APPARATUS FOR TREATMENT OF A PROCESS GAS

Abstract: The apparatus for treatment of a process gas comprises a vacuum pump provided with a heating portion (8) for preventing adhesion of reaction products on a discharge side (3) thereof.

Description: The invention relates to a vacuum pump which comprises a housing equipped with a suction port and an exhaust path and a rotor supported rotatably inside said housing, and in which a process gas sucked from said suction port is discharged from said exhaust path near to the atmosphere. Various vacuum pumps have been proposed recently in order to generate clean vacuum in apparatuses for producing semiconductors. An example of such vacuum pumps is disclosed in US-A-4,688,160. In the vacuum pump of this kind, a gas sucked from the suction port is generally compressed sequentially while it passes through a flow path defined by a rotor and a stator and the compressed gas is discharged into the atmosphere. In the vacuum pump of this kind, materials in process gases handled in a semiconductor production apparatus which are likely to be solidified adhere and are deposited in the flow path. In order to remove such deposits easily, some vacuum pumps have a structure which can be disassembled and assembled easily, as disclosed in Japanese Utility Model Laid-Open No. 43197/1985. In accordance with the prior art described above, the gas flow path is closed when the reaction products adhere or are deposited on the flow path of the process gas, so that the pump is disassembled in order to remove the deposits. Therefore, the operation of the semiconductor production apparatus connected to the vacuum pump must be stopped and the work efficiency is not high. GB-A-482884 and 2119603 as well as US-A-2139740 and 3168978 describe different devices for producing high vacuum provided with heating means on the high vacuum side for separating molecules of gas absorbed in the inside of the device, e.g. a high vacuum pump or a turbomolecular vacuum pump. It is therefore the object of the present invention to provide a vacuum pump which can prevent adhesion or deposit of reaction products on the exhaust path of the vacuum pump. The object can be accomplished with the vacuum pump of the generic kind by a device for removing reaction products situated on the low vacuum side, said device comprising a heating portion disposed in said exhaust path for preventing adhesion of the reaction products by process gas on a discharge side, and a heat source connected to said heating portion. The heating portion disposed in the exhaust path heats the flow path and the gas or gases flowing through the flow path. Therefore, even when the reaction products adhere to the exhaust path, they are gasified by the heat from the heating portion and are not deposited to the extent of a thickness exceeding a predetermined thickness. As a result, clogging of the exhaust path due to adhesion of the reaction products can be prevented. According to the present invention, since clogging of the pump exhaust path can be prevented by vaporizing the reaction products in the process gas during the operation, the rates of the operation of the vacuum pump and the production apparatus connected to the vacuum pump can be improved. Preferably said heating portion is a heating member fixed to said housing in such a manner as to be positioned inside said exhaust path. Advantageously said heating portion is disposed on the inner surface of said exhaust path. Said heating portion may be a tubular heating member. It is also convenient to provide a temperature detector for detecting a temperature of said heating member, each being disposed in said exhaust path; means for adjusting the supply quantity of said heat source; a temperature setter; and a control unit for controlling said heat supply quantity adjustment means by the set temperature from said temperature setter and the detection temperature from said temperature detector. Preferably said heat source is an electrical power source and said heat supply quantity adjustment means is a variable resistor. Said heating portion may be a tubular member having a space into which a high temperature fluid is supplied. In this case the space filled with a high temperature fluid is provided in a side wall portion of the tubular member. With this embodiment a heat source can be used which is a high temperature fluid source associated with a valve as a heat supply quantity adjustment means. Embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a longitudinal sectional view showing a vacuum pump in accordance with one embodiment of the present invention; Fig. 2 is an enlarged longitudinal sectional view showing the principal portions of the vacuum pump shown in Fig. 1; Fig. 3 is a sectional view showing an example of the heating member used in the embodiment shown in Fig. 1; Fig. 4 is a vapor pressure diagram of aluminum chloride (AlCl₃); and Figs. 5 to 8 are sectional views showing other embodiments of the present invention, respectively. The vacuum pump shown in Fig. 1, comprises a rotor 1 having a plurality of vanes and being rotatably supported by bearings 5 inside a main housing 4A and a motor housing 6A. A motor 6 is connected to the rotor 1. A stator 7 is disposed on the inner wall of the main housing 4A. A first end plate 4B is disposed on one of the sides of the main housing 4A. A second end plate 4C is disposed between the other side of the main housing 4A and the motor housing 6A of the motor 6. A suction port 2 is formed on the first end plate 4B. An exhaust path 3 reaching the vane portion of the final stage of the rotor 1 is formed in the second end plate 4C and the stator 7. A T-shaped pipe 9 is disposed in the second end plate 4C so as to communicate with the exhaust path 3. A heating member 8 is fitted into the exhaust path 3 through the T-shaped pipe 9 as shown in Fig. 2. The heating member 8 is rod-like and is connected to an electrical power source 11 as a heat source through a variable resistor 10 as a means for regulating the quantity of heat to be supplied from the heat source. As shown in Fig. 3, the heating member 8 consists of a holding cylinder or holding tubular member 8A, a heating wire 8B wound on this holding cylinder 8A, a protective cylinder or tubular member 8C covering the heating wire 8B, a fitting bracket 8D fitted to one end each of the protective cylinder 8C and the holding cylinder 8A, and insulators 8E, 8F. The gas sucked from the suction port 2 is compressed sequentially inside the flow path defined by the rotor 1 and the stator 7 and is discharged near to the atmosphere from the exhaust path 3. In the exhaust process described above, the gas attains a high temperature at the portion where the rotor 1 rotates but the gas temperature drops near the exhaust path 3 because heat escapes to the housing 4A and the second end plate 4C. Therefore, when the suction side of the vacuum pump is connected to an aluminum dry etching apparatus of semiconductor devices, for example, AlCl₃ is formed as the reaction product after etching. As can be seen from the vapor pressure diagram of AlCl₃ shown in Fig. 4, AlCl₃ turns to a solid at a temperature below about 180°C near the atmospheric pressure so that the reaction product flowing through the flow path is cooled on the inner wall of the exhaust path 3 and adheres to the inner wall. However, since this deposit is heated by the heating member 8 and gasified, it is possible to prevent clogging of the exhaust path 3 due to the deposit. In the embodiment of Fig. 5 a temperature detector 12 is disposed inside the T-shaped pipe 9 constituting the exhaust path in order to keep the heating temperature of the heating member 8 at a constant temperature, the detection temperature detected by this temperature detector 12 is compared with a set temperature set in advance by a setter 13 by a comparator 14 and this comparator 14 controls electric power which is supplied to the heating member 8 from a power source 10 by means of a variable resistor 10 so that the temperature of the heating member 8 attains the set temperature. In accordance with this embodiment, the temperature of the heating member 8 can be kept at a constant level even though the flow velocity of the gas passing through the exhaust path 3 changes. As a result, deposition and build-up of the reaction products to the exhaust path can be prevented. In the embodiment of Fig. 6 a cylindrical or tubular heating member 15 is disposed on the inner wall surface of the exhaust path 3. Reference numeral 16 represents an insulator. In this embodiment, too, deposition and build-up of the reaction products inside the exhaust path 3 can be prevented by heating and vaporizing them in the same way as in the embodiment shown in Fig. 2. In the embodiment shown in Fig. 7, a temperature detection portion 17 is disposed at part of the heating member 15, in order to keep constant the exothermic temperature of the heating member 15 and to control the supply power to the heating member 15 in accordance with the temperature detected by this temperature detection portion 17. In the embodiment of Fig. 8, a cylinder or tubular member 18 having, in a wall thereof, a space 18A into which a high temperature fluid from a high temperature fluid source 11a is supplied is disposed as the heating portion on the inner wall of the exhaust path 3. Reference numeral 19 represents a valve for controlling a flow rate of the high temperature fluid to be supplied to the space 18A. According to this construction, too, deposition and build-up of the reaction products can be prevented by the heat of the high temperature fluid supplied into the cylinder 18. In this embodiment, too, the exothermic temperature from the cylinder 18 can be kept constant in the same way as the embodiments shown in Figs. 5 and 7.

Claims: 1. A vacuum pump which comprises a housing (4A) equipped with a suction port (2) and an exhaust path (3) and a rotor (1) supported rotatably inside said housing (4A), and in which a process gas sucked from said suction port (2) is discharged from said exhaust path (3) near to the atmosphere characterized by a device for removing reaction products situated on the low vacuum side, said device comprising a heating portion (8, 15, 18) disposed in said exhaust path (3) for preventing adhesion of the reaction products by the process gas on the discharge side, and a heat source (11, 1a) connected to said heating portion. 2. The vacuum pump according to claim 1, wherein said heating portion is a heating member (8) fixed to said housing (4A) in such a manner as to be positioned inside said exhaust path (3). 3. The vacuum pump according to claim 2, wherein said heating portion (15, 18) is disposed on the inner surface of said exhaust path (3). 4. The vacuum pump according to claim 3, wherein said heating portion is a tubular heating member (15). 5. The vacuum pump according to one of the claims 1 to 4, characterized by a temperature detector (12) for detecting a temperature of said heating member (8), each being disposed in said exhaust path (3); means (10) for adjusting the supply quantity of said heat source (11); a temperature setter (13); and a control unit (14) for controlling said heat supply quantity adjustment means (10) by the set temperature from said temperature setter (13) and the detection temperature from said temperature detector (12). 6. The vacuum pump according to claim 5, wherein said heat source (11) is an electrical power source and said heat supply quantity adjustment means (10) is a variable resistor. 7. The vacuum pump according to claim 1, wherein said heating portion is a tubular member (18) having a space (18A) into which a high temperature fluid is supplied. 8. The vacuum pump according to claim 7, wherein the space (18A) filled with a high temperature fluid is provided in a side wall portion of the tubular member (18). 9. The vacuum pump according to claim 7 or 8, wherein said heat source (11a) is a high temperature fluid source associated with a valve (19) as a heat supply quantity adjustment means.

Inventors: AWADA, YOSHIHISA, GYOBU, ICHIRO, MASE, MASAHIRO, MURAMATSU, KIMIO, NAGAOKA, TAKASHI, NISHIUCHI, AKIRA, UEYAMA, KEIJI
Applicants: HITACHI, LTD.
Application year: 1988
Main classification: F04D19
IPC codes: F04D17, F04D29, F04D19