edge of the blade 48 at a radial position at a distance r0 from the rotation center of the rotor 16' is ho, then the height of the blade 48 at a radial position at an arbitrary distance r from the rotation center of the rotor 16'. h=f(r) is determined as follows.

If the thickness of the wing plate 48 is t and the number of blades is Z, then the distance fir
The total cross-sectional area A0 of each ventilation passage 50 at the radial position fl is:

A, = (2πro t-Z) ”ha.On the other hand, each air passage 50 at a radial position of an arbitrary distance r
The total cross-sectional area A is A=(2πr-t-Z)・h, and in order to make the distribution of the number of exhaust gas molecules in the radial direction follow the Boltzmann distribution,
=A, so the height H of the vane plate 48 at the peripheral edge position at the distance RR from the rotation center of the rotor 16'' is as follows.

In this way, since the top sides of each blade 48 are formed in a curved shape, the front surface of the rotor 16', which is formed by connecting the top sides of each blade 48, becomes curved. Here, as in the high vacuum pump of the first embodiment, the front surface of the rotor 16' and the back surface of the partition wall 12'' need to be brought close together to suppress backflow of exhaust gas. The back surface is also formed in a curved shape corresponding to the front surface of the rotor 16'.In order to suppress the backflow of exhaust gas, as shown in FIG. A large number of vanes 40' may be provided around the circumference, and as shown in FIG. Make it into a staircase shape,
The partition wall 12"' may be formed in a planar shape correspondingly. The configuration other than those described above is the same as that of the high vacuum pump of the first embodiment described above.

Although the present invention is constructed as described above, the scope of the present invention is not limited by the contents of the above description and drawings, and may include various modified embodiments without departing from the gist. For example, the shape of the groove serving as the ventilation path of the rotor or the shape of the vane forming the ventilation path may not be parabolic but merely radial, or may have another shape. In addition, in combination with a turbo molecular pump, the turbo molecular pump unit is placed on the front stage side,
The rotational drive shaft of the centrifugal high vacuum pump of the present invention can also be extended to serve as the rotational drive shaft of a turbo-molecular pump, and the casing can also be formed integrally to form a composite pump.

In the first embodiment shown in the first figure, the grooves 38 are carved with a constant depth and a constant width, and in the second embodiment shown in the fourth figure, the top side of each vane plate 48 is calculated according to the above calculation formula (i.e., I configured it like this, but
This is achieved by making the cross-sectional area of one ventilation passage (groove 38 in the first illustrated embodiment, ventilation passage 50 in the fourth illustrated embodiment) constant in the radial direction in both of the embodiments described above. The distribution of numbers is made to exactly match the Boltzmann distribution. However, the distribution of the number of exhaust gas molecules in the radial direction does not necessarily have to match the Boltzmann distribution.

C Effects of the invention] Since the present invention is configured and operates as explained above, it is relatively easy to manufacture including design, and with appropriate design, it is possible to move from high vacuum to atmospheric air. It is oil-free, heat resistant, and corrosion resistant, and is not affected by particles contained in exhaust gas, is maintenance free, and can be used with various ancillary equipment on the front side of the pump. The present invention has provided a high vacuum pump that has a number of advantages, such as eliminating the need for a vacuum pump and, in some cases, being able to be formed integrally with a turbomolecular pump or the like.

As described above, the present invention is highly effective in semiconductor manufacturing processes and the like.

[Brief explanation of the drawing]

1 and 2 show one embodiment of the present invention, FIG. 1 is a side sectional view of a centrifugal high vacuum pump, and FIG.
-n' is a front sectional view. FIG. 3 is a side sectional view showing an enlarged part of the same, FIGS. 4 and 5 show another embodiment of the present invention, and FIG. 4 is a front view of the rotor of a centrifugal high vacuum pump. Figure 5 is the 4th
FIG. 6 is a diagram showing the v-v' cross section of the figure together with parts of the casing and bulkhead; FIG. 6 is a diagram for explaining changes in the height of the blades of the rotor; FIGS. 7 and 8 3A and 3B are partial side sectional views showing modified examples of the rotor, respectively. 10...Casing, 12.12', 12''...
・Partition wall, 14...chamber, 16.16',
16”...rotor, 18...rotation drive shaft, 20
...Rotary drive source, 24...Casing front wall, 26.
...Casing rear wall, 28...Intake port, 30
...Exhaust port, 32...Vent hole, 34...Circular thick plate, 36...Circular recess, 38...Groove (ventilation path). 40, 40'... Guide vane plate, 46.46'... Circular thin plate, 48.48'... Vane plate, 50... Air passage. 1.7.゛:, Ll:゛P Figure 1 Figure 4 Figure 5 V! J Figure 7 Figure 8 Procedural Amendments August 25, 1986

Claims (1)

[Claims] 1. A cylindrical casing having an intake port and an exhaust port;
A plurality of vent holes are provided vertically on the inner circumferential wall surface of the casing and each has a vent hole formed in the center thereof, and the inside of the casing is divided in the axial direction into a plurality of chambers that communicate with each other via the respective vent holes. A plurality of ventilation passages extending from the center to the periphery in the centrifugal direction are formed on the partition wall and the front side of the disk, and each chamber of the casing has a plurality of air passages formed on the front side of the disk and the back side of the partition wall or the front wall of the casing. A plurality of rotors are installed with the inner surface of the casing in close proximity to each other, and with a predetermined distance between the rear surface of the disk and the inner surface of the partition wall or the rear wall of the casing. A centrifugal high vacuum pump comprising a rotary drive shaft held coaxially and a rotary drive source connected to the rotary drive shaft. 2. The rotor forms a circular recess in the center of one side of a circular thick plate, and a plurality of parabolic grooves of a constant depth and a constant width are equally spaced from the circumferential surface of the recess to the peripheral edge of the thick plate. A centrifugal high-vacuum pump (3) according to claim 1, wherein the rotor is formed of a circular plate with a central portion on one side of the circular thin plate, and the groove is a ventilation path. It consists of a circular plate in which a plurality of parabolic blades with a constant thickness are arranged vertically from the top to the periphery, and the space between adjacent blades is used as a ventilation passage, and the height of each blade is The cross-sectional area of the air passage is gradually lowered from the center to the periphery so that it remains constant regardless of the radial position, and the front surface of the disk formed by the top edge of each vane has a curved shape. A centrifugal high vacuum pump according to claim 1. 4. The rotor according to any one of claims 1 to 3, wherein a large number of guide vanes are provided circumferentially in the vicinity of the outer peripheral edge of the rotor and are inclined with respect to the normal direction. Centrifugal high vacuum pump.