JP3656532B2 - Temperature control circuit of turbo molecular pump - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a turbo molecular pump, and more particularly to a temperature control circuit for a turbo molecular pump that prevents reaction products from adhering inside a turbo molecular pump used as an exhaust system in a semiconductor manufacturing apparatus or the like.
[0002]
[Prior art]
There is a turbo molecular pump as a vacuum pump for transporting gas by mechanically imparting momentum in a certain direction to gas molecules with a rotary blade or the like. The turbo molecular pump has the same shape as a rotor blade that has a slit cut diagonally in a disk under conditions of low pressure that allows collisions between gas molecules to be ignored, and the tilt of the slit is opposite to that of the rotor blade. The stationary blades are alternately arranged, and the rotor blades are driven at an extremely high rotational speed, allowing gas molecules to pass through the gap between the blades and being evacuated to obtain an ultra-high vacuum. It is. In the vacuum pumping system of the turbo molecular pump, an oil rotary pump, a dry vacuum pump or the like is used as a back pressure pump.
FIG. 3 shows a cross section of a turbo molecular pump equipped with a magnetic bearing device. In the turbo molecular pump, the drive shaft 13 is provided with a touch-down bearing 19a on the upper side and a touch-down bearing 19b on the lower side, is provided with a magnetic levitation mechanism, and is rotated at a high speed by the high-frequency motor 11. A rotor blade 14 is provided on the rotating body, and a stator blade 15 stacked with a spacer 16 is provided on the housing side opposite to the rotor blade 14. When the rotor blade 14 rotates at a high speed, gas is supplied from the intake port of the intake port flange 21. The gas is sucked through the protective net 23 and discharged from the exhaust port flange 22 at the lower part of the housing, and is mounted on the caster 12.
Since the rotor blade 14 rotates at high speed, magnetic levitation control is performed to support the rotating body of the drive shaft 13 in a non-contact manner. A thrust magnetic bearing 18 is provided as a set of axial direction control electromagnets for controlling the position in the direction of the drive shaft 13, and two sets of position control in the directions of two axes orthogonal to each other at two points of the drive shaft 13 are provided. As the radial direction control electromagnet, a radial magnetic bearing 17a is provided at the upper portion and a radial magnetic bearing 17b is provided at the lower portion. As a displacement detection sensor for the drive shaft 13, a gap sensor 20 is provided at the bottom as an axial direction detection sensor, and a gap sensor 20a is provided at an upper portion and a gap sensor 20b is provided below as a radial direction detection sensor. Then, feedback control for magnetic levitation is performed. The turbo molecular pump is composed of a pump body and a power supply device, and is connected to, for example, a process chamber of a semiconductor manufacturing apparatus and used for exhausting process gas in a film forming process. And, vacuum devices incorporating a turbo molecular pump are not only vacuumed, but there are many devices that introduce and react various gases after being vacuumed. In apparatuses such as low pressure CVD, plasma CVD, plasma etching, reactive ion etching, and ion implantation, flammable, explosive, toxic, corrosive, and odorous gases are used, which is extremely dangerous. In particular, countermeasures against these gases are taken in various devices for manufacturing semiconductors. The active gas corrodes various materials used in the equipment (vacuum containers, gaskets, pump oil, etc.), and various ions and scattered electrons generated during the reaction are absorbed or reflected by various parts of the equipment. Or charged.
Therefore, a band heater 25 and a sheathed heater 24 are provided on the outer periphery of the casing so that reaction products in the exhaust gas do not adhere to these components and the casing. And is controlled by the temperature control circuit of the power supply device. Further, when it is desired to lower the temperature, the cooling water pipe 26 can be used for cooling.
[0003]
FIG. 4 shows a block diagram of a temperature control circuit in the power supply device. Depending on the film forming process, the reaction product may adhere to the inside of the pump, and the base portion of the pump is heated by the heater 1 to prevent the reaction product from adhering.
The temperature control circuit includes a temperature detection means 2 having a temperature detector 27 provided inside the pump body, a switching element 9 for switching and heating the heater 1, and a difference between the target temperature 8 and the pump temperature by the temperature detection means 2. The energizing time calculation means 6 calculates the on-time of the heater 1 per unit time, and the heater control means 5 turns the switching element 9 on and off based on the result.
FIG. 5 shows the relationship between the temperature rise time and the pump temperature, FIG. 6 shows the relationship between the temperature difference from the target temperature and the energization time of the heater 1 within the heater control unit time, and FIG. 7 shows the elapsed time at 180 V and 264 V drive. The relationship of heater temperature is shown.
Here, the control unit time of the temperature control is set to 2.5 seconds. During the temperature increase, the heater 1 is energized 100% during the control unit time. Then, as shown in FIG. 5, once the temperature is raised to near the target temperature, the heater 1 is turned on for a time commensurate with the difference from the target temperature in order to maintain the temperature thereafter. For example, if the temperature difference is 1 ° C., as shown in FIG. 6, it is energized for 1.25 seconds, which is 50% of the control unit time of the heater 1, and the current waveform in (3) shown in FIG. Controlled. If the temperature difference is 0.4 ° C., power is supplied for 0.5 seconds, which is 20% of the heater control unit time.
[0004]
[Problems to be solved by the invention]
The temperature control circuit of the conventional turbo molecular pump is configured as described above, but the resistance value of the heater 1 consumes enough power to raise the pump sufficiently to the target temperature in a certain time (for example, 1 hour). Designed to generate heat. That is, when the power supply voltage specification of the power supply device is 180 to 264V, the resistance value is designed to sufficiently raise the temperature at 180V.
However, if the heater 1 designed so that a current sufficient for temperature rise flows at a power supply voltage of 180 V is used at a power supply voltage of 264 V, the current that flows when the heater 1 is turned on is 264/180 = 1.47 times that consumed by the heater. (264/180) ² = 2.15 times in terms of the power to be used.
If it is used as it is, the temperature raising time will be shortened accordingly, but in the state of 100% energization during the temperature raising, there is a problem that the heater becomes overheated and the life is shortened.
Therefore, conventionally, there has been a problem that a transformer must be used to make the supply voltage constant, or a heater having a plurality of specifications must be prepared in accordance with the power supply voltage.
[0005]
The present invention has been made in view of such circumstances, and a turbo molecule that can be heated in an appropriate temperature rise state of a heater provided in a pump body even for specifications of different power supply voltages. An object of the present invention is to provide a temperature control circuit for a pump.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a temperature control circuit for a turbo molecular pump according to the present invention comprises a turbo molecular pump in which rotating blades and fixed blades are alternately arranged and driven at a high rotational speed under low pressure conditions to exhaust gas molecules. And a heater for controlling the temperature by supplying a current so that the reaction product does not adhere to the inside, a temperature detecting means for the heater, and a circuit for controlling the heater on / off from the difference between the target temperature and the pump temperature by the temperature detecting means. In the temperature control circuit of the turbo molecular pump, the heater current detection means and the heater current value square integration means are provided, and during the heater ON, the integration value from the current value square integration means, When the limit value of the square of the current value is compared and the limit value is exceeded during the unit time, the power supply to the heater is stopped for the remaining time of the unit time.
[0007]
The temperature control circuit of the turbo molecular pump of the present invention is configured as described above, and includes a current detection means for detecting the heater current, and a heater current value that integrates the heater current squared (proportional to power) while the heater is energized. Square heater, and the heater control means has a square value of the heater current square (the square of the current value) even if the heater control means is within the energization time range determined by the temperature difference from the target temperature. If the limit value) is exceeded, the remaining time within the heater control unit time has a function of turning off the heater.
For this reason, since the power supplied to the heater per unit time is constant, overheating of the heater can be prevented even when a heater designed for a power supply voltage of 180 V is used at a power supply voltage of 264 V, for example. Therefore, a single heater can cope with a plurality of power supply voltage specifications.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of a temperature control circuit for a turbo molecular pump according to the present invention will be described with reference to FIG. FIG. 1 is a block diagram of a temperature control circuit of a turbo molecular pump according to the present invention. The temperature control circuit of the turbo molecular pump includes a heater 1 that controls the temperature so that reaction products do not adhere to the inside of the pump, a temperature detection means 2 that includes a temperature detector 27 that detects the internal temperature, The on-time of the heater 1 per unit time is calculated from the current detection means 3 for detecting the flowing current, the summing means 4 for the square of the current value of the heater 1, and the difference in pump temperature between the target temperature 8 and the temperature detection means 2. The energization time calculation means 6 to perform, the indicated value from the energization time calculation means 6, the integrated value from the square of the current value of the heater 1 and the limit value 7 of the square of the current value are compared, and the result The heater control means 5 for turning on and off the switching element 9 based on the above, and the switching element 9 for turning on and off the current flowing through the heater 1 by the heater control means 5.
The turbo molecular pump temperature control circuit includes a current detection means 3 for detecting a current flowing in the heater 1 in a conventional temperature control circuit, and a current value square integration means 4 having a circuit for squaring and integrating the current value. The limit value 7 of the square of the current value is added. As a result, when a current flows through the heater 1, the integrated value from the integrating means 4 of the square of the current value (proportional to power) is compared with the limit value 7 of the square of the current value (proportional to power). When the limit value 7 of the square of the current value (proportional to power) is exceeded during the unit time, the switching element 9 is turned off from the heater control means 5 and the power supply to the heater 1 is stopped for the remaining unit time. To do.
[0009]
Next, the heater 1 whose design values of the power supply voltage and the power value are 180 V and 400 W will be described with a digital circuit using a microcomputer. The resistance value of the 180V, 400W heater 1 is 81Ω, and the current value when the heater 1 is used at 180V is 2.22A. Therefore, if the current value of the heater 1 is 2.22A, it is designed so that there is no problem in its life even if it is continuously energized. If the current does not flow 2.22A, the temperature of the pump cannot be raised within a specified time. . Accordingly, the limit value 7 of the square of the current value is set so that the heater 1 can be turned on at the power supply voltage of 180 V during the heater control unit time. Here, when the heater control unit time is 2.5 seconds and the calculation of the square of the current value is performed 50 times every 50 ms (= 2.5 s), the limit value 7 of the square of the current value is 2.22 × 2 .22 × 50 = 246.4.
And the case where the temperature control of a pump is performed with the power supply voltage 180V is demonstrated. When the temperature rise is started from the room temperature state, the energization time calculation means 6 determines the heater control unit time of 100 with respect to the heater control means 5 from the temperature difference between the pump temperature from the temperature detection means 2 and the target temperature 8. % (= 2.5 s) energization is instructed. Then, the heater control unit 5 turns on the heater 1 and monitors the integrated value of the square unit of the current value calculated every 50 ms.
FIG. 2A shows time on the horizontal axis, the integrated value of the square of the current value of the heater 1 on the vertical axis, and the heater current on the vertical axis. When the power supply voltage is 180 V, the integrated value of the square of the current value within 2.5 s naturally does not reach the limit value 7 (= 246.4) of the square of the current value, so as shown in (b) In addition, the pump continues to heat up with 100% energization (2.22 A). At this time, the power consumed by the heater for 2.5 s is 2.22 A × 180 V × 2.5 s = 1000 W · s.
When the difference from the target temperature 8 is within 2 ° C., the indicated value from the energizing time calculating means 6 is sequentially reduced from 100% along the straight line shown in FIG. 6, so that the heater control means 5 follows the heater control unit accordingly. Of the time (2.5 s), the time for turning on is sequentially reduced.
Next, consider the case where the heater 1 is used at a power supply voltage of 264V. As in the case of 180 V, when the temperature rise is started from a room temperature state, the energization time calculation means 6 instructs the heater control means 5 to energize 100% (= 2.5%) of the heater control unit time. . The heater control unit 5 turns on the heater 1 and monitors the integrated value of the square unit of the current value calculated every 50 ms.
When the power supply voltage is 264 V, the current that flows when the heater is on is 264 V / 81Ω = 3.26 A, and the integrated value of the square of the current value is 246.4 / (3.26 × 3.26) = 23. 2, and after the 24th 1.2 s, as shown in (a), the limit value 7 (246.4) of the square of the current value is exceeded. When the integrated value of the square of the current value exceeds the limit value 7 of the square of the current, the heater control means 5 is as shown in (b) even within the range of the energization time designated by the energization time calculation means 6. In addition, the heater current flowing through the heater 1 is turned off so that no more power is supplied to the heater 1.
When the next heater control unit time is started, as shown in (b), the heater control means 5 turns on the heater 1 again and repeats the above operation. At this time, the power consumed by the heater 1 during 2.5 s is 3.26 A × 264 V × 1.2 s = 1033 W · s, which is almost the same as 1000 W · s when the power supply voltage is 180 V.
When the difference from the target temperature 8 is within 2 ° C., the instruction value from the energization time calculation means 6 is sequentially reduced from 100% by the determination of the energization time of the temperature control method of FIG. When the time is 1.2 s or more, the limit value 7 of the square of the current value is effective, and the heater 1 is not turned on for a longer time. When the indicated value from the energization time calculation means 6 becomes 1.2 s or less, the heater control means 5 turns on the heater 1 for the first time as instructed by the energization time calculation means 6. Thereby, even when it is used at a power supply voltage of 264 V, it is possible to prevent the heater from being overheated.
[0010]
In the above-described embodiment, the case where a digital circuit is used has been described. However, a similar function can be implemented even with a configuration using an analog circuit.
[0011]
【The invention's effect】
The temperature control circuit of the turbo molecular pump of the present invention is configured as described above, and includes a circuit that detects the current of the heater that heats the pump and integrates the detected heater current by squaring (proportional to power). Even if it is within the range of the energization time determined by the temperature difference between the temperature detection value in the pump and the target temperature, the square value of the heater current exceeds the specified value (the limit value of the square of the current value). The remaining time within the heater control unit time has a function to turn off the heater, so that the power supplied to the heater per unit time is constant, and the heater can be prevented from being overheated.
Therefore, one type of heater can correspond to a plurality of power supply voltages without deteriorating the life of the heater. Further, it is not necessary to prepare various heaters and a voltage conversion transformer is not necessary.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a temperature control circuit of a turbo molecular pump according to the present invention.
FIG. 2 is a diagram showing a relationship of heater control currents in a temperature control circuit of a turbo molecular pump according to the present invention.
FIG. 3 is a view showing a cross-sectional structure of a turbo molecular pump.
FIG. 4 is a diagram showing a temperature control circuit of a conventional turbo molecular pump.
FIG. 5 is a diagram showing a temperature rise state of a conventional turbo molecular pump.
FIG. 6 is a diagram showing a temperature control method of a conventional turbo molecular pump.
FIG. 7 is a diagram showing a state of energization at each temperature increase of a conventional turbo molecular pump.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Heater 2 ... Temperature detection means 3 ... Current detection means 4 ... Current value square integration means 5 ... Heater control means 6 ... Energizing time calculation means 7 ... Current value square limit value 8 ... Target temperature 9 ... Switching element

Claims (1)

Temperature is controlled by supplying current to the turbo molecular pump that alternately arranges rotating blades and stationary blades and exhausts gas molecules driven at a high rotational speed under low pressure conditions so that reaction products do not adhere inside. In a temperature control circuit of a turbo molecular pump having a heater, a temperature detection means thereof, and a circuit for performing on / off control of the heater from a difference between a target temperature and a pump temperature by the temperature detection means, a current detection means for the heater current, and the heater The current value squared integration means is provided, and when the heater is ON, the integrated value from the current value square integration means is compared with the square limit value of the current value, and the limit value is determined during unit time. A temperature control circuit for a turbo molecular pump, wherein when it exceeds, the power supply to the heater is stopped for the remaining unit time.

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