JPH04238227A - Flow control device with piezoelectric valve - Google Patents

Abstract

PURPOSE:To improve the reproducibility, precision and response speed by opening or closing valves with pulse width-modulated signals. CONSTITUTION:Piezoelectric valves 5, 6 with piezoelectric elements generating mechanical distortion in response to the applied voltage control the flow. The pressure in a reaction container 1 is detected by a pressure gauge 2 and converted into the electric signal by a converter 3, and a pulse width modulation valve controller 4 controls the valves 5, 6 based on the difference between the detected pressure and the preset pressure. The flow is determined by the length of the period when the valves 5, 6 are opened, the nonlinear area of a piezoelectric element is not used, only completely opened/closed states are used, and the reproducibility, precision and sensitivity can be improved.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a technology for controlling flow rate using a piezo valve, and particularly when manufacturing thin film semiconductors using reactive gases (including ionized gases),
Or, when producing oxide superconductors using the MOCVD method or ozone, or when researching catalytic reactions or surface adsorption/desorption reactions, it is possible to quantitatively measure how many molecules of gas are introduced into the reaction vessel per second. The present invention relates to a control device suitable for controlling the flow rate of a very small amount of gas, which is desired to be measured and thereby to control the physical properties of the produced film.

0002

[Prior Art] Taking the example of gas flow rate control as a flow rate control, conventionally, a valve called a needle valve has been mainstream, and this is a thin, tapered needle valve that can be inserted into and removed from a small hole to block the small hole. In many cases, a widely used method is to control the flow rate by controlling the gap between the needle and the small hole by feeding back manually or using a step motor or the like so that the pressure remains constant. Further, a gas introduction system is also known in which a piezo element that generates distortion by applying a voltage is driven by a DC voltage, and the flow rate is controlled by adjusting the degree of opening of the small hole gap. Also,
Gas flow rate measurement technology involves bypassing part of the tube into a capillary tube, heating the capillary tube section with a heater, and determining the flow rate by measuring how much the temperature distribution in the capillary tube section changes depending on the gas flow rate. It has been known.

0003

[Problems to be Solved by the Invention] However, in the flow rate control method using a needle valve, the position of the handle that adjusts the gap between the needle and the small hole is only a guide, so the accuracy is low and delicate adjustment is impossible. There are problems in that it undergoes large changes over time and is also susceptible to mechanical vibrations. In addition, in devices that drive the piezo element with DC voltage to adjust the valve opening, the drive voltage has a threshold value (30V) due to the nonlinearity of the piezo element and the valve mechanism itself, and is not exactly proportional to the flow rate. However, there is a problem in that there is a history (hysteresis) in the relationship between flow rate and voltage. In addition, the maximum sensitivity of the flow measurement method using heater heating is 0.1 sccm (4.5 sccm).
×1016 molecules/sec), and since it takes time for the temperature distribution to become constant, the response speed is slow; even a fast one takes 0.5 seconds or more, and the sensitivity varies depending on the type of gas. Furthermore, in the production of semiconductor thin films, when supplying raw material gas from a cylinder to a vacuum device, conventionally relatively thick films of several μm or more are often produced, and precise measurement and control of the gas flow rate is not performed. In recent years, attempts have been made to grow thin films in units of one atomic layer and utilize the quantum effect of electrons, and there is a need for an apparatus that can accurately supply a small amount of gas.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a flow control device using a piezo valve that can significantly improve reproducibility, precision, sensitivity, and response speed. do.

[0005]

[Means for Solving the Problems] The present invention is a device for controlling a flow rate using a piezo valve using a piezo element that generates mechanical distortion according to an applied voltage, and the present invention provides a device for controlling a flow rate using a piezo valve that uses a piezo element that generates mechanical distortion according to an applied voltage. The piezo valve is characterized in that the piezo valve is controlled to open and close by means of a pulse width modulated signal. Further, the pulse width modulation means generates a modulation voltage so that the difference between the pressure inside the container and the set pressure value becomes zero when gas is supplied to the container from which fluid is continuously evacuated.
It is characterized by pulse width modulation, further includes a buffer tank, supplies gas from a gas supply source to the piezo valve via the buffer tank, further includes two buffer tanks, and has a differential pressure between the internal pressures of both buffer tanks. The present invention is characterized in that a means for measuring is provided, and gas is supplied to the piezo valve through one buffer tank.

[0006]

[Operation] The present invention pulse-width modulates the flow rate control signal to control the opening and closing of the piezo valve, determines the flow rate based on the length of time the piezo valve is open, and completely eliminates the use of the nonlinear region of the piezo element. By using only the open and closed states, reproducibility and accuracy are greatly improved, the maximum flow rate sensitivity is approximately 2.5 x 1013 molecules/sec, which is approximately 3 orders of magnitude higher than conventional models, and the response speed is also improved. It becomes possible to improve the time by about two orders of magnitude to several milliseconds, and in particular, it becomes possible to perform minute gas flow rate control to grow a thin film in units of one atomic layer.

[0007]

[Examples] Examples of the present invention will be described below. FIG. 1 is a diagram showing an embodiment of the flow rate control device of the present invention, FIG. 2 is a block diagram for explaining the configuration of the pulse width modulation valve controller in FIG. 1, and FIG. 3 is a diagram showing the structure of the piezo valve used in the present invention. A diagram showing an example, FIG. 4 is a diagram for explaining a pulse width modulated control signal. In the figure, 1 is a reaction container, 2
is a pressure gauge, 3 is a converter, 4 is a pulse width modulation valve controller, 5 and 6 are piezo valves (PV), 7 and 8 are buffer tanks, 9 and 10 are pressure gauges, 11 is a hydrogen gas cylinder, 12 is a helium gas cylinder, 13 is a methane gas cylinder, 14 is a rotary pump, 15-1 to 15-3 are pressure reducing valves, 16-1 to 16-10 are on-off valves, 20 is a differential amplifier, 21 is an integrator, 22 is a buffer amplifier, 23 is a A reference frequency oscillator, 24 a triangular wave generator, 25 a voltage comparator, 26 a pulse height adjuster, and 27 a high voltage amplifier.

In FIG. 1, a reaction vessel 1 for forming a thin film is supplied with clean gas such as hydrogen gas, helium gas, methane gas, etc. and raw material gas from cylinders 11 to 13 through pressure reducing valves 15-1 to 1.
5-3, through on-off valves 16-1 to 16-10, buffer tanks 7, 8, etc., it is supplied through piezo valves 5, 6, which will be described later, and is continuously exhausted. The system is evacuated by a rotary pump 14.

As shown in FIG. 3, the piezo valve is provided with an inlet communicating with the flow path L1 through an inlet mounting nut 34 in a housing 31, and an outlet 35, with an inlet and an outlet at the center of the housing 31. A flow path forming member 36 is provided perpendicularly to the center line connecting the outlet and the lower part thereof is covered with an adjustment housing 32, and the upper part of the housing 31 is covered with a cover 33. Channel forming member 36
is formed with a flow path L2 that is open at the upper end and a flow path L3 that communicates with the outflow port 35, and the vertical position is adjusted with an adjustment screw 38 against the force of a spring 37, and the upper end is connected to the piezo element 3.
A space S is provided below the piezo element 39, and the flow paths L1 and L2 communicate with each other through the space S. A piezo element 39 to which a voltage is applied through a wire 46 is pressed downward by a Teflon ball 45 attached to a preload spring fixed to a holding member 44 with a screw 42. Also,
A filter 49 pressed against an O-ring by a spring 50 is provided on the inlet side.

In the piezo valve 30 having such a structure, when a pulse width modulated voltage is applied through the wire 46 as described later, the piezo element 39 is displaced and the gap between the seat 41 and the upper end of the flow path forming member 36 is opens and closes, and when it opens, the upper end of the flow path L2 opens into the space S, and as a result, the inlet →
Filter 49 → flow path L1 → space S → flow path L2 → flow path L3
→A flow path is formed like the outlet 35 and gas flows therein, and if no voltage is applied, the seat 41 and the upper end of the flow path forming member 36 come into contact and the flow path L2 is closed and gas does not flow. In this way, the flow rate is controlled by turning ON/OFF the voltage application to the piezo element.

Control of such piezo valves 5 and 6 is as follows:
As shown in FIG. 1, the pressure inside the reaction vessel 1 detected by the pressure gauge 2 is converted into an electrical signal by the converter 3, and the pulse width modulation valve controller 4 converts the pressure into an electrical signal based on the difference between the detected pressure and the set pressure.

The controller 4 has a configuration as shown in FIG. That is, the difference signal between the detected pressure value and the set value is obtained by the differential amplifier 20, and this difference signal is sent to the integrator 2.
1, the buffer amplifier 22 converts the voltage level for modulation, and outputs it as an analog monitor for monitoring. On the other hand, the reference frequency oscillator (10
0 Hz) 23 is applied to the triangular wave generator 24, the triangular wave obtained by shaping and the output of the buffer amplifier are compared in the voltage comparator 25, and a pulse having a width corresponding to the magnitude of the output of the buffer amplifier is generated. is obtained and pulse width modulation is performed. Then, it is shaped to have a constant pulse height value by a pulse height adjuster 26, amplified, and applied to the piezo element.

[0013] In this way, the pressure inside the reaction vessel 1 is small;
When the differential pressure from the set value is large, the pulse width shown in Figure 4(a) becomes wider as shown in Figure 4(b), the time the piezo valve is open becomes longer, and the flow rate increases. do. As a result, the supply flow rate increases and the reaction vessel 1
The internal pressure increases and the difference from the set value becomes smaller, and when it becomes equal to the set value, the input to the integrator 21 becomes 0, so the output signal voltage of the integrator is maintained and the predetermined flow rate is increased. Constant supply. In this case, the supply amount is determined by setting the buffer tanks 7 and 8 in FIG. 9, since the capacity of the buffer tank 7 is determined (V1 in the figure), the total number of gas molecules supplied at this time can be determined. Therefore, the flow rate can be quantified by calibrating using the differential pressure between the buffer tanks 7 and 8.

In FIG. 5, a 100Hz, 55V pulse is used, the horizontal axis represents the modulation voltage, and the vertical axis represents the flow rate (mbar·l/s).
ec) is shown. As can be seen from the figure, the linearity is extremely good, and it can be seen that the gas supply amount can be set accurately by the modulation voltage. Therefore, since the supplied flow rate can be determined by monitoring the modulation voltage of the piezo valve, the piezo valve itself has a function of detecting the flow rate, and there is no need to provide a separate flow sensor.

[0015] Furthermore, when a reaction is started while gas is being supplied at a constant flow rate, gas molecules are consumed, so the modulation voltage is automatically changed in order to maintain a constant pressure. It is possible to estimate the reaction rate by monitoring the modulation voltage or duty ratio, which is proportional to the flow rate as described above.

[0016] In the above embodiment, the case of supplying a small amount of gas in thin film formation etc. was explained, but the present invention is not limited to gas flow rate control.
It can also be applied to liquid flow rate control in systems that monitor H, systems that separate and analyze extremely small amounts of biological substances in biological fluids such as blood, urine, and cerebrospinal fluid.

[0017]

[Effects of the Invention] As described above, according to the present invention, the following effects can be obtained. ■Since the supply flow rate can be determined by monitoring the modulation voltage of the piezo valve, the piezo valve itself has a flow rate detection function, and there is no need to provide a separate flow sensor. ■ Linearity can be improved by not using the nonlinear region of the piezo element and only using the completely open and closed states. ■Since the piezo valve itself has a response of about 2 msec, if the time constants of other devices in the system can be shortened, the response can be dramatically increased. ■With a conventional crystal oscillator film thickness meter, which measures the deposited film thickness from changes in oscillation frequency due to molecular deposition, the rate of change in surface coverage is approximately 0.1 Å/sec, or 10-1 atomic layer/sec, or 10% of the change in surface coverage. In contrast, the present invention achieves a sensitivity of about 10-6 mbar·l/sec, which corresponds to 2.5 x 1013 molecules/sec. So 10
If consumed on a substrate or target of 0 cm2, 2
．． 5 x 1011 molecules/sec cm2, and since one atomic layer is about 1015 atoms/cm2, this corresponds to a reaction rate of 10-4 atomic layers/sec, and therefore the change in surface coverage is 0.01. %/sec, and the sensitivity can be dramatically improved.

[0018] During thin film production, when gas is supplied at a constant flow rate, the modulation voltage changes when gas molecules are used in a reaction, so the reaction rate is estimated by monitoring the modulation voltage or duty ratio. be able to.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of a flow rate control device of the present invention.

FIG. 2 is a diagram for explaining the configuration of a pulse width modulation valve controller.

FIG. 3 is a diagram illustrating the structure of a piezo valve.

FIG. 4 is a diagram illustrating flow rate control of the present invention.

FIG. 5 is a diagram showing the relationship between modulation voltage and flow rate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Reaction vessel, 2... Pressure gauge, 3... Transducer, 4... Pulse width modulation valve controller, 5, 6... Piezo valve (PV
), 7, 8... buffer tank, 9, 10... pressure gauge,
11...Hydrogen gas cylinder, 12...Helium gas cylinder, 1
3... Methane gas cylinder, 20... Differential amplifier, 21... Integrator, 22... Buffer amplifier, 23... Reference frequency oscillator, 24
... triangular wave generator, 25 ... voltage comparator, 26 ... pulse height regulator, 27 ... high voltage amplifier.

Claims (5)

[Claims] Claim 1: A device for controlling a flow rate using a piezo valve using a piezo element that generates mechanical distortion according to an applied voltage, comprising a pulse width modulation means for converting a flow control signal into a pulse width, A flow control device using a piezo valve, which controls the opening and closing of the piezo valve using signals. 2. The apparatus according to claim 1, wherein the pulse width modulation means generates a modulation signal based on a difference signal with respect to a set value of the pressure inside the container or the amount of fluid flowing into the container when fluid is supplied to the container. A flow control device using a piezo valve that generates pulse width and modulates the pulse width so that this difference signal becomes zero. 3. The apparatus according to claim 1, wherein the pulse width modulation means modulates the pulse width based on the difference between the internal pressure of the container and a set value when gas is supplied to the container that is continuously evacuated. A flow control device using a piezo valve. 4. A flow rate control device using a piezo valve according to claim 3, further comprising a buffer tank, and gas from the gas supply source is supplied to the piezo valve via the buffer tank. . 5. The apparatus according to claim 4, comprising two buffer tanks, and means for measuring the differential pressure between the internal pressures of both buffer tanks, so that gas is supplied to the piezo valve through one of the buffer tanks. A flow control device using a piezo valve featuring the following.