JPH0267472A - Pressure control method for vacuum equipment - Google Patents

Abstract

PURPOSE:To make an evacuation system of a vacuum equipment into simplification and inexpensiveness as well as to secure the aimed state in a short time by directly controlling the rotating speed of a vacuum pump such as a wide range turbo-molecular pump or the like in the vacuum equipment, and performing this control in dividing it into plural numbers of stages as specified. CONSTITUTION:In a vacuum vessel 1, reaction gas or the like is made to flow in the inner part as much as constant flow via each of flow regulating valves 2, 3 after the inside is evacuated up to a high vacuum by a wide range turbo- molecular pump 5 and gas of water vapor or the like to be contained in the atmosphere is evacuated. Then, a revolution controller 6 inputs a pressure signal out of a pressure detector 4, a signal related to a revolution state of the wide range turbo-molecular pump 5 and another signal related to a flow rate out of flow detectors 2a, 3a, and it feeds a revolution control signal to the wide range turbo-molecular pump 5. In this case, the pump 5 is rotated at the specified revolution and, after being lowered to the desired revolution, revolution of the pump 5 is controlled based on pressure in the vacuum vessel 1.

Description

[Detailed Description of the Invention] [Industrial Application Field] [Prior Art] In conventional semiconductor manufacturing equipment, a semiconductor gas introduction pipe is provided with a supply gas flow rate control valve, and a supply gas flow rate control valve is provided between a vacuum vessel and a wide area turbomolecular pump. A pressure regulating valve inside the vacuum container is provided in G). In the supply gas flow control valve, the gas flow rate of the semiconductor gas introduction pipe is measured using a hot wire flowmeter, etc., and the valve opening degree is highly precisely feedback controlled based on this measurement data.
In the vacuum vessel internal pressure regulating valve, the valve opening degree is feedback-controlled based on a pressure signal obtained from a high-precision diaphragm vacuum gauge or the like attached to the vacuum vessel. This makes it possible to maintain the 8 liter amount of semiconductor gas and the pressure inside the vacuum container at desired values, and to form a uniform all in this state.

[Problems to be Solved by the Invention] In conventional exhaust system equipment for semiconductor manufacturing equipment, in order to accurately set the degree of vacuum in the vacuum container to a desired value, a stepping motor or the like is installed in the vacuum container pressure control valve. An expensive variable pressure regulating valve with high resolution was required. In addition, in the manufacturing process of semiconductor manufacturing equipment, after the wafer is loaded into the vacuum container, a wide area turbo molecular pump is used to pump the inside of the vacuum container for 10-10 minutes.
A high vacuum state of about 4 to 10-6 Torr is created, and then a semiconductor gas is passed through this state at a steady flow rate, and the variable pressure control valve is feedback-controlled to maintain the pressure state at about 10" Torr. Therefore, the pressure at the initial stage of operation is The problem is that it takes a long time for the pressure inside the vacuum vessel to be maintained at a constant level because there is a large difference between there were.

In view of the above-mentioned problems, an object of the present invention is to simplify and reduce the cost of the exhaust system by eliminating the need for a variable pressure control valve that has been used in conventional exhaust systems such as semiconductor manufacturing equipment. It is an object of the present invention to provide a pressure control method for a vacuum device that shortens the time required for transition to a state.

[Means for Solving the Problems 1] In the pressure control method for a vacuum device of the present invention, the pressure in the vacuum container is determined, and when a predetermined fluid flow rate is supplied into the vacuum container in a steady state, the pressure in the vacuum container is determined. In a vacuum device that includes a vacuum pump that maintains a predetermined vacuum state, the vacuum pump is rotated at a predetermined rotation speed to create a higher vacuum state than in the steady state, and then the rotation speed of the vacuum pump is reduced to the target rotation speed. The pressure inside the vacuum container is brought close to the steady state, and then the rotational speed of the vacuum pump is controlled based on the pressure inside the vacuum container.

[Example] Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of a vacuum apparatus for semiconductor manufacturing 8i. 1 is a vacuum container in which a semiconductor substrate is housed; 2.3
2 are flow rate control valves attached to the gas introduction pipes, respectively.
3a and 3a are flow rate detectors, and 4 is a pressure detector such as a diaphragm vacuum gauge for detecting the pressure inside the vacuum container 1. 5 is a wide-area turbo-molecular pump including an induction motor therein, and 6 is a rotation speed control device for the wide-area turbo-molecular pump 5. The rotational speed control device 6 inputs the pressure signal from the pressure detector 4, the signal related to the rotational speed state of the wide-area turbomolecular pump 5, and the signal related to the flow rate from the flow rate detectors 2a and 3a, and controls the wide-area turbomolecular pump 5. A rotation speed control signal is supplied to the

Further, 7 is an oil rotary pump, 8, 9, 10 is a pneumatic operation valve, and 11 is an exhaust pipe.

An example of the detailed structure of the wide-area turbomolecular pump 5 is shown in the second example.
This will be explained based on FIG. 3, FIG. 4, and FIG.

The rotating body 101 disposed inside includes a rotor blade group 101a arranged in multiple stages in the upper part, and a rotating body 101 in the lower part.
1, and several threaded grooves 101b formed on the outer periphery of the threaded groove 101b. The rotating bodies 101 are adjacent to each other! A pumping action is produced by rotating at high speed without contacting the stator vane group 102 arranged between the stator blades 102 and the cylindrical stator 103 facing the threaded groove portion 101b. FIG. 3 shows a front view of the moving blade and stationary blade, and FIG. 4 shows a front view of the threaded groove portion 101b formed on the outer periphery of the rotating body 101. In the illustrated embodiment, the bearings include two sets of upper and lower radial magnetic bearings 104a, 104b and one set of thrust magnetic bearings 105, and the rotating means is a squirrel cage three-phase induction of a general outer rotor type. A motor 106 is used. With this configuration, the rotating body 101 completely floats at each magnetic bearing, and the rotor blade group 101a is in complete contact with the stator blade group 102, and the threaded groove portion 101b is in complete contact with the stator 103 and the upper and lower auxiliary bearings 107, 108, etc. This enables high-speed rotation. Further, in the figure, 109 and 110 are non-contact displacement sensors that constantly measure the behavior of the rotating body 101, and 111 is a rotation speed sensor that measures the rotational speed of the rotating body 1o1 in a non-contact state. When the rotating body 101 is rotating in a floating state, the output of the non-contact displacement sensor changes the voltage and current applied to the magnetic bearing, and the output of the rotational speed sensor changes the voltage applied to the induction motor 106. controlled.

Here, the pumping operations of the wide-area turbomolecular pump 5 and the oil rotary pump 7 shown in FIG. 1 will be explained in relation to the internal pressure control of the vacuum vessel 1. A vacuum container 1 for semiconductor manufacturing is once drawn to a high vacuum by a wide-area turbo molecular pump 5 to exhaust gases such as water vapor contained in the atmosphere, and then a flow rate of 1.1 m is controlled by a valve 2.3. By continuing to flow a constant flow of reaction gas, etc. into the vacuum vessel 1 through The reaction gas flow rate and the pressure inside the vacuum vessel are maintained constant. In this state, a thin film is formed on the wafer etc. carried into the vacuum container. The above operation by the pump 5 is as follows:
This process is performed every time a thin film is formed on a wafer or the like. In connection with the above operation, the wide area turbo molecular pump 5 provided on the vacuum vessel 1 side and the oil rotary pump 7 provided at the next stage are used as follows. In the wide area turbo molecular pump 5, the yellow part on the side of the vacuum vessel 1 exhibits its performance at an inlet side pressure of about 1 Q -2 Pa or less, and has a speed of several 101/sec to several 10
It has an evacuation speed of 0.001/sec and performs gas evacuation from the vacuum container before semiconductor production. In addition, wide area turbo molecular pump 5
The thread groove on the exhaust side of
Demonstrates performance at around Pa, from several 105 CCH to several 1000
It has an exhaust flow rate of SCCH and performs the function of exhausting reaction gas, etc. during semiconductor manufacturing. Further, the oil rotary pump 7 is a roughing pump that pulls the vacuum container 1 to a low vacuum to a pressure that allows the wide area turbo molecular pump 5 etc. to exert an evacuation effect.
Demonstrates performance above grade a. The performance of these pumps 5.7 is shown in FIG. The solid line shows the pumping performance of the wide-area turbomolecular pump 5, the broken line shows the pumping performance of the turbomolecular pump without a threaded groove, and the dashed line shows the pumping performance of the oil rotary pump 7. As can be seen from this figure, the wide range turbomolecular pump 5 used in this example has a pressure of 1O-2Pa to 1
At about 0.02 Pa, it can flow a larger flow rate than conventional turbomolecular pumps. The test results shown in FIG. 5 show the performance of a composite molecular pump and a turbo molecular pump having a pumping speed of 10001/S, and an oil rotary pump having a pumping speed of 240 m3/hr.

Therefore, the vacuum container 1 is first pumped by the oil rotary pump 7.
It is roughly drawn to a low vacuum state of about 2 Pa, and then, as mentioned above, it is drawn to a high vacuum state by the wide area turbo molecular pump 5 to exhaust gas before semiconductor manufacturing, and then to the set pressure for semiconductor manufacturing. The internal pressure is adjusted so that However, in controlling the pressure inside the vacuum container 1 to the above-mentioned set pressure, the rotation speed of the wide-area turbomolecular pump 5 is further controlled in two stages, as will be described later.

Next, a specific circuit configuration of the rotational speed control device 16 that controls the rotational speed of the wide-area turbomolecular pump 5 that adjusts the pressure inside the vacuum vessel 1 as described above will be explained based on FIG. 6.

In Fig. 6, 6 indicated by the dotted chain line is the rotational speed control 1 mentioned above.
It is set at 1'VA. The rotation speed control device l16 includes a control calculation circuit 201, a voltage control circuit 202, a brake control circuit 203, a motor drive circuit 204, and a rotation speed detection circuit 20.
It consists of 5. The control calculation circuit 201 includes a signal related to the pressure in the vacuum container from the pressure detector 4, a signal related to the rotational speed detected in the rotational speed detection circuit 205 based on the output signal of the above-mentioned rotational speed sensor, and the amount of iil. Signals related to the gas flow rate from the flow rate detectors 2a and 3a of the control valve 2.3 are respectively input. The control calculation circuit 201 refers to the data provided by these input signals and outputs an instruction value for controlling the rotational speed of the wide area turbomolecular pump 5 to change in a predetermined state as described later. The voltage control circuit 202 is the control calculation circuit 201
The brake control circuit 203 converts the instruction value for determining the rotational speed given from the control calculation circuit 201 into a corresponding voltage signal, and the brake control circuit 203 converts the instruction value for reducing the rotational speed given from the control calculation circuit 201 into a voltage signal. Each output signal of the voltage control circuit 202 and the brake control circuit 203 is sent to the motor drive circuit 204.
The voltage level is then converted to a voltage level that can drive the induction motor in the wide-area turbomolecular pump 5. Note that the output signal of the voltage control circuit 202 is fed back to the control calculation circuit 201, whereby the rotational speed of the wide-area turbomolecular pump 5 is controlled to accurately and quickly reach the target value.

The principle of the method of controlling the rotational speed of the wide area turbomolecular pump 5 using the rotational speed side W device 6 will be explained next.

The rotation speed is controlled by a primary voltage control method using a thyristor. When controlling the rotation speed by feeding back the pressure inside the vacuum vessel 1 via the pressure detector 4, the effective value V of the voltage applied to the primary circuit of the induction motor is basically (where P; Vacuum vessel internal pressure, C
−03; constant). If controlled in this way, the relationship shown in FIG. 7 exists between the rotational speed of the wide-area turbomolecular pump 5 and the exhaust flow rate, so that the pressure inside the vacuum container can be stabilized.

However, in the control method using the formula (2), it takes time to shift the pressure inside the vacuum container 1 to the set state. Therefore, in the present invention, in order to shorten the time required to stabilize the set state, the voltage applied to the motor drive circuit 204 of the induction motor is controlled in two stages. That is, when the pressure inside the vacuum container 1 is transferred from a high vacuum state to a set state, in a state where the difference between the pressure inside the vacuum container and the set pressure is large, the volume of the vacuum container 1 is changed as a first step. A target rotational speed is calculated based on the signal related to the gas flow rate from the flow ffi control valve 2.3 attached to the gas introduction pipe and the exhaust performance of the wide area turbomolecular pump 5, and the induction motor is subjected to direct current braking or Regenerative braking is applied to bring the target rotational speed into a state of reaching or approaching the target rotational speed, and then, as a second step, the rotational speed is controlled by feeding back the pressure inside the vacuum container. Theoretical controllability in this case will be described next.

The pressure inside the vacuum container 1 during semiconductor manufacturing is 10-1 to 102
Since the vacuum state is less than Torr and the pumping speed is several hundred to several tens of thousand CCH, the torque required for the compression work of the pump depends on the area and gap between the rotating part and the stationary part of the pump, and the viscosity of the compressed gas fluid. , is small compared to the torque required for friction loss determined by the rotational speed, and is about 1/107th. Therefore, if we find the equation of state for the torque of the rotating body while the pump is rotating, we can ignore the torque required for the compression work of the pump mentioned above, so Jθ=T −T −■ R However, the moment of inertia of the rotating body θ; rotation Angular acceleration ■, ; Output torque of the motor TR; Friction loss torque of the rotating body Here, for a three-phase motor, the torque equation is 4πr 3 and the relationship is as follows. From both equations, the torque of the induction motor and the motor drive circuit can be calculated. The relationship with the applied voltage is expressed as:

' However, N: Number of motor poles f; Rotation frequency I: Current flowing per one coil on the primary side r1; Primary resistance r2; Secondary resistance converted to the primary side ■; Voltage applied to the primary side Effective value of If is small, then
0 type further includes K2. 3: Represented by a constant, ■ becomes 10 from the formula ■■. However, K1. A and B are constants.

On the other hand, for the load torque, only the friction loss due to gas (■8) can be considered, so μ; δ: S' R.

θ; Gas viscosity coefficient Gap between the rotating body and the opposing stationary wall: Distance from the rotation center of the rotating body surface area that causes friction loss to the surface that causes friction*a loss is the angular velocity. Expressing these coefficients more simply, Jθ−K
It can be seen that V-K OK θ- becomes 3-■, and by controlling the primary voltage V of the motor, the rotational speed θ can always be stably maintained at 1lltll.

Also, the controllability regarding the pressure inside the vacuum vessel 1 mentioned above will be described. From the relationship of the equation of state of an ideal gas (in a vacuum, it is sufficiently diluted, it can be considered an ideal gas), the equation of state inside the vacuum container is: P: Pressure inside the vacuum container o: Volume inside the vacuum container Qi ;Gas suction volumetric flow rate Qo=gas exhaust volumetric flow rate 5m Rg: gas constant T: temperature inside the vacuum container. Furthermore, the exhaust 8 of the wide area turbo molecular pump 5!
There is a relationship between constant and intake pressure as shown in FIG. 8th
According to the figure, the exhaust flow rate is approximately 1O-1 TOrr ~ 1QT
For the intake pressure of orr, is almost constant and is considered to be a function only of the rotational speed in this range, so Q - can be set as 6θ 7 -■, , , : constant. Substituting the 0 expression into the [phase] expression and converting it into -8
− to 9θ to 8. The following relationship holds true: :Constant 1■. Transforming formula 0, θ−K 1o P + K 11 −◎θ−
Since 1oP - [phase] holds true, substituting these two equations into the 0 equation -JK1゜P
− to 4 V+ to 1° (K2+ to 5) P− (K2+ to 5)
3 to K11-, ', 4 to JK10P-- 1 to V- (, (5 to K2+)
) P+ (5 for K2+) 3 for K11+ is obtained. From now on, as before, the pressure P inside the vacuum vessel 1 can be controlled by feeding back the pressure P inside the vacuum vessel 1 and controlling the primary voltage V of the IS motor.

As described above, the pressure inside the vacuum container 1 is finally detected by the pressure detector 4, and the pump rotation speed is controlled only by the pressure signal output from the pressure detector 4. According to the rotational speed control method according to the present invention, not only can the pressure inside the vacuum vessel be kept constant, but also when there is a difference of, for example, 0.2 Torr or more between the pressure inside the vacuum vessel and the target pressure, 1
The rotational speed of the induction motor is immediately controlled to the target rotational speed calculated from the internal volume of the wide-area turbomolecular pump 5, the exhaust characteristics of the wide-area turbomolecular pump 5, the intake gas flow rate, the target pressure, etc., and then the pressure detector 4 outputs the By controlling the rotational speed of the induction motor using the pressure signal, the pressure inside the vacuum container can be quickly stabilized. FIG. 9 shows the convergence state of the pressure inside the vacuum container 1 when the pressure inside the vacuum container 1 is transferred from a high vacuum state to a steady state. In FIG. 9, the time when the semiconductor gas is introduced is set to 0 minutes, and the control is started 1 minute after the introduction.

Next, the operating state of the rotation speed control device 6 when the rotation speed control device 6 performs the above-mentioned rotation speed control method will be described based on FIG. 10. The induction motor of the wide-area turbomolecular pump 5 is controlled by the Vf inverter as described above, and its rotational speed is controlled by changing the applied voltage. Apply DC power supply voltage to the induction motor through a thyristor, control the pulses applied to the gate of the thyristor,
The ratio of the rest time to the conduction time of the thyristor tr /l.

The average voltage Vt applied to the induction motor by changing is expressed as n (V,; DC power supply voltage), and the rotational speed of the induction motor can be changed by voltage control. This drive circuit has been widely known. The rotational speed control device 6 controls the rotational speed detection circuit 205 during gas discharge from the vacuum container 1 before semiconductor manufacturing.
Control is performed using the voltage control circuit 202, and the wide-area turbomolecular pump 5 is rotated at the maximum rotational speed (for example, 2400 rpm) until the internal pressure reaches the set pressure. After the gas discharge from the vacuum container 1 is completed, the semiconductor gas continues to flow at a predetermined flow rate from the flow rate control valve 2.3, while the rotational speed i control device 6 controls the semiconductor gas flow rate, the volume of the vacuum container 1, and the wide area turbo molecular pump 5. A rotational speed detection circuit 20 is used to reduce the rotational speed of the wide-area turbomolecular motor 5 to the target rotational speed of the wide-area turbomolecular pump 5 determined by the exhaust performance.
5 and brake control circuit 203 to perform regenerative braking or reverse phase III operation.

After reaching the target rotation speed, the rotation speed control device 6 performs the control shown in FIG.
1L, the pressure inside the vacuum container 1 is kept constant at a predetermined value.

In addition, in the present invention, the induction motor is not only controlled in two stages, but also the rotational speed of the induction motor is controlled by the signal related to the internal pressure of the vacuum vessel 1 as soon as the gas discharge ends.
It is also possible to do so.

Furthermore, by implementing the control calculation circuit 201 with a microcomputer and providing a digital switch in the input section of the microcomputer, it is possible to input the volume of the vacuum container 1, the target rotation speed of the composite molecular pump, etc., thereby improving operability. Increase.

Further, in the above embodiments, an example using a wide area turbo molecular pump has been described, but the present invention can be similarly applied to a thread groove bottom molecular pump.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, by directly controlling the rotational speed of a vacuum pump such as a wide-area turbo molecular pump or a screw groove bottom molecular pump in a vacuum device, it is possible to achieve the advantages that are required in conventional devices. Since there is no need to use a variable pressure control valve, the exhaust system of the vacuum device can be simplified and lowered in cost, and the rotation speed of the vacuum pump can be controlled in multiple predetermined stages. Therefore, the desired state can be obtained in a short time in a vacuum apparatus, and the time required for the manufacturing process can be shortened, especially when applied to semiconductor manufacturing equipment or the like.

FIG. 9 is a characteristic diagram showing changes in the pressure inside the vacuum container, and FIG. 10 is a circuit diagram showing the operating state of the rotation speed control device.

4,

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of a vacuum device according to the present invention applied to semiconductor manufacturing equipment, Fig. 2 is a vertical cross-sectional view showing the detailed structure of a wide-area turbo molecular pump, and Fig. 3 is a wide-area turbo molecular pump. Figure 4 is a front view of the rotor blades and stationary blades of a molecular pump, Figure 4 is a front view of the thread groove of a wide-area turbo molecular pump, Figure 5 is a characteristic diagram showing the performance of various pumps, Figure 6 is a diagram of the rotation speed side m device. A circuit diagram showing the specific configuration. Figure 7 is a characteristic diagram showing the relationship between the rotational speed and exhaust flow rate of the wide-area turbo-molecular pump. Figure 8 is a characteristic diagram showing the relationship between the intake pressure and exhaust flow rate of the wide-area turbo-molecular pump. Figure, [Explanation of symbols] 1... Vacuum vessel 2.3... Gas flow rate control valves 2a, 3a... Flow rate detector 4... Pressure detection Device 5... Wide area turbo molecular pump 6... Rotation speed control device 7... Oil rotary pump

Claims (1)

[Claims] (1) In a vacuum device including a vacuum pump that determines the pressure inside the vacuum container and maintains the inside of the vacuum container in a predetermined vacuum state when a predetermined fluid flow rate is supplied into the vacuum container in a steady state, The vacuum pump is rotated at a predetermined rotational speed to create a vacuum state higher than that in the steady state, and then the rotational speed of the vacuum pump is reduced to a target rotational speed to bring the pressure in the vacuum container closer to the steady state. . A pressure control method for a vacuum device, comprising: thereafter controlling the rotational speed of the vacuum pump based on the pressure within the vacuum container.