JPH0529798B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a vacuum pump whose exhaust port pressure is close to atmospheric pressure, and is particularly applicable to equipment that handles gases that tend to deposit or adhere in pumps such as semiconductor manufacturing equipment. The present invention relates to a vacuum pump equipped with a suitable exhaust flow path.

[Conventional technology]

A conventional example of a vacuum pump with a back pressure close to atmospheric pressure is JP-A No. 61-247893. The structure of this pump will be explained with reference to FIG. This vacuum pump includes a housing 11 having an intake port 11A and an exhaust port 11B, a rotating shaft 12 rotatably supported within the housing via a bearing 21, and an intake port 11A.
Housing 11 between the side and the exhaust port 11B side
A centrifugal compression pump stage 13 and a circumferential flow compression pump stage 14 are sequentially disposed within the pump. The rotating shaft 12 is driven by a motor 15 connected thereto.

[Problem that the invention seeks to solve]

In the steady operation state of the conventional vacuum pump as described above, the centrifugal compression pump stage operates mainly in a molecular flow, intermediate flow, and the circumferential flow compression pump stage 14 operates in a viscous flow of several Torr or more. The gas flowing into the circumferential compression pump stage 14 is sufficiently compressed in the centrifugal compression pump stage 13, so that the volumetric flow rate is almost zero. Therefore, the circumferential flow compression pump stage 14 is operated close to the shut-off condition, so that the loss, that is, the heat generated by the fluid loss, is not carried away by the gas but is accumulated, and the circumferential flow compression pump stage 14 is The temperature within the flow path of stage 14 increases. The closer the gas is to the exhaust port, the higher the gas density, so the temperature rises significantly, reaching a maximum of 200°C or more. A problem arises when this pump is applied to semiconductor manufacturing equipment that uses active gas. For example, in an aluminum plasma etching device that uses SiCl ₄ gas, a large amount of AlCl ₃ is generated by the reaction. The sublimation temperature of AlCl ₃ is approximately 40°C at a pressure of 0.3 Torr and 178°C at 760 Torr.

FIG. 6 shows a system diagram when the vacuum pump of FIG. 5 is applied to an aluminum plasma etching apparatus. Since etching is performed at a pressure of about 0.1 Torr, the pressure inside the pipe 33 between the reaction chamber 31 and the pump 34 is about 0.1 Torr. The temperature inside the piping is several tens of degrees Celsius or higher, so the temperature in the reaction chamber 31 and piping 33 is
There is little deposition of AlCl ₃ . Since the temperature inside the pump 34 is also high due to fluid loss, precipitation of AlCl ₃ is small. However, the exhaust flow path 11 of the pump shown in FIG.
At C, the pressure is almost atmospheric and the volumetric flow rate is reduced, so the gas flow rate becomes small. Since the wall temperature of the exhaust flow path 11C is usually much lower than the temperature of the pump section, the AlCl _{3 gas that has passed through the pump in a saturated state is rapidly cooled by the wall of the exhaust flow path 11C, and AlCl 3} gas is generated in the exhaust flow path 11C. There was a problem in that the powder _{No. 3} precipitated and eventually blocked the flow path.

An object of the present invention is to provide a vacuum pump that reduces the drop in wall temperature of the exhaust port of the vacuum pump, reduces deposition of AlCl ₃ powder, and facilitates removal of AlCl ₃ powder when it adheres. It is about providing.

[Means for solving problems]

The above object is achieved by inserting into the exhaust channel of the vacuum pump a tube that does not fully contact the walls of the exhaust channel and is a poor conductor of heat.

[Effect]

The process gas and the reaction product gas, which are heated inside the vacuum pump and reach a high temperature, reach the exhaust port through both the inside and outside of the pipe inserted into the exhaust flow path in a saturated gas state. The gas flowing outside the insertion tube is
As it is cooled by the wall of the exhaust flow path, reaction products are precipitated, gradually filling the flow path, and finally clogging the flow path. On the other hand, since the layered tube is a poor conductor of heat, the amount of heat transferred from the gas flowing inside the tube to the wall of the tube is small, and therefore the temperature drop of the gas is small, so reaction products are precipitated on the inner wall of the tube. Adhesion is extremely reduced, making it less likely that the flow path will be blocked by precipitates. Furthermore, since the insertion tube can be removed and cleaned, maintenance of the pump becomes easier.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is an overall structural diagram of a vacuum pump according to the present invention, and FIG. 2 is a sectional view of a vacuum pump exhaust flow path according to the present invention. In FIG. 1, this vacuum pump includes a housing 11 having an intake port 11A and an exhaust port 11B, and a bearing 2 inside the housing.
a rotating shaft 12 rotatably supported via 1;
It includes a centrifugal compression pump stage 13 and a circumferential flow compression pump stage 14 which are sequentially arranged within the housing 11 from the intake port 11A side to the exhaust port 11B side. The rotating shaft is driven by a motor 15 connected thereto. The centrifugal compression pump stage 13 includes an open impeller 13A having a plurality of retreating blades on its surface and attached to the rotating shaft 12, and an open impeller 13A attached to the inner wall of the housing 11.
Fixed disks 13B each having a plurality of blades facing inward in the direction of rotation are arranged alternately in series on the back surface and the opposite surface thereof.

The circumferential flow compression pump stage includes an impeller 14A that is attached to the rotating shaft 12 and has a plurality of blades radially provided on the outer peripheral surface, and an impeller 14A that is attached to the inner wall of the housing 11 and faces the surface of the impeller 14A. Fixed disks 14B having U-shaped grooves on their surfaces are alternately arranged in series. The U-shaped grooves of the fixed disk 14B at each stage are connected in series.
The exhaust flow path 11C has a cross-sectional shape shown in FIG.
A tube 11D made of a poor thermal conductor, for example quartz, is inserted.

Next, the operation of this embodiment will be explained. Under normal operating conditions, the gas flow near the inlet of the centrifugal compression pump stage 13, ie, the vacuum pump inlet 11A, is an intermediate or molecular flow, and the centrifugal compression pump stage 13 acts as a Siegbahn molecular pump. That is, an impeller 13A having blades.
acts as a rotating disk with a spiral groove processed, and in combination with the back surface of the fixed disk 13B (the surface without blades), acts as a Siegbahn molecular pump that compresses from the inner diameter side toward the outer diameter side. work. The fixed disk 13B provided with a plurality of blades acts as a fixed disk with a spiral groove formed thereon, and in combination with the back surface (the surface without blades) of the impeller 13A, it moves from the outer diameter side to the inner diameter side. It acts as a Siegbahn molecular pump that exerts a compressive action toward . Furthermore, since the gas flowing into the circumferential compression pump stage 14 is sufficiently compressed in the centrifugal compression pump stage 13, the volumetric flow rate is almost zero. In other words, since the circumferential flow compression pump stage 14 is operated in a state close to the shut-off state, heat due to fluid loss is difficult to be discharged by the gas, and the gas temperature in the circumferential flow compression pump stage 14 decreases from 200 to 200°C. It reaches a high temperature of 300℃. If the gas sucked into the pump is a gas containing AlCl ₃ , which tends to precipitate at high pressures and low temperatures, such as in aluminum plasma etching equipment, the pressure of the gas sucked into the pump will rise, but so will the temperature. Not much precipitation adheres to each stage. On the other hand, exhaust flow path 1
In 1C, the gas in the gap between the channel wall and the insertion tube 11D is cooled by heat escaping to the channel wall, and precipitates grow, but the inside of the insertion tube 11D is kept warm and a circular shape is formed. The high temperature gas from the circumferential pump stage 14 is discharged to the discharge port 11B without being cooled much. Therefore, the insertion tube 11D, that is, the exhaust flow path 1
1C becomes less likely to be blocked by precipitates.

The cross-sectional shape of the insertion tube 11D is shown in FIGS. 3 and 4.
Any shape as shown in the figure, that is, a shape with a small contact area with the wall surface of the exhaust flow path 11C, may be used. Further, the insertion tube 11D may be suspended in the exhaust flow path 11C.

〔Effect of the invention〕

As described above, according to the present invention, the tube made of a poor heat conductor inserted into the exhaust flow path does not come into close contact with the exhaust flow path wall, so that heat conduction from the gas in the insertion tube to the insertion tube is prevented. The amount is very small, and the gas inside the insertion tube is not cooled down. Therefore, even if gas that has the property of precipitating and depositing due to temperature drop flows from inside the vacuum pump into the exhaust flow path, the precipitates will not adhere to the inside of the insertion tube and block the flow path.
In other words, the loss of functionality of the vacuum pump can be greatly reduced. Moreover, if the insertion tube is pulled out and cleaned periodically, operation can be continued with simple maintenance.

[Brief explanation of the drawing]

1 to 4 show embodiments of the present invention,
FIG. 1 is a longitudinal sectional view showing the overall structure of a vacuum pump according to the present invention, FIGS. 2 to 4 are sectional views showing the shape of the exhaust flow path in FIG. 1, and FIG. 5 is a longitudinal sectional view of a conventional vacuum pump. It is a front view. FIG. 6 is a system diagram when this pump is applied to a dry etching device. 11...Housing, 11A...Intake port, 11
B...exhaust port, 11C...exhaust channel, 11D...
Insertion tube, 12... Rotating shaft, 13... Centrifugal compression pump stage, 14... Circumferential flow compression pump stage, 31... Reaction chamber, 34... Vacuum pump, 36... Scrubber.

Claims (1)

[Claims] 1. A vacuum pump whose exhaust port pressure is close to atmospheric pressure, characterized in that a tube is inserted into the exhaust flow path and is made of a poor conductor of heat and does not make full contact with the wall of the exhaust flow path. pump.