JP4528019B2 - Temperature control device for molecular pump - Google Patents

Description

  The present invention relates to a temperature control device for a molecular pump used for exhausting an etching apparatus or a CVD apparatus.

In this type of molecular pump, as a measure for preventing the formation of reaction products that adhere and accumulate in the pump, in a turbo molecular pump having a plurality of rotary blades and fixed blades alternately arranged in the axial direction, the gas inside the pump Provide a partition made of a heat transfer body in the flow path, connect the partition and the heating unit located outside the pump with a good heat conductor, and provide heating means such as an electric heater for heating the heating unit in the heating unit. A system that heats the entire turbo molecular pump from the outside (see Patent Document 1), or a composite molecule in which a turbo molecular pump unit and a thread groove pump unit are sequentially arranged from the intake side in a housing having an intake port and an exhaust port. In the pump, a system in which the stator of the thread groove pump portion is fixed by a support made of a heat insulating material to efficiently raise the temperature of the stator inside the pump to which the product adheres (cited patent document) In the composite vacuum pump, the thread groove pump portion of the rotor is formed in a cylinder, and an outer stator and an inner stator are disposed in the vicinity of the outer side and the inner side of the cylinder, respectively, The outer stator or casing is provided with heating means and temperature measuring means, and the base is provided with cooling means. The gas passing through the outside of the cylinder and the gas passing through the inside are separately supplied by the heating means and the temperature measuring means, respectively. A method for controlling heating (see Patent Document 3) is known.
Japanese Patent No. 2865959 Japanese Patent No. 3098140 Japanese Utility Model Publication No. 6-12794

  In the molecular pump having a thread groove vacuum pump part, in the exhaust of gas having adhesion, the higher the stator temperature, the more effective the prevention of product adhesion of the exhaust. For this reason, the stator is provided with heating means. There are many things.

  When the molecular pump is started, the stator temperature becomes higher than the rotor temperature due to the heating of the stator, and an inverse temperature difference ΔT of 70 ° C. or more may be generated between the rotor and the stator.

  In the design of the thread groove vacuum pump in which the stator is also arranged on the inner peripheral side of the rotor as in the cited document 3, considering the difference in thermal expansion between the rotor and the stator due to this reverse temperature difference ΔT, It was necessary to keep the gap (gap) between the stator and the rotor sufficiently wide.

  However, increasing the gap has a problem of deteriorating the pump performance of the thread groove vacuum pump.

  In addition, when the design of the reverse temperature difference ΔT is low and the product adheres to the stator, the rotor lock near the tip X of the inner stator in the sectional view of the molecular pump shown in FIG. There was a problem that the molecular pump may cause startup failure.

  In FIG. 5, a is an outer stator, b is an inner stator, c is a rotor, and d is a heating means.

  The present invention eliminates these problems, and provides a temperature control device for a molecular pump having a thread groove vacuum pump portion that does not cause deterioration in pump performance of the molecular pump and does not cause a starting failure. With the goal.

  In order to achieve the above-mentioned object, the present invention arranges a cylindrical rotor in a cylindrical gap formed between opposed surfaces of an outer stator and an inner stator that are connected to each other, and the rotor and stator In a molecular pump having a thread groove vacuum pump portion in which a thread groove is formed on any one of the opposing surfaces of the above, a temperature detection means for detecting the temperature of the stator, a heating means for heating the stator, and the temperature detection And a control means for inputting a detection signal from the means to output a control signal for controlling the stator to a set temperature to the heating means, and the control means is configured so that the stator temperature is equal to or higher than a predetermined temperature after the pump starts operating. The stator is heated and controlled so that the stator temperature rises with a predetermined temperature gradient only within a predetermined time when

  In a molecular pump comprising a thread groove vacuum pump portion having a stator inside the rotor, a temperature control device for the molecular pump can be provided such that the pump performance of the molecular pump does not deteriorate and the molecular pump does not start up poorly. Has an effect.

  An example which is the best mode of the present invention will be described below.

  A first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a longitudinal sectional view of a complex molecular pump 1 to which the present invention is applied.

  The composite molecular pump 1 includes a turbo molecular pump unit 2 and a thread groove vacuum pump unit 3.

  Exhaust gas is sucked from the intake port 1a and is discharged from the exhaust port 1b through the turbo molecular pump unit 2 and the thread groove vacuum pump unit 3.

  A rotor 4 is formed in a substantially covered cylindrical shape.

  The thread groove vacuum pump section 3 is formed by a cylindrical space portion formed between the opposed surfaces of an outer stator 3a1 having a cylindrical surface on the inner side and an inner stator 3b1 having a cylindrical surface on the outer side. An outer thread groove vacuum pump part 3a formed outside the cylindrical part 4a and an inner thread groove vacuum pump part 3b formed inside the cylindrical part 4a.

  In this embodiment, the thread groove of the outer thread groove vacuum pump part 3a is carved on the outer peripheral surface of the cylindrical part 4a of the rotor 4, and the thread groove of the inner thread groove vacuum pump part 3b is the inner stator. It is engraved on the outer peripheral surface of 3b1.

  A gap (gap) 3a2 is provided between the inner peripheral surface of the outer stator 3a1 and the outer peripheral surface of the cylindrical portion 4a of the rotor 4, and the outer peripheral surface of the inner stator 3b1 and the rotor 4 A gap (gap) 3b2 is provided between the inner peripheral surface of the cylindrical portion 4a. These gaps 3a2 and 3b2 are assumed to be safe sized gaps in consideration of differences in thermal expansion based on the maximum temperature difference between the outer stator 3a1 and the rotor 4 and / or the maximum temperature difference between the inner stator 3b1 and the rotor 4. Designed to be

  Since the outer stator 3a1 and the inner stator 3b1 are integrally connected to each other, the stators 3a1, 3b1 always have substantially the same temperature.

  A heating means (heater) 5 is provided on the outer peripheral portion of the outer stator 3a1 so as to surround the outer stator 3a1, and the amount of heat generated by the heating means (heater) 5 is controlled by the control means 6 described later. It has become.

  FIG. 2 shows a block diagram of a control system by the control means 6.

  That is, the temperature detecting means 7 comprises a first temperature sensor 7a for detecting the temperature of the stator and a second temperature sensor 7b for detecting the temperature of the rotor. The first temperature sensor 7a comprises a heat sensitive part of a sheath thermocouple, The heat sensitive portion 7a is attached to the rear end portion of the inner stator 3b1. The second temperature sensor 7b comprises a radiation thermometer and is provided on the inner peripheral surface of the outer stator 3a facing the outer peripheral surface of the rotor, and measures the temperature of the rotor from the radiant heat of the rotor. The second temperature sensor 7b may not be provided for the reason described later.

  The heating means 5 comprises an electric heater and is installed so as to surround the outer peripheral portion of the outer stator 3a1.

  The control means 6 is a control device composed of a CPU. The control device 6 is provided outside the molecular pump 1, and the first and second temperature sensors 7a and 7b are provided on the input side of the control device 6. While being connected via an A / D converter 8a, the heater 5 was connected to the output side of the control device 6 via a D / A converter 8b.

  The control device 6 receives a signal from the temperature detecting means 7 during normal operation and performs normal PID control, and the heater 5 receiving the control signal heats the outer stator 3a1.

  Since the heat capacity of the rotor 4 is larger than the total heat capacity of the outer stator 3a1 and the inner stator 3b1, the temperature of the stators 3a1, 3b1 rises before the rotor 4 due to this heating.

  For this reason, the control device 6 uses the first temperature sensor 7a and the second temperature sensor 7b when the stator temperature becomes higher than a predetermined temperature by the first temperature sensor 7a. When the temperature difference is greater than or equal to the reverse temperature difference during steady operation, the heater control is switched so that the temperature increase gradient of the stator temperature is the same as the temperature increase gradient of the rotor temperature only for a fixed time.

  The control of the temperature rise gradient of the stator temperature will be described using the graph of FIG.

  FIG. 3 shows the experimental values of the temperature change of the rotor and the stator when the molecular pump is started from room temperature and the stator heating is started at the same time. The horizontal axis is time, and the vertical axis is temperature ° C.

  In FIG. 3, a solid curve ABC indicates a change in the stator temperature when the stator heating control is performed by the normal PID control, and this indicates an arc-shaped temperature rise curve. Further, a substantially straight solid curve G indicates a change in the rotor temperature.

  A solid curve DEF is an inverse temperature curve showing a change in an inverse temperature difference between the rotor temperature and the stator temperature.

  Thus, in normal PID control, the maximum value of the reverse temperature curve DEF becomes a reverse temperature difference of about 70 ° C. after 3 hours of startup.

  When the molecular pump is designed with this reverse temperature difference, the gap 3b2 between the inner stator 3b1 and the rotor 4 needs to have a considerably large value.

  On the other hand, in the stator temperature control method of the present invention, heating control is performed with a predetermined temperature gradient only within a fixed time after the start of operation.

  In the present embodiment, the stator heating control method is switched when the reverse temperature difference DEF reaches about 50 ° C. by normal PID control, and the stator is heated at a temperature gradient indicated by a broken line B ′ in FIG. I made it.

  That is, as shown in the graph of FIG. 3, when the inner stator temperature reaches 70 ° C., the reverse temperature difference becomes about 50 ° C. Therefore, PID control is executed immediately after the start of operation, and the inner stator temperature is detected by the first temperature sensor 7a. When it is detected that the temperature has reached 70 ° C., the control device 6 switches from the PID control by the output signal from the first temperature sensor 7a and raises the stator at a temperature gradient of 10 ° C./h shown by the broken line B ′ in FIG. When the inner stator temperature reaches the maximum temperature of steady operation, that is, 115 ° C. in FIG. 3, the control device 6 executes the PID control from the temperature rise of the stator at the temperature gradient by the output signal from the first temperature sensor 7a. Return. In this temperature control method, the second temperature sensor 7b is unnecessary.

  When the complex molecular pump 1 includes the first temperature sensor 7a and the second temperature sensor 7b, the rotor temperature G and the stator temperature C are simultaneously measured to calculate the reverse temperature difference E, and the operation is started. When the reverse temperature difference E is likely to exceed a predetermined value (50 ° C.) later, the control device 6 switches from PID control to raise the temperature of the stator at a temperature gradient of 10 ° C./h shown by the broken line B ′ in FIG. When the inner stator temperature reaches the steady value C, the original PID control is restored.

  As described above, when the rotor temperature is measured together with the stator temperature, an improvement in control accuracy by the control device 6 is expected.

  In this embodiment, the temperature gradient is about 10 ° C. per hour, which is substantially the same as the temperature increase gradient of the rotor temperature curve G. When the temperature rise of the stator is controlled to have a predetermined temperature gradient for a certain period of time as described above, the reverse temperature difference therebetween is kept substantially constant at 55 ° C. as indicated by a broken line E ′ in FIG.

  By reducing the maximum reverse temperature difference between the rotor and the stator when the molecular pump is started, the gap 3b2 can be set small when designing the molecular pump. This leads to an improvement in the performance of the molecular pump.

  A second embodiment of the present invention will be described with reference to FIG.

  FIG. 4 shows experimental values of temperature changes of the rotor and the stator when the molecular pump is started from room temperature and the stator heating is started at the same time.

  In this embodiment, in the control means 6 substantially the same as in the first embodiment, the control method of the stator heating is switched when the reverse temperature difference DEF becomes about 37 ° C. by the heating by the normal PID control. The stator is heated at a temperature gradient indicated by a broken line B ′ in FIG.

  In this embodiment, this temperature gradient is set to 8 ° C. per hour, which is substantially the same as the temperature increase gradient of the rotor temperature curve G. Further, the reverse temperature difference at this time is as shown by a broken line E ′ in FIG. 4, eliminating the peak of the reverse temperature difference between the rotor and the stator that existed at the time of starting the molecular pump, and at most 40 ° C. occurring during steady operation The reverse temperature difference could be obtained.

  As a result, the gap between the rotor and the stator can be reduced, leading to improved performance of the molecular pump.

  Note that the temperature rise of the rotor 4 at the time of starting the molecular pump linearly changes at a substantially constant rate as indicated by the rotor temperature curve G in FIGS. Therefore, since the temperature of the rotor 4 can be estimated from the time after startup, the temperature sensor 7b of the rotor 4 may be omitted, and the heater control may be performed using only the detected value of the stator temperature sensor 7a. .

  The temperature control device for the molecular pump of the present invention is used for a complex molecular pump used for exhausting an etching device or a CVD device.

It is a longitudinal cross-sectional view of the complex molecular pump of Example 1 of this invention. It is a block diagram of a control system. 6 is a graph for explaining a temperature change in the control of the first embodiment. It is a graph explaining the temperature change in control of Example 2. FIG. It is a partial longitudinal cross-sectional view of an example of the conventional complex molecular pump.

Explanation of symbols

1 Molecular pump (complex molecular pump)
3 thread groove vacuum pump 3a1 outer stator 3b1 inner stator 4 rotor 5 heating means (heater)
6 Control means (control device)
7a, 7b Temperature detection means (temperature sensor)

Claims (4)

A cylindrical rotor is interposed in a cylindrical gap formed between opposing surfaces of the outer stator and the inner stator that are connected to each other, and a screw is provided on one of the opposing surfaces of the rotor and the stator. In a molecular pump having a thread groove vacuum pump section in which grooves are formed, a temperature detecting means for detecting the stator temperature, a heating means for heating the stator, and a detection signal from the temperature detecting means are inputted to the stator. a control signal for controlling the set temperature and a control means for outputting to said heating means, said control means said stator only within a predetermined time when the start of operation after the stator temperature of the pump is equal to or higher than a predetermined temperature temperature control of molecular pump temperature is characterized in that the heating control said stator to rise at a predetermined temperature gradient. The temperature control device for a molecular pump according to claim 1, wherein the predetermined temperature gradient of the stator temperature is substantially the same as the temperature increase gradient of the rotor temperature . 2. The molecular pump according to claim 1, wherein the heating of the stator with a predetermined temperature increase gradient is a control in which a part of the arc-shaped temperature increase curve by normal PID control is replaced with a straight line having a gradient. Temperature control device. The temperature increase gradient of the stator temperature, a temperature control device according to claim 1 or claim 2, characterized in that the hour 8 ° C. or per hour 10 ° C..

Images