Apparatus for controlling concentration, material vaporizing system, and method and program for concentration control

Abstract

To make concentration control possible at high speed and with overshoot suppressed.SOLUTION: An apparatus for controlling concentration 10, to be used in a material vaporizing system 100 to supply material gas produced by introducing carrier gas to a liquid or solid material received within a vaporization tank 2 into vaporization, comprises a flow-rate controller 5 that controls the flow rate of carrier gas, a concentration measuring unit 6 that measures the concentration of material gas, and a flow-rate control unit 11 that controls the flow-rate control input to the flow-rate controller 5 under model predictive control based on a target concentration value of the material gas and a concentration value measured at the concentration measuring unit 6.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a concentration control device, a raw material vaporization system, a concentration control method, and a concentration control program. [Background technology]

[0002] In the cleaning process of semiconductor manufacturing, reducing watermarks that occur when drying wafers is an issue. In the drying process, isopropyl alcohol (IPA) is sprayed onto the wafer along with a carrier gas such as nitrogen to dry it, and in recent years, concentration control has become important. Concentration control involves constant control of the temperature of the vaporization tank containing the raw material and the flow rate of carrier gas such as nitrogen, but with increasing demands for process reproducibility, real-time concentration control is becoming important.

[0003] Here, in a conventional raw material vaporization system, as shown in Patent Document 1, for example, it is considered that the IPA concentration is measured by an analyzer using non-dispersive infrared absorption spectroscopy (NDIR) and the flow rate of the carrier gas is controlled by PID control.

[0004] However, due to factors such as response dead time caused by gas replacement in the piping, it is necessary to adjust the PID to achieve the desired response time, making it difficult to determine the achievable response performance and increasing the amount of work required to adjust the PID. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4034344 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to reduce the number of steps for adjusting control parameters while improving response performance. [Means for solving the problem]

[0007] In other words, the concentration control device of the present invention is a concentration control device used in a raw material vaporization system that introduces a carrier gas into a liquid or solid raw material contained in a vaporization tank to vaporize it and supply the resulting raw material gas, and is characterized in that it comprises a flow control device that controls the flow rate of the carrier gas, a concentration measurement unit that measures the concentration of the raw material gas, and a flow control unit that controls the flow rate manipulation amount input to the flow control device by model predictive control based on a target concentration value of the raw material gas and the measured concentration value of the concentration measurement unit.

[0008] This type of concentration control device controls the flow rate operation amount input to the flow control device using model predictive control, which can improve response performance compared to conventional PID control. Also, with model predictive control, it is sufficient to conduct a single identification experiment of the controlled object, and parameter optimization in PID control is not required, which can significantly reduce the adjustment man-hours.

[0009] It is preferable that the flow rate control unit uses, as a prediction model for the model predictive control, a model including a dead time based on a time required for the raw material gas to reach the concentration measurement unit provided in the raw material gas discharge path. With this configuration, high-speed concentration control with reduced overshooting is possible by model predictive control that takes into account the response dead time due to gas replacement in the source gas outlet path.

[0010] It is desirable that the flow rate control unit sets a time constant of a reference trajectory relating to the concentration of the source gas slower than a time constant of a system included in a prediction model of the model predictive control. With this configuration, since the time constant of the reference trajectory is slower than the time constant of the controlled object, it is possible to control the flow rate manipulated variable so as to make the predicted trajectory of the controlled object coincide with the reference trajectory.

[0011] In addition, the raw material vaporization system of the present invention is characterized in that it comprises a vaporization tank in which a liquid or solid raw material is stored, a carrier gas supply path that supplies a carrier gas to the vaporization tank, a raw material gas discharge path that discharges the raw material gas vaporized from the raw material from the vaporization tank, and the above-mentioned concentration control device.

[0012] Furthermore, a concentration control method according to the present invention is a concentration control method used in a raw material vaporization system in which a carrier gas is introduced into a liquid or solid raw material contained in a vaporization tank to vaporize it, and the raw material gas produced thereby is supplied, characterized in that a flow rate of the carrier gas is controlled by a flow control device, a concentration of the raw material gas is measured by a concentration measurement unit, and a flow rate manipulated variable input to the flow control device is controlled by model predictive control based on a target concentration value of the raw material gas and the measured concentration value of the concentration measurement unit.

[0013] Furthermore, a concentration control program according to the present invention controls the concentration of a raw material gas in a raw material vaporization system that introduces a carrier gas into a liquid or solid raw material contained in a vaporization tank to vaporize the raw material gas produced thereby, and is a concentration and temperature control program used in a concentration control device that has a flow control device that controls the flow rate of the carrier gas and a concentration measurement unit that measures the concentration of the raw material gas, and is characterized in that it provides a computer with a function as a flow control unit that controls a flow rate manipulation amount to be input to the flow control device by model predictive control based on a target concentration value of the raw material gas and the measured concentration value of the concentration measurement unit.

[0014] The concentration control program may be distributed electronically, or may be recorded on a program recording medium such as a CD, a DVD, or a flash memory. Effect of the Invention

[0015] In this way, according to the present invention, it is possible to reduce the number of steps for adjusting the control parameters while improving the response performance. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram illustrating a schematic configuration of a raw material vaporization system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram illustrating a mechanism of model predictive control in the embodiment. [Diagram 3] FIG. 13 is a diagram showing the response results of the concentration of the source gas (IPA) when the carrier gas is flowed in a stepped manner. [Figure 4] FIG. 1 is a control block diagram for performing concentration control by conventional PID control. [Diagram 5] FIG. 13 is a diagram showing experimental results of concentration control by conventional PID control. [Figure 6] FIG. 13 is a diagram showing experimental results after adjusting PID parameters in conventional PID control. [Figure 7] FIG. 13 is a diagram showing an algorithm for performing concentration control by MPC in the embodiment. [Figure 8] FIG. 13 is a diagram showing experimental results of concentration control by the MPC of the same embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] An embodiment of a raw material vaporization system incorporating a concentration control device according to the present invention will be described below with reference to the drawings. Note that in all of the drawings shown below, for ease of understanding, some parts are omitted or exaggerated as appropriate. Identical components are given the same reference numerals and descriptions thereof will be omitted as appropriate.

[0018] <1. Basic configuration of the raw material vaporization system 100> The source material vaporization system 100 of this embodiment is used in a semiconductor manufacturing apparatus that performs a semiconductor manufacturing process such as a drying step, and supplies a source gas having a controlled concentration to a chamber that performs the drying step, for example.

[0019] Specifically, as shown in FIG. 1, the raw material vaporization system 100 includes a vaporization tank 2 that contains a liquid or solid raw material, such as isopropyl alcohol (IPA), a carrier gas supply path 3 that supplies a carrier gas, such as nitrogen (N2), to the vaporization tank 2, a raw material gas outlet path 4 that outputs the raw material gas vaporized from the vaporization tank 2, a first flow control device 5 provided in the carrier gas supply path 3, and a concentration measurement unit 6 provided in the raw material gas outlet path 4.

[0020] Here, the first flow control device 5 is a mass flow controller having a flow sensor and a fluid control valve. The flow sensor may be a differential pressure type or a thermal type. The fluid control valve controls the flow rate of the flow sensor and the flow rate manipulated variable q output by a first flow control unit 11 described later. C SET Based on this, a valve control unit (not shown) controls the valve opening degree.

[0021] The concentration measurement unit 6 uses non-dispersive infrared absorption spectroscopy (NDIR). Specifically, the concentration measurement unit 6 has a measurement cell into which the raw material gas is introduced, an infrared light source that irradiates the measurement cell with infrared light, an infrared detector that detects the infrared light that has passed through the measurement cell, and a concentration calculation unit that calculates the concentration of the raw material gas based on the light intensity signal detected by the infrared detector.

[0022] The first flow rate control device 5, the concentration measurement unit 6, and a first flow rate control unit 11 (described later) constitute a concentration control device 10 according to the present invention.

[0023] In this embodiment, a dilution gas supply path 7 for supplying a dilution gas for diluting the raw material gas is connected to the raw material gas discharge path 4, and the dilution gas supply path 7 is provided with a second flow control device 8 for controlling the flow rate of the dilution gas.

[0024] Here, the second flow control device 8 is a mass flow controller having a flow sensor and a fluid control valve. The flow sensor may be a differential pressure type or a thermal type. The fluid control valve controls the flow rate of the flow sensor and the flow rate manipulated variable q output by a second flow control unit 12 described later. D SET Based on this, a valve control unit (not shown) controls the valve opening degree.

[0025] The raw material vaporization system 100 detects the raw material gas concentration measurement value c OUT and the target concentration value c SET Based on this, the first flow rate control device 5 is controlled to control the concentration c of the raw material gas. OUT The control device CTL in this embodiment controls the flow rate q of the carrier gas supplied to the vaporization tank 2. C and the flow rate q of the diluent gas supplied from the diluent gas supply passage 7 to the raw material gas discharge passage 4. D The total flow rate (q C +q D ) is controlled to be constant.

[0026] <2. Specific configuration of the control device CTL> The control device CTL of this embodiment is a so-called computer equipped with a CPU, a memory, an A / D converter, a D / A converter, and various input / output devices. A concentration control program stored in the memory is executed, and the control device CTL functions as a first flow control unit 11 that controls the operation of the first flow control device 5 and a second flow control unit 12 that controls the operation of the second flow control device 8 by the cooperation of the various devices.

[0027] The first flow rate control unit 11 determines the target concentration value c SET and the measured concentration value c of the concentration measuring unit 6 OUT Based on this, a flow rate control amount q to be input to the first flow rate control device 5 by a model predictive controller (MPC) is C SET This controls the

[0028] Here, model predictive control is a control method that performs optimization while predicting future responses at each time, as shown in Figure 2, and by having a prediction model (controlled object model) inside the first flow control unit 11, it predicts the future behavior of the controlled object over a finite interval from the current time.

[0029] In FIG. 2, the target command r(t) is the target concentration value c SET and the control input u(t) is the flow rate control amount q C SET The control output y(t) is the concentration c of the source gas measured by the concentration measuring unit 6. OUT The concentration measurement value c OUT is applied to a prediction model inside first flow rate control unit 11, and a new control input u(t) is determined in an optimizer so as to minimize the tracking error from the current time to a predetermined time.

[0030] Here, the first flow rate control unit 11 uses, as a prediction model for the model predictive control, a model including a dead time based on the arrival time to the concentration measuring unit 6 provided in the raw material gas discharge path 4. This dead time is a response dead time associated with gas replacement in the raw material gas discharge path 4 from the vaporization tank 2 to the concentration measuring unit 6. The dead time will be described in detail later.

[0031] In addition, the first flow rate control unit 11 sets the time constant of the reference trajectory for the concentration of the source gas to be slower than the time constant of the system (transfer function) included in the prediction model of the model predictive control. The details of the time constant of the system (transfer function) and the time constant of the reference trajectory will be described later.

[0032] The second control unit 12 controls the carrier gas flow rate q C and dilution gas flow rate q D The total flow rate (q C +q D The flow rate control amount q input to the second flow control device 8 is set to be constant. D SET Specifically, the second flow rate control unit 12 controls the total flow rate setting value q of the carrier gas and the diluent gas. T SET and the flow rate control amount q of the first flow rate control device 5C SET Difference with (q T SET -q C SET ) is expressed as the flow rate manipulated variable q of the second flow rate control device 8. D SET (The set flow rate value of the dilution gas).

[0033] Hereinafter, the concentration control by the conventional PID control and the concentration control by the MPC of the control device CTL of this embodiment will be described in detail.

[0034] <3. Control target> The controlled object is the one shown in FIG. 1, and the physical quantity to be controlled is the concentration measurement value c measured by the concentration measurement unit 6. OUT and the total flow rate q T (Carrier gas flow rate q C and dilution gas flow rate q D (total flow rate of

[0035] Here, a mass flow controller is used for flow rate control, and the flow rate response performance of the mass flow controller is sufficiently faster than the response of the concentration output.

[0036] Concentration of source gas (IPA) OUT is measured by the concentration measurement unit 6 (NDIR) and can be expressed by the following formula. C is used, but since the flow rate is in the denominator, the concentration c OUT In the following equation, q V is the source gas flow rate.

[0037]

number

[0038] Figure 3 shows the concentration c OUT Here, the concentration control is not performed, and the concentration c OUT The flow rate of the carrier gas is set to 200 sccm, which is close to the actual operating condition.

[0039] From the experimental results, we performed identification and obtained the following transfer function P(s): This transfer function P(s) contains a dead time of about 1 second, which makes it difficult to adjust the response of the concentration control.

[0040]

number

[0041] This transfer function P(s) is calculated by calculating the coefficients a1, b1, b2, and L of the following general formula based on the response results shown in FIG. 3. The coefficient L indicates the dead time. Also, q C is the carrier gas flow rate in Figure 3, q V is the raw gas flow rate in Figure 3, q D is the dilution gas flow rate in FIG.

[0042]

number

[0043] <4. Concentration control by PID control> The target concentration value of the source gas c SET and carrier gas total flow rate setting value q T SET The two settings are input to the control device CTL. The response is the concentration of the raw gas c OUT and total carrier gas flow rate q T We want to converge within 10 seconds and minimize overshoot as much as possible.

[0044] Figure 4 shows a block diagram of the PID control system. In the conventional method, the control device CTL performs PID control, and the target flow rate of the carrier gas q C SET Calculate the concentration of the source gas c OUT Control.

[0045] Carrier gas total flow rate setting value q T SET is the target flow rate of the carrier gas, q, shown in the following formula. C SET and the dilution gas flow rate target value q D SETTherefore, the total flow control of this control system is q T SET andq C SET The difference between these is the dilution flow rate setting q D SET The configuration is to set it to

[0046]

number

[0047] The experimental results using the conventional PID control are shown in Figure 5. Here, the target concentration value (concentration setting) of the source gas c SET 1%, target total flow value (total flow setting) q T SET The flow rate was set to 2000 sccm, and a step response experiment was carried out.

[0048] As a result of adjusting the PID parameters, the total flow rate stabilized in about 2 seconds after setting, but the concentration output took about 15 seconds to converge.

[0049] Furthermore, the PID was adjusted so that the response would reach 10 seconds. The results are shown in Fig. 6. With PID control, adjusting the response time to 10 seconds resulted in a large overshoot. This is believed to be due to the fact that the controlled object contains dead time.

[0050] <5. Concentration control by MPC> Next, we will explain the concentration control by MPC. T The control is the same as the conventional PID control.

[0051] FIG. 7 shows the MPC algorithm of the first flow control unit 11. Here, k is the sampling period T s Let denote the discretized time.

[0052] The prediction horizon score (time to predict the future) is H P Then, the reference orbit c reftraj (k+i|k)(i=1, ,H P) shows the ideal trajectory, and its response time is expressed as the time constant T ref is determined by.

[0053]

number

[0054] Manipulated amount Δq C SET Given the predicted trajectory c ^ OUT (k+i|k) (superscript ^ represents the predicted value) is the free response c free (k+i|k) and the unit step response S(i) calculated from Equation 2 above, which is expressed by the following equation.

[0055]

number

[0056] reference trajectory c reftraj (k+i|k) and predicted trajectory c ^ OUT The sampling period T s Every Δq C SET Then, the next sampling period q C SET Determine.

[0057]

number

[0058] Next, we implemented MPC and performed an experiment on concentration control. The time constant, prediction horizon, and data interval of the predicted trajectory were as follows: Sampling period T S [s]:0.1 Time constant T of predicted trajectory ref [s]:2 Prediction Horizon Score H P [s]:5 Data section n:5

[0059] In addition, the target concentration value (concentration setting) of the source gas c SET 1%, target total flow value (total flow setting) q T SET The experiment was carried out at 2000sccm.

[0060] The experimental results are shown in Figure 8. As can be seen from Figure 8, concentration control by MPC resulted in a concentration control convergence time of approximately 10 seconds, suppressing overshoot. The total flow rate also converged in approximately 1 second, shortening the convergence time compared to the conventional method.

[0061] <6. Effects of this embodiment> In this manner, according to the raw material vaporization system 100 of the present embodiment, the flow rate manipulated variable q input to the first flow rate control device 5 is calculated by the model predictive control. C SET Since the model predictive control is based on the above, it is possible to improve the response performance compared to the conventional PID control. Also, with model predictive control, it is sufficient to carry out a single identification experiment of the controlled object, and it is not necessary to optimize the parameters in the PID control, which can significantly reduce the adjustment man-hours.

[0062] In addition, a model including a dead time based on the arrival time at the concentration measuring unit 6 provided in the raw gas outlet line 4 is used as the predictive model for the model predictive control. Therefore, the model predictive control taking into account the dead time of the response due to gas replacement in the raw gas outlet line 4 enables high-speed concentration control with reduced overshoot.

[0063] Furthermore, since the time constant of the reference trajectory for the concentration of the raw material gas is made slower than the time constant of the system included in the predictive model of the model predictive control, the flow rate manipulated variable can be controlled so as to match the predicted trajectory of the controlled object with the reference trajectory.

[0064] <7. Other embodiments> For example, the raw material in the above embodiment is a liquid raw material such as isopropyl alcohol, but a solid raw material may also be used.

[0065] Moreover, the vaporization method may be other vaporization methods such as a heating method in addition to bubbling.

[0066] Furthermore, in the above embodiment, the total flow rate of the carrier gas flow rate and the dilution gas flow rate is controlled to be constant, but the total flow rate may not be controlled to be constant.

[0067] Moreover, in the above embodiment, the dilution gas supply path is provided to dilute the source gas, but the dilution gas supply path may not be provided.

[0068] In addition, the time constant of the system included in the predictive model of the model predictive control may be the same as the time constant of the reference trajectory related to the concentration of the source gas.

[0069] Furthermore, although the concentration control device in the above embodiment supplies source gas to a chamber of a semiconductor manufacturing device, it may also supply source gas to other chambers.

[0070] Furthermore, the concentration control device in the above embodiment is incorporated in the raw material vaporization system, but it may be a separate device (module) from the raw material vaporization system.

[0071] In addition, various modifications and combinations of the embodiments may be made as long as they do not go against the spirit of the present invention. [Explanation of symbols]

[0072] 100···Raw material vaporization system 10. Concentration control device 2. Vaporization tank 3. Carrier gas supply path 4. Raw material gas outlet path 5. First mass flow controller (first flow control device) 6...Concentration measuring section 7. Dilution gas supply line 8. Second mass flow controller (second flow control device) CTL: Control device 11 First flow rate control section 12 Second flow control section

Claims

1. 1. A concentration control device used in a raw material vaporization system that introduces a carrier gas into a liquid or solid raw material contained in a vaporization tank to vaporize the raw material, and supplies the resulting raw material gas, a flow rate control device for controlling the flow rate of the carrier gas; a concentration measuring unit for measuring the concentration of the source gas; a flow control unit that controls a flow rate manipulated variable to be input to the flow rate control device by model predictive control based on a target concentration value of the source gas and the concentration value measured by the concentration measurement unit.

2. 2. The concentration control device according to claim 1, wherein the flow rate control unit uses, as a predictive model for the model predictive control, a model including a dead time based on a time taken for the raw gas to reach the concentration measurement unit provided in the raw gas discharge path.

3. The concentration control device according to claim 1 , wherein the flow rate control unit makes the time constant of the reference trajectory for the concentration of the source gas slower than the time constant of a system included in the prediction model of the model predictive control.

4. a vaporization tank containing a liquid or solid raw material; a carrier gas supply path for supplying a carrier gas to the vaporization tank; a raw material gas outlet path for discharging the raw material gas vaporized from the vaporization tank; A raw material vaporization system comprising the concentration control device according to claim 1 .

5. 1. A concentration control method used in a raw material vaporization system that introduces a carrier gas into a liquid or solid raw material contained in a vaporization tank to vaporize the raw material, and supplies the resulting raw material gas, comprising: The flow rate of the carrier gas is controlled by a flow rate control device; measuring the concentration of the source gas by a concentration measuring unit; a concentration control method for controlling a flow rate manipulated variable to be input to the flow rate control device by model predictive control based on a target concentration value of the source gas and the concentration value measured by the concentration measuring unit;

6. A concentration control program for use in a concentration control device that controls the concentration of a raw material gas in a raw material vaporization system that introduces a carrier gas into a liquid or solid raw material contained in a vaporization tank to vaporize the raw material and supply the resulting raw material gas, the concentration control program comprising: a flow rate control device that controls a flow rate of the carrier gas; and a concentration measurement unit that measures the concentration of the raw material gas, a concentration control program that causes a computer to function as a flow rate control unit that controls a flow rate manipulation amount input to the flow rate control device by model predictive control based on a target concentration value of the source gas and the measured concentration value of the concentration measurement unit.

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